[1] Relying on the U.S. Geological Survey water use data for the period 1960À2005, this paper summarizes past water use and then projects future water use based on the trends in water use efficiency and major drivers of water use. Water use efficiency has improved in most sectors. Over the past 45 years, withdrawals in industry and at thermoelectric plants have steadily dropped per unit of output. In addition, domestic and public withdrawals per capita, and irrigation withdrawals per unit area in most regions of the west, have recently begun to decrease. If these efficiency trends continue and trends in water use drivers proceed as expected, in the absence of additional climate change the desired withdrawals in the United States over the next 50 years are projected to stay within 3% of the 2005 level despite an expected 51% increase in population. However, including the effects of future climate change substantially increases this projection. The climate-based increase in the projected water use is attributable mainly to increases in agricultural and landscape irrigation in response to rising potential evapotranspiration, and to a much lesser extent to water use in electricity production in response to increased space cooling needs as temperatures rise. The increases in projected withdrawal vary greatly across the 98 basins examined, with some showing decreases and others showing very large increases, and are sensitive to the emission scenario and global climate model employed. The increases were also found to be larger if potential evapotranspiration is estimated using a temperaturebased method as opposed to a physically based method accounting for energy, humidity, and wind speed.

With urban, agricultural, and industrial needs growing throughout the past decades, wetland ecosystems have experienced profound changes. Most critically, the biodiversity of wetlands is intimately linked to its hydrologic dynamics, which in turn are being drastically altered by ongoing climate changes. Hydroperiod regimes, e.g., percentage of time a site is inundated, exert critical control in the creation of niches for different plant species in wetlands. However, the spatial signatures of the organization of plant species in wetlands and how the different drivers interact to yield such signatures are unknown. Focusing on Everglades National Park (ENP) in Florida, we show here that cluster sizes of each species follow a power law probability distribution and that such clusters have well-defined fractal characteristics. Moreover, we individuate and model those signatures via the interplay between global forcings arising from the hydroperiod regime and local controls exerted by neighboring vegetation. With power law clustering often associated with systems near critical transitions, our findings are highly relevant for the management of wetland ecosystems. In addition, our results show that changes in climate and land management have a quantifiable predictable impact on the type of vegetation and its spatial organization in wetlands.ecology | self-organization | ecosystems sensitivity | wetlands vulnerability W ith the richness and complexity of their ecosystems, wetland areas are of growing interest as they host a variety of animal and vegetal species, many of which are rare or endangered, and constitute some of the most unique and beautiful areas in the world. Once perceived simply as worthless swamps, wetlands have been subjected to a great deal of degradation throughout the past decades, as more and more of their land has been seized and reconverted to suit the needs of the growing human population (1, 2). Today, their value is being rediscovered and the preservation of their ecosystem and biodiversity is acquiring major importance. Under this perspective, understanding the dynamics that control the delicate equilibrium of wetland ecosystems is vitally important, as it is the key to develop both preservation and restoration measures. Given that ecosystems can abruptly shift from an existing state to another in response to changes in the system forcings (3-6), a quantitative analysis of wetlands dynamics is a timely issue, especially in scenarios that may be complicated by ongoing and future climatic changes (7-9).Vegetation patterns are frequently the result of the interplay between local dynamics and global forcings (10, 11) and thus can be described by the interaction between these drivers (10-16). However, given the typical complexity of wetland ecosystems and the heterogeneity of their hydrologic regimes, isolating key global drivers as well as determining the strength and range of the local dynamics is a challenging task. The number of factors that affect the spatial distribution of plant species in wet...

Abstract:Comparison of projected future water demand and supply across the conterminous United States indicates that, due to improving efficiency in water use, expected increases in population and economic activity do not by themselves pose a serious threat of large-scale water shortages. However, climate change can increase water demand and decrease water supply to the extent that, barring major adaptation efforts, substantial future water shortages are likely, especially in the larger Southwest. Because further global temperature increases are probably unavoidable, adaptation will be essential in the areas of greatest increase in projected probability of shortage. Keywords SummaryThe likelihood of future water shortages depends on how water supply compares with demands for water use. Comparison of supply and demand within a probabilistic framework yields an estimate of the probability of shortage and thus a measure of the vulnerability of the water supply system. This comparison was performed for current conditions and for several possible future conditions reflecting alternative socio-economic scenarios and climatic projections. Examining alternative futures provides a measure of the extent to which serious future risks of water shortage must be anticipated.Water supply was quantified by first estimating freshwater input as precipitation minus evapotranspiration for each point in a grid covering the study area. These water inputs were then allocated to major river basins and made available to meet basic in-stream flow requirements, satisfy off-stream demands including those from downstream basins or those reached by trans-basin diversions, and add to reservoir storage. Off-stream demands were estimated as threshold quantities of desired water use based on extending past trends in water use under the assumption that water supply would be no more constraining to future water withdrawals than in the recent past. Modeling water supply and demand in this way does not provide a forecast of future shortage levels. Rather, it provides a projection of the degree to which water shortages would occur in the absence of adaptation measures to either increase supply or decrease demand.On a per capita basis, aggregate water withdrawal in the United States has been dropping since at least 1985. This reduction has occurred largely because of changes in the irrigation, thermoelectric, and industrial water use sectors. In the West, agricultural acreage has been decreasing and water withdrawal efficiency has been improving. Water withdrawal per kilowatt hour produced at thermoelectric plants has been steadily dropping as production has moved to more water-efficient plant types. And industrial water use has been dropping as industrial capacity has moved overseas and water recycling has become more common at remaining plants.Despite the reductions in per-capita water withdrawal, total U.S. withdrawal rose from 1985 to 2000, largely in response to population growth of roughly 2.7 million persons per year. However, the most recent ...

The spatial organization of functional vegetation types in river basins is a major determinant of their runoff production, biodiversity, and ecosystem services. The optimization of different objective functions has been suggested to control the adaptive behavior of plants and ecosystems, often without a compelling justification. Maximum entropy production (MEP), rooted in thermodynamics principles, provides a tool to justify the choice of the objective function controlling vegetation organization. The application of MEP at the ecosystem scale results in maximum productivity (i.e., maximum canopy photosynthesis) as the thermodynamic limit toward which the organization of vegetation appears to evolve. Maximum productivity, which incorporates complex hydrologic feedbacks, allows us to reproduce the spatial macroscopic organization of functional types of vegetation in a thoroughly monitored river basin, without the need for a reductionist description of the underlying microscopic dynamics. The methodology incorporates the stochastic characteristics of precipitation and the associated soil moisture on a spatially disaggregated framework. Our results suggest that the spatial organization of functional vegetation types in river basins naturally evolves toward configurations corresponding to dynamically accessible local maxima of the maximum productivity of the ecosystem.ecohydrology | ecology | vegetation patterns

The increasing pressure of climatic change and anthropogenic activities is predicted to have major effects on ecosystems around the world. With their fragility and sensitivity to hydrologic shifts and land-use changes, wetlands are among the most vulnerable of such ecosystems. Focusing on the Everglades National Park, we here assess the impact of changes in the hydrologic regime, as well as habitat loss, on the spatial configuration of vegetation species. Because the current structuring of vegetation clusters in the Everglades exhibits power-law behavior and such behavior is often associated with self-organization and dynamics occurring near critical transition points, the quantification and prediction of the impact of those changes on the ecosystem is deemed of paramount importance. We implement a robust model able to identify the main hydrologic and local drivers of the vegetation species spatial structuring and apply it for quantitative assessment. We find that shifts in the hydropatterns will mostly affect the relative abundance of species that currently colonize specific hydroperiod niches. Habitat loss or disruption, however, would have a massive impact on all plant communities, which are found to exhibit clear threshold behaviors when a given percentage of habitable habitat is lost.climate change impacts | ecohydrology | ecology | habitat vulnerability A s the interest surrounding wetlands and their fate has grown throughout the last decades, the impact of the increasing anthropogenic and climatic changes on their delicate ecosystem, and in particular on their vegetation dynamics, has been the subject of numerous studies (1-5). It was shown that the spatial organization of vegetation often arises from the interplay between local endogenous dynamics and global exogenous forces (6-9). In the Everglades National Park (ENP), in particular, such interplay is responsible for power-law clustering of vegetation species (10). Moreover, the ENP is a cradle where a large variety of rare and endangered species coexist within a fragile equilibrium, and the awareness of its importance has drawn attention to the extent that it is the focus of one of the most expensive restoration projects ever attempted (11-13). With these premises, it is of paramount importance to understand and quantify the potential impacts of habitat changes on the vegetation structuring of the Everglades ecosystem. ResultsThe modeling framework adopted in this study, which reveals the feedback between vegetation structures and hydrologic forces by incorporating the effects of exogenous drivers (i.e., hydropatterns) and endogenous mechanisms of plant interactions, was successfully used as a diagnostic tool for the analysis of the spatial configuration of plant communities in wetlands, with specific focus on the power-law clustering of vegetation patterns in the Everglades (10) (Materials and Methods). Such a modeling framework is based on a cellular automaton scheme ( Fig. S1 and SI Materials and Methods) applied over a 40-× 40-m study grid covering...