Collaborative Research: Extreme Rainfall in South Asia--Mechanisms of Variability

Extreme rainfall events in South Asia affect over a billion people, causing floods that devastate agriculture, infrastructure, and communities. While scientists have long known that El Nino events typically reduce Indian monsoon rainfall, this project reveals a surprising paradox: in India's wettest regions, extreme rainfall events actually become more frequent during El Nino years, even as total seasonal rainfall decreases. Such different responses of average and extreme rainfall challenge our understanding of the underlying dynamics that relate global climate variability to regional precipitation. The research thus contributes to basic science understanding of global climate variability and regional precipitation while also addressing practical issues of water resource management, agricultural planning, and disaster preparedness across South Asia, where rainfall extremes directly impact food security and economic stability. The project focuses specifically on the pathways through which El Nino events influence extreme rainfall through their effects on Low Pressure Systems (LPSs), the weather systems responsible for much of India's intense rainfall. The work addresses three main objectives: (1) documenting how LPSs change in response to climate variability using decades of satellite and ground-based observations; (2) developing a mechanistic understanding of how large-scale atmospheric conditions control the formation, movement, and intensity of LPSs; and (3) evaluating climate models' ability to simulate LPSs and their interactions with large-scale conditions. The project leverages recent advances including high-resolution rainfall datasets, sophisticated storm tracking algorithms, new theoretical frameworks for understanding rainfall distributions, and climate models capable of simulating regional weather systems. By connecting planetary-scale climate forcing to local extreme events through intermediate-scale weather systems, this research addresses a critical gap in our ability to predict and prepare for rainfall extremes in a changing climate. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.