Water Resources in a Changing Climate

Our Nation contains regions where agricultural producers contend with an overabundance of water and regions frequently challenged by water scarcity and drought. The 100th meridian is often touted as the dividing line between the wet eastern United States and the dry, water-limited west. While this geographic division serves well as a rule of thumb, it ignores critical factors such as rainfall timing, intensity, frequency and magnitude and resulting systemic impacts.  How these events impact water supply in relation to water demand dictates impacts both now and in the future.

Hydrologists often conceptualize water from a budget perspective with inputs (precipitation) and outputs (runoff, infiltration, deep percolation) over a specified land area and time-period. Projected changes in annual precipitation show a latitudinal dipole with increases for much of the northern U.S. and decreases in the drier areas of the southern U.S. These changes could exacerbate the water-related challenges already faced in these areas. For example, an increase in spring precipitation may reduce the number of workable field days, reduce crop yields and disrupt planting operations in wetter regions.

Extreme precipitation has generally increased and is projected to continue to increase across the U.S. with a warming atmosphere. Flooding related to more extreme precipitation could lead to soil erosion and nutrient removal, impacting agricultural production and surface water quality as nutrient concentrations and sediment loads accumulate.  In addition, more extreme precipitation could increase climate risk from aging water infrastructure, in part because systems were typically not built to account for climate change.

Drought is a common occurrence in many parts of the U.S. Over most of the U.S. future declines in surface soil moisture are likely. Irrigation is necessary in much of the western U.S. to support crop production. Expanded irrigation is often suggested as one way to cope with increasing temperatures, but expanded irrigation may not be feasible in some areas. In times of surface water shortage, reliance on groundwater can augment supplies and minimize drought impacts. However in some locations, reliance on groundwater may be an unreliable solution due to declining groundwater levels and emerging groundwater regulations necessary to stave off some of the impacts of unsustainable groundwater use. Some ecosystems, such as forests, dry land farms and rangelands, rely solely upon rainfall, having no other water supply. These areas may be especially affected during periods of reduced precipitation.

Responding to Climate Change

Creative water management strategies used historically will inform future efforts. In areas where flooding and excessive water plagues production, strategies to minimize erosion and nutrient runoff will continue to be used. In dry regions, such as the Southwest, most adaptive solutions will involve water. Growers may select drought tolerant cultivars, or practice deficit irrigation to ensure enough available water during critical periods, such as flowering.

USDA’s Climate Hubs aim to better prepare farmers with adaptive responses to climate change by working with producers and partners to deliver science-based, region-specific information and technologies to enable climate-smart decision making.