How could constant or near-constant rain in an area be possible?

Question

What would cause an area to get continuous rainfall (a la Blade Runner), and what implications would that have for other parts of the world?

Ideally I'd like to hear about both natural conditions that would cause this, and man-made activities that could result in this as a side effect.

Answer 1

Maybe it's possible to achieve with enough heat and moisture in the air but even our jungles aren't as rainy. Tropical rain forest is the closest we have to a constant rain.

Some examples:

• [Quibdó, Colombia] : 304 rainy days, 83%. With more than 8m of annual rainfall.
• Kauai island, USA: has the Guinness record for the most rainy days: 350 but receive more or less only 1m in a year. Rain is more frequent but less intense.
• The Indian state of Maghalaya is probably the wettest place on Earth. They receive they most annual rainfall. They can receive twice as much rain in a year than Quibdó but they have a dry season. Most of the rain come from the Monsoon.

Now let's look at Quibdó. It is always located under the influence of the Intertropical convergence zone. This is a hot and low pressure zone where the rain converge. And lastly, it's close to the mountains. The hot and wet air is pushed but as it gain altitude it become colder and since cold air cannot contain as much moisture, it falls on the city. These are the main natural factors to consider.

• Needs to be in a low pressure area.
• Need to be close to the mountains with the winds coming toward the mountains. The city does not have to be at high altitude. In fact, it's better at low altitude = more rain.
• Ideally, it should not be too far from a large body of water. Moisture can be carried overland but the closer the city is from the sea, the more rain it should receive.

Man made activities:

• With water bombs...: I know it's possible to force the rain to fall using some chemistry but I don't know if that could lead to side effects. Obviously, the area past the city would receive almost no rain but it doesn't really matter if it's a mountain. But the water they drink must come from somewhere.
• Living in a dome: it would be very easy to control the factors generating rainfall. Moisture is natural. The rising air encounters the colder dome and transform into liquid water. With enough moisture and heat, you could achieve a water convection movement inside the dome. It might work but it would not be a pleasant place to live.

Answer 2

I don'no bout all dat at-moss-sheric stuff, but back in 2041, just south of Myrtle Beach, we had us a year n a half of hard rainfall. Every day, every hour, it rained and rained and rained. Seems one of dem solar-sats, da energy capture satellites which NASA sent up in da thirty's, it got confused. Started beam'n down its microwave power to a spot just off shore, stead of to the solar farms out in Texas. Boiled up our ocean for months an' months. Caused the rain to fall mighty fierce. Even after de fixed it, the rain didn't stop for a long time. ...and the storms that followed a year latr... don't get me started, talk'n bout storms. I've seen some bigg'ens!

Answer 3

I'd say it is possible given the right circumstances and a slight modification to earth...though it might not be stable over a long period of time (decades).

The best pattern I can think of that would account for that is what occurs to the Pacific west coast. There is a weather pattern known as the 'Pineapple Express' that is driven by trade winds. Essentially the equatorial ocean waters receive a very constant heat (near Hawaii in this case) that creates a steady stream of clouds (can be referred to as an atmospheric river). These clouds are caught up in the trade winds and sent a bit northward as it travels towards land and eventually dumps it's rain all over Seattle and Vancouver. In winter months, Vancouver is well known for entire months of clouds and rainfall (from heavy rain, to a light misting) with people never seeing the sun. The grey blahs as we will. The seasons change here though and the trade winds shift north and south as different parts of the globe are heated.

On an earth-like planet that lacks the seasons (IE, less of a tilt), these trade winds could become essentially static, allowing for this pattern to maintain itself for an extremely long period of time. Climate change here on earth seems to be making these trade winds more prominent as is...more energy in the system appears to be making these trade winds stronger.

So add a few degrees to the world and lose the seasons...and I think you can have the effect you'd want here.

Not all too sure on man-made...storm seeding is a potential, but you require the clouds to do so. Sometimes the conditions just aren't right for rain to form..the water needs something to form around or it remains a gas. Storm ceding in this case would be delivering silver iodide to the clouds. These particles act as nuclei for water particles to gather around, form water droplets, and then fall as rain.

Answer 4

Yes. Consider a warm, rapidly spinning world and a big mountain range in the right place.

One big driving force behind weather is the fact that the air at the equator is moving much faster than the air at the poles, the faster the planet spins the greater this effect is. Thus a rapidly spinning planet is a windy planet.

Since it's warm we have a lot of moisture in the air over the ocean. The wind drives that moist air into the mountain range, it rises, cools and drops it's water. It rains as long as the wind blows.

Answer 5

It's a world right on the inner edge of its star's goldilocks zone. It'll be like Venus in a few million years. But for now it has cloud cover of 95% and it's raining almost everywhere most of the time. Some places all of the time. Probably too hot and humid for humans ( especially away from the poles) but for your aliens it's home sweet home.