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You're forgetting the interaction between precipitation and temperature. The warmer the climate the greater the potential evaporation and therefore the lower the water availability for a given amount of precipitation. The warmer the climate the more rainfall a mediterranean climate requires at its lower threshold to avoid being semiarid and the more rainfall it can have at its upper threshold before it becomes too wet to qualify as mediterranean.
Perth has an annual mean temp of over 18C, Victoria is little more than 10C, so of course Perth can have more rain and still qualify as mediterranean!
Koppen recognises the temp-precip interaction with his aridity thresholds. Locations in southern England can have rainfall in the 600-800mm range and qualify as fully humid due to the cool climate. At equatorial temperatures the same rainfall would result in a rather dry savanna climate, perhaps even a semi-arid one in the hottest locations, definitely insufficient for widespread non-drought adapted tree growth.
Right but I am not seeing any formula to quantify it.
Either way I'm not sure overall aridity was ever a condition...it was summer aridity...
So by your argument the only thing stopping Southampton in the UK from having a Med climate is that it doesn't rain enough in the Winter! I'm sorry, I'm just not seeing it, Southampton is obviously NOT a Med climate and neither is Victoria BC, the climates are quite pleasant perhaps but they are both Oceanic.
In addition to a strong winter rainfall bias Koppen also requires Mediterranean climates to have less than 30mm of rain in their driest month. Thus even if Southampton received twice as much rain in the winter it would still be too wet in the summer.
There are indeed many places around Victoria that are oceanic precisely because they get too much rain in the summer despite a significant seasonal variation. Vancouver is the best known example.
So by your argument the only thing stopping Southampton in the UK from having a Med climate is that it doesn't rain enough in the Winter! I'm sorry, I'm just not seeing it, Southampton is obviously NOT a Med climate and neither is Victoria BC, the climates are quite pleasant perhaps but they are both Oceanic.
Yes, this is the point, but there is a reason for which Southampton doesn’t get bigger precipitation seasonality, and it’s due to the major circulation patterns that help understand the Oceanic-Mediterranean divide.
Yes, this is the point, but there is a reason for which Southampton doesn’t get bigger precipitation seasonality, and it’s due to the major circulation patterns that help understand the Oceanic-Mediterranean divide.
Thank you. People are blinded by their prejudices and forget that the numbers themselves are not important. What's important are the physical phenomena that create the numbers.
So its a Med climate becuase it rains a lot at the right time, the fact that its FAR too cold, the fact that its FAR too grey does'nt come into it at all? Temperature means nothing when it comes to a 'climate'? Everywhere on earth that rains more in the Winter than the Summer is a Med climate? Whether its continental or mountainous or even if its near the bloody North Pole, and therefore Southampton would be a Med climate if only it rained more between the end of November and the the beginning of March! If Victoria BC is a Med climate then I'm the Queen mother! :-)
So its a Med climate becuase it rains a lot at the right time, the fact that its FAR too cold, the fact that its FAR too grey does'nt come into it at all? Temperature means nothing when it comes to a 'climate'? Everywhere on earth that rains more in the Winter than the Summer is a Med climate? Whether its continental or mountainous or even if its near the bloody North Pole, and therefore Southampton would be a Med climate if only it rained more between the end of November and the the beginning of March! If Victoria BC is a Med climate then I'm the Queen mother! :-)
Strawmanning doesn't make the argument more convincing...
Right but I am not seeing any formula to quantify it.
Either way I'm not sure overall aridity was ever a condition...it was summer aridity...
Both are important, or rather summer aridity is influenced by total as well as summer rainfall. If the winter rainfall is heavy enough and the summer dry season short enough, drought stress can be minimal because of moisture left in the soil. Aschmann specifically uses this reason to rule out climates poleward of his true mediterranean climates in North America and Chile which have a distinct summer rainfall minimum. I would add that relatively cool temperatures help here by reducing evaporation.
We can see a similar phenomenon with tropical rainforest climates: Koppen uses 60mm in the driest month but in practice tropical rainforest can be found in places where rainfall is less than this for one or two months.
Aschmann gives a lower annual limit of about 275 mm for cool locations and 350 mm for warm ones and an upper limit of about 900 mm. He doesn't say explicitly, but from the distinction between cool and warm locations for the lower limits, I would assume 900 mm would be for the warmest qualifying climates.
Vegetation is a poor basis to judge climate. The reason why is soil can have an impact. For instance, around the Big Island of Hawaii volcanoes the soil is so porous that even though it is a tropical rainforest climate in precipitation, desert type plants grow in that region because the soil can't hold the moisture.
So do we call the climate "semi-arid" even though it gets 100" of rain a year? That's non-sense. If you have a raised flower bed you will never need to water the plants in it. The daily thunderstorm pattern is tropical.
Another example is the Gulf Coast of the US. Near the coast the clay soils prevent a lot of treed vegetation from growing. Further north where there is more acidic soil loblolly pine forests grow. Oddly enough the further north the drier it gets. However, if you amend the soil you can grow 200 ft trees and it's a subtropical climate. It's just that the native vegetation is grasslands because of the soil composition.
So using precipitation and temperatures is a more objective measurement than vegetation because of this reason.
It's generally recognised in science that climate is the major determinant of vegetation and therefore it's common for different systems to attempt to link them eg in the tropical rainforest climate category. You're right that climate is not the only factor and therefore there is always a qualification. Eg Aschmann requires sufficient precipitation for continuous vegetation "on all but the most rocky sites" for his true mediterannean climate. You could probably add a few other soil/substrate types like sand dunes, shingles etc. So typically the vegetation of "unusual" substrates would be excluded such as Hawaiian lava fields or the extremely poor sandy soils in places like Borneo where heath like vegetation grows surrounded by rainforest. You'd consider what the vegetation would be like given a more typical substrate.
Precipitation and rainfall can be measured objectively, but how can they on their own be used to determine climate type? Everyone can agree that the published data for say Victoria is correct but one person can say it's mediterranean based on some subjective feeling (say from a Canadian point of view it's a relatively warm, summer dry climate) while another says it's not based on another subjective feeling (say an Australian, for who it's a relatively cool, wet climate). At least with vegetation there's general scientific agreement about what biome type occurs where.
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