B. Ostendorf et B. Manderscheid, SEASONAL MODELING OF CATCHMENT WATER-BALANCE - A 2-LEVEL CASCADING MODIFICATION OF TOPMODEL TO INCREASE THE REALISM OF SPATIOTEMPORAL PROCESSES, Hydrological processes, 11(9), 1997, pp. 1231-1242
A general problem of hydrological modelling is parameter identificatio
n for the driving processes. To examine the longterm dynamics of the w
ater balance of a small (4.2 km(2)) forested catchment in south-east G
ermany (Lehstenbach), TOPMODEL has been adapted as a two-level cascadi
ng approach. Only the lower cascade is allowed to respond dynamically.
This modified TOPMODEL version accounts for the observations that sur
face runoff only takes place in a small portion of the catchment and t
hat water flow in large portions of the catchment occurs through groun
dwater aquifers with a lateral recharge to the downslope regions, Wate
r from an upper catchment region is transferred to a lower storage. Th
e border between the two areas is represented as a topographic index (
ATB) threshold that can be varied in the model. The best fits are obta
ined if only 60% of the catchment area is allowed to react dynamically
. A substantial improvement of the runoff description has been achieve
d 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 di
rect estimates of tree and understorey transpiration, maps of tree age
and understorey cover to estimate empirically the total catchment eva
potranspiration. The context of a dynamic hydrological model allows an
evaluation of ecological data in the context of catchment scale dynam
ics. Vapour pressure deficit can be assumed to be the major driver of
vegetation-atmosphere water transfer. Soil moisture does not affect tr
ee transpiration in this catchment. The results show that transpiratio
n measurements can be scaled to the catchment scale in spite of variat
ions between sites of up to 100%. (C) 1997 by John Wiley & Sons, Ltd.