{ "id": "R43407", "type": "CRS Report", "typeId": "REPORTS", "number": "R43407", "active": true, "source": "EveryCRSReport.com, University of North Texas Libraries Government Documents Department", "versions": [ { "source": "EveryCRSReport.com", "id": 585860, "date": "2017-11-09", "retrieved": "2020-01-02T13:54:41.148430", "title": "Drought in the United States: Causes and Current Understanding", "summary": "Drought is a natural hazard with potentially significant economic, social, and ecological consequences. History suggests that severe and extended droughts are inevitable and part of natural climate cycles. Drought has for centuries shaped the societies of North America and will continue to do so into the future. The likelihood of extended periods of severe drought and its effects on 21st-century society in the United States raise several issues for Congress. These issues include how to respond to recurrent drought incidents, how to prepare for future drought, and how to coordinate federal agency actions, among other policy choices. Understanding what drought is and its causes, how it has affected North America in the past, and how drought may affect the United States in the future all bear on actions Congress may take to prepare for and mitigate the effects of drought.\nThe 2012-2016 drought in California and parts of other western states, and 16 years of dry conditions in the Southwest, have fueled congressional interest in drought and its near-term effects on water supplies and agriculture, as well as in long-term issues, such as drought forecasting and possible links between drought and human-induced climate change. Surface water conditions in California have recovered dramatically in 2017 from the effects of the drought, but some consequences, such as the decline in groundwater levels from increased pumping, likely will linger for years and may even be permanent. In response to the California drought, the 114th Congress enacted legislation (P.L. 114-322) that altered the authorities regarding how federal water infrastructure in the state is managed and how new water storage may be developed. In the 115th Congress, there is both interest in and concern about the federal role and funding for new water infrastructure to cope with the next drought and with hydrologic conditions that can quickly transition from drought to flood conditions.\nSome scientists refer to severe drought as a recurring natural disaster in North America. Reconstructions of drought conditions that extend back over 1,000 years\u2014based on observations, historical and instrumental records, and tree rings\u2014illustrate that portions of the conterminous United States have experienced periods of severe and long-lasting drought termed megadroughts. For example, drought reconstructions from tree rings document that severe multi-decadal drought occurred in the American Southwest during the 13th century. These megadroughts have affected flows in major western rivers. For example, during the years 1130-1154, estimated Colorado River flows were less than 84% of normal. Recent data suggest that Colorado River flows since 2000 are approaching those previous lows\u2014flows have been below average for 13 of the 16 years between 2000 and 2015. \nPart of the country is almost always experiencing drought at some level. The land area affected by drought can vary widely by year and also within a particular year. In May 2017, only 3.8% of the total U.S. land area was affected by drought of at least moderate intensity. In contrast, in September 2012, 55% of the nation faced drought of moderate or greater intensity, and 35% of the country was under severe drought.\nPredicting the intensity and duration of severe drought over a specific region is not currently possible more than a few months in advance because of the many factors that influence drought. Even though forecasting drought at the regional scale is difficult, understanding potential changes in long-term trends is important for water managers at all levels\u2014federal, state, local, and tribal. Water project operations and state water allocations typically are based on past long-term hydrological trends; significant deviations from such trends may result in difficult challenges for water managers and water users alike.", "type": "CRS Report", "typeId": "REPORTS", "active": true, "formats": [ { "format": "HTML", "encoding": "utf-8", "url": "https://www.crs.gov/Reports/R43407", "sha1": "70977ec6371c36b64b6b894463f79613021aab21", "filename": "files/20171109_R43407_70977ec6371c36b64b6b894463f79613021aab21.html", "images": { "/products/Getimages/?directory=R/html/R43407_files&id=/3.png": "files/20171109_R43407_images_4a6cb25c4568f4d6eb2d354126f5e71564e77d66.png", "/products/Getimages/?directory=R/html/R43407_files&id=/1.png": "files/20171109_R43407_images_09d1a5daee572bf11af1bd3725b7c2a87585e188.png", "/products/Getimages/?directory=R/html/R43407_files&id=/2.png": "files/20171109_R43407_images_9dab4931a274f19d1c4815ee75e4e6a5c2f8c453.png", "/products/Getimages/?directory=R/html/R43407_files&id=/4.png": "files/20171109_R43407_images_ffb24bc6abd72a0f7d6b068c1f9d264781754f58.png", "/products/Getimages/?directory=R/html/R43407_files&id=/0.png": "files/20171109_R43407_images_09ae1bbf5b17baca9c20b5c016652bb9b4ca0518.png", "/products/Getimages/?directory=R/html/R43407_files&id=/6.png": "files/20171109_R43407_images_692a7a17435fd695eca3cf22c75c313f07d5dbe7.png", "/products/Getimages/?directory=R/html/R43407_files&id=/5.png": "files/20171109_R43407_images_2113b64475d3c05ab8e925f38da944e2244af18d.png", "/products/Getimages/?directory=R/html/R43407_files&id=/8.png": "files/20171109_R43407_images_fa6f5c797780329323191908cf7c62158b7f4d53.png", "/products/Getimages/?directory=R/html/R43407_files&id=/7.png": "files/20171109_R43407_images_6f06dc1e4a4ff7241700c9bc009a70291ad0f3d4.png" } }, { "format": "PDF", "encoding": null, "url": "https://www.crs.gov/Reports/pdf/R43407", "sha1": "56bbdda55763a85a61b13fa0c5caf666c1365280", "filename": "files/20171109_R43407_56bbdda55763a85a61b13fa0c5caf666c1365280.pdf", "images": {} } ], "topics": [ { "source": "IBCList", "id": 4839, "name": "Earth Sciences & Natural Hazards" }, { "source": "IBCList", "id": 4842, "name": "Climate Change" }, { "source": "IBCList", "id": 4909, "name": "Water Resource Management" } ] }, { "source": "EveryCRSReport.com", "id": 442543, "date": "2015-06-25", "retrieved": "2016-04-06T18:52:39.761770", "title": "Drought in the United States: Causes and Current Understanding", "summary": "Drought is a natural hazard, often with significant societal, economic, and environmental consequences. Public policy issues related to drought range from how to identify and measure drought to how best to prepare for, mitigate, and respond to drought impacts, and who should bear associated costs. Severe droughts in 2011 and 2012 in Texas and the midcontinent region, the current drought in California and parts of other western states, and 15 years of dry conditions in the Southwest have fueled congressional interest in drought and its near-term effects on water supplies and agriculture, as well as in long-term issues, such as drought forecasting and possible links between drought and human-induced climate change. \nSome part of the country is almost always experiencing drought at some level. Since 2000, no less than 6.6% of the land area of the United States has experienced drought of at least moderate intensity each year. The land area affected by drought of at least moderate intensity varies by year and also within a particular year. For example, since 2000, the total U.S. land area affected by drought of at least moderate intensity has varied from as little as 6.6% (July 6, 2010) to as much as 55% (September 25, 2012). Based on weekly estimates of drought conditions since 2000, the average amount of land area across the United States affected by at least moderate-intensity drought has been 27%.\nWhat is drought? Drought has a number of definitions; the simplest may be a deficiency of precipitation over an extended time period, usually a season or more, compared with average conditions. Higher demand for water for human activities and vegetation in areas of limited water supply, and warmer conditions, increase the severity of drought. For example, drought during the growing season may be considered more severe\u2014in terms of its impacts\u2014than similar conditions when cropland lies fallow. \nSome scientists refer to severe drought as a recurring natural disaster in North America. Reconstructions of drought conditions that extend back over 1,000 years\u2014based on observations, historical and instrumental records, and tree rings\u2014illustrate that portions of the conterminous United States have experienced periods of severe and long-lasting drought termed megadroughts. For example, drought reconstructions from tree rings document that severe multi-decadal drought occurred in the American Southwest during the 13th century. These megadroughts have affected flows in major western rivers. For example, during the years 1130-1154, estimated Colorado River flows were less than 84% of normal. Recent data suggest that Colorado River flows since 2000 are approaching those previous lows\u2014flows have been below average for 13 of the 15 years between 2000 and 2014.\nOne question is whether the parts of the United States, in particular the American Southwest, including California, may be experiencing the beginning of a modern-era megadrought. Because such megadroughts occurred previously, there is the possibility of a return to the long-term drought conditions experienced in previous centuries. Further, some postulate that droughts could be exacerbated if the future climate is warmer due to the buildup of greenhouse gases in the atmosphere. Predicting the severity and persistence of severe drought over a specific region of the country, however, is not yet possible more than a few months in advance because of the many factors that influence drought (e.g., precipitation, heat, soil moisture). The prospect of extended droughts and more arid baseline conditions\u2014possibly exacerbated by greenhouse gas-driven warmer temperatures\u2014in parts of the United States may challenge existing public policy responses for preparing for and responding to drought.", "type": "CRS Report", "typeId": "REPORTS", "active": true, "formats": [ { "format": "HTML", "encoding": "utf-8", "url": "http://www.crs.gov/Reports/R43407", "sha1": "f2026019cb4e33d3d099fbd153ccd37340e01332", "filename": "files/20150625_R43407_f2026019cb4e33d3d099fbd153ccd37340e01332.html", "images": null }, { "format": "PDF", "encoding": null, "url": "http://www.crs.gov/Reports/pdf/R43407", "sha1": "6111ac811f5e4e9ecb005536b48a23240f8f8372", "filename": "files/20150625_R43407_6111ac811f5e4e9ecb005536b48a23240f8f8372.pdf", "images": null } ], "topics": [ { "source": "IBCList", "id": 318, "name": "Water Resources Management and Development" }, { "source": "IBCList", "id": 3878, "name": "Climate Change Science, Technology, and Policy" } ] }, { "source": "University of North Texas Libraries Government Documents Department", "sourceLink": "https://digital.library.unt.edu/ark:/67531/metadc282354/", "id": "R43407_2014Feb26", "date": "2014-02-26", "retrieved": "2014-04-02T19:38:14", "title": "Drought in the United States: Causes and Current Understanding", "summary": "This report discusses how drought is defined (e.g., why drought in one region of the country is different from drought in another region) and why drought occurs in the United States. It briefly describes periods of drought in the country's past that equaled or exceeded drought conditions experienced during the 20th century. This is followed by a discussion of the nature and extent of recent droughts that affected Texas and the U.S. midcontinent, and the current drought in California. Lastly, the report discusses future prospects for a climate in the western United States that might be drier than the average 20th-century climate and the possible influence of human-induced climate change.", "type": "CRS Report", "typeId": "REPORT", "active": false, "formats": [ { "format": "PDF", "filename": "files/20140226_R43407_8828df3157d60e880e13f8836ae01bd025bd85ce.pdf" }, { "format": "HTML", "filename": "files/20140226_R43407_8828df3157d60e880e13f8836ae01bd025bd85ce.html" } ], "topics": [ { "source": "LIV", "id": "Droughts", "name": "Droughts" }, { "source": "LIV", "id": "Rain and rainfall", "name": "Rain and rainfall" }, { "source": "LIV", "id": "Climatic changes", "name": "Climatic changes" } ] } ], "topics": [ "Energy Policy" ] }