A noncalibrated rainfall-runoff model for large, arid catchments

A distributed, field-based rainfall-runoff model was developed for the 1400 -km(2) arid catchment of Nahal Zin, Israel. No calibration with measured fl ow data was performed. The model used rainfall radar input applied over a c atchment that was spatially disaggregated into different terrain types acco rding to hydrologically relevant surface characteristics. Hortonian overlan d flow generation on each type was parameterized independently using values of initial loss and temporal decay of infiltration determined from existin g field experiments. Delimited by topography, this catchment wide pattern o f rainfall excess was distributed over 850 tributary catchments (model elem ents). Runoff delivery from the model elements to the adjoining channel seg ments was timed by applying a mean response function determined in an envir onmentally similar experimental catchment. Inside the channel network the M VPMC3 method of the Muskingum-Cunge technique was used for streamflow routi ng, accounting for channel dimensions and roughness. For each channel segme nt a constant infiltration rate was applied to account for transmission los ses and discontinued when the wetting front reached the bottom of the avail able alluvial storage. Within two model tests, one separate for the routing component (October 1979) and one for the complete model (October 1991), ob served hydrographs and reconstructed peak discharges were successfully simu lated. The spatially distributed model output showed that during the Octobe r 1991 test, tributaries produced preceding peaks that wetted the channel a lluvium before the main flood had arrived and transmission losses lost thei r significance downstream. Total maximum model uncertainty was estimated in cluding the uncertainty ranges of each model parameter. In general, this st udy shows that field-based data on generation and losses of runoff may be i ncorporated into a distributed hydrologic model to overcome calibration wit h the poor data records of arid high-magnitude events.