Graham’s viticulturalist provides rainfall and temperature data for Douro in 2009

Most of our readers will probably know that people involved in agriculture tend to use a slightly different calendar from the rest of the world, based on the natural rhythms of plant growing seasons. With the end of the grape harvest in October, the viticultural year in the northern hemisphere is generally considered to finish on the 31st.

This occasion therefore demands a brief review of the climate during the preceding 12 months, and I have been collating our meteorological data to find out exactly where we stand relative to other years. What follows is a very brief summary of this year’s conditions. Note that this information is taken from a far more complete report that can be found amongst the monthly viticultural reviews published at http://tinyurl.com/yezksj8  Note that the data presented here is not actually from Malvedos, but from nearby Pinhão. This makes sense for two reasons – not only is Pinhão effectively right at the centre of the prime vineyard area of the Douro, but it also has a far longer history of weather records making the averages more meaningful. In other words, it is a more representative source of reference values for the Douro in general. Malvedos is invariably a little hotter than Pinhão (this year’s mean temperature there was 17.3º C, as it happens) and it also tends to be slightly drier. The total precipitation at Malvedos was just 489 mm, for example, compared with the higher total given below. 

Figure 1. Precipitation in Pinhão in 2008 / 2009

The graph above makes it abundantly clear that, in spite of a late rally, we are still finishing the year quite a bit lacking in water. The total of 529 mm for this year is well short of the mean of 675 mm. Moreover, it is the third consecutive drier than average year, and also the fifth out of last six. The last three years have brought a total of 1585 mm of precipitation, when somewhere in the region of 2025 mm would have been expected by the law of averages. The need for a very wet winter has never been clearer.

In terms of temperatures, this year was very fractionally cooler than the mean but the difference is so small that we need two decimal places to show it: 15.86º in 2008 / 09 and 15.94º for the long-term mean. In fact we had six months of above-average temperatures offset by six below-average months. What is more significant, however, is the distribution of the hotter and colder months. On the following graph the long-term mean curve is plotted on the right hand axis, and the relative difference this year is illustrated by columns on the left hand axis.
 
Figure 2. Temperatures in Pinhão in 2008 / 2009

Interestingly, this chart illustrates very clearly that it has been a year of extremes. Note the concentration of the blue bars on the left of the graph and the red bars on the right. This shows that the winter months were quite a bit colder than usual, and (July excepted) the summer was once again hotter.