Evaluating the impact of ponds on flood and drought mitigation in the Bagmati River Basin, Nepal

Abstract This study investigates the effectiveness of ponds as a nature-based solution (NBS) to concurrently ameliorate flood and drought impacts, emphasizing the need for an integrated response to multi-extreme hydrological events. We incorporate ponds into agricultural landscapes in the Bagmati River Basin of Nepal and assess their performance using the Soil and Water Assessment Tool (SWAT+). Six different scenarios are thoroughly explored to see how these interventions affect the main components of the water balance, such as surface run-off, lateral flow, percolation, and evapotranspiration. The spatial efficiency of the ponds, particularly in their immediate surroundings and downstream areas, has been proven to be a crucial factor in their overall efficacy in attenuating extremes, which increases with the size of the intervention area. Although the effects of ponds on floods and droughts are minor, they could be significantly magnified by a synergistic use of other NBS tactics, such as conservation tillage or soil conservation techniques. Future studies should establish the most appropriate sites and volumes for these interventions, as well as further investigate the possible advantages of several NBS, to optimize flood and drought management in the Bagmati River Basin and other similarly susceptible places.