5 ms·

Probably very dumb idea, but would it be feasible to just pump and sprinkle sea-water on hot, dry desert and let it naturally evaporate, and then collect it as

by zokier 3y ago

Probably very dumb idea, but would it be feasible to just pump and sprinkle sea-water on hot, dry desert and let it naturally evaporate, and then collect it as fresh rainwater back? i.e. how much water would you need to evaporate to have a noticeable increase in rainfall?

jareklupinski 3y ago
i'd like to see the xkcd author tackle this as a "What If?"
- kneebonian 3y ago
  He already has. https://what-if.xkcd.com/152/ https://what-if.xkcd.com/152/
josephjrobison 3y ago
There is talk about pumping sea water into the Saharan desert in certain parts, which gets at that. https://www.youtube.com/watch?v=V2b7ztWvFOg https://www.youtube.com/watch?v=V2b7ztWvFOg
- samstave 3y ago
  Was going to say this, there are/have been many ideas to do just this - one was to build a huge canal and just then let the sea flood the area... Also - there are lots of un-earthed treasures to be found under the saharan which was once a lush environ and have been covered with sand - so prior to flooding it, we need to lidar and excavate it. What if we vaccuumed up all the sand and built a new island/continent with the material and just revealed everything underneath - then flooded it. (I believe UAE is in the market for more sand-built-land-masses)
  - hinkley 3y ago
    One of the more feasible ones was a linear greenhouse with a canal in it. I'm sure someone has done the math to figure out what the proper length is for such a canal, to avoid problems with scaling. And if you've ever been near an ocean for much time, you know the salt tends to get around. So I'm not sure how in a multi-year project you keep that to a minimum.
- hanniabu 3y ago
  I wonder how that will affect the Amazon rainforest since it receives phosphorus and other nutrients blown of the Atlantic from the Sahara desert. If salt starts getting blown over too I wonder if that will ruin the soil fertility there.
cratermoon 3y ago
A desert is a living ecosystem. Evaporating salt water would leave behind substantial salt solids. Think Great Salt Lake.
- LordDragonfang 3y ago
  I mean, that's actually not too much of a downside, since salt is a fairly valuable economic good - Indian salt farmers do exactly that to harvest the salt crystals.
  - azernik 3y ago
    And that is the heart of a decently profitable economy around the Dead Sea, on both the Jordanian and Israeli sides.
  - cratermoon 3y ago
    Destroying existing ecosystems is kind of part of how we got where we are now.
    - justinator 3y ago
      We're coming to the inevitable conclusion that we can't keep doing this, as there's little existing ecosystems to destroy - I mean: we're looking at deserts and thinking: "why not?". Slightly more outlandish, we're looking at whole planets and thinking the same. Some call that par for the course, others unsustainable. Still others don't make a distinction and see them as the same.
ars 3y ago
Israel does this for a different reason: To collect minerals from the dead sea. It doesn't increase rainfall. Israel is actually desalinating water and rejuvenating a river, which eventually will reach the dead sea (although that's not why they are doing it, but it makes the point that evaporating water isn't doing much). Maybe you mean on a far larger scale? Well - the ocean itself is much larger, and water evaporates from its surface all the time. Humans aren't going to make an evaporation zone larger than the ocean. Also: Water does not (mainly) evaporate because of heat, but rather because of wind. There's lots of heat in the desert, but not much wind. The ocean has a ton of wind.
- eklitzke 3y ago
  Actually deserts can be quite windy, especially deserts near the ocean. Wind forms when there's a pressure differential, and the most common reason for a large pressure differential is when there are two adjacent areas with a significantly different temperature. So when you have a desert next to the ocean, the desert cools at night and then during the day, as the air in the desert heats up, it lowers the air pressure on land and pulls in air from the cooler air over the ocean. This phenomenon is why the SF Bay Area consistently has high wind and good sailing conditions during the summer, especially in the afternoons. That said, none of this contradicts the overall point you were making.
Terr_ 3y ago
My guess is that no matter how much water you manage to evaporate, the scheme will be doomed by the original causes for why the area is a "hot dry desert", the wind and geography patterns. So even if you evaporate a lot of water, it won't fall where you need it or where you can collect it.
samstave 3y ago
You know this is how the Phoenecians became the dominant culture, its also where the term "salary" comes from and "worth his weight in salt" -- as salt was the only known preservative of the massive amounts of Tuna the phoenecians were catching and shipping throughout the mediterrainian - and made them a super-power - they had control of the preservance of food over shipping distances... Salt was used as money. EDIT: Only a fn idiot without knowledge of history would downvote a comment... Jimminy Carter, what type of stupid are you trying to promote?
- eichin 3y ago
  Probably (not me, I don't have downvote bits) because it turns out there's a lot of "game of telephone"/"folk etymology" about this legend which apparently started in the 1800s in english; it's not actually historical as you've expressed it.
- soperj 3y ago
  > worth his weight in salt Never heard this saying before. I've heard "worth his weight in gold".
  - dev_slash_null 3y ago
    "worth his salt" is common, at least.
jononomo 3y ago
In other words, you want to salt the land? Isn't that what marauders do when they want to destroy an area permanently?
- qorrect 3y ago
  [flagged]
  - micromacrofoot 3y ago
    deserts are actually functioning ecosystems with life though, contrast to say, a salt flat
  - caseyohara 3y ago
    Deserts are far more alive and biodiverse than people think. > The Sonoran Desert encompasses 120,000 square miles of southwestern Arizona, southeastern California, and in Mexico, northwestern Sonora and most of the Baja Peninsula. With nearly 3500 species of plants, 500 species of birds, and 1,000 species of bees, the Sonoran is the most biodiverse desert on earth.
    - jtriangle 3y ago
      You do have to consider though, how important are those ecosystems? Because I see this often used as a reason we can't do something, but they never qualify it with reasons why one should care. I also pose this as a completely honest question, as I don't really know if you wiped out every desert ecosystem with solar/desal/etc if it'd actually affect anything else.
      - q845712 3y ago
        it's probably a good starting position to assume that since we all the share the same closed-ish system called planet earth, there's interconnections between different systems. Certainly the border areas between desert and not-desert aren't very crisply defined. Certainly (reference in other threads) nutrients can be blown by the winds from desert into non-desert areas far away. Certainly there exist some animals who go in and out of desert regions (birds, butterflies, ...). It's a really good idea to assume that things on this planet are connected to each other.
jtriangle 3y ago
Using a desert isn't a great idea, but, using the sun to evaporate water works just fine. You're just replacing an expensive heat source with a 'free' heat source. That's not unusual in desalination however, many facilities are combo plants, they're producing power and then using waste heat for desalination.
lambdasquirrel 3y ago
I think the key difficulty is condensing a very large quantity of water out of an even larger quantity of air, in the desert. The thermodynamic equilibrium of water vapor vs water-in-condensed-form isn’t going to work well for you here, even after nightfall. The very reason that it was possible to evaporate the water out (i.e. the air is very dry) cuts back the other way.

by zokier 3y ago

jareklupinski 3y ago

i'd like to see the xkcd author tackle this as a "What If?"

kneebonian 3y ago
He already has. https://what-if.xkcd.com/152/ https://what-if.xkcd.com/152/

josephjrobison 3y ago

There is talk about pumping sea water into the Saharan desert in certain parts, which gets at that. https://www.youtube.com/watch?v=V2b7ztWvFOg https://www.youtube.com/watch?v=V2b7ztWvFOg

samstave 3y ago
Was going to say this, there are/have been many ideas to do just this - one was to build a huge canal and just then let the sea flood the area... Also - there are lots of un-earthed treasures to be found under the saharan which was once a lush environ and have been covered with sand - so prior to flooding it, we need to lidar and excavate it. What if we vaccuumed up all the sand and built a new island/continent with the material and just revealed everything underneath - then flooded it. (I believe UAE is in the market for more sand-built-land-masses)
- hinkley 3y ago
  One of the more feasible ones was a linear greenhouse with a canal in it. I'm sure someone has done the math to figure out what the proper length is for such a canal, to avoid problems with scaling. And if you've ever been near an ocean for much time, you know the salt tends to get around. So I'm not sure how in a multi-year project you keep that to a minimum.
hanniabu 3y ago
I wonder how that will affect the Amazon rainforest since it receives phosphorus and other nutrients blown of the Atlantic from the Sahara desert. If salt starts getting blown over too I wonder if that will ruin the soil fertility there.

cratermoon 3y ago

A desert is a living ecosystem. Evaporating salt water would leave behind substantial salt solids. Think Great Salt Lake.

LordDragonfang 3y ago
I mean, that's actually not too much of a downside, since salt is a fairly valuable economic good - Indian salt farmers do exactly that to harvest the salt crystals.
- azernik 3y ago
  And that is the heart of a decently profitable economy around the Dead Sea, on both the Jordanian and Israeli sides.
- cratermoon 3y ago
  Destroying existing ecosystems is kind of part of how we got where we are now.
  - justinator 3y ago
    We're coming to the inevitable conclusion that we can't keep doing this, as there's little existing ecosystems to destroy - I mean: we're looking at deserts and thinking: "why not?". Slightly more outlandish, we're looking at whole planets and thinking the same. Some call that par for the course, others unsustainable. Still others don't make a distinction and see them as the same.

ars 3y ago

Israel does this for a different reason: To collect minerals from the dead sea. It doesn't increase rainfall. Israel is actually desalinating water and rejuvenating a river, which eventually will reach the dead sea (although that's not why they are doing it, but it makes the point that evaporating water isn't doing much). Maybe you mean on a far larger scale? Well - the ocean itself is much larger, and water evaporates from its surface all the time. Humans aren't going to make an evaporation zone larger than the ocean. Also: Water does not (mainly) evaporate because of heat, but rather because of wind. There's lots of heat in the desert, but not much wind. The ocean has a ton of wind.

eklitzke 3y ago
Actually deserts can be quite windy, especially deserts near the ocean. Wind forms when there's a pressure differential, and the most common reason for a large pressure differential is when there are two adjacent areas with a significantly different temperature. So when you have a desert next to the ocean, the desert cools at night and then during the day, as the air in the desert heats up, it lowers the air pressure on land and pulls in air from the cooler air over the ocean. This phenomenon is why the SF Bay Area consistently has high wind and good sailing conditions during the summer, especially in the afternoons. That said, none of this contradicts the overall point you were making.

Terr_ 3y ago

My guess is that no matter how much water you manage to evaporate, the scheme will be doomed by the original causes for why the area is a "hot dry desert", the wind and geography patterns. So even if you evaporate a lot of water, it won't fall where you need it or where you can collect it.

samstave 3y ago

You know this is how the Phoenecians became the dominant culture, its also where the term "salary" comes from and "worth his weight in salt" -- as salt was the only known preservative of the massive amounts of Tuna the phoenecians were catching and shipping throughout the mediterrainian - and made them a super-power - they had control of the preservance of food over shipping distances... Salt was used as money. EDIT: Only a fn idiot without knowledge of history would downvote a comment... Jimminy Carter, what type of stupid are you trying to promote?

eichin 3y ago
Probably (not me, I don't have downvote bits) because it turns out there's a lot of "game of telephone"/"folk etymology" about this legend which apparently started in the 1800s in english; it's not actually historical as you've expressed it.
soperj 3y ago
> worth his weight in salt Never heard this saying before. I've heard "worth his weight in gold".
- dev_slash_null 3y ago
  "worth his salt" is common, at least.

jononomo 3y ago

In other words, you want to salt the land? Isn't that what marauders do when they want to destroy an area permanently?

qorrect 3y ago
[flagged]
- micromacrofoot 3y ago
  deserts are actually functioning ecosystems with life though, contrast to say, a salt flat
- caseyohara 3y ago
  Deserts are far more alive and biodiverse than people think. > The Sonoran Desert encompasses 120,000 square miles of southwestern Arizona, southeastern California, and in Mexico, northwestern Sonora and most of the Baja Peninsula. With nearly 3500 species of plants, 500 species of birds, and 1,000 species of bees, the Sonoran is the most biodiverse desert on earth.
  - jtriangle 3y ago
    You do have to consider though, how important are those ecosystems? Because I see this often used as a reason we can't do something, but they never qualify it with reasons why one should care. I also pose this as a completely honest question, as I don't really know if you wiped out every desert ecosystem with solar/desal/etc if it'd actually affect anything else.
    - q845712 3y ago
      it's probably a good starting position to assume that since we all the share the same closed-ish system called planet earth, there's interconnections between different systems. Certainly the border areas between desert and not-desert aren't very crisply defined. Certainly (reference in other threads) nutrients can be blown by the winds from desert into non-desert areas far away. Certainly there exist some animals who go in and out of desert regions (birds, butterflies, ...). It's a really good idea to assume that things on this planet are connected to each other.

jtriangle 3y ago

Using a desert isn't a great idea, but, using the sun to evaporate water works just fine. You're just replacing an expensive heat source with a 'free' heat source. That's not unusual in desalination however, many facilities are combo plants, they're producing power and then using waste heat for desalination.

lambdasquirrel 3y ago

I think the key difficulty is condensing a very large quantity of water out of an even larger quantity of air, in the desert. The thermodynamic equilibrium of water vapor vs water-in-condensed-form isn’t going to work well for you here, even after nightfall. The very reason that it was possible to evaporate the water out (i.e. the air is very dry) cuts back the other way.