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Abstract: This paper outlines the construction of a hydrological modelling network used to underpin integrated assessment exercises such as the one reported here on water allocation in the Namoi River Basin, Australia. Details of the models and their accuracy are given. Integrated assessment tasks place special requirements on hydrological models. In order to represent the spatial and temporal scales at which policy operates, a nodal network approach was used for the integration, with flows being simulated daily at aggregated nodes of water extraction. The IHACRES rainfall-runoff model was calibrated and applied to many of the subcatchments represented by these nodes. Its parametric efficiency facilitated a regionalization procedure to simulate flow at an ungauged node. Post-extraction streamflow was routed from upstream to downstream nodes using a variable parameter lag-route method, allowing the impact of extraction decisions made by upstream users to be simulated on downstream users and the environment. [Copyright &y& Elsevier]

Abstract: This paper investigates the model sensitivities to input parameter values in a Biophysical Toolbox for integrated catchment assessment and management of land and water resources. The toolbox was developed for application in the highland regions of northern Thailand. It incorporates the IHACRES rainfall-runoff model, a crop model (CATCHCROP), and an erosion model (a Universal Soil Loss Equation [USLE], modified for application to northern Thailand). In developing the individual models in the Biophysical Toolbox, emphasis was placed on limiting model complexity. The toolbox was developed and tested using data from the Mae Chaem catchment in northern Thailand. Due to the short duration and sparse distribution of the available data, the complexity of the model structure is constrained to consider only the key processes of interest. Despite the relative simplicity of the individual models, linkages between the models encompassed in the Biophysical Toolbox increase the complexity of the modelling system. This paper explores sensitivities in the Biophysical Toolbox to the parameters of CATCHCROP as this component has the greatest potential for propagating errors though the Toolbox. A simple sensitivity analysis was undertaken, whereby parameter values were perturbed to ascertain the effect of these perturbations on output indicators. The hydrologic component showed strong non-linearity to the infiltration parameters of the CATCHCROP model, although this did not greatly impact estimates of total annual discharge. Additionally, a number of CATCHCROP parameters did not greatly impact some output indicators of the toolbox. While the CATCHCROP model is relatively parsimonious when compared with many crop models, there are still 19 model parameters that must be determined from the field or prescribed from the literature. There is potential for the model to be further simplified although more extensive model testing is required to ensure that such simplifications would not adversely impact on the utility of the toolbox. [Copyright &y& Elsevier]

The potential impacts of deforestation on hydrological response are of significant importance in highland regions of northern Thailand and other parts of southern Asia. In these regions, where climate exhibits strong seasonality, the availability of water in the dry season determines the feasibility of multiple crop rotations. Based on the IHACRES rainfall-runoff model, a simple scaling procedure and landcover data, this paper presents a simple hydrologic approach to predict hydrologic response to land use changes, and to predict streamflow in ungauged catchments. The latter is a major hurdle in water resource analyses in regions like northern Thailand where there is a lack of stream gauge instrumentation, or where assessment of water availability is required at locations between gauging sites as input to agricultural production models. A simple regionalisation of streamflow response was tested for three gauged subcatchments of the Mae Chaem catchment in northern Thailand. Overall performance was superior when calibrated parameters from the largest catchment were used to infer parameters for the regionalisation. Most importantly, the procedure was able to predict the relative pattern of annual and seasonal flows, whatever the reference catchment on which the regionalisation was based. Investigations of the impacts of forest cover changes on modelled hydrological response are presented and the key model parameters to which model outputs are most sensitive are discussed. [Copyright &y& Elsevier]