The Fingerprint of Evapotranspiration: Quantifying Moisture Source Impacts on Hydroclimate Variability and Drought Risk

January 22, 2026

Yan Jiang

Hosted by Dien Wu

Abstract

Precipitation regimes over global croplands are sustained by complex moisture transport pathways from land and ocean. Since oceanic and terrestrial evaporation regulate rainfall patterns and seasonality in distinct ways, disturbances in these sources can expose downwind croplands to different hydrological risks. Beyond traditional climate and hydrological modeling, a key question for food security is: can we empirically separate terrestrial and oceanic vapor sources? And how do moisture sources affect hydroclimatic variability and drought risk for crop production?

In this study, we combine satellite-derived water-isotope observations with physical models to trace the origin of atmospheric moisture – separating terrestrial and oceanic sources – over global croplands during 2003–2019. We demonstrate that the fraction of precipitation originating from terrestrial evaporation (f) exhibits significant spatiotemporal heterogeneity. Crucially, our analysis identifies a nonlinear regime shift in hydroclimate sensitivity: regions where the terrestrial moisture fraction exceeds a critical threshold of ~36% exhibit distinct hydrological behavior. Above this threshold, precipitation becomes increasingly coupled to upwind land surface states, leading to enhanced sensitivity to hydroclimate variability and a statistically higher probability of drought propagation and in-season rainfall deficits. Quantifying precipitation sources is therefore essential for anticipating regional vulnerability. These findings highlight upwind land management (e.g., soil/vegetation moisture retention) as a potential lever to strengthen agricultural resilience and facilitate food security.

Dr. Yan Jiang is a hydroclimate scientist specializing in atmospheric science, climate dynamics, hydrology, and satellite remote sensing. She obtained her PhD in Atmospheric Science from the University at Albany, SUNY and her BS in Atmospheric Science from Sun Yat-Sen University in China. She is currently a postdoctoral scholar at the School of Global Policy & Strategy and Scripps Institution of Oceanography, University of California, San Diego. Yan’s research centers on the global water cycle and land-human-climate interactions. Using quantitative environmental analysis, Earth Observation data, climate modeling, and machine learning, she is dedicated to understanding hydroclimatic disturbances in critical ecosystems (e.g., forests, croplands) and empowering effective water-related hazard (e.g., drought, wildfires) mitigation strategies. She has led works published in top journals including Nature Climate Change, Nature Sustainability, Environmental Research Letters, and Geophysical Research Letters. She has been awarded the 2023 MIT CEE Rising Stars and selected as the 2024 National Science Foundation (NSF) Convergence Research (CORE) Fellow.