trend (1979–2025)
trend (1979–2025)
(peak >25 kW/m)
(1979–2025, all months)
The question isn’t how many swells arrived. It’s how much energy they carried when they did. Wave power integrates wave height squared and period together — a 1.8-meter, 14-second south swell delivers eight times the energy of a 0.6-meter, 7-second chop. This analysis runs 47 years of hourly ERA5-Wave reanalysis through the deepwater power approximation P ≈ 0.5 × Hs² × Tp at the Saladita grid cell, then asks whether the number changed over time.
Four metrics, four regression tests. One passes cleanly (p<0.05): peak annual wave power is rising. The other three are flat or marginal. The mean wave energy a surfer experiences in any given week has not systematically changed in 47 years. What has changed is the upper tail — the hardest days, the heaviest swells, the events that reshape sandbars and stress coral.
One signal is real. Three are not.
OLS regression of each annual metric vs year. 47 data points; p-values approximate (autocorrelation is possible at annual scale).
Peak annual power: +4.1 kW/m per decade (p=0.032, R²=0.098). Total implied shift: +19 kW/m from 1979 to 2025.
In 1979, the single hardest hour of the year was modeled at roughly 24 kW/m. By the 2010s, the hardest hours were regularly exceeding 50 kW/m. 2018 recorded 72 kW/m and 2024 reached 81 kW/m — the highest single-hour value in the 47-year record. The trend is statistically real by conventional standards, though R²=0.098 means year-to-year variability is large.
Mean annual wave power: effectively flat at 9.5 kW/m (p=0.95).
The average week at Saladita is indistinguishable energetically from the average week in 1979. What you would notice as a regular is not a change in the baseline — it’s the occasional event that has become more severe.
September is the hardest month.
Mean and 90th-percentile wave power by calendar month, pooled across all 47 years. SH groundswell season (April–October) highlighted.
The season opens in April, peaks in September, and drops sharply after October.
September averages 12.7 kW/m mean power and a 90th percentile of 21.2 kW/m — nearly four times December's average. May and June are nearly equal in average power (~12.2–12.4 kW/m), holding slightly above July and August. October drops off but remains above the annual mean. The window April–October accounts for the bulk of all meaningful surf energy at Saladita.
Consistent energy, harder ceiling.
Wave power touches two things at Saladita: surf quality and the reef below it.
The everyday session hasn't changed. The occasional big day has.
Mean energy is flat, so the typical chest-high groundswell that makes Saladita rideable is arriving with the same average frequency and size it did in the 1980s. But the upper-tail events — the days when it closes out, when the current runs hard, when midlength equipment makes more sense than a longboard — appear to be occurring more often and reaching higher peak energies than they did in the early record. The “lots of water” days that call for different equipment are plausibly more common now.
Extreme events drive coral stress. The trend points the wrong way.
Coral structural integrity at reef-flat depths depends partly on wave-induced mechanical stress during extreme events. Rising peak energy — independent of frequency or mean energy — means higher shear stress on coral during the hardest swells. Combined with the documented surface warming at this site (+0.12°C/decade, from the companion climate analysis), the physical environment for shallow-water coral is shifting on two axes simultaneously. This analysis cannot quantify biological impact; it documents the physical driver.
ERA5-Wave is a reanalysis, not a measurement. The wave field at Saladita is derived from a global atmospheric model forced with ERA5 winds, then validated against buoy observations globally. The coastal grid cell here is not validated against any local instrument. Saladita’s particular bathymetry, headland shadow, and kelp/reef bottom interact with incoming swells in ways the 0.25°-resolution ERA5 grid cannot resolve. Local wave heights can differ meaningfully from the model output.
The deepwater power formula is an approximation. P ≈ 0.5 × Hs² × Tp assumes fully developed deepwater conditions. In the transitional depth range where Saladita breaks, wave energy is modified by shoaling and refraction. The formula gives a useful relative proxy but not an absolute physical energy at the break.
The peak-power trend is real but modest in explanatory power. R²=0.098 means about 90% of the year-to-year variance in peak power is explained by factors other than the long-term trend — ENSO state, tropical cyclone proximity, north Pacific storm tracks. The trend is statistically significant; it is not dominant.
The Open-Meteo marine API requires models=era5_ocean for pre-2022 data. Without that parameter, the default endpoint only returns data from October 2021. All values here use the full ERA5-Wave reanalysis; the script is reproducible and the parameter is documented.
The ocean at Saladita delivers about the same average energy it did in 1979. But the hardest hours — the ones that determine what boards you bring and how the reef ages — are getting harder.Synthesis · ERA5-Wave, 412,008 hourly observations · June 2026
Sources & method
Open-Meteo marine archive, ERA5-Wave reanalysis (models=era5_ocean), 17.5897°N, 101.4317°W, January 1979–December 2025. Variables: wave_height (Hs, significant wave height in m), wave_period (Tp, peak period in s). Wave power computed as P ≈ 0.5 × Hs² × Tp (deepwater approximation; P in kW/m). 412,008 valid hourly records.
Annual metrics aggregated per calendar year. Linear regression with scipy.stats.linregress (OLS). p-values approximate; temporal autocorrelation in annual series is possible. Monthly climatology pools all 47 years of each calendar month.
Script: scripts/analyze_wave_power_trend.py → functions/api/_findings_wave_power.js. Artifact JSON served at /api/findings-wave-power.