Abstract
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.
Highlights
The global soil erosion rate was estimated at 35.9 Pg yr−1 in 2012, and there is a potentially increasing trend in global soil erosion driven by cropland expansion [4]
Previous analysis has identified the decreasing trend of soil erosion with the decrease in spatial resolution of digital elevation model (DEM) [11,17,58,60,61], this study presents a similar study with the DEM resolution as high as 5 × 5 cm and identifies the changing pattern of soil erosion rate with the variation of DEM resolution from 5 × 5 cm to 10 × 10 m
Most of the freely available DEMs are medium (30 × 30 m) to coarse (90 × 90 m) resolutions, which are unable to detect micro-topographic features modified by farmers in the hill slope for crop cultivation
Summary
Land is one of the most important natural resources for agricultural activities to support people’s livelihood [1]. As being a crucial issue of decreasing productivity, the loss of fertile soil induced by soil erosion frequently happens in hilly slopes [2], and the effects of soil erosion go beyond the loss of fertile land [3]. Under the background of climate change, soil erosion has been and will always be a key issue for the sustainable development at the framework of future earth [3,5]. The catastrophic floods that have frequently happened in recent years greatly induced big amount of soil erosion, posing a big pressure on local agricultural development [6,7]
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