Urban Water Security Challenges
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Water security is a new concept for the sustainable water management. Rapid urbanization and climate change have become a burden for water security managers. It is important to understand and investigate various challenges and impacts of global environment changes for managing water-related problems like frequent urban floods; groundwater water depletion; surface and groundwater pollution; land subsidence and aquatic ecosystems. Urbanization leads to more impervious surface causing increased storm runoff and decreased groundwater recharge resulting in greater floods and groundwater table depletion. Similarly, climate change is reported for alteration of rainfall pattern with more extreme rainfall events and longer dry days resulting in greater floods and lower groundwater table. Therefore, haphazard urbanization, climate change, population growth and change in lifestyle have badly affected urban water environment. In many cases, urbanization rate is quite higher in comparison to capacity of local government which is mainly engaged in development and construction of water infrastructures like water supply and sanitation system, stormwater drainage and flood management system. This chapter is focused on various global environmental changes with focus on urbanization and climate change and their implications on urban water security. Case studies have been included for better illustrations.
Water is essential for the survival of animal and plant life. At global scale, availability of usable water resources is well above total demand (Oki and Kanae 2006). However, the distribution of water resources is not uniform either spatially or temporarily. There is a definite surplus of water during the rainy season while significant water deficit occurs during dry season. For increasing water security in urban areas, the phenomena like devastating floods, reliable water supply for drinking, irrigation, hydropower among others that are associated with excessive and scarce water must be managed well. The rapid growth of population, with extension of irrigated agriculture and industrial development has increased the demand of water. As the Earth’s population has been growing rapidly, more stress is being put on the land to support the increased population. One question that arises is how water resources will be affected. In several cases, water shortages have led to conflicts over the rights of the water. Environmental issues such as provision of clean water, production and processing of wastewater and flooding and land subsidence are frequently reported in many cities. With industrial and domestic water demand expected to double by 2050, competition among urban, peri-urban and rural areas will further deteriorate (Jalilov et al. 2018; UNDP 2006). In many urban areas, the sustainable use of water is approaching or exceeding the limits (Hatt et al. 2004; Mitchell et al. 2003). In the urban basin, competition between agriculture and industry is intensifying (Bahri 2012). The unplanned urbanization is highlighted by the degraded environment in the urban areas due to changes in hydrology of catchments and modified riparian ecosystems.
In addition to various influences, it is important to consider the effects of two crucial issues: urbanization and climate change on water environment, such as surface runoff, stream flow, flooding, river pollution, biodiversity, and groundwater recharge. In context of climate change and urbanization, the negative impacts are exacerbating resulting greater runoff, pollutant loads and pressure on existing systems.
Similar to urbanization (land-use change), climate change affects local hydrological cycles by producing more surface runoff and decreasing the base flow, interflow and depression storage. Community planners, developers and citizens should be aware of the impacts of land-use and climate change on their environmental resources. Anticipating the rate, amount and duration of rainfall in each heavy rain event under climate change is highly important in planning and designing of stormwater management facilities, erosion and sediment control structures, flood protection structures and many other civil engineering structures involving hydrologic flows.
It is well accepted that traditional urban water management approach is largely unsuitable to address current and future sustainability issues (Ashley et al. 2005; Wong and Brown 2008). The conventional approach to manage urban water systems, around the world, has seen the use of a similar series of systems for drainage of stormwater, potable water and sewerage. United Nations (UN Agenda 21 1992) defined achieving sustainable urban water systems and protecting the quality and quantity of freshwater resources as key components of ecologically sustainable development. It is important to plan, design and manage water resources system very carefully and intelligently. Minimizing the disturbance on an urbanizing watershed is one way of ensuring continued water supply and decreasing urban floods. Because each land use has different levels of influence, careful physical planning can minimize these effects. Although the influence of urban sprawl on groundwater recharge, and the quantity and quality of surface water is of considerable importance, many planners, urban managers and water resource experts lack to incorporate the potential hydrological impacts of climate and land-use change. Science-based system that justifies the relative impact of both urbanization and climate change on stormwater runoff at local scale is largely warranted in the changing environment. This chapter focuses on the risks of two major threats: urbanization and climate change on water security which is defined as ‘the reliable availability of an acceptable quantity and quality of water for health, livelihoods and production, coupled with an acceptable level of water-related risks.’ Water security also means addressing the adverse effects of environmental protection and poor management. It is also concerned with ending fragmented responsibility for water and integrating water resources management across all sectors-finance, planning, agriculture, energy, tourism, industry, education and health. A water-secure world reduces poverty, advances education and improves living standards.
Rapid urbanization and economic growth have resulted in widespread environmental degradation in urban areas. The imbalances are unavoidable, because urbanization leads to significant demographic, sociocultural, environment and political changes that eventually affect the realization of the idea of urban sustainability. City is the center of economic growth, job creation, innovation and cultural exchange. This is because the cities in developing countries are largely concentrated on production activities providing greater opportunity for additional income. Cities provide better woman participation, health access, literacy rate and upward social mobility. Grubler and Fisk (2013) found that the average urban gross domestic product (GDP) accounts for about 80% of world GDP. The concentration of people, economic activities and services in relatively small areas has big impact on urban society and the economy. Urban economies lead to better access to services, higher prosperity and lifestyle changes, but rapid urbanization also leads to increased slums and squatter settlements, social alienation and environmental pollution. Positive and negative impacts of urbanization are not evenly distributed among urban populations. Rich and powerful are more benefited from positive effects and better protected from adverse effects than poor and alienated people.
In developing countries, urbanization is occurring at a high rate. In 2013, the United Nations Economic and Social Division reported that the land-use patterns and urbanization is diverse in developed and developing countries. The growth of cities in developing countries is at rapid pace and often concentrated in the capital. Urbanization leads to increased impervious surface areas, and the construction of stormwater drainage networks increases the time of concentration and direct runoff, thereby resulting in a more rapid rise in flow rate and depletion of groundwater table (Saraswat et al. 2016, 2017; Willems et al. 2012). In addition, natural water bodies such as lakes, wetlands which can hold a significant amount of flood water are being reduced or filled resulting increased incidence of flooding. The city’s growth, reported by Seto et al. (2011), drives the change of local regional environment by creating the most human-dominated landscape and transforming the land cover, hydrology system and organisms. The hiccups are that these areas do not have the capacity to invest in building resilience to these possible disasters. Therefore, these require innovative, locally focused, new analytical space modeling methods that include all variables of land-use changes.
2.3 Climate Change
Water management is planned based on local conditions. Climate change has major impact on the water resource system (Mishra et al. 2019a, b; Kharrazi et al. 2017; IPCC 2014). Recognizing the importance of water resources, many studies have been done to investigate the effects of climate change on precipitation patterns and hydrological structures. These studies suggested varying regional trends (increasing or decreasing) in the future due to climate change. In particular, precipitation increases in wet areas, decreases in arid areas. Most of the studies indicated that heavy precipitation events (frequency and intensity) will increase in future. Changing weather regime will bring prolonged droughts and excessive rains.
Climate change impacts such as the amount, timing and intensity of rain events, in combination with land development, can significantly affect the amount of stormwater runoff that needs to be managed. In some regions, the combination of climate and land-use change may make existing stormwater-related flooding worse, while other areas may be minimally affected. Intergovernmental Panel on Climate Change (IPCC 2014) reported that among the most challenging anthropogenic environmental, economic and social global issue today is climate change. It is reported that climate change is mainly caused by the increase in the concentration of greenhouse GHG in the atmosphere. The carbon emissions are typically attributed to anthropogenic aspects such as land-use changes including agricultural, forestry sectors and city energy demand through fossil fuels and biomass consumption.
Climate change projections are widely used to assess likely future impacts. Global climate models are currently the most credible tools available for simulating the response of the global climate system to increasing greenhouse gas concentrations and provide climatic variables, such as temperature and precipitation. Several GCM projections are available based on some possible scenarios of global warming and CO2 generation rates. These projections are available for current and future climate (IPCC 2014). Multiple GCMs and scenarios are used to reflect the uncertainty associated climate change. In the climate modeling community, projections are available in terms of four emission scenarios: one mitigation scenario (RCP2.6), two medium stabilization scenarios (RCP4.5/RCP6) and one very high baseline emission scenario (RCP8.5).
Due to great amount of uncertainty associated with the scenarios and projections, use of multiple GCM is recommended to provide the range of recommendations for addressing various climate change impacts. GCM outputs are largely biased when compared with observation data due to flaws in model structure and coarse resolution input. Therefore, direct use of GCM precipitation outputs is considered not suitable for the climate change impact assessment at basin level. Downscaling enables minimization of biases in GCM outputs to be used at local scale climate change impact assessment. There are several downscaling techniques available to transform GCM outputs to local scale for reliable impact assessment. Dynamical downscaling technique converts GCM outputs into local climate data by enhancing atmospheric circulations and climate variables to finer spatial scales using regional climate models. Statistical downscaling techniques use models of correspondence between GCM contemporary climate scenarios data and real-world data.
2.4 Implications on Water Security
Population increase coupled with urbanization and changing climate out constrains water security in many ways. Rapid urbanization and global climate change will greatly alter water environment in developing cities. This section examines both qualitative and quantitative aspects of water security. It identifies water security in the megacity in terms of threats to the environment such as flood relating it to urbanization and climate change. It also examines water security threats in megacity in the case of inadequate water supply relating it to urbanization and climate change.
2.4.1 Hydrological Cycle
In a natural environment, the small percentage of precipitation becomes surface runoff, but as the urbanization is growing and the development expanding, the percentage of stormwater increased abruptly (Fig. 2.1). The surface water runoff is created when pervious or impervious surfaces are saturated from precipitation or snow melt (Durrans 2003). Pervious surface areas absorb the water naturally to the saturation point and after which the amount of the rainwater runs off and travels via gravity to the nearest stream. This point of saturation is dependent on the landscape, soil type, evapotranspiration and the biodiversity of the area (Pierpont 2008).
Greater imperviousness (roads, roofs, pavement) resulting increased surface runoff, reduced infiltration and less groundwater. Increased drainage network also results less ground recharge and quick peak discharge. As it is well-known fact that the urbanization alters watershed hydrology as land becomes more and more covered with surfaces impervious to rain, water is redirected from groundwater recharge. In a natural setting, only very small percentage of precipitation becomes surface runoff, but as the urbanization is growing and the development expanding, this percentage of stormwater increases abruptly. This runoff normally flows into the nearest stream or river and increases the percentage of water in the system, and if it is polluted, it can lead to disastrous situations. The Center for Watershed Protection has reported that areas that exceed 10% imperviousness, stream health begin to decline (Coffman and France 2002). The urbanized watershed faces increased flooding, stream bank erosion and pollutant export. The receiving streams of these intensified storm flows alter hydraulic characteristics due to peak discharges several times higher than predevelopment. With urbanization, environmental issues such as flooding, solid waste problems, proliferation of informal settlements and air pollution are prevalent in the region. Encroachment (flood plains, obstruction of water/floodways, loss of natural flood storage) results in increased flooding. Green areas hold an important role in maintaining balance in urban environment, because of their main function as water retention slow release, while enhancing inflilration in a catchment.
2.4.2 Water Shortage
Access to clean and adequate water remains a critical challenge and an acute seasonal problem in urban areas. Freshwater is crucial to human society—not just for drinking, but also for farming, washing and many other activities. It is expected to become increasingly scarce in the future, and this is partly due to climate change. Rainfall distribution/pattern in a year will alter significantly with the climate change, although it is projected to alter not much at annual scale. Greater rainfall due to climate change leads to more rapid movement of water from the atmosphere back to the oceans, reducing our ability to store and use it. The overall effect is an intensification of the water cycle that causes more extreme floods and droughts.
2.4.3 Land Subsidence
Highly urbanized cities rely heavily on groundwater for water supply resulting in uncontrolled withdrawal from groundwater aquifers. Rapid urbanization has reduced aquifer recharge and has resulted in declining groundwater levels as well as salt intrusion and land subsidence. Overextraction of groundwater is now a pressing problem in rapidly growing cities of developing nations. Illegal/unregulated construction of wells has proliferated in the region. In the urban environment, the impervious surfaces which cover the natural environment over the ground, the pattern of hydrological process of surface water runoff becomes more unnatural, causing damage to infrastructure and the impairment of receiving waters by pollutants. Indiscriminate land-use practices has impacted on the quality of surface water and modified the hydrologic conditions (Masago et al. 2019).
In urban areas, land subsidence is mainly caused by excessive groundwater extraction, higher load of constructions and infrastructures, natural consolidation of alluvium soil and natural event such as tectonic activity. For example, land subsidence in Jakarta occurs mainly because of lavish groundwater extraction and higher load of construction and infrastructures. Through years, water demand in Jakarta is gradually increasing and this phenomenon is not supported by an adequate water supply. In the long term, land subsidence would be a potential cause of flood in Jakarta. In fact, land subsidence has proven to be one of the main causes of flood in Jakarta, particularly in North Jakarta. Continuous land subsidence will also endanger drainage structures in Jakarta which can make the flood even worst.
2.4.4 Surface and Groundwater Pollution
Demands from intensive development and utilization activities, population explosion, poor environmental management—all these contribute to the poor quality of water in almost all water bodies in urban areas. The unregulated discharge of domestic and industrial wastewater and agricultural runoff had caused extensive pollution of receiving water bodies. The effluent being discharged comes in the form of raw sewage, detergents, fertilizers, heavy metals, chemical products, oils and even solid waste. Each of these pollutants has different noxious effects that influence human livelihoods and translate into economic costs. Pollutants accumulate on impervious surfaces, and the increased runoff with urbanization is a leading cause of nonpoint source pollution. Sediment, chemicals, bacteria, viruses and other pollutants are carried into receiving water bodies, resulting in degraded water quality.
It is estimated that large portion of the total garbage generated are not collected by the solid waste management agencies. The uncollected garbage goes into the river systems resulting in the clogging of waterways. This aggravates flooding in the metropolis. Wastewater is another water management issue that needs to be considered more thoroughly. Higher population density and their activity not only affect the water supply and demand but also the production of wastewater released to the river or open channel. The loss of aesthetic value of rivers and other water bodies is a direct result of the pollution of these water bodies. The presence of informal settlers living along the rivers and their tributaries also contributed to the constriction of the drainage areas, resulting to flooding during heavy rains. These informal settlers also add to the deterioration of the water quality of these water bodies.
2.4.5 Human Health
Over the last 2–3 decades, most of the water bodies in Manila have been increasingly under threat of unprecedented and uncontrolled urbanization, industrialization, population explosion in urban centers caused by mass migration into cities, unsound land-use and solid waste management practices, and unabated pollution of water and the air. With the changing climate regime as manifested by the increase in the number of typhoons resulting to flooding, the need to address the risks from a deteriorating environment has become one of the biggest challenge of the modern time. Impaired water quality will endanger community’s health, leading to the increasing of poverty level. People with lower economic condition tend to face difficulty in providing their wastewater treatment and drinking water facilities. Slum areas in Jakarta are more prone to diseases from bad sanitation and contaminated water source. People who live in those areas often suffer from diarrhea and intestinal worm infection, mainly during rainy season when flood has worsen the water contamination. The social impact apparently not only threatened community’s health but also affected community’s capacity and poverty in Jakarta.
The deteriorating quality of the water in major water bodies and urban environment situation in the metropolis is negatively affecting the overall health conditions of the population (Masago et al. 2019). A recent joint Japan International Cooperation Agency (JICA) and NSO Study (January 2011) indicated that there are four main causes of water-related diseases in the Philippines: drinking polluted water, contact with polluted water, infection by vector and infection by parasite. Cholera, typhoid, para-typhoid, hepatitis, dysentery and diarrhea are typical cases resulting from taking in polluted water. Scabies, conjunctivitis, typhus and trachoma are the common diseases that can be contracted from contact with polluted water. Infection by a vector transmits diseases such as malaria, dengue and yellow fever while infection by parasite can give rise to such illnesses as filariasis and schistosomiasis. In Metro Manila, diarrhea is the second or third leading causes of morbidity based on a 5-year average from 1996 to 2000 as well as in 2001.
2.4.6 Ecosystem and Biodiversity
The pressures that come with rapid development and urbanization have put so much stress on the water and the environment resulting in destabilization of ecosystems, destruction of natural habitats and an alarming rate of biodiversity losses. During the last 10–15 years witnessed the unregulated land use in Metro Manila and the neighboring provinces which caused deforestation of the surrounding watershed areas such as the Marikina and the Laguna de Bay watershed areas. The loss of vegetation has adversely affected the habitat and population flora and fauna in the area, both aquatic and nonaquatic. Low concentration of dissolved oxygen (DO), a common characteristic of the water bodies in Metro Manila, in combination with the presence of toxic substances may have led to stress response in aquatic ecosystem due to toxicity levels.
2.5 Case Studies
2.5.1 Bagmati River Flood, Nepal
The climate change impact on flood frequency research employed a high-resolution (approximately 20-km) daily GCM precipitation output of Meteorological Research Institute (MRI), Japan. Comparison of observation and GCM data pointed out that the MRI-GCM precipitation output has significant biases in frequency and intensity values. Quantile–quantile mapping method of GCM bias correction was applied for minimizing the biases in precipitation frequencies and intensities. Concept of homogeneous precipitation regions was introduced to link the uneven observation data stations and GCM grid cells. Analyses of return period curves, shape and scale factors at different observation stations enabled delineation of three homogeneous precipitation regions. Accordingly, regional quantile–quantile bias-correction technique was developed for minimizing biases in MRI-GCM precipitation output.
2.5.2 Ciliwung River Flood, Indonesia
Sustainable development will not be achieved without a water-secure world. A water-secure world integrates a concern for the intrinsic value of water with a concern for its use for human survival and well-being. The importance of this chapter comes from its enhanced understanding of urbanization and climate change on extreme flood events for sustainable urban water management. This chapter was aimed at suggesting policy foresight for infrastructure and land-use management facilitating the need to address challenges to urban sustainability through planning in advance for a population that is projected to come, planning at the local scale anticipating the expected urban growth or resource availability. Therefore, urban expansion through infrastructure development can be demonstrated to contribute to the adverse impacts on ecological sustainability and the high demand of natural resource use within city boundaries. Based on the modeling scenario, protected area zones are considered to constrain change during the modeling process.
The increase in the precipitation and flood pattern will have major implications on the design, operations and maintenance of municipal wastewater management infrastructure. The results of climate and land-use change impacts reflect that the design standards and guidelines currently employed needs revision. Increased peak flows and flood inundation should be considered in future flood management systems, and flexible, adaptive measures should be adopted because of the uncertainty of future climate and land-use changes.
The rapid urbanization coupled with the slow infrastructure development has exerted a tremendous impact on the water resources and urban environment. The increasing population of the metropolis had resulted in the increasing informal settler families. This contributed to the deterioration of the river systems due to untreated waste discharges and increasing incidence of flooding due to the alteration of drainage patterns and waterways. The unplanned expansion of urban areas also led to traffic congestion in the city resulting to increase air pollution and greenhouse gas emission.
Addressing the diversity of issues of urbanization, inclusive economic opportunity, technological innovations, sustainability while still offering a livelihood for the world population has been a great challenge. It has enlightened both the global and local communities to the long-term consequences of our decade-long form of designing cities. That has led to current environmental and inequality related impacts such as water scarcity, air pollution, traffic congestion, cyclones, hurricanes, floods, rampant increase of urban slums, power outages and disease outbreaks. The inequality on who receives better affordable housing and basic environmental services depends somehow on an individual’s economic level.
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