Submitted to: American Society of Civil Engineers
Publication Type: Book / Chapter
Publication Acceptance Date: 8/1/2004
Publication Date: 10/15/2005
Citation: Garbrecht, J.D., Schneider, J.M., Brown, G.O. 2005. Decade-long precipitation variations and water resources management. In: Garbrecht, J.D., Piechota, T.C., editors. Climate Variations, Climate Change, and Water Resources Engineering. Reston, VA:American Society of Civil Engineers. p. 37-50. Interpretive Summary: Changes in annual and seasonal precipitation that last ten or more years are important considerations for planning/management of water supply of growing urban communities and negotiation of water agreements. Over much of the continental United States the average precipitation from 1971-2000 was higher, on average about 4% higher, than the long-term 1895-2001 average precipitation. The distribution of this precipitation increase was found to vary by season and by region. In the Central Plains fall and winter capture a large portion of the annual increase. The impact of the increase in precipitation on streamflow was evaluated for two mid-sized watersheds in Oklahoma. For this region, streamflow response was highly related to the precipitation increase, with a large portion of the additional streamflow occurring during the fall and winter seasons. Groundwater levels and springflow in a southern Oklahoma aquifer were also correlated to the observed precipitation variations. This study suggests that management of water supply may benefit from consideration of precipitation trends and variations. Adaptation of management strategies for water supply and demand were considered to have the best short-term potential to overcome decade-long variations in precipitation, because they can be developed, modified and implemented as a pattern in precipitation variations persists.
Technical Abstract: Changes in annual and seasonal precipitation over the last half of the 20th century were investigated at national, regional and local scales. Corresponding impacts on streamflow, springflow and groundwater levels were evaluated for two watersheds and one aquifer in south central Oklahoma. The 1971-2000 and 1991-2000 precipitation was found to be higher, by 4% and 6.5%, respectively, than the long-term average over much of the conterminous United States. The seasonal distribution of these precipitation increases was found to vary by region. Fall and winter seasons appeared to capture most of the increase in precipitation in the Central Plains, whereas summer experienced the largest increase in California, Nevada, Oregon, Washington and Idaho. In 1998-2002 a decrease in annual precipitation was observed for most of the western United States. Decade-long variations in annual and seasonal streamflow between 1950 and 2002 were found to be sensitive and highly correlated to causative variations in precipitation. Similarly, average groundwater elevation and springflow showed a highly correlated pattern when compared to long-term precipitation averages. Based on these findings, it was inferred that decade-long variations in precipitation, streamflow, springflow and groundwater levels should be important considerations in planning and management of water resources systems and precipitation dependent economic enterprises.