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Let's assume a planet like ours, same size and same conditions. My characters live at approximately 60° North, in a boreal forest, with a climate much like the Nordic countries in Europe. They are travelling south and need to encounter a hot desert much like Sahara. This desert has to be placed as close to the boreal area as possible and still be believable as a hot desert. I've done some research and the Gobi desert, which is placed at ~45°N, is too extreme with temperatures as low as -40°C during winter nights and as hot as +50°C during summer days. This could be a good starting point, though, if it's possible to have a desert approximately this far north but make it less cold during winter nights (let's say no colder than -5°C).

Any factors that is true on earth, like warm or cold air and water currents, could play a part in bringing these biomes closer together.

I am looking for:

  • The shortest possible distance between a boreal area with cold winters and a hot desert that should not be colder than approx. -5°C during winter nights.
  • The factors that make it possible to place these very different biomes so close together.

(I am new and I hope this belongs here and not on the Earth Science site.)

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    $\begingroup$ Don't worry, it does seem like a good fit for Worldbuilding.SE. $\endgroup$ – Linkyu Feb 16 '15 at 15:33
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    $\begingroup$ Mountains are probably your best bet. Altitude in general is the only thing I can think of that would get you what you want. $\endgroup$ – James Feb 16 '15 at 16:12
  • $\begingroup$ What kind of distance are we talking? Or rather, what are you looking for? $\endgroup$ – James Feb 16 '15 at 16:22
  • $\begingroup$ The distances used in the answers below are fine, thanks for your help guys! $\endgroup$ – Niffler Feb 18 '15 at 6:17
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I can think of a few places where you have desert and forest near one another.

You may or may not get the TYPE of forest you want but these can serve as models for you to work from.

  1. Basically all of Peru and Chile.

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  1. The Black sea's southern coast line.

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  1. Basically the entire southern border of Tibet.

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  1. (and 5) are both from Utah actually. The first is a ten minute drive from Salt Lake. The Salt flats are nasty hot. But I think #5 is the closest for you. The national forest is beautiful the mountains are amazing...as soon as you hit St. George completely desert and dry, and a little further south once you drop through the virgin river basin you hit the desert outside Vegas and that is truly desolate.

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Notes:

  • Elevation will have to play a role, generally a mountain range. Its the only way to get the temperature swing necessary to support the two environments.
  • Proximity to water. If you want trees you need water. Mountains help make the distribution of that water uneven.

These are the two key factors to get what you are looking for. But as mentioned in other answers, the temperature swing in deserts from day to night is larger than in any other habitat, you simply don't have anything to stabilize it (water, trees, etc). Water also helps normalize temperatures a bit.

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    $\begingroup$ This. If you need abrupt transitions, you need elevation differences, plus a mountain range for wind shadow. I live on the other side of the Great Basin, and it's about 10 miles (less in a straight line) from high-altitude boreal forest (or even above tree line alpine tundra) to sagebrush desert. Another 10-20 miles brings you to dry lake beds. But note you will have oases from streams running from mountains to desert. Look for Fremont's exploration journals. $\endgroup$ – jamesqf Feb 16 '15 at 17:49
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Have them encounter a Pumice Desert

The type of dirt can change the overall environment drastically regardless of weather.

I was up in Crater Lake a few years ago and as we drove from the still snow covered Alpine we suddenly found ourselves in a vast Pumice Desert. The otherwise forested region came to an abrupt halt where the soil turned to sand for miles. Nothing can really grow there, as the entire valley had been filled thousands of years ago with pumice rock up to 300 feet deep.

enter image description here

If you are looking for the ABSOLUTE SHORTEST way to change a forested biome into a desert, go with a drastic change in soil. And if you want to keep it warmer than the immediate area, change its rock color to something more like the Shasta Lava Beds. And to further increase the temperature there year-round, lower the elevation of this desert to below sea level.

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But deserts get cold at night, all of them. Even Arizona deserts get down to -5C in January. Moving deserts north is going to make this worse. The reason is deserts have so much sand and is an excellent insulator/reflector. It's gets hot when the sun shines and quickly releases it's heat when the sun goes down. The cold is almost as dangerous to those traveling across it as the hot days.

I don't think you could get a better example to work with than the Gobi Desert.

One idea to make it 'less' cold at night would be to have the sand be black basalt. It would absorb heat all day (making it worse) and take longer to release it at night, so the temp wouldn't get as cold by morning than otherwise expected.

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    $\begingroup$ I will look into the black basalt, it could make for some interesting settings. $\endgroup$ – Niffler Feb 18 '15 at 6:24
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How large does the area need to be, are you traveling four days across it, two weeks? A month? I'm not sure I can provide a good answer for a very large desert, but in my travels I have found a small desert (that used to be much larger) in Southern Manitoba. (Latitude = 49.666)

It is called the Spirit Sands. It used to cover an area of 6,500 km, now is about 4 km across and took 5 hours to hike on a brisk September morning. 6 am was around -2 (cel) and 10 am was around 8/10 (cel). The surrounding geology is an area known as The Canadian Shield, a large rock mass. It is very diverse terrain, tons of quartz, and as well mostly boreal forest. This boreal forest extends thousands of kilometers north and east, it gives way to the (flat) prairies to the west. Edit And the Rockies are further west past that.

It was a large river basin that slowly drained giving way to the shifting sands there are there, I think some of what may have given rise to this is further north the land becomes tundra (and permafrost area) and well used to be covered by glaciers. The glacial deposits ran further east as the land experiences greater chances in elevation. The Red River to the east, and near Winnipeg floods seasonally.

Spirit Sands

This picture is just before the rise to go into the larger desert.

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  • Hot deserts: A hot desert need to be quite close to the equator because it needs a lot of heat mainly form the Sun. Most of them are located between the tropics for this reason. The northernmost hot deserts extend to 35° were they become cold desert usually For most of them, the average monthly temperature never go below 5°C. This doesn't mean that the temperature never go below 0°C but just that this is under the average.

    The farther you are form the equator, the greater the temperature variation between summer and winter. At the tropics, summers are really hot but get slowly cooler as we move toward the poles. I see it unlikely that a desert (hot) could exist closer to the poles because winter and summer would be colder.

    Being close to the sea would make the winter temperature warmer and could maintain it over 0 but would also reduce the summer maximum.

  • Boreal forest: Most of the Canadian forests are boreal. Meaning that they extend almost to 45°N. These are mostly located at a somewhat higher altitudes, and this help a lot.
  • Distance: supposing that your planet is as big as earth: 45°-35°=10° and the distance for each degree is 111,11111.... km. A plausible distance would be 1111km.

How to reduce the distance:

  • Make the planet smaller.

  • Have a high plateau near the hot desert. The temperature will be lower and although it's not really a boreal forest, it may look very similar. The hot desert has an annual temperature of 18° and the boreal forest is around 0°. Increasing the altitude by 1000m reduce the temperature of 6° each time. If the forest is at about 3000m of altitude, it can be close to the desert.

  • We also need to consider the difference in precipitations. For that, we could solve the issue by placing a mountain range in between. It might not be necessary for the mountains to be very tall because the forest is already on a plateau that is high enough to block a large portion of the precipitations by itself.

Do you really need a hot desert? Cold deserts can have hot summers too with an average of 26° in Western China for their hottest month.

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  • $\begingroup$ This is a great and well written answer, thanks! $\endgroup$ – Niffler Feb 18 '15 at 6:22

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