Category:

Climate Factors in Water Planning

In the absence of any changes in the external factors affecting climate, the historical climate experience provides a solid context for water supply planning.  Of course, there is always some chance that future droughts will be more severe than any past drought, but the historical record is a reasonable basis for estimating the probabilities of droughts of varying severity.  However, as human activities change the composition of the atmosphere, factors not present during the historical period have been introduced.  This increases the uncertainty of future climate conditions and potentially changes the probabilities of severe droughts.  Climate models, based on the laws of physics and our best understanding of how the climate system works, are the best tools available to assess how these additional factors might affect the future.

Climate is an important factor in water supply planning because it can impact the available water supply, depending upon the source, and it impacts the level of water demand.

Climate’s impact on available water supply varies depending upon the water source. Except in a geologic time frame, a lack of precipitation has little or no impact on groundwater supplies in confined aquifers deep below the surface. A lack of precipitation has a more immediate impact on available water supplies in shallow unconfined groundwater aquifers. The impact varies depending upon whether connections to the surface are more or less direct. The impacts are more apparent on groundwater supplies with direct surface connections and on surface water supplies. These supplies can be significantly diminished over relatively short periods of time.

Climate’s impact on water demand is typically driven by outdoor water use and electric power consumption. In temperate climates like in Illinois, water demand is lowest in the winter, when colder temperatures reduce the outdoor use of water and curtail demand for electric power. Even during drought conditions, per capita winter demand for water is consistent with that occurring during wetter winter conditions because the outdoor use of water is consistent. Typical winter water demand is below annual average demand.

But warmer temperatures in late spring, summer, and early fall lead to a rise in the use of outdoor water and in demand for electrical power. That demand is muted during wet, cool summer periods when water usage can typically be about 1.2 to 1.4 times annual average demand. During dry summer periods with cool temperatures, increases in water demand are somewhat muted, despite the dry conditions, due to the cooler temperatures. But demand rises significantly when dry periods, as short as 7 to 14 days, are accompanied by elevated temperatures. Peak daily demand often rises by a factor of 2 or more times the annual average demand, and peak hourly demand rises to even higher levels.

Unfortunately, the time periods when water demand is driven highest are the same periods when water supply is most at risk of being inadequate. To ensure an adequate supply of water, and the proper management of supply and demand, it is essential to have 1) an understanding of the frequency and severity of extended dry climate events and shorter events that combine dry periods with elevated temperatures, 2) an understanding of the vulnerability of the water supply source to those climate factors, and 3) the water demand response of water users to these conditions.

Publications/Information:
The Water Cycle and Water Budgets in Illinois: A Framework for
Drought and Water-Supply Planning (pdf ~6.7MB)

      National Water Program - Response to Climate Change - This
      report provides an overview of the potential effect of climate change
      on water resources in the Unites States.

      Climate Change & Drinking Water - American Water Works
      Association Research Foundation (AwwaRF) research that
      assess responses to the impacts of climate change on water
      resources; water quality; infrastructure; energy and the
      environment; and management and communication. (pdf ~1.35MB )
  

Next > Today's Climate: Precipitation, Temperature, The Water Budget