Climate Variability and Change in the Southwest

Part II: Symposium

Chapter 5

Southwest Regional Overview

Environmental Stresses and Social Concerns in the Southwest

Certain social and economic trends and environmental conditions make the Southwest especially vulnerable to climate change:

• The region is experiencing rapid population and economic growth, with tourism, development, retail, and other service sectors now making up much of the regional economy.
• An assured water supply is essential for municipal and industrial users and, to a certain extent, for irrigated agriculture and natural ecosystems (such as riparian vegetation and wildlife).
• The ranching, non-irrigated agriculture, and forestry sectors are dependent on the amount of soil moisture and the timing of rainfall.
• The restructuring of agriculture, due in part to global economic forces, is shifting the types of crops grown. In many cases, the new crop mix is much more water intensive. In other areas, agricultural land is being converted into urban developments.
• Intense differences in values and political conflicts exist over the use of land and water in the region, with disputes arising over local-versus federal-land ownership and control, resource use versus conservation and protection, and urban lifestyles versus rural livelihoods.
• Unresolved water rights for Native American tribes and binational treaty obligations with Mexico pose unique institutional challenges or uncertainties in the region to manage water and other natural resources.
• Differences in income and access to other financial or institutional resources make some segments of the society in region more vulnerable than are others to climate variations and change.

The rest of the chapter provides a socioeconomic profile of the Southwest and shows how each of these activities is affected by or vulnerable to climate change.

Economy

The economies of both Arizona and New Mexico are expanding relatively rapidly and are dominated by the service, retail, and government sectors. At first glance, these activities seem much less vulnerable to climatic variations such as drought than sectors such as agriculture, forestry, or industrial resource extraction.

Yet complex economic linkages both within and outside the region are such that impacts in one sector often affect others.

For example, heatwaves, floods, prolonged droughts, and snowstorms may affect crops, roadways, bridges, and other infrastructure, but also may change energy demand, alter retail sales, or increase insurance claims or hospital admissions in ways that affect service and retail sectors.

Key points

• The economies of Arizona and New Mexico are growing faster than most other states.
• Services and retailing are the largest sectors of the Southwest economy.
• More than 75 percent of employees work in sales, services, or government.
• Severe and prolonged climate events can have a significant direct impact on key economic sectors, as well as an indirect impact on related areas.

Lifestyle

It is important to remember that our climate has made positive contributions to the lifestyle and growth of the Southwest, attracting migrants and tourists, and enabling productive agriculture. Along the way, we have adapted to the stresses of a hot, dry climate through irrigation, air conditioning, and housing design.

The Southwest may provide a model for the rest of the country to adapt to global warming. But we must not forget that our adaptations have come at a cost--in the water transfers, energy demands, and environmental modifications that transformed the desert--and in some cases we may be reaching the limits of our adaptive capabilities.

Many have called for the adoption of more long-term and sustainable strategies, such as increasing reliance on solar energy, increasing energy efficiency, and decreasing per capita water use.

Key points

• The warm climate has attracted people to the Southwest and is an important draw for corporations, retirees, and tourists.
• In some ways the Southwest has already adapted to the warmer, drier, and more extreme climates that could be a result of global warming.
• Adaptations include large-scale water transfers and air conditioning, but these can be costly in terms of federal subsidies, environmental impacts, and individual water and energy bills.
• New, more sustainable strategies are needed to assure a high-quality lifestyle for the current population and future generations.

Land Use

Geographical patterns of vulnerability to climatic variation are suggested by the overall pattern and structure of land and water use in the Southwest.

As shown in Figure 5.1, nearly two-thirds of the land in both Arizona and New Mexico is used for ranching, and a quarter is in forests or parks. Both of these sectors depend on the soil moisture provided by rain and snow.

Hence, significant climatic changes (e.g. an extended drought) potentially can have a major impact over a large area of the Southwest. Irrigated cropland and urban settlements, while occupying relatively small areas, are vulnerable due to their heavy reliance on the delivery of groundwater or surface water supplies.

Key Points

• Pasture, forests, and parks occupy more than 90 percent of the land in Arizona and New Mexico.
• Ecosystems and human activities associated with these areas are particularly vulnerable to extended droughts and may be affected significantly by ecological changes resulting from long-term climate change.

Water Use

Though relatively small in its land use, irrigated agriculture--as shown in Figure 5.2--is by far the most extensive user of water in the Southwest. Municipal use is of growing but of secondary importance.

Vulnerability to climate is mediated by the rivers, surface reservoirs, and groundwater aquifers that supply most of the water for the region. But many aquifers are being mined and are only partly replenished by precipitation.

Hot, dry conditions bring on rapid evapotranspiration from crops and surface supplies.

Key points

• Irrigated agriculture is by far the largest user of water in the Southwest.
• Presently, water supplies in the Southwest are about 50 percent surface water and 50 percent groundwater.
• More groundwater is being pumped than replenished in most regions.
• Municipal water use is increasing with rapidly growing populations and economic development.

Colorado River and Rio Grande

The Colorado River (Figure 5.3, Plate 2) and the Rio Grande (Figure 5.4, Plate 2) have been called the lifeblood of the Southwest. Rights to their water have been fully allocated between nations, states, and different water users.

Figure 5.3. The Colorado River Basin (from Dettinger, 1997, on the U.S. Geological Survey Global Change Research Program Web site at http://geochange.er.usgs.gov/sw/changes/natural/codrought)

Figure 5.4. The Rio Grande Basin (from the Rio Grande Alliance Web site at http://www.riogrande.org/basin/basinmap.htm)

Large fluctuations in year-to-year flows in the rivers or their tributaries (Figure 5.5, Plate 2)--caused mainly by climatic variations--creates stresses for water- management institutions and conflict between users.

Figure 5.5 Mean annual flow of the Colorado River in million acre feet (from Diaz and Anderson, 1995)

Understanding variations and potential changes in the flows of these rivers is critical for water resources, energy and ecosystem management in our region.

Key points

• The Colorado River and the Rio Grande systems are the most important surface water supplies in the Southwest. Rights to the flows are fully allocated.
• Flow in these basins varies from year to year especially in relation to snow conditions in the upper parts of the basins. For example, in 1983, the Colorado River's annual flow was over 22 million acre feet (MAF), while in 1954, it was just slightly more than 10 MAF.
• International treaties divide flows with Mexico and domestic interstate compacts allocate flow between the U.S. states. The allocations stipulated in these agreements, particularly for the Colorado River, were based on periods of unusually high flow. Under present climatic conditions, the flows are inadequate to meet all potential allocations. Climate variability and change may threaten these international and interstate management arrangements if flows become further reduced.

Agriculture and Water

As mentioned earlier, irrigated agriculture uses more water than any other sector, only a portion of which is returned to the system. In hot, dry years, water supplies are limited yet crops require more water to survive.

In Arizona, irrigators are accumulating water credits for water rights they own but do not use because of low crop prices. Institutional changes may mean that farmers can sell these rights to the municipal sector and that as a result, overall water demand may level off or even decline. This could reduce climatic vulnerability.

Key points

• Irrigation is necessary for most crop production in the Southwest, and agriculture is a major water user and holder of water rights.
• Over half the water withdrawn for irrigation is consumed through evapotranspiration or is incorporated into crops, 17 percent is lost by evaporation from lakes and canals or from leaks, and only 29 percent returns to streams or groundwater.
• Climatic variations influence water supplies. High temperatures increase crop water demands.
• Land and water are shifting away from agricultural to urban use.

Urban Water Use

In the Southwest--where most of the population dwells in urban areas--populations are growing very rapidly, and municipal water use is expected to grow at least 20 percent by 2040.

Water use varies considerably between cities as a result of urban design and individual behavior. Figure 5.6 shows a dramatic difference in per capita water use between, for example, Santa Fe and Las Vegas.

Urban demands also vary seasonally due to climate and other conditions, with the greatest demand in summer months. Could climate change limit urban development in the Southwest?

Key points

• Urban populations are growing rapidly in the Southwest, at rates greater than three percent per year.
• Water use per capita varies considerably by community.
• Water use also varies seasonally, with peak demand in the summer months.
• Urban water demand is increasing and is expected to grow at least 20 percent by 2040.

Water Use in Indian Country

Resources on tribal lands have been severely affected by recent droughts. For example, the San Carlos Apache tribe had to deal with the drying up of a major reservoir and the resulting loss of income, such as from reduced fishing and water-recreation fees.

Water use is increasing on many reservations, and if water rights are settled further increases will be possible. Several groups plan to expand irrigated agriculture as illustrated by this data from the Arizona Department of Water Resources.

How vulnerable will these new irrigated areas be to climatic variation ? Will the transfer of rights increase drought impacts for other sectors?

Key points

• Agriculture, water supplies, and health are vulnerable to climate change on tribal lands in the Southwest.
• Settlement of Indian water right claims (in Arizona, about 3.1 million acre-feet) will increase overall water demand and shift drought vulnerabilities.

Climate Extremes: Floods

Variations in year-to-year precipitation and storm severity can cause serious flooding in the Southwest, particularly during the summer monsoons and spring snowmelt (Table 5.1).

During the summer of 1997, several flood-related deaths and major economic losses occurred in the region. Nationally, floods cost billions of dollars in insurance and personal losses, and in federal, state and private emergency relief. Insurance companies are very concerned about climate change.

Severe floods and droughts have often affected up to 40 percent of the area of the Southwest (see Figure 6.4 in next chapter).

Table 5.1. Chronology of major and other memorable floods in Arizona and New Mexico (from Paulson et al., 1989)

Climate Extremes: Drought

While several significant droughts have occurred during the past century or so, we only have to look at the summer of 1996 to see some of the impacts of drought in the Southwest. News articles document the losses on ranches, tribal lands, and forests as the soil and wells dried up:

• In 1996, severe drought devastated farms and ranches in Arizona and New Mexico.

• The impact of drought on tribal lands was especially serious. The San Carlos reservoir northeast of Phoenix dropped to 25 percent of its volume.

DROUGHT IN ARIZONA AND NEW MEXICO

Table 5.2. Chronology of major and other memorable droughts in Arizona and New Mexico (from Paulson et al., 1989)

Ranching

The recent (1995-96) drought also highlighted the vulnerability of ranching to climatic variations. Cattle sales increased (Figure 5.7) and several ranches went out of business as rangelands and wells dried out and feed costs soared.

But factors other than local climate have contributed to the problems of the ranching sector. Global grain reserves were low, contributing to high feed prices, and a multiyear drought in Mexico overwhelmed border markets with low-priced stock.

Key points

• Ranching by nature is particularly vulnerable to drought.
• In 1996, ranchers in Arizona and New Mexico faced drought, dry wells, high feed prices and low stock prices when they tried to sell.
• External factors such as low global grain reserves and drought in Mexico increased the vulnerability of the ranching sector in Arizona, New Mexico, and other U.S. states.
• Some smaller ranches (i.e., with fewer than 50 head) went out of business during this time period.

Energy

Another climate-sensitive sector is energy, with both supply and demand varying with climate. Hydroelectric supplies are clearly the most climate sensitive. Overall electricity demand varies with seasons and from year to year (Figure 5.8).

Extreme events can cut power supplies, and it is important to remember that many people cannot afford to heat or cool their homes properly.

Figure 5.8. Tucson, Arizona, residential energy demand

Key points

• Hydroelectric generation is very dependent on climate.
• Energy consumption also varies seasonally and interannually according to temperatures.
• Heatwaves and severe storms can disrupt power supplies.
• Those who cannot afford to pay for heating and air conditioning may suffer cold and heat stress-related illness and mortality.

Forest Fires

Another highly sensitive sector is forestry, where droughts cause economic and ecological damage. This too has been illustrated by severe fires and high economic costs of losses and fire fighting in recent years.

Fire frequency is influenced by climate variability but also by management decisions such as fire suppression and forest-access policies.

Key points

• Droughts increase fire potential by creating tinder-dry forests.
• Fire potential also depends on how forests are managed.
• Extreme fire danger ratings may close forests to users and force fire crews to suppress fires, countering ecosystem management principles.
• The U.S. Forest Service has allocated $36 million for fire management in 1998 in the Southwest.

Recreation and Tourism

Recreation and tourism are very important to the economy and to the lifestyle of the Southwest. Many climatic factors are important, including snowfall, river flows, irrigated landscape maintenance, and heat stress.

A variety of tourist enterprises is affected by climate variability and could be impacted by climate change. These include skiing, rafting, and bird watching,

Key points

• The warm climate of the Southwest offers many recreation opportunities.
• Climate change could affect many activities by reducing river flow for white-water rafting and water for irrigating golf courses.
• The number of bird species and thus bird watchers could decline if habitats are altered.
• Changing snowfall patterns would affect the ski industry.

These are just some of the ways in which climate affects society and economy in the Southwest. The climate sensitivities and impacts provide an important reason for trying to understand better what is happening to our climate and for finding ways to better use climate information in our planning and decisions.

Sources

Dettinger, Michael D. 1997. Coping With Severe and Sustained Drought in the Southwest. From online USGS Web Workshop (geochange.er.usgs.gov).

Diaz, Henry F., and Craig A. Anderson. 1997. Precipitation Trends and Water Consumption in the Southwestern United States. From online USGS Web Workshop (geochange.er.usgs.gov).

Paulson, R.W., E.B. Chase, R. S. Roberts, and D. W. Compilers. 1989. National Water Summary 1988-89: Hydrologic Events and Floods and Droughts. U.S. Geological Survey Water-Supply Paper 2375, 591p.