北方农牧交错区生态退耕的气温调节效应及其机理研究

Abstract: Ecological de-farming has a profound influence on ecosystem service of the farming-pastoral ecotone, especially in modulating the land-atmosphere exchange of energy and water vapor. However, air temperature regulation effect of ecological de-farming and its mechanism are still uncertain in sign and magnitude due to the influences of factor complexity and regional differentiation. Therefore, the farming-pastoral ecotone of northern China (FPEN) is selected as the study area in view of its ecological de-farming characteristics. Based on previous studies, satellite remote sensing, flux site observation and field sampling data, the project tries to: (1) optimize the radiative and energy transfer scheme of CEVSA model by improving and correcting model algorithms and parameters, with special focus on forest, cropland and grassland ecosystems; (2) carry out the scenario simulations based on optimized model with the aid of different historical land cover data; (3) evaluate quantitatively air temperature regulation effect caused by the impact of ecological de-farming on surface net radiation and evapotranspiration, and clarify its mechanism. The innovations of this proposed project focus on two major points—theoretically and experimentally. In theory, we suggest to employ a better index for quantitative evaluation of air temperature regulation effect caused by ecological de-farming. Experimentally, we use higher precision land cover data to drive the model, and optimize and improve its algorithms and parameterization in water and energy budgets. This project will be helpful for layout optimization of the ecological restoration and regional sustainable development.

农牧交错区生态退耕对区域生态系统服务产生了深刻影响，但受驱动机制复杂性及区域分异性的影响，目前农牧交错区生态退耕的气温调节效应及其机理仍未被有效认知。因此，本项目拟以中国北方农牧交错区生态退耕为研究对象，基于文献、遥感、通量观测、地面调查等多源资料开展以下内容的研究：（1）改进和优化CEVSA模型在辐射能量平衡模拟过程中的关键算法和参数，重点优化森林、农田和草地生态系统，提高模型模拟表现；（2）借助历史时期土地覆盖数据驱动优化后的模型开展情景模拟；（3）结合土地利用变化影响地表净辐射和蒸散发两个方面，开展研究区生态退耕气温调节效应定量评估及其变化机理研究。本项目在定量评估生态退耕气温调节效应的新指标、将高精确度土地覆盖数据集嵌入模型并改进模型在水热能量模拟的算法和参数方面的研究成果，有助于深入认识区域土地利用变化的气温调节机理，同时也可为该区生态恢复工程布局优化提供科学依据。

本项目以样地调查数据、地面观测数据和卫星观测数据为数据源，通过站点观测-遥感反演-模型模拟-时空分析等多源研究手段，探讨了北方农牧交错区生态退耕的气温调节效应及其机理。取得了以下四个方面的主要进展：①基于通量观测和遥感数据的模型优化与改进。在前人研究的基础上，通过耦合碳水过程优化植被蒸散发模拟提高模型在辐射和能量平衡方面模拟表现，这一研究结果为优化生态过程模型中水热能量平衡关键过程提供了理论参考。②发展了农田春季物候反演算法，提高模型对农田物候模拟的表现。植被物候的变化是植被适应气候变化的重要过程，同时也通过改变地表植被覆盖状况改变着地表能量平衡。研究结果为更好的理解长时间序列区域物候变化以及改进区域模型中物候反演算法提供了理论参考。③发展了像元尺度TPR模型，厘定北方农牧交错带人类活动对土地覆盖变化的贡献。研究成果建议人类生态工程和相关保护措施应当考虑不同地区的生态气候特点，因地施策最大程度的发挥生态工程的作用。④分别从站点和区域两个尺度解析土地利用变化生物物理效应。在典型水分限制区的模拟试验表明，退耕还草措施对潜热和净辐射分量变化的影响机制存在差异。研究成果对于理解水分限制区退耕还草措施的气温调节效应有一定的帮助。研究结果有望为北方农牧交错区生态治理及生态工程布局优化提供科学支撑。