Agriculture is a significant part of the culture and economy of the Southeast, and its success or failure has far-reaching effects. This lush region, historically one of the wettest in the nation, supports a unique combination of crops that include citrus fruits, vegetables, strawberries, sugar cane, fruits and nuts, rice, and field crops such as peanuts, cotton, corn, wheat, tobacco, and soybeans. About 50 % of the fresh winter vegetables in the United States are produced in Florida alone.

Because agriculture is one of the most weather-dependent of all human activities, climate variability can make agricultural production uncertain, posing risks to individual farmers, local, and regional economies. Climate variability and long-term climate change could present benefits as well as drawbacks to the crops of the Southeast region.

Local climate change and variability already have been documented in the Southeast; for example, the EPA, in a 1997 report, noted decreased precipitation over the past century in the Florida Keys and southern parts of the state and increased precipitation in central Florida and the Panhandle. Temperature trends have also been variable, with the average temperature of Ocala, Florida (in the central part of the state) having warmed about two degrees in the past century, even as other parts of the Southeast have cooled. In general, climate and particularly water variability in this region are closely linked with ENSO weather events. During El Niño years, the months from October through April tend to be cool and wet in the Southeast; during La Niña periods, those months are warm and dry.

The results from the two climate models recommended for use by the National Assessment suggest differing patterns of future climate for this region. One of the models projects conditions that will be more warm and moist and the other can be characterized as hot and dry. Even the warm, moist model results suggest that some areas, like the Gulf and Delta regions, could experience decreases in rainfall. Such site-specific differences have influences on the details of the agriculture and forest assessments. Increased irrigation can address some of the vulnerability of the region's crops to changes in rainfall, but these crops will still remain susceptible to high- and low-temperature stresses. Further, increased irrigation in some areas of the Southeast would be difficult because of low groundwater tables, the susceptibility to salt water intrusion problems along coastal regions if the fresh water level becomes too low, and the problem of salt residues from irrigation. Increased irrigation could result in increased leaching of pollutants that could compromise the quality of the runoff water. This could be especially important because pollutants tend to be concentrated during times of low flow. There is also the issue of competition for additional water by

Projected changes in 30-year average rainfed yields of four major crops in the Southeast by the years 2030 and 2090 using the Hadley model scenario.

In the discussion that follows, potential environmental impacts on agriculture in the Southeast are examined; social and economic impacts, closely connected and discussed jointly, follow. Strategies that could be helpful in addressing these impacts conclude this discussion.

The climate models recommended for study in this assessment project that average temperatures over the US could increase by about 5˚ to 10˚F over the 21^st century. The Southeast's temperatures were projected to increase by anywhere from 4˚ to 10˚F. The most significant change for this major food-producing area is projected to be an increase in the frequency of extremely hot summer days. Extremely hot weather and major precipitation variations are currently serious concerns for agriculture in the region because irrigation is not as prevalent in the Southeast as it is in other food-producing regions. This creates a greater dependence on rainfall for agricultural production.

Rainfall from the previous one to three years, which is stored as groundwater, is the primary water source for agricultural irrigation. Much of the replenishment of groundwater stores is the result of El Niño/Southern Oscillation (ENSO) events. However, even rainfall levels in wet months are insufficient to meet the growing demand for water in portions of the Southeast. Much of coastal Florida and southwestern Georgia already are experiencing groundwater overdrafts, or overuse of this stored water. One of the models projects droughts resulting from warmer temperatures and decreased precipitation. Such droughts would only increase the demand for water and create further water shortages. The other model projects an increase in water availability and that increase would reduce some of the present pressures on the water supply.

Temperature increases alone could have several effects on this region's agriculture. Continued increases in temperature could increase the yields of citrus by reducing losses to freezing events; they could also reduce the yields of citrus groves because of loss of a sufficient dormant period that these plants require. Warmer temperatures could increase the evapotranspiration rate (loss of water by the soil and by plants) and, in turn, the need for more extensive crop irrigation, a solution that is becoming more difficult because of the Southeast's increasingly limited water supply.

Increases in temperature beyond a plant's preferred range could result in heat stress during the day and increased nighttime respiration. Both stresses often result in reduced growth and decreases in potential yields. As temperatures increase, soils can become drier, which can suppress both root growth and decomposition of organic matter. With warmer and wetter soils, soil processes that affect plant fertility could be speeded-up. This acceleration of growth could require increased use of fertilizers, which would pose other environmental concerns. Should an increasing percentage of rainfall come in heavy downpours then run-off containing fertilizers, pesticides, and animal wastes from agricultural activities would contribute to reducing water quality for other uses.

The fertilization effect of higher levels of carbon dioxide on agriculture in the Southeast is uncertain. Many crops will benefit from increased levels of carbon dioxide in the atmosphere. However, how much benefit depends on the plant type, the temperature, the availability of water (even though increased CO2 generally makes plants more efficient users of water), and available plant nutrients. Further, some combinations of elevated carbon dioxide levels and temperature are more beneficial than others. If adequate water is available, increased carbon dioxide and temperatures often increase crop yields. In general, rice, soybeans, cotton, and peanuts benefit more from the fertilizer effect of increased levels of carbon dioxide than do corn, sugar cane, and sorghum.

However, if the Southeast experiences increased carbon dioxide levels and moderate temperature and precipitation increases, then the region is likely to experience only modest increases in yields of many crops. But if high temperatures (+3oF) and decreases in precipitation (-20% or more) accompany increases in carbon dioxide levels, reduced yields are likely to occur for all field crops without invoking adaptation strategies such as irrigation and fertilization. Increased carbon dioxide and rainfall could result in higher agricultural yields, but higher temperatures could actually shorten the growing season. A shortened growing season would decrease yields if, for example, plants produced fewer or smaller seeds and fruit.

Supplemental irrigation could reduce the risk climate change poses for agriculture in the Southeast. However, this solution could heighten the competition for fresh water among the agricultural sector and the other regional water users, including industrial users, communities with their growing populations, and water uses that enhance ecological sustenance. In addition, there is an important interaction between groundwater and surface water, because surface water helps recharge groundwater supplies. As a result, over use of groundwater for irrigation would likely harm the region's wetlands, lakes, streams, and aquifers and contribute to further subsidence (land sinking), which is already troublesome in parts of the region. Further, increased groundwater withdrawal is not always possible in Florida's low-lying communities because of saltwater intrusion into aquifers, an effect that will become more important as sea level rises. Groundwater is also not readily available in most of Alabama.

Because the Southeast yields a wide range of crops of high value, changes in the individual farm or the regional production capability would have disruptive effects on local economies and communities. Such stresses have already begun to take their toll, for example, corn yields have typically been high in La Niña years and low in years that followed. Historical records suggest that El Niño events cause a 26-percent, or $200-million, variability (+/-) in corn yield values in Alabama, Georgia, Florida, and South Carolina. El Niño events also reduce the production values of soybeans, peanuts, and tobacco, but not to the extent of the reduction in corn production. Because agricultural impacts can be both positive and negative as a result of climate variations, they are site specific and crop specific so that generalizations are difficult. Further effects on crop values as a result of a warming climate are likely to create additional stresses for some farm communities, exacerbating the reduction in the number of farm families whose numbers have already dwindled by 50% since 1920.

The amount of irrigated acreage in the Southeast is already expanding -- up 36% in the last decade of the 20^th century. The largest gains in crop productivity are occurring for areas that were previously dependent on rainfall, even though such steps typically require significant investments and stress already limited regional water resources.

Dryland yields changes in 2030(above) and 2090(below) without adaptation for various climate sensitivity scenarios. Source: Auburn University, Global Hydrology and Climate Center; University of Florida, Agricultural and Biological Engineering Department.

Several strategies could assist in mitigating the potential effects of climate change on agriculture in the Southeast. They include efforts to:

• Provide improved El Niño/La Niña forecasts with the needed lead-time and the accuracy to enhance effective agricultural and water use planning;
• Support programs and policies to make financial assistance more available to those in agriculture;
• Improve availability of timely updates and predictions of productivity, time-to-market, and other evolving characteristics of competing markets;
• Extend knowledge about economically viable alternatives to the present distribution of crops and methods;
• Develop plans and capabilities for planting crops and crop varieties that are better adapted for projected changes in temperature and precipitation;
• As climate changes, adjust field operations by, for example, switching crops; sowing earlier, later, or twice during the season; and conserving soil moisture through conservation tillage methods;
• Consider and introduce more efficient irrigation technologies, especially where water resources are becoming limited; and
• Invest in agricultural biotechnology to expand the set of crop options for responding to climate changes.