I live in rainy Wales. I often carry a sturdy umbrella for day-hikes and overnights in spring or summer; but I wouldn’t rely on it for more than that.
– umbrellas are best in summer, when there is little or no wind and the rain comes straight down. You wear less clothing and stay cooler.
– in winter, in gusty rain it won’t keep your body or your shoes dry. Also, my fingers freeze from holding it.
– In towns umbrellas work because the buildings block out most of the wind. In open country you get the full force in a windy region.
– an umbrella keeps my specs dry. But I also have a cap with a big peak for that.
– You can hunch down under it, to eat, or take a rest, study a map, etc. Leafy trees are better, but umbrellas are handy too ;)
Steve


