According to the NCA5, Colorado is part of the Southwest region. 

Here are applicable Key Messages for the Southwest related to Water, Precipitation, and Drought. 

Key: blue highlight = historical trends, yellow highlight = projected trends, and green highlight = both historical and projected trends. 

Summary

In a region largely defined by extreme wildfires and increasing aridity, water is a critical resource in the Southwest. This region is made up of deserts and grasslands in warmer, low elevations to forests and alpine meadows in cooler, high elevations (10). Climate change will intensify historic and present concerns about water resources that will severely affect communities in the Southwest; impacts on water resources due to climate change include: 

• Temperature increases due to climate change are projected to cause an increase in the annual average minimum air temperatures; an increase in growing degree days, a measure that “relates the development of plants, insects, and disease organisms to environmental air temperature; and an increase in average number of days above 86 F (12). 
• Changes in timing, form, and amount of snow, as low-snow years are projected to increase over the next fifty years (11). 
• Reduction in mountain snowpack due to increase in air temperatures; the process of melting snowpack creates a positive feedback loop, where high air temperatures cause snow to melt, revealing darker rock underneath (which will absorb heat rather than reflect it), which leads to increased surface temperatures and more snowmelt (11). This process has led to an overall decrease in available water resources for lower-elevation communities (11, 12). For example, acequias (community-based irrigation systems that utilize snowpack for irrigation in the high-elevation watersheds of New Mexico and Colorado) are particularly vulnerable to decreases in annual snowpack (12). 
• Surface and groundwater reductions due to reduced streamflows, higher temperatures, and the resulting demand for water; this will result in historically low water levels in lakes and reservoirs (11). In addition, higher temperatures and changes in precipitation will result in less groundwater recharge from rainfall, snowmelt, and runoff (11). 
• Soil moisture will continue to decrease due to increases in air temperature and frequency of droughts (11, 2). 

“Climate change is projected to reduce snow water equivalent and alter trends in soil moisture and annual runoff” (10) 

Figure 28.2: "These maps show projected average mid-21st century (2036-2065; top row) and late-21st-century (2070-2099; bottom row) differences in annual soil moisture, snow water equivalent (the amount of water contained within the snowpack), and runoff over the Southwest region relative to the baseline period, 1991-2020. The data in these maps come from a land-surface hydrological model that simulates different parts of the water and energy balance. The model takes temperature and precipitation data from an ensemble of downscaled Coupled Model Intercomparison Project, Phase 5 (CMIP5) global climate model susing an intermediate scenario (RCP4.5) to create future projections of soil moisture, snow water equivalent, and runoff. Warming temperatures and precipitation variability are expected to reduce snow water equivalent and alter trends in soil moisture and annual runoff (KM 4.1). The historical record shows that the climatology of 1991-2020 was substantially warmer than the climatology of preceding 30-year periods. Thus, the areas of projected lower soil moisture, snow water equivalent, and runoff in this figure, especially at higher elevations, present marked deficits in comparison to 30-year periods in the 20th century. There are also areas of projected increases in soil moisture and runoff. Some CMIP5 global climate models project increased precipitation over parts of the Southwest, and when these are included in calculating average soil moisture or runoff, the result indicates wetter conditions in some locations, predominantly in Nevada, Utah, southwest Arizona, and southeast California. For more detail on variability, Figures 4.5, 4.6, and 4.7 show data from the same source that illustrate the wet to dry range of projections for the mid-21st century. Figure credit: New Mexico State University; Arizona State University; University of Nevada, Reno; NOAA NCEI; and CISESS NC" (10).

• “Reduced flows in major river basins,” such as the Colorado and Rio Grande Rivers, have caused “conflict, competition, [and] collaboration” across the Southwest (11, 4). Use of water from the Colorado River is largely based on the Colorado River Compact, which was negotiated in the early 1900s in a time with ample water availability in the Colorado River Basin (4). The agreement therefore “allocated far more water than the river has since provided” (4). Changes in water policy and collaboration among communities will be required to address the “projected 30-year-average wet and dry spells on the Colorado River” (4). 
• Flooding caused by extreme precipitation events can occur and will threaten “life, property, and freshwater ecosystems” (11). Increases in flooding also lead to an increase in water-borne diseases “and exposure to toxic hazards” (13). Outbreaks of the West Nile virus, in particular, may increase “due to changes in the climate, human population, and mosquito distribution” related to changes in water availability (13). 
• Evapotranspiration, or evaporated and transpired water from the environment, is an important factor in water availability and greatly affects irrigation water demand (2). As temperatures increase, evapotranspiration will increase as well, reducing the amount of surface water available for irrigation and other uses (12). This will have the highest impacts on “dryland farmers growing rain-fed crops and producers raising livestock on rangelands” (12). 
• Forest water resources are frequently tied to extreme events, such as floods, droughts, and wildfire; following fires, water quality severely decreases as runoff of sediments, metals, and other potential pollutants are discharged into downstream water sources (6, 7). Warming and changes in precipitation affect wildlife, forest ecosystems, and water availability (7). 
• Disproportionate impacts: Communities that have been “systematically excluded from water management processes” - including Indigenous, Hispanic, and low-wealth communities - have and will continue to face disproportionate impacts of climate change such as access to clean water, availability of services and infrastructure, and exclusion from management decisions (11, 3, 4). Tribes and Indigenous communities have been disproportionately impacted by diseases, including COVID-19, due to a lack of clean water and sanitation services and the cost of water infrastructure (11). In addition to impacts on human health, climate change impacts to water resources will disproportionately affect Tribal communities that depend on agriculture for food security and/ or income (12). 
• Impacts to ecosystems due to changes in precipitation timing, form, and quantity: These impacts will include increased erosion; deterioration of riparian systems; risks to riparian, riverine, and threatened or endangered species; and increased populations of non-native species (14). Reduced snowpack also has limited ecosystem recovery after disturbances, such as wildfires, as the decrease in water availability creates a barrier to tree and shrub establishment after fires (14). Ultimately, this may lead to future shifts in “species competition or vegetation types” (14). 

“Climate change and climate-related disturbances are affecting the availability and quality of water from forests in the United States” (5)

Figure 7.9: "Panel (a) shows the percent of surface water originating on forest lands across the continuous US, illustrating that forests are a critical source of water. Panel (b) shows decadal average variations in average annual streamflow (measured in cubic feet per second [ft³/s]) from Hydrologic Unit Code 8 (HUC8) watersheds with greater than 50% forest cover, no impoundments above the streamflow gauges, at least four gauges per basin, and complete records back to 1950 in the Great Basin (number of HUC8 gauges = 6), Upper Colorado (16), Lower Colorado (5), and Rio Grande (4). Data generally show annual streamflow has been comparatively lower in more recent years compared to earlier decades. Panel (c) shows projected changes in suitable coldwater fish habitat in the Southeast under 3.6 degrees F and 7.2 degrees F warming air temperature over contemporary (2012) air temperature. Projections suggest suitable coldwater fish habitat will decline in the future as air temperatures increase. figure credits: (a) adapted from Liu et al. 2022; (b, c) USDA Forest Service" (5).

How are communities addressing these changes?

• Colorado River basin communities’ drought response and conservation measures “incentivize collaboration among diverse participants to develop innovative solutions” (11)
• “Transitions toward more sustainable water management under climate change [such as] innovative infrastructure (e.g., enhanced aquifer storage, recharge, and recovery) and institutional practices (e.g., integrative land and water management practices, changes in rate structures, water sharing agreements, and reservoir operations)” are being explored in the Southwest (11). Widespread support for these strategies has led to opportunities for education (11). 
• Localized adaptation strategies, such as “crop- and locality- specific combinations of irrigation, site management (e.g., use of cover crops), and cultivar selection,” have been implemented across the region (12). 
• Nature-based solutions (NBSs), or “ecosystem-based mitigation and adaptation opportunities,” are another pathway for adapting management practices to climate change; when NBSs are “managed in collaboration with affected communities and… local knowledge,” these can be effective solutions for addressing multiple management goals in an inclusive, cost-effective method (9). Ecosystem-based adaptations, a type of NBS, have been used in solutions such as “protecting and restoring floodplains to help reduce flood impacts or helping farmers cope with drought through soil conservation measures” (9).