How can I explain a planet with perpetual rain?
I was planning a short story that focuses on a rainy day in a city, and I realized that there's one interesting feature of it: Even though the weather seems bleak, and it affects the actions of those in the story, anyone reading it knows that the next day will be, in all probability, sunny, bringing a lighter mood to the city.1
But what if the next day wasn't sunny? What if it rains then? And the next day, and the next day, and the next day? What if it were to rain forever?
I'm trying to figure out how I can make an earth-like world - very Earth-like world - support a weather system that continuously rains everywhere on the planet. there are some issues with this:
- The clouds would block sunlight, making evaporation difficult.
- The shear volume of water would require a large source, and I doubt that evaporation can cover it.
How can I explain the perpetual rain?
I'm not using the hard-science tag because I realize that this could be a tough question, and might require some stretches of the imagination. Answers should, of course, be realistic - i.e. obeying all natural laws.
I should add that I'm okay with answers explaining that this scenario is unrealistic. I rather like the current answers, but I'm fine with someone criticizing my idea.
1 Perhaps not in this case, because the city in question is London.
1 answer
If the planet was a bit closer to the star, like Venus, had a lot of surface water, and slightly higher gravity, you'd end up with a kind of runaway greenhouse effect, where water would evaporate into the atmosphere at a greater rate, and higher gravity would mean thicker atmosphere which would mean higher humidity and more water in the air.
The water would form clouds and rain, and the perpetual cloud cover would reflect some of the solar insolation, which would help balance the greenhouse effect a bit, making it livable.
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