Rainfall-frequency mapping for Greece

For the design of hydrotechnical projects in ungauged watersheds, the flood flow is estimated by various methods, which demand the estimation of rainf all of particular critical duration and return period. For medium-sized and large basins, the storms causing flood flows have usually duration larger than 24 hours. In this study daily rainfall data from 24 meteorological sta tions for the period 1950 to 1981 were used. These stations are evenly dist ributed over Greece. From these data, the rainfall depths for various durat ions were computed, i.e. 1 to 7 days. The Extreme Value I (Gumbel) theoreti cal distribution had the best fit to the data from other theoretical distri butions and it was fitted to the maximum annual rainfall depths for various durations. As a result, the Depth-Duration-Frequency relationships for eac h station were estimated and mapped for Greece. Moreover, the analysis show ed that the rainfall of various durations and return periods represents a c ertain percentage of the mean annual precipitation for hydrologically homog eneous areas of Greece. The homogeneous areas were identified through facto r analysis of monthly precipitation data from 37 meteorological stations. T he results of this study can be used for the estimation of rainfall at unga uged sites in medium and large watersheds, but they should be applied with caution in mountainous areas. For the estimation of rainfall in these areas the climatic conditions of the region and the orographic enhancement of ra infall should be considered. (C) 2001 Elsevier Science Ltd. All rights rese rved.