Introduction

Soil erosion represents a great hazard to agricultural and residential areas, causing relevant socioeconomic and environmental impacts, especially in the Global South (Dagar 2018; Kuhn et al 2023). Ravines and gullies are the most recurrent types of soil erosion and are characterized by steep incisions in soils, forming unstable channels that range from a few to many meters in depth and up to hundreds of meters in extension during its final stages, when erosion naturally stabilizes establishing the new balance profile (Dagar 2018; Kuhn et al 2023).

The development of ravines and gullies is generally the result of several different factors, which may include heavy rainfall, topography (e.g., slope, critical drainage area, shape of the catchment), geology and the geotechnical conditions of the soil (e.g., porosity and permeability, compaction, slope instability, hydrological condition) (Akgün and Türk 2011; Castillo and Gómez 2016; Amorim et al. 2017; Dagar 2018; Pereira Filho et al. 2018; Kuhn et al 2023). Anthropogenic activities constitute another important element in ravine and gully development, especially related to deforestation, forest fires, overgrazing, mining, intensified agriculture, and urbanization, which all can cause enhanced runoff (Busnelli et al. 2006; Akgün and Türk 2011; Ozer 2014; Castillo and Gómez 2016; Amorim et al. 2017; Dagar 2018; Golosov et al. 2018; Guerra et al. 2018; Xu et al. 2019; Kuhn and Reis 2021).

Ravines and gullies are mainly a result of poor territorial planning, and lack of governance (Ozer 2014). Territorial space is an increasingly scarce resource, so the implications related to land degradation are serious (Pani 2016). Ravines and gullies can damage agricultural land, infrastructure, and urban areas, also leading to increased injustice and finally social segregation (Kayembe and Wolff 2015; Arabameri et al. 2019). Moreover, ravines and gullies are one of the most efficient processes in sediment mobilization (Gayen et al. 2019), contributing to the silting up of rivers and dams if the sediment load is higher than the transport capacity of watercourses.

According to the Brazilian federal classification, the negative impacts of ravines and gullies are considered as a type of natural disaster (Brasil 2012a) and the economic impacts caused by ravines and gullies are recorded worldwide (Kuhn et al 2023). The destruction of houses, bridges, and other types of infrastructure, as well as fatalities, are some of the results of linear erosion in countries such as Nigeria (Balzerek et al. 2003) and the Democratic Republic of Congo (Ozer 2014; Imwangana et al. 2015). In Australia, Abdo et al. (2013) describe the loss of agricultural areas due to erosion caused by ravines, similarly to what is observed in in India (Pani 2017), for instance. In Algeria and India, erosion is reported to severely impact these countries’ infrastructure, damaging, and destroying roads, dikes, bridges, water lines, increasing the costs for road and railway maintenance (Pani 2017; Kouidri 2018).

In Brazil, gullies and ravines are a historical problem in several regions, especially in those that experienced different colonization cycles (Bezerra et al. 2009). During the gold cycle in the Minas Gerais state, starting at the end of the seventeenth century, rural roads linked to gold mining contributed to the development of gullies and ravines due to the concentrated surface runoff of rainwater (Ferreira et al. 2011). On the western plateau of the São Paulo state, coffee farmers’ occupation in the 1920s, known as the coffee cycle, is also closely linked to the development of ravines and gullies caused by deforestation and intensified agriculture (Bezerra et al. 2009). More recent occupational territory cycles encouraged by the Federal Government in the 1950s, especially in the central and northern areas of the country, are connected to the increasing challenges related to ravines and gullies (De Lima and Guerra 2019).

The increase in the frequency of heavy rain events, consequences of climate change, will likely contribute to worsening erosion, with more intense droughts that can weaken soil structure and favor instabilities (Valentin et al. 2005; Cabral et al 2022). Projections of climate change in Brazil indicate an increase in temperatures across all regions and more frequent intense rain events in the South and Southeast, as well as more droughts in the Amazon and in the Northeastern region (Marengo et al. 2021; Pereira Filho et al. 2018; Lopez et al 2023).

Knowledge of the economic impacts of ravines and gullies is an important prerequisite to develop actions and public policies aiming at land degradation mitigation. Although this is a problem affecting many regions in Brazil, few studies have been carried out quantifying the impacts caused by ravines and gullies (De Brito Galvão et al. 2011; Rotta and Zuquette 2014; Souza et al. 2017; Guerra et al. al. 2018) and no previous study exists on a national level. Thus, this study aims at providing an overview of the official record of natural disasters caused by ravines and gullies, in Brazil, with a focus on analyzing economic impacts, by evaluating the S2ID database and complementing it with other databases and a literature review. Based on these results, recommendations are drafted on how to improve the long-term record of ravines and gullies in Brazil, which is fundamental for the prevention and mitigation of future disasters.

Methods

The study was conducted in three stages: (1) collection and analysis of civil defense data available in the S2ID system, (2) bibliographic search in the Scopus database, and (3) data integration and discussion based on the scope of the research.

Even though records of natural disasters caused by ravines and gullies in Brazil are available since 2003, we analyzed in greater detail the information between January 2013 (implementation of the S2ID, available in: https://s2id.mi.gov.br/) and May 2019 (date on which data acquisition was performed). This time interval was chosen due to a more systematic record of disasters in the S2ID database, covering two levels of detail (Fig. 1):

  1. a.

    Occurrence record: location (city and state and basic information), date, type of disaster and estimated number of people affected.

  2. b.

    Complete record: general information on impacts, damages and actions taken.

Fig. 1
figure 1

Timeline of the disaster record in the S2ID system, and the type of information available at each stage

Full size image

The latter (b) can be extracted in documents attached to the S2ID, namely the Municipal Declaration of Emergency Action (DMATE) and the Disaster Information Form (FIDE). In FIDE, in addition to basic information, data related to municipal finances are recorded, as well as description of the affected area, causes and effects of the disaster, human, material or environmental damage, and public and private economic losses. The DMATE includes the history of the disaster, information about the municipal disaster management, mobilization, and use of material and financial resources. This information is usually accompanied by technical and photographic reports on the affected area. Usually, the occurrence record occurs when the disaster is restricted to a single municipality, while the complete record occurs when the magnitude of a disaster is higher, when there is a need for resources from institutions at a state or federal level.

For all events identified, additional data from the National Department for Civil Defense and Protection (SEDEC) was requested, mainly the economic impacts caused, using the Citizen Information Service (SIC, available at: https://www.gov.br/economia/pt-br/acesso-a-informacao/servico-informacao-cidadao-sic). Financial losses reported in Brazilian currency (Reais—BRL) were converted into United States Dollars (exchange rate: R$ 3.20 U$ 1 representing an average between R$ 2 and R$ 3.9 over the period between January 2013 and May 2019).

The bibliometric analysis was performed considering the results acquired in the Scopus database. Scopus provided the largest diversity of publications on the subject, according to our analysis. The following keywords were chosen: “ravines or gully” and “Brazil”, limited to the subarea “earth” or “environment”. The survey was conducted in English. Research in Portuguese were considered in those cases that had an abstract in English. Documents not indexed in the Scopus database, such as theses and dissertations, technical reports, or non-indexed articles were not considered. Single events such as in Bauru in 1993 (Almeida Filho 2000; Salomão 1994) and other historical cases outside the time period were not considered due to the lack of precise records.

Results and discussion

Data overview

The data extracted from the S2ID system and the information available in the Scopus database allowed the identification of municipalities with records of impacts related to ravines and gullies (Fig. 2). The S2ID database indicated the occurrence of ravines and gullies in 46 municipalities, while the bibliographic analysis indicated their occurrence in 68 municipalities, with a single municipality (Deodápolis) appearing in both analyses (Table 1). Therefore, 113 municipalities have recorded significant impacts related to ravines and gullies.

Fig. 2
figure 2

Distribution of the municipalities and regions; in red, municipalities where cases have been reported by the civil defense database and in blue the location of the studies analyzed in the literature review (Scopus); biomes (IBGE 2019) are indicated in colors and the arrows indicate the frontier of agricultural expansion in Brazil

Full size image
Table 1 Limitations and contributions of each source of information used in this study
Full size table

S2ID database

A total of 76 cases were registered in the 46 municipalities in the S2ID database. Of this total, 52 contain only “occurrence records”, in which solely the typology of the process is classified and an estimate of the number of people affected is presented. For the other 24 cases, full information was available, which documents describing the impacts caused by the disaster and the inclusion of documents such as the DMATE and FIDE. None of the documents had information about the measures taken after the federal recognition of the disaster.

A total of 296,324 people were affected between 2013 and 2019 and 75% of the recorded events (57) are concentrated in 5 states: Mato Grosso—MT (19 cases); Pará—PA (16 cases); Goiás—GO (11 cases), Mato Grosso do Sul—MS (9 cases) and Amazonas—AM (7 cases). From 2010 to 2019, a growing trend in the number of annual records of natural disasters caused by ravines and gullies was observed, peaking in the last year with a complete dataset (2018) (Fig. 3).

Fig. 3
figure 3

Number of disasters caused by ravines and gullies per year, based on civil defense data obtained in May 2019

Full size image

The municipalities with the highest number of records were Oriximiná (PA) with 7, Novo Gama (GO) with 5, Iranduba (AM) with 4, and Canarana (MT), Comororo (MT) and Coronel Sapucaia (MS) with 3 events each. The municipalities with disasters induced by ravines and gullies are among the 50% most populous and/or among the 50% with the best proportion of Gross Domestic Product (GDP) per capita in the country, according to official information from the Brazilian Institute of Geography and Statistics (IBGE 2020).

Literature review

The Literature review considered 63 publications, which recorded the occurrence of ravines and gullies in 68 municipalities. Published studies are concentrated in the states of São Paulo (SP), Minas Gerais (MG), and Rio Grande do Sul (RS). The municipality of São Pedro was the most studied area 6 publications, followed by São Luis (4), Nazareno (3) and Marília (3). Among the articles available in the literature, none focused on assessing the economic impacts caused by ravines and gullies in Brazil. Other relevant information presented in the articles analyzed was used in the discussion of the work.

Records of damages in the S2iD database

According to the information available in the Disaster Information Form (FIDE) (Table 2), 20 of 24 cases affected urban areas, 1 of them a rural site and three of them affected both (Figs. 4, 5). Economic impacts were characterized by: (1) material damage causing a total cost of US$ 26 million covering public infrastructure, residences, public health facilities, public facilities providing other governmental services, and public infrastructure; (2) economic losses in the public and private sector of approximately US$ 17.9 mi, including damage in the sanitary and rainwater system, drinking water supply, medical care, public health and emergency medical care; (3) public losses of U$ 4.73 mi in local and regional transport systems, public security, disinfestation and disinfection of insects, pest and vector control, schools, electricity generation and distribution; (4) private losses of US$ 3.45 mi in the service sector, livestock and industry; and, finally, (5) costs of ongoing actions of US$ 2.55 mi to be covered by the municipal annual budget and municipal extra-budget sources (Table 3). Ravines and gullies in most cases initiated due to atypical rainfall, lack of drainage infrastructure or insufficient urban planning.

Table 2 Analyzed events in relation to the biomes they are inserted in
Full size table
Fig. 4
figure 4

(Source: S2ID system reports)

Examples of gullies and ravines in Brazil. A, B Gully located at Rua 14-E, municipality of Aparecida de Goiânia, state of Goiás (Cardoso 2013); C unstable areas with imminent risk of landslide. Santana do Mundaú, state of Alagoas (Da Silva 2018); D ravine under development, 3 m from residences, municipality of Timon, state of Maranhão (De Oliveira Filho and Dos Santos 2014)

Full size image
Fig. 5
figure 5

(Source: S2ID system reports)

Examples of gullies and ravines in Brazil. A, B Rural roads affected by erosion in Tiros, Minas Gerais state (Longe 2014); C, D residence close to erosion and the Cascalheira stream where water is collected for public supply, municipality of Comodoro, state of Mato Grosso (dos Santos 2014)

Full size image
Table 3 Costs caused by ravines and gullies according to the records described in FIDE between January 2013 and May 2019
Full size table

The municipality of Novo Gama (GO), with five records, was the municipality with the most affected people (Fig. 6). The cases with the greatest material damage were Anápolis (GO) (U$ 6.4 mi); Aparecida de Goiânia (GO) (U$ 5.46 mi) and Novo Gama (GO) (U$ 3 mi). The greatest public and private economic losses were recorded in Aparecida de Goiânia (GO) in 2013 (U$ 5.81 mi) and 2017 (U$ 5.46 mi), followed by Timon—MA in 2019 (U$ 2.37 mi). The largest private economic losses were recorded in Comodoro—MT, related to the livestock sector in 2014 (U$ 0.95 mi) and in the municipality of Novo Gama (GO), in the service sector both in 2013 (U$ 0.87 mi) and 2014 (U$ 0.87 mi).

Fig. 6
figure 6

(Source: S2ID system reports)

Destruction of public structures and residences in the municipality of Novo Gama, state of Goiás (Pimenta 2015).

Full size image

Although the data available by the S2ID database includes different types of impacts, the total sum US$ 54 million (Table 3), is interpreted as an underestimation. The records do not adequately consider post-impact costs, such as declining economic activities, expenses for land recuperation, changes in the type of economic activity, etc. Another existing shortcoming is that the impacts on the ecosystem are not considered. Environmental impacts are mentioned in FIDE as a percentage of contamination or pollution of water, air, and soil, in addition to water reduction or depletion. The reports do not present information on the dimension of environmental impacts in the watershed or even the volume of eroded sediments. Magnitude estimation and a more detailed description of the dimension of the event are important indicators, identifying areas impacted by silting and production losses, thus contributing to the improvement of the economic and environmental impacts records.

The Municipal Declaration of Emergency Action presents information on how the municipality organizes itself in relation to the national policy for civil protection and defense, describing the municipal capacity to deal with adverse events. Out of the 24 cases analyzed, 16 of them occur annually, with only 6 being “first time” records.

The magnitude of many events exceeded the capacity of the municipal management to deal with the disaster in most cases (21 of 24) and the losses affected the response capacity of the municipal government in 22 cases. In 13 cases, public and private economic losses were separated, and in 20 cases, economic losses caused by ravines and gullies were mentioned. Most municipalities have municipal committees, or a corresponding body structured to monitor disaster situations, in addition to having the support of state agencies and institutions. In 22 of the 24 cases, municipal maps of geological hazard areas already existed.

In most cases, however, there is no provision for programs and projects for actions aimed at tackling the problem in the Multiannual Plan (PPA), which is the document that guides the application of public resources over a 4-year period, or in the Budget Guidelines Law (LOA), which approves the city's annual budget. When a disaster occurs, it is necessary to approve extraordinary resources, either from the municipal budget itself or from the National Fund for Public Disasters, Protection and Civil Defense (PNPDEC), which grants resources to municipalities that have an emergency recognized by the federal government, so that they carry out prevention, mitigation, preparation, response, and recovery measures (Brasil 2010, 2012b).

In Brazil, despite recent advances in the mapping of risk areas in the municipalities of the country by the Geological Service of Brazil, which produced Geological Risk Sectorization maps in 1607 of the 5568 municipalities (CPRM 2021), the incorporation of prevention and mitigation measures has not yet occurred in most of the municipalities analyzed. Complete records of the disasters in the S2ID system can contribute to the analysis of impacts, which is important to convince public managers to develop preventive measures, as well programs that consider the planning and recuperation of areas affected by ravines and gullies. The integration between the technical analysis that is consolidated through maps of risk areas and the evaluation of damage caused by natural disasters can complement each other, demonstrating the potential losses if a disaster occurs and that preventive measure can lessen the socioeconomic impacts.

Integration of the S2iD database and the results of the literature review: an analysis of the economic impacts of ravines and gullies in Brazil

The cases reported in the S2ID system are mainly related to the urban perimeter. Urbanization results in changes in runoff behavior, due to impermeable surfaces (paving and buildings), and an inadequate urban planning can favor the development of ravines and gullies (De Albuquerque et al. 2020). Only 4 of the 24 the impacts recorded in rural areas amount to U$ 0,96 mi damage and are mainly related to livestock in a single event in the state Mato Grosso (Table 2). De Brito Galvão et al. (2011) mention that in the last decades, there has been an increase in the number of studies that pursue to understand the impacts of ravines and gullies on agriculture, land conservation and water dams.

Brazilian studies address the impact of ravines and gullies, but in general, they do not measure economic losses, focusing more on the characterization of the process and the qualification of socio-environmental impacts. The few studies that focus on the economic losses are discussed in the following. Guerra et al. (2018) cited that severe erosion poses risk to people in the state of Maranhão. The economic losses reported in Rotta and Zuquette (2014) are related to unsuccessful land recuperation measures in cities such as São Pedro, Franca, São Carlos, Casa Branca and Cajuru, all of them in São Paulo state. The impacts caused by the development of ravines and gullies in railways are mainly interruptions in cargo and passenger transport (Souza et al. 2017). Few studies address socioeconomic losses on the country's agricultural frontier and are in Mato Grosso and in the northern region, where the highest numbers of disasters caused by ravines and gullies are recorded. Although they are mostly described for urban areas, they are not limited to these but can also occur on agricultural land.

S2ID presents raw data with important information about disasters and the impacts caused throughout the national territory. This database can be an important source of information to indicate potential areas for scientific research, which can study and understand the most significant disasters, seeking to strengthen the protection and civil defense policy in Brazil. In addition, transforming database information into scientific publications is a way of validating existing information.

To reduce underreporting and expand information on existing disasters in the country, the federal government and the civil defense could establish the obligation that public concessionaires, be they highways, gas pipelines, sanitation infrastructure, transmission lines, etc.…, must report cases of ravines and gullies in the S2ID. This type of action would allow recording small-scale impacts. Another gain that could be achieved with this measure is the identification of areas where problems with ravines and gullies are recurrent, which is essential for public institutions to be able to identify the environmental sensitivity of areas with low population density, such as the agricultural frontier of Brazil.

In some cases, as in the cities of Novo Gama (GO) in 2014 and Pirapetinga (MG) in 2017, the existence of two or more different processes in the same year, may indicate duplication of registration, or register damage caused due to the evolution of the same erosion at different times. To improve the analysis on the recording of natural disasters, it is necessary to add information describing the evolution processes that caused the disaster. In addition, it is necessary that a new event can be linked to the previous one, creating a documentary timeline of the impacts and actions carried out.

The fact that disaster records only exist in municipalities with Gross Domestic Product (GDP) per capita among the 50% largest in the country, and/or in municipalities among the 50% most populous, suggests that smaller and poorer municipalities can experience difficulties carrying out disaster cataloguing. The increase in the number of recorded events after 2012 may represent a growth trend or an improvement in reporting due to changes in the civil defense system and the structuring of public policies related to the disaster database in the country (Kuhn et al. 2022).

The significant number of disasters in the states of Mato Grosso, Mato Grosso do Sul, Pará, Amazonas and Goiás suggests a relationship between the expansion of the agricultural frontier in Brazil and accelerated erosion processes due to changed land use. The formation of ravines and gullies are directly connected to the release of high sedimentary loads, which may contribute to the silting of rivers and changes in water dynamics. The data related to deforestation in Brazil demonstrate that in the Amazon biome between 1988 and 2020 most accumulated deforestation was with 157,667 km2 in the state of Pará and with 147,926 km2 in the state of Mato Grosso, corresponding to more than 66% of the biome's total deforestation (INPE 2021). In the Cerrado Biome, between 2001 and 2020, 4,878,192 km2 were deforested in Mato Grosso, followed by Goiás with 4,586,154 km2 (INPE 2021). These changes occurred mainly due to the growth of agricultural and livestock activities.

The S2ID data showed that in 22 of the 24 cases analyzed, the municipalities had maps of risk areas in the municipalities. Although the ravines and gullies are considered a common process in 16 of the 24 cases analyzed. In most municipalities, there are no permanent programs or resources foreseen in government budget instruments for erosion prevention or control. This indicates that although the risk areas are known, most municipalities have not developed measures to prevent and contain ravines and gullies.

In rural areas, the production of erosion susceptibility maps has been simplified due to technological development, especially GIS software. Remote sensing methods combined with artificial intelligence were used in the Brazilian Cerrado (Minas Gerais), for automatic classification of optical images to identify ravines and gullies with high precision (Vrieling et al. 2007). Image analysis through remote sensing thus is an important tool to quantify the size, volume, downstream silted areas and affected infrastructure. Furthermore, the use of drones can provide more quantitative information related to estimates of economic and environmental impacts.

The existing data in the bibliography review indicates that in several places in the world the control of ravines and gullies is part of a regional strategy, with costs that in general exceed the municipal capacity to deal with this process of the physical environment alone. Therefore, the help of regional and national governments is needed for better management and financial support.

In addition to accounting the direct impacts of ravines and gullies, it is necessary to expand the studies to consider the cost of land recuperation and the losses related to halting the economic activity. Romero-Díaz et al. (2019) analyzed 26 documented cost actions to control ravines and gullies and indicate that costs could vary by a factor of 100, e.g., between US $ 100 and US $ 10,000 per hectare. While the annual maintenance costs for 50% of cases are less than US $ 100 per hectare, for the other 50%, it can be as high as US $ 1000 per ha. According to De Brito Galvão et al. (2011), traditional methods of movement of large volumes of soil and measures of revegetation works, while drainage infrastructure is more expensive. While bioengineering methods tested by the author such gully revetment with blankets and revegetation works and partial grading of the gully and cheaper drainage system works. These large inconsistencies in costs reported demonstrates the need to carry out further research and studies in search of cost-efficient solutions to contain ravines and gullies in diverse climate and geological–geotechnical settings.

Conclusion

Our analysis suggests a growing trend in the number of disasters related to ravines and gullies in Brazil. The data suggest a correlation between the higher concentration of cases of disasters caused by ravines and gullies, and the growth of cities and changes in land use, especially in the Biomes Cerrado and Amazonia, where significant deforestation has been recorded in recent decades, according to INPE (2021).

The cases analyzed show that costs of erosion impacts are probably underestimated, because the long-term effects are not accounted for in the methodology used by the civil defense authority. Ravines and gullies gradually evolve over time scales of many decades, and this must be considered in the S2ID record. The relatively small number of publications on ravines and gullies in the states of the Midwest and Northern regions of Brazil, combined with the high number of disasters recorded in these two regions, indicates a major gap between research interest in universities and current development trends ravines and gullies. The S2ID data are registered by the civil defense, in general, municipal, therefore, all municipalities in Brazil, if they have active civil defense, can carry out the registration. On the other hand, academic articles are prepared by research groups, which are generally linked to universities. The main Brazilian universities are in the south and southeast regions, the proximity to the research areas, may have been one of the factors that favored the concentration of case studies in these regions.

The impacts caused by erosion were recurrent in several municipalities, with a better report in those with higher GDP and/or with higher population. Underreporting is common especially in small municipalities and in rural areas. Thus, the poorest and least populated municipalities are affected most and financial and technical support from the state and federal government is required, and long-term territorial planning must be improved.

Land use guidelines for territorial management and erosion susceptibility maps may help to prevent ravines and gullies Municipal preventive action programs are needed to control erosion in early stages and to reduce resources for mitigation and control of gullies and ravines.

Although the economic loss associated with disasters related to gullies and ravines is probably underestimated in Brazil, because available civil defense and the disaster databases lack information on long-term effects. The analysis carried out in our study allows us to suggest improvements in record keeping and in economical assessment of the impacts caused by ravines and gullies in Brazil, as summarized in Table 4. The measures suggested mainly target on strategies to reduce the underreporting of events, how to expand information of the damage and the measures that could be adopted in land recuperation of affected areas (Table 4).

Table 4 Summary of the challenges identified and suggestions that could be taken to improve the record of the impacts caused by ravines and gullies
Full size table