Impacts of extreme drought on rice planting calendar in Vietnamese Mekong Delta

This research examined the impact of extreme drought on rice planting dates in the Vietnamese Mekong Delta (VMD) region from 2014 to 2018 using the time series of Normalized Difference Vegetation Index (NDVI). The Savitzky–Golay filter method was applied to remove noises and smooth the NDVI time series. Rice planting dates were determined by using the threshold of increasing NDVI to 20% of the amplitude for each season using TIMESAT. The research findings show that the remotely sensed-based sowing batches and the cultivation areas matched the official statistics with an estimated error of less than 12%. In the 2015/2016 extreme drought, the rice planting dates were delayed compared to the neutral years, especially in the winter–spring (WS) and summer–autumn (SA) crops. In general, the WS crop was more affected in the double rice crops than the SA crop in the triple rice crops. The results also pointed out various ecoregions facing different problems that should be addressed to ensure farmers' livelihood, primarily water management. Further research is necessary to understand the combined impacts of drought and changes in sowing dates on rice yield and the vulnerability of different farming models in the VMD.