Dr Lei Gu

Abstract:

Understanding changes in precipitation is crucial for society and ecosystems1,2. Studies have documented the respective contributions of anthropogenic forcing and internal variability to precipitation trends3,4, yet discrepancies persist between observed and simulated patterns. In Northern Hemisphere winter, these mismatches are often attributed to unforced internal variability that dominates observed trends5. However, growing evidence also indicates that climate models underestimate the total response of precipitation to human forcings6-8. Here we show that the thermodynamic contribution is broadly reproduced by climate models, whereas the dynamic contribution can diverge more substantially. Our approach disentangles the anthropogenic forced thermodynamic and dynamic components from internal variability in winter precipitation trends (1950-2022) to investigate their contribution to the trend discrepancies. In the Mediterranean, the forced dynamic signal from model simulations explains only about 10% of the observed dynamic trend, making detection challenging. Under continued anthropogenic emissions, the projected circulation response intensifies and more closely resembles observed trend patterns. Although internal variability in the observed record may contribute to this similarity, the results indicate an uncertain yet potentially emerging role of dynamic response in shaping regional winter precipitation trends. A reliable representation of the forced large-scale circulation response in climate models remains key for increasing confidence in regional precipitation projections.

Abstract:

<jats:title>Abstract</jats:title> <jats:p>Flash droughts—characterized by their rapid onset—can cause devastating socioeconomic and agricultural damage. During such events, soil moisture depletion is driven not only by precipitation shortages but also by the elevated atmospheric moisture demand arising due to extreme heat. However, the role of extreme heat in shaping the evolution of flash droughts and their ecological impacts remains uncertain. Here we investigate the processes involved by analysing global reanalysis data from 1950 to 2022. We find that, when flash droughts are accompanied by extreme heat, they exhibit 6.7–90.8% higher severity and 8.3–114.3% longer recovery time than flash droughts without extreme heat. The presence of extreme heat during flash droughts accelerates soil moisture drawdown over high latitudes, where wet soils and enhanced radiation foster evapotranspiration. By contrast, it slows the absolute onset speed in subtropical transitional climate zones owing to evapotranspiration throttling. Our machine learning approach further reveals that hot flash droughts lead to sharper declines in ecosystem productivity, particularly in croplands, thereby threatening global food security. These findings underscore the pressing need for enhanced infrastructure and ecosystem resilience to hot flash droughts in a warming future.</jats:p>

Abstract:

Increasing atmospheric moisture content is expected to intensify precipitation extremes under climate warming. However, extreme precipitation sensitivity (EPS) to temperature is complicated by the presence of reduced or hook-shaped scaling, and the underlying physical mechanisms remain unclear. Here, by using atmospheric reanalysis and climate model projections, we propose a physical decomposition of EPS into thermodynamic and dynamic components (i.e., the effects of atmospheric moisture and vertical ascent velocity) at a global scale in both historical and future climates. Unlike previous expectations, we find that thermodynamics do not always contribute to precipitation intensification, with the lapse rate effect and the pressure component partly offsetting positive EPS. Large anomalies in future EPS projections (with lower and upper quartiles of -1.9%/°C and 8.0%/°C) are caused by changes in updraft strength (i.e., the dynamic component), with a contrast of positive anomalies over oceans and negative anomalies over land areas. These findings reveal counteracting effects of atmospheric thermodynamics and dynamics on EPS, and underscore the importance of understanding precipitation extremes by decomposing thermodynamic effects into more detailed terms.