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Changes in land cover and climate are the dominant factors that significantly impact the hydrological process. However, the impact on flood response behaviour varies spatiotemporally. This study quantitatively assessed the effects of individual and coupled changes in land cover and climate on peak and high flows in the upstream and downstream parts of the Upper Awash River basin. Two time periods were chosen for comparison: baseline (1988–2001) and evaluation (2002–2015). The Soil Water and Assessment Tool (SWAT) was used to estimate the impact of these changes. The model satisfactorily simulated daily and extreme flows. The evaluation of annual maximal discharge variability between 1985 and 2015 at upstream and downstream stations showed significant positive and insignificant negative trends, respectively. However, the sub-basin's annual wet day rainfall (PRCPTOT) showed a downward trend. The annual maximal discharge–PRCPTOT relationship was significant during the baseline but later had no significance. The SWAT model showed that the main factor that affected the changes in upstream flow was the land cover change, increasing peak and high flow by 38.69% and 11.95%, respectively, compared to the baseline period. However, combined changes resulted in downstream peak and high flow reductions of 19.55% and 50.33%, respectively. As a result, changes in flood characteristics are strong functions of land cover, especially in the upstream sub-basin and land cover and climate in the downstream sub-basin. Overall, the impact of changes in the cropland-dominated basin was noticeably different. The study assists water resource managers in understanding the causes of hydrological dynamics and developing mitigation strategies. [ABSTRACT FROM AUTHOR]

Land use and land cover (LULC) changes, climate variability and climate change (CC) contribute hydrological response in tropical catchments, but their individual and combined effects are not yet well known. To understand watershed hydrology, remote sensing was used for quantifying the change in land use for the years 1992 and 2015. Subsequently, the spatial distributed SWAT model was implemented to simulate the hydrological responses for the Nam Rom Catchment of Vietnam. It was found that the SWAT model could be well simulated flow in the catchment by the value of Nash–Sutcliffe Efficiency (NES), coefficient of determination (R2), and percent bias (PBIAS) values 0.76, 0.76, and 6.76 for the calibration and 0.64, 0.65, and 8.37, for the validation, respectively. In addition, a strong correlation between land use changes (1992 and 2015) and increasing evapotranspiration, percolation, groundwater, and water yield was found. On the other hand, change in climate results in decrease in all hydrological components (ET (2.3%), percolation (9.8%), surface runoff (11.5%), groundwater flow (10.5%), and water yield (10.8%). The correlative distributions of combined LULC and CC led to decrease in significantly in groundwater (−5.7%), surface flow (−16.9%), and water yield (−9.2%). In short, CC had a more significant effect on hydrological responses than LULC in the Nam Rom Catchment in the period of 1992–2015. A simulation was also done to evaluate the projected LULC and CC on catchment hydrology in 2030. The simulation results showed that evapotranspiration and surface flow are the most sensitive hydrological responses in the future. These findings could be used in developing long-term LULC planning programs and CC adaptation as well in the Nam Rom catchment and other regions of Vietnam. [ABSTRACT FROM AUTHOR]