Summer fog variability in the coast redwood region: climatic relevance and ecological implications James A. Johnstone Department of Environmental Science, Policy, & Management University of California, Berkeley

Coast Redwood Sequoia sempervirens (D. Don) Modern distribution suggests a dependence on marine conditions / coastal fog

Research Questions: How and why does summer fog in the redwood region vary on annual to multi-decadal time scales? How is its variability connected to marine conditions and regional climate patterns (e.g. ENSO, PDO)? How have these conditions changed over the past century? Impacts on redwood function / ecology?

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Arcata Monterey Primary data: Hourly airport readings of cloud ceiling height June-September summers Near-continuous records ( ) in the Redwood region Fog = cloud ceiling at/below 400 m Sonoma 2003

Hourly cloud height Sonoma County Airport June 2003

Hourly cloud height Sonoma County Airport Coast Redwood Forest 300m elev. Sonoma County June 2003

Hourly cloud height Sonoma County Airport Coast Redwood Forest 300m elev. Sonoma County June 2003 Fog raises humidity, controls water loss by Redwoods.

Summer Climate of the NE Pacific Key elements: North Pacific High Alongshore winds Coastal upwelling Coastal stratus/fog

Coastal temperature inversion, vertical humidity contrast Mean summer profiles at Oakland: 400 m Relative Humidity Temperature

Summer Daily Maximum Temperatures: Northern California Inland-coast T MAX contrast Data: PRISM (Oregon State U.) Daly et al. 2004

Summer Daily Maximum Temperatures: Northern California Capping inversion restricts marine layer to coastal elevations below ~ 400m

Summer mean fog frequency Redwood distribution ~ 30% coastal fog threshold

Diurnal cycle of ceiling height clear sky

Interannual fog variability Varies by a factor of 2.3

Extreme years: 1951 (14.8 hrs) 13 fog-free days (daytime hrs) 1997 (6.4 hrs) 62 fog-free days Hours of Fog per day

Extreme years: 1951 (14.8 hrs) 13 fog-free days (daytime hrs) 1997 (6.4 hrs) 62 fog-free days 2009 near-average (~10 hrs) Hours of Fog per day

Palo Alto Airport

Fog enhanced with NE-ward expansion of N Pacific High

Fog correlations with sea-level pressure (SLP) r = 0.58

Fog vs. Oregon coast meridional wind speed (r = -0.69)

Fog correlations with sea surface temperature (SST) PDO-type SST signature Summer Fog- PDO correlation r = -0.52

Fog correlations with summer land T MAX Coherent pattern over the entire U.S. west coast

Fog correlations with upper-air temperatures at Oakland 500 m

Fog vs. Oakland Inversion Strength (r = 0.67) T – T 0-400

Inversion strength correlations with T MAX

Vertical and longitudinal temperature variations related: Weak inversion permits marine air and cloud to rise and penetrate to interior Subsidence tends to warm the interior and intensify the coastal inversion

Strong coupling among: Inland-coast T MAX contrast Inversion strength Fog frequency Cross-correlations:

T MAX Inland-Coast Contrast Fog correlation: r = 0.84 Suggests ~33% reduction in inversion strength and fog frequency.

Ukiah (interior) Berkeley (marine) Change in T MAX contrast exemplified by Ukiah-minus-Berkeley difference : 9.6°C difference : 6.3°C difference 50% reduction

T MAX Contrast, Northern California SST r = -0.73

Conclusions: 20 th century weakening of T MAX contrast implies: Greater inland penetration of marine air in summer Weakened inversion Reduced fog frequency Important terrestrial climate changes linked to ocean-atmosphere variability along the U.S. West coast and the broader N. Pacific. Greater evaporative demands may have important implications for coastal terrestial species and ecosystems, including redwood (heightened drought sensitivity?)

Further work: Stable isotope tree-ring calibration: 4 Redwood sites: ~50-yr analysis of δ 18 O, ∆ 13 C (discrimination)

∆ 13 C: Expected positive relationship with humidity / fog Positively correlated with: Summer fog frequency

∆ 13 C: Expected positive relationship with humidity / fog Negatively correlated with: Coastal SST PDO

δ 18 O correlated with sprintime pressure over the California coast and much of the globe (Multiple local factors appear to be involved)

Research funded in part by: The Save-the-Redwoods League The Berkeley Atmospheric Sciences Center The National Science Foundation Thanks to collaborators: Todd Dawson (Berkeley) John Roden (Southern Oregon Univ.)