Once again, smugglers are bringing hundreds of women and children each day to the Mexican banks of the river and sending them across in rafts. In a season when illegal crossings normally go down, “The numbers have started going the other way,” said Raul L. Ortiz, acting chief of the Border Patrol for the Rio Grande Valley. Since Oct. 1, official figures show, Border Patrol apprehensions of migrant families in this region have increased 150 percent over the same period last year, while the number of unaccompanied children caught by agents has more than doubled.

The new flows here are smaller than the surge in the summer of 2014, but come after a year of declines in illegal crossings across the southwest border. The increases come as Americans’ concerns about border security are heightened after the Nov. 13 attacks in Paris raised fears that terrorists would try to sneak into the United States. And they are complicating the Obama administration’s efforts to reassure the country that the border is under control…

A mix of factors seems to be driving the new flow. Many of the migrants are women and children fleeing vicious gangs and endemic sexual violence in Central America who are hoping for asylum in the United States. Rather than hiding from Border Patrol agents they often try to find them, to ask for protection and start the long legal battle to remain here.

In October, the United Nations High Commissioner for refugees, António Guterres, said uncontrolled violence by the gangs had become “pervasive” in El Salvador, Guatemala and Honduras. He issued an “early warning” of “a looming refugee crisis.”