Recent changes in the climatological characteristics of daily contiguous rain areas over India

This study documents the climatological feature (1951-1980) and recent changes (1981-2020) in rainfall characteristics considering the observed nearly full spectrum of rain event sizes (daily contiguous rain area (CRA) events) in all seasons over India. It is found that the low frequency very large CRA (similar to synoptic scale) from monsoon season contributes similar to 50% of annual rainfall. However, the small-sized CRA (isolated thunderstorms) are the most frequent daily rain events (similar to 70% of annual frequency) and hence are important for rain-fed agricultural practices. The well-documented widespread drying trend in the monsoon season has manifested in the annual rainfall trend but with reduced magnitude illustrating the compensatory effect from other seasons. Spatial aggregated annual statistics show that there is no significant change in rainfall amount and frequency of occurrence of rain events in the recent past compared to the base period. However, seasonally the pre-monsoon rainfall amount has increased significantly. Annually, the number of extremely heavy CRA (EHR) events have significantly increased by similar to 55% owing to a significant increase in pre-monsoon and monsoon rainfall. In all seasons, small-sized extremely heavy CRA has intensified substantially by 50-200% as compared to the base period. Additionally, the rain events from areal category large (similar to Mesoscale Convective Complexes (MCC)) have intensified in all seasons except winter. Thus, to decrease the uncertainty in rain-fed agricultural practices and better prediction of EHR to develop effective climate change mitigation strategies; process studies beyond monsoon season and processes other than synoptic scales are also required.

Automated summary

This study examines the rainfall characteristics in India over different seasons and sizes of rain events. The findings show that large continuous rain areas in the monsoon season contribute significantly to the annual rainfall, while small continuous rain areas are important for agriculture. Although there is a drying trend in the monsoon season, other seasons compensate for this trend. Overall, there is no significant change in rainfall amount and frequency of rain events in recent years compared to the base period, except for an increase in pre-monsoon rainfall and extremely heavy rain events.