Climate change

From Water Wiki

The overall effects of climate change on water in the southeastern United States are uncertain; the various models currently used for predicting changes do not clearly predict whether there will be more or less precipitation and runoff. They do seem to suggest the precipitation  will be flashier--that is, fewer rain events with longer dry periods between them, but with greater intensity when they do occur.^[1] 
Whatever happens with precipitation, there are two incontrovertible changes in the future that will have an effect on water allocation in the southeast: hotter temperatures and sea level rise.^[2] Hotter temperatures mean more evaporation, which means less water remaining in streams and reservoirs. Hotter temperatures also mean more energy use; demand for power rises as temperatures rise, and this increased power production consumes fresh water. Hotter temperatures will probably cause more water use for many reasons:

The potential for increased demand due to higher temperatures comes from all types of water use.
Domestic use, especially for outdoor purposes (such as yard and garden irrigation) is expected to rise with warming
temperatures. Industrial use may increase as well. Water is used for cooling on many electrical generating systems.
An increase in water temperature would decrease the cooling efficiency of the water and require more water to be used. Similarly, demand for water will increase to compensate for loss of precipitation in many areas.^[3]

Sea level rise means more saltwater intrusion into coastal aquifers. Both results mean less fresh water available for users.

The firm Tetra Tech analyzed the likely effects of climate change on water sustainability in 2010 and found that climate change will dramatically increase the scarcity of fresh water in many U.S. counties, including many in the southeast. The Tetra Tech report is here.

Warming The 2007 IPC report summarizes the near-term forecast for the global surface as a whole:

"For the next two decades a warming of about 0.2°C per decade is projected for a range of SRES emissions scenarios. Even if the concentrations of all GHGs and aerosols had been kept constant at year 2000 levels, a further warming of about 0.1°C per decade would be expected. Afterwards, temperature projections increasingly depend on specific emissions scenarios."^[2] The IPCC actually depict a range of predicted temperature increases by 2100 that vary widely upwards from a little less than 1 degree Celsius to a little less than 4 degrees Celsius (1.8 to 7.2 degrees Fahrenheit).

Beyond the climate change driven by CO2 levels, there is the question of change driven by land use changes. Do changes from forested cover and perhaps from agricultural land significantly alter regional precipitation patterns? Some scientists think so. See, for example, the research group working with Roger Pielke, Sr.

Notes

1. ↑ See Fig. 2.8, Weather and Climate Extremes in a Changing Climate, Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands. U.S. Climate Change Science Program Synthesis and Assessment Product 3.3 June 2008 (thumbnail on this page).
2. ↑ ^{2.0 2.1} Intergovernmental Panel on Climate Change, Climate Change 2007: Synthesis Report Summary for Policymakers 2-3
3. ↑ Noah D. Hall, Bret B. Stuntz, & Robert H. Abrams, Climate Change and Freshwater Resources, 22 NAT. RES. & ENV’T (2008).