Diaz, H. F., 1991: Some characteristics of wet and dry regimes in the contiguous United States: Implications for climate change detection efforts. In Greenhouse-Gas-Induced Climate Change: A Critical Appraisal of Simulations and Observations, M. E. Schlesinger (Ed.), Elsevier, 269-296.


The climatology of wet and dry regimes in five different regions of the contiguous United States is examined using station records of daily precipitation for the period 1931-86. The regions were selected to be representative of different climatological synoptic regimes, and hence are associated with different large-scale atmospheric forcing patterns. The results show that the precipitation-producing processes operating during the wettest and driest years are substantially different, with wet years generally displaying large increases in the heavier precipitation categories compared to dry years. These differences may be related to changes in the large-scale atmospheric circulation patterns associated with the development of persistent oceanic anomalies associated with variations in air-sea exchange processes over the Pacific Ocean and, depending on the particular region of the country, in the Atlantic Ocean as well.

It is shown that sequences of wet and dry years are rather common throughout the country. The 1930s and 50s saw prolonged periods of severe, and in some instances, extreme drought conditions in many parts of the country. There does not appear to be any secular trend in the frequency of either wet or dry regimes through the analysis period. Wet conditions prevailed in much of the country in the early 1980s; a return to drier conditions in the past couple of years, therefore, appears to be just a normal swing to an opposite regime.