finding 10.2 : key-message-10-2

The degradation of critical soil and water resources will expand as extreme precipitation events increase across our agricultural landscape (high confidence). Sustainable crop production is threatened by excessive runoff, leaching, and flooding, which results in soil erosion, degraded water quality in lakes and streams, and damage to rural community infrastructure (very likely, very high confidence,). Management practices to restore soil structure and the hydrologic function of landscapes are essential for improving resilience to these challenges.

This finding is from chapter 10 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

Each regional author team organized a stakeholder engagement process to identify the highest-priority concerns, including priorities for agriculture and rural communities. Due to the heterogeneous nature of agriculture and rural communities, the national chapter leads (NCLs) and coauthor team put in place a structured process to gather and synthesize input from the regional stakeholder meetings. Where possible, one or more of the authors or the chapter lead author listened to stakeholder input during regional stakeholder listening sessions. Information about agriculture and rural communities was synthesized from the written reports from each regional engagement workshop. During the all-authors meeting on April 2–3, 2017, the NCL met with authors from each region and other national author teams to identify issues relevant to this chapter. To finalize our regional roll-up, a teleconference was scheduled with each regional author team to discuss agriculture and rural community issues. Most of the regional author teams identified issues related to agricultural productivity, with underlying topics dominated by drought, temperature, and changing seasonality. Grassland wildfire was identified as a concern in the Northern and Southern Great Plains. All regional author teams identified soil and water vulnerabilities as concerns, particularly as they relate to soil and water quality impacts and a depleting water supply, as well as reduced field operation days due to wet soils and an increased risk of soil erosion due to precipitation on frozen soil. Heat stress in rural communities and among agricultural workers was of concern in the Southeast, Southern Great Plains, Northwest, Hawaiʻi and Pacific Islands, U.S. Caribbean, and Northeast. Livestock health was identified as a concern in the Northeast, Midwest, U.S. Caribbean, and Southern Great Plains. Additional health-related concerns were smoke from wildfire, pesticide impacts, allergens, changing disease vectors, and mental health issues related to disasters and climate change. Issues related to the vulnerability and adaptive capacity of rural communities were identified by all regions. Discussions with the regional teams were followed by expert deliberation on the draft Key Messages by the authors and targeted consultation with additional experts. Information was then synthesized into Key Messages, which were refined based on published literature and professional judgment.

Description of evidence base:

Evidence of long-term changes in precipitation is based on analyses of daily precipitation observations from the National Weather Service’s Cooperative Observer Network.e8089a19-413e-4bc5-8c4a-7610399e268c

Groisman et al. (2012)5d909426-fab3-4dc8-af56-e5fe414ca97a reported that for the central United States, the frequency of very heavy precipitation increased by 20% from 1979–2009 compared to 1948–1978. Slater and Villarini (2016)a0905615-ac31-42ba-a70f-592a5729fdf7 report a significant increase in flooding frequency in the Southern Plains, California, and northern Minnesota; a smaller increase in the Southeast; and a decrease in the Northern Plains and Northwest. Mallakpour and Villarini (2015)d2af0d06-91aa-4e53-99e1-4dad2ac9195a report an increasing frequency of flooding in the Midwest, primarily in summer, but find limited evidence of a change in magnitude of flood peaks.

Infrastructure: Severe local storms constituted the largest class of billion-dollar natural disasters from 1980 to 2011, followed by tropical cyclones and nontropical floods.4fe32146-a968-4dde-8a2b-df2aa2eabdd4 Špitalar et al. (2014)3f57831b-3c94-4ca9-863b-594a81f51b20 evaluate flash floods from 2006 to 2012 and find that the floods with the highest human impacts, based on injuries and fatalities, are associated with small catchment areas in rural areas. Rural areas face particular challenges with road networks and connectivity.40fd4927-7950-49c8-b022-31a8fbafa9d4

Soil and water: Soil carbon on agricultural lands is decreased due to land-use change and tillage,fecb7170-32c4-498a-95c0-b374d9ce845b,47bd7d77-45fb-4ebe-9ea6-a7b3ce8077e7 resulting in decreased hydrologic function.483ba799-c3e0-4852-9fc0-85cf5632efd3 Practices that increase soil carbon have an adaptation benefit through improved soil structure and infiltration, improved water-holding capacity, and improved nutrient cycling. There are many practices that can enhance agricultural resilience through increased soil carbon sequestration.f2e6034d-169d-46c0-8b78-1eb46e73bfc8,fecb7170-32c4-498a-95c0-b374d9ce845b,5e24bc5b-9bbc-4c3b-b990-bf22e3359c7f,50f5fa01-b559-4c5b-a9b1-4ab35d132a64,3f959f26-3b66-4479-a100-1e788a0868b0,8e77c2a4-9af8-428f-b5fd-67bf2ece89cb Houghton et al. (2017)ced8505a-f36f-4c7b-8a0d-ec7f08482297 identify the health effects associated with poor water quality that can be associated with nutrient transport to water bodies and subsequent eutrophication.

New information and remaining uncertainties:

Floods are highly variable in space and time,a29b612b-8c28-4c93-9c18-19314babce89 and their characteristics are influenced by a number of non-climate factors.b8d001bf-c47f-40f8-91f1-a252a46381b8 Groissman et al. (2012)5d909426-fab3-4dc8-af56-e5fe414ca97a note that the lack of sub-daily data to analyze precipitation intensity means that daily data are normally used, which limits the ability to detect the most intense precipitation rates. While many practices are available to protect soil and reduce nutrient runoff from agricultural lands,fecb7170-32c4-498a-95c0-b374d9ce845b,3f959f26-3b66-4479-a100-1e788a0868b0 adoption rates by producers are uncertain. Additionally, there is uncertainty about the extent to which agribusiness will invest in soil improvement to mitigate risks associated with a changing climate and its effects on water, energy, and plant and animal supply chains.9b37a44d-d7d9-4720-988f-99e726feef94

Assessment of confidence based on evidence:

The evidence on increasing precipitation intensity, with the largest increases occurring in the Northeast, is high (very likely, high confidence). The increase in flooding is less certain (likely, medium confidence). The evidence of the impact of precipitation extremes on infrastructure losses, soil erosion, and contaminant transport to water bodies is well established (very likely, high confidence). Based on medium confidence on flooding but high confidence in increasing precipitation intensity and the impacts of precipitation extremes, there is high confidence in this Key Message.

References :

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