Abstract
The amount of soil moisture affects water availability, the occurrence of droughts and floods, and the frequency and intensity of heat waves in many regions across the globe. Here, we evaluate historical trends in soil moisture estimated by land-surface models (LSMs) with observed atmospheric forcing and trends simulated by global climate models participating in the Coupled Models Inter-comparison Project Phase 5 (CMIP5). We classify northern hemispheric land into wet and dry regions and analyze soil moisture changes in these regions. We find a significant decrease in soil moisture from 1951 to 2005 in the northern hemispheric land areas, in particular in dry regions, both in LSM and CMIP5 model simulations. Soil moisture trends in wet regions are less consistent among simulations. The increase in the area affected by drought (defined as the area where soil moisture is below its 10th percentile) from 1951 to 2005 is estimated to be 20 % (LSMs) and 30 % (CMIP5 models). A comparison between soil moisture simulated by LSMs and CMIP5 model output under different external forcings suggests that anthropogenic forcing contributed significantly to the observed drying and could explain the increase in the area affected by drought. As increases in atmospheric greenhouse gas concentrations will continue in the near future, dry areas are projected to become drier and larger in extent, which could negatively impact future water supply and food security.
Highlights
Changes in soil moisture can have significant impacts on water availability and food security and are important aspects of climate change that society needs to adapt to
Our analysis of warm season soil moisture simulated by land-surface models (LSMs) and comparison Project Phase 5 (CMIP5) models shows that northern hemispheric land areas have experienced drying in the last 55 years (1951–2005)
During the same period of time, the fraction of drought affected area has increased by 20 % and 30 % in LSMs and CMIP5 model outputs, respectively
Summary
Changes in soil moisture can have significant impacts on water availability and food security and are important aspects of climate change that society needs to adapt to. Zonal mean precipitation has been shown to increase in equatorial and mid- to high-latitude regions and decrease in the subtropics (Zhang et al 2007, Zahn and Allan 2012, Laine et al 2014, Allan et al 2014, Marvel and Bonfils 2013). This can be explained by an enhanced moisture flux from regions with climatological moisture divergence (dry, subtropical areas) to regions with moisture convergence and to polar regions (Chou et al 2009, Bengtsson et al 2011) that results in dry regions becoming drier and wet regions wetter. Human influences have contributed to observed global scale changes in precipitation patterns (Zhang et al 2007, Marvel and Bonfils 2013, Bindoff et al 2013, Polson et al 2013a)
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