Early Signs of Global Warming?
During the last few decades, there has been a widespread shift toward earlier springs. Over much of western North America, that shows up in some key hydrological and ecological measures. This shift is associated with warmer winters and springs since the mid-1970’s, an increase of approximately 1-3 degrees C over the previous three decades. Responses to this warming have included a trend for more precipitation to fall as rain rather than snow, an advance in the timing of snowmelt and snowmelt-driven streamflow, less spring snowpack, and earlier spring plant development. Largest changes in mountain snow-fed watersheds have occurred in lower, transition-zone elevations where average temperatures are close to freezing, and near the altitude separating rain from snow. A large proportion of the snowmelt-dominated watersheds in Alaska, western Canada and the western conterminous United States have shifted toward earlier spring flows, while many of the rainfall-dominated streams along the West
