The influence of spatial radar rainfall resolutions and land-use data on the urban water balance in Rotterdam

Abstract

While rainfall is the key input to most hydrological models, its precise characteristics are often uncertain. Runoff generation does not only depend on the measured rainfall resolution but also on the level of detail of land-use and therefore of the runoff generation. This study aims at identifying the influence of rainfall radar resolution and land-use data on the urban water balance in Rotterdam. Results show that the water balance in this study does not close properly, as more volume enters than leaves the system. This is most probably because infiltration is neglected and the reliability of the pumping data is uncertain. Furthermore, the Combined Sewer Overflow (CSO) volumes are overestimated which might be caused by the high uncertainty of the weir parameters and of the water levels at the non-monitored CSO weirs. This error multiplies with an increase in sewer district size, a higher amount of unmonitored CSOs and lower weir levels. When comparing the different resolutions, the water balance degrades remarkably with coarser land-use data detail and improves slightly with higher rainfall radar resolution, until reaching a certain threshold where the error is minimized. After this threshold the water balance closes less again. Possibly, the reduction in noise and in sensitivity to shifts in timing and location of the radar data with coarsening rainfall radar resolutions is responsible for these unexpected results. Furthermore, this study suggests that there might be a relationship between the changes in land-use resolution and the changes in rainfall radar resolution.