Preliminary research by the IPCC has shown that climate change is already affecting the Midwest. Over the 20th century, mean annual temperatures throughout the region have increased by 0.6°C ± 0.2°C. Climate change models predict a continuation of this trend, with spring temperatures expected to increase from 0.75°C to 5.0°C and summer temperatures expected to increase from 1.5°C to 4.0°C. Interestingly, climate models also predict a decrease in temperature variability, as minimum temperatures are expected to increase at a greater rate than maximum temperatures.
Warmer temperatures will result in increased drought- like conditions and dryer summers. Hotter, dryer air will reduce surface water supplies during the summer and fall as a result of an increase in evaporation and transpiration. Lower reservoir levels will force water resource managers to adjust utility operations and supply side management, while possibly requiring the implementation of new consumer demand management strategies.
Increased temperatures throughout the Midwest will also produce hydrological impacts. Most prominently, warmer temperatures will lead to an increase in both annual precipitation and extreme events. Wetter conditions will result in a greater number of rain-on-snow events, leading to earlier spring snow melt and an increase in spring time flooding. An increase in spring snow melt and flooding will result in a decrease in summer and fall water supply. This change has been forecasted in a number of models, with one model depicting an increase in the number of rain events and a decrease in the number of snow events by 2050.
Another hydrological impact resulting from climate change is an increase in the number of extreme events throughout the Midwest. Periods of extreme precipitation will lead to greater flooding and result in water runoff loss, meaning less water will reach groundwater supplies. This is a particularly important impact for states relying heavily on groundwater and aquifers. Increases in extreme precipitation will also reduce water quality by causing greater turbidity and sedimentation in surface water. This will force water resource managers to adjust water treatment processes to accommodate a new water quality baseline.
In addition to direct hydrological impacts, increases in temperature will also impact watershed vegetation. Changes in vegetation will impact soil permeability and water infiltration. This, in turn, will impact groundwater recharge rates, possibly leading to a reduction in groundwater supplies as more rainfall is lost to runoff.
The Midwestern United States faces a number of climate change related challenges. Increased temperatures will result in drought, changes in precipitation frequency and intensity, changes in snowmelt timing, changes in groundwater recharge rates, and the potential for a greater risk of flooding. These challenges will force water resource managers to develop innovative solutions and long-term plans to mitigate threats to water quality, water supply, and utility infrastructure.