TY - JOUR T1 - Annual precipitation forecast in two arid and semi-arid regions TT - پیش‌یابی بارش سالانه در دو اقلیم خشک و نیمه خشک JF - geospace JO - geospace VL - 20 IS - 71 UR - http://geographical-space.iau-ahar.ac.ir/article-1-3507-en.html Y1 - 2020 SP - 159 EP - 175 KW - Annual Precipitation Prediction KW - Artificial Neural Network KW - Chaharmahal-Bakhtiari KW - Regression Model KW - Yazd. N2 - Introduction Annual precipitation forecasting usually guarantees success in sustainable management of water resources and watersheds in cases like determination of rain-fed and water cultivation area and water resources consumption planning. Although precipitation does not follow a specified pattern; however, it has a correlation with some climatic parameters. If these parameters were easy to find, simple applicable models could be developed to predict annual precipitation. One of the simplest methods for predicting annual precipitation is regression models. The block box models such as Artificial Neural Network (ANN) has also been used for precipitation forecasting. This study was an attempt to predict annual precipitation using some climatic parameters by multiple linear regression and ANN models. Materials and Methods Chaharmahal-Bakhtiari and Yazd provinces are located in the southwestern and central part of Iran with semi-arid and arid climate, respectively. Mean annual precipitation of these two provinces are 560 and 110 mm, respectively. Meteorological data of the weather stations belong to 2001-2011 in Chaharmahal-Bakhtiari and 2003-2013 in Yazd province; respectively, were analyzed. Various parameters were calculated for predicting annual precipitation using long-term daily precipitation and temperature data of the meteorological stations. Among the parameters, total precipitation in the first half of the water year (R6m, mm), time to 47.5 mm cumulative precipitation since the beginning of autumn (t47.5, day), long-term mean annual precipitation (Rm, mm), average summer temperature of the preceding water year (Tsu, °C) and average temperature of preceding summer and current autumn of water year (Tsu.au, °C) that had a high correlation with annual precipitation, were used in multiple linear regression (MLR) models and artificial neural network (ANN) techniques. normalize mean square error (NRMSE) and degree of agreement (d) were used to evaluate accuracy of the models for predicting annual precipitation. Results and Discussion Results showed that the obtained MLR models were significant at a probability level of less than 0.01. Results also showed that both methods (MLR and ANNN) could accurately estimate the annual precipitation. Evaluation and verification of the models with NRMSE values less than 0.3 and d values greater than 0.8 confirmed the performance of the models. The best topology of the ANN network in the study was a multiple layer perceptron network with one hidden layer and two neurons and sigmoidal activation function. The findings of the study support the fact that higher temperature in summer and autumn was a sign of higher and lower annual precipitation in Chaharmahal-Bakhtiari and Yazd Provinces, respectively. Besides, higher time period to 47.5 mm cumulative precipitation from the beginning of autumn implies fewer amount of annual precipitation. Conclusion This study showed that annual precipitation could be predicted by MLR and ANN methods in both arid and semi-arid regions with acceptable accuracy. According to the results, a rainy water year will be expected continuing a warmer summer and autumn in Chaharmahal-Bakhtiari Province; however, there will be a dry water year in Yazd Province followed by these conditions. Furthermore, if 47.5 mm cumulative precipitation takes a longer time since the beginning of autumn annual precipitation will decrease. M3 ER -