Assessment of the impact of land use change on the rainfall-runoff relation of the Meuse river

With the objective of assessing the impact of land use change on the rainfall-runoff relation the already calibrated and validated IHMS-HBV-96 hydrological model was applied in the Meuse basin upstream of Borgharen over the period of 1912-2000. The Meuse river basin was schematised into fifteen subbasins. Multiple linear regression models developed between rainfall of sub basins (dependant variables) and rainfall from seven stations (independent variables) generally simulated both the dynamics and the volume of the rainfall time series over the entire study period. Temperature time series for each of the fifteen sub basins were also generated with similar regression equations. Potential evapotranspiration (PET) of the entire Meuse basin was estimated with the model for unsaturated flow and evapotranspiration (MUST).Discharge was simulated with four different PET scenarios as estimated with the MUST model. The different land use scenarios include: (1) the current land use prevails throughout the entire study period, (2) the historical land use change is averaged into three periods, (3) all forest area is converted into coniferous trees and (4) all forest area is converted to deciduous trees.The hydrological year average simulated discharge over the entire study period was compared with the different scenarios. The result revealed that the discharge decreased by 2.7 % and 7.8 % for the conversion of deciduous forest to coniferous forest on respectively 6 % (1260 km2) and 19 % (3990 km2) of the basin. These land use changes exert more influence on the simulated discharge during dry years than during wet years. Significant change in the annual maximum daily discharge (AMAXD) and the annual minimum daily discharge (AMIND) was noted only when the simulated discharge for scenario three (all forest coniferous) and scenario four (all forest deciduous) are compared. The ranges of discharge significantly influenced by this land use change were from 600 m3s-1 to 1875 m3s-1 and from 30 m3s-1 to 60 m3s-1 for AMAXD and AMIND, respectively