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Water & Weather in Napa County
Water
Of the basic natural resources that make up a watershed, water is perhaps the most critical. All life depends on water for survival. Protecting the quality and quantity of water are two goals of watershed protection efforts in Napa County. Improving water quality means preventing water pollution. Non-point source pollution (pollution from diffuse or scattered sources) is the nation's leading cuase of water degradation and is a concern in Napa County. As rainwater flows across streets and yards, as well as construction and agricultural sites, it picks up sediment, oil, fertilizers, pet droppings, and other pollutants. These are carried into channels and storm drains that empty directly into our waterways. Understanding and managing non-point source pollution is a major strategy for protecting water quality in Napa County.
Ensuring long-term availability of adequate water supplies means making better use of what we already have. Establishing long-term water budgets, monitoring groundwater and stream flows, minimizing water use, and increasing the use of recycled water are some of the practices being implemented throughout the county to manage water use more efficiently. Residential water conservation information may be available through your local water provider, or visit www.wateruseitwisely.com
Weather
The Napa Valley has a Mediterranean climate characterized by warm, dry summers and cold, moist winters. The majority of annual precipitation occurs as rain that falls during the winter and early spring. The highest rainfall occurs on the western side of the watershed. Between 1961 and 1990, the average annual precipitation was 35–40 inches (89–102 cm) in the western portion of the watershed, and 20–25 inches (51–64 cm) in the eastern portion of the watershed (Western Regional Climate Center 2002). Rainfall gages also show a north-south trend of precipitation in the watershed. Precipitation decreases southward through the Napa Valley with average annual precipitation equal to 38 inches (96 cm) at Calistoga2, 35 inches (89 cm) in St. Helena3, and 25 inches (64 cm) at the Napa State Hospital4 (Western Regional Climate Center 2002). The average daily maximum temperature decreases to the south (Western Regional Climate Center 2002), because coastal fog keeps the lower valley cooler.
Sources: Napa County Resource Conservation District, Stillwater Sciences Napa River Limiting Factors Report
Photos (in vertical order) by Jonathan Koehler, Todd Adams
