Hydrology starts with your gaze

Modelling a river without gauging stations: how citizen science and a bit of creativity are reshaping hydrology

One of the main challenges of contemporary hydrology is that most rivers worldwide lack discharge gauging stations that continuously record water flow. Many hydrologists acknowledge that continuous discharge data are extremely limited outside well-developed monitoring networks. This limitation has historically motivated global initiatives such as the Decade on Prediction in Ungauged Basins (PUB) launched by the International Association of Hydrological Sciences (IAHS), precisely because a significant portion of the world’s river basins lacks the continuous measurements required to apply traditional hydrological prediction techniques.

Without discharge data, however, anticipating floods, understanding droughts, or assessing climate-driven changes becomes a major challenge.

A recent study, Value of water level class observations for parameter set selection in hydrological modelling (Clerc-Schwarzenbach et al., 2025), offers a powerful alternative: combining simple citizen observations with approximate hydrological estimates to calibrate models in data-poor basins.

And it doesn’t just work — it works surprisingly well.

When there are no data… but there are people

The study analyses so-called water level class observations (WLC): simple records in which volunteers note how water levels rise or fall using a visual scale. They do not provide exact discharge values, but they capture what matters most: dynamics — the rhythm with which a river “breathes” over time.

The authors explain it clearly:

“The dynamic information provided by water level classes allows to select parameter sets that better reproduce the temporal pattern of streamflow.”

In other words, even without full gauging stations, citizen observations help models understand how a river behaves. The study also highlights that consistency matters:

“One diligent citizen scientist provided useful information, while data from many contributors were uninformative.”

The value of the approximate: when a water balance replaces a gauging station

One of the most striking findings of the study is that a formal gauging station is not strictly necessary to obtain useful information. Using an approximate water balance — a simple calculation of how much water enters the system (precipitation) and how much leaves it (evaporation) — it is possible to estimate mean annual discharge with a reasonable margin of error.

And even with high uncertainty, this estimate significantly improves model performance.

“Providing a range would lead to improvement while not providing a value that was too restrictive.”

In other words, even a broad range of annual discharge stabilizes models better than a single “precise” value. This has major implications for basins without permanent monitoring infrastructure.

A few direct measurements can change everything

Even without official stations, a basin can obtain real discharge values using methods accessible to volunteer teams. These spot measurements are essential to transform water levels into discharge estimates and to refine models.

Some effective techniques include:

Direct float measurements: timing floating objects over a known river reach to estimate surface velocity. Approximate, but useful.

Salt dilution measurements: a known quantity of salt is added and changes in conductivity are recorded downstream. This allows discharge estimation without entering the river.

Georeferencing every measurement: recording precise locations, photos, and contextual information enables comparison over time and the construction of preliminary rating curves.

Citizen science + incomplete data = democratic hydrology

The core idea of the study can be summarized as follows:

“A wide range of mean annual discharge estimates would improve model performance… more informative than providing an accurate single value.”

This is an invitation to democratize data production. A dense network of gauging stations is no longer the only path to useful hydrological knowledge. Instead, robust results can emerge from combining multiple imperfect sources:

• HOBO sensors,

• committed citizen observers,

• a few direct discharge measurements,

• an approximate water balance,

• and support from remote sensing data.

  
  

Together, these elements generate meaningful hydrological knowledge even in historically overlooked basins.

Climate justice: why collecting data is also an act of equity

Regions with fewer gauging stations are often the same regions most affected by the climate crisis: flash floods, severe droughts, glacier changes, and extreme storms. Without data, communities have less capacity to argue, plan, negotiate, or access funding.

Collecting data — even simple, approximate data — is a way to reduce that inequality.

It allows communities to:

• better understand their rivers,

• document the impacts they experience,

• negotiate with evidence,

• and actively participate in water-related decision-making.

  
  

In this sense, citizen science and participatory monitoring help fill the gap left by the historical absence of official gauging stations. They are tools for empowerment, adaptation, and climate justice. This is not only about science — it is about equity between mountain regions facing emerging climatic trends.

Join the HIDROCLIM network to collectively generate river data in El Chaltén!

Source:Clerc-Schwarzenbach, F., Seibert, J., Vis, M. J. P., & van Meerveld, H. J. (2025). Value of water level class observations for parameter set selection in hydrological modelling. Hydrological Sciences Journal, 70(9), 1464–1480. https://doi.org/10.1080/02626667.2025.2489994