The Seasons - seriously confused here

[The Snark]

Okay, I'm a northern hemisphere guy who is mucho attuned to the earth and things that grow.
So in the hemispheres you have four seasons. Logical progression, Spring, Summer, Fall, Winter.

Spring. Rains and getting over the dog of winter. Trees start to bud. Flowers grow. Then a world of green.
Summer. Dries up. Hot. Arid. Growing season over.
Fall. Trees lose leaves. Grass turns brown. Berries and nuts, harvest time.
Winter. Sap stops running. Deciduous trees lose their leaves. Dormant. Waiting for spring.

Now the tropics. There is no exclusively spring season. So start with...
Cool season. Sap slows but doesn't stop running. Leaves still on trees. The rains have stopped. Everything starts drying out.
Hot season. Like spring but arid and parched. Trees looses their leaves and commonly start new leaf growth in a matter of weeks. Before and during the leaf growth trees bud and flower. Until the rains start most of the tropics qualifies as a desert.
The rainy season. The major growth season.

Cool season, End of November through half way into March.
Hot season, March through June.
Rainy season, July through October.

The logical progression of moist ground then growth is backwards. Nearly all trees and shrubs flower and start new growth during the driest time of the year.
Fall doesn't really happen. It's part of the hot season.

As a typical example, the common tree here, the Rain Tree, Albizia Saman, looses it's leaves at the end of January. From green to bare branches in about 2 weeks, bare by the end of February. The first week of march is has new leaf growth and by the end of March it is in full flower. The equivalent of Fall, Winter and Spring packed into a little over 1 month.

I'm royally confused.

 

[schmiggle]

I'm sure the reason they keep their leaves for so long is because they want to get as much sunlight as possible. I would also imagine that the reason they flower during the hot season is to get their seeds in the ground in time for the rainy season. I guess the reason they probably wait during the cool season is that the most stressful time of the year is the hot season--no precipitation and a very high evapotranspiration rate. They might want to get as much sugar as possible during the cool season (which is generally sunny? If it's dry?) to give them the best shot at survival during the hot season and to allow them to flower during that time. Also, if the hot season is hot enough, it might go past the peak of the photosynthesis effectiveness curve, and if so, it would be the least efficient time for photosynthesis, because that curve drops very fast.

At least where I'm from, spring and fall have the most precipitation, but that's not really associated with the change. Plants can't grow during the coldest part of the winter (at least pre-climate change), and they have to grow during spring to get a head-start on summer and to flower in time to get their offspring to a sufficient size to survive winter. Growth also doesn't exactly stop in the summer, because the rain is fairly consistent year-round (although the evapotranspiration rate is, again, higher in the summer). I will say that it does slow down, though, and the reason is partly because plants need to collect sugar to last them through the winter when they won't have leaves, so they can't spend it on growing new leaves. However, there are flowers essentially throughout the growing season (spring to fall) because many plants produce seeds that lie dormant throughout the winter then begin growth in the spring.

I think Mediterranean climates basically work this same way, except that the rains happen in winter, which is, of course, the cool season.

 

[The Snark]

That makes sense. Definitely fill in some blanks.

There are some oddities the tropics throws into the works. Generally speaking here.
In SE Asia. The first week of November temperature drops like a rock and it dries up completely. 10 degrees F cooler day and night. January is the coldest month of the year. Very little measurable rain, December through March. April gets occasional thunder showers.
Now here it gets strange. This happens all over the world but I confine to observations. Here the rains start in May then in June they nearly stop. They start again in July. It starts getting very hot in March and by the end of April it's around 100F day and night.
In Darwin Aus it's similar. Temperature drops like a rock the end of June. Rains almost cease in April and almost no precipitation until August. The rains start at the end of August early September then a pause in October with less rain. The rains start seriously in November. Why the rains start then almost stop I have no idea.

Perhaps most interesting is the variations experienced in the past 7 years. 2010 we had no hot season. Rains started in February without let up until the end of October. This year we had 2 1/2 inches of rain in January. The Almanac shows no measurable rain in January ever. Also, the SE Asia cold season start has shifted to the first week of December, very predictable, one month late.


It is really bizarre watching our huge shade tree over our house. Full of green leaves until the first week of February. In about 10 days it sheds all leaves. Then the end of February it is covered in leaves again.

 

[schmiggle]

The seasonal onset shift, if predictable, is a known outcome of climate change in temperate zones, and I imagine, therefore, others as well.

The reason for shifting rain patterns is that the area of the earth with the most intense sunlight gets, counterintuitively, the most rain. This is due to huge amounts of evaporating water cooling as they rise and forming rainclouds. The equatorial rainbelt is caused by this effect, but the equator is not always the place with the most intense sunlight, and that line shifts especially far north in southeast Asia. However, it also moves throughout the year. India has up to three monsoons in some regions, if I remember right, because of this line moving up and down. All of which is to say that if it moves predictably towards and away from thailand, that probably accounts for a lot of your rain patterns.

 

[The Snark]

Seems quite accurate. The monsoons come from the Bay of Bengal at the beginning of the rains. Towards the end, Sept-Oct, it shifts to the east and we get influences from the Pacific region and the yearly typhoons stomping into the S China sea.
The monsoons in SE Asia can be KERZAPS. Clear and warm from dawn until about 15:00 then thunderheads roll in over a 1 hour period. Sudden squalls, wind gusts up to 60 MPH, and up to 4 inches of rain in one hour. Then by dusk the sky is almost clear. I once watched a house next door to my apt. 1 inch every 10 minutes of rain, the wind blowing so hard the water was a solid sheet blowing UP the steep slope of the roof and blasting off the hip like breaking seas on the ocean.

The tree Albizia Saman is very interesting. Hypersensitive to weather conditions. When it rains, it's leaves droop and branches sag. I once watched a 4 inch thick blranch 50 feet long sag from 8 feet above our roof to about 1 foot in 10 minutes. At night it again furls it's leaves. A testament to the power of the photosynthesis and other engines since we are talking thousands of pounds of branches and leaves. I compare this tree to Sequoia Sempervirens I observed just as closely. It takes several months to move a fraction of the mass and distance Saman moves in a few minutes.

Another interesting aspect of A Saman is all branches must get photosynthesis from the leaves. Thus it grows a thin layer of foliage at the outermost perimeter. If a branch gets shadowed by another branch and not enough leaves get sunlight, the entire branch dies that year. I discovered this the hard way. Trimmed back the end of a branch and all 40 feet of it died in a month. So these trees are giant thin canopy umbrellas with near zero leaf growth beneath the canopy.

 

[schmiggle]

That's crazy, I guess it's probably an adaptation to growing in jungles where available light has to be absolutely maximized because it gets shaded out so fast. I wonder why the tree droops when it rains, though.