questions will have to be explored in conjunction with other projects, notably GOALS, to maximize the efficiency of research efforts.

Use Observations and Models to Assess Quantitatively the Impacts of Individual Land Surface and Atmospheric Processes on Large-Scale Water and Energy Transport

Key GCIP process issues concerning the land environment include the identification and quantification of the factors that control evapotranspiration in the absence of water stress and the interseasonal storage of water to support dry season evapotranspiration. The influence of extensive areas of shallow groundwater, swamps, or lakes on the dynamics of water and energy balances is yet to be characterized. GCIP also provides an opportunity to determine the predictive value of standard physical soil water transport theories at GCIP scales. To what extent does the water balance manifest a nonlinear dependence of runoff on rainfall intensity, and what is this dependence as a function of spatial and temporal scales? To what extent is soil infiltration capacity a factor in the water balance? How do seasonal freezing and changes in soil structure affect infiltration and runoff? Finally, do the details of land surface topography play a significant role in the area-averaged water balance?

GCIP can also contribute to the improved understanding of atmospheric processes, complementing related studies, for example, in the GEWEX Cloud System Study. What atmospheric processes control the structure of the low-level jet over the southern Great Plains? How does cloud-scale mixing affect large-scale water vapor and heat transport? How do mesoscale circulations contribute to local precipitation and larger-scale atmospheric transport?

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