Two sub‐annual timescales and coupling modes for terrestrial water and carbon cycles,Global Change Biology

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Two sub‐annual timescales and coupling modes for terrestrial water and carbon cycles
Global Change Biology ( IF 10.8 ) Pub Date : 2024-08-09 , DOI: 10.1111/gcb.17463
Daniel J Short Gianotti ₁ , Kaighin A McColl _{2,

3} , Andrew F Feldman _{4,

5} , Xiangtao Xu ₆ , Dara Entekhabi ₁

Affiliation

To bridge the knowledge gap between (a) our (instantaneous‐to‐seasonal‐scale) process understanding of plants and water and (b) our projections of long‐term coupled feedbacks between the terrestrial water and carbon cycles, we must uncover what the dominant dynamics are linking fluxes of water and carbon. This study uses the simplest empirical dynamical systems models—two‐dimensional linear models—and observation‐based data from satellites, eddy covariance towers, weather stations, and machine‐learning‐derived products to determine the dominant sub‐annual timescales coupling carbon uptake and (normalized) evaporation fluxes. We find two dominant modes across the Contiguous United States: (1) a negative correlation timescale on the order of a few days during which landscapes dry after precipitation and plants increase their carbon uptake through photosynthetic upregulation. (2) A slow, seasonal‐scale positive covariation through which landscape drying leads to decreased growth and carbon uptake. The slow (positively correlated) process dominates the joint distribution of local water and carbon variables, leading to similar behaviors across space, biomes, and climate regions. We propose that vegetation cover/leaf area variables link this behavior across space, leading to strong emergent spatial patterns of water/carbon coupling in the mean. The spatial pattern of local temporal dynamics—positively sloped tangent lines to a convex long‐term mean‐state curve—is surprisingly strong, and can serve as a benchmark for coupled Earth System Models. We show that many such models do not represent this emergent mean‐state pattern, and hypothesize that this may be due to lack of water‐carbon feedbacks at daily scales.

中文翻译：

陆地水和碳循环的两个亚年时间尺度和耦合模式

为了弥合（a）我们对植物和水（瞬时到季节尺度）过程的理解和（b）我们对陆地水和碳循环之间长期耦合反馈的预测之间的知识差距，我们必须揭示什么主要动力学是将水和碳的通量联系起来。本研究使用最简单的经验动力系统模型（二维线性模型）以及来自卫星、涡流协方差塔、气象站和机器学习衍生产品的基于观测的数据来确定与碳吸收和碳吸收相关的主要次年时间尺度。（标准化）蒸发通量。我们发现美国本土有两种主要模式：（1）负相关时间尺度约为几天，在此期间降水后景观干燥，植物通过光合作用上调增加碳吸收。 (2) 缓慢的、季节尺度的正协变，景观干燥导致生长和碳吸收减少。缓慢（正相关）过程主导了当地水和碳变量的联合分布，导致空间、生物群落和气候区域的类似行为。我们提出，植被覆盖/叶子面积变量将这种跨空间行为联系起来，导致平均水/碳耦合的强烈新兴空间模式。局部时间动力学的空间模式（凸形长期平均状态曲线的正倾斜切线）非常强大，可以作为耦合地球系统模型的基准。我们表明，许多此类模型并不代表这种新兴的平均状态模式，并假设这可能是由于缺乏日常尺度的水碳反馈。

更新日期：2024-08-09

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