Simulation of Hydrological Processes in Dry Areas Case study; Kardeh watershed in Razavi Khorasan Province

Water demand is one of the main components of decision making to manage resources, watersheds and phenomena such as droughts. Therefore, recognizing water capacities and demand for water are the main components of decision making for management of water resources and phenomena such as drought. The management of surface water resources and dangers in the country continues to face a lack of a system that supports decision-makers in making timely and correct decisions. In order to establish such a system, it is necessary to consider and evaluate the basic steps in identifying the subject and the country's data capacities. Considering that runoff simulation is one of the most important hydrological researches in water engineering sciences. Therefore, in this study, the simulation of the hydrologic processes of the basin, located in the dry area of Khorasan Razavi province, has been studied using the "Precipitation Index" (API), which estimates the threshold of runoff using the rainfall and trap simulator. The previous rainfall index was calculated and then the results were compared between the two indexes with the previous days 1, 2, 3, 4, 5, 6, 7, 10, 15, 20, 25 and 30 days with the flood waters of the basin. The results of this study showed that the pre-rainfall index with runoff in the catchment area had the most differences between days 20 and 30 with a difference of 4% explanation coefficient. Finally, the highest correlation between the previous rainfall index and runoff is on day one,with an explanatory factor of 56%.