Calibration of GenRiver with GLUE for Northern Vietnamese conditions :

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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 n...