بررسي كشت مخلوط ذرت و آفتابگردان

Evaluation of drought situation and its process in Hamadan region on the basis of drought statistical indexes

Drought is one of the natural disasters that inflict serious damages on human life and natural ecosystems. It differs from other natural phenomena such as flood, tornado and earthquake. Most of these differences relate to the gradual effect of drought during a relatively long–term periods, impossibility of determining its exact beginning and end, and the geographic extent of its impact. In the other hand, the lack of an exact and acceptable universal definition of drought has mad this phenomenon complicated. Generally there are three types of drought: meteorological, hydrological and agricultural. Meteorological or climatic drought is basically caused by rainfall deficiency which in case of continuation culminates in hydrological and agricultural drought.Precipitation is the most important parameter that is used for defining drought and its lack or deficit implies the threshold of drought. In this paper, considering 52 year of rainfall data from Ekbatan and Nogeh Metrological, stations (1328-1329 to 1379-1380), drought in Hamadan region has been evaluated on seasonal and yearly basis. At first the homogeneity of data was evaluated using Double Mass and Run- Test methods. Then, drought was explained on the basis of fallowing indexes: 60% threshold index, percent of normal index, rainfall standard index, deviation form mean index, and classification of rainfall range on seasonal and yearly scale index. Considering the decrease of precipitation it was concluded that in Hamadan region drought has occurred as a seasonal or a yearly basis. Considering the decrease of precipitation in Hamedan region, drought has occurred either on seasonal or yearly basis.