|Ostendorf, B; Manderscheid, B: Seasonal modelling of catchment water balance: a two-level cascading modification of topmodel to increase the realism of spatio-temporal processes, Hydrological Processes, 11, 1231-1242 (1997)|
A general problem of hydrological modelling is parameter identification for the driving processes. To examine the long term dynamics of the water balance of a small (4.2 km2) forested catchment, TOPMODEL has been adapted as a 2-level cascading approach. Only the lower cascade is allowed to respond dynamically. This modified TOPMODEL version accounts for the observations that near surface lateral flow only occurs in a small portion of the catchment and that water flow in large portions of the catchment occurs through ground water aquifers with a lateral recharge to the lower part regions. Water from an upper catchment region is transferred to a lower storage. Results of a Monte Carlo simulation showed that the model structure has a flat global optimal solution. For a large area of the catchment, water storage may not immediately affect runoff dynamics but rather provides a constant contribution to the discharge. The results show that the best fits are obtained if only 60% of the catchment area is allowed to react dynamically. A substantial improvement of the runoff description has been archived by a moderate increase of model complexity. Whereas several possibilities for a good representation the discharge pattern exist, a Monte Carlo simulation showed that the model structure does have a global optimal solution. In order to quantify the bondery conditions, we combined direct estimates of tree and understory transpiration, maps of tree age and understory cover to estimate empirically the total catchment evapotranspiration. The context of a dynamic hydrological model allows an evaluation of ecological data in the context of catchment scale dynamics. Vapour ressure deficit can be assumed to be the major driver of the vegetation-atosphere water transfer. Soil moisture does not affect tree transpiration in the catchment. The results show that the transpiration measurements can be scaled to the catchment scale in spite of variations between sites of up to 100%.