“…Rating curves are particularly uncertain in unstable river channels that adjust their form due to erosion or sediment deposits, ice build‐up, vegetation growth, and blocked wood debris, or after major floods (Lang, Pobanz, Renard, Renouf, & Sauquet, 2010; Mansanarez, Renard, Coz, Lang, & Darienzo, 2019). These biases and errors have been shown to be particularly pronounced for floods (Steinbakk et al, 2016) and low flows (Sörengård & Di Baldassarre, 2017) because these extreme events occur rarely and are difficult to measure with a high precision. - Data access : Publicly available streamflow datasets are still rare because of data licensing restrictions, strict access policies, or the time required to make these datasets readily usable at the global scale (Coxon et al, 2020). Data access is often also hampered by storage in non‐centralized databases, which are maintained by regional rather than national authorities, and may only be accessible in the local language.
- Lack of spatial information : Observations of discharge and other hydrological variables, such as surface water storage in rivers, lakes, reservoirs, and wetlands, are currently available for selected locations and poorly observed at the global scale (Biancamaria, Lettenmaier, & Pavelsky, 2016).
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