Marlborough's weather: that was the driest October since at least 1984 - and the River Kennet needs lots of rain

Written by Eric Gilbert on .

 

The last week in October at Westonbirt Arboretum (Photo by Eric Gilbert)The last week in October at Westonbirt Arboretum (Photo by Eric Gilbert)Another rainfall record has been broken - exactly twelve months after it was set. That record is for lack of rain - as recorded at my Marlborough weather station.   



With just 31.3mm of precipitation, October has been the driest month since my records began all those years ago in 1984.

The previous record low for rain in October was set in 2016 with 31.5mm - against  the average of 86.4. This means a short fall of rain during this October of 55.1mm compared to the long-term average - or just 36 per cent of the average.

The month's heaviest twenty-four rainfall total was 10.2mm on October 19.  This was midway in the wettest period of October 17 to October 24 - bringing 73 per cent of the monthly rainfall. We enjoyed 14 totally dry days.

The wettest October I have recorded in Marlborough was in 2004 with 159.3mm, which was almost twice the average.

It has been the ninth driest January to October period I have recorded with a total of 572mm. The extremes for these ten months are 409.0mm in 1996 and 920.6mm in 2014.

It is interesting to note that the equivalent moisture lost to the atmosphere from ground sources and plant life during the month was 27.9mm. Therefore most of the rain that fell in October has been offset by evaporation.

Due to the Jet Stream providing a conveyor belt of frequent depressions the wind has been predominantly between south and west, bringing mild air, sometimes from as far south as the Azores.

This mild, moist air has meant a relatively warm month with the mean temperature 1.4C above the 33-year average. There were 21 days with above average maxima. The peak temperature of 18.9C was recorded on October 16, some 4.3C above the average.

The stormy period around October 21 brought very strong winds gusting to 40mph. However, at the end of the month the opposite was true as a couple of very still days occurred with hardly a breath of wind - for instance there was a maximum wind speed of just 7mph on October 30.

We suffered one air frost, that on the night of October 30, when the thermometer fell to -0.5C, cold enough to bring to an end the wonderful colour of bedding plants that we have enjoyed for so many months.

During the month we have enjoyed 82.3 hours of strong sunshine, the sunniest days being October 5 with 7.9 hours followed by 7.36 hours on October 25.

There were several dismal days of thick cloud, which were often low enough to drape the tops of the Downs in mist giving us eight sunless days. Fog was recorded on three days.

Again this year we have enjoyed the colourful spectacle as leaves turn colour when light and warmth are reduced.  Such was the feeling of George Eliot: “Delicious autumn! My very soul is wedded to it, and if I were a bird I would fly about the earth seeking the successive autumns”.

Footnote:  several people have commented to marlborough.news that the River Kennet is running at very low levels.

Charlotte Hitchmough, Director of Action for the River Kennet (ARK) writes:  The Kennet is very low at the moment. November is usually the lowest flow month on the annual cycle:  the river is still being fed from the dwindling aquifer.

River Kennet behind Town MillRiver Kennet behind Town MillRiver Kennet - looking west from Town Mill River Kennet - looking west from Town Mill Until the aquifer recharges with rainwater the river flow won't pick up. Current aquifer levels at Rockley Observation Borehole are well below average, but not as bad as in 2010 or 2011. We need a period of prolonged steady rain.

The same aquifer which feeds the river also provides all our drinking water along the Kennet Valley and a portion of Swindon’s water too. Thames Water’s new pipeline has dramatically reduced the quantity of water exported to feed Swindon, but some water is still exported every day. ARK are talking to Thames Water about reducing this export still further.

ARK’s volunteers are out checking the health of the river every month by monitoring riverfly populations, and are seeing a steady decline in numbers as the flows drop. At the upper end of the river isolated pools are beginning to develop.

Fish are usually quite good a recognizing falling levels, and swim downstream to deeper water, but where there are artificial barriers like weirs they can get trapped and fall prey to heron, egret and kingfisher.   Everyone can play their part by using only the water they need.

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