An open software environment for hydrological model assessment and development

The hydromad (Hydrological Model Assessment and Development) package provides a set of functions which work together to construct, manipulate, analyse and compare hydrological models. The class of hydrological models considered are dynamic, spatially-aggregated conceptual or statistical models. The package functions are designed to fit seamlessly into the R system, and builds on its powerful data manipulation and analysis capabilities. The framework used in the package encourages a separation of model components based on Unit Hydrograph theory; many published models are consistent with this and implementations of several are included. For comparative assessment, model performance can be analysed over time and with respect to covariates to reveal systematic biases. Support has been built in for event-based analysis of data and assessment of model performance. Fit statistics can be defined by choices of (1) temporal scale and aggregation function; (2) weighting and transformation; and (3) reference model. One can define new Soil Moisture Accounting models, routing models, calibration methods, objective functions, and evaluation statistics, while retaining as much of the default framework as is useful. And as the package code is available under a free software licence, one always has the freedom to adapt it as required. Use of the software is demonstrated in a case study of the Queanbeyan River catchment in South-East Australia.