Weather on a Dry World

[Balrog]

What kind of weather patterns would you see on a world, Earth-like in every other respect, except with no large bodies of water, instead just rivers and lakes? What if there were one or two large bodies (like the Black Sea)?

[Junghalli]

I'd bet that, most of the time, the result would be a generally dry world. You might end up with a classic SF-type desert world. Or you might end up with a planet where you have large fertile areas near the seas but the majority of the surface is parched and waterless. If it was a cold planet you might get something like a more habitable Mars, with huge cold deserts. Although I suppose one can envision a set-up where you have no big oceans but lots and lots of medium to large lakes.
It would depend a lot on the topography of the planet.

[Broomstick]

You have much greater temperature extremes - water vapor helds moderate temperature, as well as providing clouds that can, depending on circumstance, either reflect heat back into space or hold it near the surface of a planet. This is one reason deserts can be above human body temperature in the early afternoon and drop to freezing at night.

You wouldn't have hurricaines/typhoons - they require large open and warm ocean water to power up.

That's all I can think off off-hand, but I'm sure there would be other effects.

[Guardsman Bass]

The barrenness of the desert areas would beggar the mind, unless there was underground water available to surface life.

[GrandMasterTerwynn]

What kind of weather patterns would you see on a world, Earth-like in every other respect, except with no large bodies of water, instead just rivers and lakes? What if there were one or two large bodies (like the Black Sea)?

A couple of possibilities:

Small bodies of water would dry up rapidly and any free water would be relegated to springs and underground. With a paucity of water to drive the hydrological cycle, you'd certainly not see thunderstorms, or any sort of storms. The most cloud you'd see is, perhaps, some early morning fogs that settle into the deep valleys, and some mid to high-altitude ice-crystal clouds. If you could see the planet from space, you'd notice that it would probably have more substantial cloud cover over the poles, where the atmospheric circulation ends up depositing water picked up from more "temperate" regions. Around the poles, the weather would probably be a blt more familiar. You'd have polar mesocyclones and storms depositing snow and frost onto the planet's ice caps.

Make it a little wetter, and you have a scenario like Titan, where, while there is rainfall, it occurs in great, scattered bursts seperated by long periods of drought.

In both cases, when the rain isn't falling, the soils will weather quickly due to the temperature extremes. You'd get a lot of fine sandy or dusty soil, and during the winter months of one hemisphere, where cold, heavier polar air pushes further into the temperate latitudes, you'd have great temperature differentials across polar frontal boundaries colliding with warm air, (hell, due to the lack of moderating bodies of water the extremes temperature spread between night and day would ensure that there would be winds blowing much of the time.) Such severe temperature differences would generate wind. ANd the wind would pick up the fine sandy soils prevalent on the planet. Winter would herald the arrival of dust-storm season, and dust storms will grow to magnitudes rivaled only by those found on Mars. (Certainly the denser atmosphere will moderate temperatures a fair bit more than the near-vacuum that passes for air on Mars, so the dust-storms won't be quite so extensive as Martian dust-storms. They will, however, exceed anything found on Earth.)

[CaptainChewbacca]

Also, the weather would be very unpredictible, with wind currents dependent on heating/cooling of the surface and sunlight reflected into the atmosphere.

[Gil Hamilton]

You wouldn't have hurricaines/typhoons - they require large open and warm ocean water to power up.

That's all I can think off off-hand, but I'm sure there would be other effects.

It wouldn't preclude massive storms though, including tornados. Mars, for instance, has virtually no water at all on the surface (though, in fact, has close to 100% humidity for its atmosphere) but has truly impressive planet wide storm effects on occasion thanks to solar heating and picking up electric charges from other sources. This is really kicks in when Mars hits perihelion and is close to Earth, which were the conditions in 2001 when Mars had the massive super global dust storm that covered the entire planetary surface for weeks, doing this.

I imagine that if our hypothetical desert world could have some beastly monster equivlent of dust devils, powered by an electric charge from the planet itself or its primary and solar heating. Mars in 1999, for example, had a cyclone over four times the size of Texas nears its pole thanks to such things, they think.

[Balrog]

So it would probably be a sort of desert world then, except for the polar regions and wherever there was water? Would any sort of animal/human life survive and thrive on such a world?

[Stormin]

Earthlike life requires a lot of water so unless the planet changed slowly enough that evolution could have time to adapt the species, a dry world like the one described would probably not have much in the way of thriving higher level life.

[GrandMasterTerwynn]

So it would probably be a sort of desert world then, except for the polar regions and wherever there was water? Would any sort of animal/human life survive and thrive on such a world?

Most of the water would be locked up in polar ice caps, or just underground. Certainly if human colonists were willing to drill for water, they could probably create small oases where they and their attendant plants and animals could survive, but it'd be a continuous battle against windstorms, sandstorms, and wild temperature swings. And the planet's ability to support biomass would be crippled, relative to Earth (owing to the comparative lack of habitat,) so you won't be able to expect much oxygen in the atmosphere either.

[Junghalli]

So it would probably be a sort of desert world then, except for the polar regions and wherever there was water? Would any sort of animal/human life survive and thrive on such a world?

Well, the OP said it has seas, so I'm presuming you envision something a bit more Earthlike than GMT's near-Mars... Yeah. You'd basically have a very extreme desert ecosystem.

[GrandMasterTerwynn]

So it would probably be a sort of desert world then, except for the polar regions and wherever there was water? Would any sort of animal/human life survive and thrive on such a world?

Well, the OP said it has seas, so I'm presuming you envision something a bit more Earthlike than GMT's near-Mars... Yeah. You'd basically have a very extreme desert ecosystem.

The OP said that there might be a couple of bodies of water as large as the Black Sea. The Black Sea is a piddling body of water, being maybe twice the surface area of the Great Lakes combined and about a third of the surface area of the Mediterranean. A body of water that small will probably not be stable for geologically long periods of time on a planet that is otherwise dry. The only way it might be stable is if it were at a high enough latitude that it takes part in the polar hydrological cycle. Otherwise, you'd have an enormous band of the planet, centered about the equator that will be a pretty good approximation of Mars, if Mars had lots of air.

[Junghalli]

Well, you could still have abundant life around the sea. Plus, if there's oxygen, even the deserts could probably support some higher life.

[GrandMasterTerwynn]

Well, you could still have abundant life around the sea. Plus, if there's oxygen, even the deserts could probably support some higher life.

You may have abundant life up around the small polar seas, but it's debatable whether the planet will be able to support a biomass hefty enough to generate significant (to us) atmospheric oxygen (which is generated by the splitting of water molecules into oxygen and hydrogen.) Below a certain tipping point, the life will generate oxygen, but not in the quantities needed to oxidize all the available oxidizable minerals on the planet and still leave enough left over for free atmospheric molecular oxygen. And it's not enough to just have free molecular oxygen, you need enough of it to make ozone up in the stratosphere. Without an ozone, or reasonable chemical analogue, layer, the surface of the planet will be bathed high quantities of UV radiation. While subsurface or life existing a little ways down the water column in the polar seas won't suffer because of that . . . the UV will react with minerals in the dust and soil to produce more of those minerals that soak up free oxygen.

So, really, it all depends on the amount of photosynthesizing life the planet can support, and how long it can support them for, and I'm not quite sure whether the desert planet in the OP has enough habitat for life available to render it more than a marginally habitable Mars-like wasteland. Now if this planet was just recently coming off a much wetter, more-habitable phase, then yes, there may well still be enough free oxygen to support more complex life. But, if it had been stable in this relatively dry state for a very long time, then most of the free oxygen will be locked up in the planet's crust.

[Guardsman Bass]

How much surface water would be needed, then, for a large body of water to survive on a geological scale below the polar latitudes? Are we talking about a body the size of, say, the Mediterranean Sea, with the same depth?