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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Jun 2019

Research article | 03 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Earth System Dynamics (ESD).

Contributions of climate change and groundwater extraction to soil moisture trends

Longhuan Wang1,2, Zhenghui Xie1, Binghao Jia1, Jinbo Xie1, Yan Wang1,2, Bin Liu1,2, Ruichao Li1,2, and Si Chen1,2 Longhuan Wang et al.
  • 1State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • 2College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China

Abstract. Climate change affects water availability for soil, and groundwater extraction influences water redistribution by altering water demand, both of which significantly affect soil moisture. Quantifying their relative contribution to the changes in soil moisture will further our understanding of the mechanisms underlying the global water cycle. In this study, two groups of simulations were conducted with and without groundwater (GW) extraction (estimated based on local water supply and demand) from 1979–2010 using the land surface model CAS-LSM with four global meteorological forcing datasets (GSWP3, PRINCETON, CRU-NCEP, and WFDEI). To investigate the contribution of climate change and GW extraction, a trajectory-based method was used. Comparing the simulated results with the in-situ dataset of the International Soil Moisture Network (ISMN) and the satellite-based soil moisture product of the European Space Agency’s Climate Change Initiative (ESA-CCI) indicated that the CAS-LSM reasonably reproduced the distribution of soil moisture, and well matched the temporal changes. Globally, our results suggested a significant decreasing trend in surface soil moisture (0.98 e−4 mm3 mm−3 yr−1) over the 32-year period tested. The drying trends were mainly observed in arid regions such as the tropical desert regions in North Africa and the Arabian Peninsula. While the wetting trends were primarily in tropical forested areas in South America and Northeast Asia. Climate change contributed 101.2 % and 90.7 % to global drying and wetting trends of surface soil moisture, respectively, while GW extraction accounted for −1.2 % and 9.3 %, respectively. In deep soil, GW extraction contributed 1.37 % and −3.21 % to the drying and wetting trends, respectively. The weak influence of GW extraction may be because this activity occurs in limited areas. GW extraction contributed more than 35 % to the change in surface soil moisture in wetting areas where GW overexploitation occurs. GW is mainly extracted for irrigation to alleviate soil water stress in semiarid regions that receive limited precipitation, thereby slowing the drying trend and accelerating the wetting trend of surface soil. However, GW exploitation weakens the hydraulic connection between soil and aquifer, leading to deeper soils drying up. Overall, climate change dominated soil moisture trends, but the effect of GW extraction cannot be ignored.

Longhuan Wang et al.
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Short summary
We quantify the contributions of climate change and groundwater extraction to the trends in soil moisture through two groups of simulations. In summary, climate change dominates the soil moisture trends, while GW extraction accelerates or decelerates soil moisture trends under climate change. This work will improve our understanding of how human activities affect soil water content and will help to determine the mechanisms underlying the global water cycle.
We quantify the contributions of climate change and groundwater extraction to the trends in soil...