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.

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.

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.

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.

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.