考虑中线调水的海河流域水文-气候双向耦合模拟与评估

Terrestrial hydrological process is an essential but very weak part for current regional climate models, in which the land surface models are lack of accurate estimation for two-dimensional hydrologic processes, particularly for little consideration of impacts of human activities on the hydrological processes. Therefore, the project intends to select the advanced regional climate model (RegCM4.0) and the community land surface model (NCAR_CLM4.5) which can be coupled with RegCM4.0 as the basis of coupled simulation, and choose the Haihe River Basin, the intake area of the Middle Route of the South-to-North Water Transfer Project (MRSNWTP), as the study area. And the project will try to improve the hydrology parameterization of CLM4.5 based on the runoff yield and concentration mechanism of distributed hydrologic models with physical mechanism, meanwhile a new embed module will developed to reflect the combined influence of natural water cycle，living water, ecological water，groundwater exploitation and agricultural irrigation on the Haihe River Basin under the condition of the opening of MRSNWTP, and then results in a new large-scale terrestrial water cycle model（CLM-DTVGM）which is able to be coupled with RegCM4.0, and can describe the natural features of the Haihe River Basin and water diversion effects. Linked with the key scientific issue of ‘The interaction and feedback mechanisms of MRSNWTP-Terrestrial Hydrology-Regional Climate’, the study intends to reveal the response mechanism and temporal-spatial difference rule of precipitation, evaporation, runoff and other factors to MRSNWTP in the next 20-30 years in the Haihe River Basin through scientific assessments of the accuracy and uncertainty of the coupled system, and the project will provide a scientific basis for reasonable assessment of the effect of large water diversion project on Beijing-Tianjin-Hebei regional climate and hydrological cycle.

陆地水文过程是区域气候模式重要不可少、又十分薄弱的环节，现有多数气候模式中的陆面模型较缺乏二维水文过程精细描述，尤其缺乏人类活动对水文过程的影响考虑。基于此，本项目拟选择国际先进的区域气候模式（RegCM4.0）和可与之耦合的陆面模型（CLM4.5）作为基础，以南水北调中线调水和海河流域为对象，利用具物理机制的分布式水文模型产汇流机制改进CLM4.5的水文过程参数化，同时嵌入中线调水对流域自然-社会经济水循环的影响模块，发展一种能描述海河流域自然特征、调水综合影响、且能与RegCM4.0双向耦合的大尺度水循环模型（CLM-DTVGM）。围绕“中线调水-陆地水文-区域气候相互作用与反馈机理”这个关键科学问题，通过科学评估该耦合系统的精度和不确定性，揭示未来20-30年流域主要水文-气候要素对中线调水的响应机理及时空分异规律，为合理评估重大调水工程对京津冀地区水安全及气候的影响提供科学依据。

本项目基于分布式时变增益水文模型DTVGM改进陆面模式CLM3.5中的水文过程，精细化了产汇流过程；考虑南水北调中线调水工程以及人类取用水活动（生活、工业和灌溉用水），研制了能够刻画海河流域主要地理-水文特征和调水影响效应的大尺度分布式水循环模型CLM-DTVGM，最终耦合国际先进的区域气候模式RegCM4.0，构建了一种能够反映海河流域陆面-气候交互作用的区域气候耦合模式（CD-RegCM），可实现在南水北调中线调水以及流域内人类取用水活动背景下，模拟海河流域的气候效应。依据上述模式，项目设置不同的试验方案模拟不同调水量对海河流域气候带来的影响。结果表明，南水北调中线调水输水线附近的地下水位有所抬升，二期工程因输水量较大而使得地下水位抬升高度更高。但由于调水量相比总用水量而言较小，所以总体上，调水工程并没有使海河流域的地下水位达到恢复效果，只是减缓了其下降速度。此外，中线调水轻微加剧了海河流域因人类取用水活动造成的湿冷状况，一期调水工程和二期调水工程的输水方案使得海河流域土壤湿度分别增加0.0008m3/m3和0.001m3/m3，土壤温度分别下降0.04℃和0.05℃，降水量平均增加0.93mm/yr和1.55mm/yr，2m气温平均下降0.02℃和0.03℃。在夏季或初秋，南水北调中线工程导致海河流域降水和土壤水分进一步增加，在春季，中线调水对热通量的影响比其他季节更为显著。但因调水总量相比总用水量较少，故其对局地气候的影响有限，气候要素年际变化趋势并不显著。CD-RegCM模型能够体现人类取用水活动对区域气候造成的影响效应，进一步深入了解人类活动与气候变化之间的相互联系，丰富创新了气候变化研究的学科内容。