Abstract
Soil moisture variations and its relevant feedbacks (e.g., soil moisture–temperature and soil moisture–precipitation) have a crucial impact on the climate system. This study uses reanalysis and Coupled Model Intercomparison Project phase 6 simulations datasets to detect, attribute, and project soil moisture variations. The effect of anthropogenic forcings [greenhouse gases (GHG), anthropogenic aerosols (AA), and land use (LU) change] on soil moisture is much larger than that of the natural forcing. Soil moisture shows a drying trend at a global scale, which is mainly attributed to GHG forcing. The effects of external forcings vary with the regions significantly. Over eastern South America, GHG, AA, and natural forcings make soil dry, while LU forcing makes the soil wet. Over severely drying Europe, all the external forcings including GHG, AA, LU, and natural forcing exhibit drying effect. The optimal fingerprint method detection results show that some of GHG, AA, LU, and natural signals can be detected in soil moisture variations in some regions such as Europe. The soil will keep drying in all scenarios over most parts of the globe except Sahel and parts of mid-latitudes of Asia. With the increase of anthropogenic emissions, the variation of global soil moisture will be more extreme, especially in hotspots where the land–atmosphere coupling is intensive. The drying trend of soil moisture will be much larger on the surface than in middle and deep layers in the future, and this phenomenon will be more severe under the high-emission scenario. It may be affected by increased evaporation and the effect of carbon dioxide fertilization caused by global warming.
Highlights
As an essential parameter of the land surface process and the climate system, soil moisture affects surface air temperature, atmospheric humidity, precipitation, stability of the atmospheric boundary layer, and atmospheric circulation by influencing the surface evapotranspiration, surface albedo, soil heat capacity, and vegetation growth conditions (Delworth and Manabe, 1988; Zuo and Zhang, 2016; Liu et al, 2017)
The results show that global soil moisture is mainly a drying
Trend in summer, and the extent of the drying region is more prominent in CMIP6-model ensemble mean (MMEM) than in ERA5 and GLDAS
Summary
As an essential parameter of the land surface process and the climate system, soil moisture affects surface air temperature, atmospheric humidity, precipitation, stability of the atmospheric boundary layer, and atmospheric circulation by influencing the surface evapotranspiration, surface albedo, soil heat capacity, and vegetation growth conditions (Delworth and Manabe, 1988; Zuo and Zhang, 2016; Liu et al, 2017). Zhang and Zuo (2011) found that spring soil moisture significantly impacts the East Asian summer monsoon and the precipitation in East China by changing the surface thermal conditions. The abnormal soil moisture affects evaporation and temperature, causing an anomalous land–sea. Attribution of Soil Moisture Variation temperature difference, that affecting the East Asian summer monsoon circulation. Berg et al (2017) indicated that soil moisture is essential for the mean circulation and precipitation of the West African monsoon. Anomalous soil moisture changes evaporation and transpiration, resulting in anomalous land–ocean thermal contrast. The anomaly of surface evaporation changes the meridional temperature gradients and causes large-scale circulation changes, affecting West African monsoon circulation and precipitation
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