Six reservoirs located in the Western United States (F. D. Roosevelt, Dworshak, Wallula, Shasta, Oroville, and New Melones) were sampled in order to estimate their greenhouse gas (GHG) emissions.

Two types of fluxes were assessed : 1) diffusive fluxes of methane (CH4) and carbon dioxide (CO2) at the air/water interface; 2) degassing fluxes of CH4 and CO2 from water passing through the turbine spillways.

Diffusive flux measurements indicated that the surface of the reservoirs were a source of CH4 during the sampling period (from +3,2 to +9,5 mg CH4

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.