天山南坡高冰川覆盖率的木扎提河流域水文过程对气候变化的响应

Response of the hydrological processes to climate change in the Muzati River basin with high glacierization,southern slope of the Tianshan Mountains

木扎提河是天山南坡冰川面积覆盖率最大(48.2%)的河流,流域径流过程对气候变化极为敏感,为了合理管理和规划水资源,确保水资源的可持续利用,亟需定量评估气候变化对该流域水文过程的影响。以VIC-CAS分布式水文模型为计算平台,利用实测的径流和两次冰川编目间的冰川面积变化数据开展了模型的多目标参数化校正和验证,有效提高了模拟结果的"真实性",然后通过数值模拟结果结合观测数据定量解析了流域径流的组成、变化特征及对气候变化的响应机理。结果表明:木扎提河总径流集中在暖季(5-9月),占全年总径流量的77.9%,冰川径流、融雪径流和降雨径流分别占总径流量的66.6%、26.4%和7.0%。1971-2010年木扎提河流域气温和降水呈显著增加趋势,由于降水的增加,降雨和融雪径流均呈增加趋势,但冰川径流呈现明显减少趋势,导致总径流呈现下降趋势。在RCP4.5情景下,未来该流域气温呈现明显升高趋势,降水表现为微弱下降趋势;气候变暖后,更多降水以降雨形式发生,未来降雨径流将明显增加,降雪和融雪径流已于20世纪90年代达到峰值,随后明显减少;冰川面积将持续萎缩,冰川径流于21世纪10年代达到拐点,随后明显减少,导致河道总径流量也将明显减少。

Muzati River is the most glacierized catchment on the southern slope of the Tianshan Mountains. As the high sensitivity of hydrological processes of the catchment to climate change,it is essential to quantify the impacts of climate change on hydrological processes for the scientific water resources planning,management and sustainable utilization. The VIC-CAS model was adopted as computing platform. The glacier inventory data and observed runoff were accounted for multi-objective calibration and validation to improve the"truth"of simulations. Then the runoff components,runoff variation characteristics and response mechanism of runoff to climate change were quantitatively analyzed using the simulations and observations. The following major conclusions are drawn:The runoff is concentrated in warm season(May to September),accounting for 77.9% to the annual runoff. The contribution of glacier runoff,snowmelt runoff and rainfall runoff to the total runoff was 66.6%,26.4% and 7.0%,respectively. Over the past 40 years(1971-2010),the annual average air temperature and precipitation had shown a significant increasing trend. Due to increasing precipitation,the snowmelt runoff and rainfall runoff had shown increasing trends. But the annual runoff had shown a slight decreasing trend because of decreasing glacier runoff. Air temperature was projected to rise,while precipitation was projected to slightly decrease under RCP4.5 scenario. As air temperature rise,more precipitation will be in the form of rain.The rainfall runoff is predicted to obviously increase,while the snowfall and snowmelt runoff had been reached peak in 1990 s,and significantly decline later. The glaciers are projected to retreat steadily,so the glacier runoff had reached a tipping point in 2010 s. Annual runoff was projected to decrease significantly as a result of decreasing glacier runoff.