Unraveling the July 2023 extreme rainfall in New Delhi: microphysical insights and large-scale atmospheric drivers
摘要
In July 2023, a series of intense rainfall episodes caused significant social and economic disruptions in New Delhi. Typically, the city experiences moderate rainfall during the monsoon season (June–September), with daily climatological means ranging from 5.5 to 7.8 mm day⁻¹ due to its inland location. However, these episodes saw mean rainfall values spike to an unprecedented 80.05 mm day⁻¹, far exceeding the usual district averages of 6.4 mm day−1, as per IMD (India Meteorological Department) rain gauge data. This sharp deviation underscores the intensity and frequency of these episodes, emphasizing the need to examine the underlying physical processes in the context of evolving climate patterns. This study investigates these anomalies through a multi-technique approach, integrating ground-based disdrometer and rain gauge data with Doppler Weather Radar, satellite observations from INSAT-3D/DR, GPM, and MODIS, as well as ERA-5 reanalysis and Numerical Weather Prediction models such as IMD-GFS and IFS. The findings reveal periods of enhanced rain rates and elevated cloud liquid water content driven by large-scale moisture transport, subtropical influences, and Rossby wave propagation. Ground and satellite radar observations indicate predominantly convective precipitation during these episodes, amplified by an atmospheric river originating from the sea. This moisture surge, combined with the subtropical jet shifting southward, formed a low-pressure system near the region. Rossby wave propagation further contributed to these extreme rainfall events. These insights highlight the interaction of larger atmospheric dynamics, offering a critical understanding of extreme urban rainfall in historically less-affected areas like New Delhi.