Trend and Change Point Analysis of Seasonal SPI Drought Index in Iran

Drought as shortage of rainfall compared to its long- term mean in a period can be affected by climate change. Evaluationof drought changes can be useful tool for water resources management. In this study, to investigate the trend of drought in Iran, the monthly rainfall data of 119 meteorological stations in 1366-1390 are considered and SPI drought index are calculated based on these data. The Mann-Kendall and Pettitt tests are used for trend and change point analysis. Results of Pettitt test show change points for 42, 27, 35 and 16 stations in spring, summer, autumn and winter seasons respectively that demonstrates disregarding of change point analysis in trend test application can lead to non- negligible mistakes in results. The results of the trend analysis indicate that there are 4, 10, 8 and 9 increasing and 6, 1, 0 and 2 decreasing tren in stations in spring, summer, autumn and winter seasons respectively. Moreover, investigation of spatial distribution show most of stations with trend in SPI index in different seasons are located in west region of the country so that there are decreasing trend in spring and increasing trend in summer and winter while there is no specific spatial pattern in autumn.