CLIMATE CHANGE IN THE HEADWATERS WATER AND SNOW IMPACTS

Saunders, Stephen; Easley, Tom

This report summarizes existing information on how climate change may affect the snow and water resources of six Colorado counties that include the headwaters of the Colorado River and its tributaries. These headwaters counties are Eagle, Grand, Gunnison, Pitkin, Routt, and Summit counties. The water and snow resources of this six-county region are essential ingredients of its spectacular natural resources, opportunities for recreation and tourism, local economies, and quality of life, all of which are treasured locally and worldwide. To begin with, there is the Colorado River itself—starting here, draining onetwelfth of the contiguous United States, providing the largest source of water in the country’s driest region, but still being diverted beyond its basin to meet other needs across the West. Altogether, the Colorado provides drinking water for 22 of the 32 largest cities across the West1 and irrigation water for some of America’s most productive growing areas. Another hallmark of the headwaters counties is their 16 ski resorts, which include seven of the 10 mostvisited ski areas in the nation. One quarter of the nation’s skiing is on Colorado slopes,2 and most of that in the headwaters counties. Truly, the water and snow resources of these counties are something special. But as this report documents, the water and snow of the headwaters counties and the many economic and social values that depend on them are at risk as the climate changes. Temperature. In Colorado, all but one of the last 40 years have been hotter than the 20th century average and this century has had seven of the state’s ten hottest years on record. Mid-century temperatures are projected to average 1.5° Fahrenheit* to 6.5° hotter than in 1971–2000, and late-century temperatures 1.5° to 9.5° hotter, depending on future levels of heat-trapping emissions. Precipitation. To offset the impacts of higher temperatures on snow and water resources, there would need to be large increases in total precipitation and snowfall. But only the wettest 10 percent of climate projections suggest that Colorado precipitation amounts could increase by even six to nine percent. Water and snow resources. Across the West, less winter precipitation is falling as snow and more as rain, snowpacks are declining, and snowmelt is occurring earlier. Colorado’s mountains, with the highest terrain in the West, are buffered somewhat against the larger changes happening at lower elevations, but changes are happening in the headwaters, too. The flows of the Colorado River, fed mostly by mountain snow, have recently been the lowest in the past century—driven in large part by the evaporative effects of higher temperatures. Projections are that these changes will become more pronounced, with greater shifts from snowfall to rainfall, earlier snowmelt, decreased river flows, and increased likelihood of water restrictions and curtailments. Impacts on winter recreation and tourism. If Colorado snowfall and snowpacks decline as projected, the state’s skiing, snowboarding, and other opportunities for snow-dependent winter recreation could suffer. This could have economic consequences throughout the state, as the skiing/snowboarding industry alone contributes about $5 billion to the state’s economy. Impacts on warm-season recreation and tourism. If climate change projections materialize, fishing, boating, rafting, and other warm-season, water-dependent outdoor recreation could be adversely affected by hot temperatures, low water levels, and other manifestations of climate change. Impacts on water quality. Climate change may lead to decreases in water quality, including violations of water quality standards that specify maximum stream temperatures to protect fish and other resources. Further, climate change is projected to lead to major increases in wildfires, which in turn can increase flooding and sedimentation from burned areas.

CLIMATE CHANGE IN THE HEADWATERS WATER AND SNOW IMPACTS

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