Water in a Changing World

Abstract

Abstract. Renewable fresh water comprises a tiny fraction of the global water pool but is the foundation for life in terrestrial and freshwater ecosystems. The benefits to humans of renewable fresh water include water for drinking, irrigation, and industrial uses, for production of fish and waterfowl, and for such instream uses as recreation, transportation, and waste disposal.In the coming century, climate change and a growing imbalance among freshwater supply, consumption, and population will alter the water cycle dramatically. Many regions of the world are already limited by the amount and quality of available water. In the next 30 yr alone, accessible runoff is unlikely to increase more than 10%, but the earth's population is projected to rise by approximately one-third. Unless the efficiency of water use rises, this imbalance will reduce freshwater ecosystem services, increase the number of aquatic species facing extinction, and further fragment wetlands, rivers, deltas, and estuaries.Based on the scientific evidence currently available, we conclude that: (1) over half of accessible freshwater runoff globally is already appropriated for human use; (2) more than 1 ϫ 10 9 people currently lack access to clean drinking water and almost 3 ϫ 10 9 people lack basic sanitation services; (3) because the human population will grow faster than increases in the amount of accessible fresh water, per capita availability of fresh water will decrease in the coming century; (4) climate change will cause a general intensification of the earth's hydrological cycle in the next 100 yr, with generally increased precipitation, evapotranspiration, and occurrence of storms, and significant changes in biogeochemical processes influencing water quality; (5) at least 90% of total water discharge from U.S. rivers is strongly affected by channel fragmentation from dams, reservoirs, interbasin diversions, and irrigation; and (6) globally, 20% of freshwater fish species are threatened or extinct, and freshwater species make up 47% of all animals federally endangered in the United States.The growing demands on freshwater resources create an urgent need to link research with improved water management. Better monitoring, assessment, and forecasting of water resources will help to allocate water more efficiently among competing needs. Currently in the United States, at least six federal departments and 20 agencies share responsibilities for various aspects of the hydrologic cycle. Coordination by a single panel with members drawn from each department, or by a central agency, would acknowledge the diverse pressures on freshwater systems and could lead to the development of a well-coordinated national plan.

Terrestrial invertebrates of dry river beds are not simply subsets of riparian assemblages

“…Temperatures recorded in dry river beds can exceed the thermal tolerances of many organisms; therefore future temperature increases may extend the duration of periods when dry river beds are inhospitable to most life. The combined effects of climate change and water management may increase or decrease the duration of the wet and dry phases in rivers (Jackson et al 2001;Chiew and McMahon 2002;Lehner et al 2006). Reduced flood frequency has negatively impacted the aquatic biota of temporary rivers and streams (Jenkins and Boulton 2007), and may have negative effects on habitat and diversity of terrestrial invertebrates in dry river beds.…”

Long‐term trends in evapotranspiration and runoff over the drainage basins of the Gulf of Mexico during 1901–2008

“…Paired watershed experiments and statistical methods are watershed-specific and thus are difficult to apply elsewhere [Liu et al, 2012]. In addition, understanding how human activities interact with climate in changing water fluxes is far from sufficient [Vorosmarty and Sahagian, 2000;Jackson et al, 2001;Piao et al, 2007]. Some scientists have emphasized the effects of climate and/or atmospheric chemical compositions [Gedney et al, 2006;McLaughlin et al, 2007;Qian et al, 2007], while others highlighted the importance of human influences in the water cycle [Vorosmarty and Sahagian, 2000;Jackson et al, 2005;Sun et al, 2005].…”

“…[2] The global water cycle has been substantially altered by the changing climate and intensifying human activities [Hutjes et al, 1998;Jackson et al, 2001;Foley et al, 2005;Huntington, 2006]. Increased air temperature (T) enlarges the holding capacity of air moisture and potentially increases the evapotranspiration (ET), which eventually intensifies precipitation (P) [Intergovernmental Panel on Climate Change (IPCC), 2007].…”

Arsenic and Fluoride Variations in Groundwater of an Endorheic Basin Undergoing Land-Use Changes

“…During the past two centuries, many arid and semiarid areas worldwide have experienced important changes in land use as humans continue to occupy and diversify the land, thus invariably stressing the availability of water and often causing water tables to decrease (Jackson et al 2001;WHO 2005;Kafri and Yechieli 2010;Pascual-Ferrer et al 2014). Within arid areas, a common occurrence are closed (endorheic) basins whose surface water and groundwater are enriched with salts Elmore et al 2008;Kafri and Yechieli 2010;Rodríguez-Rodríguez et al 2012).…”