The Patterns in mediterranean climates chart at right was created from average precipitation and maximum temperature data for the following mediterranean climate cities: Adelaide, Athens, Barcelona, Cape Town, Eureka, Genoa, Jerusalem, Lisbon, Los Angeles, Montpellier, Palermo, Perth, Rabat, San Diego, San Francisco, Santiago, Tunis.
'Click' the chart at right to compare with the Patterns in non-mediterranean climates chart, created from average precipitation and maximum temperature data for the following non-mediterranean climate cities: Atlanta, Aukland, Boston, Charleston, Columbus, Copenhagen, Delhi, London, Luxembourg, Oklahoma City, Ottawa, Paris, Sydney, Tokyo, Toronto, Washington DC.
When it comes to explaining the impact of summer dryness in the mediterranean climate, a picture is worth a thousand words. The blue areas of the chart shows the average rainfall received in one of various mediterranean climate cities, and the overlap of these areas creates a deeper blue. The yellow areas show the average maximum temperature of the same cities, deepening with their corresponding overlaps. From left to right the seasons progress — mid-winter, spring, summer, autumn, mid-winter.
Green areas can be thought of as the seasons in which conditions are best for growing things. Note that the green area almost disappears in mid-summer — this is the true dormancy period in a mediterranean climate, when the temperature is the warmest and water is the least available.
When compared ('click' the chart image) with a the same type of chart for non-mediterranean climates, the distinction between them is clear. It is easy to see that the green area of the non-mediterranean chart is at its peak in mid-summer — the time most of the world associates with the growth of plants. Even though rainfall is more consistent throughout the year, there is a relatively low amount of green area in mid-winter. This is because temperatures are often lower and water might actually be frozen, making it unavailable.
Because the mediterranean climate is such a desireable place to live, many people decide move there, bringing preconceived notions of climate and seasonal dormancy. In spite of the evidence all around them — the greening of the landscape with the winter rains and the dry summer induced dormancy — it is common to maintain the ideas brought from other climates. In order to be truly effective as a gardener in a mediterranean climate, we must embrace its unique seasonality.
While it might be tempting to 'induce' a wet-summer effect using copious supplemental irrigation, because of other climatic factors, the effect will never be as successful (as well as being very unsustainable!). Plants adapted to wet-summer regions will not thrive under these conditions, and species adapted to a dry-summer might even fail when provided high levels of water when they'd prefer to be semi-dormant. It makes far more sense to adapt your concepts and practices to the realities of the mediterranean climate, working with the natural cycles that have evolved to fit these regions.
Seán A. O'Hara