Meteorological drought assessment for the Vietnamese Mekong Delta during 1998–2018 based on satellite data

Droughts have been reported to cause socio-economic disruption in the Vietnamese Mekong Delta (VMD), threatening the region’s sustainable development. However, it is difficult to monitor droughts in the VMD due to the lack of ground-based rainfall stations. Alternatively, remote-sensing technologies that provide regular temporal and spatial data are analysed. We verify the correlation between the Tropical Rainfall Measurement Mission (TRMM) 3B42 product and rainfall data collected from meteorological (gauged) stations in the VMD. Next, we assess the reliability of TRMM for monitoring meteorological drought and quantifying the drought characteristics based on the standardised precipitation index (SPI) at a wide range of time scales (1-12 months) during the period 1998-2018. TRMM shows a good match to station data at the monthly scale, as evidenced through biases < 5% and RMSE < 80 mm at selected sites. The driest episode was from 2014 to 2016, with a widespread drought area, most severely (with SPI < –1.5) in the northern part (Dong Thap, Tien Giang and parts of adjacent provinces). We also show that drought severity follows an increasing trend during 1998-2018, as indicated through Mann-Kendall tests on SPI time series, potentially due to changes in regional climate variability.