There are two outputs from TasLUCAS which are:

• Mean annual stream flow
• Flow duration curves

The key focus of the TasLUCaS model is to allow the assessment of long term changes in stream flow due to changes in forest cover. Thus, the model only simulates the changes over time for a mean annual rainfall and does not account for the variability due to climate. In reality the stream flow response in the catchment will be highly dependent on the climatic variability. TasLUCaS also does not take into account other potential influences on stream flow such as climate change, irrigated agriculture or farm dams. When using TASLUCaS the modeller needs to take into consideration that:

This tool is only appropriate for changes in forest cover and is not appropriate for other land use changes.

The tool is not appropriate in catchments with significant irrigation or regulation. Particular limitations of mean annual stream flow component and FDC component are described below. The mean annual stream flow component has been specifically designed to model three types of forest cover change. These are the conversion of native forest to plantation, the conversion from grass/agriculture to plantation and the harvesting of native forest. The amounts of data used to develop these models are limited with the grass to plantation model being based on 7 catchments ranging in size from 27ha to 310 ha and the forest to forest model being based on 8 catchments ranging in size from 4 ha to 261ha. When using the mean annual stream flow component of the TasLUCaS tool the user needs to take into account the following limitations:

1. The model does not consider all forms of land use change. Specifically, it does not consider the expansion of urban areas, or subtle changes such as the thickening or thinning of woodlands.
2. For ungauged catchments the model uses an estimate of the current mean annual flow based on the relationships of Zhang et al., (2001). These estimates are far less reliable than estimates based on local measurements. In this instance users should place more confidence in the predictions of the change of mean annual flow than in the absolute value of the predictions of mean annual flow.
3. The predictions of this model are based upon a careful analysis of paired catchment studies from around the world that are relevant to the intended applications. The limited evaluation of the model in Tasmania suggests the model does perform well in that environment. However further local evaluation is warranted. Ideally, a local paired catchment study and associated analysis would be used to improve the confidence in local predictions.

The FDC Component of the tool has been specifically designed to investigate the impacts of changes in forest cover on flow duration curves. The amount of data used to validate this model was quite limited. The major data sets used to assess the methodology were from Australia and South Africa, for catchments ranging in size from 18 to 320 ha. Consequently the methodology has only been validated for a small range of climatic conditions for predominantly small catchments. When using The FDC component of the tool the modeller needs to take into consideration that:

This component uses several optimisers to find the optimum solution for fitting flow duration curves and estimating a single bucket rainfall runoff model. Under certain circumstances this may not reach a suitable solution, in such cases the model will give an error message. This tool is not appropriate for these catchments.

A results screen is provided so that modellers can assess and adjust the fit of the model. If the fit is too poor then this component of TasLUCaS should not be used. The change in flow due to forest cover is small compared to other factors such as climate variability. Consequently only major changes in forest cover will results in significant changes in flow.