Assessing the Impact of Meteorological Factors on Streamflow in Aksu River

【Background】The effects of potential climate change on water flow in rivers have been well documented but with the focus putting on precipitation and potential evapotranspiration (PET). There is a lack of study on the impact of individual meteorological factors. 【Objective】Taking Aksu river in Xinjiang as an example, this paper investigated the relationship between water flow rate in the river and some meteorological factors. 【Method】The trends and abrupt changes in hydrological and meteorological data measured from the basin were analyzed using the Mann-Kendall-Sneyers test and Mann-Kendall nonparametric trend test; three improved elastic coefficient methods were used to evaluate the influence of the meteorological factors, particularly temperature, on water flow rate in the river. 【Result】Both water flow rate in river and temperature in the basin had increased at rates of 11.73 (m3/s)/10a and 0.26 ℃/10a, respectively, at significant level (P<0.01). The precipitation trended up at a rate of 14.31 mm/10a at significant level (P<0.05), while the potential evapotranspiration had been in decline at a rate of 21.89 mm/10a at significant level (P<0.01). The test results showed that the temperature changed abruptly in 1993, the precipitation in 1991 and the potential evapotranspiration in the early 1990s. Water flow rate in the river underwent an abrupt change in 1993, indicating that water in the river has changed significantly since 1994 due to climatic impact. A multi-year average water flow rate and climate factors from 1960 to 1993 were thus used as the baseline to measure the change in water flow after 1993. From 1994 to 2010, streamflow, precipitation and temperature increased by 23.1%, 22.5% and 32.4% respectively, while the potential evapotranspiration reduced by 7.6%, compared to the averages over 1960 to 1993. The linear relationship between temperature, precipitation, potential evapotranspiration and streamflow passed the statistical test at significant level of 1%, indicating that the linear regression coefficients reflect the relationship between surface runoff and climate factors and that it can be used to deduce the climate elasticity. Sensitivity analysis showed that the elasticity of the streamflow to the temperature (εT) and the precipitation (εP) was 1.138 and 0.270 8 respectively, meaning that every 1% increase in the temperature and precipitation will lead to 1.138% and 0.270 8% increase in streamflow respectively. The elasticity coefficient of the streamflow to the potential evapotranspiration was -1.003(εPET), indicating that a 1% decrease in potential evapotranspiration would lead to a 1.003% rise in streamflow. Water flow in the river is most sensitive to temperature and least to precipitation, with the potential evapotranspiration between. It was also found that the relative contribution of temperature to streamflow was 46.7%, while the contribution of precipitation and potential evapotranspiration was 20.5% and 24.9% respectively. Non-climatic factors, such as anthropogenic activities, contributed only 7.9% to the streamflow change. 【Conclusion】Our analysis showed that climate change is currently the main factor behind the streamflow change in Aksu river, despite the increasing influence of the continuous intensified anthropogenic activities at upper and lower reaches of the basin.