Expert Commentary

Building border walls and barriers: What the research says

Are border walls effective at deterring migrants? Do they harm wildlife? How are indigenous groups in the area impacted? We explain the research.

border wall barrier research democratic presidential candidates
Construction workers build border wall prototypes in 2017. (U.S. Customs and Border Protection/Mani Albrecht)

In the lead-up to the 2020 elections, the Journalist’s Resource team is combing through the Democratic presidential candidates’ platforms and reporting what the research says about their policy proposals. We want to encourage deep coverage of these proposals — and do our part to help deter horse race journalism, which research suggests can lead to inaccurate reporting and an uninformed electorate. We’re focusing on proposals that have a reasonable chance of becoming policy, and for us that means several top-polling candidates say they intend to tackle the issue. Here, we look at research on building border walls.

Candidates who oppose expanding the U.S.-Mexico border barrier

Bernie Sanders, Tom Steyer*, Elizabeth Warren*

Candidates who would expand the barrier if experts recommend it

Pete Buttigieg,* Tulsi Gabbard

Candidates whose position is unclear

Joe Biden, Michael Bloomberg*, Amy Klobuchar*

What the research says

Border barriers can discourage unauthorized border crossings, but the research is mixed in terms of how much they deter migrants from entering the U.S. without permission. Border walls and fences also can damage local habitats and impede the migration of wildlife. A number of academic articles document how the barriers that line the U.S.-Mexico border infringe on the religious and property rights of indigenous nations living in the region.

Meanwhile, hundreds of migrants die or are injured each year trying to go over and around barriers that block off much of America’s nearly 2,000-mile southwestern border. Such structures do not stop foreign visitors from arriving by air and sea and establishing residence without authorization.

Key context

Throughout time, cities, kingdoms and nation-states have built physical barriers to mark their territory, protect their inhabitants and control who and what enters and exits. In just the past few decades, countries worldwide — including the U.S. — have erected thousands of miles of border walls and fences, largely to prevent unauthorized migration. Barriers, writes researcher Elisabeth Vallet, are becoming “a norm of International relations, and a solution in the quest for security.”

“It seems like every month brings news of another border wall going up,” she wrote in The Conversation in 2017. As of 2019, there were about 70 border barriers in existence across the globe, up from about 15 in 1990, according to Vallet, author of Borders, Fences and Walls: State of Insecurity and director of the Center for Geopolitical Studies at the University of Quebec in Montreal.

When the migrant crisis in Europe emerged several years ago, countries there began erecting barriers. Since 2015, “at least 800 miles of fences have been erected by Austria, Bulgaria, Greece, Hungary, Macedonia, Slovenia and others — a swift and concrete reaction as more than 1.8 million people descended on Europe from war zones from Afghanistan to Syria,” USA Today reported in mid-2018.

The U.S. first built a barrier along its southwestern border between 1909 and 1911 — a barbed wire structure in southern California to keep cattle from moving between the U.S. and Mexico, Smithsonian Magazine has reported. The federal government has expanded and reinforced the barrier over time. The Wall Street Journal describes construction efforts in recent decades:

“About 119 miles of barriers were in place before 2005, according to the Government Accountability Office. Work ramped up significantly during the George W. Bush administration, particularly around El Paso, Texas. Over the next 10 years, stretching into the Obama administration, the barriers were extended to cover 654 miles in areas including Tucson, Ariz., the Rio Grande Valley and the San Diego vicinity.”

U.S. Customs and Border Protection spent $2.3 billion on fencing at U.S.-Mexico border from fiscal years 2007 through 2015, notes a 2018 report from the U.S. Government Accountability Office, the federal government’s watchdog agency. Of the 654 miles of barrier that line the U.S. border with Mexico, 300 are vehicle barriers and the rest are designed to keep pedestrians out. The border stretches 1,954 miles and runs through four states — California, Arizona, New Mexico and Texas.

While most immigrants living in the U.S. are here legally, nearly one-quarter — 10.5 million — do not have permission to be in the country, according to a 2019 report from Pew Research Center.

Donald Trump made unauthorized immigration a signature issue of his 2016 campaign. The president vowed to build at least 500 miles of new barrier by early 2021 for what will be one of the largest federal infrastructure projects in American history, The Washington Post reported earlier this month.

Shortly after Trump took office in 2017, he signed three executive orders aimed at ramping up federal efforts to control the U.S.-Mexico border and clamp down on unauthorized immigration. The first calls for an improved border barrier. It directs the U.S. Department of Homeland Security to “take all appropriate steps to immediately plan, design, and construct a physical wall along the southern border, using appropriate materials and technology to most effectively achieve complete operational control of the southern border.”

About 110 miles of the new barrier have been finished, and federal officials say a total of 450 miles will be completed or under construction by late 2020, The Washington Post explains. The federal government expects to earmark $18.4 billion for the project — enough to put up nearly 900 miles of new barrier before 2022.

Most of the new wall will replace older and smaller barriers. As the Post describes it, the wall is “far more formidable than anything previously in place along the border. The new structure has steel bollards, anchored in concrete, that reach 18 to 30 feet in height and will have lighting, cameras, sensors and improved roads to allow U.S. agents to respond quickly along an expanded ‘enforcement zone.’”

Over the years, the U.S. Department of Homeland Security has cited reductions in border apprehensions as evidence of the barrier’s effectiveness. It offers this example: When it installed fencing near Yuma, Arizona, the number of people caught crossing the border without permission plunged 90%.

In late 2017, Elaine Duke, then the acting secretary of U.S. Department of Homeland Security, wrote an editorial in USA Today explaining that border apprehensions in Yuma in fiscal year 2016 were about 10% of what they had been in fiscal year 2005. Yuma, she wrote, had been one of the first sectors along the southwestern border to receive “infrastructure investments” under the federal Secure Fence Act of 2006, which authorized the construction of hundreds of miles of additional border fencing as well as additional checkpoints, vehicle barriers and lighting.

The U.S. Department of Homeland Security released a report in 2011, however, suggesting federal officials were unsure why apprehensions along the entire U.S.-Mexico border fell 61% between 2005 and 2010. It “may be due to a number of factors including changes in U.S. economic conditions and border enforcement efforts,” the report states.

A recent report from the U.S. Border Patrol shows that the number of people apprehended in all nine sectors of the southwestern border rose from a combined 327,577 in fiscal year 2011 to 479,371 in fiscal year 2014. While apprehensions dropped to 303,916 in fiscal year 2017, they more than doubled by the end of the 2019 fiscal year to 851,508.

Recent research

Published research on the effectiveness of border barriers is limited and offers conflicting results in terms of how much of a role barriers play in deterring unauthorized entry in the U.S.

“While advanced as a popular solution, the evidence is mixed on whether walls are effective at preventing large movements of people across borders,” Reece Jones, a political geographer at the University of Hawaii at Manoa and an international expert on border barriers, writes in a 2016 analysis for the nonpartisan Migration Policy Institute.

Jones notes that border crossings in the U.S. plummeted in the 1990s, after fences were built along the southwestern border and backed up with large deployments of Border Patrol agents. He also points out that the barriers did not prevent all unauthorized crossings, but rather shifted the stream of migrants to other parts of the border.

“As high-traffic urban routes were closed, migrants and smugglers began to cross in the remote and dangerous deserts of western Arizona,” Jones writes. “Child migration from Central America to the United States, which surged in 2014, has also been undeterred by enforcement.”

Border barriers “are not particularly effective at stopping migration on their own,” he explains in the Journal of Latin American Geography in 2018. “They require constant surveillance by agents, high tech sensors, aircraft, and drones or else they can easily be climbed with a ladder.”

A 2017 report from the U.S. Government Accountability Office, criticizes the U.S. Customs and Border Protection for failing to develop metrics to assess the effectiveness of the U.S.-Mexico border barrier. The report notes that Customs and Border Protection spent about $2.3 billion from fiscal year 2007 through 2015 on fencing there and that, in 2009, the agency estimated fencing maintenance would cost more than $1 billion over the next 20 years.

“Despite these investments, CBP cannot measure the contribution of fencing to border security operations along the southwest border because it has not developed metrics for this assessment,” the U.S. Government Accountability Office writes in the 75-page report.

The federal watchdog agency points out that the U.S. Customs and Border Protection “could potentially use these data to determine the extent to which border fencing diverts illegal entrants into more rural and remote environments, and border fencing’s impact, if any, on apprehension rates over time. Developing metrics to assess the contributions of fencing to border security operations could better position CBP to make resource allocation decisions with the best information available to inform competing mission priorities and investments.”

The report states that the U.S. Department of Homeland Security had begun making changes according to the U.S. Government Accountability Office’s recommendations.

A paper forthcoming in the American Economic Journal: Applied Economics, however, indicates the border barrier has discouraged unauthorized entry. In the paper, Benjamin Feigenberg of the University of Illinois at Chicago looks at how Mexico-to-U.S. migration changed as a result of the Secure Fence Act of 2006, which prompted the federal government to add 548 miles of fencing between 2007 and 2010.

Feigenberg estimates the additional fencing resulted in a 39% decline in migration among Mexicans who live close to the border. The reduction is a bit smaller — 38% — among Mexicans who live farther away from the border, in areas of Mexico that, historically, have had little access to smugglers.

Feigenberg concludes that, overall, 41,500 Mexican migrants are deterred by the barrier each quarter, and he estimates the cost of each deterred migrant to be about $4,820.

A 2018 working paper from the National Bureau of Economic Research, updated twice in 2019, also finds that border barriers curbed migration from Mexico to the U.S., but slightly. Researchers from Dartmouth College and Stanford University found the Secure Fence Act reduced the number of Mexican nationals living in the U.S. from 2005 and 2015 by an estimated 46,459 people. That accounts for about 5% of the actual decline in migration during that period.

The paper also finds that even if the U.S. had built a barrier along the entire length of border, that would have had a relatively small impact as well. It would have reduced migration by an estimated 129,438 people, which, the researchers note, “still comprises a small portion (13%) of the observed decline in migration flows between 2005 and 2015.”

Impacts on migrant safety, indigenous rights and the environment

While scholars will continue to study border barriers’ impact on illegal entry, they have established that numerous migrants have died or been injured trying to go over or around them and that the barriers used to separate countries harm natural habitats and local wildlife.

A 2019 study published in Neurosurgery looks at injuries from jumping or falling off a section of the border wall in Arizona. From January 2012 through December 2017, 64 people sought help at Banner University of Arizona Medical Center-Tucson, a hospital adjacent to the border, for treatment of head and spine injuries.

Doctors diagnosed 78% of these individuals with a spine injury and 23% with head trauma, including skull fractures, intracranial hemorrhaging and traumatic brain injury, according to the paper. The authors estimate the cost of patients’ care at Banner totaled $6.3 million, and that public money was the primary source of funds used to pay those bills.

Hundreds of migrants die each year along the U.S.-Mexico border, particularly in southern Arizona and Texas. Multiple studies over the years have found a direct link between increased border security and migrant deaths. As the U.S. ramped up its border control efforts, more migrants sought entry through remote areas in an attempt to avoid detection, a research team led by Daniel E. Martínez of the University of Arizona writes in a 2014 paper in the Journal on Migration and Human Security.

“Previous research has illustrated that segmented border militarization has resulted in the ‘funnel effect,’ or the redistribution of migratory flows away from traditional urban crossing points into remote and dangerous areas such as the deserts of southern Arizona,” Martínez and his colleagues write. “The Sonoran Desert, which spans much of southern Arizona and northern Sonora, Mexico, is an ecologically diverse region characterized by rugged terrain, pronounced elevation changes, and relatively little rainfall. Temperatures can reach 120 degrees Fahrenheit during the summer months and drop below freezing in the winter and, at higher elevations, in the spring and fall as well.”

Researchers explain in a 2014 paper in the Journal on Migration and Human Security that more aggressive border enforcement has prompted migrants “to travel for longer periods of time through remote areas in an attempt to avoid detection by US authorities, thus increasing the probability of death.”

The U.S. Border Patrol reported 300 deaths at the southwestern border in fiscal year 2019, up slightly from 283 in fiscal year 2018 but considerably lower than the decade high of 471 deaths in fiscal year 2012.

Researchers warn, though, that government tallies might not be accurate.

David K. Androff and Kyoko Y. Tavassoli of Arizona State University write in the journal Social Work that it’s difficult to know how many migrants have died in the desert after crossing into the U.S. without permission. “Medical examiners can only investigate deaths where remains are recovered; as most of the Sonoran desert is an uninhabited, remote wilderness, the discovery of remains is dependent on their identification by U.S. Border Patrol agents or others, and researchers agree that not all remains are recovered,” they write.

Androff and Tavassoli also note in their paper, published in 2012, that “government figures tend to minimize estimates, whereas advocacy groups use higher estimates to draw attention to an issue.”

While much of the focus nationally has been on whether and how to curb illegal entry at the southwestern border, tens of thousands of foreign visitors arrive by air or water each year and do not leave. A significant number of those who stay required visas to get into the U.S. and then let them expire.

Almost 667,000 foreign visitors who were supposed to leave in fiscal year 2018 did not, including 36,289 from Brazil, 29,723 from Nigeria and 35,931 from Venezuela, according to the most recent Entry/Exit Overstay Report from the U.S. Department of Homeland Security.

“Nearly half of the estimated 11 million undocumented immigrants now in the country did not trek through the desert or wade across the Rio Grande to enter the country; they flew in with a visa, passed inspection at the airport — and stayed,” Miriam Jordan, a national immigration correspondent for The New York Times, wrote last year.

In fiscal year 2019, about 4% of international students and exchange visitors from countries outside North America — a combined 68,593 people — stayed in the U.S. after their expected departure date, the U.S. Department of Homeland Security report shows.

More than 40% of international students and exchange visitors who arrived by air or sea from Yemen, Chad, Eritrea and the Democratic Republic of the Congo did not leave when their visas expired in fiscal year 2019. The largest group of students and exchange visitors who overstayed their visas — totaling 12,924 people — came from China, the U.S. Department of Homeland Security report shows.

In April 2019, Trump signed a Presidential memorandum directing federal officials to find ways to address the “rampant” number of visa overstays.

The total number of suspected visa overstays rose from 482,781 in fiscal year 2015 to 739,478 in fiscal year 2016, according to a recent policy paper from Blas Nuñez-Neto, a former senior advisor to the commissioner of U.S. Customs and Border Protection who now is a senior policy researcher at Rand Corp.

A chart in Nuñez-Neto’s paper shows that visa overstays far outpaced border apprehensions between fiscal years 2015 and 2018. However, he writes in the September 2019 paper that “given the ongoing surge in unauthorized migration this year, which has resulted in more than 766,000 apprehensions in FY2019 through July 31, 2019, it appears likely that individuals apprehended along across our southern border will outstrip visa overstays in 2019.”

While U.S. border walls and fences have failed to block all migrants, legal and academic scholars have documented the various ways the structures interfere with the daily lives and rights of indigenous people living in the area.

A 2017 analysis in the American Indian Law Journal, for example, looks at the barrier’s impact on the civil and property rights of the Tohono O’odham Nation and Pascua Yaqui Tribe in Arizona, the Kickapoo Traditional Tribe of Texas and other federally recognized tribes. The barriers have kept tribal members from accessing the southern parts of their land. They also impede the sharing of customs and have led to the desecration of burial sites, the author writes.

“Some United States Natives who have forgotten some of their customs depend on the elders on the Mexican side of the border to come teach youth culture,” the author writes. “Some Natives need to gather plants and other materials important to their spiritual practices in the deserts of Mexico, and are either unable to travel into Mexico or unable to return with those items, as overzealous border guards mistake them for forbidden plants.”

According to anthropologist Christina Leza of Colorado College, tens of thousands of U.S. tribal members live in the Mexican states of Coahuila, Chihuahua, Baja California and Sonora. She wrote in The Conversation last year that her research indicates these individuals routinely cross the U.S.-Mexico border for cultural, ceremonial or social purposes. They are treated as visitors to the U.S., required to pass through security checkpoints, where they can be interrogated, rejected or delayed.

A 2019 article in the American Indian Law Journal examines the U.S. laws that give the federal government vast authority to acquire and use land for immigration security purposes. The paper focuses on how the Illegal Immigration Reform and Immigrant Responsibility Act of 1996, the Secure Fence Act of 2006 and more recent federal actions have affected the Tohono O’odham. The tribe’s 2.8 million-acre reservation includes 62 miles of border between Arizona and Mexico.

“The Tohono O’odham’s mobile way of life and tribal sovereignty has progressively been infringed upon by immigration policies that have continued to tighten border security,” writes Keegan C. Tasker, from the Seattle University School of Law.

She later adds: “The imposition of these sections of the border wall through Tohono O’odham lands would cause irreparable harm to the Nation in several ways, including: (a) implications on the tribe’s sacred lands and environmental resources; (b) implications to the tribe on free movement and tribal sovereignty; and (c) stripping the tribe of sacred natural resources for spiritual and cultural practice.”

Other research finds that border construction has harmed plant and animal life in the U.S. and across the globe.

The Trump administration’s plan to build a continuous wall between the U.S. and Mexico threatens some of North America’s most biologically diverse areas, researchers write in BioScience. In the 2018 article, which includes a call to action, the authors explain that the barrier splits the geographic ranges of more than 1,000 terrestrial and freshwater animal species and 429 plant species, including 62 species the International Union for Conservation of Nature lists as critically endangered, endangered or vulnerable.

“Physical barriers prevent or discourage animals from accessing food, water, mates, and other critical resources by disrupting annual or seasonal migration and dispersal routes,” they write.

A 2016 analysis in the Review of European Comparative & International Environmental Law examines the issue from an international law and policy perspective. The authors explain that different types of border barrier affect wildlife differently. Across the globe, barriers are made of a range of materials, including concrete, sand, barbed or razor wire and electrified fencing. In some cases, metal walls extend underground. Some fencing strategies involve land mines.

Barriers are of particular concern in Central Asia, home to a variety of migratory and nomadic mammals, the authors write:

“By splitting populations, impeding migrations and killing animals attempting to cross, border fences pose an actual or potential threat to many of these, including the Mongolian gazelle (Procapra gutturosa), saiga antelope (Saiga tatarica), Asiatic wild ass (Equus hemionus, also known as khulan), Bactrian camel (Camelus ferus), argali sheep (Ovis ammon) and snow leopard (Panthera uncia).”

These barriers “have the potential to undo decades of conservation and international collaboration efforts, and their proliferation entails a need to realign our conservation paradigms with the political reality on the ground,” write the authors, from the Tilburg Law School’s Department of European and International Public Law in the Netherlands.

Another 2016 paper, this one published in PLOS Biology, finds that border barriers in Eastern Europe and Central Asia present a major threat to wildlife. A team of researchers estimates there is a total of 30,000 kilometers of border fencing in the study area and that Central Asia is one of the most heavily fenced regions on the planet.

The researchers express concern for rare or endangered species, including three mammals in Europe — the brown bear, gray wolf and Eurasian lynx. “Large spatial requirements and low population densities make conservation of these species particularly challenging, and the current successes in their conservation rely largely on the ability of individuals to move between subpopulations,” write the authors, who represent several universities and research organizations, including the Research Institute of Wildlife Ecology in Austria and the Mongolian Academy of Sciences.

Further reading

From a Distance: Geographic Proximity, Partisanship, and Public Attitudes toward the U.S.–Mexico Border Wall
Jeronimo Cortina. Political Research Quarterly, forthcoming.

The gist: “Although the American public is often aligned with partisan predispositions, often ignored is the role that geographic distance to the border plays in forming attitudes. … Using geocoded survey data from 2017, this paper shows that as the distance to the U.S.-Mexico border increases, Republicans are more likely to support building a wall along the entire border with Mexico due to a lack of direct contact, supplanting direct information with partisan beliefs.”

Barriers Along the U.S. Borders: Key Authorities and Requirements
Michael John Garcia. Report from the Congressional Research Center, March 2017.

The gist: This 44-page report, issued by Congress’ public policy research arm, offers a close examination of the federal laws and policies that govern how barriers can or should be used along America’s international borders. The report outlines the various laws that can be waived to proceed with the construction of border walls and fencing, including the Safe Drinking Water Act, Archeological Resources Protection Act and the Migratory Bird Treaty Act.

Expert sources

Treb Allen, associate professor of economics, Dartmouth College.

Peter Andreas, John Hay Professor of International Studies, Brown University.

David Androff, associate professor in the School of Social Work, Arizona State University.

Benjamin Feigenberg, assistant professor of economics, University of Illinois at Chicago.

Reece Jones, professor and chairman of the Department of Geography and Environment, University of Hawaii at Manoa.

Kenneth Madsen, associate professor of geography, Ohio State University.

Daniel E. Martínez, assistant professor of sociology, University of Arizona.

Melanie Morten, assistant professor of economics, Stanford University.

William Ripple, Distinguished Professor of Ecology, Oregon State University.

Arie Trouwborst, associate professor of environmental law, Tilburg Law School.

Elisabeth Vallet, associate professor in the department of geography, director of the Geopolitics Observatory, University of Quebec in Montreal.


*Dropped out of race since publication date.

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