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Photographer's Note

The mildest climates in the world ordered by the minimal sum of Cooling Degree Days and Heating Degree Days, HDD + CDD, referred as the SDD criteria [1], are microclimates from:
- Madeira Island (Funchal) and neighboring Porto Santo Island;
- Sao Miguel Island (Vila Franca do Campo) in the Azores;
- some of the Canary Islands: Gran Canaria, Tenerife, Gomera, La Palma, El Hierro;
- Southern California (San Diego oceanfront; Santa Barbara Foothills); South Africa (Mossel Bay, Santos Bay). [2]

All these microclimates correspond to
- sun facing exposure (this equals a south exposure except for South Africa in the southern hemisphere) reducing HDD. Exception: the Canary Islands, NE exposure, facing the trade winds, reducing CDD.
- subtropical oceanic islands, except for Southern California and South Africa;
- oceanfront location at elevations between sea level and 350 meters, depending on each microclimate. Exception: Santa Barbara Foothills, coastal foothills location.
- ocean currents with a strong cooling effect on the air masses, except for Madeira (almost neutral effect) and the Azores (strong warming effect).
- the share of CDD in SDD decreases from nearly 100% at the Canary Islands, 90% at Madeira and 85% at Porto Santo to microclimates where cold air drainage and protection from cold winds becomes relevant to reduce HDD: 65% in the Azores and 60% in Southern California;
- the importance of cooling onshore winds to reduce CDD decreases from 9 months in the Canary Islands to 7 months in Madeira and 5 months in the Azores to 80 to 60 days scattered througout the year in South Africa and Southern California.

Madeira and Porto Santo
The south coast of Madeira below 200 meters (best locations: clifftop locations which reduce CDD compared to sea level, like the Reid's hotel; nearest WMO station: Funchal city) and neighboring Porto Santo Island (best location: the beachfront which has a semi-arid climate; nearest WMO station: Porto Santo airport) boasts the lowest sums of Heating and Cooling Degree Days worldwide, 700 to 750 SDD.

Azorean Riviera
The Azorean Riviera boasts the second mildest climate of the world: 850 SDD (65% CDD), 710 mm precipitation.
The best location is the oceanfront between 15 and 40 meters above sea level, as it allows for cold air drainage into the ocean.
This south coast protected by a east-west oriented mountain range accounts for 12 km out of near 1000 km of the Azores shoreline.

Canary Islands
The Canary Islands have the lion's share of all areas below 1000 SDD. Mildest microlimate between 100 and 300 meters of NE coasts of islands with mountains high enough to cause orographic precipitation. Lowest DD sum is 850, 95% CDD.

Coastal Southern California and continents
San Diego Lindbergh, coastal Southern California, is the mildest WMO station on a continent, recording a sum of 1000 SDD [3]. Mossel Bay, South Africa (best location: nearby Santos Bay, protected from the constant ocean wind), boasts the lowest sum on a continent except for Southern California, with 1100 SDD. In both areas temperature highs are moderated by a cold ocean current, but in Mossel Bay (like in Azores and Madeira)it surpass more often the comfort range due to higher dew point temperature.

Actually the mildest area on a continent are the Santa Barbara Foothills (Goleta Foothills, the frost-free "plumeria belt") with 950 SDD thanks to slightly higher minimum temperatures throughout the year than San Diego's mildest coastal location (La Jolla).

Azorean Riviera compared with Santa Barbara Foothills
As in the Azorean Riviera there is no WMO station at the Santa Barbara Foothills.
Like the Azores Riviera clifftops, Santa Barbara Foothills also allows for perfect cold air drainage and also has a similar protection from a west-east oriented mountain range.

The difference about the location of the mildest climates of Southern California (cold ocean current) and Azores (warm ocean current) is that unlike the Santa Barbara Foothills the best location at the Azorean Riviera is directly at the oceanfront.

Notes
[1] All sums of DD (SDD) for World Meteorological Organization (WMO) stations
- are rounded;
- refer to the period 1998-2011;
- ignore totally comfortable days defined as
humidex factor for daily maximum and minimum within the 60 F to 80 F range;
- use base 65 F, the same it is used for calculating heating and cooling requirements in buildings as a function of HDD and CDD.
- source is the GSOD data set.
World map for WMO stations in:
http://203.158.253.140/media/e-Book/Engineer/Mechanical%20Handbook/ASHRAE%20Handbook/F05_28SI.pdf
Humidex formula and calculator:
http://www.physlink.com/reference/weather.cfm

[2] These WMO stations not taken in account:
- tiny Lord Howe Island (300 inhabitants), Norfolk Island (2000) and Rapa Iti Island (500) in the subtropical South Pacific;
- semi-arid and arid climates without sustainable water supply (like for instance the supply provided by nearby mountains originating an orogaphic precipitation process): S Peru / N Chile (Iquique); NW Mexico (Ensenada), S Morocco (Essaouira).

[3] Cooling Degree Days and Heating Degree Days for San Diego Lindbergh, 1971-2000, without ignoring totally comfortable days, what almost doubles the SDD value.
http://drought.unl.edu/archive/climographs/pdf/SanDiego.pdf


See also themes "Azorean Riviera" and "World's Mildest Climates".

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