Assessment of the Relations between the Trends of Climatic Factors and River Flow in Southern Coastal Watersheds, Iran

Climate change will lead to an intensification of the global hydrological cycle and can have major impacts on regional water resources, affecting both ground and surface water supplies. A better understanding of hydrological changes associated with climate change can be achieved by analyzing the temporal trends in river discharge time series. We used the parametric test (regression analysis) and non-parametric Spearman's rho, Mann- Kendal and TFPW Mann- Kendal approaches to evaluate annual and seasonal trends in river flow data from 22 sub basins (based on the classification of the Ministry of Power) located in the southern regions of Iran over a 31-year period spanning the hydrological years 1981–1982 to 2001–2013. The data used include pan evaporation, discharge, minimum and maximum air temperatures, depth, intensity and duration of rainfall at each sub basin. Results showed that in more than 50% of the hydrometric stations, runoff had a decreasing trend. This trend was apparent in the central watershed consisting of Bandar-Sedij and Kol-Mehran sub basins. Conversely, more than 90% of the stations, duration and intensity rainfall had decreasing and increasing trends, respectively. Furthermore, minimum and maximum air temperature trend had an increasing while evaporation had a decreasing trend. In conclusion, factors influencing the declining discharge trend can be changed by changing the rainfall pattern, decreasing the rainfall duration and increasing its intensity.