Land use change affects water erosion in the Nepal Himalayas

Water Yield Alteration in Thailand’s Pak Phanang Basin Due to Impacts of Climate and Land-Use Changes

Climate and land-use change are important factors in the hydrological process. Climatic and anthropic changes have played a crucial role in surface runoff changes. The objective of this research was to apply land-use change and future climate change to predict runoff change in the Pak Phanang River Basin. The Cellular Automata (CA)-Markov model was used to predict the land-use change, while the climate data from 2025 to 2085 under RPC2.6, RPC4.5, and RPC8.5 were generated using the MarkSim model. Additionally, the Soil and Water Assessment Tool (SWAT) combined land-use change and the generated meteorological data to predict the runoff change in the study area. The results showed that the annual runoff in the area would increase in the upcoming year, which would affect the production of field crops in the lowland area. Therefore, a good water drainage system is required for the coming years. Since the runoff would be about 50% reduced in the middle and late 21st century, an agroforestry system is also suggested for water capturing and reducing soil evaporation. Moreover, the runoff change’s overall impact was related to GHG emissions. This finding will be useful for the authorities to determine policies and plans for climate change adaptation in the Malay Peninsula.

Making the Case for Parks: Construction of an Ecological Network of Urban Parks Based on Birds

Urban expansion occurs in horizontal and vertical directions, but the construction process of a traditional planar ecological network (EN) ignores the ecological protection of the vertical space. Birds, as representative species in urbanized areas, are important for expanding the vertical analysis dimension of ENs. In this study, urban parks with good habitat quality were extracted as ecological sources from the perspective of birds. Then, 2D and 3D ecological resistance surfaces were constructed on the basis of the perspective of influencing bird migration, and planar and 3D ecological corridors were extracted and compared for analysis. Finally, accessibility analysis was performed to identify the parks in the study area that need priority protection. Results show that building height is an important factor affecting bird migration, and the introduction of 3D resistance surfaces into EN construction is important for adapting to the trend of vertical urban expansion. The combination of accessibility and EN analyses can help identify ecological spaces having the dual role of “species conservation” and “human well-being enhancement.” This study can provide a reference for refining the service species of ENs, exploring the vertical dimension of ENs, and improving the health of urban ecosystems and the rationality of urban planning.

Ecological Risk Assessment of Transboundary Region Based on Land-Cover Change: A Case Study of Gandaki River Basin, Himalayas

Land-cover change is a major cause of global ecosystem degradation, a severe threat to sustainable development and human welfare. In mountainous regions that cross national political boundaries, sensitive and fragile ecosystems are under complex disturbance pressures. Land-cover change may further exacerbate ecological risks in these regions. However, few studies have assessed the ecological risks in transboundary areas. This study focused on the Gandaki Basin (GRB), a typical transboundary region in the Himalayas. Based on the dynamic change in land cover, the landscape ecological risk index (ERI) model was constructed to assess the ecological risk in the GRB, revealing the evolution characteristics and spatial correlation of such a risk during the period 1990–2020. The results showed that all land cover types in the GRB have changed over the last 30 years. The interconversion of cropland and forestland was a distinctive feature in all periods. Overall, the medium and medium to low ecological risk level areas account for approximately 65% of the study area. The areas of high ecological risk were mainly distributed in the high elevation mountains of the northern Himalayas, while the low risk areas were located in the other mountains and hills of Nepal. In addition, the ecological risk in the Gandaki basin has shown a fluctuating trend of increasing over the past 30 years. However, there were different phases, with the order of ecological risk being 2020 > 2000 > 2010 > 1990. Ecological risks displayed positive spatial correlation and aggregation characteristics across periods. The high–high risk clusters were primarily located in the high and medium high ecological risk areas, while the low–low risk clusters were similar to low risk levels region. The findings provided the reference for ecosystem conservation and landscape management in transboundary areas.

Assessment of soil erosion extent using RUSLE model integrated with GIS and RS: the case of Megech-Dirma watershed, Northwest Ethiopia

Soil erosion valuation at a spatial scale is crucial for assessing natural resource quality in a farming country like Ethiopia. The study's goal was to determine the rate of soil erosion in the Megech-Dirma catchment in Northwest Ethiopia using the Revised Universal Soil Loss Equation model aggregation with Geographic Information System and Remote Sensing. Sediment yield and transport were also estimated using sediment delivery ratio. Revised Universal Soil Loss Equation model data inputs included precipitation data for the R value, soil data for the K value, land cover data from satellite images for the C and P value, and topographical data from a Digital Elevation Model for the LS component. It was completed using the ArcGIS 10.4 software. The mean annual soil loss is 110.60 t ha^-1 yr^-1. Each year, a total of 8499.74 t ha^-1 yr^-1 of soil eroded and on average resulting in 1605.30 t/km²/yr, sediment material has been transported to the stream channels and deposited with a sediment delivery ratio of 1.87. The strength of soil erosion in the area is divided into six categories. The erosion rate classes were 46.38 percent (0-12 t ha^-1 yr^-1) low, 13.63 percent (12-20 ha^-1 yr^-1) moderate, 9.22 percent (20-35 ha^-1 yr^-1) high, 12.30 percent (35-50 ha^-1 yr^-1) very high, 7.20 percent (50 up to 100 ha^-1 yr^-1) severe, and 11.27 percent (>100 ha^-1 yr^-1) very severe erosion. According to erosion severity, 46.38 percent of the watershed is at risk of low erosion, while 11.27 percent is at risk of extremely severe erosion. The north and northeastern sections of the watershed have a moderate to extremely severe erosion risk due to steep slopes, high rainfall, and weak conservation measures. The severely eroded parts of the plateau and steep portions are proposed to be covered by plantation, stone bund, and check dam constructions.

Have anthropogenic factors mitigated or intensified soil erosion over the past three decades in South China?

As a form of land degradation, soil erosion directly threatens the sustainability of natural resources and the environment. The impacts of humans on soil erosion are profound and complex, especially in the areas with frequent human activities. Moreover, the great variability of human activities at the spatial and time scales precludes a comprehensive understanding of how humans affect regional erosion. This study evaluated soil erosion by water from 1985 to 2015 occurring in South China, which is densely populated and has been intensively exploited, based on the Chinese Soil Loss Equation (CSLE) and multisource data including remote sensing images, meteorological station information and geographic data. A quantitative method combining traceability thinking and residual trend approach was employed to distinguish the relative contributions of climate change and human activities. The results showed that the average amount of soil erosion exhibited a significant decreasing trend from 1985 to 2015, which was consistent with the national water census data and previous studies. Anthropogenic factors played a more vital role than natural variables in the evolution of soil erosion, the multiyear average contribution of which was 63.90%. The area in which anthropogenic factors alleviated soil erosion covered approximately 83.70% of the study area. These results indicate that soil and water conservation practices have made outstanding contributions to the reduction of soil erosion in South China. However, the impacts of the expansion of building land and the development of plantations on aggravating soil erosion cannot be ignored. For future soil erosion control, we observed the diminishing marginal effect of investments in soil and water conservation, and a higher governance potential in the severely eroded regions, which made the severely eroded poor land a primary for comprehensive ecological management. This study aims to provide valuable insights for decision makers in South China to better understand the impacts of humans on the evolution of soil erosion and could provide scientific support for reducing regional soil loss and enhancing the sustainable development of the ecological environment.

Understanding hydrogeomorphic and climatic controls on soil erosion and sediment dynamics in large Himalayan basins

The Himalayan basins are characterised by severe soil erosion rates and several basins are among the largest sediment dispersal systems in the world. Unsustainable agricultural activities increase the soil erosion rates and influence the overall hydro-geomorphic regime of river basins. Consequently, the water holding capacity of soil reduces, which enhances the flood risk in the lowland regions. In addition, excessive sediment flux severely affects the reservoir capacity in the mountainous regions, thus amplifying the flood hazard in the upland regions. Here, we have analysed two large and hydro-geomorphically diverse Himalayan River basins, namely, the Ganga Basin (GBA) from source to Allahabad in northern India and the Kosi Basin (KB) draining through Nepal and north Bihar plains in eastern India. Based on RULSE and region-specific SDR modelling framework, which includes model calibration, validation and uncertainty assessment, we demonstrate that spatial variation in rainfall, hydrogeomorphic conditions, the presence of hydraulic structures, and large-scale agricultural activities influence the overall pattern of sediment production and transport in these two large river basins. Total soil erosion in GBA and KB are estimated to be ~404 × 10⁶ t/y and ~724 × 10⁶ t/y respectively, a large part of which comes from the mountainous regions in both basins. Sediment yield at the mountain exits of the GBA and KB are computed as 14.1 × 10⁶ t/y and 86.4 × 10⁶ t/y respectively, which work out to be ~5% and ~15% of total soil erosion from the respective contributing areas of the KB and GBA respectively. Similarly, sediment yields at outlets in the alluvial plains are estimated to be 32.2 × 10⁶ t/y and 37.3 × 10⁶ t/y in the GBA and the KB, respectively suggesting that a large part of sediments are accommodated in the alluvial plains of KB. These results have significant implications for sediment management in the Himalayan River basins.

Interaction between urbanization and the eco-environment in the Pan-Third Pole region

Due to the high ecological vulnerability of the Pan-Third Pole region and the complexity of its ecological process, the impact of urbanization on the ecological environment (eco-environment) in this specific region attracts global attention. Here, we established an effective framework to evaluate the coupling coordination process of urbanization and eco-environment, and investigated the spatial distribution and dynamic evolution of this coupling coordination. Results showed that the Pan-Third Pole is undergoing an accelerated process of urbanization. Meanwhile, the overall eco-environment has profoundly changed from an ecological reserve to an ecological deficit. The coupling degree between urbanization and eco-environment shows an upward trend, and the decoupling process dynamically changes between various types. Regional convergence is remarkably embodied in the coupling and decoupling types. We found four coupling categories and three decoupling categories for the interaction between urbanization and eco-environment. Among them, the first coupling category contains 35 countries, which maintained a basically coordinated pattern with eco-environment lag. The initial urbanization level of the first category was higher than 35%, indicating that countries with higher urbanization levels were more likely to achieve coordinated development between urbanization and eco-environment. There was a noteworthy "path-dependence" in the evolution of the coordinated relationship between urbanization and eco-environment in the Pan-Third Pole. These findings will have important policy implications for decision-makers to explore coordination and sustainable development path for urbanization and eco-environment conservation.

Long-term non-sustainable soil erosion rates and soil compaction in drip-irrigated citrus plantation in Eastern Iberian Peninsula

Agriculture is known to commonly cause soil degradation. In the Mediterranean, soil erosion is widespread due to the millennia-old farming, and new drip-irrigated plantations on slopes, such as the citrus ones, accelerate the process of soil degradation. Until now, the published data about soil erosion in citrus orchards is based on short-term measurements. Long-term soil erosion measurements are needed to assess the sustainability of drip-irrigated citrus production and to design new strategies to control high soil erosion rates. The objective of this study is to assess long-term soil erosion rates in citrus plantations and report the changes in soil bulk density as indicators of land degradation. We applied ISUM (Improved Stock-Unearthing Method) to 67 paired trees in an inter-row of 134 m (802 m² plot) with 4080 measurements to determine the changes in soil topography from the plantation (2007) till 2020. Soil core samples (469) were collected (0-6 cm depth) to determine the soil bulk density at the time of plantation (2007) and in 2020. The results demonstrate an increase in soil bulk density from 1.05 g cm^-3 to 1.33 g cm^-3. Changes in soil bulk density were higher in the center of the row as a result of compaction due to passing machinery. Soil erosion was calculated to be 180 Mg ha^-1 y^-1 due to a mean soil lowering of 1.5 cm yearly. The highest soil losses were found in the center of the inter-row and the lowest underneath the trees. The extreme soil erosion rates measured in new drip-irrigated citrus plantations are due to soil lowering in the center of the inter-row and in the lower inter-row position where the incision reached 80 cm in 13 years. The whole field showed a lowering of the soil topography due to extreme soil erosion and no net sedimentation within the plantation. The results show the urgent need for soil erosion control strategies to avoid soil degradation, loss of crop production, and damages to off-site infrastructures.

Soil erosion and sediment yield assessment using RUSLE and GIS-based approach in Anjeb watershed, Northwest Ethiopia

Soil erosion is a serious and continuous environmental problem in Ethiopia. Lack of land use planning, environmental protection, over-cultivation, and overgrazing are prominent causes of erosion and sedimentation. This study is conducted in Anjeb watershed located in the Upper Blue Nile Basin, Ethiopia. In this study, the quantity and distribution of soil erosion, sediment delivery ratio (SDR), and sediment yield of the watershed were assessed by employing remote sensing, geographic information system (GIS), and revised universal soil loss equation analysis capabilities. Important data sets of topography, soil, conservations practices, cover management, and rainfall factors were processed and superimposed in GIS analysis, and soil loss rate, SDR, and sediment yield of the watershed were derived. Based on the result found, the watershed was categorized into six classes of erosion: slight (0–5), moderate (5–10), high (10–15), very high (15–30), severe (30–50), and very severe (> 50) t ha−1 yr−1. The estimated average annual soil loss was 17.3 t ha−1 yr−1. The soil loss rate is higher in the steeper and topographically dissected part of the watershed. The average sediment delivery capacity was about 0.122. The result showed that the average sediment yield in the watershed was grouped into classes of low (< 2.5), moderate (2.5–7.5), high (7.5–12.5), very high (12.5–22.5), severe (22.5–40), and very severe (> 40) t ha−1 yr−1. It is found that from a total of 20,125.5 t yr−1 eroded soil over the whole watershed 2254.5 t yr−1 of sediment has been brought and deposited to the channels. Sediment accumulation from the watershed threatens the storage capacity and life span of Anjeb reservoir which is the source of irrigation water downstream. The study provides an insight to planners and resource managers to design and implement practices of watershed management to reduce erosion and enhance land productivity and to minimize the reservoir sediment accumulation.

Spatio-temporal distribution and classification of utilization of urban bare lots in low-slope hilly regions

Urban bare lots are persistent phenomena in urban landscapes in the course of urbanization. In the present study, we examined the spatio-temporal distribution of urban bare lots in low-slope hilly areas, and to assess the major pathways by which they are generated and later re-transformed for exploitation. We extracted land use and land cover (LULC) change information and analyzed spatio-temporal distribution characteristics of urban bare lots using Landsat TM/OLI series remote sensing images. Subsequently, we proposed an index system for their evaluation and classification, and identified five types of urban bare lots. Urban bare lot quantity and distribution are closely correlated with human activity intensity. Stakeholders should consider the multiple effects of location, topography, landscape index, transportation, service facilities, and urban planning in urban bare lot classification activities for renovation and re-transformation.

Sensitivity Assessment of Spatial Resolution Difference in DEM for Soil Erosion Estimation Based on UAV Observations: An Experiment on Agriculture Terraces in the Middle Hill of Nepal

Soil erosion in the agricultural area of a hill slope is a fundamental issue for crop productivity and environmental sustainability. Building terrace is a very popular way to control soil erosion, and accurate assessment of the soil erosion rate is important for sustainable agriculture and environmental management. Currently, many soil erosion estimations are mainly based on the freely available medium or coarse resolution digital elevation model (DEM) data that neglect micro topographic modification of the agriculture terraces. The development of unmanned aerial vehicle (UAV) technology enables the development of high-resolution (centimeter level) DEM to present accurate topographic features. To demonstrate the sensitivity of soil erosion estimates to DEM resolution at this high-resolution level, this study tries to evaluate soil erosion estimation in the Middle Hill agriculture terraces in Nepal based on UAV derived high-resolution (5 × 5 cm) DEM data and make a comparative study for the estimates by using the DEM data aggregated into different spatial resolutions (5 × 5 cm to 10 × 10 m). Firstly, slope gradient, slope length, and topographic factors were calculated at different resolutions. Then, the revised universal soil loss estimation (RUSLE) model was applied to estimate soil erosion rates with the derived LS factor at different resolutions. The results indicated that there was higher change rate in slope gradient, slope length, LS factor, and soil erosion rate when using DEM data with resolution from 5 × 5 cm to 2 × 2 m than using coarser DEM data. A power trend line was effectively used to present the relationship between soil erosion rate and DEM resolution. The findings indicated that soil erosion estimates are highly sensitive to DEM resolution (from 5 × 5 cm to 2 × 2 m), and the changes become relatively stable from 2 × 2 m. The use of DEM data with pixel size larger than 2 × 2 m cannot detect the micro topography. With the insights about the influencing mechanism of DEM resolution on soil erosion estimates, this study provides important suggestions for appropriate DEM data selection that should be investigated first for accurate soil erosion estimation.

Assessment of Soil Erosion Using the RUSLE Model for the Epworth District of the Harare Metropolitan Province, Zimbabwe

Urban development without adequate soil erosion control measures is becoming a major environmental concern in developing urban areas across Africa. These environmental disturbances encompass rampart Land Use and Land Cover changes (LULC) due to a high population growth rate and increased economic activities. To understand the influence of accelerated LULC changes and urban expansion as major drivers in landscape degradation in the Epworth district of the Harare Metropolitan Province, the RUSLE model was employed. This considers land use, soil, climate and topography as input parameters in the assessment of the extent and impact of these drivers on soil erosion. The Revised Universal Soil Loss Equation (RUSLE) was used to predict the potential erosion between 1984 and 2018 and soil erosion risk for the years 2000 and 2018. The mean rate of the predicted potential soil erosion was 13.2 t ha−1 yr−1 (1984–2018); areas especially vulnerable to erosion were predicted for foot slope areas with direct tributaries to the major streams and steep sloping zones. The average soil erosion risk was estimated at 1.31 t ha−1 yr−1 for the year 2000 and 1.12 t ha−1 yr−1 for 2018. While the overall potential soil loss decreased between 2000 and 2018, the potential soil loss was observed to increase tremendously in residential areas, which doubled in extent between 2000 and 2018. The findings reveal that about 40% of the Epworth district was threatened by unsustainable soil loss resulting from increased soil erosion risk within the built-up areas.