Arroyo willows show drought stress as streamflow drops

July 21, 2026

along the stream corridors are displaying a contradiction in mid-July: leaves turning color and senescing while simultaneously pushing new breaking buds. This split signal is not a seasonal rhythm but a sign of drought stress — the tree's conflicting response to water scarcity. Streamflow this week is barely above 8 cubic feet per second, near the low end of its recent range, and water temperatures have climbed past 20°C. The arroyo willow is foundational to these riparian edges: its canopy shades the water, its roots hold the banks, and its leaf litter feeds the aquatic invertebrates that everything else depends on.

The Coast Miwok communities who lived throughout these hills and drainages regarded the arroyo willow as a reliable water-finder — where it grows healthy, water persists. That traditional knowledge carries weight now. Across the inland slopes, have already entered midsummer dormancy. Both signals together — the willow's stress and the buckeye's shutdown — suggest that the drought pulse running through the landscape is now reaching the stream margins, not just the uplands. The riparian refuge is contracting.

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