Seasonal modelling of catchment water balance: A two‐levle cascading modification of TOPMODEL to increase the realism of spatio‐temporal processes

摘要

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 km) forested catchment in south-east Germany (Lehstenbach), TOPMODEL has been adapted as a two-level cascading approach. Only the lower cascade is allowed to respond dynamically. This modified TOPMODEL version accounts for the observations that surface runoff only takes place in a small portion of the catchment and that water flow in large portions of the catchment occurs through groundwater aquifers with a lateral recharge to the downslope regions. Water from an upper catchment region is transferred to a lower storage. The border between the two areas is represented as a topographic index (ATB) threshold that can be varied in the model. 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 achieved by a moderate increase of model complexity. Results of a Monte Carlo simulation showed that the model structure has a flat global optimal solution.In order to quantify the boundary conditions, we combined direct estimates of tree and understorey transpiration, maps of tree age and understorey 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 pressure deficit can be assumed to be the major driver of vegetation–atmosphere water transfer. Soil moisture does not affect tree transpiration in this catchment. The results show that transpiration measurements can be scaled to the catchment scale in spite of variations between sites of up to 100%. © 1997 John Wiley & Sons, Ltd.