西北干旱区径流补给来源单一，均来自山区降水和冰雪融水，而这部分水资源对全球气候变化的响应十分敏感。气候变暖下，部分降雪转变为降雨、降雪率下降，导致降水形式的改变，对以冰雪融水为主要径流来源地区产生重要影响。然而，在降水量不变甚至有所增加或减少的情势下，降水形式的改变会如何影响径流？如何定量辨识降水形式改变对径流产生的影响？这属于亟待解决的问题。本研究以西北干旱区为典型区：1）基于序列气象资料，分析近60多年降水形式演变特征、趋势及原因，评价气候变暖对西北干旱区降水形式改变的影响；2）基于Budyko假设的物理和数学意义，与水量平衡方程和弹性系数相结合，以时间序列降雪率作为驱动变量，改进基于Budyko假设的流域水热耦合平衡计算，提出改进的算法；3）利用改进算法估算降水形式改变对西北干旱区河川径流产生的影响；预期研究成果对明确气候变暖下西北干旱区径流动态及降水形式变化关系具有理论与现实意义。

Runoff in the arid regions of Northwest China is primarily fed by snow and ice melt, and extremely sensitive to climate change. In a warmer world, more precipitation falls as rain rather than as snow, decreases the amount of snow fraction, and causes shifts in regional precipitation phase. A shift from a snow- towards a rain-dominated regime is assumed to affect sreamflow. However, how these changes in precipitation phase impact on streamflow, and how to decipher the degree of impact is, still, unclear. Based on long term observed hydrometerological data and through the case study from arid regions of Northwest China, this study aimed at: 1) to analyze changes, trends, and possible reasons in the shifting of precipitation phase over the last more than 60 years, and assess the impacts of global warming on the changes in precipitation type in the arid Northwest China; 2) based on the sound physical and mathematical facts of Budyko framework, and by further combining the water balance equation and concept of elasticity, to enhance the water-energy balance estimation of Budyko framework with the time series snow fraction as a climatic variable, and present an enhanced calculation method; 3) using the enhanced method, estimate the impact of changes in precipitation phase on streamflow throughout the continuous watersheds of Northwest China. The results of this study can clarify the underlying fact of changes in precipitation types in the arid regions of Northwest China, and quantify the estimation of changes in water availability caused by changes in precipitation phase.