Analysis of Hydroclimatic Trends in the Atrak River Basin, North Khorasan, Iran (1975–2008)

Hydrologic regime is highly dependent on climate change, as hydrologic cycle components are directly influenced by climatic conditions. this paper analyzes the impacts of climate change on the hydrologic regime of the atrak river basin in the northeast of iran. the river drains to the caspian sea in its southeastern coasts. the data collected at 11 hydrometeorological stations were examined to detect trends in hydroclimatological variables. ten variables including annual mean discharge, annual maximum discharge, annual precipitation, maximum daily precipitation, annual minimum, mean and maximum temperatures, diurnal temperature range, annual pan evaporation and annual potential evapotranspiration during 1975–2008 were analyzed using mann-kendall non-parametric test. the long term observations of annual mean discharge at 8 hydrometric stations were analyzed to reveal indications of increasing or decreasing trends. then, the long term records of precipitation, temperature, pan evaporation and potential evapotranspiration were examined to detect signs of climate change. finally, the relationship between trends in streamflow and meteorological variables was investigated. the results indicate that although the annual mean discharge at all stations across the atrak river basin is decreasing, but the decrease is statistically significant at only 6 stations (75 percent of stations). however, there is no evidence of significant increasing or decreasing trends in the precipitation variables. analyses of temperature and evaporation variables show increasing trends in most of the stations. therefore, it is concluded that decreasing trends of mean annual discharge is most likely related to an increase in the evaporative power of atmosphere.