… As an environmental scientist, I see big changes in store for Muir’s Range of Light. … What does climate change mean for backpackers, tourists, and skiers, for agriculture and cities? In all cases, water is at the heart of the story. Sixty percent of all of California’s water supply comes from the Sierra. That water irrigates the great orchards and crops of the Central Valley, supports municipal water supplies, and nurtures the extensive wetlands of the San Francisco Bay area. Precious water is wasted when a big flush of spring runoff overwhelms reservoirs. Agriculture and cities depend on snowpack to gradually release water and maintain reservoirs. … With climate change, water runoff will occur much earlier, and flooding will be more severe. California will suffer even more drought, stimulating more water projects.