Evaluation of stream flow drought characteristics of the Agmion Chai river on the sahzab hydrostation

Droughts are related with extremely long periods of abnormally low water availability. Such low levels are coming from reduced precipitation periods, and they can be observed over different hydroclimatic variables related with water availability. Examples are precipitation (meteorological drought), soil moisture (agricultural drought), or streamflows (hydrological drought). Result of the research presented in this article was carried out in the framework of the natural Project (Historic Hydrological Drought Monitoring and Zonation in EAST Azarbijan province), supported by the Agricultural Extension, Education & Research Organization of Jihad-e-Agriculture Ministry of IRAN. Study area located on the East Azarbyjan Province on the Aji-chai basin. This research adopted the definition of hydrological droughts introduced by Yevjevich. Here a threshold, is defined below which the flow of a stream becomes a drought flow. This Approach allows simultaneous characterization of stream flow droughts in terms of stream flow, duration and frequency of occurrence. In this research, the analysis of hydrological drought was based on daily stream flow of Sahzab hydro-station (1974-2007).Firstly, required daily data set are evaluated based on their suitability for drought analysis. This includes two main aspects: the quality of the data and properties of the time series, such as trends and seasonality.The program NIZOWKA2003 is based on a method presented by Zelenhasić & Salvai was applied to ferquency analysis of drought event. Based on this method, The Q80(0.29m3/sec) was selected as threshold level which derived from Flow Duration Curve. The most commonly applied deficit characteristics such as drought’s time of occurrence, its duration, its deficit volume or severity, and the minimum flow occurring during the drought event. As well as drought intensity are derived by comparing each daily stream flow series with selected threshold level. Inter-event critria(IC) was applied as pooling method to eliminate minor as well as mutualy dependent drought. Resultes showed, maximum drought duration related to 2001(with 183days),2000and1999(with139days), 1984(with 119days) and 1983 with 114 days respectivelly. While, there are 8 years with zero drought events. Poisson and Generalized Pareto distributions was selected as suitable probability distributions for number of drought event and drought duration frequency analysis respectively. Here, goodness of fitting is tested with the use of X2 test

کلیدواژه ها:

hydrological drought ، Sahzab ، NIZOWKA2003