Dryland Social-Ecological Systems in Central Asia

Abstract

The countries of Central Asia are collectively known as Uzbekistan, Kyrgyzstan, Turkmenistan, Tajikistan and Kazakhstan. Central Asian countries have experienced significant warming in the last century as a result of global changes and human activities. Specifically, the five Central Asian countries’ populations and economies have increased, with Turkmenistan showing the fastest growth rates in GDP and per capita GDP. Farmland change, forestry activities, and grazing are examples of land use/land cover change and land management in Central Asia. Land degradation was primarily caused by rangeland degradation, desertification, deforestation, and farmland abandonment. The raised temperature, accelerated melting of glaciers, and deteriorated water resource stability resulted in an increase in the frequency and severity of floods, droughts, and other disasters. The increase of precipitation cannot compensate for the aggravation of water shortage caused by temperature rise in Central Asia. The ecosystem net primary productivity was decreasing over the past years, and the organic carbon pool in the drylands of Central Asia was seriously threatened by climate change. Grassland contributed the most to the increase of ecosystem service values in recent years. Most ecosystem functions decreased between 1995 and 2015, while they are expected to increase in the future (except for water regulation and cultural service/tourism). Global climate change does pose a clear threat to the ecological diversity of Central Asia.

1 Introduction

Central Asia is vulnerable to global climate change, which has a significant impact on the region’s ecological environment and has long been a source of concern and research. Central Asian drylands have experienced significant warming in the last century as a result of global climate change and anthropogenic activities. The drylands also experienced more frequent extreme weather events, such as prolonged drought or flooding, which could exert serious consequences for the arid regions’ ecosystem structure and functions.

This section will (1) explain the distribution of drylands in Central Asia; (2) illustrate the climate, soils, land use/land cover types, water resources, ecosystem structure and functions, and social and economic development of Central Asia; (3) examine the land use/land cover change, land degradation and desertification, dynamics of ecosystem structure and functions (including ecosystem productivity and carbon stock), ecosystem services, and human well-being; (4) investigate the driving forces of dryland changes from the perspective of climate change and anthropogenic activities as well as their combination; and (5) elaborate the ecosystem networks and Aral Sea crisis and discuss the conservation and effective practices of drylands in Central Asia. The main objective of this section is to improve the understanding of characteristics, ecosystem dynamics, and driving forces of drylands in Central Asia, an arid and semi-arid area that is extremely sensitive to climate change. Knowledge of dryland changes and driving forces in Central Asia in the context of global climate change and anthropogenic activities is important for environmental protection and improvement as well as sustainable social and economic development.

2 Major Characteristics of Dryland SESs in Central Asia

2.1 Distribution of Drylands in Central Asia

Central Asia refers to the central part of the Asian Continent. According to the United Nations Educational, Scientific and Cultural Organization (UNESCO), Central Asia includes the vast area between the Altay Mountains in the north, the Himalayas in the south, the Caspian Sea in the west, and the Da Hinggan Ling in the east. Following the UNESCO definition, Central Asia includes Afghanistan, Pakistan, Tajikistan, Turkmenistan, Uzbekistan, Kyrgyzstan, Kazakhstan, the northern part of Iran, the northwestern part of India, the northwestern part of China (Xinjiang Uygur Autonomous Region, Tibet Autonomous Region, Qinghai Province, Inner Mongolia Autonomous Region, the Hexi Corridor in Gansu Province, and the northern part of Ningxia Hui Autonomous Region), and the southwestern part of the Mongolian People’s Republic (Hu 2006).

Former Soviet scholars considered the term Central Asia to refer specifically to the regions where the five Central Asian republics are located (Kazakhstan, Uzbekistan, Kyrgyzstan, Tajikistan, and Turkmenistan). The Soviet Union’s official definition of Central Asia was widely used internationally during the Soviet period (Editorial Board of the Silk Road Dictionary 2006). In this section, Central Asia primarily refers to the area of Kazakhstan, Tajikistan, Turkmenistan, Uzbekistan, and Kyrgyzstan.

The geographical location of Central Asia is bounded by longitudes 46°29′47″–87°18′55″E and latitudes 35°07′43″–55°26′28″N (Chen et al. 2014a, b) (Fig. 7.1). In the southeast, the altitude is higher, while in the northwest, it is lower. The Turfan Depression, located on the western side of Central Asia, is home to the Kara Kum Desert and the Kyzyl Kum (Chen and Zhou 2015). Terraces and hills can be found on the northern and northeastern sides of the Turgai region. The majority of the flat land is located between −28 m below sea level and 300 m above sea level.

Fig. 7.1

Sketch map of Central Asia

However, some of the marshy basins in the Karagiye Depression are located at altitudes as low as −132 m below sea level. Aktau Mountain, at 922 m above sea level, is the highest point in the middle of Central Asia. The Tianshan Mountains Range and the Pamir-Alai, which are located on the southeastern side, reach a height of 7,495 m above sea level at their highest point. They are also known as the “water tower” of Central Asia because they provide a vital source of water for rivers and lakes. The Kopet-Dag Range is located on the southwestern side.

With a total area of 4.0 × 10⁸ hm² and a total population of around 65 million, Central Asia mainly consists of arid and semi-arid regions (Yang and Du 2013; Yu et al. 2019). Wet air from the Pacific and Indian Oceans is difficult to reach these regions due to the isolation by the Pamirs in Tajikistan, the Tibetan Plateau, and the Tianshan Mountains on the border between China and Kyrgyzstan.

Central Asia is mainly covered by drylands (arid, semi-arid, and semi-humid areas as defined by the United Nations Convention to Combat Desertification), with ecosystems that are extremely sensitive and vulnerable to climate change (UNDP 2005). Due to the continental location of Central Asia, climate and water resources are the key factors in Central Asia’s social and economic development (Yu et al. 2019, 2020).

2.2 Climate, Soils, Land Use/Land Cover, and Water Resources in Central Asia

Climate

Because of its special geographical location and complex topography, Central Asia is dominated by an arid and semi-arid climate that is primarily controlled by the westerly winds (Chen and Zhou 2015; Lioubimtseva and Cole 2006; Ta et al. 2018). The Atlantic and Arctic Oceans provide the most moisture fluxes to the regions, while moisture fluxes from the Pacific and Indian Oceans are largely obstructed by the Tianshan Mountains and Pamirs (Schiemann et al. 2008). During El Nio, a portion of the moisture fluxes from the Indian Ocean is carried by the westerly wind, which increases precipitation over most area of Central Asia, particularly the middle southern region (Hu et al. 2017; Mariotti 2007).

Precipitation in Central Asia is mainly distributed in the Pamirs and Tianshan Mountains; it has a significant spatial distribution pattern: less precipitation in the western and eastern edge regions, and more precipitation in the central mountainous regions (Chen 2012; Chen et al. 2013). The windward slope of the Pamirs receives 2000 mm of precipitation per year, and the west windward slope of the Tianshan Mountains receives 1000 mm (Balashova et al. 1960; Hu 2004; Yang and Du 2013). Less precipitation is observed on the leeward slopes, valleys, basins, and valleys that are influenced by the mountains (Donat et al. 2016). Therefore, some valleys and basins (such as A Keqi Valley, Caracol) are famous for an arid climate. Precipitation of these basins is lower than 100 mm; in the Issyk-Kul Basin, annual precipitation ranges from 200 to 400 mm, with 399 mm in the northern region and 242 mm in the southern region. Precipitation in winter and spring is significantly higher than that in summer and autumn due to the Mediterranean climate that affects the five Central Asian countries from the southwest to the northeast.

Temperature in Central Asia has the opposite distribution with precipitation. Specifically, precipitation in the plain regions of Uzbekistan, Turkmenistan, and the southern region of Kazakhstan is less than 15 mm, especially in summer, despite average temperature of more than 24.0 °C in these regions. In winter, average temperature in Uzbekistan and Turkmenistan is higher than 0.0 °C, and it is nearly 0.0 °C in the southern region of Kazakhstan. Among the five Central Asian countries, Turkmenistan has the highest temperature (annual mean temperature >15.0 °C), followed by Uzbekistan. Annual mean temperature is lower than −3.0 °C in the western region of Tajikistan and lower than 0.0 °C in the southeastern part of Kyrgyzstan.

Soils

The most important factors affecting soils in Central Asia are rapid evaporation of soil water and lack of water resources. Desert covers two-thirds of the land area, with soils varying significantly from the north to the south and from the west to the east. The soil patterns follow climatic gradients of decreasing precipitation and increasing temperature as they move from the north to the south (Chen et al. 2014b). A comparatively high proportion of sodic soils and saline soils, which are common in alluvial plains, is a distinguishing feature of soil patterns in Central Asia (Chen et al. 2014b).

The landscape here is typical of temperate desert in the world. Soil profiles do not contain any obvious weathered materials, because the weathered products have been removed by erosion. Due to the low vegetation cover, soils have low humus and fulvic acid contents. Central Asia has a great diversity in soil types. According to the 1974 Food and Agriculture Organization (FAO) soil classification, 18 of the 26 soil orders are distributed in Central Asia, covering 244 soil associations. The most important ten soil types in Central Asia are as follows: Orthic Solonetz, Luvic Kastanozem, Haplic Kastanozem, Lithosol, Mollic Gleysol, Luvic Xerosol, Calcic Chernozem, Calcic Xerosol, Eutric Histosol, and Haplic Chernozem (Chen et al. 2014b).

Land Use/Land Cover

Based on the land classification system of the Chinese Academy of Sciences (CAS), land use/land cover in Central Asia can be classified into the following types: cropland, forestland, grassland, wetland, urban land, bare land, and water bodies. In 2015, grassland is the most important land use/land cover type in Central Asia, with a total area of 19,948.14 × 10⁴ hm², followed by bare land (9,183.36 × 10⁴ hm²), cropland (8,814.59 × 10⁴ hm²), water bodies (1,049.48 × 10⁴ hm²), forestland (800.48 × 10⁴ hm²), wetland (125.25 × 10⁴ hm²), and urban land (89.19 × 10⁴ hm²) (Li et al. 2019).

Water Resources

The five Central Asian countries located in Eurasia’s hinterland have various geographical conditions, numerous trans-border rivers, and significant differences in water resource formation and consumption. The problems and contradictions of water resource utilization are very visible, which is representative of the development and utilization of the water resources of trans-border rivers as well as the protection of ecological environment in the world. Most rivers in the five Central Asian countries have no ocean outlet, and the water is diverted for irrigation, lost to the desert, or injected into inland lakes (Deng et al. 2010; Yang et al. 2013).

There are more than 10,000 rivers (such as the Syr Darya River and Amu Darya River) and 10,000 natural lakes (such as the Balkhash Lake and the Aral Sea) in Central Asia (Yu et al. 2019). The Syr Darya River, with the length of 3,019 km, originates from the West Tianshan Mountains in Kyrgyzstan and crosses through Kyrgyzstan, Uzbekistan, Tajikistan, and Kazakhstan (Wang et al. 2021). The Amu Darya River, with the length of 2,540 km and an average annual runoff of 780 × 10⁸ m³, originates from the Pamirs, Hindu Kush, and Tianshan Mountains before crossing through Tajikistan, Afghanistan, Uzbekistan, and Turkmenistan (Chen et al. 2018). The total lake area in Central Asia is more than 0.50 × 10⁶ km², about 1/5 of the Earth’s total lake area. The Aral Sea, located between Kazakhstan and Uzbekistan, is the largest tail lake of two inland rivers (the Amu Darya River and Syr Darya River), ranking the fourth largest lake in the world (Deng et al. 2010).

Kyrgyzstan and Tajikistan are primarily located in the upper reaches of trans-border rivers, where there is an abundant supply of water from the mountains (Yu et al. 2019). Water users from Uzbekistan, Turkmenistan, and Kazakhstan frequently complain about a lack of river outflow into their countries in the lower reaches (Fig. 7.2) (Yu et al. 2019). Rivers in Central Asia have two major characteristics. For starters, the seasonal fluctuations in the hydrographs are frequently significant (Yu et al. 2015, 2019). Peak flows are typically observed in summer, while most rivers experience a glacier period in winter. Intermittent streams and channels with an unstable flow are quite common. Second, water volumes are usually low in the downstream with less precipitation, higher evaporation and infiltration losses, and great water consumption (Yu et al. 2019). Temporary flow in rivers has a special biological significance, enabling certain species to breed while eliminating others (Karthe 2018; Yu et al. 2019). The growth of most natural vegetation (also known as Tugai vegetation) in Central Asia’s arid and semi-arid regions is highly dependent on groundwater conditions (Yu et al. 2018).

Fig. 7.2

Source Yu et al. (2019)

Water resources in five Central Asian countries. The double-counting of the interface between surface water and groundwater was eliminated when calculating the total water resource. The negative value of trans-border water represents the net outflow out of the country.

The exploitation and utilization rates of groundwater are relatively low when compared to surface water, and groundwater is primarily used for irrigation and domestic purposes (Liu et al. 2018). Tugai vegetation is highly resistant to dry and saline soils (Thevs et al. 2012). In farmlands, crops often have to grow under water-stressed conditions (Yu et al. 2019).

2.3 Ecosystem Structure and Functions

Desert, semi-desert, and steppe are the most common ecosystem types in Central Asia (Zhang et al. 2020). These ecosystems are found throughout the lower mountain slopes and foothills, as well as in some outlying ranges and major basins, covering nearly 75% of Central Asia (Zhang et al. 2020). The gravel desert flora comprises more than 400 species, including representatives of the genera Seriphidium, Anabasis, Atraphaxis, and Caragana, along with the species Halolachne songaricum, Krascheninnikovia ceratoides, Iljinia regelii, Salsola gemmascens, and Artemisia pectinate (Zhang et al. 2020). Central Asian deserts are centers of origin and differentiation of ephemeral plants and contain more than 400 such species.

Figure 7.3 depicts the major vegetation types of Central Asia (Zhang et al. 2020). Approximately 7,000 species of vascular plants can be found in Central Asia’s mountains, accounting for more than 75% of the region’s total plant diversity (Zhang et al. 2013). Dryland ecosystems predominate at lower elevations and in the foothills. Grasslands, shrubs, and forests are common at middle elevations on the mountain slopes. Higher elevations have meadows and tundra-like ecosystems. Spruce and birch forests are mostly found in the Tianshan Mountains, whereas old-growth juniper forests are more common in the Pamir-Alai Mountains. In Central Asia, many mountain and riverside forest ecosystems are legally protected (Zhang et al. 2020).

Fig. 7.3

Main vegetation types in Central Asia (Zhang et al. 2020)

In Central Asia, various land use/land cover types can provide different ecosystem services as follows: provisioning (food production and raw material), regulating (gas regulation, climate regulation, and water regulation), supporting (soil formation and retention, waste treatment, and biodiversity), and culturing (recreation, culture, and tourism). Based on Li et al. (2019), for the seven land use/land cover types in Central Asia, wetland has the highest ecosystem service value (US$ 25,681/(hm²·a)), followed by water bodies (US$ 12,512/(hm²·a)), urban land (US$ 6,661/(hm²·a)), cropland (US$ 5,567/(hm²·a)), grassland (US$ 4,166/(hm²·a)), and forestland (US$ 3,137/(hm²·a)). It should be noted that the bare land has no ecosystem service value.

2.4 Dryland SES Development in Central Asia

Central Asia mainly comprises the countries of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan. It is a diverse area with a mix of upper-middle and low-income countries with major strategic importance due to their geographical locations and natural resource endowments (https://www.worldbank.org/en/region/eca/brief/central-asia).

The economy in Kazakhstan (as an upper-middle-income country) is primarily comprised of petroleum, natural gas, agriculture, and livestock. From 1991 to 2019, the population increased by 12.54%, rising from 16.45 million in 1991 to 18.51 million in 2019 (see Table 7.1). The rural population rate is decreased from 44% at 1991 to 42% at 2019. The Gross Domestic Product (GDP), increased from US$ 248.81 × 10⁹ in 1991 to US$ 1,816.66 × 10⁹ in 2019, with an increase rate of 630%.

Table 7.1 Population, GDP, per capita GDP, and the increasing rate of Kazakhstan (KAZ), Kyrgyzstan (KGZ), Tajikistan (TJK), Turkmenistan (TKM), and Uzbekistan (UZB) in 1991 and 2019

The other four countries, i.e., Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan, are low-income countries. From 1991 to 2019, the population in these four countries increased by more than 44.00%, with Tajikistan having the highest increase rate (72.59%) (Table 7.1). Specifically, the population in Tajikistan increased from 5.40 million in 1991 to 9.32 million in 2019, and with the rural population rate 69% at 1991 and 73% at 2019. Uzbekistan had the second highest population growth rate among the four countries, increasing from 20.95 million in 1991 to 33.58 million in 2019 at a rate of 60.27%, but the rural population rate is decreased from 58% at 1991 to 50% at 2019. However, the rural population rate in Kyrgyzstan has tiny variations. For the variations of GDP, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan had the GDP values of US$ 25.69 × 10⁹, 25.35 × 10⁹, 32.08 × 10⁹, and 136.78 × 10⁹ in 1991, respectively. In 2019, the values were US$ 84.55 × 10⁹, 81.17 × 10⁹, 452.31 × 10⁹, and 579.21 × 10⁹, respectively, for the four countries. The corresponding increase rates of GDP were 229.12%, 220.20%, 1,309.94%, and 323.46% from 1991 to 2019 for Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan, respectively (Table 7.1).

3 Changes of Drylands in Central Asia

3.1 Land Use/Land Cover Change

From the 1970s to 2015, the characteristics of land use/land cover change in Kazakhstan are as follows: cropland decreased and was mainly converted into grassland. Water bodies (including wetland) decreased, due to the shrinkage of the Aral Sea. Grassland increased significantly from the 1970s to 2015, which was primarily resulted from the abandonment of cropland and frequent conversion of cropland and grassland in northern Kazakhstan.

The following is the characteristics of land use/land cover change in Uzbekistan:

• (1) Cropland expansion was primarily due to the conversion of grassland or sparse shrubs.

• (2) The shrinkage of the Aral Sea was responsible for the decrease in water area.

• (3) The majority of the water bodies were converted into bare land or sparse vegetation, swamp wetland, and grassland.

• (4) The conversion of cropland has led to a significant increase in urban land.

In Turkmenistan, land use/land cover change showed a significant increase in cropland, mainly from the conversion of grassland or sparse vegetation. The increase in water bodies was mainly caused by bare or sparse vegetation and a small amount of grassland. A significant increase in urban land area was mainly due to the conversion of cropland and grassland.

Land use/land cover change in Kyrgyzstan was characterized by: (1) a reduction in cropland, mainly converted into grassland; (2) a significant decrease in water area because of the shrinkage of glaciers and the sharp reduction of permanent snow cover area; and (3) an increase in urban land area, primarily from the conversion of cropland and grassland. In Tajikistan, the increase of farmland was from the conversion of grassland. The significant reduction of water area was resulted from the shrinkage of glaciers and the sharp decrease of permanent snow cover area, while the increase in urban land area was mainly resulted from the conversion of cropland and grassland.

Cropland change, forestry activities, and grazing were the main land use/land cover changes and land management in Central Asia, each of which had different impacts on the ecosystem structures and services in Central Asia. The major land use/land cover change in Central Asia from the 1970s to 2015 can be summarized as follows: (1) continued desiccation of the Aral Sea; (2) continuous increase of urban land area; and (3) significant increase in grassland from the conversion of cropland in Kazakhstan and Kyrgyzstan and significant increase of cropland from the conversion of grassland in Uzbekistan, Turkmenistan, and Tajikistan. Rapid urbanization also caused the proportion of urban land to increase from 27.57 × 10⁴ hm² in 1995 to 60.21 × 10⁴ hm² in 2005 and then to 89.19 × 10⁴ hm² in 2015, with an average growth rate of 10.64%/a (Fig. 7.4) (Li et al. 2019).

Fig. 7.4

Source Li et al. (2019); https://doi.org/10.7717/peerj.7665/fig-2

Spatial distribution of land use/land cover (LULC) in Central Asia in a 1995, b 2005, c 2015, d 2025, and e 2035.

3.2 Land Degradation and Desertification

The main regions affected by land degradation were concentrated in the north of Kazakhstan, and extended across the eastern Kazakhstan of the southern part of Central Asia, covering Kyrgyzstan, the northwest of Tajikistan, and the southern parts of Uzbekistan and Turkmenistan (Mirzabaev et al. 2016). Mirzabaev et al. (2016) also estimated that the annual cost of land degradation in Central Asia due to land use/land cover change was about US$ 6.00 billion, most of which can be attributed to grassland degradation (US$ 4.60 billion), followed by desertification (US$ 0.80 billion), deforestation (US$ 0.30 billion), and the abandonment of cropland (US$ 0.10 billion). Further, the costs of action against land degradation were found to equal about US$ 53.00 billion over a 30-year period, whereas if nothing is done, the resulting losses may equal to almost US$ 288.00 billion during the same period (Mirzabaev et al. 2016).

From 2000 to 2014, the area of desertification land in Central Asia increased; the increasing magnitude of desertification land was 98,912.26 km² and the growth rate was 0.11% (Liu et al. 2017). Among them, 30,889.73 km² land was transferred from non-desertification to desertification, which was larger than the land transferred from desertification to non-desertification (266,497.67 km²). In terms of spatial distribution, desertification land in Central Asia gradually decreased from severe desertification in the southwest to mild desertification in the northeast and continued to move toward the northern part of Kazakhstan (Liu et al. 2017).

Kazakhstan is a country with a large desert area and severe desertification. According to the Kazakhstan’s “Second National Report on the Implementation of the United Nations Convention to Combat Desertification” issued in 2002, desertification affected two-thirds of the country’s land to varying degrees.

From 1995 to 2001, the total area of desertification land in Kyrgyzstan increased by 0.41 × 10⁵ km², an average annual increase of 590.00 km²/a. The proportion of both severe and very severe desertification types in the country decreased in 2001 compared with 1995, while the land area of mild and moderate desertification increased.

Degradation of vegetation is the main cause of desertification in Turkmenistan. The desert vegetation covers most of the land in Turkmenistan and plays an important role in environmental protection. Desertification caused by vegetation degradation covered an area of 367,522.00 km². Under extreme desert conditions, trees can prevent soil erosion by winds and water, serve as fodders and fuels drain water ecologically, and help to protect settlements from dry winds and dust storms.

3.3 Dynamics of Ecosystem Structure and Functions

Changes in Ecosystem Productivity

Net primary productivity (NPP), as an important indicator of ecological health, has been widely used in studies of the effects of climate change on ecosystem functions (Zhang and Ren 2017). In the context of climate change, it is necessary to understand the temporal and spatial characteristics of NPP in Central Asia based on various climatic factors. Such knowledge is important for developing effective climate adaptation strategies in Central Asia.

The average annual NPP in Central Asia was 1125 (±129) Tg C (1 T = 10¹²) or 218 (±25) g C/m². The annual NPP value was higher in the northern part of Kazakhstan 349 (±39) g C/m². In terms of vegetation types, the NPP value was the highest (556 (±82) g C/m²) in the temperate coniferous forest, while the non-deep root shrub had the lowest NPP value (158 (±25) g C/m²) (Zhang and Ren 2017). Climate change in Central Asia affected the temporal and spatial patterns of NPP, GPP (gross primary productivity), and RA (autotrophic respiration) (Figs. 7.5 and 7.6). From 1980 to 2014, the annual NPP in Central Asia showed a decreasing trend of 0.82 g C/(m²·a), with high interannual variability (Zhang and Ren 2017). The changes in NPP were relatively stable during the period of 1980–1997 and more variable during the period of 1998–2008, with the lowest values found in 2001 2006, and 2008 when major La Niña events took place.

Fig. 7.5

Temporal patterns of a NPP, b GPP, and c RA from 1980 to 2014 in response to climate change factors. NPP, net primary productivity; GPP, gross primary productivity; RA, autotrophic respiration; CLIM, climate change effect; CO₂, CO₂ fertilization effect; PREC, precipitation change effect; TEMP, temperature change effect; OVERALL, combined effects of climate and CO₂ changes

Fig. 7.6

Spatial patterns of a NPP, b GPP, c RA, and d precipitation from 1980 to 2014

Compared with the average annual NPP from 1980 to 1984, the total NPP in Central Asia decreased by 118 Tg (–10%) between 1985 and 2014 (Zhang and Ren 2017). Temperature was the main factor controlling NPP in 9% of Central Asia, which was primarily distributed in high-latitude alpine regions such as the Tianshan Mountains; precipitation was the main factor impacting NPP in 69% of Central Asia, which was mainly distributed in desert plains; CO₂ was the dominant factor influencing NPP in 20% of Central Asia, which was distributed in areas with good hydrothermal conditions, such as forest areas and low-altitude areas (Zhang and Ren 2017).

Changes of Carbon Stock

Central Asia is one of the largest drylands in the mid-latitude, containing over 80% of the world’s temperate desert. Central Asia has become one of the most uncertain regions in global carbon cycle research (Lioubimtseva and Henebry 2009). The carbon stock of Central Asia was approximately 31.34–34.16 Pg, with 10.42–11.43 Pg stored in the deep soils (1–3 m) of its temperate desert, amounting to 24% of the global carbon stock in desert and dry shrubland (Li et al. 2015). The ecosystem carbon density (6.6–7.3 kg/m² in 1 m soil depth) in Central Asia was very close to that in Australia (7.1 (±1.4) kg/m²). In Central Asia, soils stored approximately 90% of carbon stock, which was significantly higher than that in Australia (55%) and most other regions of the world. Kazakhstan had the largest carbon stock among the five Central Asian countries, accounting for more than 70% of the total carbon stock, followed by Kyrgyzstan and Tajikistan.

The mean vegetation carbon density in Central Asia was low, approximately 0.65 and 0.88 kg C/m² from the inventory method and arid ecosystem modeling, respectively (Li et al. 2015). This was mainly due to the low vegetation carbon density in grassland (0.40–0.50 kg C/m²) and temperate desert (0.40–0.87 kg C/m²), which together covered 82% of the land area in Central Asia. Vegetation carbon density was highest in the evergreen needle leaf forests, approximately 13.85 and 18.13 kg C/m² from the inventory method and arid ecosystem modeling, respectively (Li et al. 2015).

The mean soil organic carbon density in the top 1 m of soil was 5.81 and 6.59 kg C/m² from the arid ecosystem modeling and inventory method, respectively (Li et al. 2015). When the deep-soil carbon storage was considered, the regional mean soil organic carbon (SOC) density was 8.25 and 8.81 kg C/m² based on the arid ecosystem modeling and inventory method, respectively (Li et al. 2015). In this case, the lowest SOC was in grassland, approximately 5.52 and 6.84 kg C/m² based on the arid ecosystem modeling and inventory method, respectively (Li et al. 2015). The highest level of SOC was found in evergreen needle leaf forests, approximately 32.60 and 42.99 kg C/m² from the arid ecosystem modeling and inventory method, respectively (Li et al. 2015). The temperate desert and grassland together contributed to 51–60% of the regional vegetation carbon stock and 77–79% of the SOC stock (deep soil) because of their large coverage (82%) in Central Asia (Li et al. 2015).

Climate change posed a serious threat to the organic carbon pool in Central Asian drylands, which lost approximately 0.46 Pg C between 1979 and 2011 (Li et al. 2015). The long-term drought in northern Kazakhstan was the primary cause of the loss of regional carbon stock. The drought was closely related to the La Nia phenomenon, which has resulted in an 8% decrease in the vegetation carbon pool, mainly in northern Kazakhstan. Central Asia can be further divided into semi-arid grassland areas in northern Kazakhstan, arid desert in Central Asia, and Tianshan cold and wet forest-meadow area to analyze the carbon stock changes of ecosystems under different climatic zones (Fig. 7.7). Because of the persistent drought between 1998 and 2008, the semi-arid grassland of northern Kazakhstan has become the largest carbon source in Central Asia.

Fig. 7.7

Ecosystem carbon pool (TOTC), vegetation carbon pool (VEGC), soil organic carbon pool (SOC), and liter carbon pool (LTRC) changes in a northern Kazakhstan, b arid desert, c Tianshan cold and wet forest-meadow area, and d Xinjiang of China during the period of 1979–2011

Climate change exhibited the greatest impact on the central arid desert shrub area. In contrast, the carbon pools in the Tianshan cold and wet forest-meadow area remained relatively stable in response to climate change, implying that forest ecosystems in Central Asian have a strong buffer capacity against climate change.

3.4 Changes in Ecosystem Service Values and Human Well-Being

Ecosystem services include regulating services (such as water regulation, climate regulation, and gas regulation), provisioning services (such as food and raw materials), supporting services (soil formation, waste treatment, and biodiversity), and culturing services (such as recreation, culture, and tourism) (Hassan et al. 2005; Li et al. 2019). Land use/land cover change can alter the ecosystem structures and functions and influence the ecosystem services (Hu et al. 2008; Li et al. 2019; Yirsaw et al. 2017).

Acute farmland expansion and rapid urbanization in Central Asia have accelerated land use/land cover change, which had substantial effects on ecosystem services. Evaluating changes in ESV in response to land use/land cover change and exploring the elasticity of the response of ecosystem service value to land use/land cover change could provide policy makers with important references for ecological environmental protection and the sustainable development of Central Asia.

The total ecosystem service value in Central Asia was approximately US$ 1505.31 billion in 1995 (Table 7.2) (Li et al. 2019). Grassland had the highest contribution the ecosystem service value (56.90%), followed by cropland and water bodies (28.09% and 11.15%, respectively) (Fig. 7.8) (Li et al. 2019). The total ecosystem service value increased by US$ 5.68 billion from 1995 to 2005, mainly due to the increased ecosystem service values of cropland and urban land. The total ecosystem service value increased by US$ 5.23 billion from 2005 to 2015 (Li et al. 2019). Overall, the total ecosystem service value in Central Asia increased by US$ 10.91 billion during the period of 1995–2015 (Li et al. 2019). It is noteworthy that the proportion of water bodies decreased sharply by 21.80% from 1995 to 2015, resulting in a loss of US$ 36.61 billion (Li et al. 2019). These trends were expected to continue to occur in 2025 and 2035 (Table 7.2) (Li et al. 2019). Land use/land cover change is correlated with other global processes such as climate change and land degradation, which directly or indirectly affect local ecosystem services. Ecosystem service value in Karakalpakistan, Uzbekistan, decreased by more than 50% during 1995–2035, which was mainly caused by the shrinkage of the Aral Sea (Li et al. 2019).

Table 7.2 Ecosystem service values in Central Asia from 1995 to 2035 (Li et al. 2019)

Fig. 7.8

Source Li et al. (2019); https://doi.org/10.7717/peerj.7665/fig-3

Percentage of land use/land cover area (a) and percentage of ecosystem service value (ESV) of different land use/land cover types (b) from 1995 to 2035.

Table 7.3 shows the changes in individual ecosystem functions (Li et al. 2019). The most important ecosystem functions in Central Asia were biodiversity, food production, and water regulation, contributing 40.44%, 28.30%, and 11.78% of the total ecosystem service value in 1995, respectively, 40.03%, 29.47%, and 10.21% of the total ecosystem service value in 2015, and 40.51%, 30.14% and 8.93% of the total ecosystem service value in 2035 (Li et al. 2019). Most of the ecosystem functions decreased during the period of 1995–2015 except for food production, raw materials, climate regulation, soil formation, and waste treatment, which increased by 4.87%, 7.92%, 12.11%, 12.01%, and 2.91%, respectively (Fig. 7.9) (Li et al. 2019). It is noteworthy that the ecosystem service value of water regulation declined more rapidly than other ecosystem services (−12.70%), followed by gas regulation (−3.00%), culture and tourism (−3.14%), and biodiversity (−0.29%). However, most of the ecosystem functions were expected to increase from 2015 to 2035 (Fig. 7.9) (Li et al. 2019). It should be noted that only the ecosystem service values of water regulation and culture/tourism were expected to decrease in the future (Li et al. 2019).

Table 7.3 Estimated values for different ecosystem functions in Central Asia from 1995 to 2035 (Li et al. 2019)

Fig. 7.9

Source Li et al. (2019); https://doi.org/10.7717/peerj.7665/fig-5

Changes of ecosystem service functions in Central Asia from 1995 to 2035.

4 Driving Forces of Dryland Changes

4.1 Climate Change and Extreme Events

Based on the most recent CRU dataset, Central Asia has experienced a significant increase in temperature, at a rate of 0.38 °C/decade from 1991 to 2019 (Fig. 7.10a). It had a slight increase in annual precipitation, at a rate of 0.52 mm/a (Fig. 7.10b). With rising temperature and increased precipitation, potential evapotranspiration has increased significantly, reaching 0.85 mm/a (Fig. 7.10c).

Fig. 7.10

Variations of a annual temperature, b annual precipitation, and c PET in Central Asia from 1991 to 2019. PET: potential evapotranspiration

For the seasonal variations, temperature showed significantly increasing trends in spring (March, April, and May) and summer (June, July, and August), with the increasing trends of 0.87 °C/decade and 0.49 °C/decade, respectively (Table 7.4). In autumn (September, October, and November), it exhibited a weak increasing trend. A weak negative trend of temperature was observed in winter (December, January, and February). For precipitation, positive trends were observed in spring and autumn, with the rates of 0.36 mm/a and 0.43 mm/a, respectively. While precipitation in summer and winter exerted negative trends, with the rates of −0.21 mm/a and −0.04 mm/a, respectively. The potential evapotranspiration in Central Asia showed significant positive trends in spring (0.37 mm/a) and summer (0.49 mm/a) during the period of 1991–2019 (Table 7.4). There was no discernible linear trend for the remaining two seasons (autumn and winter). The significant increases of temperature and precipitation in spring could result in spring flooding in Central Asia, especially in mountainous areas (Hu et al. 2014, 2016, 2017, 2019a, b).

Table 7.4 Seasonal linear trends of the temperature, precipitation, and PET in Central Asia from 1991 to 2019

Recent studies mainly focused on the extreme climate events in Central Asia using observed records and climate model results (CMIP 5: Coupled Model Intercomparison Project 5) (Liu et al. 2021; Peng et al. 2020; Yao et al. 2021). is the following findings were discovered (i) significant wetting and warming trends occurred in Central Asia during the period of 1881–2018, with 42.5%, 59.4%, and 79.2% of stations having change points for extreme precipitation, maximum temperature, and minimum temperature, respectively; (ii) the occurrences of extreme climate events showed spatial heterogeneity, with the highest risks of meteorological drought, flood, and frost events occurring in the southwest, southeast, and northeast of Central Asia, respectively; and (iii) global warming significantly affected the intensities and frequencies of extreme precipitation and temperature, and their univariate and multivariate risks were intensified in most regions of Central Asia (Liu et al. 2021; Peng et al. 2020; Yao et al. 2021).

4.2 Anthropogenic Activities

Variations in the cultivated land area (arable land and permanent cropland) always have significant effects on water consumption and withdrawal, particularly in arid regions. Another significant anthropogenic activity influencing dryland changes in the five Central Asian countries is livestock grazing. In this sub-section, anthropogenic activities in Central Asia were examined through the lens of two factors: cultivated land area variation and livestock grazing.

The cultivated land area of Kazakhstan increased from 2,847.00 × 10⁴ hm² in 2002 to 2,953.00 × 10⁴ hm² in 2014 with an increasing rate of 8.83 × 10⁴ hm²/a. For Uzbekistan, the cultivated land area decreased from 483.00 × 10⁴ hm² in 2002 to 469.00 × 10⁴ hm² in 2007 and then increased to 477.00 × 10⁴ hm² in 2014. The cultivated land area of Kyrgyzstan decreased from 141.10 × 10⁴ hm² in 2002 to 135.60 × 10⁴ hm² in 2014. A weak decrease of the cultivated land area was observed in Tajikistan, from 88.10 × 10⁴ hm² in 2002 to 87.00 × 10⁴ hm² in 2014. For Turkmenistan, the cultivated land area decreased from 210.00 × 10⁴ hm² in 2002 to 200.00 × 10⁴ hm² in 2014 (http://www.fao.org/nr/water/aquastat/data/query/index.html?lang=en). The results demonstrated that Kazakhstan had the largest cultivated land area, followed by Uzbekistan and Turkmenistan.

Kazakhstan had a very small percentage of the cultivated land area in terms of irrigated land area, and the cultivated land area of the other four countries was nearly equal to the irrigated land area. For example, Uzbekistan exhibited the largest irrigated land area with the value of 430.00 × 10⁴ hm² in 2008, followed by Kazakhstan (188.70 × 10⁴ hm²) and Turkmenistan (185.00 × 10⁴ hm²). Tajikistan had the smallest irrigated land area, with the value of 71.00 × 10⁴ hm² in 2008 (Deng et al. 2010).

Grazing can result in rapid changes in ecosystem states that affect carbon stock (Grace 2004; Hobbs and Norton 1996). It can reduce the growth, survival, and fitness of most grazed plants, as well as the above-ground carbon stock (Tanentzap and Coomes 2012). The Gridded Livestock of the World (GLW) database of the Food and Agriculture Organization’s Animal Production and Health Division (FAO-AGA) can be used to obtain the grazing intensity data (Wint and Robinson 2007).

The data for cattle, buffalo, sheep, and goats were created in the ESRI grid format with a spatial resolution of 3 min of arc (roughly 5 km at the equator), which were freely available for download from FAO’s GeoNetwork data repository. Based on the Biome-BGC grazing model (Han et al. 2014), grazing resulted in a total carbon loss of 1,985 Tg C in grassland of Central Asia from 1979 to 2015. During the former Soviet Union period (1979–1991), 1,456 Tg C was emitted from grazing (an average annual emission intensity of 64 Tg C), showing an obvious strong carbon source process. Since the disintegration of the former Soviet Union (1992–2015), 529 Tg C has been emitted from grazing. The emission intensity was greatly reduced, with an average annual emission intensity of 22 Tg C. Therefore, grazing was converted into a process of weak carbon source.

4.3 Interactions Among Different Drivers

It has been widely observed that Central Asian oases have lower temperatures than the surrounding deserts, owing to evaporative cooling caused by plant transpiration and irrigation (Kai et al. 1997). The interactions among different drivers in Central Asia are demonstrated from the following aspects: (1) the influences of irrigation on temperature change and terrestrial water storage; and (2) the impact of urbanization on temperature change. To investigate the effects of irrigation on temperature change, the United Nations FAO global map of irrigated land was used to identify all meteorological stations that were located within 5 km of irrigated land. They were then assigned to the nearest non-irrigated land stations (Fig. 7.11). The result showed that there was no significant positive effect from the de-intensification of agriculture following the collapse of the former Soviet Union in the early 1990s on the observed temperature increase in Central Asia (Hu et al. 2014).

Fig. 7.11

© American Meteorological Society. Used with permission

Pairing of meteorological stations located in the irrigated land with the closest stations outside the irrigated land (Hu et al. 2014).

A similar approach was used to investigate whether urbanization in Central Asia may have affected the observed temperature change. Paired t-test showed no significant differences in temperature change rates between the urban and rural meteorological stations (P > 0.05). These test results suggested no significant effect from urbanization on the observed temperature change in Central Asia (Fig. 7.12) (Hu et al. 2014).

Fig. 7.12

© American Meteorological Society. Used with permission

Pairs of meteorological stations located in the urban areas and the closest rural stations (Hu et al. 2014).

To investigate the impact of irrigation on terrestrial water storage, Central Asia was classified into irrigated regions and non-irrigated regions (Hu et al. 2019a). Figure 7.13a shows the irrigated regions in Central Asia and Northwest China. The data were extracted from the Global Map of Irrigation Areas (GMIA) V 5.0 of the FAO (http://www.fao.org/nr/water/aquastat/irrigationmap/index10.stm). Based on the Student’s t-test at the 95% significance level, the annual terrestrial water storage anomaly of the irrigated grids was compared to the averaged terrestrial water storage anomaly of the non-irrigated grids surrounding them. The comparison excluded any irrigated grids that did not have any surrounding non-irrigated grids. Approximately 81% of the irrigated grids showed no significant difference when compared to the non-irrigated grids surrounding them (Fig. 7.13b) (Hu et al. 2021).

Fig. 7.13

Source Hu et al. (2021), with permission from Copyright Clearance Center’s RightsLink®, Order Number: 5216920963705)

Comparison between the irrigated grids and the matched non-irrigated grids based on the annual CSR dataset. a Irrigated area, and b insignificant irrigated grids and significant irrigated grid. Results of Student’s t-test was used to test annual CSR between irrigated grids and their surrounding non-irrigated grids. The red dots represent irrigated grids with significantly different terrestrial water storage anomaly values from their surrounding non-irrigated grids, and the black dots represent that their differences are insignificant.

5 Ecosystem Management of Central Asia

5.1 Ecosystem Networks in Central Asia

The CAS Research Center for Ecology and Environment of Central Asia (RCEECA) was launched in 2013 by the Developing Countries Science and Education Cooperation Programme of the CAS. The RCEECA is based on the Xinjiang Institute of Ecology and Geography (CAS), and it is co-founded by the Institute of Tibetan Plateau Research (CAS), Institute of Earth Environment (CAS), Northwest Institute of Eco-Environment and Resources (CAS), Institute of Geographic Sciences and Natural Resources Research (CAS), Nanjing Institute of Geography and Limnology (CAS), Institute of Remote Sensing and Digital Earth (CAS), Shenzhen Institute of Advanced Technology (CAS), and the University of CAS.

Faced with the strategic demand of the Shanghai Cooperation Organization and the construction of the Belt and Road Initiative for scientific and technological cooperation, the RCEECA established research centers and overseas sub-centers to carry out joint scientific and technological research on sustainable development of natural resources and environmental protection between China and Central Asian countries.

The research center focuses on mutually beneficial cooperation research in climate and environmental changes, mineral resources, and water and soil resources, modern agricultural and biological resources, geoeconomic and regional development, ecological restoration and environmental governance, transportation, and information technology. In addition, it seeks to develop professional research teams both home and abroad for long-term scientific and technological cooperation in Central Asia. The establishment of an ecological and environmental research platform with field observation, indoor basic experimental analysis, satellite remote sensing monitoring, and technical demonstration will provide scientific and technological support as well as the basic platform for the implementation of resources and environment development strategy of the Shanghai Cooperation Organization and the Belt and Road Initiative.

Currently, the RCEECA operates three overseas branches (Almaty, Bishkek, and Dushanbe), several information centers and analytical testing laboratories, and 19 field observation and research stations that cover the entire Central Asian area. The 19 field observation and research stations covering the landforms of glacier, mountain, forest, desert, oasis, farmland, wetland, grassland, and other ecosystems were established in Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan Mongolia, and Iran based on the typical landscape characteristics of different regions in Central Asia (Table 7.5; Fig. 7.14). The RCEECA has spent more than 3,000 million CNY on more than 60 sets of experimental analysis equipment and positioning observation instruments.

Table 7.5 Details of field observation and research stations in Central Asia

Fig. 7.14

Field observation and research stations in Central Asia

Kazakhstan has a vast territory, containing almost all ecosystem types in Central Asia. Six field observation and research stations have been established in Kazakhstan, focusing on desert, oasis, farmland, grassland, and woodland ecosystems. Tajikistan has constructed one mountain research station, one grassland/farmland research station, and one plateau research station in Pamirs. Furthermore, Kyrgyzstan plans to construct a mountain research station with three monitoring sites based on the altitude gradient, and Uzbekistan also intends to construct one oasis farmland research station and two desert research stations.

5.2 Aral Sea Crisis

Significant changes in water resources have occurred in the past three decades in Central Asia, including large inland rivers and the Aral Sea. Water scarcity affected the majority of Central Asian regions.

Water resources have been transferred from the west to the east and from the lower reaches to the upper and middle reaches. This water transfer was primarily accomplished through upstream river closure (reservoirs) and diversion (irrigation). The transferred water was used for regional agricultural and industrial development, causing water shortages downstream. Furthermore, it is reasonable to assert that the downstream ecological crisis was caused by the irrational exploitation of water resources in the upstream, which warns again the unsustainable development of Central Asian countries. The water storage in the northeast of Kazakhstan showed an increasing trend, while the water storage in the Aral Sea area exhibited an obvious decreasing trend.

During the period of 1910–1960, the level, area, and volume of the Aral Sea had been increasing, with the peaks in 1960: the highest lake level of 53.40 m, the largest lake area of 69,000.00 km², and the largest lake volume of 10,830.0 × 10⁹ m³. After 1960, the water from the upstreams and deltas of the Amu Darya and Syr Darya has been cut off by hydroelectric stations, reservoirs, and agricultural irrigation, so the water volume flowing into the Aral Sea has been decreasing. The Aral Sea was completely divided into two parts in 1986: the Large Aral Sea (south) and the Small Aral Sea (north). Following this division, the Amu Darya River supplies water to the Large Aral Sea, while the Syr Darya River supplies water to the Small Aral Sea. During the period of 1960–1986, the water level of the Aral Sea declined from 53.40 to 41.94 m, the lake area has decreased from 69,000.00 to 43,000.00 km², and the lake volume reduced from 10,830.0 × 10⁹ to 4,446.0 × 10⁹ m³, corresponding to a 60% decrease.

During the period of 1986–2006, the level, area, and volume of the Small Aral Sea were remained unchanged, while those of the Large Aral Sea was decreased rapidly: the lake level decreasing from 41.02 to 30.40 m, the lake area from 38,000.00 to 13,000.00 km², and the lake volume from 3,806.3 × 10⁹ to 814.0 × 10⁹ m³. In total, the lake area of the Aral Sea had decreased from 43,000.0 to 16,000.0 km², and the lake volume decreased from 4,446.0 × 10⁹ to 1,054.1 × 10⁹ m³ from 1986 to 2006. The lake volume in 2006 was approximately 10% of that in 1960.

In 2006, the Large Aral Sea was divided into the west Aral Sea and east Aral Sea. The lake level of the Small Aral Sea was increased by 0.4 m between 2007 and 2014. The lake area of the Small Aral Sea showed an “increase–decrease” pattern during the period of 2007–2014, with the peak value in 2011 and a small change range. The level, area, and volume of the east Aral Sea and west Aral Sea exhibited a continuous reduction trend, with the eastern part decreasing faster than the western part. From 2009 to 2013, the lake area of the Aral Sea changed to some extent, but showed a downward trend on the whole (Figs. 7.15 and 7.16).

Fig. 7.15

Changes of lake surface area of the Aral Sea

Fig. 7.16

Current status of the Aral Sea

The shrinkage of the Aral Sea cannot be solely attributed to water abstraction over the past 30 years (Yu et al. 2019). Varis (2014) has proposed that irrigation-intensive industries in the former Soviet Union have drained water bodies in the Central Asian countries. Massive amounts of water consumption have indeed resulted in a reduction in the lake area of the Aral Sea since the 1960s (Saiko and Zonn 2000), but the situation has not substantially changed in the last three decades (Yu et al. 2019). Water inflows have been much lower than water losses since the disintegration of the former Soviet Union, and the Aral Sea has gradually dried up due to excessive irrigation water use in the upper tributaries (Yu et al. 2019). Today, the gradual draining of the Aral Sea is not only a regional issue, but also becomes a world-renowned transnational ecological disaster (Cai et al. 2003; Kitamura et al. 2006; Yu et al. 2019).

5.3 Response Measures to Aral Sea Crisis

The Muynak Aral Sea Ecosystem Field Observation and Research Station (see Fig. 7.17) is located in the Nukus region of Karakalpakstan Autonomous Republic of Uzbekistan, about 100 km away from the capital Nukus City. The station has an elevation of 52 m above sea level, with the geographical coordinates of 43°41′57.03″N and 59°02′10.04″E. The station is dedicated to studying the Aral Sea crisis.

Fig. 7.17

Photography of Muynak Aral Sea Ecosystem Field Observation and Research Station

On April 16 2019, the station was completed and began normal operation, with the assistance of the Institute of Botany, Uzbekistan Academy of Sciences. Total solar radiation, scatter radiation, ultraviolet radiation, net radiation, sunshine duration, soil temperature, and soil heat flux are the six meteorological elements measured by the station. In addition, there are CO₂/H₂O flux observations and corresponding biometeorological observation systems in the station. The observation indicators include soil temperature, humidity, heat flux, etc.

Central Asia is located in an arid area with a fragile ecological environment, and is sensitive to climate change. Due to the limitations of the natural environment, historical changes, and socio-economic development conditions, there is a lack of long-term and reliable monitoring data on climate change and environmental factors in Central Asia. The scientific community generally has a limited understanding of environmental impact and green sustainable development model of climate change and human activities in this area. The construction of the ecosystem observation and research network in Central Asia will significantly enhance the long-term monitoring capacity of the area, provide a more comprehensive understanding of the basic information of the natural environment, and deepen the understanding of the relationship between climate change and social development.

The Aral Sea has shrunk dramatically since the second half of the twentieth century. The Aral Sea was divided into the Large Aral Sea (south) and the Small Aral Sea (north) in 1986, and the Large Aral Sea was further divided into the east Aral Sea and the west Aral Sea, due to the continuous decline of water level. The surrounding climate has changed as the shrinkage of the Aral Sea. The establishment of long-term observation sites in this region will be extremely useful for the study of the Aral Sea issues.

The Muynak Aral Sea Ecosystem Field Observation and Research Station is based on the frontier of the Aral Sea research, taking the Aral Sea ecosystem in the arid area as the objective to carry out long-term positioning monitoring and research on the Aral Sea ecosystem and environmental factors in the arid area. It helps to study the change law, evolution trend, driving mechanism, and environmental effects of the Aral Sea and its environmental factors, as well as the ecological engineering models and ecological technologies for the restoration, reconstruction, protection and rational utilization of the Aral Sea, which can provide theoretical basis and long-term data support for solving some fundamental problems in the study of the Aral Sea and its regional environment.

5.4 Conservation and Effective Practices of Drylands in Central Asia

To address the dryland changes, the five countries employed many policies, actions, and projects in multiple sectors, especially in saving water resources and increasing water use efficiency. These policies, actions, and projects are mostly supported by the United Nations Economic Commission for Europe (UNECE) and World Bank.

For the water and soil conservation measures, modernized irrigation system was established in the five countries of Central Asia. For example, water saving irrigation technologies and efficient irrigation technologies are used in the agriculture irrigation. When drip irrigation and spray irrigation are employed, water consumption per ton of produce is low and crop yield is high, which can improve the irrigation water efficiency (Fig. 7.18) (Rau 2016). Water conservancy projects are largely built across the whole Central Asia.

Fig. 7.18

Drip irrigation in Central Asia

The irrigation water efficiency of irrigation systems in Kazakhstan is determined by a variety of factors, including crop structure, land-use intensity, and technologies. One method for increasing irrigation water efficiency is to build technically advanced irrigation systems that allow the use of water-saving irrigation technology such as drip irrigation, which can save 20–30% of irrigation water while increasing productivity by 2.0–2.7 times. The Second Irrigation and Drainage Project (IDIP-2) contributes to addressing a key pillar of the Kazakhstan Green Economy Concept: effective water resource management. The seven-year project aims to improve irrigation and drainage service delivery as well as the participation of water users in developing and managing the modernized systems in the four most densely populated regions in the south of Kazakhstan: Almaty, Kyzylorda, South Kazakhstan, and Zhambyl oblasts (The World Bank 2014).

For Uzbekistan, the total annual water withdrawal increased steadily from 45.50 km³ in 1975 to 62.80 km³ in 1985, mainly due to the expansion of irrigated land. The total annual water withdrawal was 62.50 km³ from 1990, a declined trend because of agricultural water-saving methods and the recession in the industrial sector. In 2001, the total annual water withdrawal was estimated as 60.60 m³, of which 3.90 km³ was groundwater; in 2005, this was an estimation of 56.00 km³, of which 5.00 km³ was groundwater. Water allocations were regularly reduced to promote savings, satisfy demand from new users, and increase water flow to the Aral Sea. The total annual irrigation water withdrawal declined from 58.80 km³ in 1990 to 50.40 km³ in 2005 (FAO 2012a). Seventy kilometers of the Bustan irrigation channel will be modernized to significantly reduce water losses (50%) and decrease water withdrawn from the Amu Darya River. Irrigation supply will become more reliable, and farmers will be able to cultivate higher-value crops such as fruits and vegetables, which require less water and can generate five times the income of cotton and wheat.

The best water saving technologies in Kyrgyzstan were proposed by a team of national and international experts, focusing on the most promising of existing global practices. Currently, land is irrigated using surface water by distributing water to the surface of agricultural land through a system of ditches, but the associated water loss is about 50.0%. Comparing the advantages and disadvantages of two irrigation methods: sprinkler irrigation and drip irrigation, both require significant upfront investments but aid in the conservation of water resources and increase productivity (UNECE 2015; https://unece.org/press/unece-helps-kyrgyzstan-identify-more-efficient-irrigation-technologies).

For Tajikistan, the irrigation potential area was estimated as 1,580,000.00 hm², which is about 11.0% of the country’s total area. Surface irrigation is the main irrigation technique used in Tajikistan. Drip, sprinkler, and micro-sprinkler irrigation technologies were applied in a small area only at the experimental level. In 2009, the surface water irrigation area was about 696,476.00 hm² (or 93.9% of the total full control irrigation area), the groundwater irrigation area was about 32,500.00 hm² (4.4%), and the mixed surface water and groundwater irrigation area was approximately 13,075.00 hm² (1.8%). Monitoring of direct use of agricultural drainage water and treated wastewater is difficult. The irrigated area pumped water from rivers is 298,500 hm². A new test shows that cotton water use can be saved effectively by a new irrigation technology (FAO 2012b).

For Turkmenistan, the irrigation area is 7,013,000.00 hm², which is equal to the cultivated land area. However, the area irrigable by water resources is estimated to be 2,353,000.00 hm². In 2006, the area equipped for irrigation was estimated as 1,990,800.00 hm². The whole area is the irrigation area, which is larger than the cultivated land area, because the irrigation area includes irrigated permanent pasture, which is not included in the cultivated land area. In 1994 and 1975, the area equipped for irrigation was 1,744,100.00 hm² and 857,000.00 hm², respectively. Cotton, wheat, vegetables, beetroot, melons and watermelons, lucerne, and corn are being planted in the field for the first time in many years. It is shown that the combination of modern water-saving irrigation technology and high-tech agricultural crop cultivation method has achieved good results. A 2.5–3.0 times reduction in irrigation water compared to conventional irrigation in 2018 could produce about 60 centers/hm² of cotton. At the same time, the amount of harmful salts in the soil has been significantly reduced (UNDP 2019).

6 Summary and Perspectives

With a total area of 4.0 × 10⁸ hm² and a total population of around 65 million, Central Asia mainly consists of drylands, which are very sensitive to global climate change. In recent years, the five Central Asian countries’ populations and economies have increased, with Turkmenistan showing the fastest growth rates in GDP and per capita GDP.

Desert, semi-desert, and steppe are the most common ecosystem types in Central Asia; and vegetation types in Central Asia are diverse, rich, and unique. Farmland change, forestry activities, and grazing are examples of mainland use/land cover changes and land management in Central Asia, each of which has a unique impact on the ecosystem structures and functions. Land degradation in Central Asia was primarily caused by rangeland degradation, desertification, deforestation, and farmland abandonment. The temperature in Central Asia continues to rise, glacier melting accelerates, water resource stability deteriorates, and uncertainty grows, resulting in an increase in the frequency and severity of floods, droughts, and other disasters.

The ecosystem and environment of the Aral Sea have become the key issues to be solved urgently for the sustainable development of Central Asia. The ecosystem NPP was decreasing over the past years, and the organic carbon pool in the drylands of Central Asia was seriously threatened by climate change, losing approximately 0.46 Pg C from 1979 to 2011. Grazing was an obvious strong carbon source process during the former Soviet Union period (1979–1991), but since the disintegration of the former Soviet Union (1992–2015), this activity has been converted into a weak carbon source process.

From 1995 to 2015, the value of ecosystem services in Central Asia increased overall, with grassland contributing the most. Except for food production, raw materials, climate regulation, soil formation, and waste treatment, most ecosystem functions decreased between 1995 and 2015; however, most ecosystem functions are expected to increase between 2015 and 2035 (except for water regulation and cultural service/tourism).

Global climate change poses a clear threat to the ecological diversity of Central Asia. Drylands in Central Asia are threatened by both natural and anthropogenic disturbances. The increase of precipitation cannot compensate for the aggravation of water shortage caused by temperature rise in Central Asia. The following suggestions are proposed for the long-term management of Central Asia’s hydrology, socioeconomics, and ecosystems:

• (1) Initiating an international joint research plan on water-social economy-ecosystem in the Aral Sea Basin.

• (2) Implementing a scientific research plan on water and ecosystem in the context of climate change.

• (3) Conducting joint monitoring research on the sources and diffusion paths of salt dust in the Aral Sea.

• (4) Researching salt-tolerant and drought-tolerant vegetation cultivation and ecological restoration of the arid lakebed.

• (5) Increasing international cooperation in biodiversity conservation and ecological security among the Central Asian countries and supporting the implementation of international joint protection actions are now of great importance.