Prasanna Gowda, USDA Agricultural Research Service
Jean L. Steiner, USDA Agricultural Research Service
Tracey Farrigan, USDA Economic Research Service
Michael A. Grusak, USDA Agricultural Research Service
Mark Boggess, USDA Agricultural Research Service
Georgine Yorgey, Washington State University
Susan Aragon-Long, Senior Scientist
Allyza Lustig, Program Coordinator
<b>Gowda</b>, P., J.L. Steiner, C. Olson, M. Boggess, T. Farrigan, and M.A. Grusak, 2018: Agriculture and Rural Communities. In <i>Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II</i> [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 391–437. doi: 10.7930/NCA4.2018.CH10
Food and forage production will decline in regions experiencing increased frequency and duration of drought. Shifting precipitation patterns, when associated with high temperatures, will intensify wildfires that reduce forage on rangelands, accelerate the depletion of water supplies for irrigation, and expand the distribution and incidence of pests and diseases for crops and livestock. Modern breeding approaches and the use of novel genes from crop wild relatives are being employed to develop higher-yielding, stress-tolerant crops.
Climate projections to the year 2100 suggest that increases are expected in the incidence of drought and elevated growing-season temperatures.86 Elevated temperatures play a critical role in increasing the rate of drought onset, overall drought intensity, and drought impact through altered water availability and demand.87,88 Increased evaporation rates caused by high temperatures, in association with drought, will exacerbate plant stress,89 yield reduction,90,91,92 fire risks,93,94,95,96 and depletion of surface and groundwater resources.97,98,99,100 Soil carbon, important for enhancing plant productivity through a variety of mechanisms,101 is depleted during drought due to low biomass productivity, which in turn decreases the resilience of agroecosystems.23 In 2012, the United States experienced a severe and extensive drought, with more than two-thirds of its counties declared as disaster areas.102 This drought greatly affected livestock, wheat, corn, and soybean production in the Great Plains and Midwest regions 44,103,104,105 and accounted for $14.5 billion in loss payments by the federal crop insurance program.106 From 2013–2016, all of California faced serious drought conditions that depleted both reservoir and groundwater supplies. This lengthy drought, attributed in part to the influence of climate change,88,107 resulted in the overdrawing of groundwater, primarily for irrigation, leading to large declines in aquifer levels (Ch. 3: Water, KM 1).98,108 In 2014, the California state legislature passed the Sustainable Groundwater Management Act to develop groundwater management plans for sustainable groundwater use over the next 10–20 years.109,110,111
Average yields of many commodity crops (for example, corn, soybean, wheat, rice, sorghum, cotton, oats, and silage) decline beyond certain maximum temperature thresholds (in conjunction with rising atmospheric carbon dioxide [CO2] levels), and thus long-term temperature increases may reduce future yields under both irrigated and dryland production.37,91,92,97,103,112,113 In contrast, even with warmer temperatures, future yields for certain crops such as wheat, hay, and barley are projected to increase in some regions due to anticipated increases in precipitation and carbon fertilization.97,114 However, yields from major U.S. commodity crops are expected to decline as a consequence of higher temperatures,45 especially when these higher temperatures occur during critical periods of reproductive development.115,116,117 Increasing temperatures are also projected to have an impact on specialty crops (fruits, nuts, vegetables, and nursery crops) (Ch. 25: Southwest, KM 6), although the effects will be variable depending on the crops and where they are grown.118 Additional challenges involve the loss of synchrony of seasonal phenomena (for example, between crops and pollinators) (Ch. 7: Ecosystems; Ch. 25: Southwest, KM 6). Further, the interactive effects of rising atmospheric CO2 concentrations, elevated temperatures, and changes in other climate factors are expected to enhance weed competitiveness relative to crops,119 with temperature being a predominant factor.120,121
Irrigated agriculture is one of the major consumers of water supplies in the United States (Ch. 3: Water; Ch. 25: Southwest, KM 6). Irrigation is used for crop production in most of the western United States and since 2002 has expanded into the northern Midwest (Ch. 21: Midwest, KM 1) and Southeast (Ch. 19: Southeast, KM 4). Expanded irrigation is often proposed as a strategy to deal with increasing crop water demand due to higher trending temperatures coupled with decreasing growing-season precipitation. However, under long-term climate change, irrigated acreage is expected to decrease, due to a combination of declining water resources and a diminishing relative profitability of irrigated production.97 Continuing or expanding existing levels of irrigation will be limited by the availability of water in many areas.11,98,108 Surface water supplies are particularly vulnerable to shifts in precipitation and demand from nonagricultural sectors. Groundwater supplies are also in decline across major irrigated regions of the United States (see Case Study “Groundwater Depletion in the Ogallala Aquifer Region”) (see also Ch. 3: Water, Figure 3.2; Ch. 25: Southwest, KM 1; Ch. 23: S. Great Plains, KM 1).
Crop productivity and quality may also be significantly reduced due to increased crop water demand coupled with limited water availability122,123,124 as well as increased diseases and pest infestations (Ch. 25: Southwest, KM 6).125 The expected demand for higher crop productivity and anticipated climate change stresses have driven advancements in crop genetics.126,127 Seed companies have released numerous crop varieties that are tolerant to heat, drought, or pests and diseases. This trend is expected to continue as new crop varieties are developed to adapt to a changing climate.128 Recent advances in genetics have allowed researchers to access large and complex genomes of crops and their wild relatives.129 This has the potential to reduce the time and cost required to identify and incorporate useful traits in plant breeding and to develop crops that are more resilient to climate change. Currently, the United States has the largest gene bank in the world that manages publicly held crop germplasm (genetic material necessary for plant breeding). However, progress in this area has been modest despite advances in breeding techniques.130,131,132,133 Further, institutional factors such as intellectual property rights, and a lack of international access to crop genetic resources, are affecting the availability and utilization of genetic resources useful for adaptation to climate change.134 Investments by commercial firms alone are unlikely to be sufficient to maintain these resources, meaning higher levels of public investment would be needed for genetic resource conservation, characterization, and use. Societal concerns over certain crop breeding technologies likely will continue, but current assessments of genetically engineered crops have shown economic benefits for producers, with no substantial evidence of animal or human health or environmental impacts.135
Climate-smart agriculture136 can reduce the impacts of climate change and consequent environmental conditions on crop yield.137,138 Not only do producers take climate forecasts into consideration when deciding what to produce and how to produce it, they also adapt management strategies to cope with expected weather conditions. For example, drought resilience can be improved by adopting high-efficiency precision irrigation technologies.139,140,141 In order for these systems to work effectively, a network of weather stations is required in agricultural regions. Currently, 23 states have one or more publicly funded agricultural weather networks, such as the Oklahoma Mesonet142 and the Nebraska Agricultural Water Management Network.143
The same aspects of climate change that affect the incidence of drought also affect the frequency and intensity of wildfires, which pose major risks to agriculture and rural communities. Grassland, rangeland, and forest ecosystems, which support ruminant livestock production, represent more than half of the land area of the United States.144 Wildfires are a normal occurrence in these ecosystems, and they play an important role in long-term ecosystem health. However, climate change threatens to increase the frequency and length of the wildfire season, as well as the size and extent of large fires.95 Increasing temperatures also promote an increased spread of invasive or encroaching species,145 which exacerbate wildfire risks. Beyond economic losses, wildfires also contribute to climate change by releasing CO2 into the atmosphere (Ch. 6: Forests, KM 1; Ch. 13: Air Quality, KM 2). The increased extent of high-severity fire expanding into communities further reduces the capacity to provide other services and puts communities, personnel, and infrastructures at higher risk.146,147 Tribal communities are particularly vulnerable to wildfires, due to a lack of fire-fighting resources, insufficient experienced internal staff, and remote locations (Ch. 15: Tribes).148,149 In addition, firefighting in many tribal communities requires coordination across fire-prone landscapes with various jurisdictional controls.150 On average, the United States spends about $1 billion annually to fight wildfires, but it spent more than $2.9 billion in 2017 due to extreme drought conditions in some regions.151 States, local governments, and the private sector also absorbed additional costs of firefighting and recovery. (For more on wildfires, see Ch. 5: Land Changes; Ch. 6: Forests; Ch. 15: Tribes.)