Precipitation
| “ | It has four months of winter, no more, and in them, except when there is a quarter moon, when it rains one or two days, all the other days have such beautiful suns... | ” |
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—Pedro de Valdivia to Charles V, Holy Roman Emperor |
During summer, regions of Mediterranean climate are dominated by subtropical high pressure cells, with dry sinking air capping a surface marine layer of varying humidity and making rainfall impossible or unlikely except for the occasional thunderstorm, while during winter the polar jet stream and associated periodic storms reach into the lower latitudes of the Mediterranean zones, bringing rain, with snow at higher elevations. As a result, areas with this climate receive almost all of their precipitation during their winter season, and may go anywhere from 4 to 6 months during the summer without having any significant precipitation.
Toward the equatorial latitudes, winter precipitation decreases as a share of annual precipitation as the climate grades equator-ward into the steppe climate usually characterized as BSHs normally too dry to support unirrigated agriculture. Toward the polar latitudes, total moisture usually increases; in Europe there is more summer rain further north while along the American west coast the winters become more intensely wet and the dry seasons shorter as one moves north. In the northwestern Mediterranean Basin, the rainiest season is divided into a primary maximum during the autumn and a secondary in spring, making for a shorter dry season than in the classic rainforest climate.
Read more about this topic: Mediterranean Climate