We awoke to snow over Lake Titicaca yesterday - well, more of a mix of hail and sleet really. It looks beautiful on the surrounding hills, but it's not meant to happen. My guidebook gives the average rainfall for this month in this part of the world as zero.

But whether it's global warming, a mini el Niño or just the Incas' revenge, the dry season in Peru and Bolivia has turned distinctly wet. For thousands of gringos panting over the Inca Trail to Machu Picchu this July, life has become a lot more uncomfortable.

Be warned: the trail is four days of strenuous walking at the best of times, climbing to 4,200m (well over 12,000 feet) at its highest point, the ominously named Dead Woman's Pass, before dropping steeply...and then climbing steeply again. We did it in four days of almost continuous rain and there were times when it became a slog rather than a mystical life-changing experience. At one point we were trudging up a steep stone pathway with torrents pouring down either side, and a third torrent coming down the middle of the path. You can't help being full of admiration for the Inca road builders whose work has survived more than five centuries of extreme weather conditions. Meanwhile, my boots were full of Andean rainwater.

(We came across a party of contemporary path-makers a few days later on the Island of the Sun in the middle of Lake Titicaca - men and women carrying massive rocks behind their backs - about two dozen local villagers chattering and all pitching in together.)

The worst thing about the Inca Trail in the rain wasn't so much the struggle to keep dry in small dripping tents, as missing the views along the way - there was merely the suggestion of vast peaks and deep valleys through the clouds.

At least we got through. Several parties a day behind us were turned back by their guides because there was thick snow on Dead Woman's Pass and it was thought unsafe. Backpackers' gossip was that they didn't all get their money back.

Don't let me put you off if you are thinking of doing the Inca Trail. Machu Picchu really is marvellous - and in our case the rain stopped as we reached the spot overlooking the extraordinary complex of buildings, which made up for everything.

But do take waterproof trousers and buy a poncho in Cusco (where there is now a roaring trade). You will look a bit daft but they keep off some of the wet. Several of our fellow trekkers did the walk in trainers - but they squelched. Moral: decent boots.

And when the going gets tough you want a good tour company - everyone going on the Inca Trail now has to go with an organised tour and official guide. We went with SAS, which was a bit more expensive than some (US$240 as opposed to US$180 for a lot of Cusco companies), but the service was good. Our porters produced amazing hot meals in very adverse conditions, quite apart from lugging four days provisions, ranging from gas cylinders to trays of eggs, up and over the mountains on their backs, packing up the tents behind us and still getting to the end of the day's trek before us to get the tents up and offer cups of hot tea.

You could try checking on the weather in advance but everyone seems a bit mystified. The South American Explorers Club has a Cusco branch (cuscoclub@saexplorers.org), although they didn't seem very well briefed on the current situation when I dropped in on them. There is also the English language Cusco Weekly.

If the unseasonable rain is inconvenient for tourists, spare a thought for the campesino farmers who at this time of year are trying to harvest, maize and dry their potatoes. We passed whole families painstakingly putting out potatoes (they come in a wide variety of colours and sizes) on straw mats one day. The next day it poured with rain, and they had to start again from scratch.