Morning vs Afternoon Climbing at Kalymnos: the key role of humidity (hygrometry) and wind

When it comes to choosing between morning or afternoon for climbing in Kalymnos, most people instinctively think morning is better because it's cooler. And yet... it's often the opposite! Humidity in the air (hygrometry) plays a huge role, and it varies dramatically throughout the day. I'll try to explain this simply, with a bit of science behind it, based on my 10 years of experience on the island and what the climbing community knows.

Humidity on Kalymnos: Average 60-80 %, but it changes a lot during the day

Humidity ranges from 45 % to 90 %, with an average around 60-80 %. It depends on temperature: the warmer it gets, the lower the relative humidity (warm air can hold more moisture, so the percentage drops). On Kalymnos, the typical daily curve shows a peak in the morning (often over 80 %, sometimes with dew on cars or the road), a low point around 12-3 pm (when it's hottest, often below 65 %), and a rise again in the evening.

Why? The island is arid but close to the sea: sea breezes and the Meltemi (northern wind) influence everything. Southern winds are often more humid (bringing Mediterranean moisture), while northern ones dry the air. A sudden wind shift or marine air mass can change it all quickly.

Why humidity impacts climbing so much (simplified science)

Humidity reduces grip (friction) between your skin/shoes and the rock. Scientifically, the friction coefficient drops because water molecules from the air adsorb onto the porous limestone surface, making holds slippery (like an invisible thin film of moisture). Studies (e.g., in Sports Biomechanics) show that on limestone, humidity above 70 % can reduce friction by 20-30 %, and chalk only partially compensates (boosting grip by about 18 % on damp limestone).

On Kalymnos, the limestone is Quaternary (recent geological period, ~2.5 million years old), but exposure makes all the difference:

• Grey rock (vertical or slightly overhanging): exposed to rain for millennia, it's "washed" and less porous – so less sensitive to humidity (stable grip even at 70-80 %).

• Overhanging rock (orange, red, yellow, white): protected from rain, more porous, it absorbs air moisture easily – grip drops as soon as 65 % (holds feel "greasy", more effort needed to hang on).

Wind helps: it dries your skin and the wall, increasing friction (northern wind is noticeably better than southern).

In summary:

• Below 65 % humidity: excellent grip

• 65-75 %: average grip (doable but more effort)

• Above 80 %: poor grip (slippery holds, wasted energy)

Counter-intuitive: why afternoons are often better than mornings

Mornings are cooler (less sweating, better thermal comfort), but more humid (hygrometric peak, possible dew). Result: reduced grip, "sweaty" holds, more energy needed just to hang on (when you can even hold them!).

Afternoons are hotter, but humidity drops (low around 12-3 pm): drier air, better grip, less effort for the same holds. On small crimps or overhangs, between 11 am and 3 pm with wind are often optimal conditions.

How to choose: check the humidity curve on a weather app, plus wind and direction.

• On grey vertical rock, humidity isn't much of an issue even when high.

• On overhanging sectors (orange, yellow, white), humidity below 65 % gives the best grip conditions.

• Strong wind and its direction improve your climbing.

Humidity-sensitive sectors:

• Kalydna, Secret Garden: very hygrometric, tough above 70 %.

• Grande Grotta / Panorama: less affected.

• Protected caves with little air movement like Dragoras Cave, Rocknroll Cave, Sikati: stable humidity but less drying wind, which can make them trickier.

Conclusion

On Kalymnos, forget the intuition "cool morning = best climbing": humidity often rules the game.

With me, we'll pick the perfect sector and time slot based on your goals, your level, and of course the weather!If you'd like a custom program with the best timings, just contact me and we'll sort it out together!

See you soon on the rock!

Fred