CHANGING ANNUAL AND SEASONAL PRECIPITATION PATTERNS: AN ISSUE FOR WATER RESOURCES MANAGEMENT?

Authors: Garbrecht, Jurgen; Schneider, Jeanne

Submitted to: Environmental and Water Resources Institute World Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/10/2003
Publication Date: 11/25/2003
Citation: Garbrecht, J.D., Schneider, J.M. Changing annual and seasonal precipitation patterns: an issue for water resources management? CD-ROM. Proceedings of the World Water & Environmental Resources Congress. 2003. Environmental and Water Resources Institute, American Society of Civil Engineers.

Interpretive Summary: Enduring changes in annual and seasonal precipitation are important considerations for planning/management of water supply of growing urban communities and for negotiation of long-term water agreements. Over much of the continental United States the average precipitation over the last three decades of the 20th century has been higher, on average about 4% higher than the long-term 1895-2001 average precipitation. The precipitation increase was found to vary by season and by region. 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 annual precipitation and streamflow occurring during the fall and winter seasons. These are also the seasons with reduced water needs, and the increase in precipitation contributed less than desired to directly alleviate any water supply shortages during the high demand summer season. This study suggests that management of surface 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 in a timely manner as a pattern in precipitation variations emerges.

Technical Abstract: Changes in annual and seasonal precipitation over the last 30, 10 and 5 years of the 20th century were investigated and the corresponding impact on streamflow was evaluated for two watersheds 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. Fall and winter seasons appeared to capture most of the increase in precipitation. Changes in average annual and seasonal streamflow were found to be sensitive and highly correlated to causative changes in precipitation. Based on these findings, it was inferred that decade-long variations in precipitation can impact operation strategies of water storage and supply systems, and should be important considerations in water resources planning and management.