Investigation and Evaluation of Base flow Response to Precipitation in Different Climates of Iran

Base flow response to rainfall components varies in different climates and knowing the interaction between rainfall components with the base flow can lead to improvement and development of prediction in ungagged catchment. In this study, the catchments in each climatic zone were separated using the intersection of the climate map and the boundary layer of catchments. At least 30 hydrometric stations from each climatic zone were selected with common period of 1976-2011. Then, average annual rainfall and rainy days in each basin were calculated. The base flow index was separated using daily flow data and with B-Flow-Lynie & Holick algorithm. The relationships between the base flow index and the number of rainy days and average annual rainfall in different climate were calculated and the results were analyzed and interpreted. The results showed that in more than 66% of the catchments of different climatic zones, the average base flow index was more than 50%. Also, the highest frequency of catchments with base flow index less than 0.50 were for humid, semi-humid and very humid climates and the highest frequency of catchments in the range of more than 0.5 were found for “arid “and” semi-arid”. The Correlation between annual rainfall and base flow in the very humid, humid, semi-humid and Mediterranean" climatic zones have a positive coefficient and in the "arid" and "semi-arid" regions were negative. Correlation of the number of rainy days with the base flow in the selected catchment in all climatic zones showed a positive correlation. The highest coefficient of determination between rainy days and base flow index was 0.57 to semi-arid regions and the lowest coefficient was 0.14 to the catchments of arid zone. This was approximately equal to about 0.34 for humid and semi-humid zones.