An Evaluation of Proposed Representations of Subgrid Hydrologic Processes in Climate Models

The temporal and spatial scales that characterize surface hydrologic processes provide conceptual and practical difficulties to the development of parameterization schemes for incorporation into climate models. In particular, there is a requirement to develop process descriptions applicable to large areas but that can model (capture) day-to-day and even hour-to-hour temporal change We compare two recently proposed methods of simulating subgrid-scale heterogeneity in precipitation distribution. These schemes diverge significantly when the fractional areal extent of the precipitation falls below about 0.2. We have also examined two recently proposed parameterizations of surface hydrologic processes in the context of basin-scale data from the Hunter Valley in southeastern Australia. We find that although both models capture the predominant characteristics of the annual and monthly surface runoff adequately, the day-to-My variability in the observed flow requires a more explicit identification and treatment of the predominant runoff-generating processes.