Abstract for GLOBE annual meeting, July 2000

Relating Air and Water Temperatures: Implications for Climate Variability and Change

Roger Bales, Martha Conklin, Jean Morrill

University of Arizona

In considering the potential impacts of climate change on freshwater ecosystems, water temperature is a primary issue. Water temperatures vary seasonally in response to the annual solar cycle, and exhibit year-to-year variations owing to natural climate variability. Because of time lags the temperature of streams and lakes is generally different from air temperature, especially during the times of year when temperature is changing most rapidly. GLOBE data are used to develop year-round relationships between air and water temperature, and are compared with data and relationships from other sites. Many GLOBE data have the advantage of near co-location of air and water temperature measurements. Stream temperature measurements by the U.S. Geological Survey and other agencies are often several kilometers from the nearest weather station. Also, many GLOBE data are from small, unregulated streams, eliminating the effect of dams and reservoir releases. Relationships between air and water temperature on a daily basis exhibit considerable high-frequency variability; averaging over periods of one week eliminates much of this variability. The relationships are generally non-linear, and differ from site to site. Regionally, relationships depend on elevation. Multiple regression and other statistical techniques are compared, and their ability to give regionally relevant relationships evaluated. The resulting relationships can be used to estimate changes in the temperature patterns in freshwaters in response to changes in the mean and variability of air temperature. We use recent general circulation model analyses of changes in air temperature in response to greenhouse gas forcing of climate to analyze the expected impacts on the temperatures in lakes and streams.