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Kadzar
2015-08-08, 12:36 AM
So I have an idea for a desert region: A once prosperous empire existed in a lush, possibly jungle area. Then they got all decadent and pissed off a deity. So the deity cursed their lands to never have rain fall upon them again. With no rainfall, the jungle eventually dried up an burned up, and with no vegetation in place, the land succumbed to erosion and became a sandy desert.

So now the area exists mostly as a trade route and a jumping off point for adventurers to loot the ruins of the dead empire, with oasis cities dotted across the region hydrated solely by wells which the native people must dig deeper and deeper on a regular basis. And sometimes there's just no more water, no matter how much they dig, and, with no water to support it, the place becomes a ghost town.


So how much of what I wrote above makes sense from a scientific standpoint, and at what kind of timescale can the parts that make sense be expected to happen?

Fri
2015-08-08, 12:45 AM
...it's divine magic, anything can happen?

That's a serious answer, honest. What do you mean by scientific accuracy for this anyway? As you said, a deity cursed the land. The land become desert. What kind of scientific accuracy do you need? Or the deity need to use scientific principle to do it?

I mean, if a deity will it, he can curse a land into only producing candy plants, and there aren't much scientific accuracy of that. Why should this be different?

Once again, this is a serious answer and doesn't meant to be sarcastic or sneering at all.

And I guess if you still insist that you need scientific accuracy, as I said, you need to answer what kind of scientific accuracy you need and for what purpose.

NRSASD
2015-08-08, 12:47 AM
Besides the gods saying "NO WATER FOR YOU!"? It's pretty accurate. One question I have for you: is this a hot desert or a cold desert? For example, the Atacama desert is the driest place on earth, but not very hot, in comparison to the Sahara. They are two very different kinds of desert.

Using the Sahara as an example though, rock art from there indicates it was a much wetter place until about 1600 BCE. Since that time, it went from being a region like the great plains to a desert. In terms of accurate timescale? Depends on how forested the kingdom was prior to its cursing. A forested region will stay dry but not desert-like far longer than a grassland, because even dead trees help hold the soil in place. I'm not a geologist/climatologist, but I would say anywhere from 50-300 years sounds about right, depending on the severity of the winds. Going back to the Sahara, it's expanding because the locals raise large herds of livestock and overgraze/deforest the edges, causing more erosion and more devastation. The survivors of your empire might be doing the same thing, and be running around as nomadic Mongol/Tuareg types harassing those who try to loot the crumbling remains of their ancestors.

Hope this helps!

P.S. Look up the American Dustbowl of the 1930's. It destroyed over 400,000 km2 in ten years.

dream
2015-08-08, 12:54 AM
So I have an idea for a desert region: A once prosperous empire existed in a lush, possibly jungle area. Then they got all decadent and pissed off a deity. So the deity cursed their lands to never have rain fall upon them again. With no rainfall, the jungle eventually dried up an burned up, and with no vegetation in place, the land succumbed to erosion and became a sandy desert.

So now the area exists mostly as a trade route and a jumping off point for adventurers to loot the ruins of the dead empire, with oasis cities dotted across the region hydrated solely by wells which the native people must dig deeper and deeper on a regular basis. And sometimes there's just no more water, no matter how much they dig, and, with no water to support it, the place becomes a ghost town.


So how much of what I wrote above makes sense from a scientific standpoint, and at what kind of timescale can the parts that make sense be expected to happen?
You used "science" with D&D stuff :smalltongue:

What kinds of lifeforms lived in the jungle? They probably died, eaten by the more adaptable creatures. Lizards can adapt. I see a culture of Lizard men taking advantage of the terrain, spending hot days underneath the sands and nights hunting. Giant spiders/scorpions the same. Arachnids are so adaptable. Giant ticks? Yikes. The ghosts of travelers who couldn't handle the expanse, guiding PCs to water and harassing their dreams. Hot air elementals, masquerading as water elementals, pushing PCs in the wrong direction, trying to steal their gear. The PCs gods sending avatars to guide them along the way. Undead skeletons and zombies wandering around in full sight of the PCs but not paying them any attention ("I'm dead but I need a drink of .... something").

Deserts are ideal places to mess with your PCs perception. "Oh --- you thought that was water you saw .... yeah..."

Kadzar
2015-08-08, 01:22 AM
@Fri Only the god(dess) (haven't decided) cursing the land to not rain ever again is supposed to be the magic part. I'm hoping all the rest can come about as a consequence of that.

@NRSASD It's intended to be a hot desert. And I think I intended it to be a jungle so that the place could go up in a great inferno. Though I suppose it wouldn't hurt to have some grassland in there to get the blaze started.

@dream Now that you mention it, I think that the reason I originally made it a jungle may actually have been so that I could make it a lizardman empire. And I like your other ideas too. Except the giant ticks; regular ticks are bad enough.:smalltongue:

goto124
2015-08-08, 07:09 AM
If things became dry enough, someone could've accidentally (or 'accidentally') dropped a small flame and set the forest on fire.

Did the deity take away all the water, or did she just stop giving the place water? Did the natives attempt to keep the place alive by bringing in water (which probably wouldn't have worked very well)?

Kalmageddon
2015-08-08, 08:11 AM
"Scientific accuracy"
"Magic Desert"
...? :smallconfused:

PersonMan
2015-08-08, 10:13 AM
"Scientific accuracy"
"Magic Desert"
...? :smallconfused:

The idea, as far as I read, is:

-Magic happens -> No rain. Ever.

-Science happens -> Jungle turns to desert

-OP asks about the second part

Reltzik
2015-08-08, 10:35 AM
The only thing that struck me as off about this was the "sandy" part. Whenever people think of deserts they typically think of great sand dunes, but that's not the most common form of desert, and I wondered how likely that would be in this case. So I hit wikipedia.

Outside of mountainous or rocky terrain, tropical jungle soils are typically oxisols, with some alfisols, ultisols, and entisols. None of these have high concentrations of sand, and all of these have a very thick layer of clay and organic material before you hit the parent rock layer. Remove the vegetation and you'd end up with a packed clay layer that would bake under the sun and resist wind erosion for a real long time.

Also, what would be the factors of erosion? Obviously not water or ice. Your primary erosion factor would be wind, which clay is resistant to. The tropics aren't noted for high winds, because they are seasonally quite stable. However, if you had greatly different biomes, smaller wind systems might form between them. A desert would be warmer than a neighboring jungle, producing a low pressure cell above the desert, a high pressure cell above the jungle, and surface winds from the jungle to the desert. This would normally cause rain in the desert, but that's blocked by the deity. It would also tend to impede rain in neighboring jungles. The only way I see this reaching an equilibrium is for the humid air being sucked up into the low pressure cell to form a thick, oppressive overcast, preventing the desert from getting too hot. This would put an end to the low pressure cell and the associated winds and allow rains to fall in the neighboring jungles. I imagine it would balance out as a light breeze and heavy but not total clouds, which turn into total, world-darkening thunderheads that never manage to rain on really hot days. (You'd get LOTS of lightning out of them, though.)

So the base of the desert is clay and you wouldn't get much sand out of it. What you WOULD get, if the remains of the jungle burnt down, is ash. Given the extensive dried out vegetation and the lightning, the jungle would burn down, and you would get ash. LOTS of it.

Even without rain, there would be a water cycle from dew, as the humid air cooled in the wee hours and precipitated on the surface. Unless the deity blocks this as well.

I don't know if this is what you were looking for, but I LIKE this for a cursed land. Warm, humid air, but on average cooler than you'd expect for that latitude. Oppressive skies, often turning unnaturally dark (due to thick thunderheads) and producing extensive lightning strikes. Ashes and cinders everywhere, ten feet deep, blown about by mild winds and forming dunes.

neonagash
2015-08-08, 11:16 AM
The only thing that struck me as off about this was the "sandy" part. Whenever people think of deserts they typically think of great sand dunes, but that's not the most common form of desert, and I wondered how likely that would be in this case. So I hit wikipedia.

Outside of mountainous or rocky terrain, tropical jungle soils are typically oxisols, with some alfisols, ultisols, and entisols. None of these have high concentrations of sand, and all of these have a very thick layer of clay and organic material before you hit the parent rock layer. Remove the vegetation and you'd end up with a packed clay layer that would bake under the sun and resist wind erosion for a real long time.

Also, what would be the factors of erosion? Obviously not water or ice. Your primary erosion factor would be wind, which clay is resistant to. The tropics aren't noted for high winds, because they are seasonally quite stable. However, if you had greatly different biomes, smaller wind systems might form between them. A desert would be warmer than a neighboring jungle, producing a low pressure cell above the desert, a high pressure cell above the jungle, and surface winds from the jungle to the desert. This would normally cause rain in the desert, but that's blocked by the deity. It would also tend to impede rain in neighboring jungles. The only way I see this reaching an equilibrium is for the humid air being sucked up into the low pressure cell to form a thick, oppressive overcast, preventing the desert from getting too hot. This would put an end to the low pressure cell and the associated winds and allow rains to fall in the neighboring jungles. I imagine it would balance out as a light breeze and heavy but not total clouds, which turn into total, world-darkening thunderheads that never manage to rain on really hot days. (You'd get LOTS of lightning out of them, though.)

So the base of the desert is clay and you wouldn't get much sand out of it. What you WOULD get, if the remains of the jungle burnt down, is ash. Given the extensive dried out vegetation and the lightning, the jungle would burn down, and you would get ash. LOTS of it.

Even without rain, there would be a water cycle from dew, as the humid air cooled in the wee hours and precipitated on the surface. Unless the deity blocks this as well.

I don't know if this is what you were looking for, but I LIKE this for a cursed land. Warm, humid air, but on average cooler than you'd expect for that latitude. Oppressive skies, often turning unnaturally dark (due to thick thunderheads) and producing extensive lightning strikes. Ashes and cinders everywhere, ten feet deep, blown about by mild winds and forming dunes.

Damn. That does sound apocalyptic.

I would think about where the people went to.

Chances are they moved as close as possible. Putting them all around the fringes of the magic dessert, probably in competition with whoever already lived there.

So depending on how long ago this happened travelers could be walking into a warzone or a region awash in starving refugees overtaxing the land long before seeing your dessert.

Real life jungle cultures tend to be pretty small due to the difficulty in gathering food and traditional farming in jungles. Dumping the population of a whole additional kingdom on a region like that is bound to be devastating to the locals and the environment.

Keltest
2015-08-08, 11:22 AM
It sounds fairly like a fairly plausible chain of events to me, assuming you accept the initiator of the deity. I do agree that a rainforest is rather unlikely to contain significant amounts of sand though. You would certainly end up with a barren area, but it would be dirt and clay (and mud, were water to somehow arrive).

And on that note, what about rivers? Is there any that travels through the area without being sourced there? That would certainly explain the continued use of it as a trade route, if it is in a convenient enough location relative to the actual roads that would be taken.

goto124
2015-08-08, 11:45 AM
Won't the river dry up? Or does it still recieve water from its source?

... Nile river?

Keltest
2015-08-08, 11:50 AM
Won't the river dry up? Or does it still recieve water from its source?

... Nile river?

If the source is sufficiently removed from the no-rain zone, it could plausibly run through the desert. It might end up drying up there, or maybe not, depending on how the no-rain spell takes effect.

VoxRationis
2015-08-08, 11:57 AM
Well here's a question. What happens to the rain that now doesn't fall on the area we're talking about? Does it just disappear? Does it remain in the clouds, creating an ever-thicker, ever-more-tantalizing layer of rain clouds that never yield water? Or, since those would both eventually dry up the rest of the world too, does it get shunted off to nearby regions? Is there now a 30N band that was once desert now getting a ridiculous amount of rainfall?

Kadzar
2015-08-08, 12:17 PM
@Reltzik: Yeah, I kind of figured the jungle would screw up my idea of a sand desert. Though an ash desert is kind of appealing. I'll have to think it over.

And I'm not that knowledgeable about atmospheric cycles, so thanks for working that out for me. While I'll agree that a land that never rains but instead has constant lightning storms is really awesome, I'm afraid it might not work out for the plans I originally had for the region. I might need to add something in the deity's curse about clouds no longer gathering over the land.

@everyone else: I think I'll add in that no rain clouds will gather over the place, in addition to it not raining. That doesn't rule out dust (either sand or ash) clouds, though, but in general, there won't be much cover from the sun.

Also, the curse prevents rain from falling on the land, but it doesn't prevent water from evaporating away. And water flowing from outside sources is permitted, I guess, but it can't ever be fed by rainwater in the region, so it might dry up faster than normal.

Keltest
2015-08-08, 12:35 PM
@Reltzik: Yeah, I kind of figured the jungle would screw up my idea of a sand desert. Though an ash desert is kind of appealing. I'll have to think it over.

And I'm not that knowledgeable about atmospheric cycles, so thanks for working that out for me. While I'll agree that a land that never rains but instead has constant lightning storms is really awesome, I'm afraid it might not work out for the plans I originally had for the region. I might need to add something in the deity's curse about clouds no longer gathering over the land.

@everyone else: I think I'll add in that no rain clouds will gather over the place, in addition to it not raining. That doesn't rule out dust (either sand or ash) clouds, though, but in general, there won't be much cover from the sun.

Also, the curse prevents rain from falling on the land, but it doesn't prevent water from evaporating away. And water flowing from outside sources is permitted, I guess, but it can't ever be fed by rainwater in the region, so it might dry up faster than normal.

so when it evaporates, does it just disappear, or does it all get pushed somewhere in a neighboring region? Is there somewhere subject to constant floods because of all the rain the tropical desert would otherwise get?

golentan
2015-08-08, 12:49 PM
If it was a jungle before, a year without rain could wipe out the local plant life and with it the wildlife... When decay sets in, and those roots wither up and weaken or decompose, all the anchor that they give against wind vanishes, and the topsoil can start to blow away (happens at transitional dune ecologies near me)... If there's not a good subsurface reservoir or aquifer, I can see how in a mere few years you'd have blighted decaying wreckage of all the plant life, basically a dry-rot forest, within decades you'd have blighted lifeless (or low life) soil, and within centuries nothing remaining but a dry-baked clayfield or swept sand-dunes.

Any rivers remaining are likely standing remnants of the jungle that once was... Riverbeds which flood might actually help spread silt, or wash it away, and either account for a burgeoning floodplain like the Nile where people can use irrigation techniques to bring life to (parts) of the desert or speed the erosion of the existing topsoil. Either way, that initial society would have been prone to a radical ecological readjustment or what's sometimes called an out of context problem: Any new society would need to be descended from the survivalist tribes who survived the cataclysm or a new colonization.

TheCountAlucard
2015-08-08, 05:27 PM
...it's divine magic, anything can happen?



As you said, a deity cursed the land. The land become desert. What kind of scientific accuracy do you need? Or the deity need to use scientific principle to do it?

I mean, if a deity will it, he can curse a land into only producing candy plants, and there aren't much scientific accuracy of that. Why should this be different?You're starting off with some bad assumptions here.

The biggest being the idea that gods are all-powerful, to the extent that anything they want to come to pass happens exactly the way they want it to with no further effort on their part. That is pretty ignorant of what gods are and how they work.

"All-powerful" is not a base descriptor for what a god is. Some gods are depicted as all-powerful (particularly for monotheistic religions), but the vast majority are not.

The definition of "god" is "a superhuman being or spirit worshipped as having power over nature or human fortunes." The only thing stopping most comic book superheroes from fitting that exact definition is a lack of worshippers, yet we don't assume that the Flash can just will a forest of candied plants into existence; Green Lantern can make a place into a barren wasteland in a dozen different ways, but he'll probably need to keep stepping in to keep it that way.

Gods are generally pretty amazing, even arbitrarily powerful, but seldom all-powerful; even cursory looks at myth and fiction shows this. Loki can't lift Thor's hammer. Zeus wields the thunderbolt that the Cyclopes forged for him (as opposed to forging his own, or forgoing the "having a weapon" thing altogether, because what one weapon is greater than omnipotence?).

The Monkey King's magical jumping/cloud-riding abilities take him 30,000 miles in the time it takes you to hop over a match, but he still can't just teleport wherever he wants to go, nor can he just put Tang Sanzang over his shoulder and jump, shaving fourteen years off of their journey.

Anansi had to use a gourd and trickery to trap the hornets as part of his quest to own all the stories; he couldn't just will them into being trapped, or skip all that and own all the stories from the start.

The river-god couldn't just want Achilles dead to kill him, he had to physically confront him (and got stomped for trying). Ares descended to the battlefield in the Iliad (and got stomped by the mortal Diomedes) rather than just willing his side victorious.

Thor can roast and eat his chariot-pulling goats down to the bone each night and resurrect them each morning, but he can't just go without eating, or not need a chariot, or divinely fix his goat instantly when a mortal unknowingly screws things up by cracking one of the bones to suck the marrow.

It's probably a lot more useful to discussions to assume that gods can do what they're described as doing, but still possess a number of limitations.

bulbaquil
2015-08-08, 06:41 PM
Well here's a question. What happens to the rain that now doesn't fall on the area we're talking about? Does it just disappear? Does it remain in the clouds, creating an ever-thicker, ever-more-tantalizing layer of rain clouds that never yield water? Or, since those would both eventually dry up the rest of the world too, does it get shunted off to nearby regions? Is there now a 30N band that was once desert now getting a ridiculous amount of rainfall?

With Kadzar's stipulation that rain clouds also can't form over the region: In that case, any existing rain clouds that would otherwise "blow into" the area must either do one of two things:

1). Precipitate out their water before entering the cursed area, and/or
2). Be magically shunted around the cursed area.

Assuming this region is tropical (OP said originally a jungle) and prograde planetary rotation, that means prevailing winds are going to largely be from the east. I would therefore expect a region that is even rainier than it should otherwise be along the eastern (or otherwise windward) rim of the cursed zone, since if 1). is true the water, which would have otherwise rained in the cursed zone, must rain in advance, and if 2). is true then you'd have enforced moisture convergence with the air just skirting the cursed zone.

Similarly, the lee side (westward, here) of the cursed zone is likely to be drier than normal, for much the same reasons, gradually tapering back to normal weather as you go further away from the zone.

golentan
2015-08-08, 07:52 PM
With Kadzar's stipulation that rain clouds also can't form over the region: In that case, any existing rain clouds that would otherwise "blow into" the area must either do one of two things:

1). Precipitate out their water before entering the cursed area, and/or
2). Be magically shunted around the cursed area.

Assuming this region is tropical (OP said originally a jungle) and prograde planetary rotation, that means prevailing winds are going to largely be from the east. I would therefore expect a region that is even rainier than it should otherwise be along the eastern (or otherwise windward) rim of the cursed zone, since if 1). is true the water, which would have otherwise rained in the cursed zone, must rain in advance, and if 2). is true then you'd have enforced moisture convergence with the air just skirting the cursed zone.

Similarly, the lee side (westward, here) of the cursed zone is likely to be drier than normal, for much the same reasons, gradually tapering back to normal weather as you go further away from the zone.

They could also "dry out" becoming non-cloud atmospheric vapor, and possibly condense into clouds again on the far side.

Reltzik
2015-08-08, 08:13 PM
Temperature dictates how much water the air can hold; the warmer the air, the more water it can have in it. This is what relative humidity indicates -- the percentage of water in the air relative to the absolute amount that can be held. Relative humidity increases when more water gets added to the air, or when the air cools. When relative humidity hits 100%, you start to see steam, mist, fog, or clouds, because the air isn't really holding the water well and it's coalescing into droplets. Low pressure cells occur when air gets sucked upward into the upper atmosphere. If this is humid air, the cold at higher elevations increases relative humidity. This is why low pressure is closely linked to stormy weather, and why barometers (which measure pressure) can be used to predict storms. High pressure cells are the opposite. They pull air down from the upper atmosphere.

As an alternative, the curse could actually work by placing a permanent HIGH pressure cell over the region. Everything will be hot, still, and stifling. What surface and low-atmosphere winds exist will be from the middle of the curse to the surrounding regions. (This is reversed higher up, but it's too high for clouds to be carried into the region). Humidity would be very low. All the air entering the region would initially be very cold, descending from the upper atmosphere, but by the time it reaches the ground it would have reached ambient (hot!) temperature, and the relative humidity will have been reduced to almost nothing by the rising temperature. NORMALLY this hot air would rise, turning the region into a low pressure cell, but the divine curse prevents this from happening. So instead it has to escape out the sides. This probably wouldn't result in HIGH winds, though.

There would be no clouds and no lightning, but something would EVENTUALLY cause all that hot, dry, dessicated vegetation to catch fire. You'd still get the ash and cinders, but perfectly clear skies, stifling heat, still, suffocating air, and zero precipitation. At night temperature would drop severely without cloud cover and humidity. You'd basically have an ash desert in the tropics.