2 graphs from the article.
Performance of the standard way of upscaling stream directions (D8) and the new scheme (SCC) as measured from 187 stream gauges in the Rhine basin. The left figure shows the frequency distributions of the Kling Gupta Efficiency (KGE). The KGE is a measure of how well observed streamflow is simulated: a KGE of 1 is perfect and of -0.41 (the vertical dashed line) is the baseline if the mean of the observations is taken. The left figure shows that the traditional D8 algorithm only performs as well as the SCC at very high resolutions, which would be computationally prohibitive. The SCC performs well at all resolutions so that accurate results can be achieved at limited computational cost. The right figure shows the difference between SCC and D8, confirming that SCC outperforms SCC for all but the finest resolutions. Credit: Shrestha et al. [2025], Figure 10 (a, b)
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Water Resources Research

One of the challenges in global hydrology is to simulate water resources globally at a resolution that is fine enough to be of local relevance. However, these hyper-resolution (less than 1 kilometer) simulations are limited by the very high computational demand of routing water through the global river system.

Shrestha et al. [2025] devise a very clever upscaling algorithm for stream directions that allows simulating streamflow at low-resolution, while still being able to locally refine ate points of interest, such as locations where streamflow is measured. This computational breakthrough opens the door to very detailed global hydrological simulations, not only for global hydrology, but for Earth system science at large.

Citation: Shrestha, P. K., Samaniego, L., Rakovec, O., Kumar, R., & Thober, S. (2025). A novel stream network upscaling scheme for accurate local streamflow simulations in gridded global hydrological models. Water Resources Research, 61, e2024WR038183.  https://doi.org/10.1029/2024WR038183  

—Marc F. P. Bierkens, Editor, Water Resources Research

Text © 2025. The authors. CC BY-NC-ND 3.0
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