CHANGES IN DAILY PRECIPITATION UNDER ENHANCED GREENHOUSE CONDITIONS

An increase in global average precipitation of about 10% is simulated by two global climate models with mixed layer oceans in response to an equilibrium doubling of carbon dioxide. The UKHI model was developed in the United Kingdom at the Hadley Centre for Climate Prediction and Research and the CSIRO9 model was developed in Australia by the CSIRO Division of Atmospheric Research. Regional changes in daily precipitat ion simulated by these models have been compared. Both models simulate fewer wet days in middle latitudes, and more wet days in high latitud es. At middle and low latitudes, there is a shift in the precipitation type toward more intense convective events, and fewer moderate noncon vective events. At high latitudes, the precipitation type remains non- convective and all events simply get heavier, resulting in fewer light events and more moderate and heavy events. The probability of heavy d aily precipitation increases by more than 50% in many locations. Extre me events with a probability of 1% or less were considered in terms of return periods (the average period between events of the same magnitu de). For a given return period of at least 1 y, precipitation intensit y in Europe, USA, Australia and India increases by 10 to 25%. For a gi ven precipitation intensity, the average return period becomes shorter by a factor of 2 to 5. Given that larger changes in frequency occur f or heavier simulated events, changes may be even greater for more-extr eme events not resolved by models.