Comment by danans | Hacker News Reader

Comment by danans | Hacker News Reader

It's not clear to me what the source of water is relative to the size of the forest, because IIUC, in dry regions like Egypt (and California, Israel, etc), unless you use drip-irrigation with targeted crops (which won't grow a forest), agriculture requires a huge amount of water compared to domestic water consumption, so the wastewater stream from the latter intuitively can't be nearly enough to support a forest.

Perhaps they are drip irrigating the entire floor of the artificial forest to minimize evaporative losses? The paper linked in the article [1] doesn't really explain how they are doing this.

EDIT: this article [2] explains the system in a bit more detail. For a sense of the scale of forest vs the wastewater supply, it's a city of 400K people whose wastewater is supporting a .78 square mile "forest". So it's really more like a large park. It's a great demonstration nonetheless, especially if it can be a productive source of food for the city.

1. http://www.fao.org/forestry/35800-094f4eedb0c86a4a33be1a3d90...

2. https://www.intelligentliving.co/egyptian-desert-forest-recy...

Your water needs might drop significantly once the forest is established. Depending on the trees, the established canopy might drop the evaporative losses dramatically.

True, but I think the GP's danans overall point still stands. Household water consumption (and waste) just isn't that much. It takes a lot of households to support a pretty little forest. Maybe a mature canopy increases your efficiency by 50% or more, but you're still working with a pretty small volume of water.

also there is a systemic effect. More forests means more rain.

Under the current models we send most of the rainfall immediately back into rivers + oceans. By creating inland forests we get mini little "oceans" to evaporate and move water for a 2nd rainfall. Each cycle the plants + ground hold onto a little, but mostly it can be evaporated and re-rained again and again. Deserts have the issue that they have little to hold onto the water, and to reevaporate it for subsequent rainfalls.

Maybe they emulate a canopy with some kind of tarp while the trees are growing?

Wouldn't a tarp get in the way of sunlight, stopping photosynthesis?

We have a small 15m by 15m garden here in Kuwait (we have a similar climate to Egypt if not a little more hot). To keep planting all year long, we run a “protect from insects” fine mesh over the entire garden and it feels significantly cooler while still allowing sunlight through. Not scientific enough, but we never thought to check the temperature drop or the sunlight reduction. I may do that this summer just to see how much light is blocked.

Plants don't use most of the sunlight that hits them, and too much will cause heat stress making them less efficient.

The right tarp or net that lets through the most useful wavelengths seems to help more than hurt.

A lot of places are starting to install solar over farm installations on a small scale. Yields are tending up while also generating electricity to run the operation

I think you are looking for a greenhouse, all evaporated water will condence inside and you will need dramatically less for your plants

You still need more than you'd expect. Plants need CO2 to live, and with CO2 at just 0.04% of atmospheric air, you need to let a lot of air (and accompanying water vapour) in and out of your greenhouse to let the plants have the CO2 they need.

Or you burn natural gas to produce CO2 (and some water), but then your carbon sequestration goals go up in smoke...

How much of a difference could that make?

That's the current forest that was started in 98. The one that they're starting now is 100 million hectares (1 million sq km).

That is 380 times larger. Unless they are massively underutilizing the current wastewater stream, they need to multiply the irrigation water use efficiency that much, unless they think of forest is going to alter weather systems in such a way that brings rain to the area.

> unless they think of forest is going to alter weather systems in such a way that brings rain to the area.

I am not an expert, but based on books and articles I've read[1], forests tend to do that. I think you don't even need a large patch of forest for it to attract rain, anecdotally.

[1] Get an old copy of The Forest and The Sea by Marston Bates, if you can.

"In 1960, he published the ecological science book The Forest and the Sea, an introduction to how ecosystems work. He compares a rain forest and a tropical sea, their similarities and differences, and through it demonstrates how to understand biological systems."

https://en.m.wikipedia.org/wiki/Marston_Bates

Influential book, I believe.

Something worth reading into are the Nile Water Treaties put into place under British rule of the area, which strongly favour Egypt.

This has come up due to Ethiopia’s Grand Ethiopian Renaissance Dam and the plans being made on how quickly to fill up its reservoir.

I mention this as making forests in the desert is going to end up being a political issue and will likely be used in arguments over water rights in the region, even if its total draw is inconsequential.

The Egyptian argument is likely going to be that the the forests will more than pay for they cost in water due to the lower albedo and induced rainfall, and will eventually become self-suficient as well as provide excess rainfall.

Is there any man made forest on Earth that started to induce rainfall?

that's literally what rainforests do, after all.

Have you got any English source for this?

It's in the linked article?

The point is to get rid of the wastewater safe/cheap/efficient rather than grow the forest. Water consumption isn't the concern. They certainly wouldn't be doing drip irrigation with wastewater because wastewater would clog the equipment. Evaporation is expected and desired. Treated human waste is full of pharmaceuticals and phosphates from detergents. It should not be used to grow food unless it is feed for animals. Drainage is a concern on sandy soil. You wouldn't want these sites anywhere near your groundwater supply. You can't dump phosphates and nitrogen in your rivers because the result is algal blooms -> depleted oxygen -> fish kills and really toxic shit like Pfiesteria, which can give you headaches, cognitive problems, and nerve damage just from standing knee deep in the water.

Really, how well the forest grows is beside the point. They're doing this to dispose waste water. If they can make a tree crop to offset costs a bit, then great. The "climate change" angle is lipstick on the pig.

> It should not be used to grow food unless it is feed for animals

If the potential toxins on the crop are the concern, these animals can also then not be for human consumption (directly or indirectly). In a lot of cases they probably can't even produce things for human consumption. There's not a whole lot of use left once you eliminate those use cases.

It depends on what is in your wastewater of course, but most toxin typically concentrates in the leaves rather than the beans/corn. From there, the toxin remaining concentrates mostly in organs which can be discarded, rather than the meat. Each step in the food chain acts as a filter. You do not want to consume the crop directly and have buildup in your organs.

Also, eating food irrigated with waste sludge is a great way to catch e-coli. Treated waste is aerated and anaerobic pathogens like that largely neutralized, but it could still happen. If a hog is sick/dies, it's not as big a deal as a human.

Steps in the food chain are concentrators for toxins, not filters. Discarding organ meat isn't a given, though I suppose throwing away the liver in a lot of cases would be a solution. It seems like it is a risky play for relatively little gain, but I'm not a food regulator.

>but I'm not a food regulator

I take it you've never set foot inside a waste treatment plant either.

It would certainly help if you explained why you feel the need to snark about something you can't really know about. That way the comment might serve as a vehicle for interesting conversation, instead of whatever this is.

I can't imagine the phosphates and nitrogen are especially good for the trees, either. TFA says the wastewater is "treated", but it's not specific on just how much they clean it. Presumably more than nothing and less than enough to return it to the municipal water supply.

> Perhaps they are drip irrigating the entire floor of the artificial forest to minimize evaporative losses?

More or less (saw it on german TV a few weeks ago) - here ( https://www.planet-wissen.de/video-aegypten--ein-wald-mitten... ), if you jump to 01:55 you'll see the small pipes that distribute the water, but it's a bit more than just "drip irrigation" (at 02:34 it's visible that it's more than just a few drops).

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