Trends In Monthly Southwest Border Apprehensions

They Seem to be Gradually Rising

Since everybody is talking about immigration right now, I figured I’d get in the game and talk about an immigration topic nobody is talking about that I believe will shortly become contentious. So consider this a data-driven “heads up.”

Measuring illegal immigration is challenging. Heck, talking about it is challenging: the fact that I said “illegal” instead of “unauthorized” probably bothered some readers. I say “illegal” not out of any specific judgment, but because that’s the term that most widely communicates to the most people the phenomenon I am describing. I get why many people prefer other terms, and I’m personally agnostic about the best term, but I want people to understand what I’m talking about so, “illegal immigration” it is.

Aside from that terminological challenge, we’ve got the issue of actually measuring inflows. How many people are coming? There’s a lot of debate about this. Sources of information include Mexican-administered surveys of emigration, residuals-based methods from population estimates, and enforcement data on apprehended immigrants at the border. Each method has its pitfalls. Mexican survey data excludes Central American immigrants. Residuals methods make it very hard to pinpoint short-term change, and are subject to survey reporting bias and margins of error. Enforcement data will be impacted by changing laws or rigor of enforcement.

But for its faults, enforcement data is my preferred metric because it is timely. We have enforcement data up to December 2016 on a monthly basis. This is timely stuff that is transparently reported. We even get breakouts of how many of these apprehensions are of kids or family units!

Here’s the data, going back to 1999, in terms of monthly apprehensions.

I want to point out 3 key factors to be aware of in the recent period:

  1. Rising Total Levels
  2. Composition Shift
  3. Changed Seasonality

Illegal Immigration MAY Be Rising Again

We should be careful not to overstate the case here. Although monthly inflows have shown a fairly steady rise in apprehensions, 12-month rolling totals still aren’t very high. Here’s a graph of the total apprehensions in the preceding 12 months:

As you can see, since early 2015, border apprehensions have been on the rise. Now, 12-month totals remain below their recent peak in 2014, when a wave of unaccompanied children and family units pushed inflows upwards. However, we are beginning to approach those levels. Readers will recall that the previous crest caused at least a few headlines. If this trend continues into the summer, it seems likely media attention will start to heat up, especially if Congress is debating a border wall at the same time. I want to say here that I am only providing the facts: I make absolutely no comment here about border security, how best to address these issues, etc. I am only and exclusively making reasonable forecasts of likely future outcomes.

However, the 2014 wave should give us pause in saying we face a large problem. The 2014 wave crested and fell. Review the monthly data again. We saw a huge spike, then a huge decline. Increases in monthly apprehensions today do not mean that we face a long-term increase, and these increases remain far below levels of illegal immigration seen in years before 2010.

Demographics of Arrivals Are Changing

We are seeing fewer individual working-age men and women, and more children and families. For the first time on record, December 2016 saw more family-and-children apprehensions than non-family apprehensions! Here’s the family-and-children share of total apprehensions, going back to when this demographic data begins in October 2009:

As you can see, we are experiencing a massive composition shift in who is apprehended at the border. Now, it may be that some of this is due to real or perceived policy changes. For example, if Salvadorean families believe they can successfully claim asylum for their children, they may migrate more than in the past. The extent to which policy changes, or Latin American perceptions of policy changes, correct or not, have driven the rise in child and family inflows is hotly debated. I will again profess agnosticism here. What I will note is that this trend is a long-term trend.

It is closely associated as well with declining apprehensions from Mexico, and rising apprehensions from Central America. And that change leads us to our next major factor.

Seasonality of Migration Is Changing

If you review the first monthly apprehensions chart, you’ll notice strong seasonality. Inflows usually peak in March and April, and have troughs around December. This is largely driven by climate, which both drives the agricultural calendar that attracts many migrants, as well as determining what times of year are easy for travel.

The chart below shows a rough estimate of how much each month deviated from the seasonal “normal” amount.

As you can see, monthly variation from seasonal trends has grown dramatically in recent months. We are seeing migration flows that are structured in a wholly new way. This is partly because child and family inflows have always been less seasonal than labor inflows, but also because more labor inflows are coming from more distant countries, where seasonal entry/exit is more difficult. These composition shifts result in an altered seasonal pattern, which makes it harder to predict where apprehensions may head in the future. Any prediction must be ventured with a grain of salt.


Increased apprehensions could come from many sources. For example, children and families may be easier to apprehend than traditional forms of illegal immigration, thus rising apprehensions may not reflect rising total illegal immigration. Changes in border enforcement may also drive rising apprehensions; I do not know if man-hours of enforcement have changed over this period. Changing seasonality trends may also be misleading us about what the future looks like, and could be either over- or under-stating true trends in illegal immigration.

However, this data is the most widely-used proxy on both sides of the aisle. If it continues to rise, migration-watchers of all stripes will take notice, and will begin to raise the volume of the discussion. If this occurs alongside other migration-related political debates, it has the potential to create an extremely high-volume national debate alongside rhetoric of immediate crisis. Those interested in migration questions, then, should take note of these developments now and invest resources in determining what is driving these increases, and how the United States can respond.

Check out my Podcast about the history of American migration.

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I’m a native of Wilmore, Kentucky, a graduate of Transylvania University, and also the George Washington University’s Elliott School. My real job is as an economist at USDA’s Foreign Agricultural Service, where I analyze and forecast cotton market conditions. I’m married to a kickass Kentucky woman named Ruth.

My posts are not endorsed by and do not in any way represent the opinions of the United States government or any branch, department, agency, or division of it. My writing represents exclusively my own opinions. I did not receive any financial support or remuneration from any party for this research.