A 440-Year Reconstruction of Heavy Precipitation in California from Blue Oak Tree Rings

Abstract

Abstract The variability of water year precipitation and selected blue oak tree-ring chronologies in California are both dominated by heavy precipitation delivered during just a few days each year. These heavy precipitation events can spell the difference between surplus or deficit water supply and elevated flood risk. Some blue oak chronologies are highly correlated with water year precipitation (r = 0.84) but are equally well correlated (r = 0.82) with heavy precipitation totals ≥25.4 mm (1 in., ≈95th percentile of daily totals, 1949–2004). The blue oak correlation with nonheavy daily totals is much weaker (<25.4 mm; r = 0.55). Consequently, some blue oak chronologies represent selective proxies for the temporal and spatial variability of heavy precipitation totals and are used to reconstruct the amount and number of days with heavy precipitation in northern California from 1582 to 2021. Instrumental and reconstructed heavy precipitation totals are strongly correlated with gridded atmospheric river–related precipitation over the western United States, especially in central California. Spectral analysis indicates that instrumental heavy precipitation totals may be dominated by high-frequency variability and the nonheavy totals by low-frequency variance. The reconstruction of heavy precipitation is coherent with instrumental heavy totals across the frequency domain and include concentrations of variance at ENSO and biennial frequencies. Return period analyses calculated using instrumental heavy precipitation totals are representative of the return periods in the blue oak reconstruction despite the large differences in series length. Decadal surges in the amount, frequency, and interannual volatility of heavy precipitation totals are reconstructed, likely reflecting episodes of elevated atmospheric river activity in the past. Significance Statement Tree-ring chronologies of blue oak are highly correlated with precipitation delivered to northern California during just the heaviest days of precipitation each year. The reconstruction of heavy precipitation indicates decadal episodes with a high frequency of extreme precipitation. These episodes of frequent heavy precipitation likely arose because of elevated atmospheric river activity and are relevant to the analysis of water supply and flood hazard in California.