Epsilon Archive for Student Projects

Abstract

Global population growth and increasing wealth exerts pressure to convert forest into
agricultural land. The forest area in the Red River Basin in Vietnam has decreased
and is now less than 20 %. The consequences of land use conversions include changes
in water demand, in water supply, and in water quality. Using models to predict
effects of land use change is common in research since these tools are quick, cheap,
powerful and are useful complements to field measurements. The objectives of this
study were first to calibrate the watershed model GenRiver, developed by the World
Agroforestry Centre South East Asia, for the Dong Cao catchment situated in North
Vietnam, and secondly to predict the effects of agroforestry land use taking into
account the parameter "uncertainty" in the predictions of GenRiver. Six parameters in
GenRiver were analysed using GLUE (Generalized Likelihood Uncertainty
Estimation). The predicted simulations of agroforestry and secondary forest were then
compared in terms of changes in river discharge from the catchment. The GLUE
method resulted in clear identification for only two of the analysed parameters. The
highest likelihood value of the GLUE simulations was low (0.26) since GenRiver
generated too low discharge peaks, especially during the rainy season. The model
generated too little rapid drainage in the soil macropores at the expense of an
overestimation of evaporation. This was due to the order of water redistribution
assumed in the model (the priority is given first to evaporation, then drainage to the
groundwater reserve and lastly to percolation by macropore flow). The conclusion is
that GenRiver does not seem to be a suitable tool for Dong Cao conditions unless a
structural change concerning water redistribution is made in the model. This should
make the predictions less uncertain.