Researchers Uncover the Global Critical Soil Moisture Threshold of Plant Water Stress
The critical soil moisture threshold (θcrit) of plant water stress is defined as the soil moisture (SM) level at which evapotranspiration becomes SM limited in that environment. Lab and field experiments have found diverse values for θcrit, but the global distribution of θcrit is not known, due to a lack of global observations. Better quantification of θcrit is needed for improving future projections of climate and water resources, food production, and ecosystem vulnerability.
According to a new study published in Nature Communications, researchers led by Prof. FU Zheng at the Institute of Geographic Sciences and Natural Resources Research of the Chinese Academy of Sciences, present the results of a new approach to quantify θcrit based on the diurnal amplitude of the land surface temperature and daily soil moisture measurements during periods of consecutive days without rain, using in-situ flux tower networks and satellite observations from different sensors.
This work shows that the global average θcrit is 0.19 m3/m3, with a large gradient ranging from 0.12 m3/m3 in arid ecosystems to 0.26 m3/m3 in humid ecosystems. Compared to the observation-based map, θcrit simulated by Earth System Models is underestimated in wet areas and overestimated in dry areas, and models show an erroneous spatially uniform pattern. Moreover, they find that the annual fraction of days with water stress, when soil moisture stays below θcrit, has increased in the past four decades.
These results have key implications for improving the representation of water stress in models and identifying soil moisture tipping points that could result in impaired ecosystem functioning over drying areas.
This work was financially supported by the IGSNRR, National Natural Science Foundation of China, CNES, and the ANR CLAND Convergence Institute.
Reference:
Fu, Z., Ciais, P., Wigneron, J. P. et al. (2024). Global critical soil moisture thresholds of plant water stress. Nature Communications, 15, 4826.
Fig. 1 Global distribution of critical soil moisture threshold (Image by FU Zheng)
Fig. 2 Global distribution of critical soil moisture threshold from Earth System Models (Image by FU Zheng)
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