Trends in streamflow and climate variables within the Atrak River basin, North Khorasan, Iran

In the present study the relationship between climate change and hydrologic regime of the Atrak River basin in the northeast of Iran has been investigated. Overall, 10 hydrometeorological stations were chosen and trends in annual mean discharge, annual precipitation, annual mean temperature, and potential evaporation were analyzed using the nonparametric test of Mann-Kendall. First, the long term observations of discharge variable (annual mean) at 7 hydrometry stations have been analyzed to find out whether there is any indication of increasing or decreasing trends. Second, the long term records of meteorological variables including annual precipitation, annual mean temperature, and pan evaporation were examined to see the sights of climate change. Finally, the relationship between trends in streamflow and meteorological variables were discussed. The results indicate that annual mean discharge in the Atrak River basin is decreasing significantly at more than 70 percent of stations. However, there is no evidence of significant increasing or decreasing trends in the annual precipitation. Investigation on temperature and pan evaporation shows increasing trends for them in most of the stations. Generally speaking, although the decreasing trends in the mean discharge is in agreement with the Intergovernmental Climate Change (IPCC) report in 2007 which has predicted about 10 to 30 percent decrease in the annual average runoff over some dry regions at mid-latitudes and in dry tropics by mid century but it can not be explained by variations in the annual precipitation. Since there is a significant increasing trend in the average values of mean temperature and pan evaporation across the basin, it has been concluded that the decreasing trends of annual mean discharge is most likely related to an increase in the evaporative power of atmosphere.

کلیدواژه ها:

climate change ، discharge ، trend ، Mann-Kendall ، Atrak River basin