Intrinsic spatial scales of river stores and fluxes and their relative contributions to the global water cycle

The Earth’s rivers vary in size across several orders of magnitude. Yet, the relative significance of small upstream reaches compared to large downstream rivers in the global water cycle remains unclear, challenging the determination of adequate spatial resolution for observations. Here, we use monthly simulations of river stores and fluxes to investigate the intrinsic spatial scales of the global river water cycle. We frame these scale-dependent river dynamics in terms of observational capabilities, assessing how the size of rivers that can be resolved influences our ability to capture key global hydrologic stores and fluxes. By filtering reaches by estimated river widths, we quantify the relative contribution of global river reaches by size and estimate that over 17% of global discharge to ocean and nearly 9% of the world’s river storage lies within rivers smaller than 100 m – hence revealing both strengths and limitations of current observational capabilities.

全球河流的规模差异可达数个数量级。然而，在全球水循环中，小型上游河段相较于大型下游河道的相对重要性仍未明确，这为确定观测所需的合理空间分辨率带来了挑战。本研究借助河流蓄量与通量的逐月模拟数据，探究全球河流水循环的固有空间尺度。我们从观测能力的视角构建尺度依赖的河流动力学分析框架，评估可分辨河道的规模如何影响我们捕捉关键全球水文蓄量与通量的能力。通过按估算河道宽度对河段进行筛选，本研究按规模量化了全球各河段的相对贡献，并估算得出：全球入海总径流量的17%以上、全球河道总蓄水量的近9%，均来自宽度不足100米的河道——这一结果既揭示了当前观测能力的优势，也点明了其局限性。