"Our results show that common and widespread water-management practices can have similar effects on local and basin-scale water budgets as those due to climate change," Reed Maxwell of Colorado School of Mines told environmentalresearchweb. "These results highlight the need to consider water management practices in climate-change impact assessments and adaptation studies."

Maxwell and colleague Ian Ferguson used the ParFlow integrated hydrologic model, which looks at groundwater, surface water and land-surface processes. They compared scenarios for the Little Washita River watershed, Oklahoma, in its natural state, under climate change and under different management systems. Agriculture in the region typically relies on groundwater pumping for irrigation, as do many other semi-arid agricultural areas, including the North China Plain and northern India.

"While many previous studies have evaluated the impacts of climate change on surface water and groundwater resources, the vast majority of these studies focus only on natural hydrologic processes and do not consider the role of water management," said Maxwell. "It is well known that water management has a big impact on the hydrology of basins around the world. Groundwater pumping, for example, has been shown to decrease stream flow, while widespread irrigation has been shown to increase groundwater recharge."

Climate change affects terrestrial water and energy budgets by altering precipitation and the amount of potential evapotranspiration. In turn this will feed through to surface water and groundwater resources. Water management, on the other hand, directly affects terrestrial water storage, including groundwater storage (when groundwater pumping is used) and shallow-soil moisture (via irrigation).

At local scales, pumping and irrigation had a similar impact on latent heat flux, potential recharge and water-table depth to changes in temperature and precipitation, the researchers found. But the spatial distribution of the impacts resulting from climate and water management were different. The climate-change scenarios differed from the control scenario across the whole study area, whereas the management scenarios were different only in crop areas where pumping and irrigation occurred.

On a basin scale, the impacts of climate and water management on stream discharge and groundwater storage were "remarkably similar", with changes in response to a temperature rise of 2.5 °C nearly equivalent to those resulting from groundwater-fed irrigation. Maxwell said this means some basins may already be seeing impacts similar to climate change due to another anthropogenic influence – pumping and irrigation.

"Our results also show that impacts of water management and climate change both depend on groundwater–surface water interactions," said Maxwell. "These results emphasize the need for water managers to use modelling tools that include realistic, physically based representation of key processes such as groundwater."

Now the researchers plan to conduct joint assessments of climate change and water management "including evaluation of conjunctive-use strategies to adapt to climate change while minimizing water-management impacts on groundwater and surface-water budgets". They will also continue to develop integrated hydrologic modelling tools, "including expansion of surface water and groundwater management modules to include water allocation and optimization routines".

The scientists reported their work in Environmental Research Letters (ERL).