… On the trail, water truly does dictate most decisions. The availability and quality of drinking water dictates how much to carry, how to purify it and how far to walk each day. Water from the weather—rain, snow, sleet, humidity—dictates when the PCT thru-hiking season begins. It usually begins between March and May so a northbound hiker hits the Sierras after the snowpack on its passes has sufficiently melted to allow for safe passage, and ends by September or October, before the snow begins to dump on Washington. … “Part of the reason it’s so hard to see climate change is that there’s so much variation from year to year that it hides the trend,” said Naomi Tague, a professor in ecohydrology and ecoinformatics at University of California, Santa Barbara. “Everybody wants these easy prescriptions that work everywhere,” she said, but “How much water you have in a particular stream depends on the snow it got that year. It depends on geology. It depends on how big that watershed is. It depends on the type of vegetation. You want to start putting all the pieces together. That’s how you get an integrated systematic perspective.”