Because scientists have observed changes in weather patterns and their influence on water in the West generally, a group of scientists from the University of Colorado and the NOAA Earth Systems Research Laboratory and its Western Water Assessment group produced this report to target their investigation on Colorado specifically. They analyzed peer-reviewed studies of "observed trends, modeling, and projections of temperature, precipitation, snowmelt, and runoff" (p. 1), making predictions out to 2050.
Based on the examination, the authors made fourteen "observations, attribution, and projections" (p. 1), detailed in the Executive Summary. First, the authors noted that "climate change has been linked to observed and projected changes in the water cycle. By the mid-21st century, average river runoff and water availability are projected to increase at high latitudes and decrease over dry regions at lower midlatitudes" (p. 1). The western United States fell within both scenarios. The authors anticipated these changes even without concurrent changes in precipitation. Second, the authors attributed climate alterations in the past fifty years to growing concentrations of greenhouse gases in the atmosphere.
Third, Colorado conformed to the general rising temperatures in the West in all sections of the state except the southeastern portion. Fourth, "no studies have specifically investigated whether the detected trends in Colorado can be attributed to anthropogenic greenhouse gases" (p. 1). Fifth, the authors projected a warming trend to 2050 with data to support their claim. Sixth, consistent with the fifth point, the authors projected decreasing extremes in colder months and increasing extremes in hotter months. They stated, "in all seasons, the climate of the mountains is projected to migrate upward in elevation, and the climate of the Desert Southwest to progress up into the valleys of the Western Slope" (p. 1). Seventh, no graphs of data on precipitation plotted a discernible change. Eighth, the researcher detected little change in the ratio between rain and snow, except in elevations below 8200 feet. Ninth, the researchers projected the range of future changes in snowpack: "precipitous decline in lower-elevation (below 8200 feet) . . . modest declines are projected (10-20%) for Colorado's high-elevation snowpack (above 8200 ft) within the same timeframe" (p. 2).
Tenth, the researcher found that from 1978 and 2004 the "spring pulse (the onset of streamflows from melting snow)" (p. 2) occurred earlier, by about two weeks, than previously recorded. Attributing the trend to climate change, the authors surmised that "the timing of runoff is projected to shift earlier in the spring, and late-summer flows may be reduced" (p. 2).
Eleventh, although researchers lack data on the Rio Grande, Platte, and Arkansas, they predicted a decrease in runoff in these river basins. These rivers, and the Colorado, have headwaters in Colorado. Twelfth, focusing on the Colorado River specifically, the authors noted that the river had between 2000 and 2004 its "lowest five-year period of Colorado River natural flow since records began in the late 1800s" (p. 2). Thirteenth, the influence of climate change on drought has inconclusive evidence. The authors cited paleoclimate data that revealed "less frequent and less severe drought conditions" in the 20th century compared to findings of the past 1000 years. The absence of precipitation cause droughts; "however, warming temperatures may have increased the severity of droughts and exacerbated drought impacts" (p. 2).
Lastly, the uniqueness of Colorado's topography forced researchers to 'downscale', correct bias, and calibrate to "adjust for the effects of elevation and the mountains on snowfall and temperature" (p. 2) on climate. These efforts enabled researchers to further understand how Colorado, with its mountains, plains, and plateaus, differs from other states in the Western region of the United States.
Risks
The authors identified two risks to the state in their assessment of the effect of climate change on water resources: future droughts and compact calls on Colorado rivers from downstream states with which Colorado has contractual obligations. The report would aid the state and water providers in conducting vulnerability analyses and formulating an integrated resource and adaptation plan to mitigate risks. The authors suggested incorporating climate change potentialities into water managers' integrated resource plans (IRP), a common long-range planning tool employed by water managers. It structures "a strategy for keeping a wide range of options open and maintaining flexibility in the face of an uncertain future" (p. 42).
The authors categorized potential vulnerabilities into ten areas: "water demand for agriculture and outdoor watering . . . water supply infrastructure . . . legal water systems . . . water quality . . . energy demand and operating costs . . . mountain habitats . . . interplay among forests, hydrology, wildfires and pests . . . riparian habitats and fisheries . . . water and snow-based recreation . . . groundwater resources" (p. 41). Higher temperatures cause greater evapotranspiration by plants, which results in increased watering and demand. Variations of accumulation of "snowpack, streamflow timing, and hydrologic evolution may affect reservoir operations" and the infrastructures that convey, divert, store, and control water flows. Changes in seasonal water availability may necessitate a review of the prior appropriations doctrine and other legal water contracts. As to water quality, "changes in the timing and hydrograph may affect sediment load and pollution, impacting human health" (p. 41). Hydropower plants may experience greater levels of demand from higher temperature, along with other energy and temperature-sensitive industries. Previously, the researchers noted the potential for mountain habitats to move to higher, cooler elevations. Climate change "may affect the relationships between forests, surface and ground water, wildfire, and insect pests. Water-stressed trees, for example, may be more vulnerable to pests" (p. 41). Aquatic and riparian habitats may evolve, favoring the species, non-native or native, that can adapt to warmer temperatures and changing streamflows. Rafting, trout fishing, and winter recreation will undergo adjustments with a new climate environment. Finally, temperature increases and precipitation variability will impact groundwater recharge activities and subsequent groundwater availability.
The researchers isolated two approaches to assess climate change and its impact on Colorado water resources, bottom -up and top-down. The four steps of the bottom-up approach include "1. Identification of Vulnerability . . . 2. Articulation of Drivers and Stressors . . . 3. IWRM to Assess Vulnerability . . . 4. Regional Scenarios from Historical Analog and/or Extremes and GCM output" (p. 42). The top-down model has five steps: 1. Climate and socioeconomic scenarios . . . 2. AOGCM Output . . . 3. Regional downscaling . . . 4. Hydrologic Reaction . . . 5. UIVRM Assessment and Response. To produce quality analysis, the authors recommended further advancements in modeling, in data of basins previously unstudied, in research on drought and its causes, and in "hydrologic projections for the Colorado River" (p. 43).
University of Colorado, Boulder & National Oceanic and Atmospheric Administration's Western Water Assessment. (2008). Climate change in Colorado, a synthesis to support water resources management and adaptation: A report for the Colorado Water Conservation Board. Boulder, CO: CU-NOAA Western Water Assessment.
Obtain a copy of this report at http://wwa.colorado.edu/
Acronym List
AOGCM Atmospheric-Oceanic General Circulation Models
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