This paper examines catchments that are almost ungauged, i.e., catchments for which only a small number of point flow measurements are available. In these catchments, hydrologists may still need to simulate continuous streamflow time series using a rainfall‐runoff model, and the methodology presented here allows using few point measurements for model parameterization. The method combines regional information (parameter sets of neighboring gauged stations) and local information (contributed by the point measurements) within a framework where the relative weight of each source of information is made dependent on the number of point measurements available. This approach is tested with two different hydrological models on a set of 609 catchments in France. The results show that on average a few flow measurements can significantly improve the simulation efficiency, and that 10 measurements can reduce the performance gap between the gauged and ungauged situations by more than 50%. The added value of regional information progressively decreases until being almost insignificant when sufficient flow measurements are available. Model parameters tend to come closer to the values obtained by calibration in fully gauged conditions as the number of point flow measurements increases.

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[1] The Turc-Mezentsev water balance formula is a simple and efficient mathematical formulation relating long-term average streamflow to long-term average precipitation and potential evaporation. Usually, it is applied in its original form, i.e., without parameterization. This paper aims to assess the possibilities of regionalizing this formula for improved efficiency on ungaged catchments. Four regionalization options are compared based on: (i) the relative error, (ii) the arithmetic difference, (iii) the correcting factor of the aridity index, and (iv) the shape factor. The four alternatives are assessed in terms of efficiency and robustness on a large set of 609 French catchments. We show that introducing a correcting factor of the aridity index provides the best regionalization solution.Citation: Lebecherel, L., V. Andreassian, and C. Perrin (2013), On regionalizing the Turc-Mezentsev water balance formula, Water Resour. Res., 49,[7508][7509][7510][7511][7512][7513][7514][7515][7516][7517]

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