Analysis of Trends in Temperature and Precipitation in Doroodzan Dam Basin using the Modified Mann-Kendall Test

Doroodzan Dam basin is one of the strategic agricultural areas in Fars province. Changes in time series of climatic parameters, especially temperature and precipitation parameters, can have a significant impact on the growth cycle of agricultural products, the status of water resources and the economy of the populations in the area. In the present study, rainfall and temperature trends were investigated in 13 rainfall stations and 4 thermometric stations. Initially, the change point pettitt test was used to assess the homogeneity and change point in the time series. Then, trends in the rainfall, average monthly and annual temperature time series were investigated using Mann-Kendall (MK), modified Mann-Kendall (MMK) and the sen’s slope methods. The results of the pettitt test showed that there is no significant change point in the monthly and annual rainfall and monthly temperature time series, only in the annual temperature of two stations, there is a significant change point at the 95% confidence level. The results of the trend analysis with all three abovementioned methods showed that the monthly precipitation in all stations and annual precipitation in most stations have a decreasing trend and the average monthly and annual temperature have an increasing trend; however, in none of the time series, the trend was significant in the confidence level of 95%. Based on the results, in the whole area, the mean annual temperature increased by 3.7 percent and precipitation decreased by 9.1 percent compared to the mean.