Thursday, 13 February 2003
The seasonal pattern of recent change in precipitation normals
Previous research has identified a general precipitation trend over much of the continental United States towards higher precipitation values. This trend has also been recognized in the updated precipitation Normals for 1971-2000 and in the precipitation averages over the last 20 and 10 years. Recognition of trends in annual precipitation is important to identify climate change, yet from a hydrologic cycle and water resources application point of view, the seasonal distribution of this change/trend is more important. For example, urban and industrial water supply in dry climates is highly dependent on seasonal water storage, whereas agricultural production is centered around seasonal water availability. Changes in seasonal precipitation patterns would required adaptation of water management and utilization strategies. Here, the changes in the seasonal distribution of precipitation associated with the general climate trend are identified for several large regions in the United States. The results show that in some regions precipitation increased in all four seasons (e.g. Northeast), whereas in other regions the increase is predominantly during the winter and spring months (e.g. Southcentral). Time series of seasonal precipitation also show that in some regions the contrast between successive seasons seems to be increasing towards the end of the 20th century, thus suggesting more frequent occurrences of extreme wet and dry seasons during a given year. These findings show the seasonal character of the climate trend, and also provide useful information for the management and utilization of water resources.