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The flooding in the lower basin of the Colorado River during the spring and summer of 1983 led to discussion of the management of the heavy spring runoff from the upper basin. This analysis stresses that the reasons for the flooding go beyond the climatic events of the year and the U.S. Bureau of Reclamation's response to them. It is argued that the flooding is the result of the convergence of three factors: 1) the 17-year period of filling Lake Powell (Glen Canyon Dam) has ended and the system of water storage reservoirs on the river now considered full; 2) during the filling period, physical encroachment into the lower basin flood plain accelerated; and 3) the climatic variability experienced in the Colorado River...
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In western North America, snow provides crucial storage of winter precipitation, effectively transferring water from the relatively wet winter season to the typically dry summers. Manual and telemetered measurements of spring snow-pack, corroborated by a physically based hydrologic model, are examined here for climate-driven fluctuations and trends during the period of 1916–2002. Much of the mountain West has experienced declines in spring snowpack, especially since midcentury, despite increases in winter precipitation in many places. Analysis and modeling show that climatic trends are the dominant factor, not changes in land use, forest canopy, or other factors. The largest decreases have occurred where winter...
Rain-on-snow events pose a significant flood hazard in the western United States. This study provides a description of the spatial and temporal variability of the frequency of rain-on-snow events for 4318 sites in the western United States during water years (October through September) 1949–2003. Rain-on-snow events are found to be most common during the months of October through May; however, at sites in the interior western United States, rain-on-snow events can occur in substantial numbers as late as June and as early as September. An examination of the temporal variability of October through May rain-on-snow events indicates a mixture of increasing and decreasing trends in rain-on-snow events across the western...


    map background search result map search result map Declining snowpack in western North America Declining snowpack in western North America