Approaches to continental scale runoff for integrated assessment models

The need to incorporate water resources into regional and global integrated assessment models for evaluating global change impacts has been identified as being important, but given the spatial and temporal variability of freshwater resources and limited data availability, the inclusion of water within these large scale models has proven to be difficult. A compromise between accurate regresentation of complex processes and simplistic parameterization is necessary for capturing regional and temporal variability and to minimize computational requirements. An analysis of Western Europe's and Africa's freshwater runoff, which spans a range of climate variability, was performed at varying levels of spatial aggregation and at both monthly and annual time steps. Model results showed that regional runoff characteristics were lost beyond a data aggregation of 1 x 1 resolution. A monthly soil moisture model proved to he adequate for assessing annual water availability, which is the scale often used in integrated assessment models. Simpler methods, such as an empirical annual model and a simple monthly model did not consistently replicate annual historic runoff.