Current loss and degradation of critical agricultural soil and water assets due to increasing extremes in precipitation will continue to challenge both rainfed and irrigated agriculture unless innovative conservation methods are implemented.

This finding is from chapter 6 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: A central component of the process was the development of a foundational technical input report (TIR), “Climate Change and Agriculture in the United States: An Assessment of Effects and Potential for Adaptation”.3baf471f-751f-4d68-9227-4197fdbb6e5d A public session conducted as part of the Tri-Societies (https://www.acsmeetings.org/home) meeting held in San Antonio, Texas, on Oct. 16-19, 2011, provided input to this report. The report team engaged in multiple technical discussions via teleconference, which included careful review of the foundational TIR3baf471f-751f-4d68-9227-4197fdbb6e5d and of approximately 56 additional technical inputs provided by the public, as well as other published literature and professional judgment. Discussions were followed by expert deliberation of draft key messages by the authors and targeted consultation with additional experts by the lead author of each message.

Description of evidence base: The key message and supporting text summarizes extensive evidence documented in the Agriculture TIR, “Climate Change and Agriculture in the United States: An Assessment of Effects and Potential for Adaptation.”3baf471f-751f-4d68-9227-4197fdbb6e5d Additional Technical Input Reports (56) on a wide range of topics were also received and reviewed as part of the Federal Register Notice solicitation for public input. Soil erosion is affected by rainfall intensity and there is evidence of increasing intensity in rainfall events even where the annual mean is reduced.7ae7606e-7f35-456d-8ace-2456b176956b Unprotected soil surfaces will have increased erosion and require more intense conservation practices.1ace4f2c-8946-4ad2-bc9c-6aa0047f03a4 443cb593-4f06-425b-9da9-bc74fc513caf Shifts in seasonality and type of precipitation will affect both timing and impact of water availability for both rainfed and irrigated agriculture. Evidence is strong that in the future there will be more precipitation globally, and that rain events will be more intense, even if separated by longer periods without rain.c54b9473-cdc3-4f22-97a8-4df5253f9682

New information and remaining uncertainties: Important new evidence (cited above) confirmed many of the findings in the past Synthesis and Assessment Product on agriculture,76db17ce-354b-4f0c-ad10-3e701c0387fc which informed the 2009 National Climate Assessment.e251f590-177e-4ba6-8ed1-6f68b5e54c8a Both rainfed and irrigated agriculture will increasingly be challenged, based on improved models and observational data related to the effects of increasing precipitation extremes on loss and degradation of critical agricultural soil and water assets.0ebef171-4903-4aa6-b436-2936da69f84e 49d8bcd1-1adb-4617-b2db-f7fa9c5987d2 Precipitation shifts are the most difficult to project, and uncertainty in regional projections increases with time into the future.bc4e302f-0956-4bb0-b345-e84dfb03223f To improve these projections will require enhanced understanding of shifts in timing, intensity, and magnitude of precipitation events. In the northern U.S., more frequent and severe winter and spring storms are projected, while there is a projected reduction in precipitation in the Southwest (see Ch. 2: Our Changing Climate).

Assessment of confidence based on evidence: The precipitation forecasts are the limiting factor in these assessments; the evidence of the impact of precipitation extremes on soil water availability and soil erosion is well established. Confidence in this key message is therefore judged to be high.

References :

• Predicting Rainfall Erosion Losses: A Guide to Conservation Planning. Agriculture Handbook No. 537 (1ace4f2c)
• Uncertainty in future soil carbon trends at a central U.S. site under an ensemble of GCM scenario climates (7ae7606e)
• SAP 4.3. The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity. (76db17ce)
• Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (c54b9473)
• Global observed changes in daily climate extremes of temperature and precipitation (bc4e302f)
• Conservation practices to mitigate and adapt to climate change (443cb593)
• Climate Change and Agriculture in the United States: Effects and Adaptation. USDA Technical Bulletin 1935 (3baf471f)
• Global Climate Change Impacts in the United States (e251f590)
• Extreme Precipitation over the West Coast of North America: Is There a Trend? (49d8bcd1)
• Regional Climate Trends and Scenarios for the U.S. National Climate Assessment: Part 9. Climate of the Contiguous United States. NOAA Technical Report NESDIS 142-9 (0ebef171)