Hydrological Drought Risk Assessment in an Anthropogenically Impacted Tropical Catchment, Central Vietnam

Seasonal meteorological and hydrological droughts are a recurrent phenomenon in water-abundant tropical countries and are expected to become more frequent in the future. Unusual water shortage in recent years has severely affected societies living in South East Asia in general and Vietnam in particular. Preparedness, however, is absent and site-appropriate water management measures and strategies are not available. While drought-related research and water management in recent years have been addressed in water scarce sub-tropical regions, the US and Europe, more limited research has been focused on drought risk in tropical catchments. In this study, the drought characteristics of a large tropical catchment in Central Vietnam, the Vu Gia Thu Bon, were analysed in an integrated assessment framework. Daily precipitation and runoff time series for the VGTB catchment were analysed applying statistical methods to compare historical meteorological and hydrological drought, in addition to low flow frequency and seasonality. The role of tropical catchment characteristics, storage and climate variability in seasonal drought evolution were analysed by applying statistical analyses and the spatially distributed J2000 rainfall-runoff model. To assess anthropogenic impacts on hydrological drought, human interventions in the hydrological system due to hydropower development were quantified with the HEC-ResSim Reservoir operation model and the implications of low flows for salt water intrusion in the delta were simulated by the hydrodynamic Mike 11 model. It can be concluded that such an integrated model-data analysis which accounts for both landscape controls and anthropogenic impacts on the local hydrological system is a useful approach for drought management in tropical countries.