The Western United States is dominated by natural lands that play a critical role for carbon balance, water quality, and timber reserves. This region is also particularly vulnerable to forest mortality from drought, insect attack, and wildfires, thus requiring constant monitoring to assess ecosystem health. Carbon monitoring techniques are challenged by the complex mountainous terrain, thus there is an opportunity for data assimilation systems that combine land surface models and satellite-derived observations to provide improved carbon monitoring. Here, we use the Data Assimilation Research Testbed to adjust the Community Land Model (CLM5.0) with remotely sensed observations of leaf area and above-ground biomass. The adjusted simulation significantly reduced the above-ground biomass and leaf area, leading to a reduction in both photosynthesis and respiration fluxes. The reduction in the carbon fluxes mostly offset, thus both the adjusted and free simulation projected a weak carbon sink to the land. This result differed from a separate observation-constrained model (FLUXCOM) that projected strong carbon uptake to the land. Simulation diagnostics suggested water limitation had an important influence upon the magnitude and spatial pattern of carbon uptake through photosynthesis. We recommend that additional observations important for water cycling (e.g., snow water equivalent, land surface temperature) be included to improve the veracity of the spatial pattern in carbon uptake. Furthermore, the assimilation system should be enhanced to maximize the number of the simulated state variables that are adjusted, especially those related to the recommended observed quantities including water cycling and soil carbon.

中文翻译：

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使用数据同化系统改善美国西部的 CLM5.0 生物质和碳交换

美国西部以自然土地为主，这些土地对碳平衡、水质和木材储备起着至关重要的作用。该地区还特别容易受到干旱、昆虫袭击和野火造成的森林死亡的影响，因此需要持续监测以评估生态系统健康状况。碳监测技术受到复杂山区地形的挑战，因此有机会将地表模型和卫星观测相结合的数据同化系统提供更好的碳监测。在这里，我们使用数据同化研究试验台通过对叶面积和地上生物量的遥感观测来调整社区土地模型 (CLM5.0)。调整后的模拟显着降低了地上生物量和叶面积，导致光合作用和呼吸通量的减少。碳通量的减少大部分抵消了，因此调整和自由模拟都预测了对土地的弱碳汇。这一结果不同于一个单独的观察约束模型 (FLUXCOM)，该模型预测了陆地的碳吸收量很大。模拟诊断表明水分限制对通过光合作用吸收碳的量级和空间格局有重要影响。我们建议包括对水循环重要的额外观测（例如雪水当量、地表温度），以提高碳吸收空间格局的准确性。此外，应增强同化系统，以最大化调整后的模拟状态变量的数量，