U.S. CitiesCity-Data Forum Index
Go Back   City-Data Forum > General Forums > Weather
 [Register]
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
View detailed profile (Advanced) or search
site with Google Custom Search

Search Forums  (Advanced)
Reply Start New Thread
 
Old 03-19-2019, 01:56 PM
 
258 posts, read 42,955 times
Reputation: 138

Advertisements

According to Koppen's climate classification system for a climate to be a tropical rainforest one, it must have an average temperature of at least 18C in every month and a rainfall of at least 60 mm in every month.

For a climate to be semi-arid, it must have less rainfall in millimetres than (average temperature in C x 20) + 140, if between 30 and 70% of the rainfall falls in the higher-sun half of the year.

This raises the intriguing and counter-intuitive possibility of a climate being on the margin of being semi-arid and tropical rainforest.

For example a climate could be Af with as little as 720 mm of rain per year, if it was absolutely evenly distributed throughout the year and the average annual temperature was less than 29C. But a climate that was almost the same with 719 mm of rain or an annual average temperature of 29.1C would be BSh.

But does such a climate actually exist anywhere? Usually Af climate regions are separated from BSh ones by Am and then Aw. The problem I see is that climates that are warm enough to qualify but with that little rainfall tend to have very seasonal rainfall and would have a lot less than the required 60 mm in the driest months. Af climates with more or less aseasonal rainfall tend to be among the wettest ones. Also 29C average temperature seems to be towards the upper limit of A-type climates, but it may be possible as some of the hottest A-climates get that hot, eg Valledupar exceeds 29C even in its wet months.
Reply With Quote Quick reply to this message

 
Old 03-19-2019, 09:44 PM
 
Location: Seattle
68 posts, read 17,283 times
Reputation: 53
The thing is, most RL Af climates exhibit significant month-to-month variation in precipitation, since the ITCZ passes through the entire tropics over the course of a year. It’s just that these climates are consistently rainy enough throughout the year for no month to have less than 60 mm of rain.

That being said, a dry tropical climate close to the equator, in a rain shadow, that has an average annual temperature over 30 C, could theoretically exist. Idk how it could realistically have a constant rate of sporadic thunderstorms to maintain a long-term average of ~60 mm/month throughout the year, so that it would barely meet the Af precipitation threshold. Maybe it could exist in a 3 C+ warmer world with higher temps and possibly less low-latitude precipitation?
Reply With Quote Quick reply to this message
 
Old 03-19-2019, 10:41 PM
 
Location: Seattle
68 posts, read 17,283 times
Reputation: 53
This is what I imagine such a climate would look like:

Reply With Quote Quick reply to this message
 
Old 03-20-2019, 05:24 AM
 
Location: Sydney, Australia
10,122 posts, read 7,471,493 times
Reputation: 5056
I initially thought of this, but it seemed too dry:

https://en.wikipedia.org/wiki/Aruba#Climate
Reply With Quote Quick reply to this message
 
Old 03-20-2019, 07:21 AM
 
Location: Buenos Aires, Argentina
692 posts, read 652,125 times
Reputation: 869
It doesn't exist, and it is impossible under the current climate conditions. As psyche_da_mike24 pointed out, there is always a significant variation in precipitation month to month due to due to the fluctuation of the ITCZ throughout the year, and even if it’s extremely stable somewhere, the very complex nature of the atmospheric system prevents it from delivering a static climate pattern (let’s say, all months averaging between 60 and 65 mm).

For a climate like such, in order to exist at least a close call, we need the ITCZ to pass through the same area the whole year and a deep valley/depression, behind a significant mountain range to provide the required rain shadow that diminishes the huge amount of rain that would be expected to receive a place permanently subjected to the ITCZ.

Nowhere in the world fulfills this, albeit western Colombia may give us an idea. The Humboldt Current pushes the ITCZ to the northern hemisphere even in the southern winter so the Colombian Pacific gets a huge amount of rain throughout the whole year (see Quibdó, López de Micay, etc.). The humid air goes quickly upslopes and then it descends across the Cauca Valley, where the precipitation is much lower, yet more or less steady.

The town of Dagua, Valle de Cauca, has these monthly averages (IDEAM), but it’s at 800 meters approximately:

Jan: 67.6 mm (driest month)
Feb: 70.6 mm
Mar: 85.2 mm
Apr: 113.4 mm
May: 127.1 mm
Jun: 103.3 mm
Jul: 79.7 mm
Aug: 75.8 mm
Sep: 92.5 mm
Oct: 134.1 mm
Nov: 145.6 mm (wettest month)
Dec: 90.3 mm
YEAR: 1185.2 mm

Is there a drier Af climate?
Reply With Quote Quick reply to this message
 
Old 03-20-2019, 10:52 AM
 
258 posts, read 42,955 times
Reputation: 138
Quote:
Originally Posted by Mhc1985 View Post
It doesn't exist, and it is impossible under the current climate conditions. As psyche_da_mike24 pointed out, there is always a significant variation in precipitation month to month due to due to the fluctuation of the ITCZ throughout the year, and even if it’s extremely stable somewhere, the very complex nature of the atmospheric system prevents it from delivering a static climate pattern (let’s say, all months averaging between 60 and 65 mm).

For a climate like such, in order to exist at least a close call, we need the ITCZ to pass through the same area the whole year and a deep valley/depression, behind a significant mountain range to provide the required rain shadow that diminishes the huge amount of rain that would be expected to receive a place permanently subjected to the ITCZ.

Nowhere in the world fulfills this, albeit western Colombia may give us an idea. The Humboldt Current pushes the ITCZ to the northern hemisphere even in the southern winter so the Colombian Pacific gets a huge amount of rain throughout the whole year (see Quibdó, López de Micay, etc.). The humid air goes quickly upslopes and then it descends across the Cauca Valley, where the precipitation is much lower, yet more or less steady.

The town of Dagua, Valle de Cauca, has these monthly averages (IDEAM), but it’s at 800 meters approximately:

Jan: 67.6 mm (driest month)
Feb: 70.6 mm
Mar: 85.2 mm
Apr: 113.4 mm
May: 127.1 mm
Jun: 103.3 mm
Jul: 79.7 mm
Aug: 75.8 mm
Sep: 92.5 mm
Oct: 134.1 mm
Nov: 145.6 mm (wettest month)
Dec: 90.3 mm
YEAR: 1185.2 mm

Is there a drier Af climate?
Interesting, and good explanation of the cause of western Colombia's extremely heavy and consistent rainfall. You've also asked my follow up question.

The middle to lower Cauca river valley is very deeply incised between the western and central cordilleras of the Andes and seems to have a strong rain shadow, so it might be possible that there's a drier Af climate there.

The other possibility that comes to mind is an extra-tropical location that just manages to scrape past the 18C coolest month threshold and where oceanic influences bring enough rain to counteract the winter drying trend. Of course this wouldn't be marginally semi arid as the rainfall threshold for such a cool climate would be too low.
Reply With Quote Quick reply to this message
 
Old 03-20-2019, 12:36 PM
 
Location: Buenos Aires, Argentina
692 posts, read 652,125 times
Reputation: 869
Quote:
Originally Posted by Mhc1985 View Post
Nowhere in the world fulfills this, albeit western Colombia may give us an idea. The Humboldt Current pushes the ITCZ to the northern hemisphere even in the southern winter so the Colombian Pacific gets a huge amount of rain throughout the whole year (see Quibdó, López de Micay, etc.). The humid air goes quickly upslopes and then it descends across the Cauca Valley, where the precipitation is much lower, yet more or less steady.
I meant the southern summer.
Reply With Quote Quick reply to this message
 
Old 03-20-2019, 12:56 PM
 
1,626 posts, read 614,791 times
Reputation: 3596
While not exactly what you are looking for, McAllen, Texas borders on 3 climactic zones, humid subtropical (Cfa), semi-arid (Bsh), and tropical savannah (As).

With different yearly weather, it slips from semi-arid to subtropical, to tropical zones.

Last edited by BusinessManIT; 03-20-2019 at 12:58 PM.. Reason: More info.
Reply With Quote Quick reply to this message
 
Old 03-20-2019, 01:25 PM
 
258 posts, read 42,955 times
Reputation: 138
Quote:
Originally Posted by BusinessManIT View Post
While not exactly what you are looking for, McAllen, Texas borders on 3 climactic zones, humid subtropical (Cfa), semi-arid (Bsh), and tropical savannah (As).

With different yearly weather, it slips from semi-arid to subtropical, to tropical zones.
Interesting, does it really have a summer drying trend?
Reply With Quote Quick reply to this message
 
Old 03-20-2019, 01:46 PM
 
258 posts, read 42,955 times
Reputation: 138
The landscape around Dagua looks surprisingly dry for a climate with a minimum of 67 mm of monthly rainfall, but that may be to do with deforestation as it also looks rather degraded.

For a barely tropical climate with just enough winter rain to qualify as Af, I'm thinking of something similar to St Lucia. Unfortunately there are only estimated data but the driest month has 58 mm of rain and the coolest month is 17.5C, so it's not quite Af but very close and the total rainfall is 1129 mm.
Reply With Quote Quick reply to this message
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.

Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.


Reply

Quick Reply
Message:


Over $104,000 in prizes was already given out to active posters on our forum and additional giveaways are planned!

Go Back   City-Data Forum > General Forums > Weather
Follow City-Data.com founder on our Forum or

All times are GMT -6.

© 2005-2019, Advameg, Inc. | Please obey Forum Rules | Terms of Use and Privacy Policy

City-Data.com - Archive 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35 - Top