Evaporative Cooling

I don’t think there is anyone who hasn’t experienced an extreme heatwave this past month. Rin, who is spending the summer in Savannah, experienced their first East Coast heatwave (with accompanying high humidity) a couple of weeks ago. Here in the West, we too have had our share of extreme heat, though not the humid kind. Our backyard weather station hit 116 degrees several times this week, and I instantly start sweating the moment I walk outside.

I have discovered recently that I am a ‘sweater.’ I don’t mean that I’m always sweating; but yes, when the circumstances are right, I will sweat more than the average person. I learned this because Tom and I have joined a local gym. The reason for joining began with injury recovery, but quickly morphed into something else - another tool to build our resilience. We are planning a month-long walking trip next summer for our 25th anniversary, so we are both working hard to build muscle, improve balance, regain agility, and increase flexibility. We’ve added all kinds of different exercises to our daily routine; simply hiking up a hill is not going to prepare us for hiking 16 miles a day for weeks on end.

So now we are in training. And man, when I train, I sweat. I mean not just in the usual places. When I’m done with, say, a spin class, my calves are slicked with sweat. And after a TRX class, my forearms are dripping. I suppose it could be embarrassing, but I don’t look at it that way - I consider it a sign of a healthy vascular system that is performing one of the jobs it has uniquely evolved to do.

Sweat is a beautiful human adaptation. Chimpanzees and macaques have sweat glands, but humans have 10 times the amount that they do and are the sweatiest among the great apes. Scientists have discovered that “the higher density of sweat glands in humans is due, to a great extent, to accumulated changes in a regulatory region of DNA that drives the expression of a sweat-gland-building gene.” This happened through repeated mutations and contributed to an evolution of higher sweat gland density in humans. We are meant to sweat! It’s our primary way of cooling ourselves. As the water in sweat evaporates, the surface of our skin cools. This is true of any evaporative cooling. A liquid will remove latent heat from a surface, and that evaporating liquid will cool the air around it.

Since most animals do not sweat, they have to cool themselves in other ways, and sometimes they too use evaporative cooling. During this heat wave, we’ve been closely watching the behavior of our backyard bees on our water fountain.

Bees use water to cool their hive. Some worker bees are tasked with finding, collecting, and bringing water back; it is spread in a thin surface over the surface of the comb and the bees then fan their wings to evaporate it. A hive may use a quart of water a day in the hot months for this purpose.

Honeybees are not the only ones who do this. Some wasp colonies (many wasps are social insects and, like honeybees, live in large groups) use water the same way. They collect it and spread it on the surface of their nests. Today, while filling the one of the water bowls at the school garden, I watched both paper wasps and yellow jackets collecting water from the edges.

This is one of the most important ways we can help insects; we can place shallow bowls of water around our gardens and yards. Put a rock in the bowl, or several rocks, so that the insects don’t drown (they have poor depth perception). If mosquitos are a worry, change the water daily or weekly (it’s good to do this anyway to keep the water clean). Birds will love this, too.

Many insects will also get water from the soil in your garden, so it’s nice to have a bare space which you keep wet for this purpose. Butterflies especially adore a muddy spot.

Another creature in our garden that appreciates evaporative cooling is the chickens. Chickens, like dogs, pant when it’s hot, and this past week they’ve been panting from dawn until full dark. I actually spray them with water, and though they seem to dislike me doing that, they really love when the ground in their run is wet. So when the temperature is over 100, I go out several times a day and spray them, and the dirt in the run, thoroughly. Immediately afterward, the chickens will congregate in the wet place, and they really perk up.

Chickens also dig holes in the dirt to find the cooler place under the surface. Many creatures do this, too. While dogs and coyotes pant, owls use something called ‘gular fluttering’ which is flapping the loose skin under the throat to move air over the throat cavity. Vultures urinate on their legs to keep cool, another form of evaporative cooling!

That last fact makes me appreciate anew the way we humans use sweat to keep ourselves from overheating.

Stay cool, everybody.

Climate Zones

Environmental Center in August - Oakland

It’s a great privilege to work and farm two gardens; my own garden on my own home property, Poppy Corners, in Walnut Creek, and my school garden, behind the Environmental Center at Merritt College, in Oakland.

In some ways, these two gardens are very much the same. They were both conceived and begun by the same gardener - me. I have a certain gardening aesthetic, which you’ll find reflected in both spaces; I have a certain way of doing things that works well for me, and I use those methods in both gardens.

However, there are a lot of differences, too. I’ve been working in my home garden for nearly 19 years, while the school garden was started in January 2022. My home garden’s design, planting, and maintenance are largely done by me, with a little assist from Tom once in awhile, while the school garden is designed, planted, and maintained by a whole host of folks, mainly students, a new group of which arrives each semester. Each garden has been built using what materials could be found or purchased at the time, and the landscapes reflect that. The soils are different: In Walnut Creek, we have 100% clay, because this land was under water a long time ago; the school garden is on top of a hill which is uplifted volcanic matter that has greatly eroded, which gives it a rocky, sandy texture. (*Note - in both gardens I grow annual vegetables in soil that is brought in, because neither original soil is great for growing veg.) The goals for my home garden are to provide food for my family, habitat for wildlife, and beauty for the neighborhood. The goals for the school garden are to provide a safe learning space and a lovely place for students to gather; this forms community, which our program is determined to provide.

But another main difference between the two spaces is climate.

Walnut Creek is about 20 miles inland from San Francisco and its bay. It has mountains surrounding it to the east and west, while to the north and south are long valleys. Oakland is directly on the bay, about 10 miles east of San Francisco. Oakland runs from the flats in the west, up into the hills to the east; this divides the city in many negative ways, while also dividing it climatically. My school, as I mentioned, is in the hills.

Why does this matter, you might ask? We all have climate differences depending on where we live, but here in the Bay Area, we have far more differences than most, thanks to the influence of the San Francisco Bay and the Pacific Ocean. We call these ‘microclimates.’ I’ll get to those in a minute.

But first, this is the USDA Plant Hardiness Map. This map was developed primarily as a tool for farmers, but gardeners use it frequently as well. These zones are divided by the lowest temperatures rather than the highest; for instance you can see that the central northern part of our country gets quite cold in winter, while the southern part of the country stays warm (or at least temperate) in winter. If you look at this map, and the close-up below, it looks like the Bay Area (about a third of the way down the state from Oregon) is generally homogenous. That is, that the coldest temperatures in San Francisco are about the same as the coldest temperatures in Antioch. There are some slight differences, but it’s not markedly different. According to the USDA, Poppy Corners is in Zone 9b, which gets down to a low of 25 degrees, while the Environmental Center is in Zone 10a, which can get down to 30 degrees.

Not a lot of difference, according to the lowest temps.

Those lows are extreme examples, of course - they are what ‘might’ happen, while the lows over time are not nearly that low. I have found that wintertime in Walnut Creek includes a few nights under 30, while most of the time we are in the upper 30s to low 40s. In Oakland, the low rarely gets below 50, as is more usually around 55 at night.

The USDA doesn’t take in to account the high temperatures during the day, which are also quite different. For instance, summers at Poppy Corners generally involve regular daytime temps in the 90s, with many days over 100. Summers at the Environmental Center are much more temperate, and generally stay in the high 60s to the mid 70s.

Here’s another difference: The humidity in each place varies greatly. Walnut Creek rarely gets summer fog from the bay - we’re just too far inland and the fog has to make its way over the Berkeley hills to get to us. But we do tend to get ‘tule’ fog in winter, which is moisture creeping in from the Sacramento/San Joaquin river delta to our east. However, Oakland regularly gets fog in the summer, as it’s much closer to the bay. In fact there are many mornings when I arrive at work in the summer to find the path soaked by fog drip. And in winter, Oakland does not get the tule fog. All of these things determine what and how you grow plants, and the differences can get a little frustrating.

Long ago, it became clear that Bay Area gardeners needed some guidance; growing things in San Francisco was obviously not the same as growing them in San Jose, or Mill Valley, or Richmond, or Vacaville. Gardeners clamored for more specific zones, and in 1954, a local magazine called Sunset published a book called The Western Garden Book, which redefined the climate zones and in turn, local horticulture. The Western Garden Book was, and still is, considered the bible of western gardening. Many gardeners use solely the Sunset zones (17 of them across the west) to plan and plant their gardens.

The Sunset climate zones take in to account all of the things I mentioned above: Not just the wintertime low temps, but also the summertime highs, and the humidity, and even the elevation. On this map, you can see that my garden in Oakland is in zone 16, while my garden in Walnut Creek is in zone 14. The descriptions Sunset gives for each zone is great, but here’s what I think is the most salient point: The coastal climate of Oakland is dominated by the ocean weather about 85% of the time, and by inland weather about 15% of the time, while the inland valleys in Walnut Creek are the opposite.

On top of that, as an observant person, I have discovered that there are micro-climates within microclimates. Poppy Corners, being in the deep valley on the west side of Mount Diablo, tends to get even more extreme temperatures, because the air is trapped by the mountain. Our winter temps are lower, and our summer temps are higher, than other cities in zone 14. We know this because we have recorded it for several years on our weather station. Here’s another interesting and salient fact: In the Bay Area, it cools down at night. It very rarely stays warm, no matter how high the temperature gets during the day.

“Ok,” you might be asking, “so what does all this have to do with actual growing in each garden? What’s your point, Elizabeth?” Why am I obsessively pondering this climate-zone stuff?

Here’s why: Everything in the school garden grows better.

Now, the school garden is not as mature; the perennials haven’t been there as long, and haven’t had as much time to grow. The space is changing all the time, as we determine what the needs of our classes/desires of all the instructors are. These things are reflected in the appearance of the garden. But even still - I look at the vegetables and flowers and herbs and natives and fruit trees and I think, damn. Oakland’s got it going on.

This is counter-intuitive. You’d think that the higher heat of my inland garden would be better for summer veg, at least. Tomatoes and peppers like it hot, right? And you’d think that the inland winter chill would be better for fruit, right? And at one time, maybe that was true - maybe the differences wouldn’t have been so marked, 50 years ago. Just little things, little tweaks here and there, would help the gardeners in different zones to make subtle changes that gave them success.

But in our changing climate, we already know that the extremes are getting more extreme. In my Walnut Creek garden in the summer, I either have full sun which bakes everything to an absolute crisp, or I have partially shady conditions that sure, don’t burn the plants, but also don’t allow for maximum production. In the Oakland garden in the summer, there is full sun nearly all day - but the plants don’t burn, and the fruit and veg ripens spectacularly. Take this example of the tomatoes in each garden:

Poppy Corners - spindly and not a lot of fruits

Environmental Center - chubby and huge, and full of large as-of-yet-unripe fruits

Why is this? Here’s my theory: It’s all about the range of temperatures. In Walnut Creek, in the course of a year, we range from 25 degrees to 115. That’s not too different than many places in the United States. But, over the course of a summer day, we often range from 50 degrees to 100. A difference of 50 degrees is not unusual here. That’s a HUGE daily change. In Oakland? Over the course of a year, it ranges from about 40-80 degrees. Much less of a range than most places in the United States. And over the course of a summer day? Mainly about 65-75 degrees. Not a very large daily change.

And this, my friends, is the big difference in my two gardens. In a study on Elsevier called “Ambient Temperature Signalling in Plants,” the introduction states, “Plants are exposed to daily and seasonal fluctuations in temperature. Within the ‘ambient’ temperature range… temperature differences have large effects on plant growth and development, disease resistance pathways and the circadian clock without activating temperature stress pathways.”

Plants are adapted to yearly, monthly, daily, and hourly temperature ranges. What they are NOT adapted to is increased temperature stress. And it is extremely clear to me that we are experiencing increased temperature stress at Poppy Corners. What I could grow easily 15 years ago, or even 10 years ago, I cannot grow now. And for now, at least, Oakland’s extremes are mostly mitigated by the beautiful San Francisco Bay. THAT is why everything grows better at the Environmental Center. And it’s why we, as gardeners, have to be aware of what’s happening in our own plots in our own cities, and why we have to learn to adapt to how conditions are now, not how they were when we started.

Heat Dome

You know, it’s already been a hot summer here in the Bay Area.

Actually, it’s been a hot summer all over the world, with new records being set all the time. The NOAA’s July report was, frankly, depressing.

And here we are again, on Labor Day weekend, about to experience another heat dome - and this one will create hotter temperatures than we’ve seen in a long time. What’s really bad about this particular event is the length of time it will be present (over a week in some places), and the fact that it won’t cool off overnight.

Southern California has already been baking for days; the Central Valley has been terrible; and it’s only going to get worse for all of us. Usually, the Bay Area tends to experience more moderate temperatures, since we are situated near the lovely cooling effects of the Pacific Ocean. That won’t be true this weekend or next week, unfortunately. And where we live in Walnut Creek, about 20 miles east of San Francisco, it’s generally hotter anyway (the fog rarely reaches us). It’s looks like we’re in for it.

The thing that makes this kind of heat bearable for humans is that it is extremely dry. Don’t get me wrong - we still have to be careful, especially if we’re outdoors (people die all the time hiking in hot California weather, thinking it’s not that bad). But heat plus humidity? That’s when things get really dangerous. Wet-bulb temperatures are deadly for humans. So in many ways, we are very lucky.

But the bad thing about the dryness is that our vegetation is at record low levels of moisture. That means fire. Many new fires have already started, unfortunately.

Most likely there will be more before this heat dome moves off the West Coast.

Due to the heightened risk of fire, most of our regional and local parks have been closed through Labor Day.

This means that everyone is out walking in the neighborhood, on the sidewalks, and on the streets, and most of us are doing it very early. Tom and I certainly got started early, and it wasn’t long before a fire truck passed us, siren blaring. We looked up, all around, at the open space hills that surround our neighborhood. No smoke, thankfully. We noticed that an older couple walking near us did the exact same thing. It wasn’t long before we heard more sirens, and a family with kids who was near us at the time also did the neck-crane. I realized that this has become normal, when you live in the West. It’s hot? Dry? Windy? You hear sirens? The head starts to move, warily eying the sky. It’s a chronic stressor, in late summer and early autumn.

Our family is lucky. We have air conditioning, and as long as the power stays on (another stressor), we’ll be ok. These sorts of times make me think a lot about the folks that aren’t so lucky. And about the folks who are being told to evacuate their homes, due to approaching fire. All we can do is hope that will never happen to us.

IPCC Mitigation Report

My news feeds are full of commentary on the IPCC’s release of their mitigation report. Of course, since I have long been a student (formally and informally) of environmental issues, this is the kind of news I look for - maybe you haven’t been reading as much about it as I have. Plus, I do find these reports confusing for the average layperson. So imagine my delight when I came across a great eight-minute video, summing up the report.

This video was recommended by Katharine Hayhoe, climate scientist, University professor, and recently-named Chief Scientist for The Nature Conservancy. I have read several of her books, and she has a unique take on environmental issues, being both a Christian and a scientist, and someone who believes in active faith and hope. She is a good resource for scientific facts, but also for a positive outlook in the face of very frightening information. So, I knew this video would be helpful and I feel confident recommending it. I hope you enjoy it too, and are able to learn something from it - I sure did.

Summer in December

Here’s a happy honeybee aiming towards a fully-opened sunflower on the first day of December in my garden. It’s been chilly at night, but the daytime has been beautiful and warm and in the 70s. Yes, this is unusual. Yes, this concerns me. But I must confess it also delights me. I am enjoying the summer blooms in my garden, and the warm afternoon temperatures which are perfect for walking. I think it’s important that we remember to be present, whatever the moment gives us. I can be worried about our place on this planet and happy to bask in the afternoon’s slanted glow. Environmental work can be draining, so let’s take the joy where we can.

The cover crops in my garden also include, at the moment, cosmos. And borage, cilantro, buckwheat. I used our homemade compost to top off these beds, and the seeds that didn’t die in that pile have germinated and are flowering freely. It’s all good. A cover crop can be any crop, and it’s all improving the soil.

A side benefit to these sunflowers growing this time of year is that the goldfinches leave them alone. In summer, my sunflowers are always decimated, the leaves eaten down to the veins. This means the plant can’t photosynthesize and can’t bloom properly. Why don’t the goldfinches do this in winter? It could be that they don’t need greens this time of year, requiring only protein and fat to prepare their bodies for laying eggs. It could also be that most have migrated for the season, and the ones I see around the bird feeder are too few to do much damage.

Hey, maybe I’ll only grow sunflowers in the autumn and winter from now on.

Happy December, everyone.