Nonlinear Granger Causality and ERA-5 based Approach in Assessing the Impact of ENSO and Climate Variability on Extreme Events in India

Abstract Over the past few decades, there has been a significant emphasis among hydro-climatologists on understanding the intricate teleconnections that exist between the El Niño Southern Oscillation (ENSO) and various hydro-meteorological phenomena, such as droughts and floods. Large-scale climatic circulation patterns like ENSO have a profound impact on both global and regional hydrometeorological events. India is also experiencing frequent droughts as a significant climatic calamity; thus, knowing these teleconnections at the physiographical division level would be highly beneficial in improved drought management and planning. In the present study, the long-term trend of meteorological drought was evaluated by two drought indices, viz., the Standardised Precipitation Evapotranspiration Index (SPEI) and the Standardised Precipitation Index (SPI), at time scales of 3, 6, 9, and 12 months using the Modified Mann-Kendall (MMK) Test and Innovative Trend Analysis (ITA) for the period 1901–2021. Furthermore, this study used the Non-linear Granger Causality Test (NGCT) due to its ability to identify complex and nonlinear relationships among variables to investigate the teleconnection between the drought indices and four climate indices (Southern Oscillation Index, Northern Oscillation Index, NINO 3, and NINO 3.4) from 1951 to 2021. ECMWF (European Centre for Medium-Range Weather Forecasts) ReAnalysis v.5 (ERA-5) data was used to explore the major climatic cause of the drought. According to the MMK test, the north Deccan and western coast regions show the most significant positive trend in SPEI 12 and SPEI 3 (0.071 and 0.078, respectively), as well as SPI 12 (0.072 and 0.098). In contrast, only the Himalayan region shows the most significant negative trend of -0.205 for SPEI 12 and SPI 12, respectively. Additionally, results from the MMK test and ITA indicate an increasing risk of drought in the Great Indian Desert, eastern and western coasts, and northern and southern Deccan regions. However, a decreasing trend was observed in the Himalayan and Northern Plain regions. The study emphasises that the effect of ENSO on evapotranspiration-based drought (i.e., computed using SPEI) is more significant than precipitation-based drought (i.e., computed using SPI). According to ERA-5 reanalysis data, changes in convective precipitation and rainfall rate, low cloud cover, insufficient vertical moisture divergence, and decreased snowfall rate all contributed to drought in a few locations in India.