Space-time heterogeneities of rainfalls on runoff over urban catchments

Simulated outlet flow series are compared downstream of a 14 sq. km. urban watershed. They are generated either with design rainfall, with long-term point rainfall series, or with long-term space distributed rainfall series (measured with 3 raingauges or with radar). The use of the double-triangle shaped hyetograph as design rainfall provides the same T-year flow as the long term 3 raingauge series, if it is used with a areal reduction factor and uniformly applied to the watershed. For the same T-year mean areal precipitation depth during the time of concentration, the rainfall spatial and temporal heterogenities may induce differences up to +/− 30% on the peak flow, compared to the T-year peak flow.