Evan K. Paleologos

Analysis of Process Controls in Land Surface Hydrological Cycle Over the Continental United States

The paper uses two years (1997–1999) of data from the North American Land Data Assimilation System at National Centers for Environmental Prediction to analyze the variability of physical variables contributing to the hydrological cycle over the conterminous United States. The five hydrological variables considered in this study are precipitation, top layer soil moisture (0–10 cm), total soil moisture (0–200 cm), runoff, and potential evaporation. There are two specific analyses carried out in this paper. In the first case the principal components of the hydrological cycle are examined with respect to the loadings of the individual variables. This helps to ascertain the contribution of physical variables to the hydrological process in decreasing order of process importance. The results from this part of the study had revealed that both in annual and seasonal timescales the first two principal components account for 70–80% of the variance and that precipitation dominated the first principal component, the most dominant mode of spatial variability. It was followed by the potential evaporation as the secondmost dominant process controlling the spatial variability of the hydrologic cycle over the continental United States. In the second case each hydrological variable was examined individually to determine the temporal evolution of its spatial variability. The results showed the presence of heterogeneity in the spatial variability of hydrologic variables and the way these patterns of variance change with time. It has also been found that the temporal evolution of the spatial patterns did not resemble white noise; the time series of the scores of the principal components showed proper cyclicity at seasonal to annual timescales. The northwestern and the southeastern parts of the United States had been found to have contributed significantly toward the overall variability of potential evaporation and soil moisture over the United States. This helps in determining the spatial patterns expected from hydrological variability. More importantly, in the case of modeling as well as designing observing systems, these studies will lead to the creation of efficient and accurate land surface measurement and parameterization schemes.

Infiltration in stratified, heterogeneous soils: Relative importance of parameters and model variations

[1] This study presents a framework that accounts for the uncertainty, relative importance, and relative contribution of uncertain and spatially variable parameters and the influence of statistical model assumptions in problems of infiltration in unsaturated, heterogeneous formations. The relative importance of the saturated hydraulic conductivity K s , the van Genuchten α, and 3 parameters was quantified toward the mean pressure head profile and the fluctuations about it. The broad implications of our study for site characterizations efforts are the following. Statistical moments were seen not to be sufficient for producing reliable modeling estimates. Significant information on the detailed shape of the probability distribution is required in order to produce meaningful predictions. When limited data are available, optimum allocation of resources is accomplished by concentrating on K s . When more extensive sampling can be done, both K s and β appear to be critical. Total system performance analyses may not provide the most appropriate modeling estimates. The results of the relative importance of the parameters for a specific layer did not coincide with the conclusions drawn from an analysis of the system as a whole.

Control function measures for hydrodynamic problems

This short paper shows that different choices made for control functions of information in hydrodynamic flow problems can have significant implications for interpretations of the system. Using as a simple illustration the case of a steady-state, one-dimensional flow model with no internal sources or sinks and with the hydraulic conductivity depending on a single parameter and the distance from the origin, it is shown that, even when a continuous, error-free head data set is provided, statements about the uniqueness or not of the inverse solution are conditioned on the choice of the control function. Care has to be exercised in obtaining physically meaningful results and, depending on the model assumptions and the data available, there may not be acceptable models. It is also shown that there may be more than one model behavior that is acceptable. The results have implications for the hydrodynamic upscaling problem for flow in permeable media, for ensemble averaging methods, and for parameter determination for deterministic models of permeable flow.

Environmental concerns: Catastrophic events and insurance

Two conditions can occur in exploration problems that require that a corporation consider some form of insurance. First is the possibility of a catastrophic event occurring during exploration, for instance spilling oil, thereby involving massive and expensive clean-up costs. A corporation would surely like to take out insurance against this possibility. Second is the possibility that the regulatory agencies may consider a unilateral change in the environmental stringency conditions after the project is under way. In this case the corporation could be involved in further costs, thereby lowering potential profitability of a pre-existing contract. The corporation would surely like to option against the possibility of such an event occurring prior to the chance that the contract terms could be changed. These two forms of insurance are not equivalent. In the catastrophic loss event situation one would like to pay an insurance premium to cover the unknown catastrophic costs should they occur. In the regulatory stringency conditions situation, one usually knows ahead of time precisely how such more stringent conditions, if enacted, would influence the corporate profitability and one would like to have a contingency option operating that would be activated if and only if the regulatory agency does indeed enact the new more stringent regulations.