Climate and Water Science Advisory Panel — Summary
Climate Change in New Mexico Over the Next 50 Years: Impacts on Water Resources
- The earth is warming in response to increasing atmospheric carbon dioxide, which will result in greater aridity in many parts of the world, including New Mexico.
- Global climate models driven by increasing greenhouse gases project an average temperature increase across New Mexico of between 5° and 7°F over the next 50 years.
- The coupled trends of increasing temperature with no increase in average precipitation enables a confident projection of increasingly arid conditions, resulting in decreased soil moisture, stressed vegetation, decreased snowpack, and more severe droughts.
- All water in New Mexico originates as rain or snow, but most returns to the atmosphere. The small percentage of rain and snow (~3.5%) that supplies groundwater and surface water will decrease as aridity increases, reducing water resources that support wildlife habitat and are available for human use and consumption.
- Climate is a fundamental driver of ongoing and future vegetation changes that will affect the distribution and abundance of water resources.
- Delicate soils on New Mexico’s landscapes will be damaged by increasing temperature, fire, and erosion, leading to dustier conditions and less hospitable environments for vegetation.
- New Mexico has a dynamic landscape; climate change and increasing fire frequency over the next 50 years will amplify recently observed instability, potentially damaging infrastructure and endangering the public.
- Surface water supply shortages will drive both agricultural and municipal/industrial water users to rely more heavily on groundwater, a limited resource.
- A warming atmosphere could increase the magnitude of future storms, leading to extreme precipitation events and increased flooding.
- The quality of surface and groundwater resources will be impacted by warming climate; the most likely effects may include increased temperature along with higher concentrations of nutrients, dissolved oxygen, and pathogenic organisms.
- Statewide impacts will include higher temperatures, greater aridification, lower water quantity and quality, and possibly increased extreme precipitation events. But the topographic complexity of New Mexico will lead to some prevalent impacts within four distinct regions:
- High Mountains—less snowfall and higher evapotranspiration, fires, and erosion, and loss of vegetation
- Northwestern High Desert—loss of soil, increased dustiness, possible arroyo incision and change in vegetation patterns
- Rio Grande Valley and Southwest Basins—lower river flows (25% decrease in Rio Grande flow in 50 years) and greater loss of water from reservoirs
- Eastern Plains—loss of soil, desertification, increased dustiness and possibly higher incidence of extreme precipitation events
- Research topics that need to receive increased attention from the state’s science community include: better understanding of precipitation; improved modeling; and observational data acquisition (aquifer levels, soil moisture, and landscape and vegetation response).
Below is an overview of the report that summarizes each chapter. For a thorough analysis, consult each chapter in the full report.
(see Chapter I)
The Earth is warming in response to increasing atmospheric carbon dioxide, and this warming will result in greater aridity in many parts of the world, including New Mexico. The primary observed and projected impacts include warmer temperatures, decreased water supply (partly driven by thinner snowpacks and earlier spring melting), lower soil moisture levels, increased frequency and intensity of wildfires, and increased competition and demand for scarce water resources. These effects may be accentuated by positive feedback cycles, tipping points, or compounding events. This report compiles, assesses, and integrates existing peer-reviewed published research, technical reports, and datasets relevant to the broad topic of changes to New Mexico’s climate over the next 50 years and resultant impacts on water resources, and represents the scientific foundation upon which New Mexico’s 50-Year Water Plan will be developed. New Mexico is a geographically, geologically, and climatically diverse state. Projected climate changes, and related impacts on water resources in different geographic areas of New Mexico over the next 50 years, will vary not only by region but also as a function of local elevation, and even by hillslope orientation. The currently observed trends of increasing temperature and constant, but more variable, precipitation will continue over the next 50 years.
Future Climate Projections
(see Chapter II)
Global climate models driven by increasing greenhouse gases project an average temperature increase across the state of New Mexico of between 5° and 7°F over the next 50 years. This regional temperature increase follows the trend observed over the past half-century, at a somewhat amplified rate, with the northwest corner projected to experience a slightly higher rise during the same period. Although all models indicate significant increases in temperature, these models do not consistently project a significant change in average annual precipitation across the state, mirroring the absence of a clear trend in recent historical observations. However, some consistent differences in seasonality of precipitation emerge. During the winter, the northern mountains may receive somewhat more precipitation, whereas the southern parts of the state may be drier. Spring precipitation, critical for snowmelt runoff and ecosystems, may decline. Also in the southern part of the state, a trend towards somewhat stronger monsoonal activity may result in more summer precipitation, perhaps shifting toward somewhat later in the year.
The coupled trends of increasing temperature with no clear increasing trend in precipitation leads to a confident projection of increasingly arid conditions, including decreased soil moisture, stressed vegetation, and more severe droughts. Snowpack and associated runoff are projected to decline substantially by 2070, generating diminished headwater streamflow. Warmer temperatures will also cause lower river flows due to increased evaporation as rivers flow downstream. The impact of climate change on New Mexico’s resources are, unfortunately, overwhelmingly negative.
Impacts on the Land-Surface Water Budget
(see Chapter III)
All water that we use in New Mexico originates as rain or snow falling onto the landscape, which either goes to groundwater, surface water, or returns to the atmosphere. Of the precipitation that falls on the state, 1.6% runs off into streams and rivers and 1.8% infiltrates into the ground, recharging subsurface aquifers. Much larger proportions are transpired by plants (78.9%), or evaporated (17.7%). The impact of climate change on all of these pathways will affect our state’s water budget. Notably, because of the larger percentages of water lost to evaporation or transpiration, even very small changes in these factors will result in large changes to runoff and recharge. As mentioned in Chapter 2, the climate will continue to warm over the next 50 years without a likely increase in precipitation, leading to greater statewide aridity. Hydrological modeling indicates declines in both runoff and recharge going forward, amounting to 3 to 5% per decade for both quantities. Historical trends in runoff indicate significant year-to-year variability, as do trends in soil moisture and recharge. But all are generally decreasing, consistent with the results of climate models that project a drying climate. Combining the historical trends with modeling of future changes, significant decreases in runoff and recharge seem very likely.
Terrestrial Ecosystem Responses and Feedbacks to Water Resources
(see Chapter IV)
Climate is a fundamental driver of ongoing and future vegetation changes in New Mexico. Future changes in vegetation will affect the distribution and abundance of water resources in New Mexico. Major shifts in climate and vegetation across New Mexico’s landscapes have occurred in the past, but the scale and rate of recent and projected climate change is probably unprecedented during the past 11,000 years. Recent warming, along with frequent and persistent droughts, have amplified the severity of vegetation disturbance processes (fire, physiological drought stress, insect outbreaks), driving substantial changes in New Mexico vegetation since the year 2000. Ongoing and projected vegetation changes include growth declines, reduced canopy and ground cover, massive tree mortality episodes, and species changes in dominant vegetation—foreshadowing more severe changes to come if current warming trends continue as projected. Such major alterations of New Mexico vegetation likely will also have substantial ecohydrological feedbacks with New Mexico water resources. Since water-related environmental stresses occur in parallel with water supply shortages for people, such climate-change driven water stress could lead to increasing conflict between management of declining water availability for human use (e.g., irrigation) versus "wild" water retained for the maintenance of historical ecosystems.
Impacts on Soils
(see Chapter V)
Soils play a strong role in determining how New Mexico’s diverse landscapes will respond to climate change. Soil cover acts like a sponge, holding in water that falls as rain or snow. The presence of soil supports vegetation, and substantially reduces runoff and erosion. Soil enhances other processes such as infiltration of water and aquifer recharge. Soils can be damaged by a warming climate. Loss of vegetation in the northwest high desert and eastern plains, where soils are not well developed and easily damaged, will lead to dustier conditions in much of the state. On mountain hillslopes, the loss of vegetation cover in response to ongoing climate change will increase soil erosion, which then increases hillslope runoff. This, in turn, causes additional increases in soil erosion and bedrock exposure, which can largely prevent widespread recolonization by most plants, including trees. Soils on mountain hillslopes that face south, which are typically hotter and drier, will be damaged sooner by a warming climate than those on generally north-facing hillslopes that are slightly cooler and moister. Soils take many thousands of years to form, so these hillslopes will increasingly support sparse forests, or, in some circumstances, be entirely deforested. These changes are already well underway in some mountains in New Mexico.
Landscape Change, Fire, and Erosion
(see Chapter VI)
New Mexico has a dynamic landscape; climate change and increasing fire frequency over the next 50 years will amplify recently observed instability. As the climate changes to warmer conditions, less rainfall will infiltrate into aquifers, leading to increased overland runoff. Landform processes can be complex but, in general, the predicted changes in climate and precipitation will lead to increased upland erosion caused by runoff and increased downstream sediment deposition. Canyons, mesas, and small basins or valleys filled with sediment will be particularly affected. Rapid rearrangement of sediments by water is disruptive and potentially hazardous to ecosystems and societies. Dramatic examples of accelerated erosion following the Whitewater–Baldy, Las Conchas, and other wildfires here in New Mexico illustrate the types of hazards created when forested landscapes are severely burned. Post-wildfire erosion is typically initiated by intense rainfall events. Given that both the number of wildfires and rainfall intensities are likely to increase as the climate warms, New Mexico can expect to see increases in widespread erosion and sedimentation across and downstream from upland forested areas in the state. The large volume of sediment predicted to be on the move will be of concern for many reasons, including filling reservoirs, choking channels, and blocking or destroying infrastructure. Positive feedback loops lead to further reductions in slope stability.
Surface and Groundwater Supplies and Impacts on Users
(see Chapter VII)
Surface-water supply shortages induced by climate change will drive both agricultural and municipal/industrial water users to rely more heavily on groundwater. Less surface water will lead to lower recharge to some groundwater aquifers. The Lower Rio Grande is an in-progress example of this effect, with prolonged surface-water shortage leading to plunging groundwater levels. All water users in the state will experience decreased water availability as the climate warms and aridification occurs. This decrease in water availability will likely trigger changes of use from lower-value uses to higher-value uses, and this generally means a migration from agricultural water use to municipal/industrial uses. New Mexico has a rich and diverse history of water use that is central to its collective identity. This permanent shift towards a more arid climate will upset the hydrologic balance that has weathered cyclical drought. The declining mean and increasing variability in the surface-water supply is not cyclical, and recovery periods will be fewer and farther between. This will require difficult and divisive policy and management decisions, undoubtedly accompanied by an increase in disputes and litigation. New Mexico is by no means alone in facing these daunting challenges.
Extreme Precipitation and Stormwater Management
(see Chapter VIII)
A warming climate could increase the magnitude of future storms, leading to extreme precipitation events and increased flooding in New Mexico. Warmer air can hold more water vapor, approximately 7% more moisture for each 1°C (1.8°F) increase in temperature. Global climate models (GCMs) used to predict future conditions are not detailed enough to simulate individual storms. Three major types of storms occur in New Mexico: short duration, high intensity local storms in summer (usually monsoonal); long duration general storms (caused by winter weather fronts); and occasionally the remnants of tropical storms. The principal risk from extreme precipitation events will be flooding in small watersheds from high-intensity local storms, precisely the storms that are hardest to simulate in climate models. Large-scale regional studies have corroborated the hypothesized increase in extreme precipitation with warming temperature, but few such studies exist on the impact on local storms in the four-corner states. A study of extreme precipitation events in Colorado and New Mexico was recently completed and has updated estimates of the magnitude of severe storms possible in our state. Data and modeling studies suggest that while the risk of the most severe storms might not increase beyond current estimated values, less severe (but still high intensity) storms may occur more frequently than at present, which could impact existing stormwater management infrastructure.
Impacts on Water Quality
(see Chapter IX)
A warming climate may affect the quality of both surface and groundwater resources in New Mexico; the most likely effects may include increased temperature along with concentrations of nutrients, dissolved oxygen, and pathogenic organisms. Although the quality of groundwater may be affected, it is likely to be limited to locations with shallow groundwater depth and where surface water recharges the aquifer. The New Mexico Environment Department publishes an assessment of the quality of the state’s surface waters every two years. This recent assessment finds that the major causes of impairment of streams and rivers are temperature, nutrients (nitrogen and phosphorous compounds), E. coli bacteria, turbidity, and dissolved aluminum. The parameters most likely to be affected by a warming climate are temperature, nutrients, and E. coli concentrations. Studies suggest that loss of riparian vegetation is the biggest factor affecting water temperature. Modeling studies of the effects of climate warming on nutrient concentrations are somewhat inconclusive. Recent investigations suggest that E. coli concentrations may increase as a result of microbial regrowth in warming stream sediments in slow moving stream reaches. A future threat to water quality is runoff following wildfire events. Postfire runoff can cause depletion of dissolved oxygen far downstream from the burned watershed.
Statewide and Regional Impacts
(see Chapter X)
All regions of New Mexico will be affected by climate change, but the topographic complexity of the state will generate distinct impacts by location. The average temperature will warm across the state, probably between 5° and 7°F, whereas average precipitation is likely to remain constant, even if more variable from year to year, with the possibility of more extreme precipitation events. Snowpack, runoff, and recharge will decline, stressing both surface and groundwater resources. Surface-water quality will decline. Plant communities will be stressed by higher temperatures and greater aridity, leading to more extreme wildfires and increased erosion. Damage to soils, related to a number of factors, will create greater atmospheric dustiness and lower water infiltration to aquifers.
Although latitude plays a role in the effects of climate change, the bigger impact in New Mexico is related to local topography and elevation. For the purposes of this report, we are dividing New Mexico into four physiographic regions, based on projected climate change impacts and associated effects on hydrology. These four regions, which are defined by a combination of latitude and topography, are: the High Mountains (northern mountains, Gila/Mogollon–Datil, and Sacramento Mountains); the Northwestern High Desert (Colorado Plateau, San Juan Basin, and Zuni Mountain region); the Rio Grande Valley and Southwestern Basins; and the Eastern Plains.
Recommendations: Data Gaps and Challenges
(see Chapter XI)
The process of evaluating and projecting climate change in New Mexico over the next 50 years, and examining the impacts on water resources, illuminated a number of research topics that should receive attention from the state’s science community. A highpriority research target is to better understand a number of facets of precipitation that New Mexico might experience over the next half century. These would include seasonality of precipitation, snowpack dynamics, and extreme precipitation. Better understanding of the latter would allow New Mexico planners to be able to consider how to put localized, heavy precipitation to good use, and to mitigate damage associated with flooding. Climate, hydrology, and ecology numerical models, which allow projection of conditions and behaviors of these natural systems in New Mexico over the next half century, are also needed. Finally, a number of observational data gaps have been identified, most notably a thorough and geographically distributed assessment of the water levels in New Mexico aquifers. Other topics include impact of climate change on soil moisture and groundwater quality, as well as landscape and ecological responses to climate change, both in terms of magnitude and timescales of response. This can be carried out, in part, by long-term ecological monitoring.