Friday, 16 December 2016

Storm Angus

The UK was battered by rain and high winds in November this year as a storm named 'Angus' made an appearance.

Angus hit the south of England during the 19th and 20th of November, but it wasn't until the day after when the heavy rains had moved north and reached the Peak District and South Pennines, that we were able to record the storm.

This blog post looks at how the equipment installed on our Community Science environmental monitoring sites reacted to this event. 

Volunteers collect information from these sites each month, and use the same equipment and methods as Moors for the Future science team do on other sites where conservation works have taken place. In this case though, we're interested in capturing long-term climate datasets on sites where conservation works haven't taken place.

The bar chart below shows how much rain fell on each of our five sites over four days:

Click on the image to see a larger version
Marsden had the most consistent rainfall with 71.2 mm recorded across the four days. Despite Holme only recording rainfall on the second couple of days of the storm (21st and 22nd), it received the second highest amount, with 73 mm in total. The Roaches had 45.6 mm over the four days and Edale had a surprisingly small 33.6 mm. Out in front was Burbage Moor, which recorded a total of 78mm over the 4 days, with nearly 70% of this falling on Monday 21st.

So how did all this water behave once it reached the ground? The line graph below shows how the water table on the sites changed over the days around the storm. The 'zero' mark on the left hand axis represents ground level, and each line shows how close to the surface the water was (in metres) over the four days of the 'official' storm, and a couple of days afterwards.

Click on the image to see a larger version

We can't be certain what is happening here, but from a quick look at the graph we could surmise that despite having less rainfall than the other sites the water table at Edale (the driest of the sites) increased the most, jumping up by around 10 cm, before rapidly decreasing again as water drained away. 

The Roaches water table also had a sharp increase, however as the water on the site is consistently close to the surface, it only increased to around ground level - but then seemed to stay there, possibly because the site has plenty of Sphagnum moss, and clay underlying the peat layer. 

On the Holme site the water was also already close to the surface, and despite having very high rainfall, the water table didn’t change dramatically, or as quickly. 

Marsden did show an increase in water table - but it was gradual and the new higher level was maintained in the days after the storm event. The site is very flat and also contains Sphagnum moss among its vegetation, which could perhaps help to explain this pattern. 

The site which had the most rainfall (Burbage) also showed a small response - the water was almost at surface level; and you can see it even exceeds zero, forming a puddle! This is another very flat site and does have some Sphagnum moss present. 

The complexity of  hydrological data - taking into account the many variables which can affect the way water behaves on a site - means that we cannot draw any firm conclusions just yet. However, our volunteers will be analysing our environmental data in more depth in the near future...

Graphs and text by volunteer Mollie Hunt, and the CSP team....

No comments:

Post a Comment