A new coupled chemistry-carbon-climate Earth system model has been developed at the Geophysical Fluid Dynamics Laboratory. This model unifies component advances in chemistry, carbon, and ecosystem comprehensiveness within a single coupled climate framework. This model features much improved climate mean patterns and variability from previous chemistry and carbon coupled models.

In this study, a groundwater (GW) extraction scheme was incorporated into the Community Earth System Model, version 1.2.0 (CESM1.2.0), to create a new version called CESM1.2_GW, which was used to investigate hydrologic and climatic responses to anthropogenic GW extraction on a global scale. An ensemble of 41-yr simulations with and without GW extraction (estimated based on local water supply and demand) was conducted and analyzed. The results revealed that GW extraction and water consumption caused drying in deep soil layers but wetting in upper layers, along with a rapidly declining GW table in areas with the most severe GW extraction, including the central United States, the north China plain, and northern India and Pakistan. The atmosphere also responded to GW extraction, with cooling at the 850-hPa level over northern India and Pakistan and a large area in northern China and central Russia. Increased precipitation occurred in the north China plain due to increased evapotranspiration from irrigation. Decreased precipitation occurred in northern India because the Indian monsoon and its transport of water vapor were weaker as a result of cooling induced by GW use. Additionally, the background climate change may complicate the precipitation responses to the GW use. Local terrestrial water storage was shown to be unsustainable at the current high GW extraction rate. Thus, a balance between reduced GW withdrawal and rapid economic development must be achieved in order to maintain a sustainable GW resource, especially in regions where GW is being overexploited.

Both anthropogenic water regulation and groundwater lateral flow essentially affect groundwater table patterns. Their relationship is close because lateral flow recharges the groundwater depletion cone, which is induced by over‐exploitation. In this study, schemes describing groundwater lateral flow and human water regulation were developed and incorporated into the Community Land Model 4.5. To investigate the effects of human water regulation and groundwater lateral flow on land processes as well as the relationship between the two processes, three simulations using the model were conducted for the years 2003–2013 over the Heihe River Basin in northwestern China. Simulations showed that groundwater lateral flow driven by changes in water heads can essentially change the groundwater table pattern with the deeper water table appearing in the hillslope regions and shallower water table appearing in valley bottom regions and plains. Over the last decade, anthropogenic groundwater exploitation deepened the water table by approximately 2 m in the middle reaches of the Heihe River Basin and rapidly reduced the terrestrial water storage, while irrigation increased soil moisture by approximately 0.1 m3 m−3. The water stored in the mainstream of the Heihe River was also reduced by human surface water withdrawal. The latent heat flux was increased by 30 W m−2 over the irrigated region, with an identical decrease in sensible heat flux. The simulated groundwater lateral flow was shown to effectively recharge the groundwater depletion cone caused by over‐exploitation. The offset rate is higher in plains than mountainous regions.