Rainfall-Runoff and Sediment Yield Modelling under Climate Change

Abstract

The primary aim of this research is to improve soil conservation practices in the Tekeze watershed. To achieve this goal, several procedures were carried out, including assessing the amount of erosion in the basin, evaluating different techniques to prevent erosion, and examining the impact of climate change on the watershed. For a better understanding of the work and findings, the abstract is described in three separate sections. Each section provides more detail on different aspects of the research, such as the methodology used, the results obtained, and the implications of the findings. The details of each abstract are described as follows: Assessment of erosion in each sub basins Land erosion is a significant issue worldwide because of inadequate land use and changes in land cover. This phenomenon results in the loss of the top layer of nutrient-rich soil, which is crucial for the productivity of the land and the storage capacity of reservoirs. As a result, it has negative impacts on the global economy. Therefore, soil conservation practices are being implemented globally to address this issue. However, carrying out large-scale soil conservation in developing nations can be difficult without significant investment. To increase the efficiency of soil conservation efforts, it is essential to identify the region’s most vulnerable to erosion and implement necessary remedial measures. In this study, the SWAT model was used to determine areas prone to erosion. While the model is widely accepted for water resource management, allocation, and prediction globally, there is uncertainty in the model's results that may arise from measured data, model structure, or input data. Therefore, extensive sensitivity analysis, uncertainty prediction, and model calibration are necessary to obtain accurate simulation results. The study employed several algorithms, namely SUFI-2, ParaSol, GLUE, and PSO, that are integrated with SWAT-CUP software for model calibration, sensitivity analysis, and uncertainty prediction. Results show that out of these four algorithms, the SUFI-2 algorithm provided the most accurate simulation outcomes, with R2 values of 0.76 and 0.85 under streamflow and R2 values of 0.8 and 0.66 under sediment for calibration and validation, respectively. After simulating 34 sub-basins, the study found that five sub-basins, namely 1, 3, 5, 14, and 17, are the most susceptible to erosion. These sub-basins exhibit a mean annual sediment yield of 23 tons/ha/year, indicating a high risk of soil erosion. This result emphasizes the importance of identifying areas prone to erosion and implementing effective soil conservation practices to mitigate the negative impacts of erosion on the global economy. Assessment of soil conservation options Soil conservation (SC) is essential to maintain the reservoir service life and increase the yield since soil erosion is a major global concern that adversely affects the storage capacity and land fertility. This study evaluates the spatio-temporal variation of soil erosion using popular SWAT model and identifies the best SC practice for Tekeze watershed located in Northern part of Ethiopia. To accomplish this, four soil conservation management scenarios involving baseline, terracing, contouring, and grassed waterway scenarios are selected for soil loss evaluation. The SWAT model was calibrated and validated with R2 values of 0.7 & 0.9 and NSE values of 0.8 & 0.7, respectively, indicating satisfactory model performance. Five sub-basins of the catchment were found to be more susceptible to erosion with an average annual soil loss of 25.15 tons/ha/yr. However, by implementing terracing, grassed waterways, and contouring techniques, the level of erosion in the watershed has significantly decreased when compared to the baseline scenario. Specifically, the implementation of terracing led to a 35.18% reduction in erosion, while grassed waterways and contouring resulted in reductions of 27.11% and 18.76%, respectively. These results demonstrate the effectiveness of these techniques in mitigating erosion within the watershed. Since the investment cost of the execution of an SC measure in a large watershed is very high, priority areas are also identified for cost savings as well as improved work efficiency.