Investigating the effect of dry land area extension on annual peak flow variation trend, case study: Ghizilozan basin

Increasing runoff coefficient and flood intensity and extending dry land areas over the country basins are due to the destruction of vegetation cover. For monitoring the trend of temporal variation, maximum peak flows and maximum 24 hr rainfall data have been gathered from all climatologic and hydrometric stations of Ghizilozan basin. The acquisition data repaired and standardized within a period of 30 years. Then the data were divided into three categories with period of 10 years and finally six categories with period of 10 to 30 years were produced. The mean of variables for every period was calculated based on two years return period by fitting the distribution function of Pearson type III to selected data series. The mean of every category plotted with time period and fitted a line to them. The results showed that based on Kendall’s Tau method, there are significant and positive harmonizing between measured variations respect to time only in two climatology stations named Gitoo and Salamatabad and so two hydrometry stations named Sarcham and Dehgolan and in the others there aren’t any positive or negative harmonizing of data variations respect to time. But the slope of regression line of maximum 24 h of annual rainfall as an index of climate variations to the time, equal 0.031 and in contrast the slope of regression line of peak flow to time equal 0.059. Therefore, the slope of peak flow is 1.9 times of maximum 24 h of annual rainfall with time. This finding says that the vegetation cover because of dry land extending is destroyed and runoff coefficient and flood intensity is increased at studied basin.