– how can a place be constantly extremely rainy? Eg Maui is said to be one of the wettest places on earth where it rains constantly. What is the explanation behind this? Why would one place be constantly rainy as opposed to another place?
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The rain follows the forest is a Hawaiian proverb. (Ha hai no ka ua ika ulu la au) Maui is pretty heavily forested.
The basics of the water cycle is the sun evaporates water, water goes up, water collects together into a cloud,the get blown around and collect more water, and when it gets too heavy it rains.
But plants also help here. They act like massive straws. Leaves have a decent amount of surface area. The leaves collect sunshine and evaporate water, this creates a negative pressure that allows the tree to suck water from it’s roots and back to the leaves.
When you get enough trees together, this creates a feedback loop. When an area is heavily forested, there is a tonne of water going into the air at any given time. Remember the water cycle? Near forests you skip a step. When the cloud gets too heavy it rains. But Forests throw so much water into the air that the clouds don’t have a chance to get blown away. They form and rain in basically the same spot. This means there’s more water on the ground for the trees to suck up and throw into the air, which makes clouds quickly, and so on.
There are other factors that can have the same effect. Anything that can push moisture into the air to make clouds heavy at a given spot will make them rain. Like mountains. Wind pushes water-heavy air around, when it hits a mountain. It goes up and forms a cloud heavy enough to rain.
Rain forms when moist air rises and condenses. I grew up in Norway, where the city of Bergen is notoriously rainy. The wind from the North Sea carries tons of moisture, and the city lies at the foot of tall coastal mountains, which force the air upwards, forming rain clouds. So look for tall mountains and moist air, and you’ll find where it rains.
Fun fact: some of the world’s driest places lie inland from such mountain ranges. They squeeze the moisture from the air like a sponge, so there’s none to go around farther inland.
So, I’ve only visited Maui. It did rain there every day but, only at the top of the island. Disclaimer:I do not live there but, there is an island across from the Westin that I was told a story about while on an excursion.
Basically there was an island that nothing would grow on because it wouldn’t rain. This island passed hands until one guy bought it and got the big idea to plant some trees at the very top. He watered them by hand until they were tall enough. Once they were tall enough, clouds started to form around the tops of the trees bringing rain and now that island is a whole pineapple farm.
I don’t know if this concept holds true for other places but for Maui (and I’d guess other Hawaiian islands) it depends on elevation.
Btw, Maui does not rain constantly. The Hawaiian Islands get most of their rainfall during winter.
One of the best predictors of constant or higher than average precipitation is coastal elevation changes (mountains)
Warm moist air coming off the coast is pushed up where it cools and condenses and rains.
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Lived on Maui for 3 years and worked as s tour guide, best job you could ever have. The wettest spot is a small area in the volcano in the west Maui mountains but just on the other side is Lahaina, about couple miles or so away which is incredibly dry. The clouds get “caught/trapped” in the volcano tops. Very often if it’s raining where you are, if you just go to the other side it’s not raining. It’s very rare that the whole usland is rainy.
So I recently got back from Maui. Half the island is actually a desert only getting rain in the winter. However one side of the mountain is just a lush rainforest because the moisture from the sea is forced up by the mountains and condenses and turns into rain. It’s kinda wild actually to see a place that is so tropical and then 20 minutes away is a desert.
Instead of a remote island, lets take rain forests. These areas are called rain forests for a reason; it rains a lot.
If you look up their location, they have something similar: they are near the equator. Something about the equator is creating a good environment for these forests to develop; lots of rain. What causes rain? The water cycle.
1. Water exists on earth
2. Water evaporates into the air
3. The water in the air rises up, cools down, and clumps together, forming clouds
4. The clouds condense far enough and become cold enough to become rain, until the water is gone.
5. Water exists on earth (repeat)
Warmth helps the water to evaporate and rise up into the air faster (warm air goes up). On earth, most of the warmth comes from the sun. The sun shines the heaviest and warmest on the equator (on average). So on the equator, air rises the most, and water should evaporate the fastest, creating great conditions for rain to form.
It gets even better through the forming of planet-scale air circulation: the air that goes up at the equator has to come from somewhere. The air comes from the areas north and south of the equator. That means there is a general tendency for the air to move towards the equator, and then go up. So most of the moisture from nearby areas will travel towards the equator, where it will gather and form rain.
Of course the air and moisture has to go somewhere once it has travelled up at the equator, and because it cannot go back the way it came (can’t swim against the current) it will go up and over the incoming air, moving north and south of the equator. This is why the rain forests are not limited directly to the equator, but a larger portion north and south as well.
To go beyond your question; this also causes the extreme drought (lack of rain) in for example the Sahara. By the time the air gets here, it no longer carries enough moisture to form clouds, and the air wants to move down to earth again, meaning that what little moisture was left, is now low enough in the atmosphere that it won’t cool down sufficiently to form droplets.
[The diagrams on this wikipedia article should be of help to visualise the air circulation pockets, and see the shift in average rainfall on earth through changing seasons.](https://en.wikipedia.org/wiki/Atmospheric_circulation)
To answer your question for islands (like the British Isles as well): land warms up faster than water. This is why a city on the coast will be cooler in the summer than a city further inland: the air above the sea simply warms slower. However, the air above the sea will carry more moisture. So once above land, this moisture has a nice opportunity to start rising with the warmer air, and form clouds that bring rain. For all the air moving from the Atlantic Ocean towards Europe, the British Isles will be the first landmass that the air will encounter, so most rain will fall there before the air will move on across the Channel and the North Sea towards the rest of Europe, which will have relatively less rain than the British Isles receive.
Another way to force air to go upwards is mountains; air cannot move through the earth or a mountain, so when blown against it, it can only go up. This rapid rising of air causes the air to cool rapidly as well, forcing out clouds and rainfall on the side of the mountain that gets the most wind from the sea. In the above example, you could see the British Isles as a sort of mountainous wall, shielding the rest of Europe from rain.
Kauai is an interesting place as well. The center of the island averages rain 364 days a year. But theres an area maybe 5-10 miles from that wet area that’s considered the dryest area on the island. It is or is almost considered a desert.
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