Broad-scale studies of climate change effects on freshwater
species have focused mainly on temperature, ignoring critical
drivers such as flow regime and biotic interactions. We use
downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows andincreased temperatures on four interacting species of trout across the interior western United States (1.01 million km2), based onempirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast amean 47% decline in total suitable habitat for all trout, a groupof fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species’ physiological optima and continuednegative biotic interactions. Habitat for nonnative brook troutSalvelinus fontinalis and brown trout Salmo trutta is predictedto decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, isprojected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations.

Hydropower represents approximately 20% of the world’s energy supply, is viewed as both vulnerable to global climate warming and an asset to reduce climate altering emissions, and is increasingly the target of improved regulation to meet multiple ecosystem service benefits. It is within this context that the recent decision by the United States Federal Energy Regulatory Commission to reject studies of climate change in its consideration of reoperation of the Yuba-Bear Drum-Spaulding hydroelectric facilities in northern California is shown to be poorly reasoned and risky. Given the rapidity of climate warming, and its anticipated impacts to natural and human communities, future long-term fixed licenses of hydropower operation will be ill prepared to adapt if science-based approaches to incorporating reasonable and foreseeable hydrologic changes into study plans are not included. The licensing of hydroelectricity generation can no longer be issued in isolation due to downstream contingencies such as domestic water use, irrigated agricultural production, ecosystem maintenance, and general socioeconomic well-being. At minimum, if the Federal Energy Regulatory Commission is to establish conditions of operation for 30-50 years, licensees should be required to anticipate changing climatic and hydrologic conditions for a similar period of time.

We evaluated the impact of land cover on fish assemblages by examining relationships between stream hydrology, physicochemistry, and instream habitat and their association with fish responses in streams draining 18 watersheds of the Lower Piedmont of western Georgia. Several important relationships between land use and physicochemical, hydrological, and habitat parameters were observed, particularly higher frequency of spate flows, water temperatures, and lower dissolved oxygen (DO) with percentage impervious surface (IS) cover, higher habitat quality with percentage forest cover, and elevated suspended solid concentrations with percentage pasture cover. Fish assemblages were largely explained by physicochemical and hydrological rather than habitat variables. Specifically, fish species diversity, richness, and biotic integrity were lower in streams that received high frequency of spate flows. Also, overall fish assemblage structure as determined by nonmetric multidimensional scaling was best described by total dissolved solids (TDS) and DO, with high TDS and low DO streams containing sunfish-based assemblages and low TDS and high DO streams containing minnow-based assemblages. Our results suggest that altered hydrological and physicochemical conditions, induced largely by IS, may be a strong determinant of fish assemblage structure in these lowland streams and allow for a more mechanistic understanding of how land use ultimately affects these systems.

Many challenges, including climate change, face the Nation’s water managers. The Intergovernmental Panel on Climate Change (IPCC) has provided estimates of how climate may change, but more understanding of the processes driving the changes, the sequences of the changes, and the manifestation of these global changes at different scales could be beneficial. Since the changes will likely affect fundamental drivers of the hydrological cycle, climate change may have a large impact on water resources and water resources managers.

The purpose of this interagency report prepared by the U.S. Geological Survey (USGS), U.S. Army Corps of Engineers (USACE), Bureau of Reclamation (Reclamation), and National Oceanic and Atmospheric Administration (NOAA) is to explore strategies to improve water management by tracking, anticipating, and responding to climate change. This report describes the existing and still needed underpinning science crucial to addressing the many impacts of climate change on water resources management.

The potential effects of climate change on the hydrology and water resources of the Columbia River Basin (CRB) were evaluated using simulations from the U.S. Department of Energy and National Center for Atmospheric Research Parallel Climate Model (DOE/NCAR PCM).

This study focuses on three climate projections for the 21st century based on a ‘business as usual' (BAU) global emissions scenario, evaluated with respect to a control climate scenario based on static 1995 emissions. Time-varying monthly PCM temperature and precipitation changes werestatistically downscaled and temporally disaggregated to produce daily forcings that drove a macroscale hydrologic simulation model of the Columbia River basin at 1/4-degree spatial resolution.

The Pacific Northwest (PNW) hydropower resource, central to the region's electricity supply, is vulnerable to the impacts of climate change. The Northwest Power andConservation Council (NWPCC), an interstate compact agency, has conducted long termplanning for the PNW electricity supply for its 2005 Power Plan. In formulating its power portfolio recommendation, the NWPCC explored uncertainty in variables that affect theavailability and cost of electricity over the next 20 years. The NWPCC conducted an initialassessment of potential impacts of climate change on the hydropower system, but these results are not incorporated in the riskmodel upon which the 2005 Plan recommendations are based. To assist in bringing climate information into the planning process, we present an assessment of uncertainty in future PNW hydropower generation potential based on a comprehensive set ofclimate models and greenhouse gas emissions pathways. We find that the prognosis for PNW hydropower supply under climate change is worse than anticipated by the NWPCC's assessment. Differences between the predictions of individual climate models are found to contribute more to overall uncertainty than do divergent emissions pathways. Uncertainty in predictions of precipitation change appears to bemore important with respect to impact on PNW hydropower than uncertainty in predictions of temperature change. We also find that a simple regression model captures nearly all of the response of a sequence of complex numerical models to large scale changes in climate. This result offers the possibility of streamlining both top-down impact assessment and bottom-up adaptation planning for PNW water and energy resources.

Climate change is likely to affect the generation of energy from California's high-elevation hydropower systems. To investigate these impacts, this study formulates alinear programming model of an 11-reservoir hydroelectric system operated by theSacramento Municipal Utility District in the Upper American River basin.

Observations have shown that the hydrological cycle of the western United States changed significantly over the last half of the 20th century. We present a regional, multivariable climatechange detection and attribution study, using a high-resolution hydrologic model forced by globalclimate models, focusing on the changes that have already affected this primarily arid regionwith a large and growing population. The results show that up to 60% of the climate-related trendsof river flow, winter air temperature, and snow pack between 1950 and 1999 are human-induced.These results are robust to perturbation of study variates and methods. They portend, in conjunction with previous work, a coming crisis in water supply for the western United States.

Freshwater resources, because of a host of human assaults, but especially because of dams, are the most degraded of the Earth's major ecosystems. Now the future of every dam on Earth is threatened-- not by environmental protests or economic constraints-- but by the Greenhouse Effect and the world's changing climate. Historical and geological evidence over past millennia indicate that even small changes in climate can cause major changes in the size of floods. Insurers increasingly are convinced that global warming is to blame for the greater frequency and severity of violent storms, floods and droughts since the late 1980s.
Hydrologists cannot predict exactly how much water will flow into a planned reservoir. To make a "best guess," they project past streamflow data into the future. Overestimates of average flows mean that many dams fail to yield as much power and water as predicted, the Buendia-Entrepenas reservoir in Spain is an example.
Sedimentation, despite over 60 years of research, still may be the most serious technical problem faced by the dam industry. In the US, large reservoirs lose storage capacity at an average rate of 0.2% per year, in China the rate is closer to 2.3%. Despite all the uncertainties surrounding reservoir sedimentation, authorities very rarely stop planned projects due to a lack of adequate sediment data.

Several aspects of flow have been shown to be important determinants of biological community structure and function in streams, yet direct application of this approach to large rivers has been limited. Our results synthesize, simplify, and interpret the complex changes in flow occuring along the Missouri and lower Yellostone Rivers, and provide an objective grouping for future tests of how these changes may affect biological communities.