Submitted to: American Society of Civil Engineers
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2002
Publication Date: 6/23/2002
Citation: GARBRECHT, J.D., SCHNEIDER, J.M. CHANGING ANNUAL AND SEASONAL PRECIPITATION PATTERNS: AN ISSUE FOR WATER RESOURCES MANAGEMENT? CD-ROM. RESTON, VA: AMERICAN SOCIETY OF CIVIL ENGINEERS, EWRI. 2002. Interpretive Summary:
Technical Abstract: Changes in long-term annual and seasonal precipitation can have consequential implications for water resources management. The updated precipitation Normals for 1971-2000 and precipitation averages over the last 10 to 20 years show an increasing annual precipitation trend for many regions of the contiguous United States. The current annual precipitation Normal for the entire contiguous United States is about 4% higher than the 1895-2001 average precipitation. However, changes at a regional scale and over periods lasting about 10 years can be well in excess of 10%. The seasonal distribution of these annual changes in precipitation is important for applications related to water resources management and agriculture. On average over the contiguous United States, the fall and winter seasons experienced a 5.9% precipitation increase during 1971-2000 over the long-term 1895-2001 average precipitation, whereas spring and summer only saw a 2.6% increase over the same period. At the regional scale, these changes in seasonal distribution are also magnified. In the Central Plains the increase in annual precipitation over recent decades has lead to a substantial increase in average streamflow. On selected watersheds in the Central Plains an observed 12% increase in precipitation over two decades has lead to a 60% increase in streamflow over the same two decades. The impact of the precipitation trend on evapotranspiration was less pronounced when measured as a percentage change. The 12% increase in precipitation over two decades lead to only a 5% increase in ET. Given the magnitude of the precipitation and streamflow trends, analyses and operational methodologies based on assumptions of climate stationarity, such as reservoir operation strategies, streamflow regulations, environmental sustainability and ecosystem climax, should be carefully re-examined in light of the changing annual and seasonal pattern of precipitation over 30, 20 and 10-year time spans.