The value of stream level observations to constrain low-parameter hydrologic models

Abstract:

While conceptual runoff models with a low number of model parameters are useful tools to capture the hydrological catchment functioning, these models usually rely on model calibration, which makes their use in ungauged basins challenging. One approach might be to take at least a few measurements. Recent studies demonstrated that few streamflow measurements, representing data that could be measured with limited efforts in an ungauged basin, might be helpful to constrain runoff models for simulations in ungauged basins. While in these previous studies we assumed that few streamflow measurements were taken, obviously it would also be reasonable to measure stream levels. Several approaches could be used in practice for such stream level observations: water level loggers have become less expensive and easier to install; stream levels will in the near future be increasingly available from satellite remote sensing resulting in evenly space time series; community-based approaches (e.g., crowdhydrology.org), finally, can offer level observations at irregular time intervals. Here we present a study where a runoff model (the HBV model) was calibrated for 600+ gauged basins in the US assuming that only a subset of the data was available. We pretended that only stream level observations at different time intervals, representing the temporal resolution of the different observation approaches mentioned before, were available. The model, which was calibrated based on these data subsets, was then evaluated on the full observed streamflow record. Our results indicate that streamlevel data alone already can provide surprisingly good model simulation results in humid catchments, whereas in arid catchments some form of quantitative information (streamflow observation or regional average value) is needed to obtain good results. These results are encouraging for hydrological observations in data scarce regions as level observations are much easier to obtain than streamflow observations. Based on runoff modeling it might be possible to derive streamflow series from level observations using loggers, satellites or community-based approaches. The approach presented here also allows comparing the value of different types of observations and, thus, to guide the monitoring of (previously) ungauged basins.