东北寒区流域水-碳循环耦合模拟研究

Carbon and the water cycle of terrestrial ecosystem are the core of material and energy cycle at the land surface. They are closely linked to the land surface, have interactions and feedback all the time, and are closely related to climate. Water-carbon coupling mechanism is the core and hot topic of global change research. Considering the impact of the carbon cycle is also the development trend of the hydrological model, it has important research value. Cold region where frozen soil is distributed is important carbon sink due to the low temperatures, its mechanisms of water and carbon cycle have unique characteristics, and cold regions are sensitive and vulnerable to climate change. So the research on water-carbon coupling mechanism in cold regions deserves more attention. Evolution rule of water and carbon flux in cold region is studied by monitoring data and the field experiment. Then, based on the water-carbon interaction mechanisms, distributed hydrological model and biogeochemical model are "two-way" coupled. For the characteristics of cold regions, the watershed scale water-carbon coupling model of cold region is established and it could simulate the frozen soil process, water and carbon cycle, energy budget, vegetation growth, human activities and their interactions. Based on the model, the watershed spatial and temporal pattern of water and carbon flux and their response to climate change is studied in the Northeast Cold Regions. The project will provide a useful reference and modeling tools for the research on watershed scale water-carbon cycle in cold regions.

陆地生态系统碳循环和水循环是陆地表层系统物质能量循环的核心，在陆地表面有着紧密联系，时刻发生着相互作用与反馈，并与气候密切相关。水碳耦合机制是目前全球变化科学研究的热点与核心问题，考虑碳循环等生态过程的影响也是新一代流域水文模型的发展趋势，具有重要研究价值。而寒区因气温低，存在冻土，是重要碳汇，其水、碳循环机制有独特的特点，并对气候变化敏感脆弱。因此寒区水、碳循环规律更值得关注。本项目通过资料收集、数据监测与野外试验，研究寒区水碳通量演变规律。然后基于水碳相互作用机制，将分布式水文模型与生物地球化学模型进行"双向"耦合，针对寒区特点研制能够对冻土水热过程、水循环、碳循环、能量收支、植被生长、人类活动及其相互作用进行综合模拟的寒区流域水-碳循环耦合模型。基于所构建的模型研究东北寒区流域水、碳通量的时空分布规律及对气候变化的响应。项目研究能够为寒区流域水碳循环研究提供有益参考与模型工具。

陆地生态系统碳循环和水循环是陆地表层系统物质能量循环的核心，是地圈-生物圈-大气圈相互作用的纽带。碳循环是推动全球生物地球化学循环的主要动力，水循环深刻影响着碳的生物地球化学循环，其耦合机制是目前全球变化科学研究的热点与核心问题，受到越来越多的关注。本项目取得的主要成果和结论如下：（1）基于水、碳循环的相互作用机制，通过分布式水文模型与生物地球化学模型的“双向”耦合，研制流域水-碳循环耦合模型，同时进行了多种模型耦合的尝试与探索，主要包括VIC+CASACNP、DTVGM+CASACNP、WEP+BIOME -BGC；（2）基于CO2同化模拟与碳分配的过程机制模块，改进了植被物候及LAI模块，基于原有冻土模型从数值方法、壤中流计算等方面改进土壤水分运动模块，使模型更适合于寒区水、碳循环模拟；（3）以CERN的长白山站点、Ameriflux的Duke站点、Mead站点、第二松花江流域、滦河流域为研究对象，利用站点监测数据、NPP资料数据、LAI遥感数据、水文站径流数据等多源数据对耦合模型在点和流域尺度进行了综合验证，还分析了CO2通量的日内变化规律、NPP的年际变化规律、不同植被类型NPP随高程或降水的变化规律，以及水碳循环的相互作用关系；（4）研究了气候变化对水、热与碳循环对的影响，在考虑氮循环对碳循环的约束作用下，以林地植被类型为研究对象，定量分析了CO2浓度升高对GPP、土壤含水量、土壤温度等影响的程度，发现在双倍CO2情景下，GPP增加了9.3%，ET减小了18.2%，土壤湿度在干旱阶段的增加最为明显，而在冬季基本保持不变。上层土壤日内温度的增量要高于深层温度的增量。同时土壤温度增量频率都呈双峰状，其中0.23°为整个剖面频率最高的土壤温度增量。预测未来不同气候情景、CO2排放情景以及土地利用/植被覆盖变化情景下滦河流域径流的响应，通过数值试验发现气候变化及LUCC对径流产生的影响较CO2浓度升高作用强。