December 2024 Storm

On December 13, 2024, it started raining in the evening, and mostly stopped by 9am on Saturday December 14th.

The Nov 22nd and Dec 14th peak flows on San Geronimo Creek were the same: 1,105 cfs. Daily average flows were 423 cfs & 356 cfs, respectively. In November it took 8.75 hrs of 2.34" of rain (1/4" per hour) to get to peak from 113 cfs; In December it took 7.25 hrs of 2.32" of rain (1/3" per hour). These calculations use rounded times to the nearest hour for rain and quarter hour for flow & add an hour of lag time between rain and flow.

And then things got crazy.

Out at Limantour Beach at 8:51 am there was a 7.2-foot high tide. It felt like a hurricane, with blowing sand at eye level, sea spray, and foam. That day the King Tide plus winds wreaked havoc across West Marin, knocking  down trees, blocking roads and causing power outages, flooding low-lying areas, and damaging or destroying all the docks in Tomales Bay. The Point Reyes Christmas Bird Count was happening that day, and many areas were inaccessible or too dangerous to visit. Twenty trees were down on Limantour Road, and people stuck all day out there and on the point were only able to return at the end of the day (including me and my son). The count dinner at the Dance Palace was by candlelight for the second time in history.

Our rain total for the 2025 water year so far (Oct-Dec) in San Geronimo Valley is just over 25 inches--average is about 15". If it doesn't rain at all in January it would still be above average on February 1st. Other wet falls included 2012 (25.01" and then it essentially stopped raining for all of 2013), 2014 (28.38" and then it got very dry in 2015), 2021 (35.72", with 17" of that in a remarkable October storm and again it got very dry in 2022). In fact, it appears to be a rule over the last 14 years that a very wet fall (with over 25" of rain) precedes a very dry rest-of-the-season. Will this year be different?

25.16" of rain at the end of December 2024 is 57% of our annual
average and 164% of the Oct-Dec average.

2013 water year (30" of rain) for comparison. The 2013 calendar
year was the driest on record. Average is 45".

And now for something fascinating--I divided the volume of runoff by the volume of rain (estimated for a 6,000-acre watershed) to estimate the runoff efficiency of the last three water years. I got a very surprising result. We know 2023 was a wet year--but only for rain. A lot of that rain soaked into the ground, making the runoff that year actually lower than 2024. 2024 had near-average precipitation, but more runoff than the wet year of 2023.

2023 was wetter for rain and 2024 was wetter for runoff. So far,
Oct-Dec of Water Year 2025 has similar runoff efficiency as 2024.

For just October-December:

So the interesting question this table raises is, "what happened in the Autumn of 2022?" For similar rainfall as 2023, why was the runoff efficiency less than half of the other years? Summer 2023 had a much higher baseflow than 2022. Even though there was 3/4 of an inch of rain near the end of September 2022, October of 2023 started out with more than double the baseflow of October 2022. So the antecedent conditions--groundwater levels and flows--were much wetter in 2023.

November 2023 had a storm that dropped 3" of rain in a couple of days, while November 2022 had less than 2" spread out all month with about 1" on the wettest day. I previously noted that an inch of rain is needed the day before a flood in order to get a big flood. So if we recalculate this table and subtract the first inch of each storm (because it doesn't generate much runoff), or more appropriately only sum any rainfall following an inch in a day, we get the following:

Rain vs. Runoff (blue) and Effective Rain vs. Runoff (red).
Subtracting an inch from each 2-day total that has less than an inch
of rain on a day shifts the "effective" rain totals to the left, lining up our outlier
year 2021 a bit better and resulting in a better R-squared. This still
doesn't capture the whole story, but is fun to play with.

They turned it into Muir Woods

 "They turned it into Muir Woods," I heard someone say as I was leaving Roy's Redwoods yesterday. Roy's Redwoods is San Geronimo Valley's busiest and most famous local redwood grove. There grows the tallest tree in Marin County. 

I had heard this criticism of the $3.5 million Roy's Redwoods rehabilitation project before. The Marin County Open Space District site was closed all summer and completely redone. It is nice to be able to go back this fall and see what it looks like.

The goal of the project was to "

• Restore the hydrologic function of the alluvial valley;
• Improve redwood forest and wetland habitats;
• Guide visitors through an immersive and accessible experience of the redwoods."

When something like this happens, it is like gentrification of the woods. The "new" Roy's Redwoods looks nice--nice trails, well-organized, nice stone work (although the large boulders are a bit out of place and seem to belong in the Sierra Nevada), nice new boardwalks and bridges. It is welcoming in a familiar National Park sort of way, and makes walking the trails pleasant and efficient. I really like the nested loops of the named trails--once you figure out that pattern it is fairly easy to remember where the trails go. The Wilderness Way exploration and adventure zone is a nice (and surprisingly hazardous, and a totally fun mud pit when rainy) touch.

Beautiful stonework at the entrance to Roy's Redwoods

Nice new bridges

Wilderness Way adventure area

November 2024 Atmospheric River

The November 20-22, 2024 Atmospheric River dropped 11.65" in San Geronimo Valley compared to much higher amounts to the north. It was not as wet as the October 2021 storm (that dropped 12.67" in 36 hours causing San Geronimo Creek to peak over twice as high). But the 2024 storm lasted longer--it rained for three days straight (except for a break during the second night). It was so nice to see the sun again on the bright yellow fall leaves on Saturday! San Geronimo Creek peaked at 1,105 cfs at 2:15 pm on Friday November 22nd (at day 3 hour 14 on the graph below). The creek started at its late summer-fall baseflow of less than 1 cfs at the Lagunitas gauge, and as of December 1st is still flowing at 7 cfs. The peak flow was similar in magnitude to last winter season's highest flow in January. We already have about a third of our annual average rainfall as of the end of November, and our 3rd-highest to-date total since water year 2012. Along with over an inch of rain in early November, this has been a wonderful start to our rainy season.

Barnabe and Woodacre rain are reported about 10 minutes before and after the hour, respectively, but shown on the hour here (the hourly differences are mostly due to that). The x-axis is day.hour. 

Reconciliation

On October 26, 2024, the Alliance for Felix Cove hosted a reconciliation conversation between a Tamal-Ko (Tomales Bay Coast Miwok) family and a Point Reyes settler family. The settler family's ancestor, C.W. Howard--who owned most of the land on the west side of Tomales Bay--in 1887 hired Captain Henrik Claussen to evict all the Indians living on the west side of Tomales Bay. Their houses were destroyed and the people were forced to leave. One house remains standing at Felix Cove (Laird's Landing, used by the Lairds to ship dairy products to San Francisco 1860-1866). The last of the Felix family was evicted from their ancestral home by ranchers in 1952, and then later the ranches became part of the Point Reyes National Seashore--owned by all of us and managed for us by the National Park Service.

Felix Cove in 2020

Looking up Tomales Bay from above Felix Cove

The road to nearby Marshall Beach

The thought-provoking conversation included how family members learned of their ancestors' history and how they feel about it, complete with long-overdue apologies. It also included discussion of reparations--specifically, returning Felix Cove to the now landless (aside from a recently-acquired parcel in Nicasio) and federally-unrecognized tribe. You can support their efforts here.

Etcha Tamal, rematriated Coast Miwok Tribal Council
land in Nicasio (photo taken in 2015 after pile burns, and
prior to the 2023 purchase)

The conversation was relevant to all of us, since we all are either indigenous to the land where we live or from somewhere else, and many of us from somewhere else have ancestors who came here and displaced the indigenous people. It felt personal to me, because I too have ancestors that pioneered a dairy industry in the 1850s on stolen indigenous land. And it made me realize that I too would like to apologize for those actions. This is that apology.

"At some point, you have to decide, are you going to live in a world of abundance, open-heartedness, and open-mindedness, or are you going to live in a world of exclusion, isolationism, and scarcity?"

--Theresa Harlan, founder of the Alliance for Felix Cove, describing why she laughed at herself when contacted by a descendant of the Point Reyes colonizers

October 2024 Heat Wave

 The October 2024 heat wave was the warmest early-October weather in the Bay Area since 1980. Above average temperatures began for San Geronimo Valley just before the autumnal equinox, which was the beginning of 18 days over 80 degrees F, 10 days over 90 F, and 3 days over 100 F. Two of the days in the 90s occurred in September, then there was one cool day--September 25th, where the high only reached 69 degrees. After that there were 13 days in a row exceeding 80 F and 8 days in a row exceeding 90 F. In October, it had never been over 95 F before, but 3 days over 100 F and 3 days over 95 F set new October monthly records (since I started recordkeeping in 2012). October has now become a month when it can not just get hot, but really hot.

As with many heat waves, the remarkable thing was how warm it was at night above the inversion layer. In the graph below, you can see red and blue lines for the temperature on the ridges, and a green square for the highs and lows on the valley floor (with blank spots for occasional missing data). Starting September 30th, for 9 nights in a row, valley floor temperatures were below 60 F while ridgetop temperatures were in the upper 60s or warmer. And some nights were much warmer, with the ridges staying near 80 F all night! Who would have guessed that Marin County would have low temperatures in the 80s in October, rivaling Death Valley temperatures!

Death Valley-like nighttime temperatures in the 80s in Marin County

The third remarkable thing (after the extreme October heat and the heat above the inversion layer) was the short duration of each day's heat on the valley floor. Because the October days are shorter, the 50-degree temperature uptick was packed into fewer daytime hours. On multiple days I would be cold all morning, then go outside in the afternoon to warm up, then get too hot. Inside our house, temperatures never got above the upper 70s, with some mornings starting at a cool 62 F. Another year (like 2017 or 2019, when nights were in the 30s and highs were in the 70s) we might have turned on our heat to keep our house warm, but this year the heat wave provided our house heating!

So while this October heatwave was extremely anomalous and concerning, the impacts were lessened on the valley floor due to the lateness of the season and the nighttime cooling. But the concerns are big ones--warmest October high temperatures ever, warmest October water temperatures ever, driest soils and vegetation ever, and the impacts to plants and animals on the ridges of seven days in-a-row of low temperatures in the 70s and 80s.

The California Water Cycle

 The causes of most problems are solutions. We rarely unbuild big things that we've built. Instead we layer on solutions--some of them big new things that create their own big new problems. Sometimes you gotta just take out the big thing that started the whole cycle.

Soil Science Joke

 Mono Basin Textural Triangle:

Note that in some lentic zones you might encounter loamy sand, sandy loam, sandy clay loam, or sandy clay. But there will be sand. In other areas you might encounter gravelly sand, cobbly sand, stony sand (not just near the dispensary), or bouldery sand.