Regional Analysis of Drought Intensity (Case study: Tehran Province

Drought analysis is of very much importance in evaluation of water resources projects. Based on regional analysis of hydrologic drought, it is possible to develop relations between watershed characteristics and flow indices to estimate drought intensity. In this research, frequency analysis based on normal distribution was performed for 12 watersheds in Tehran province. In addition, Factor analysis on 19 variables including physiographic, climatic and geologic factors resulted in four effective variables of: watershed area, annual average precipitation, weighted mean infiltration and average slope. Cluster analysis was carried out for determination of homogenous regions in which watershed were divided into two homogenous groups. Run theory was used to estimate intensity of hydrologic drought. To find relation between 4month _ 10 yr drought intensity and characteristics of the watershed, multivariate regression technique was used, the best model being proposed. Finally, using data of three control stations, accuracy of the proposed regional model was evaluated. Results show that, in the study area, regression models developed for homogeneous regions are of a higher accuracy as compared with the models developed for the entire region.