Prediction of Drought in Lake Orumiyyeh Basin Using SARIMA Models

Since immemorial past, drought has been one of the dangerous natural disasters for human life. As it is seen in historical texts, this phenomenon has always caused many social-economic changes, such as wars, famine and immigration. In this research, the wet and dry periods of some of meteorological stations of Lake Urmia Basin, located in the northwest of Iran, have been analyzed. For this purpose, first the stations of Urmia, Tabriz, Saqez and Miandoab have been normalized using yearly methods. In other words, the precipitation was turned into a standard score (Z-Score). Then, the intensity of either of dry and wet periods was defined in two classes: weak to average dry (-1.5 <z <-0.5), severe dry (z<-1.5), weak to average wet (+0.5 <z <+1.5) and extreme wet (z> +1.5). In addition, the roughly normal period (-0.5 <z <+ 0.5) was considered as a period neither significantly wet nor suffering from drought. In the next step, a Run Test was performed on monthly precipitation data and their homogeneity was confirmed. Subsequently, using time series method (SARIMA), the monthly precipitation of these stations was modeled and predicted for the future (based on the most appropriate model) until 2002. Finally, according to the predicted values, the degree of severity of the year’s wet-or-dryness has been determined. The results of the study show that the annual precipitation of this basin in the years 2001 and 2002 is almost normal and will be accompanied by an upward trend and exit the state of drought.