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Old 01-14-2019, 12:29 AM
tij tij started this thread
 
Location: Providence, RI
454 posts, read 165,592 times
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Why is the Dwx boundary so much stricter than the Dsx boundary? Why does the wettest month in summer have to be more than 10X the driest month in winter? The Dsx criteria only requires 3X the wettest month have as much rain as the driest month....

For example.....

Should Minneapolis and westward in NA be Dwx climates? It receives (3.36+4.25+4.04+4.30+3.08+2.43)/30.61= 70.1% of rainfall in the warmest 6 months....so it meets the Dwa criteria by the other metric, even while the wettest/driest month ratio is more like 4.30/.77=5.6X times as wet (quite a substantial difference)..

It would probably "feel" closer to Shenyang, with a ratio of 6.83/.27=25.2X as wet, than it would to Sapporo or Boston, which would have much more even winter precip (rain+snow), even though it would be classified with the latter two by the 10X criterion. However, if the precipitation pattern was reversed, it would qualify as a Dsa...

What is the significance of the Dfa/Dwa distinction?
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Old 01-14-2019, 12:40 AM
 
897 posts, read 312,592 times
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There is a natural tendency for precipitation to peak during summer due to increased evapotranspiration, and with a 3x threshold, many places without consistent high pressure will be Cwx/Dwx. Winter high pressure is not as consistent in Minneapolis compared to Shenyang. Compare East Asia/Siberia and North America in this map, for example: https://en.wikipedia.org/wiki/Siberi...erian_High.png.

Btw, could consistent high pressure be the reason why East Asia is more stable than North America in winter?
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Old 01-14-2019, 01:59 AM
tij tij started this thread
 
Location: Providence, RI
454 posts, read 165,592 times
Reputation: 268
Potentially...

Compare Savannah, Georgia to Nantong, Jiangsu at the same latitude on the coast. (Nantong actually doesn't meet the dry-winter criterion, and remains a Cfa when it shows a clear monsoonal/Cwa pattern)

https://en.wikipedia.org/wiki/Savannah,_Georgia#Climate

https://en.wikipedia.org/wiki/Nantong#Climate


While the former averages 60/39 and the latter only 44/32 in winter, Nantong has a significantly milder record low (15 vs 3)! The American South, for its average temperatures, can get quite extreme cold snaps, probably reducing the vegetation difference with latitude


The effect persists inland even more starkly, when we compare Chengdu with Austin, which receives Chengdu's record low temperature in an average winter. Perhaps the Sichuan basin is shielded by mountains?

https://en.wikipedia.org/wiki/Chengdu#Climate
https://en.wikipedia.org/wiki/Austin,_Texas#Climate

Again, the effect is more pronounced in Japan (probably due to more oceanic influence):

Compare Sendai or Niigata, which still have record lows milder than Savannah despite much colder winters, and located 6 degrees poleward!

Perhaps this justifies moving the Cxa/Dxa boundary northward in East Asia to areas with chillier winter averages due to increased stability?
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Old 01-14-2019, 02:26 AM
 
Location: White House, TN
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Because evapotranspiration is lower in colder months, so 1" of precip in a cold month goes farther and feels moister than 1" in a warm month.
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Old 01-14-2019, 02:31 AM
 
897 posts, read 312,592 times
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Quote:
Originally Posted by tij View Post
Potentially...

Compare Savannah, Georgia to Nantong, Jiangsu at the same latitude on the coast. (Nantong actually doesn't meet the dry-winter criterion, and remains a Cfa when it shows a clear monsoonal/Cwa pattern)

https://en.wikipedia.org/wiki/Savannah,_Georgia#Climate

https://en.wikipedia.org/wiki/Nantong#Climate


While the former averages 60/39 and the latter only 44/32 in winter, Nantong has a significantly milder record low (15 vs 3)! The American South, for its average temperatures, can get quite extreme cold snaps, probably reducing the vegetation difference with latitude


The effect persists inland even more starkly, when we compare Chengdu with Austin, which receives Chengdu's record low temperature in an average winter. Perhaps the Sichuan basin is shielded by mountains?

https://en.wikipedia.org/wiki/Chengdu#Climate
https://en.wikipedia.org/wiki/Austin,_Texas#Climate

Again, the effect is more pronounced in Japan (probably due to more oceanic influence):

Compare Sendai or Niigata, which still have record lows milder than Savannah despite much colder winters, and located 6 degrees poleward!

Perhaps this justifies moving the Cxa/Dxa boundary northward in East Asia to areas with chillier winter averages due to increased stability?
To be fair, records for Chinese cities only go back to 1951 while NOAA has begun recording for most major cities much earlier. East Asia is still much more stable though. However, I don't think the Cxa/Dxa threshold should be adjusted because it would make the system more complex. Unnecessary complexity that has little real effect is not good.

The Sichuan basin very stable due to being shielded by mountains. Chongqing has a record low of -1.8 C (28.8 F) and is in hardiness zone 10, the same as southern Florida. It's also the mountains that cause it to be very cloudy, as they trap clouds and fog.

I'm not really sure about the timeframes of record temperatures for Japanese cities, but I think they would have milder records for the averages anyways.
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Old 01-15-2019, 11:26 AM
 
Location: Live:Downtown Phoenix, AZ/Work:Greater Los Angeles, CA
24,917 posts, read 9,695,680 times
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Quote:
Originally Posted by tij View Post
Why is the Dwx boundary so much stricter than the Dsx boundary? Why does the wettest month in summer have to be more than 10X the driest month in winter? The Dsx criteria only requires 3X the wettest month have as much rain as the driest month....

For example.....

Should Minneapolis and westward in NA be Dwx climates? It receives (3.36+4.25+4.04+4.30+3.08+2.43)/30.61= 70.1% of rainfall in the warmest 6 months....so it meets the Dwa criteria by the other metric, even while the wettest/driest month ratio is more like 4.30/.77=5.6X times as wet (quite a substantial difference)..

It would probably "feel" closer to Shenyang, with a ratio of 6.83/.27=25.2X as wet, than it would to Sapporo or Boston, which would have much more even winter precip (rain+snow), even though it would be classified with the latter two by the 10X criterion. However, if the precipitation pattern was reversed, it would qualify as a Dsa...

What is the significance of the Dfa/Dwa distinction?
It's because winter evapotranspiration rate is over 3 times less than in summer, that's why
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Old 04-12-2020, 08:52 PM
 
Location: Chicago, Illinois
59 posts, read 15,238 times
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Quote:
Originally Posted by QIDb602 View Post
To be fair, records for Chinese cities only go back to 1951 while NOAA has begun recording for most major cities much earlier. East Asia is still much more stable though. However, I don't think the Cxa/Dxa threshold should be adjusted because it would make the system more complex. Unnecessary complexity that has little real effect is not good.

The Sichuan basin very stable due to being shielded by mountains. Chongqing has a record low of -1.8 C (28.8 F) and is in hardiness zone 10, the same as southern Florida. It's also the mountains that cause it to be very cloudy, as they trap clouds and fog.

I'm not really sure about the timeframes of record temperatures for Japanese cities, but I think they would have milder records for the averages anyways.
That's my problem with hardiness zones - Chongqing, and even the Isles of Scilly, in zone 10 with south Florida, which sustains natural Coconut Palms and native Mangroves? Absurd.

Ignoring latitude, Chongqing has a similar natural environment to somewhere in Arkansas, not southern Florida. I've been to both, and both also have similar climates.

I don't think record lows mean much, I think averages set the hardiness of plants - occasional cold extremes make a plant just make native plants more hardy. It's why Arkansas has at least a native palm, while Chongqing doesn't.
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Old 04-13-2020, 04:44 AM
 
Location: Live:Downtown Phoenix, AZ/Work:Greater Los Angeles, CA
24,917 posts, read 9,695,680 times
Reputation: 8103
Quote:
Originally Posted by tij View Post
Why is the Dwx boundary so much stricter than the Dsx boundary? Why does the wettest month in summer have to be more than 10X the driest month in winter? The Dsx criteria only requires 3X the wettest month have as much rain as the driest month....

For example.....

Should Minneapolis and westward in NA be Dwx climates? It receives (3.36+4.25+4.04+4.30+3.08+2.43)/30.61= 70.1% of rainfall in the warmest 6 months....so it meets the Dwa criteria by the other metric, even while the wettest/driest month ratio is more like 4.30/.77=5.6X times as wet (quite a substantial difference)..

It would probably "feel" closer to Shenyang, with a ratio of 6.83/.27=25.2X as wet, than it would to Sapporo or Boston, which would have much more even winter precip (rain+snow), even though it would be classified with the latter two by the 10X criterion. However, if the precipitation pattern was reversed, it would qualify as a Dsa...

What is the significance of the Dfa/Dwa distinction?
The reason that the dry winter ratio is 3 times the dry summer ratio is because evapotranspiration rates are much higher in summer than winter due to the longer days/shorter nights, warmer temps and much higher sun angles which all dry soil out quicker than in a dry winter
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Old 06-17-2020, 05:23 PM
 
163 posts, read 31,652 times
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Quote:
Originally Posted by FirebirdCamaro1220 View Post
The reason that the dry winter ratio is 3 times the dry summer ratio is because evapotranspiration rates are much higher in summer than winter due to the longer days/shorter nights, warmer temps and much higher sun angles which all dry soil out quicker than in a dry winter

Yes. In general, the warmer air in the summer can hold more moisture and is often accompanied by higher precipitation naturally. Dwa/Dwb should exist due to an external monsoon pattern (e.g. northeastern China) rather than as the natural consequence of temperature variation. With a 30ºC difference between summer and winter, the expected precipitation factor is already at 8x more in summer. I even think that for Dwa/Dwb/Dwc the precipitation factor limit to define the boundary should be greater than that in Cwa/Cwb (maybe 20x? Shenyang would still be Dwa, but Fargo and Minneapolis would be Df).
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