Climate Variability and Change in the Southwest

Part III: Workshop: Sectoral Issues

Chapter 11

Natural Environment

Workshop report prepared by:

Robert S. Thompson, Chief Scientist
Global Change & Climate History Program
U.S. Geological Survey
Denver, CO

Workshop Participants (2 sessions): Laura Huenekke and James Shuttleworth (facilitators), Margi Brooks, David Brookshire, Tim Brown, Kevin Dahl, Prabhu Dayal, Robert Gerard, Bruce Goff, Jim Gosz, Gerald Gottfried, William Harris, Robinson Honani, Hoyt Johnson III, Bruce Kimball, Dave Kirtland, Cynthia Lyndquist, Beau McClure, Michael Molitor, Curtis Monger, Melvin Podwysocki, Kelly Redmond, Richard Reynolds, Marco Rivera, Marja Shaner, Everett Springer, Sheridan Stone, Robert Thompson, Selso Villego, Meg Weesner, Douglas Weiner, Jake Weltzin, Larry Winter

Ecosystems, hydrological systems, and the land surface respond directly to many aspects of climatic variations and climate change and thus may provide "early warnings" of the consequences of such fluctuations.

Historical records and geologic studies indicate that the landscapes and ecosystems of the Southwest have continually changed in response to climatic variations over time-spans from decades to tens-of-thousands of years.

Large changes in the landscape may be expected in the future as ongoing climate change interacts with human use of the land and natural resources. Society in the Southwest will have to adapt to changes in the availability of water and other resources, and to transformations of the appearance and composition of ecosystems.

The native vegetation and wildlife of the Southwest are central to the "sense of place" that people feel in regard to this region, and ecosystem changes may alter this perception.

Impacts and Vulnerability

The assessment of the impacts and vulnerabilities of the southwestern environment is based on the perceptions, beliefs, and values of those undertaking the task.

A consensus must be developed on the processes and features that must be maintained in the environment and ecosystems of the Southwest.

Should the lands, the natural processes, or the species and features of the region be preserved? What is more highly valued when preservation of one aspect of the environment conflicts with another or with a societal need?

Although change is a natural part of the southwestern environment, have human activities accelerated the rate of change to an unacceptable degree?

For ecosystems in particular, society must decide how "natural" an ecosystem needs to be. Should ecosystems be maintained in a fashion that maximizes diversity and biomass? Should they be self-maintaining and adaptable? How valued are the roles of natural ecosystems in fire and watershed management, in the maintenance and regeneration of soil, and in the sequestration of carbon?

The rapid population growth of the Southwest will increasingly affect the natural environment of the region and may increase its vulnerability to climatic variations.

In other words, even disregarding the possibility of global warming, climatic fluctuations such as those seen over the past century will have large impacts in the Southwest as the increasing human population demands more water and other resources.

The impacts of climate change in other regions could affect the rate of migration into the Southwest and thus accentuate these impacts.

The environment of the Southwest has changed during the historic period due to agriculture, ranching, other human activities, and due to the invasion of alien species.

Given this backdrop of human-induced change, it is difficult to assess whether on-going ecosystem response to climatic variations exceeds those in the historical record. Human activities, perhaps in concert with historical climatic fluctuations, have caused the regional extinction of wolves, grizzly bears, and other animals.

Land-use and urbanization are closing many of the natural corridors for the movement and migration of wildlife, avenues that may be important for the dispersion of plants and animals in reaction to future climatic variations.

Riparian habitats are of great importance in this regard, both as migration corridors and as habitats for a large number of species. The "sky island" habitats of the Southwest mountain ranges are particularly vulnerable to climatic change, and presently endangered species may face extinction. The reproductive cycles of animal species may be disrupted throughout the Southwest, and changes in selective pressures will impact both plants and animals.

The changes in abundance and geography of species, coupled with regional or total extinction, will change the ecosystems of the Southwest. A measure of the biodiversity of the Southwest has already been lost, and much more may be lost in the future with increasing pressure from human-population growth, habitat loss, and climatic variations.

Desert ecosystems are often dominated by a few plant species, and environmental changes that impact those key species may have wide-ranging impacts on the ecosystems.

Climatic change may accentuate the rate of loss, and alien species may gain competitive edges over native species due to climatic variations.

Climatic fluctuations and changes may also impact agricultural productivity, as variations in the severity of winter freezes and other climatic factors may lead to increases in insect populations and other agricultural "pests."

Human- and climate-induced changes in fire regimes may alter the balance of species and may have impacts on watersheds as well. Water quantity and quality issues will continue to be central to societal concerns about climatic change and land use.

Flooding may increase as soil loss is accentuated by human activities and climatic change, and the withdrawal--and non-replenishment under the current climate--of groundwater for human use not only will affect directly the land surface through subsidence but also will impact water quality.

Soil loss, arroyo-cutting, and other forms of increased erosion will lead to increased sediment loads in the rivers and, consequently, to increased infilling of reservoirs.

The loss of cryptobiotic soils will impact many aspects of the ecosystems, and enhanced surface instability in general may increase dust and visibility problems. The potential loss of the Southwestern "sense of place" may impact recreational opportunities and the associated industries.

The environment of the Southwest will be affected by changes in both the mean climate of the region and by changes in extreme weather events. Small changes may be important for some issues, particularly in ecosystems and erosion processes.

The abruptness of climatic change may also be important, with the same degree of change having a larger effect if it occurs over a short period of time.

Minor changes in climate variability may affect crop yields, both directly and through their effects on pest outbreaks.

Future changes in atmospheric carbon dioxide concentrations will directly affect plant growth and may alter the competitive balance of species within the ecosystems and affect overall primary productivity.

Responses

Responses to climate-induced changes on ecosystems in the Southwest have varied. Many recognize that cattle ranching as currently practiced across most of the Southwest is not sustainable and with recent droughts, ranchers have had to decrease herd size by 80,000 head.

The U.S. Forest Service has acknowledged the importance of fire in maintaining forest health, and has implemented selective anti-fire suppression measures.

Utility companies understand the role that vegetation, such as the saguaro cactus, play in carbon sequestration. Programs such as GLOBE have been designed to educate today's youth on climate change are have been implemented in schools around the Southwest.

Research and Information Needs

Research is required to close gaps in the current understanding of interconnected landscape and ecosystem processes, in how such processes respond to climatic variations, in what the natural ranges and rates of changes that occurred under natural conditions in the Southwest and in

how human activities have altered these processes and rates of change.

Models should be developed not necessarily to predict the future, but rather to organize research activities, identify information gaps, and to investigate the interconnections among processes.

Such models can be used in uncertainty analyses and sensitivity tests, and to look for non-linear reactions to climatic changes. These efforts should provide the basis to formulate and test hypotheses about how the Southwest environment will respond to future climatic changes and changes in land use.

Efforts should be made to understand the patterning and rates of change of the Southwest's climate over various time scales, from annual to millennial in length. Does the current range of climatic variability fit into the natural patterning of change, or can we detect a human-induced element of change?

In the area of primary data collection in the natural world, long-term studies should be conducted to understand the connections among biological, climatic, surficial process, and hydrological systems in different environments in the Southwest. Some environments and processes may be sensitive to changes in the mean climate, whereas others may respond to changes in extremes or in variability.

Ecosystem and landscape changes should be closely monitored at a series of long-term protected sites and in a variety of environments. Such plots might be placed on National Park Service or other protected lands.

Special efforts should be devoted to monitoring and understanding the behavior of invasive alien species. These species are currently having large effects on the Southwest's ecosystems. Will they thrive under future climatic conditions and increasingly outcompete native species?

Scientists should develop scenarios of the potential future environmental impacts of climatic change on the Southwest and use these to communicate the issues to the public. Scenario development will also identify gaps in data and in the understanding of processes.

Given the public awareness of El Niño/Southern Oscillation (ENSO) effects on the climate of the region, it could be used as the center of one scenario of possible future climate variation and its consequences.

Regional climate models may provide sufficient structure to permit investigation of potential future climates of the Southwest based on numerical climate models. Such models can be used to explore the potential regional consequences of changing levels of carbon dioxide and other aspects of the global climate system.

Climate models and scenarios should feed into new ecosystem and land-surface models that allow the investigation of the broad-scale impacts of climate change. Sensitivity analysis can then be used to investigate how short-term land-use or political decisions can impact the environment and how small changes in one aspect of the environment influence the rest of the system.

Uncertainty analysis can also be employed to determine if other factors may have caused the observed changes. These studies could then form the basis for communicating the issues and concerns about vulnerabilities to policymakers and to the public.

Improved methods and channels of communication are necessary to direct relevant climatic and environmental data to potential users. Federal, state, and other governmental agencies must improve their intercommunication and foster policies that work across boundaries and borders.

These agencies should seek to build partnerships among themselves, with the private sector, and with the public to increase the regional scope, rationality, and effectiveness of ecosystem and landscape management.

Scientists should participate in this process and should also seek to reach out to the public through increased participation in GLOBE and other programs.

Policy Issues

Political leaders should be involved in the effort to develop a consensus view of what should be preserved in the Southwest's landscapes and ecosystems.

Current regulations place constraints on land managers and often result in conflicting and overlapping mandates. Land-management agencies require policies that give them more flexibility to respond to climate change.

Land-management agencies should utilize scientific data for decisionmaking and should seek to develop common goals and strategies across institutional and geographic boundaries.

Zoning laws, taxes, and other governmental tools should be used to channel growth to preserve corridors for migration and important habitats. A regulatory environment needs to be developed that is aimed at a healthy environment overall, rather than at the maintenance of single species.

The endangered species act mode of a regulation forces agencies to focus on individual species. We need policies that will shift regulatory mandates to a broader scale of species management while including single species as a part of it. Policies should reflect the prioritization of issues and objectives identified by new research.

For additional discussions on this topic, see the presentations for Panel 2: Natural Ecosystems, in Chapter 8.