Mediterranean Garden Society

Rainfall and watering at Sparoza

Sally Razelou writes:
We are all familiar with the basic characteristics of the mediterranean climate: a hot, dry summer and rainfall concentrated in the winter months. Yet the unpredictability of the month-by-month rainfall is less often mentioned. This is one of the things that makes mediterranean gardening so fascinating.

I have been measuring and recording the rainfall at Sparoza for several years and present below the figures for 2003 to autumn 2016. Over thirteen years the average annual rainfall at Sparoza was about 516 mm. However, annual averages by no means tell the whole story. The year 2003/2004, for example, was remarkable for the fact that no rain at all fell in September and October 2003, followed by no rain at all from April to October 2004. Similarly July 2005 and July 2009 were exceptional for their rainfall (63 and 22mm respectively) since this is usually a completely dry month. No rain fell in January 2007, although there was snow.

Mediterranean plants are prepared for the dryness of the summer months but are subject to great stress if the autumn rains arrive late, as in 2003, or if the winter rainfall is exceptionally low. This was seen in winter 1999/2000 (figures not included below) when only 190mm of rain fell and we were watering the garden of Sparoza in February. In 2000 the spring flowers failed to appear on the hillside. Plants are also in trouble if the first autumn rains are followed by a month or more of drought. This occurred in autumn 2008: 33mm of rain fell in three consecutive days in the third week of September, encouraging plants into new growth, after which no more rain fell until half-way through November.

Caroline Harbouri writes:
Many parts of the Mediterranean had little rain during the winter season of 2015/2016. At Sparoza, where the rainfall is recorded month by month, the figures for the whole gardening year (September 2015 to August 2016) are striking.

The annual rainfall for this period was 408 mm, however it is not the total annual rainfall but rather its distribution, particularly over the winter months, that is crucial for the garden; from November 2015 to March 2016 there were only 169 mm of rain. And of course with the garden bone-dry after little rain in November and none in December, the small amounts of rain that fell in January and February – usually the two rainiest months – barely did more than wet the surface of the soil.

A comparison with the two previous years shows that in 2014/2015 out of a total annual rainfall of 590.5 mm, 463.5 mm fell in the months November to March, while in 2013/2014 out of a total annual rainfall of 458 mm, 392 mm fell in the months November to March. The result of this paucity of the winter rain on which mediterranean plants rely is that this year by April the garden of Sparoza looked as it usually does in August. Plants that had sprung into growth with the rains of September and October suddenly found themselves checked by thirst by the end of November. On the hillside, to cite two normally drought-tolerant plants, Pistacia lentiscus exposed to the full sun is now completely brown; only those plants that receive a little bit of shade still have some green on them. Agave americana has lost all its turgidity.

It is impossible to know whether this low winter rainfall is associated with climate change or whether it is part of the normal year-by-year climatic variation. At any rate we await this autumn to see how much rain will fall, whether severely stressed plants will be able to recover and how many plant losses we shall have to record at Sparoza.”

Rainfall at Sparoza in millimetres

Over thirteen years the average annual rainfall at Sparoza was about 516 millimetres.




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