Temporal and spatial variability of rainfall at the urban hydrological scale

The main objective of this paper is to characterize the spatial and temporal variability of different types of rain events at scales that are consistent with urban hydrological applications. In this way, a total of 24 rain periods have been analyzed according to a geostatistical approach. This analysis has focused on the non-zero rainfall variogram. The studied rain periods were recorded by the weather radar of Treillières (10 km north of Nantes, France) in 2009. This radar device provides rainfall radar images with a high level of spatial resolution (250 m × 250 m) and instantaneous temporal resolution. Results indicated four different types of rainfall fields, which display very different variability scales, including double structures within the same field. These four types of rainfall fields can be characterized by their climatological variograms, as calculated for increasing time resolutions: instantaneous, 5 min, 15 min, and 30 min, thus making it possible to estimate the decorrelation distance (i.e. range). This study highlights the benefit of radar images featuring high temporal and spatial resolution, which in turn allow studying small-scale variability.