| For optimal protection and integrated management of water resources, it is
essential to quantify the impact of land-use change on hydrological regimes at various
scales. Using the process-based catchment model TACD (tracer aided catchment
model, distributed) two land-use scenarios were analysed for the rural and mountainous
Dreisam basin (258 km2): (i) an increase in urban area from 2.5% to 5%) and
(2) a change in a natural land-use to a different kind of forest. The first scenario was
executed using the land-use change modelling kit LUCK, which takes into account the
topology of land-use patterns in their true positions. The TACD model simulated
all hydrological processes both spatially and temporally (200 m x 200 m grid, hourly mode).
For this study, physically-based modules for interception and evapotranspiration (Penman
and Monteith approach) were introduced. The model was applied to the Dreisam basin with
minimal calibration. Both an independent validation period and discharge in four nested
sub-basins were modelled well without recalibration. Evapotranspiration patterns were
simulated, successfully, both temporally and spatially. Increased urbanisation had an
insignificant effect on the modelled single events and on the yearly water balance.
Simulations of discharge from forest assuming natural land-use conditions indicated an
increase in transpiration, a decrease in groundwater recharge and, consequently, in
groundwater discharge (–15%), in surface water discharge (–4%), and in flood peaks
(–22.7% and –7.3% for convective and advective floods, respectively). Land-use impact
was also investigated by applying rainfall scenarios of different durations (12, 24, 48,
and 72 hours), magnitudes (recurrence intervals of 1, 5, and 10 years) and distributions
of rainfall intensity, i.e. maximum intensity at the beginning, middle or end of the
event. Clearly, the intensity distribution has a greater influence on the simulated
events than different land use scenarios. This indicated the importance of careful
determination of the temporal intensity distribution for flood peak predictions. The use
of the process-based model enabled analysis of the altered composition of internal runoff
components. This demonstrated the potentially significant local effects of land-use change
on flood runoff and water quality.
Keywords: land-use change, predictions, process-based catchment modelling, flood modelling, evapotranspiration
modelling TACD model, LUCK |