The Role of Antecedent Southwest Summer Monsoon Rainfall on Occurrence of Pre- Monsoon Heatwaves over India

Abstract Global warming increases the risk of heatwaves (HWs) globally. In India, HWs during the summer (March-June; MAMJ) are characterized by prolonged high temperatures, exacerbated by low soil moisture. Speculation suggests that droughts during the Indian summer monsoon (ISM), which provides 80% of India's annual rainfall, may lead to more HWs in the following MAMJ period. In this research, an examination is carried out on the climatic patterns, inter-annual variability (IAV), and coefficient of variation (CV) of maximum temperatures (Tmax) throughout MAMJ across the Indian subcontinent using India Meteorological Department's (IMD) gridded observed Tmax dataset covering 1951 to 2023. The dataset is divided into two periods: an earlier period (1951–1999, P1) and a recent warming period (2000–2023, P2). This study compares Tmax between these periods and evaluates HW duration using IMD criteria, distinguishing between short-duration HWs (SHWs, lasting 2 days) and long-duration HWs (LHWs, lasting 5 days or more). Additionally, it explores the relationship between preceding All India Summer Monsoon Rainfall (AISMR) and various HW types, while analyzing the impact of extreme AISMR events (such as drought or excess rainfall) on heatwave occurrences. This study thoroughly examines how Tmax and HWs are distributed across India, shedding light on notable variations in Tmax patterns and HW occurrences. It finds a clear rise in Tmax across various regions, accompanied by an increase in the frequency of HW days, particularly evident during the MAMJ. The study emphasizes the crucial role of AISMR in shaping HW events, highlighting that drought conditions during AISMR are closely linked to a higher chance of experiencing above-normal HW frequencies. This study is very useful in determining the effects on various sectors in planning of adaptation techniques through appropriate strategies for a sustainable future over India in the present global warming era.