HETEROGENEITY AND SCALING LAND-ATMOSPHERIC WATER AND ENERGY FLUXES IN CLIMATE SYSTEMS

Summary

ABSTRACT The effects of small-scale heterogeneity in land surface characteristics on the large-scale fluxes of water and energy in the land-atmosphere system have become a central focus of many of the climatology research experiments. The acquisition of high resolution land surface data through remote sensing and intensive land-climatology field experiments (like HAPEX and FIFE) has provided data to investigate the interactions between micro scale land-atmosphere interactions and macroscale models. One essential research question is how to account for the small-scale heterogeneities and whether ‘effective’ parameters can be used in the macroscale models. To address this question of scaling, three modeling experiments were performed and are reviewed in this paper. The first is concerned with the aggregation of parameters and inputs for a terrestrial water and energy balance model. The second experiment analyzed the scaling behaviour of hydrological responses during rain events and between rain events. The third experiment compared the hydrological responses from distributed models with a lumped model that uses spatially constant inputs and parameters. The results show that the patterns of small scale variations can be represented statistically if the scale is larger than a representative elementary area scale, which appears to be about 2–3 times the correlation length of the process. For natural catchments this appears to be about 1–2 km². The results concerning distributed versus lumped representations are more complicated. For conditions when the processes are non-linear, lumping results in biases; otherwise a one-dimensional model based on ‘equivalent’ parameters provides quite good results. Further research is needed to understand these conditions fully.