Rainfall Trend Analysis of Hydrological Subbasins in Western Iran

Abstract

Precipitation is one of the main components in water budget balance and its trend analysis could help to understand the hydrological features of a basin in the future. In this study, 10 subbasins in western Iran are selected. One rain gauge station is chosen as a control station and three more are selected upstream, in the middle, and downstream of each subbasin. Average monthly and annual rainfall time series are analyzed and then the trends are investigated. Analysis of mentioned time series of control stations reveals that 51% of time series have decreasing trends, while 49% experience increasing trends. Six out of 10 studied subbasins have decreasing trend of average annual rainfall time series all over the basin. Among the most rainy months in the country (November to May), in November 68% of the stations have upward trend, while in March 92% of the stations have downward trend.