I would propose boundaries that align partly with how I perceive the weather, and partly with how we plan our year (by months): Summer starts June 1st, Fall starts September 1st, Winter starts December 1st, and Spring starts March 1st.
There's no need to change the dates. They're already arbitrary based on the position of the sun and the earth and people have the experience to take them with the grain of salt necessary to the region they live in. People who live near the equator probably don't have much care for the notion of the winter at all. Folks who live far up north know that spring actually comes in much later than march 21st. People who climb glaciated mountains in the canadian rockies know they won't get summer conditions until late june.
My understanding is that tropical regions tend to divide the year into "wet season" and "dry season".
I've also always thought that the equinoxes and solstices should be the middle of the seasons, so using the 'cross-quarter' days as the beginning of seasons makes more sense.
probably same for other post-soviet countries too?
But we lost a lot of nice symmetries that way, which is unfortunate
Summer doesn't work with that association though, with the latest sunset being the end of June instead of the start.
You do realize there's also a southern hemisphere on planet Earth?
In Australia it's just split up by months, with each season being 3 months long:
March 1 - Autumn starts June 1 - Winter starts Sept 1 - Spring starts Dec 1 - Summer starts
Of cause, those in far northern Australia, only really have Dry and Wet seasons. I have no idea when those are.
Adelaide’s climate anecdotally feels to be more humid in recent years (historically bone dry Mediterranean climate) and the seasons feel like they’ve shifted a few weeks forward.
The Kaurna (Australian Aboriginal people of Adelaide, pronounced Gar-nuh) apparently mapped seasons a little differently, with a longer summer that resonates with my experience:
https://www.bom.gov.au/resources/indigenous-weather-knowledg...
The Noongar people of Western Australia have a 6 season model that also maps pretty well to my experience in South Australia.
https://australiassouthwest.com/six-seasons-of-the-south-wes...
But most countries other than the USA use meteorological definitions of the seasons starting on the 1st of December, March, June, and September.
In India our summer holidays start at the end of March and finish in the start of June. That’s usually our hottest months too. And a lot of our regional “New Year” calendar’s and related festivals are on April 14th and can probably be considered the start of summer.
I played around with weatherspark and all the places I tried looked like this :
https://weatherspark.com/compare/y/1705~8813/Comparison-of-t...
That said being an English speaking country and absorbing a lot of media from other English speaking countries, there’s been a slow drift towards the American system making its way in, so younger generations are more likely to use American seasons and older people more likely to use traditional seasons, though you’ll find people of all age groups using either. Certainly they taught the traditional seasons in school when I was a kid, I wonder which they teach now.
(Of course, you could make yet another system based on the weather where summer is approximately two weeks in July, winter is a thing that happens every few years and the rest is a sequence of mild weather with occasional wind and scattered showers)
In Finland the traditional division is that winter is Dec-Feb, spring is Mar-May, summer is Jun-Aug, and autumn is Sep-Nov. Historically it has made perfect sense, weather and climate wise – particularly from the point of view of agriculture, which is of course the reason people used to think about seasons in the first place!
February in particular is 100% winter in Finland with no signs of spring besides the days starting to get very noticeably longer by then. It's often the coldest month of the year and when schools usually have a week-long winter break. Similarly, August is very definitely a summer month except in the far north where spring comes late and autumn early. The academic year in schools and universities typically starts at the end of August, so that's a clear and important dividing line in many people's lifes. In Southern Finland, December is these days rather autumny more often than not, and there's often no lasting snow until January (if even then). June is a crapshoot, it can be nice and warm or surprisingly cold.
I guess Jan-Feb are definitely winter, Apr-May definitely spring, Jul-Aug definitely summer, and Oct-Nov definitely autumn. The rest are kind of transitional and their weather unpredictable. Of course, the climate change isn't helping things, either.
https://sv.wikipedia.org/wiki/V%C3%A5r_i_Sverige
The definition would certainly work in English countries, seeing it is just 0 to 10 degrees Celsius average over the course of a week (and after 15th of February).
https://youtu.be/y8HEZ-x4-_w?t=402
Getting the shade right could be tricky though.