July 2010 Douro Insider

The weather this month was pretty much as one would have expected for July in Portugal.  It was very hot and very dry.  The extreme heat basically came in two waves – one at the start of the month and the second at the end, with some moderately warm respite in the early middle.  To begin with a mass of warm and dry air moved into the country from the north of Africa and Spanish interior.  This meant that temperatures rose steadily during the first week, generally peaking above 40º C by about the 7th, depending on your location.  (Incidentally, there was a similar situation on east coast of US around this time, with a high pressure area clearing the skies and keeping temperatures up.)  In Germany the heatwave caused chaos for the transport network before suddenly being swept aside by storms that were responsible for a small number of fatalities.  Fortunately for us, relief here came soon afterwards as a depression off the coast of Morocco extended northwards, bringing the mercury down again.  The 8th was thundery and very humid but it stayed dry, and maximum temperatures then began to drop more or less consistently until the middle of the month.

It cooled down considerably over the second weekend and some clouds started to appear, even leading to an occasional overcast moment over the next few days.  In the Douro this was accompanied by the start of the summer winds: the ones that blow strongly upriver from the late afternoon until after sunset almost every day.  Porto kept alive its reputation as a rather damp city with some respectable drizzle.  France, however, had severe storms with heavy rain and winds strong enough to bring down trees, one of which fell on an unfortunate Gallic citizen on Bastille Day.

After this momentary hiccough the heat returned with a vengeance all across Europe.  Italy went on red alert with 40º-plus days, and high temperatures combined with ongoing drought devastated crops across Russia.  Conditions were similar here for the second half of the month – scorching.  In the Douro there was a tiny lull in temperatures around the 20th with a couple of clouds turning up (mists wafted into Porto too) and some gusty winds but apart from that it was all high 30s and low 40s.  Although of course we didn’t realise it at the time, this was the start of a remarkable wave of extreme temperatures that was to stretch unabated until mid-August.

Things really turned hellish from the 26th onwards.  A second mass of hot and dry air moved into Portugal, again from the east.  That night there were power cuts in parts of Porto which meant no fans or air conditioning.  It was probably also the day that the forest fire season got underway for real.  The city awoke on the 27th to the spicy smell of burning eucalyptus and pine.  By 9 am that day the temperature was already 29º in spite of the smoke haze.  It apparently then went on to peak at 38º which is extremely rare on the coast.  The next day more fires were burning strongly both in the districts of Porto (which still seemed to be sitting under a brownish gauze) and of Vila Real.  Towards the end of the day hairdryer-hot winds blew a heavy column of smoke straight up the Douro valley that almost blacked out the evening sun.  Over the next couple of days several weather stations across Portugal registered their highest ever temperatures.

The extreme heat of July perhaps seemed even worse due to the fact that the relative humidity was generally fairly high and yet there was really no let-up in the form of a cooling shower, or even a quick thunderstorm to clear the air.  According to our Pinhão weather station it was a completely dry 31 days in the Douro.  Statistically, this is of course the month with the lowest average precipitation (14 mm) so entirely rain-free Julys are actually reasonably common; this is the fourth in the last 10 years (if we round down the 0.2 mm of 2008), and also the eighth with a below average total over the same period.  As the graph below clearly shows, we are still well ahead of average in spite of the flattening off of this year’s curve.  Our cumulative total remains unchanged at 489 mm while the long term value rises to 369 mm for this stage of the year.

It should come as no surprise, therefore, to discover that the average temperature in Pinhão for July was way above the norm, the fourth consecutive such month.  Some might be interested to hear that the 26.5º recorded here was exactly the same value as in 2005, nearly two full degrees above the mean of 24.7º.  Curiously that year also registered no July rainfall.  More positively perhaps, the comparison is not really fair; in 2005 the agricultural year had provided less than 200 mm of rain by this stage.  In 2010 the total is already more than four times that amount.  Furthermore, it was still quite a bit cooler than July of 2006.  The overall minimum this month was a tolerable 12.4º and the absolute maximum a frightening 41.8º.  For those who prefer to work in Fahrenheit, this corresponds to 107º F.  There were a number of days with an average above 30º C and also many with minimum temperatures comfortably into the 20ºs.

July can be something of a mixed blessing for a viticulturist.  By the end of the month the completion of veraison would be expected for most varieties (at least in the low to medium altitude quintas) and this phenological stage heralds an almost complete suspension of human intervention in the vineyards.  We have prepared the vines over the course of the last few months and now it is over to them.  Ripening the fruit is one area where there is not much that people can do to help.  The relationship between the vines and the weather is now the primary factor determining how much sugar will be produced and stored in the grapes, while the hardworking viticulturist finally takes a well-earned break relaxing on the beach.

On the other hand, we must make absolutely sure that everything that needs to be done before the vineyard workers go on holiday has in fact been dealt with.  This means that there can sometimes be a bit of a last-minute panic as we hurry to finish the final round of despontas (shoot tipping), for instance.  Normally our workforce will knock off for the summer at the start of the last week of July, and then only return towards the end of August.  The fact that the vineyards are effectively left untended for at least a month is made possible by a number of factors.  Firstly the hot and dry weather that invariably comes in July means that the probability of any fungal diseases occurring is virtually nil.  This is coupled with a toughening of the grape skins as they change colour, making them even more resilient.  Furthermore temperatures as high as we have experienced this month will almost certainly have eliminated any risk of traça (the European grapevine moth) since moths’ eggs, much like a chicken’s, are not viable once they have been fried.

As has been the case for some months, mowing the cover crops continued.  Reseeding should have occurred by now, and if they have not already dried up then a final cut will do the trick.  We use shallow-rooted species so that they do not compete with the vines for humidity at depth, and most have already died back on their own.  Now the cut grasses and clovers will form an organic mulch on the surface of the soil that serves two main purposes: it shades the soil, keeping its temperature down, and it breaks up the flow of air over the ground.  These effects combine to drastically reduce evaporation from the surface of the soil and so the mulch is effectively keeping in the water that the vines will need to sustain them through the height of the summer.  Incidentally, we have also been cutting back spontaneous vegetation in the olive groves but this is as much a precaution against fires as anything else.

Veraison came relatively early this year (again, we have been catching up slightly on the late start to the year caused principally by cold weather in February) but it was still two days later than in 2009.  The average date this year for the various varieties in our experimental vineyard was the 22nd July.  Often this point isn’t reached until early into August.  As usual the Touriga Nacional was the last variety to change colour, almost a week later than the other castas (varieties).  Low-lying vineyards are normally the first to reach veraison, and the actual process can take a very long time to finish throughout the region given the Douro’s heterogeneity and microclimates.  It is quite common to see bunches at high altitude still turning a full month later, in late August, when the lower properties are planning to start harvesting within a few days.

In spite of the extreme air temperatures there was still plenty of damp soil deep down, and as a result vine growth had been strong until this point.  It didn’t really slow significantly until this month’s despontas and these were probably the main undertakings for July.  The increasing heat and drought should in theory mean that this will bring about the end of vine growth.  Now that the focus of the vines’ attentions should be on ripening the berries, it is not in our interests to have new shoots springing forth.  As we saw last month, these are sometimes substituted by enrolas (rolling down the shoot tips along the top wire) in the vinhas velhas.

There was also time for one last vine treatment before the break.  The real risk at this time of year is cicadela (a leaf-hopper), particularly as it is not inhibited by the hot weather.  It can be particularly dangerous if the vines are suffering from water stress as they are then less able to resist its evil sap-sucking ways.  Normally we only need to treat the Tinta Roriz as it is by far the most susceptible variety, and to take advantage of the necessary labour and fuel costs many decided to mix in some wettable sulphur in the treatment as the Roriz has been quite prone to oídio this spring.  Inclusion of copper in the spray might also not be a bad idea as it toughens up the leaves on the vines and improves drought resistance to some degree.

The other main activity carried out this month was talude (terrace bank) clearing, often done manually with hoes or with strimmers, as it was clearly a good time to cut back unwanted vegetation knowing that it will not spring up again.  In the new plantations we were obviously watering this year’s rootlings fairly regularly to mitigate the effects of the hot weather, and in one or two instances this also required some work maintaining the caldeiras (depressions) prior to applying water.

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