Safety
Safety on the GR20
Even in the height of summer, the GR20 remains a high-mountain route. Thunderstorms, early-season snowfields, heat, fire, no phone coverage: here are the real risks and the reflexes that matter. Not to scare you, but to get you home.
The context
Not your average hike
The GR20 strings together technical terrain, exposed ridges and long days, under mountain weather that can flip in an hour. Escape routes are rare. Being fit isn't enough: you have to know how to read the conditions, anticipate, and accept changing the plan. Most real trouble comes less from sheer difficulty than from a bad decision at the wrong moment.
Weather
Thunderstorms and mountain weather
In summer, storms often break in the early afternoon, sometimes very violently. It was a storm that caught hikers out in the Cirque de la Solitude in June 2015, killing seven. The lesson is simple and holds for the whole route: never commit to a ridge or an exposed passage when the weather looks doubtful.
The right reflex: check Météo-France Montagne Corse every day, start early to clear the high sections in the morning, and know how to wait, go around or turn back if the sky clouds over.
Early season
Snowfields: June is not September
In early summer, snowfields can linger at altitude and turn some northern stages genuinely alpine: typically Carrozzu → Asco, Asco → Tighjettu, Manganu → Petra Piana or Onda → Vizzavona. Depending on the year, the Park explicitly recommends crampons, an ice axe and rigid or semi-rigid mountaineering boots, along with the skills to use them.
In other words, the June GR20 is not the September one. Before an early-season departure, always check the PNRC page and the Météo-France bulletin: good trail-running shoes may be enough on dry ground, but not on a snow gully.
Summer
Fire and leaving Calenzana
From 15 June to 30 September, lighting a fire and smoking are forbidden in the massifs, forests, heathland and scrub. When the risk is severe (strong winds, heatwave), massifs can be closed temporarily, the GR20 included.
The official fire-risk map for Corsica is updated every evening, around 6 p.m., for the next day: check it the day before any high-risk day. And in the north, remember the rule: no departure on the GR20 from Calenzana is allowed after 11 a.m. Plan 1 to 2 days of margin in your schedule, because a closure can push back a flight or ferry.
Communication
Phone coverage and emergency numbers
Phone coverage is patchy, even non-existent, near several refuges: Ortu di u Piobbu, Carrozzu, Tighjettu, Ciottulu di i Mori, Manganu, l'Onda, Usciolu, Paliri. Make the most of covered zones to let your loved ones know you're safe, check the weather and manage a booking. A power bank is no luxury, especially if you navigate from your phone.
The reflex in an emergency: 112. Dialable from any mobile, it automatically switches to the first available network, even without a signal from your own operator, which is decisive in the GR20's dead zones. If the coverage only allows a text message, write to 114.
Emergency: dial this first
112, the European number, the priority in the mountains. It routes everywhere, even without your operator's network.
Emergency by text
114, when the network only allows a text (dead zone), or for deaf and hard-of-hearing people. Reachable 24/7.
Police / Fire brigade
17 (police, gendarmerie) and 18 (fire brigade).
PGHM: mountain rescue
The high-mountain gendarmerie unit. For an actual rescue, you go through 112; the direct lines are mainly there for advice before setting out: 04 95 24 24 00 (Ajaccio) and 04 95 47 71 46 (Corte, the closest to the GR20).
Deciding
Knowing when to turn back
On the GR20, real courage is often turning back: shortening a stage, waiting for a weather window, or stopping when your body gives out. Vizzavona, at the halfway point and reachable by train, is the logical cut-off point to finish, take a break or head home without drama.
We had to adapt our own plan along the way. There's no shame in cutting it short: the mountain will always be there. Better a shortened GR20 lived to the full than one day too many that ends badly.
Sources
Check before you go
Conditions change every season. The reference sources are the Parc naturel régional de Corse, Météo-France Montagne Corse and the official fire-risk map. Mon GR20 is a personal account: it complements these sources, it doesn't replace them.