Microwave and optical satellite data fusion for meteorological drought monitoring in the Ganga-Brahmaputra basin

The increased meteorological drought conditions are very prominent in the Ganga-Brahmaputra (GB) basin due to the impacts of climate change. In the context of meteorological drought in India, particularly within the GB basin, this study explores the effectiveness of the Microwave Integrated Drought Index (MIDI). The study analyses the use of microwave dataset combined with optical remote sensing data for meteorological drought assessment for 18 years (2003–2020). The MIDI was calculated for the month of October, using multiple datasets (Precipitation (Chips, Cmorph, Persiann CDR, Persiann CCS CDR), Temperature (MODIS Land Surface Temperature (LST)), and Soil Moisture (Climate Change Initiative Soil MoistureCCISMv.02.2)) and their ensemble. MODIS-based Enhanced Vegetation Index (EVI), Standardized Precipitation Index (SPI), and Standardized Precipitation Evapotranspiration Index (SPEI) were calculated from 1991 to 2020, to understand the previous conditions of drought as well as for correlation analysis. After the analysis of drought conditions based on MIDI, the major drought years observed in the Ganga-Brahmaputra basin were 2011–2012, 2014–2015, 2017–2018, and 2020. The MIDIs were then correlated with the SPI, SPEI, and EVI where the highest significant correlation was found between MIDI and SPEI (0.876), emphasizing the importance of incorporating diverse environmental factors for a comprehensive understanding of drought dynamics. The highest correlation was observed with Chirps precipitation-based MIDI (0.87 to 0.83) and the lowest with MIDI CDR and CCS CDR (0.29 and 0.37 respectively) specifically in the Brahmaputra basin. The various precipitation products reflected different characteristics in their behaviour for different topography that can be analyzed for better monitoring.