person. Greenhouse spaces are wet. Underground greenhouses are essentially basements with glazing on top. Are there dug or excavated basements where you live, or are most newer dwellings slab-on-grade? And any older basements there---wet or dry?

I have half-assed architecture and new construction techniques not completely-groked. My house is 30 y/o. Ahead of superinsulated for the time. Now I have mice. BUT: it is very expensive to build now. Materials are expensive. Going with home-made (like bags o dirt) is asking for water and mold problems down the path. But architects are expensive, I got spoiled by having one in-house. I have been screwed over by a dumb builder since. So I may not be the best source.

Best advice: if you are not The Pioneer, find relevant folk in the same area of TX who were. Good luck!

Underground greenhouses are one of the very few things that an individual can do to prepare. Of course, it won't be any more reliable than your water supply.
There's more to it than just a "basement with a glass roof", though it is certainly that. Basements have lousy ventilation, you can have as much ventilation of this as you want. For example, a small solar panel directly driving a DC fan. When the sun shines it moves air, don't worry about it the rest of the time.
The whole idea is to stabilize the temperature without major energy inputs. Keep it warm enough in the winter with little or no supplemental heat, keep it cool enough in the summer that the plants survive when the farmers around you are losing their crops. Heat, drought, floods, hail, high winds are what are going to decimate agriculture. You're building a fortress around your carrots to protect them from all that.
The worst of flooding can be dealt with by berming above grade - what's your frost line there? You don't have to go any deeper than that, and then you build up and pile dirt against your walls, sloping away.
Dig a dry well (just a few feet) and put a sump pump in it. If you have enough slope to work with you can just install a regular gravity drain.
Most greenhouses are pretty flimsy. They are more concerned with being cheap and just replacing them if they get flattened. We can expect unprecedented storms of all kinds, so don't skimp on the framing and provide something, for example 3/4 inch plywood with pre-drilled holes, that can be easily attached to the outside with wing nuts.
Get yourself a copy of "Four Season Harvest" by Elliot Coleman. A quick google shows he has a website that I didn't look at, http://www.fourseasonfarm.com/.
Commercial greenhouses try to supply, for example, tomatoes in winter. That's hard to do (but can be done, of course). You need to regulate artificial light to force flowering, etc. Hot weather vegetables are that much harder to grow out of season. Instead, concentrate on things like leafy greens for your fresh veggies in the winter.
People use some sort of greenhouse fabric on the inside to shade the interior in the height of summer.

for your kind words.

Secondly, AWESOME on building your own greenhouse, so you can grow your own food! What a way to take personal responsibility for your own life, and be an outstanding example of the kind of “thinking” that IS required NOW to weather the storm of Climate Change that is not 50 to 100 years off into the future, but happening in real time right now.

Suggestions

Start with an analysis of the soil and water drainage in your area. Here in Dallas the soil, for the most part we call black gumbo. In the heat it cracks like crazy and when it gets wet, it becomes like quick sand, almost. And most especially check your county records for flood plain area and drainage. Nothing like a flash flood to ruin a winter harvest.

You might consider making your own bricks, especially if there is clay shallow enough for you to reach or if there is enough available commercially and not to costly. Just consider the Great Wall of China.

From TravelChinaGuide.Com:

Bricks were more a convenient material than earth and stone as their small size and light weight made them convenient to carry and thus quickened the speed of construction. Bricks are also the ideal material to bear the weight. According to a sample experiment experiencing gravity and erosion over a hundred years, the compressive strength, resistance to freezing and absorbency of the bricks of the time are similar to today's common bricks. A huge brick from a hundred years ago showed a high level of technological skill for that time. For further ease of construction, different shapes of brick were also burned and made to stuff into different positions.

Brick are easier to carry and stronger than sand bags, and don't require any additional resources like canvas or burlap.

I'm inspired by ancient technologies that were used to build things, that still exist today, like the pyramids, the Great Wall of China but also things like;

From Crackle.Com (yeah I know it's crackel, but...)

Historians are digging up evidence that indicates some ancient humans had their shit together in ways modern humanity can still barely manage. Just look at ...

This article points out 5 items built / constructed back in the day (lol) that still exist and challenge our best scientist to measure up. For example, Ancient Metal Plating.

We know that people of the middle ages and earlier had the ability to coat materials with thin films of metal like gold and silver. In fact, their methods functioned even better than the ones we use today. We still haven't caught up to the middle ages. But it gets better: the Iron Pillar is a column in the Qutb Complex of Delhi. It was built around A.D. 400 and enjoys thoroughly mocking archaeologists and metallurgists, because it's 1,600 years old and it has not corroded yet. Compare that to your 1994 Ford Festiva and you might start to see what an accomplishment that truly is.

Studies of the Iron Pillar show that its composition is unusually high in phosphorous, which seems to have shielded the metal underneath from the ravages of nature. It basically nurtures a thin film of harmless rust that gets metallic Stockholm Syndrome and fights off deeper, more damaging rust. That's not an accident: earlier iron works are lacking that phosphorous, while several later structures were forged in the same fashion.
(emphasis mine)

Of course you'll need to get your hands of some phosphorus and then figure out, what our scientists can't...how the ancient Indians were able to "do" metal plating better than we can today. (gee, ain't I a lot of help??? lol)

But what that informs me, is that what we know today is not always the best way to do things, hence my inspiration for old tech that still works. Old tech might be a bit more labor intensive (get the whole family involved), but, it will save money in the long run, and last a long time as well.

What I take into consideration, is that much of what we do (design / build) today is done within the confines of the current Zeitgeist, that is "consumerism". Most of the things we build today, are built to last only a short while, then disregard to the trash dump and replaced with new and improved consumer widget that won't last very long either. Rinse and repeat as required or as you can afford it, is the consumer mantra instructs.

Heck for another example, look at this light bulb, that is still burning over 100 years later, which was not designed and manufactured by our beloved Ben Franklin, but by an unknown professor, Adolphe Chaillet.

From Livermore California:

Welcome to the homepage of the Centennial Bulb, the Longest burning Light Bulb in history. Now in its 115th year of illumination.
(emphasis mine)

Think for a moment, why does not every home, every office, every bread and circus stadium, every highway or city street, not have lights with these type bulbs? Think of the maintenance and labor cost savings by having these type of light bulbs, that burn for over 100 years! (No profit!)

For me, I think about what I can do with my hands and available resources. What I don't know, I deal with at garage sales, estate sales, half priced books and as you are doing know, crowd sourcing on line with other liked minded people.

I wished I owned some land. Before my wife passed away last year, we were looking into (wishing really) moving out of the city and getting some land to where we could begin the process of transforming our lives, from mindless consumer existence driven by propaganda, to becoming masters of our own destinies, that is, not having to rely on others for anything.

She had the green thumb, I'm was the labor (lol). I'm allergic to wasps, bees and such, and she found plants and flowers that were natural pesticides to those flying death bugs, and was able to bring “beauty” as well as functionality to our little home, when we actually had one.

But most importantly, thank you, you just brighten my day 1000 fold! That, in the world / words of consumerism, is priceless.

RR

(I was in the middle of a writing rant about the seeming flood of endless click bait essays, over shit we can't do anything about or just mindless speculation, when I noticed a comment showed up on the left hand side of the page and then saw the essay title. And for a moment, was like, oh hell what did I do now to be called out in the title of an essay. But I must say, I was please as a pig in shit when I read your essay, which help pull me out of my "funky mood today". So again thank you! I "needed" that!

Unfortunately the only thing I've ever tried to grow, well is illegal in Texas and I didn't do a very good job at it, my crop failed. )

Two small units might be better than one larger unit. Take what you learn from the first one and improve the design for the second. If one unit fails, or gets infested, perhaps the other stays in production. Smaller project more likely to get done.