Comparing the variations in hydrologic response of Ardabil Province watersheds using precipitation-runoff polygons

Rainfall-runoff relationship is one of the most sophisticated hydrological processes which helps to understand the watershed hydrologic response assessment. The rainfall-runoff relationships of Ardabil Province watersheds were analysed to investigate the spatial variability of rainfall-runoff responses using precipitation-runoff polygons technique at a monthly temporal time scale. Therefore, variations of recorded precipitation and runoff data were analysed over a period of 22 years from 1990-2011 in 20 watersheds of the Ardabi Province. According to the results, the maximum runoff coefficient is corresponding to Doostbeighlou Station by the value of 33%. The analysis of precipitation-runoff polygons reveals that the Arbabkandi, Polealmas, Samian and and Doostbeighlou watersheds had the higher amount of runoff coefficient. As well as, the hydrologic response of Shamsabad, Kozetopraghi and Ahmadkandi are similar and homogeneous in term of runoff generation. Based on the relationship between monthly runoff coefficient and the area, the highest correlation coefficient was observed in the March (0.92), and the lowest was assigned to August (0.0089). The larger the area of the polygon and the highest coefficient of variation is corresponding to Doostbeighlou and Samian watersheds. The distribution of the runoff coefficient over the months showed that the Hir and Ahmadkandi watersheds had the highest runoff coefficient in June and August which is related to the delay in runoff production. Based on the results, precipitation-runoff polygon technique is a suitable way to compare the hydrological response and changes in rainfall-runoff relationship of watersheds. It should be noted that the comlexity of rainfall-runoff process causes an overlapping in polygon portions and irregular shapes which caused a difficulty in interpretating of watershed response and needs much more furture researches.