Constructing a desert area

Question

I'm trying to construct a most realistic desert possible. I've made a continent with my little knowledge and may ask further questions about climate and similar stuff, but now I want to center on a desert area that I want to locate.

Our little world

I have a large continent, large as Europe and Asia together.

It has a mountain change that divides the continent almost in half, except for a few spots where there is lower terrain and in the northernmost part of the continent the mountain chain dies. I want there to be a forest on both west and east sides of the mountains, being more vast in the southwestern part.

I want to focus on the west side, having a great green land on the south with a template climate and as you approach the mountains colder temperatures would be found, and in the north side a more cold green land that advance into a boreal area.

I want to somehow get a desert between them; the desert may occupy from the west coast to the mountains on the east part (like Sahara in Africa).

Questions

1. Is it possible given the actual conditions I've just given to you?
2. Would it be possible for the desert to have one or two large rivers?
3. Where can I find large amounts of trees on a desert like this?
4. Where may I find large mines?

(*I have little knowledge about how large amounts of minerals are created so this question may be a stupid one or minerals would depend on factors other than just position)

Edit:

Here's a map of how I imagine my world.

Gretland is a vastly green land, has lot of agriculture zones, and template climate. Imagine Gretland climate as southamerica-like.

Winthold is more like a Canada climate place.

Little triangles are mountains.

I want my desert to be in Thaliak.

More info will be provided if needed

Answer 1

Is this desert possible?

Yes, If you have cold ocean currents flowing south from the cold northern hemisphere regions and an predominant onshore wind direction you can get a dry interior where you want it. Without a gulf stream equivalent bringing warm moist air to the West coast of your northern reaches (Europe), you can have much dryer conditions in your Winthold and Thaliak regions.

I drew all over your map (not as nicely as Hofmannfan). I guestimated your equator. But feel free to move it if necessary. This is just to show you the idea. Black - Equator. Red - warm ocean current. Blue - cold ocean current. Green - predominant wind direction. Numbers - rough temp scale indication

Wind flowing over cold water is generally dry. As soon as the wind hits land it will no longer pick up any new moisture and become dryer and dryer the further into the interior you go. In our world on a west coast, with a cold ocean current this normally means fog banks and very little actual moisture making it far into the interior Eg Namib Desert in SW Africa. It would be a different story if you had had an east coast with a warm ocean current and no mountain range blocking it, this would have allow the moist air to reach quite far inland (eg north America great plains).

The Winthold coast will have slightly more rain than the Thaliak regions. As any moisture the coastal air is holding will fall first on the coast and then the winds will become drier and drier the further East you go.

With your N/S mountains, you will be pulling cold air down from the Arctic nearly all the way to the Equatorial regions. Expect some mega storms when warm air meets cold air. But back to the desert. Cold air will flow from the mountain to the interior (mountain anabatic winds), bringing very cold dry air to your Thaliak desert region eg 'Berg winds. Winds blowing in the opposite direction, katabatic winds (typically sea breezes) would be weaker and wouldn't bring much moisture to the mountain range. What little air moisture there is, will experience orographic uplift and probably fall as a light sprinkling of snow along the entire stretch of your range.

The only reason Gretland isn't dried out by the dry winds from the mountains is because of the Hadley cell circulation. This is where hot moist air rises at the equator and sinks at roughly 30 degrees North and south of the equator (the tropics). You might want to move the equator a bit further south than in my drawing. This will still allow the Thaliak desert region to exist. Probably a bit better as my map doesn't give the currents a lot of time to cool down!

Can I have 1 or 2 major rivers?

Your northern and eastern Thaliak regions will be drier than the south and western regions which could still receive some rainfall. Rivers can flow anywhere you like, as you will have a large amount of snow in your northern mountain regions. This can supply water for rivers. You just have to decide where to place them. If you wish to keep the NE regions as dry as possible, have only very small streams/rivers flow out in the top sections of the desert and the main river/s flow further South and then across to the west.

This river supply could also explain why Winthold is more fertile as the river winds it's way through the coastal hills.

One thing to take into account, the rivers formed from the rainfall from the Hadley cell convection should not be allowed to flow into the Desert (too much or too frequently). You need a geological boundary to force the river flow back into Gretland. This does not need to be a mountain range, but a change in underlying rock type or tectonic fault line will do the trick. Even a small range of hills should prevent the rivers from flowing north (if you use a fault line, lots of water can trigger frequent earthquakes).

Your current map, shows a mountain range jut out of your N-S range. This should prevent any rivers from flowing directly into your driest desert regions. You can have a major river flow through the SW Thaliak region into S Winthold.

Large groups of trees in the desert?

Wherever there is water, you can have vegetation. You can have several smaller rivers from the north mountains feed underground aquifers. These could provide water for several oasis's in your dry region if you wish. You can also have hidden valleys, protected from the cold dry wind. If water flows through them they can be little Sangri La's. Pretty much, if you want them, you can have them. Just justify where the water is coming from. It doesn't have to be air or surface based moisture.

Where would I find mines?

This is really a whole other question. But quick answer. ANYWHERE you want them. Geological deposits are not constrained by current-day surface conditions. You can give your world any sort of geological history you feel necessary to explain why you have certain deposits where you have them. The trick is to explain how your inhabitants found them. This is why a lot of mines are found in the mountains. The rock we were interested in was very near the surface and we literally tripped over the shiny metal stuff.

Granite, marble etc are metamorphic rocks and formed during intense heat (think lava). The finer grained rocks will have cooled over a much longer time/higher pressure than the coarser grained rocks. Generally that can mean that the coarser grained rocks will be found above the higher 'quality' stuff.

Rivers wash away rocks and minerals from the mountains, and are another excellent source of 'easy' mining. Gold, Diamonds, Titanium, Aluminium can all be found in alluvial deposits.

Like I said, you can decide what you want and where, and then if you really need to you can research the geological history of your world...as long as you can explain why your inhabitants knew there was a deep gold reef at location X, you don't have to explain how the gold mine actually got there.

Answer 2

Deserts are just places where plants don't grow, and there are many reasons why plants wouldn't grow in an area. These include:

1. Not enough water.
2. Poor soil.
3. Too rocky.
4. Too cold. (Obviously not an option for you.)

It should be simple enough to have there be a combination of too rocky and poor soil for sustained plant life. It could be a great salt flat, for instance. The large rivers would have washed out the salt from their local environment, but everywhere around them is still too salinated for plant life.

So, 1 and 2 are yes.

3 is a no, for obvious reasons, if you think about it. If there were large amounts of trees, it would not be a desert, it would be a forest. For some amounts of trees, look to the river flood plains. The flood plains would wash away enough of the salt for plant life to grow. It's likely this is where 99% of the farms would be, including any timber farms. Most likely, however, lumber would be imported; it's more important for food to be local, since it's more perishable.

4. The mines would be found in the mountains. Mineral deposits are found in bedrock, and mountains are basically bedrock extruded to the surface. That being said, salt is one of the most valuable commodities in the medieval world.

5. The capital city would be located on the largest river at the most advantageous farming location. Great import/export, enough food to support itself.

Answer 3

Is it possible given the actual conditions I've just given to you?

The desert you describe, between a green and lush temperate land to the south, and a cold taiga/tundra to the north does exist in places on the earth. The best example is the Gobi Desert in eastern Mongolia and north Central China (Inner Mongolia, Gansu, Ningxia, and Shaanxi). To the south(east) there is mainland China, lush enough to be home to a billion people. Directly to the east is Manchuria, cold but still fertile. To the north is the taiga and tundra of Eastern Siberia.

Another half example is the Northern Great Basin (Idaho, Oregon) and Columbia Basin (Washington, Idaho) of the United States. In this case, a range of mountains cuts the basin off from the the precipitation of the coast in near Portland and Seattle making a desert. In this case, there is no green land to the south, but given the right climactic conditions, Arizona/Nevada could be much more lush. Eliminate the mountains in New Mexico and Chihuahua, and you would get much more summer precipitation, eliminate the mountains in Southern California, and there would be more in the winter. Not as wet as in China, but wet enough.

You can look to to cities like Boise and Spokane, or Yinchuan and Hohot for guidance to what the climate would be like.

Would it be possible for the desert to have one or two large rivers?

Yes. One large river would be like the Nile. The nile's source is in Ethioia which has a summer (June-Sep) rainfall regime. Just as summer's heat is peaking in August in Egypt, a huge flood of water comes down river (or did, before the Aswan High Dam). The Nile also has a source in Lake Victoria, a huge lake with steady yearlong precipitation hat provide a baseline flow. The Sudd, a huge swamp in the Sudan also helps regulate this flow, so the Nile gets water year-round and does not run dry.

An example of a pair of desert rivers are the Amu Darya and Syr Darya of Central Asia. They run exclusively through deserts, but get their water from glacial meltwater in the Tien Shan mountains. The large central mountain range in your map could provide a flow in this case.

Since we identified two similar geographies above, you can look at the large rivers from those two regions, the Huang He (Yellow) of China, and the Columbia/Snake in North America. Both of those are fed by water in high mountains, snowmelt in Tibet in the case of the Huang He, and high mountain rainforests in Idaho, Montana, and British Columbia in the case of the Columbia/Snake.

Where can I find large amounts of trees on a desert like this?

So trees in a desert are not common. One option that I saw mentioned above is cacti. You can have a desert that is populated by giant Saguaro cactus and call them trees. Another option is Dry Thorn Forest. These conditions exist where there is a short, rainy season followed by a lengthy dry season. The Caatinga in Brazil, Deccan Thorn Forest in India, and the Mopane forests of South Africa are examples of these. Unfortunately, on earth these only show up in tropical climates, so this is less realistic for a cold desert like yours.

A last option is that there are spots of life amongst the desert. In the Great basin, in particular, as elevation rises, rainfall goes up. So the basin 'floor' at 2000m is dry sagebrush, up at 3000m, a forest of Juniper and Pinyon pine starts, then at even higher altitudes you get aspen, Douglas Fir, and spruce. So you could have these forests exist in 'Sky Islands' (as they are termed in Arizona) amidst a dry desert plain.

Where may I find large mines?

Anywhere you want! There are a variety of geological processes that cause good mining locations. An ancient craton, like the one in South Africa, can be motherlode of gold and diamonds and such, or ancient volcanic tubes like in the US Southwest can be brimming with Copper. Just go ahead and put mines wherever you like. Its not like you are going to add enough detail about cratons and igneous extrusions to have a geologist throw the bullshit flag on you.

Answer 4

Deserts are defined by the lack of rainfall.

Rainfall is stopped by either triggering it earlier or making the conditions that cause rainfall not to happen over that area. In general this is caused by ocean and wind currents which and there is a long explanation about how all that works, but unless you want to map out the entire world you're not going to easily figure this out. The biggest contributor to your desert is likely the mountain range which will make it rain on the eastern side. more over, your desert would extend all the way to the west coast rather than dip down like you show. The western mountain range would cause the desert to be there and the coast would be desert due to the various currents.

As far as your exact questions...

1. Yes
2. Yes, Ever heard of the Nile?
3. Nowhere, because the lack of rain, but the area on the east, south of that little mountain range offshoot would be extremely lush. Generally speaking, there is an area of steppes/plains between the desert and forest. Also you'd find trees along the rivers probably, but those would be quickly cut down and cleared for agriculture.
4. Anywhere... I guess, by the mountains are the mostly though probably.

Answer 5

Clarifying a distinction between this post and the previous answer, I will point out that the definition for a desert is NOT that "trees do not grow", it is that the area receives very little precipitation. That is a significant difference. Note that a desert can also be hot (like the sahara) OR cold (like antarctica), and the temperature (hot, cold, or in the middle) should be specified.

I'm going to give you control of the prevailing winds and general climate of your world, which means you can definitely make Thaliak a desert if you wish.

Now let's answer your questions...

Is it possible given the actual conditions I've just given to you?

Yes, conditionally.

You state that you want forests to the west of your mountains. You can have a desert in a forest, but not with just any kind of trees. Trees suited for anything other than an arid climate would not do well, and near the mountain it's still likely to be mostly scrag and brush as there would be rocky soil and very little precipitation.

As for the types of trees you can have, I'll let you research that further. Cactus comes to mind, and perhaps an elephant tree... but again, I'm letting you research that.

The key to remember is that if you have a water source and a hot day there will be evaporation. If you want that evaporated water away from your desert, you need a wind current to carry it away before the vapor condenses. Hot deserts can be particularly tricky that way because wind-blown dust provides that vapor something to condense around, so you can't just carry it away an unlimited distance.

Would it be possible for the desert to have one or two large rivers? Under the right conditions.

The first and easiest statement is that the rivers would be easiest to place on the extreme edges of the desert; prevailing winds could then blow atmospheric humidity north or south.

The next way to do it would be to have underground rivers, which perhaps become exposed in a few places if you need that for your story. Significant amounts of water on the surface in the middle of a desert though would beg the question "why doesn't any evaporated water rain back down?". One answer is to perhaps mirror Egypt - green(er) along the Nile, desert elsewhere.

Where can I find large amounts of trees on a desert like this?

Anywhere you want to plant them, with restrictions on the types of trees. Again, you can research the types of trees themselves, but anything that stores water for a long time or can draw from a particularly deep underground water source is fair game.

Note however that if you have a dense forest of any kind of scrub you are going to increase the chance for rain. Even with a waxy coating those plants will give up some water to the atmosphere, and with a sufficient number and density you will get some occasional rain.

Where may I find large mines?

Wherever you want to find them. Mines are built according to where minerals are found, and you get to place your minerals. For convenience I might place them in the mountains, but this is your world.