Effects of transient climate change on basin hydrology. 1. Precipitation scenarios for the Arno River, central Italy

Abstract

AbstractLong‐term simulations of temporal rainfall and temperature under transient global climate conditions are discussed to give an insight into potential modifications of atmospheric inputs at the basin scale in the Arno River in central Italy. The outputs from a global circulation model (GCM), simulating climate changes due to an increase in the greenhouse effect resulting from a continuous trend in the growth of CO2 atmospheric concentration and accounting for the influence of both CO2 and sulphate aerosols, are downscaled using a stochastic approach based on the observed non‐stationarity of precipitation and temperature patterns. By using the historical joint variability of the internal structure of storm events, one can infer future changes in storm duration and depth from GCM trend variables, thus indicating the extent of changes in the occurrence of wet and dry periods and in the daily rates, including those of distributional properties at the monthly and annual scales. Because the changes detected mainly affect the tails of the distributions, one can conclude that modifications can occur in both low and high values of rainfall at the monthly and annual scales, with a shift of the storm patterns towards shorter and more intense convective rainfall, especially in the summer season. Stochastic simulation also shows that the distributional and scaling properties of rainfall extremes may progressively change, thus indicating that some revision of current practices to estimate extreme storms is needed to account for possible effects of non‐stationary climate conditions. This approach provides local precipitation that, together with temperature scenarios, can be used for hydrological simulation of basin water fluxes in the Arno River, as reported in a companion paper (Burlando P, Rosso R. Hydrological Processes this issue). Copyright © 2002 John Wiley & Sons, Ltd.