天山西部巩乃斯河流域草地生长季蒸散过程对季节性积雪的响应

Evapotranspiration (ET) and seasonal snow are both important hydrological variables. The seasonal snow impacts the vegetation phenology and productivity, as well as the soil water volume in the growing season. There will be an effect of seasonal snow on ET in the growing season. Investigating the characteristics of the response of ET in the growing season to seasonal snow is an important research subject. Taking the grassland in the Künes River Basin located in the alpines of the Western Tianshan Mountains as an example, the ecohydrological model (Vegetation Interface Process Model) is improved based on the analysis of the observed soil water and temperature. In order to reproduce the spatio and temporal distribution of seasonal snow properties, the spatial pattern of the sensitive parameter of snow model (Snowpack) is reproduced with the observed snow data and DEM. The snow model is then coupled with the ecohydrological model via data transfer in this research. The dynamics of seasonal snow and ecohydrological variables of regional grass is reproduced by the coupled model. The period in the growing season when ET is sensitive to seasonal snow will be identified, as well as the key processes that impact this response. Further, the effect of seasonal snow on grassland ET in the growing season will be quantified based on the scenario analysis. This work will provide scientific and technological supports to the water management, animal husbandry and ecological construction in Xinjiang.

季节性积雪和蒸散是水循环的重要变量，积雪水热和生态效应影响植被生长季蒸散，生长季蒸散过程对季节性积雪的响应特征是水循环研究的重要课题。本研究拟以位于天山西部高寒山区的巩乃斯河流域为研究对象，以草地为例，在分析土壤水热变化特征的基础上，改进生态水文过程模型（VIP模型）土壤水热模拟；利用研究区积雪观测资料和DEM实现积雪模型（Snowpack模型）参数的区域化，重现流域积雪时空分布；通过数据传输实现VIP与Snowpack的耦合，构建积雪-生态水文模拟系统，预测区域草地季节性积雪演变特征和生态水文要素动态变化，揭示草地生长季蒸散对季节性积雪响应的主要时段、关键过程；基于情景分析，量化季节性积雪对草地生长季蒸散的影响，为新疆畜牧业生产、生态文明建设提供科技支撑。

季节性积雪的水热和生态效应影响植被生长季蒸散，生长季蒸散对季节性积雪的响应是水循环研究的重要课题。本项目针对中国天山西部巩乃斯河流域草地，开展了不同土层水热参数的连续观测，并采集了不同时期草地表层土壤的水热参数，在分析土壤水热参数时空变化的基础上，考虑土壤冻融对土壤水热影响，改进了生态水文模型VIP导热系数和导水率的计算，使对生长季土壤水分和蒸散的模拟精度得到提高。积雪期，在代表性站点开展了积雪物理特性连续观测，发现积雪密度随时间的演变主要受气温与雪表温度差和时间的影响；在区域尺度开展了积雪物理特性地面调查，获得了积雪深度空间分布与海拔的经验关系式，结合Snowpack模型敏感参数粗糙度长度与同期积雪深度的定量关系式，建立了粗糙度长度与海拔的经验关系，借助DEM数据实现了Snowpack模型敏感参数的区域化；并通过积雪密度与微波亮温经验关系式，获得了研究区草地积雪密度空间分布。将Snowpack模型输出积雪消融量作为VIP模型输入，通过数据传输实现了两者的耦合，构建了积雪-生态水文模拟系统，有效模拟了草地积雪深度和雪水当量的动态变化和生长季各月蒸散的时空分布。通过耦合模型，基于情景分析的研究表明，积雪消融量减少12%，将使生长季蒸散减少7%，结合遥感蒸散和积雪数据，识别出草地生长季蒸散对积雪期积雪响应的敏感时段为4月份、关键过程为植被蒸腾和积雪消融。项目研究结果增进了对高寒山区积雪和生态水文过程的认识，可供新疆生态文明建设和水资源管理参考。