As global warming intensifies, terrestrial ecosystems are increasingly facing compound climate extremes. Predicting how these ecosystems will respond—whether they will survive or collapse—remains a major challenge in Earth system science.

A new study published in AGU Advances—and selected as an Editor’s Pick for its significant contributions—has revealed a critical "personality switch" in ecosystem responses. Led by Prof. Dan Li from the Institute of Atmospheric Physics, Chinese Academy of Sciences, the research team discovered that the impact of climate extremes is not just about the current stress, but is fundamentally governed by "hydrological memory"—the antecedent soil moisture conditions.

The study was selected as an Editor’s Pick by AGU Advances. The editors highlighted the work for revealing "how previous soil moisture levels serve as a 'hydrological memory' in ecosystems' response to change."

The study focused on the Low-Latitude Highlands of Southwest China, a biodiversity hotspot known for its sensitivity to climate variations. The team utilized a "natural experiment" by comparing two distinct extreme events with similar large-scale atmospheric circulation backgrounds but vastly different outcomes: the severe winter-spring drought of 2010 and the record-breaking heatwave of 2019.

"Ecosystems, much like people, react to stress differently depending on their prior state," explains PanWei, the first author of the study.

The researchers found that during the 2010 drought, the ecosystem suffered a systemic collapse in carbon uptake (Gross Primary Production). However, during the 2019 heatwave—despite temperatures being even higher—the vegetation remained resilient and even thrived in some areas.

Why did the ecosystem crash in 2010 but withstand the heat in 2019? The study identifies antecedent root-zone soil moisture as the master switch.

· In 2010 (Water-Limited Paradigm): The soil was already dry before the event. This lack of "memory" meant the ecosystem hit a physiological hard limit, leading to widespread suppression of photosynthesis.

· In 2019 (Energy-Driven Paradigm): The months preceding the heatwave were wet. This accumulated "hydrological memory" acted as a buffer, allowing the vegetation to tap into the abundant soil water. Consequently, the high temperatures, instead of scorching the plants, actually boosted their activity by providing more energy for photosynthesis.

This finding highlights a phenomenon the authors describe as a "state-dependent mechanistic shift." The ecosystem's response pathway flips from being water-limited to energy-driven based entirely on its hydrological history.

This discovery challenges the static assumptions currently used in many Earth System Models (ESMs). Current models often struggle to capture these nonlinear transitions, leading to uncertainties in predicting future carbon sinks.

"Our results emphasize that geography and history are not just backdrops; they are key players," says Prof. Dan Li, the corresponding author. "Incorporating this 'hydrological memory' and state-dependent nonlinearity is crucial for minimizing uncertainties in climate projections and correctly assessing ecosystem vulnerability in a warming world." 

Paper info: 

Pan, W., Dan, L., Peng, J., Yang, Q., Zheng, H., Yang, F., et al. (2025). Why hydrological memory dominates in low-latitude highlands: A mechanistic shift in ecosystem response to extremes. AGU Advances, 6, e2025AV001973. https://doi.org/10.1029/2025AV001973