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Influence of rainfall spatial variability on flood prediction |
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| Authors: | Patrick Arnaud Christophe Bouvier Leonardo Cisneros Ramon Dominguez |
| Institution: | a ENGEES, 1 Quai Koch, BP 1039F, 67070 Strasbourg, France b IRD, BP 5045, 34032 Montpellier Cedex, France c UNAM, Instituto de Ingenieria, CD. Universitaria, Apdo. Postal 70-472, 04510 Mexico D.F., Mexico |
| Abstract: | This paper deals with the sensitivity of distributed hydrological models to different patterns that account for the spatial distribution of rainfall: spatially averaged rainfall or rainfall field. The rainfall data come from a dense network of recording rain gauges that cover approximately 2000 km2 around Mexico City. The reference rain sample accounts for the 50 most significant events, whose mean duration is about 10 h and maximal point depth 170 mm. Three models were tested using different runoff production models: storm-runoff coefficient, complete or partial interception. These models were then applied to four fictitious homogeneous basins, whose sizes range from 20 to 1500 km2. For each test, the sensitivity of the model is expressed as the relative differences between the empirical distribution of the peak flows (and runoff volumes), calculated according to the two patterns of rainfall input: uniform or non-uniform. Differences in flows range from 10 to 80%, depending on the type of runoff production model used, the size of the basin and the return period of the event. The differences are generally moderate for extreme events. In the local context, this means that uniform design rainfall combining point rainfall distribution and the probabilistic concept of the areal reduction factor could be sufficient to estimate major flood probability. Differences are more significant for more frequent events. This can generate problems in calibrating the hydrological model when spatial rainfall localization is not taken into account: a bias in the estimation of parameters makes their physical interpretation difficult and leads to overestimation of extreme flows. |
| Keywords: | Rainfall variability Distributed hydrological model Rainfall fields Sensitivity Flood estimation Mexico |
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