With a slew of border closures in the European Union, refugees and economic migrants have increasingly looked to make the longer and more dangerous trip to Europe by traveling on small boats from North Africa to Italy. As a result, more than 100 people died in a series of shipwrecks in the Mediterranean Sea throughout the past weekend, the International Organization for Migration said Tuesday.

“It is becoming the preferred route. So therefore we are very mindful of what could be coming in the next few months,” Joel Millman, a spokesman for the organization, told a news conference.

Warmer weather often precedes more frequent migration attempts to reach Southern Europe, and summer has historically been the time when most economic migrants and asylum-seekers attemp to leave their home countries for the region’s shores.

More than 1 million people crossed into Europe illegally in 2015, with the vast majority of them qualifying as bona fide political refugees, according to the United Nations. The surge in arrivals has been caused by ongoing and escalating violent conflicts throughout the world, particularly in Iraq and Syria.

As Europe has increasingly struggled to cope with this refugee crisis, countries throughout the 28-country bloc have closed their borders, particularly along the once-popular Balkans route that leads from Greece through Eastern Europe and up to Germany. A new deal between the EU and Turkey has slowed migration to Greece, however, as all migrants risk being sent back to Turkey upon arrival at the eastern Greek islands under the deal passed earlier this year.

“It’s clear that the Balkan route is a thing of the past and no longer will or should be a place again from where people will be waved through to Germany and Austria and to the center of Europe,” German Interior Minister Thomas de Maizière said in April, Reuters reported.