Increased stream temperature in response to extreme precipitation events
MS: University of Colorado Boulder, 2017.
Aquatic ecosystem temperature regulation is essential to the survival of riverine fish species restricted to limited water temperature ranges. Thermal effluent regulations in place to protect these ecosystems restrict thermoelectric power generation when water temperatures are too warm. Climate change projections forecast increased precipitation intensities, a trend that has already been observed in the past century. Though extreme events are becoming more common, the stream temperature response to high-intensity rainfall is not yet well understood. Precipitation (33) and stream temperature records (52) from gages in the upper Midwestern United States were analyzed to determine whether there exists a positive relationship between high-intensity rainfall and warming stream temperature response. This region was chosen for its already observed trends in increasing precipitation intensity, and both urban and rural gages were used in order to account for the effect of impervious surfaces on runoff amounts and temperature. Days with recorded precipitation were divided by an intensity threshold and classified as either high-intensity or moderate-intensity days. While the effects of rain events on stream temperatures are variable, increases in stream temperature in response to high-intensity rainfall were observed. For some basins, daily maximum rates of stream temperature increase were, on average, greater for higher intensity events. Similarly, the daily maximum rate of temperature increase was higher in most streams on days of high-intensity precipitation, compared to days of moderate-intensity events. Understanding the effect of increasing precipitation intensity in conjunction with rising air temperatures will provide insight into the future of aquatic ecosystems and their adaptation to climate change.