The Modeling of Precipitation and Future Droughts of Mashhad Plain using Stochastic Time Series and Standardized Precipitation Index (SPI)

The purpose of this study is to model precipitation characteristics and simulation of drought using the Standardized Precipitation Index (SPI) during 2011-2020 in Mashhad station, Iran. To this end, first, the data related to the average of monthly precipitation in synoptic station of Mashhad (from 1951 to 2010) were obtained from the Meteorological Organization of Iran. Using the method proposed by Box-Jenkins, the monthly precipitation was modeled in 2011 to 2020, with respect to its preceding series trend. In addition, using SPI, climatic conditions in the upcoming years were investigated in terms of drought. The results indicated that the seasonal-multiplicative statistical model of SARIMA (2, 0, 1) (2, 1, 1)12 is a good technique for fitting the precipitation data. Using this model, the pattern of monthly precipitation in Mashhad station from 2011 to 2020 was modeled. The results revealed that the average of monthly precipitation in the next 10 years will decrease about 26mm compared with the last 10 years (2001-2010). The correlation of precipitation in the upcoming 10 years compared with the previous 10 years is about 96%. The SPI suggested that in a 6- month timescale, in the upcoming 10 years, Mashhad station will face drought about 18%; in a 12-month timescale it would be about 17%.