The CLASS Modelling Framework: A platform for distributed eco-hydrological modelling

This paper describes development and testing of the components of a distributed eco-hydrological modelling framework CLASS (Catchment Scale Multiple-Landuse Atmosphere Soil Water and Solute Transport Model). The CLASS modelling framework, its components and their algorithms are described in a detailed technical report (Tuteja et al., 2004; available for download from Catchment Modelling Toolkit website http://www.toolkit.net.au/class). CLASS can be used to predict land-use effects at paddock, hillslope and catchment scales. Effects of climate scenarios predicted by stochastic climate models as well as the effects of spatio-temporal climate variations within a catchment can also be analysed. CLASS can be used for water balance, solute balance, vegetation growth and terrain modelling. Recharge-discharge dynamics, lateral flow and streamflow can also be modelled using CLASS. CLASS uses "bottom-up" modelling approach and offers an alternative to the commonly used simple "top down" modelling approaches. Distinctive features of CLASS include grid cell based analysis and the ability to allow for interactions within the model structure between energy (turbulent and radiation exchange), vertical and horizontal redistribution of soil moisture, plant growth, surface and groundwater fluxes, transport of conservative solutes and streamflow routing. Sufficient tools and databases exist in the CLASS framework that can be used for generating the information generally not available for catchment scale implementations (eg. flow path, soil depth, climate zoning, pedotransfer functions etc.). Tools in the CLASS modelling framework can be implemented easily at the hillslope scale. However, at the catchment scale, CLASS is a computationally demanding modelling approach and requires good understanding of the modelling concepts. New South Wales Department of Natural Resources has developed the CLASS framework. The work formed part of the Cooperative Research Centre for Catchment Hydrology (CRCCH) Associate Project. CLASS is supported by a windows based user friendly graphical users interface (GUI). It is fully object oriented and has been developed on Microsoft. Net platform. Considerable effort has been made in representing vegetation growth as well as in the pathways that water takes from hillslope to stream. The framework consists of seven tools of which three are available for free download from the CRCCH Catchment Modelling Toolkit website (about 430 downloads to date). Three other CLASS modelling tools would be available through the Toolkit web site by December 2005 and the catchment model would be available by June 2006. All modelling tools in the CLASS framework (with the exception of 3PG+) have been developed as an integral part of CLASS using comprehensive and published scientific methods. State of the art numerical, scientific and software development technologies have been used. CLASS has been peer reviewed by experts in distributed eco-hydrological modelling.