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<p>This study investigates the spatiotemporal evolution of monsoon rain spell characteristics across India, focusing on changes in maximum rain spell volume (V<sub>max</sub>), intensity (R<sub>max</sub>), and their compound extremes. Using long-term observational data (1901–2023), rain spells are classified into short (≤ 10 days), moderate (10–30 days), and high (≥ 30 days) durations, allowing for a duration-specific understanding of monsoon behaviour. The analysis compares pre-1960 and post-1960 periods, guided by breakpoints identified through Sequential Mann-Kendall trend detection. Results reveal significant spatial heterogeneity in rainfall extremes across the country. North Eastern India shows a substantial rise in both V<sub>max</sub> and R<sub>max</sub>, particularly in high-duration events, with nearly 37% of the region affected by severe High Volume–High Intensity (HVHI) extremes. South Eastern Peninsular and Western India also exhibit increasing exposure to moderate and high-duration compound events. In contrast, Western Ghats and Himalayan regions reveal a widespread shift toward Low Volume–High Intensity (LVHI) events, indicating declining rainfall volumes but persistent short bursts of intense precipitation. Central India experiences growing short-duration LVHI extremes, heightening short-duration flood potential. The study emphasizes the importance of compound indices, which provide a more integrated view of rainfall extremes than volume or intensity alone. These compound extremes have critical implications for flood risk, water management, and infrastructure design. Region-specific adaptation strategies and hydrological models must incorporate compound rainfall behaviour to address emerging monsoon risks in a changing climate. The findings offer a valuable baseline for developing multi-hazard early warning systems and long-term climate resilience planning across India.</p>

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Evolving monsoon rain spells and compound extremes across india: A Century-Long assessment

  • 期刊论文

  • 发表日期：

    2025年9月27日

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  • Vishwajit Namdev Kolekar,
  • Somil Swarnkar,
  • Suneel Kumar Joshi

摘要

This study investigates the spatiotemporal evolution of monsoon rain spell characteristics across India, focusing on changes in maximum rain spell volume (Vmax), intensity (Rmax), and their compound extremes. Using long-term observational data (1901–2023), rain spells are classified into short (≤ 10 days), moderate (10–30 days), and high (≥ 30 days) durations, allowing for a duration-specific understanding of monsoon behaviour. The analysis compares pre-1960 and post-1960 periods, guided by breakpoints identified through Sequential Mann-Kendall trend detection. Results reveal significant spatial heterogeneity in rainfall extremes across the country. North Eastern India shows a substantial rise in both Vmax and Rmax, particularly in high-duration events, with nearly 37% of the region affected by severe High Volume–High Intensity (HVHI) extremes. South Eastern Peninsular and Western India also exhibit increasing exposure to moderate and high-duration compound events. In contrast, Western Ghats and Himalayan regions reveal a widespread shift toward Low Volume–High Intensity (LVHI) events, indicating declining rainfall volumes but persistent short bursts of intense precipitation. Central India experiences growing short-duration LVHI extremes, heightening short-duration flood potential. The study emphasizes the importance of compound indices, which provide a more integrated view of rainfall extremes than volume or intensity alone. These compound extremes have critical implications for flood risk, water management, and infrastructure design. Region-specific adaptation strategies and hydrological models must incorporate compound rainfall behaviour to address emerging monsoon risks in a changing climate. The findings offer a valuable baseline for developing multi-hazard early warning systems and long-term climate resilience planning across India.