Satellite based impact assessment of temperature and rainfall variability on drought indices in Southern Pakistan

The impacts of temperature and rainfall on drought indices were derived from satellites by using remote sensing techniques over the southern areas of Pakistan from 2000 to 2018. Rainfall from Tropical Rainfall Measuring Mission (TRMM) and temperature from Climate Prediction Center (CPC) are the best performing satellite and observational gridded datasets for studying drought in the region. These two datasets were used to calculate drought indices i.e. Standardized Precipitation Index (SPI), Reconnaissance Drought Index (RDI), and Rainfall Deciles (DI) on a 6-month time scale characterized by the concept of the hydrological year starting from October to March and April to September. Five drought years (2000, 2001, 2002, 2004, and 2018) were identified based on the consensus of three drought indices namely SPI, RDI, and DI. The results of these indices are compared with MODIS products of 16 days Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI), and 8 days Land Surface Temperature (LST) composites to evaluate the impact of rainfall and temperature. Results show that the Sindh province remains moderately dry from October-March, while the failure of monsoon further intensifies the situation of droughts as observed in 2004. Winter or early spring rainfalls turn out beneficial for Sindh as they reduce the severity of emerging drought. The meteorological drought of October-March may lead to agricultural drought in April-September due to the deficit of summer monsoon having a direct impact on vegetation. Similarly, Balochistan province faces moderate to severe drought conditions due to increased evapotranspiration losses from the surface. RDI based on potential evapotranspiration is more suitable for studying drought as compared to SPI. In addition, EVI is categorized as a more suitable index to monitor drought conditions in Sindh.