INTRODUCTION

Atmospheric and hydrological models provide a framework within which the relationships between climate and water resources can be conceptualized and investigated. These investigations can range from simple one-way couplings using atmospheric model outputs as adjustment factors for measured inputs to hydrological models, to more complex, fully coupled atmospheric and hydrological model applications that incorporate feedback mechanisms between the two systems.

The scientific literature contains a large number of reports on the variety of atmospheric and hydrological models that have been used to investigate the effects of increasing greenhouse gases on climate, and the resulting impacts of any associated changes in climate on local and regional hydrology. Current atmospheric models have generally been shown to have a limited ability to simulate present climate conditions, and thus a large degree of uncertainty exists as to their applicability for impact assessments. Similar uncertainties have been identified in the applicability of the wide range of hydrological models. The purpose of this chapter is not to provide an extensive review of the findings of these reports, but to characterize the state of atmospheric and hydrological modelling for use in simulating the effects of climate change and current climate variability. Methodologies of modelling and climate scenario development are reviewed, their deficiencies are discussed, and additional research needs are identified.

HYDROLOGICAL MODELS

‘Hydrological modelling is concerned with the accurate prediction of the partitioning of water among the various pathways of the hydrological cycle’ (Dooge, 1992).