Modeling, Forecasting and Trend of Selected Precipitation Stations in Fars Province

Forecasting climatic procedures provides an appropriate instrument for directors of different fields، so that by considering such for castings، they are able to plan for future policies to optimize the use of expense and productivity facilities. Forecasting precipitation is of great importance for a variety of purposes such as assessing flood، drought، managing water shred basin، agriculture and etc. The aim of the present study is to model and for cast the rain in stations in Fars province which are under investigation and to consider precipitation trend in such stations. The temporal period in this study is a 33- year period which has occurred during 1356 to 1389. This involves stations of Shiraz، Abadeh، Fasa and Lamerd. In this study three methods of Box Jenkins، decomposition and Holt Winters are used and due to the errors of forecasting in each method the most appropriate model for forecasting the precipitation in each station is chosen and finally the existence of the trend is analyzed. According to the results due to the comparison between errors of the three models، Box Jenkins is the most appropriate model for precipitation forecasting in Shiraz. For precipitation forecasting in Lamerd station for monthly- seasonal data due to the squares of the errors of forecasting، decomposition is the appropriate model. For forecasting the monthly precipitation in Abadeh station، decomposition and for seasonal precipitation Box Jenkins is the best model. For forecasting the monthly- seasonal precipitation in Fasa station، Box Jenkins was chosen due to the rate of errors in forecasting. In considering monthly- seasonal precipitation trend in these 4 stations by Mann-Kendall and Sense Estimator methods، the following results were obtained. Seasonal precipitation trend in Lamerd station shows that among the four seasons precipitation trend in fall in 95- percent reliability level is decreasing and in winter is a very weak decreasing in 95- percent reliability level. Spring and summer show increasing precipitation trend، and monthly precipitation trend was also considered i. e. in June and July increasing trend and in April a weak increasing trend is observed and there is a decreasing trend in 95- percent reliability level in December and February، and just a weak decreasing trend in 95- percent reliability level in May precipitation is observed in monthly- seasonal trend in Shiraz station and in other months and seasons no trend is observed. Precipitation trend in Abadeh station just in winter has the 95- percent reliability level trend which is decreasing and there is a weak increasing trend in summer، and other seasons lacks the trend and among the 12 months only March has weak decreasing trend in 95- percent reliability level and no significant trend is observed in Fasa station except in March in which a decreasing trend in precipitation in 95- percent reliability level is observed and in other trends and months no trend is observed.