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Imagine an Earth-like planet with no major oceans, all the water has collected into circular craters from impacts that are no longer occurring. Let's say the planet is covered evenly with 50% water pooled into these lakes and seas, with rivers distributing water from the smaller lakes to larger seas. No crater is larger than the continent of Australia.

EDIT: There's no reason this planet can't have mountains, valleys, streams, rivers, lakes, etc. I just want the defining feature to be the crater lakes and seas with no body of water larger than Australia.

What would the climate and environment on this planet look like? How and where would forests/deserts/jungles/tundras form?

lonewookie
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    Imho, the idea needs some work. Why would the planet not have mountains, valleys, and whatnot if it has so much water? Think about it, if there is a land mass then the water inside these impact craters would still be evaporating and normal erosion would be occurring all over the land mass. Which would in turn lead to lakes and rivers and streams outside the craters. – Rob Apr 26 '19 at 19:11
  • I'm not ruling out mountains, valleys, and other lakes - and I don't think these things would make these lakes/seas impossible. It's just that the dominant feature of the planet is these lakes and seas and most of the way does flow into them. – lonewookie Apr 26 '19 at 19:51
  • So what's to prevent the water from leaving these craters and distributing itself elsewhere? – Rob Apr 26 '19 at 20:39
  • With the craters being the lowest points on the planet, I would assume the water would naturally flow there? – lonewookie Apr 26 '19 at 20:51
  • So does this planet have no tectonic plates? You said "Earth-like" so I would assume the landscape is constantly changing: uplift, erosion and so on. All the normal ecological transformations of an Earth-like planet. What I am saying is there was a point in Earth's history where the land was pock-marked with craters; however, as time goes on those things go away. – Rob Apr 26 '19 at 20:55
  • I'm not sure, whichever would allow the craters to stay relatively stable for as long as possible? I'm more curious what the climate would be like in this scenario. – lonewookie Apr 26 '19 at 20:59
  • Well then I think the question can be boiled down to something like: "What would Earth's climate be like with 20% less water on it?" – Rob Apr 26 '19 at 21:04
  • I was more curious what the composition and spread of the crater lakes would have - vs. having a large ocean that circulates water and air. If there is no difference between these crater lakes and a world with 20% less water, that's fine. But I'm curious what impact (if any) these circular seas and lakes would have on the climate and environments. – lonewookie Apr 26 '19 at 21:06
  • Just like on Earth, that would be highly dependent on the landscape. However, I can see no reason why your world's climate would not act in an extremely similar fashion to Earth's. – Rob Apr 26 '19 at 21:10
  • Okay, that does provide insight - I wasn't sure if the lack of large continuous oceans would have a large impact or not. – lonewookie Apr 26 '19 at 21:13
  • Climate is, on the whole, a localized phenomenon. As I said before, the main contributing factor, to the differences between your planet and the one we currently live on would be the 20% reduction in water. This would expose more land which, on the whole, would make things more dry. – Rob Apr 26 '19 at 21:19
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    This is very broad and well outside the scope of WB.SE. The climatology of an entire planet is incredibly complex with massive variation. Just the variation from poles to equator is difficult to ascertain without a complete topological map of the planet. "Earth-like" can tell us star type/stats, orbital distance, axial tilt, planetary mass/diameter, but that's where "Earth-like" ends. On Earth, currents massively affect climate. You have few currents. You might consider the tools for low-level climate analysis here. – JBH Apr 27 '19 at 00:29

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If the topography is flat other then the craters, you would have environment temperature be based on distance from the poles, and closeness to the equator. The flat surface would lead to massive winds as well, with nothing to divert the pressure you might create a vacuum that would be devastating to most life. Assuming those winds do not exist:

On earth, you often have deserts and jungles form from the excess of (or lack of excess) moisture. Usually you see this occurring by mountain ranges, one side will end up dry because the moisture is held to one side of the mountain. If everything is flat except for the craters, the growth of vegetation and life would be focused around the pools where precipitation is more likely to occur.

Even though 50% is water, nothing is requiring the pools to be evenly spread, so I see huge amounts of land with few pools becoming the deserts and tundra due to lack of moisture. Tundra near the poles, and warm deserts the closer you get to the equator. Similarly, the region with the densest pool amount would create the jungles. These places would likely be wet, and rain at least once a day like the rain forests of Brazil and Africa. Moderate spreading of pools would result in a traditional forest, and the further you go from the equator towards the poles the forests would transition to having tropical plants, to having deciduous plants, to having a Taiga biome.

Plains would exist between the deserts and the forests, but as a transitional biome, most of their water would likely be rains pushed from the jungle/ forests.

check out this site to see how and why biomes on earth formed the way they did: https://www.blueplanetbiomes.org/

Alex
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  1. Less water would mean less rain and a globally dryer climate. At 50% water the climate wouldn't be one third dryer than that of Earth. You probably wouldn't have large areas of wet biomes like the Amazonian rain forest, and you would probably have larger deserts.

  2. Lack of mountain ranges and oceans would mean a more uniform distribution of weather. It would be dryer at the poles and at 30° latitude north and south, wetter in between.

  3. There would be strong continuous winds in more uniform directions. (See https://en.wikipedia.org/wiki/Atmospheric_circulation for the distributions of winds, rain, and temperatures.)

All in all, what I envision is a planet with continuous strong winds, broad stripes of desert around 30° latitude north an south, subtropical dry forest vegetation around the equator and temperate broadleaf forest around 60° latitude, steppe between the forests and the deserts, and poles with thinner ice. There would be small areas of wet biomes around the rivers and lakes, dry areas an the windward sides of the crater rings, and so on.