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finding 25.6 : key-message-25-6
Food production in the Southwest is vulnerable to water shortages (medium confidence). Increased drought, heat waves, and reduction of winter chill hours can harm crops (medium confidence) and livestock (high confidence); exacerbate competition for water among agriculture, energy generation, and municipal uses (medium confidence); and increase future food insecurity (medium confidence).
This finding is from chapter 25 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.
Process for developing key messages:
The authors examined the scientific literature in their areas of expertise. The team placed the highest weight on scientific articles published in refereed peer-reviewed journals. Other sources included published books, government technical reports, and, for data, government websites. The U.S. Global Change Research Program issued a public call for technical input and provided the authors with the submissions. The University of Arizona Center for Climate Adaptation Science and Solutions organized the Southwest Regional Stakeholder Engagement Workshop on January 28, 2017, with over 70 participants at the main location in Tucson, AZ, and dozens of participants in Albuquerque, NM, Boulder, CO, Davis, CA, Los Angeles, CA, Reno, NV, and Salt Lake City, UT, all connected by video. Participants included scientists and managers. The author team met the following day for their only meeting in person. Subsequently, authors held discussions in regular teleconferences. Many chapter authors met at the all-author meeting March 26–28, 2018, in Bethesda, MD.
Description of evidence base:
Climate change has altered climate factors fundamental to food production and rural livelihoods in the Southwest. Abundant evidence and good agreement in evidence exist regarding regionally increasing temperatures, reduced soil moisture, and effects on regional snowpack and surface water sources.a42c4f5e-f16b-4196-af05-61f117e0491d,29960c69-6168-4fb0-9af0-d50bdd91acd3,9f637046-58b9-4716-82e6-afbd33fe4fa8,a29b612b-8c28-4c93-9c18-19314babce89,a30e16b4-cf09-4037-9f32-3d8a4b109884 The heat of climate change has intensified severe droughts in Californiaba57f86f-c42f-4bba-83f6-676d6875c176,89e08a41-6091-45fa-a92e-6168a90a8151 and the Colorado River Basin.a42c4f5e-f16b-4196-af05-61f117e0491d Hotter temperatures and aridity in the Southwest affected agricultural productivity from 1981 to 2010.c5857041-2594-47cf-a6bc-3fab052fa903
Elevated temperatures can be associated with failure of some crops, such as warm-season vegetable crops, and reduced yields and/or quality in others.c29be9d3-c558-41ec-979c-f8d0c0b6f0e6 Temperatures in California, Nevada, and Arizona are already at the upper threshold for corn53efddbf-8a1f-44fb-83e2-167fde08c9aa and rice.a7cfed2a-25b6-4d4f-a9dc-49e1568e2aea While crops grown in some areas might not be viable under hotter conditions, other crops such as olives, cotton, kiwi, and oranges may replace them.0a8508df-df59-4080-89a2-52bfeaca47e0 In the Southwest, climate change may cause a northward shift in crop production, potentially displacing existing growers and affecting rural communities.4442506b-fbba-41ea-9cef-1eac88ce2049 Quality of specialty crops, both nutritive and sensory, declines because of increased temperatures and other changes associated with a changing climate,3baf471f-751f-4d68-9227-4197fdbb6e5d,f7e0b49e-7cf3-4392-b455-305c0db13545 which is particularly important in a region producing a majority of the Nation’s specialty crops. Decreases in winter chill hours may reduce fruit and tree nut yields, though the magnitude may vary considerably.504c60ae-db5f-4b9c-bb9f-2dd7701dc31c,0190c6b6-6e8c-4988-837a-b984e69b3dd9
High ambient temperatures associated with climate change could decrease production of rangeland vegetation across the Southwest,aa6f4075-c70e-43f8-969e-b5625ad25449 reducing available forage for livestock. Ranching enterprises across the region have vastly different characteristics that will influence their adaptive capacities.c779538d-b066-4e38-8527-ff3f7552f26e
Local-scale impacts can vary considerably across the region depending upon surface and groundwater availability. Drought causes altered water management, with heavy reliance on a limited groundwater to sustain regional food production.7aecf6b3-0b12-40d7-8c61-c1b72cc14289 Despite severe localized impacts, losses in total agricultural revenue are buffered by groundwater reliance to offset surface water shortage.53ceb8c3-f1b8-4cc1-bb65-3268f4f8bb74 Parts of the Southwest have exhausted sustainable use of groundwater resources. When surface water supplies are reduced, farmers shift to increased groundwater pumping, even when pumping raises production costscf96b502-57a2-4b76-bffc-750e1bf668d6—declining groundwater tables significantly increase pumping costs and require drilling of deeper wells.7aecf6b3-0b12-40d7-8c61-c1b72cc14289 Continued climate change may reduce aquifer recharge in the southern part of the region 10%–20%.2042ab8a-6a82-40a2-99ba-7e67babf8ffc Climate change is projected to cause longer and more severe drought periods that will intensify the uncertainty associated with Southwest water supply and demand. Water-intensive forage crops and the livestock industry are especially vulnerable to climate-related water shortages.bf7e284b-6333-477d-883f-23e002742a6c
New information and remaining uncertainties:
The impacts of climate change on food production depend upon microclimatology and local-scale environmental, social, and economic resources. While the scientific community relies upon computer models and generalized information to project likely future conditions, unforeseen consequences of warming temperatures, such as those related to pests, pollinators, and pathogens, may be more detrimental than some of the well-documented projections, such as temperature impacts on reduced yields. The effects of increased precipitation supplying the deep root zone may somewhat offset the increase in temperature, so agricultural drought may be less frequent for trees and other crops dependent on deeper soil moisture.4fbaaa13-99d2-43df-93db-2be546f18892 Scientists are producing more drought- and heat-tolerant cultivars, which may be suitable to production in the projected warmer and more arid climate of the Southwest.
Since food security relies on complex national and international trade networks, how regional climate change may affect local food security is uncertain. Many adaptation options, such as using alternate breeds, crops, planting and harvest dates, and new (sometimes untested) chemicals, may work in certain situations but not others. Thus, predicting impacts to food production in a hotter/drier land is likely to vary by crop and location, necessitating flexibility and adaptive management. Of paramount uncertainty is the impact of water shortage on regional food production as other uses may outcompete producers for limited supplies.
Assessment of confidence based on evidence:
Since the availability of affordable food around the world depends upon complex trade and transportation networks, the effects of climate change on Southwest food availability, production, and affordability remain highly complex and thereby uncertain and classified with medium confidence. While the viability of rural livelihoods is vulnerable to water shortages and other climate-related risks, rural livelihoods may be supplemented by other nonagricultural income, such as recreation and hunting. The viability of rural livelihoods is highly complex, and risk is, therefore, classified with medium confidence. Crop impacts related to hotter and drier conditions and reduced winter chill periods, caused by climate change, are classified with medium confidence. Not all crops are directly harmed by warming temperatures, and the simulation impacts of reduced chilling hours can produce a fairly wide range of results depending upon model assumptions. Hotter and drier conditions can directly harm livestock via reduced forage quantity and quality and exposure to higher temperatures, conferring a high confidence classification. Projections of future drought and water scarcity portend increased competition for water from other beneficial uses with medium confidence.
ProvenanceThis finding was derived from scenario rcp_8_5
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