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

Abstract

A general problem of hydrological modelling is parameter identi®cation for the driving processes. To examine the longterm dynamics of the water balance of a small (4 . 2 km 2 ) 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 modi®ed TOPMODEL version accounts for the observations that surface runo only takes place in a small portion of the catchment and that water¯ow 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 ®ts are obtained if only 60% of the catchment area is allowed to react dynamically. A substantial improvement of the runo description has been achieved by a moderate increase of model complexity. Results of a Monte Carlo simulation showed that the model structure has a¯at 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 de®cit can be assumed to be the major driver of vegetation±atmosphere water transfer. Soil moisture does not aect 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%.

Groundwater dynamics along a hillslope: A test of the steady state hypothesis

“…The main message here is that there may be a number of dynamic behavior patterns in any catchment, which can be captured by a few key landscape elements. This is in agreement with the idea to delineate differently reacting regions in a catchment based on topographical indices [e.g., Ostendorf and Manderscheid , 1997] or with the hydrogeomorphic concept proposed by Sidle et al [2000], in which different components of a catchment are supposed to exhibit unique hydrologic behaviors. We propose that while the steady state assumption for entire hillslopes or catchments may be inappropriate, this does not rule out the value of applying this assumption to individual zones within a catchment.…”

Evaluating explicit and implicit routing for watershed hydro‐ecological models of forest hydrology at the small catchment scale

“…In general, TOPMODEL assumptions appear to hold in humid catchments with rolling topography. Several studies (Barling et al, 1993;Ostendorf and Manderscheid, 1997;Woods et al, 1997) have found that the assumption of steady state flux is violated during drier periods. In drier periods, areas of the catchment may become disconnected and thus the extent of effective contributing areas becomes more local.…”

Reservoir rainfall–runoff geomorphological model. I: application and parameter analysis

“…In Beven and Kirkby's TOPMODEL (1979), the watershed's topography is the major factor in the generation and control of the runoff, with surface flow occurring only in those parts of the watershed where saturation is reached. From this model's basis, many variations have been described to add or change some of the processes involved (Band et al, 1993;Troch et al, 1994;Ambroise et al, 1996a;Ambroise et al, 1996b;Beven, 1997;Iorgulescu and Musy, 1997;Ostendorf and Manderscheid, 1997;Piñol et al, 1997;Saulnier et al, 1997;Woods et al, 1997;Lane et al, 2004;Niu et al, 2005;Wang et al, 2005Wang et al, , 2006Llorens et al, 2006;Wu et al, 2006;Chen et al, 2007).…”