Outdoor climbing is different from indoor climbing. For example, you need to take the weather into account. Rock climbing in the rain is unpleasant, much harder, and can be dangerous. Sometimes it takes a long time for the rock to dry again. When the sun is shining, it usually dries quickly, although on a north-facing wall it can take much longer. A breeze also helps to dry a route. In some areas, there are routes that stay dry longer (think of a large overhang or a cave), but once they become wet, they often stay damp for a longer time as well.
Furthermore, the temperature can fluctuate significantly. Always think carefully about what to wear and what to bring to the rock. Don’t forget your sunscreen during the warm months; sometimes it’s not possible to belay or climb in the shade.
Never climb in a thunderstorm (or when it one forecast) or when there are very strong winds.
In short: know what the weather is going to do and plan accordingly.
Thunderstorms: why climbing during them is dangerous and what to do
Thunderstorms are generally a hazard in mountaineering, and this also applies to rock climbing. An obvious danger is the risk of lightning strikes. Rocks and tall climbing walls often act like natural lightning rods, attracting lightning bolts. Additionally, many climbing materials are made of metal and therefore conduct electricity well, which can result in high currents that cause severe burns.
Besides the direct dangers from lightning strikes, there are also indirect risks. These include an increased chance of falling rocks, slipping on wet rock, poor visibility due to heavy rain, mist, or clouds, and accidents caused by rushed decisions or actions. The majority of accidents during thunderstorms in the mountains are caused by these indirect hazards.
Of course, the most important thing is to be well prepared. Check the weather forecast beforehand and do not go climbing if thunderstorms are predicted. If you still get caught in a thunderstorm, stay calm and exit the route. Once at the bottom of the route, the safest option is to put away your metal gear and look for a spot with minimal risk of lightning strikes, falling rocks, or electrical conduction.
If the rest of the terrain poses a risk, the best option is to sit on your rope or backpack at some distance from the rock wall (see the illustration).
For those who want more information, see the detailed guides by the NKBV (in Dutch): https://nkbv.nl/kenniscentrum/onweer-in-de-bergen-deel-1.html en https://nkbv.nl/kenniscentrum/onweer-in-de-bergen-deel-2.html
The holds are not color-coded outdoors. For many, this is a positive aspect: each route is a puzzle. However, it can sometimes be difficult to follow or even find a route. The topo (climbing guide for an area) includes photos or drawings that indicate the course of the route. Still, you will often need to search for where a route begins or realize halfway up that you are somewhere else than you thought. Learning how to use a topo and find a route is part of the course. ASAC has topos available to borrow for most climbing areas. See https://asac.nl/topos/ for an overview.
Most climbing areas also have information boards or websites where additions or changes to the topo are noted. Sometimes certain routes or parts of the area are closed for safety or nature conservation reasons. Additionally, climbing areas often have special features or specific (behavior) rules that apply. Make sure to familiarize yourself with these when entering the climbing area or beforehand on the website.
The NKBV provides an overview of climbing areas (in Dutch) near the Netherlands.
Rock can take many forms. Sometimes it’s smooth, other times it’s sharp, be aware of this. Falling on lead outdoors can be very different from indoors, as rock faces almost never go straight up. While climbing and belaying, you can usually estimate the fall risk, but in case of an unlucky fall, you're more likely to hit something than indoors. This is one of the reasons why we always wear a helmet. Also, there’s no padded floor outside, so take extra care when climbing and belaying up to the first bolt (and often a bit beyond that). During an ASAC course, there is always a first aid kit available, and all SKIs (climbing instructors) are first aid certified. If you go climbing independently, bring your own first aid kit and make sure you know how to use it.
In climbing gyms, ropes are always long enough to lower the climber back to the ground. Outdoors, you don’t have that guarantee! If the climber goes too far, the rope may run out while lowering, which can result in the climber hitting the ground. So always tie a knot in the end of the rope. A stopper knot or figure-eight knot with a long tail is suitable (see Chapter 5). ASAC single ropes are standard 70 meters long. Check the topo for the route length and whether your rope is long enough.
Always make sure you know the emergency number (in almost all of Europe this is 112), and whether there is a specific number for a (mountain) rescue service in the area you’re climbing. Store the local mountain rescue number in your phone. In case of an emergency, it’s important to be able to clearly describe your location: which area and which specific crag you’re on. So always know where you are climbing, even if you’re with more experienced climbers. Sometimes local rescue teams are familiar with specific routes in the area. You can also describe the path you took to get to the route.
In addition to a first aid kit and proper clothing, it's also smart to bring enough food and water. Make sure your phone is fully charged or bring a power bank. And if you need to find your way back in the dark, a headlamp is much more useful than your phone flashlight.
Climbing areas are almost always lovated in nature reserves. Because of their steep terrain and limited accessibility, rock faces form unique ecosystems. Be aware of the privilege it is to enter these areas and act as a respectful guest. Don’t leave any trash behind, and clean up before you leave. Want to know more? Read about the 7 principles of Leave No Trace.
One thing Dutch (groups of) climbers sometimes forget is that natural areas are also places of peace and quiet — for the animals, but also for the other people visiting. Talk quietly and avoid shouting. Don’t play music, and so on. We don’t have any actual rocks in the Netherlands, which is why we’ve made agreements with mountaineering associations in other countries that allow us to climb there. Let’s make sure we remain welcome.