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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.

 

2003/4

2004/5

2005/6

2006/7

2007/8

2008/9

2009/10

2010/11

SEPT

0

0

91

45

0

33

32

42

OCT

0

66

20

188

135

0

101

102

NOV

69

59

320

52

38

65

50

64

DEC

78

189

29

27

65

75

103

38

JAN

217

129

98

0 snow

29

75

52

54

FEB

15

116 snow

46

71

22 snow

56

64

148

MAR

21 snow

33

62

80

83

101

15

31

APR

12

2

17

10

76

37

3

75

MAY

0

23

0

132

3

5

13

48

JUN

0

7

0

21

0

3

16

24

JUL

0

63

0

0

0

22

10

0

AUG

0

0

0

0

0

0

0

0

TOTAL

412

687

683

626

451

469

458

639


 

2011/12

2012/13

2013/14

2014/15

2015/16

SEPT

0

8

0

54.5

102

OCT

42

32

21

19.5

103

NOV

0

93

156

64

36

DEC

78

135

71.5

144

0

JAN

32

73.5

63.5

51.5

45

FEB

106

105

48

53

25

MAR

23

23

54

151

59

APR

57.5

2.5

20.5

5

0

MAY

27.5

12.5

0

15.5

11

JUN

0

22

2.5

33

27

JUL

0

0

20

0

0

AUG

0

0

2

0

0

TOTAL

366

506.5

436

568

408

These figures show the very great variability of month-by-month rainfall over a period of eight years.

Some parts of the garden at Sparoza are watered, including of course the nursery and plants grown in pots. Other parts are left unwatered, including 'Derek’s Garden', the border round the 'threshing floor' (since 2008) and the hillside (with the exception of newly planted trees which receive water during their first year).

During the early part of the year, this water comes from the well. However, as a result of the increased building on the Sparoza hill the well now runs dry every year by late spring or early summer, after which mains water (the urban water supply that also serves the house) is used. There is no separate meter so it is not possible to distinguish between water used in the house and water used in the garden, but the following table gives the total consumption of mains water from 1999 to 2008.

Consumption of water from mains (urban water supply) at Sparoza
for the years 1999 to 2008 in cubic metres.

Year

m3

Notes

1999

219

 

2000

231

 

2001

174

 

2002

356

Watering of 90 trees planted on the hillside

2003

250

 

2004

325

A leak in old piping from the reservoir; uncertain how much water was lost before the leak was mended

2005

262

 

2006

239

 

2007

173

 

2008

151

 

The following lists show the plants at Sparoza that receive no summer water at all.
Those marked with an asterisk survive the dry months with no sign of stress. I have not marked the drought-deciduous species with an asterisk, although of course they are unstressed since they are dormant in summer. If one is not familiar with this drought-resisting strategy of summer dormancy, these plants might appear to be dead – but they come back to life and put out new leaves with the autumn rains, just as do the native geophytes which are abundant at Sparoza.

Drought-deciduous species:
Euphorbia acanthothamnos
E. dendroides
Clematis cirrhosa
Medicago arborea
Prasium majus
Sarcopoterium spinosum

Plants with foliage adaptations:
Ebenus cretica
Euphorbia characias
Phlomis fruticosa
P. italica
Ptilostemon chamaepeuce
Teucrium fruticans

Plants with grey foliage to resist drought:
Anthyllis barba-jovis
Artemisia arborescens
A. californica
*Atriplex halimus
Ballota acetabulosa
Convolvulus oleifolius
Coronilla valentina
*Dorycnium hirsutum
*Eriocephalus africanus
*Helichrysum thianschcanicum
Lavandula allardii
L. angustifolia
L. dentata
L. ‘Goodwin Creek Grey’
Limoniastrum monopetalum
Phagnalon graecum
Salvia chamaedryoides
S. officinalis
Santolina chamaecyparissus
Teucrium polium

Shrubs and trees that are evergreen:
Acacia cyanophylla
Brachychiton sp.
Bougainvillea sp.
*Bupleurum fruticosum
*Buxus sempervirens
*B. balearica
Ceratonia siliqua
*Cneorum tricoccon
Cotinus coggygria
Cupressus sempervirens
Eucalyptus globulus
Grevillea robusta
*Juniperus communis
*J. oxycedrus
*Myrtus communis
Nandina domestica
Olea europaea
*Phillyrea latifolia
Pinus halepensis
P. pinea
*Pistacia lentiscus
*Quercus coccifera
*Retama raetam
Rhamnus alaternus
Rosmarinus sp.
*Ruscus aculeatus
*R. hypoglossum
*R. hypophyllum
Ruta graveolens
Santolina viridis
*Teucrium flavum

Deciduous trees:
Ailanthus altissima
Cercis siliquastrum
Jacaranda mimosifolia
Melia azederach
Morus alba
Parkinsonia aculeata
Pistacia atlantica
P. vera
Punica granatum
*Ulmus parvifolia

Cacti and succulents:

Agave sp.
Aloe sp.
Crassula sp.
Cotyledon orbiculata
Haworthia sp.
Opuntia sp.
Sedum sp.
Yucca sp.

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