The soil is essential for life and plays a crucial role in the Earth's ecosystem, providing support for plant roots and hosting countless microorganisms. As the atmosphere warms up, it is important to understand how soil hydrothermal conditions, particularly dry-hot extremes, have changed and will respond.

Recently, researchers led by Prof. ZHANG Yunlin from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS), along with collaborators from the Helmholtz-Centre for Environmental Research (UFZ) and Bangor University, have quantified global soil compound drought-heatwave (SCDHW) events from 1980 to 2023 and predicted their evolution until the end of this century.

The study was published in Proceedings of the National Academy of Sciences (PNAS) on October 7.

In the study, researchers combined three state-of-the-art reanalysis datasets and four Earth System Model datasets to analyze global SCDHW trends and variabilities in the past and future. They also incorporated long-term observational data to enhance their conclusions.

The authors showed a global increase in the occurrence, duration, extremeness, severity, and affected area of SCDHWs over the past 44 years. "We observed a notable escalation of SCDHWs from 1980 to 2023, particularly in this century. Global warming took the major responsibility, and the situation worsened in El Niño years. More importantly, the escalation of SCDHWs was concentrated in summer, posing a significant challenge to water security," said Prof. ZHANG Yunlin, corresponding author of the study.

They found compound drought-heatwaves in soils were stronger and increased faster than those in the air. "For the sake of data accessibility, we used to express compound drought-heatwaves in terms of meteorological measures such as air temperature. However, this common practice might underestimate the severity of SCDHWs, and the adverse impact on carbon cycle," said Dr. Fan Xingwang, first author of the study.

In general, SCDHWs were more intense in the northern hemisphere and longer-lasting in the southern hemisphere. The severity of SCDHWs increased rapidly in the northern high-latitudes, where soil temperatures were typically low and warming was highly pronounced. These events may threaten carbon neutrality goals in the north and food security goals in the south.

The degradation of forests and conversion of wetlands to croplands will worsen the severity of SCDHWs. Integrated watershed management requires sustainable policies and actions to protect soils from the risks of desiccation and overheating. "We must continue our efforts to preserve natural ecosystems," said ZHANG.

If no action is taken, formidable global SCDHWs will occur by the end of this century, with a mean duration exceeding 70 days and a soil temperature anomaly reaching 10 °C under the SSP5-8.5 emission scenario. “The mean duration of individual SCDHWs will increase substantially, which means that soil biota and plant root systems will struggle to recover from extreme water and heat stresses," said FAN.

JOURNAL

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2410294121

ARTICLE TITLE

Surging compound drought-heatwaves underrated in global soils

ARTICLE PUBLICATION DATE

07-Oct-2024