Drought lingers as harvest ripens

Tuesday, 3 February, 2004
Leonie Joubert
Climate Column
By Leonie Joubert

This is the first in a monthly series by Leonie Joubert, long time contributor to winenews.co.za, who has embarked on her Masters degree in Science Journalism, specializing in Climate Change. During the next few weeks we will also be initiating a regular weather report, linked to the long range, and global changes that are, undoubtedly, going to affect agriculture in the future.

The picture is bleak. A NASA satellite image taken in July 2003 shows the Western Cape scorched to a dry, khaki brown. Compared to an image of the same region taken exactly a year earlier, only remnants of green remain, mostly on the Agulhas Plain.

This week, six months later, grape growers are sending workers into the vineyard to begin harvesting the 2004 crop. At the same time the Western Cape MEC for Agriculture, Environmental Affairs and Development Planning is appealing to the national government to give assistance to the region’s farmers who have not yet seen relief from the drought whose hold was first recorded in those satellite images taken last winter.

Small quantities of rain have fallen since then, but in many cases it is too little, too late. Vinpro SA’s Francois Viljoen this week said the problem for the Cape’s wine farmers began with last year’s uncharacteristically dry winter, where underground water levels were not sufficiently replenished by seasonal rainfall. Many farmers reliant on irrigation also found their dam and reservoir water below required levels.

The vintner’s situation is not as dire as that of the wheat farmer who, if the rains don’t come on time, can see a complete crop failure. Because vines are perennial, they are more able to handle boom and bust weather. But lack of rain still impacts on the plant and its output.

Now, as farmers gear to bring in their harvest, soil moisture is crucial to the correct ripening of grapes, particularly in the four to six weeks prior to harvest.

‘If there isn’t enough moisture in the ground, the vine slows and shuts down photosynthesis. If the situation gets very bad, the vine may shed leaves to stop transpiration (the way in which water evaporates from the plant) and may then even extract water from the grapes in order to survive,’ explained Viljoen.

Grapes may not ripen properly under conditions of drought stress – if photosynthesis shuts down, berries lose acidity, the pH climbs, aroma and flavour components disappear and the grapes may become sunburned and dehydrated and without the correct sugar levels. Red variety berries may not develop a rich, full colour but remain pink.

Already vines in some of the dry land regions are reported to be shedding leaves, a sure sign of drought stress. ‘If we don’t have some rain in the next few weeks we could see a loss of quality and quantity in the harvest,’ said Viljoen.

It’s not that there’s been no rain - it’s that the rain that has come has been out of synch. Chrisna du Preez, a meteorologist working for the Institute of Soil, Climate and Water, says that while rain did fall within the past six months, not only was it below average overall (with some months showing regional above average rain) but it was outside of the usual seasonal parameters.

Winter rains came very late last year. July was exceptionally dry but was followed by above-average rainfall in August. Rain fell in many places in the following months and even December saw a particularly wet spell reaching some parts of the region.

Out of synch rain confuses the vine, often resulting in uneven budding, which later means uneven ripening and a complicated harvest. When the December rains fell, some vines were even reported to have started sending out shoots, probably thinking spring had come around again.

A long-range forecast from the South African Weather Bureau suggests the region may experience ‘below normal rainfall’ for the next month.

To view comparative satellite images of the Western Cape, visit NASA’s Earth Observatory site at http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=11129