A Simple Model for Prediction of Annual Precipitation in the Southern and Western Provinces of I. R. Iran

Dryland agriculture plays an important part in the agricultural production of the southern and western provinces of I. R. Iran. Since it utilizes precipitation directly, it is considered an optimal method of water use. The purpose of this research was to develop a simple model for the prediction of annual (water year) precipitation in southern and western provinces of I. R. Iran, so that dryland farming can be properly planned in these areas. The relationships between annual precipitation and the duration of 37.5, 42.5, and 47.5 mm of precipitation since the onset of autumn (t37.5, t42.5, and t47.5) were analyzed using simple regression for all stations in the study areas. The results showed that 47.5 had higher correlation with the annual precipitation than t37.5 and t42.5. Furthermore, 47.5 was inversely related to the annual precipitation for all stations in the study areas. Among different parameters such as mean of annual precipitation, Prna (mm), elevation, longitude, and latitude of the stations, the mean of annual precipitation was the most appropriate one to be included in a linear multiple regression model along with 47.5 to estimate annual (water year) precipitation, P, (mm) as follows: Southern provinces Pa=-1.83 t47.5 + 0.76 Pma + 228.3, R^2=0.71 Western provinces Pa=-1.88 t47.5 + 0.94 Pma + 146.8, R^2=0.76 These models were validated by using data from the study areas not used for model development. The regression analysis showed a high correlation with a slope of approximately one between the predicted and observed values.