党河上游寒区水文过程的观测与模拟研究

Cryosphere changes have a significant effect on the water safety in Northwest China. To carry out integrated observations on meteorology-hydrology-glacier/snow-frozen soil in a typical cold river basin, will be helpful in studying the interactions of atmosphere-hydrosphere-cryosphere and thus enhance the modeling and prediction capability of the regional surface water resources. This project aims to take the upper Dang River basin at Qilian Mountain (water source region for Dunhuang oasis) as the study region. Based on the newly-built rainfall observational network in 2014 by our group, we will continue strengthening the other observations on meteorology, glacier, snow, frozen soil, and glacier melt. Based on the first-hand observations in the region, we can develop a comprehensive hydrological model for the upper Dang River basin. The study can be summarized as follows. (1) Selecting a typical glacier sub-basin, we will build the meteorological and mass balance observations over glacier, and also monitor the glacial runoff. It will provide valuable data for validating and improving a 1-D glacier surface mass and energy balance module; (2) Selecting another typical mountain plot, the meteorology-snow-frozen soil observations will be carried out. This can facilitate the validation and improvement of the 1-D energy balance based snow and frozen-soil coupled module; (3) The 1-D glacier module as well as the 1-D coupled snow and frozen soil module will be incorporated into a distributed land surface hydrological modelling framework, to build an integrated cryosphere hydrological model for the upper Dang River basin (hereinafter WEB-DHM-DR). With the latest observations by this project, the WEB-DHM-DR model can be well evaluated; (4) Finally, the validated WEB-DHM-DR model will be used to project the future surface water resources changes in the upper Dang River, and explore the factors those contribute to the runoff changes.

冰冻圈变化显著影响我国西北干旱区的用水安全。选择典型寒区流域、开展气象-水文-冰雪-冻土的综合观测与模拟，可深入研究大气圈-水圈-冰冻圈相互作用、提升对地表水资源的模拟和预测能力。本项目拟以祁连山党河上游流域（敦煌绿洲的水源地）为例，在本课题组已安装的雨量观测网基础上，继续强化气象、冰川、积雪、冻土以及冰雪消融径流的观测；进而基于观测资料发展党河山区综合水文模型。研究内容包括：(1)选取冰川子流域，开展冰川气象-物质平衡-径流观测，并在此基础上验证和改进冰川表面物质与能量平衡模块；(2)选取典型区开展气象-积雪-土壤冻融监测，并在此基础上验证和改进基于能量平衡的积雪和冻土耦合模块；(3)在已有的分布式陆面水文模型框架中、集成冰川模块以及积雪和冻土耦合模块，构建党河山区的冰冻圈水文模型，并利用最新观测资料进行模型评估；(4)利用模型预估党河上游未来地表水资源的变化并探讨其影响因子。

气候变化背景下，冰冻圈的变化显著影响我国西北干旱区的用水安全。本研究以典型寒区流域——祁连山党河上游流域为研究区域，开展气象-水文-冰雪-冻土的综合观测与模拟，提升对高寒干旱地区地表水资源的模拟和预测能力。课题组强化气象的综合观测，构建党河上游气象观测网（2个自动气象观测站，11个雨量观测点）。对观测数据的分析发现，党河上游高海拔区域（>2500m）的降雨量具有明显的海拔依赖性。课题组开发并验证了耦合积雪和冻土物理过程的陆面模式（HydroSiB2-SF），新的陆面模式耦合了基于能量平衡的三层积雪方案以及冻土参数化方案，并且以焓作为新的预测变量，提高了计算的稳定性。新的陆面模式更准确地模拟春季消融期土壤温度曲线及土壤水相态的转化；更好地模拟土壤的冻融过程。在此基础上，课题组将积雪-冻土模块集成到分布式陆面水文模型（WEB-DHM）中，开发了能模拟冰雪和冻土的分布式冰冻圈水文模型WEB-DHM-SF。初步验证结果表明，与WEB-DHM相比，WEB-DHM-SF可以有效提高寒区流域径流的模拟精度；提高空间尺度上的陆面温度、雪深分布的模拟精度；提高站点尺度土壤温度、土壤含水量的模拟精度。课题组利用WEB-DHM-SF模型构建了党河上游寒区流域的冰冻圈水文模型，并初步开展了出山口径流的模拟与预测。本研究首次在党河流域建立了气象观测网，获得了重要的、一手的寒区气象观测资料；完成耦合积雪-冻土参数化方案的陆面模式的开发及验证，并集成到WEB-DHM模型中，推动了基于物理过程的冰冻圈水文模型的发展，为气候变化背景下的高寒地区水文水资源研究提供了重要基础。