Assessment of drought conditions over Vietnam using standardized precipitation evapotranspiration index, MERRA-2 re-analysis, and dynamic land cover

Study region: Vietnam. Study focus: In recent years Vietnam has experienced historical drought events possibly affected by climate change, but the analysis is challenging due to lack of necessary observations for monitoring drought conditions. The goal of this study is to analyze the characteristics of droughts over a 30-year period, using three spatial-resolution MERRA-2 datasets in Vietnam. The Standardized Precipitation Evapotranspiration Index (SPEI) was used as an index for drought based on precipitation and temperature. We also estimated the impacts of drought on agriculture using annual land cover datasets. New hydrological insights for the regions: Our results identified significant increasing trends in precipitation in Northern Vietnam and decreasing trends in Southern Vietnam. The increasing trends in temperature occurred mainly in Southern Vietnam. These trends in rainfall and temperature resulted in an increasing trend in drought frequency and severity in Southern Vietnam, especially in the South-Central Region and the Mekong Delta. The comparison between the observed drought records and modeled drought index demonstrated that the simulated drought conditions are better at higher spatial resolution. The area under drought in agricultural lands calculated using dynamic land-cover data sets resulted in a better agreement with observed records. Our findings reveal the feasibility of using a model-based drought index in data-sparse areas for long-term trend drought analysis, and for practical applications of advanced re-analysis products in water resource management.