Dry spell continues

The dry theme that started in late March continues into the last week of April, especially over central southern parts of England (where some stations are still in a state of partial drought), as this graph of precipitation illustrates from Benson in Oxfordshire since the start of this year (fig 1).

Figure 1

A big part of why it’s been so dry is the anticyclonic weather of the past month, as you can see from the Benson barograph (fig 2).

Figure 2

A state of type is now well under way, with cold air set to flood south across the country in a N or AN, but according to the latest NWP guidance that meridional type looks like it will be a relatively short-lived affair, before things become more mobile from Sunday, putting an end to the dry spell even across southern counties.

Latest April 2017 rainfall totals

You’re all probably all getting fed up to the back teeth hearing me prattle on about what a dry first half of April it’s been, so I’ll let the graphic do the talking.

Accumulations from available SYNOP – Data courtesy of OGIMET

Absolute drought frequency in the British Isles

Figure 1 – Courtesy of the Met Office ©Crown Copyright

I was interested in the average number of droughts they were each year across the British Isles and came across an article in an old Met Mag (vol 76 No 903. September 1947) with the above maps of droughts for the period 1906 to 1940. These might be old climate stats but that doesn’t mean they have no value. Back in 1887 the British Rainfall Organisation introduced the following definitions for absolute and partial drought:

  • An absolute drought is a period of at least 15 consecutive days, to none of which is credited 0.01 inches of rain or more.
  • A partial drought is a period of at least 29 consecutive days, when the mean daily rainfall does not exceed 0.01 inches.

I assume that the partial drought limits the total of rain in any 29 day period to less than 0.29 inches (~7 mm) but I’m guessing, the definitions will have no doubt been changed since 1947, but I have no idea to what. The chances of an absolute drought of 15 days or more (which some stations this April have at the moment) looks to be highest, as you would expect, across the southeast of England, and south of 52° north the average looks to be around 1 or 1.2 occurrences a year. Curiously, there doesn’t look that much overall difference between the map of absolute drought and the map of partial drought (fig 1).

It’s refreshing to see that climate maps in 1947 included the whole of Ireland as well as the rest of the UK, it’s a shame the head of international climate service development at the Met Office can’t get around to talking to his counterpart at Met Éireann and share our climate data! Perhaps if we make this a stretch target or SMART goals for Dr Chris Hewitt (who I believe is the present incumbent in this role) he will make it happen. Weather and climate know no man-made political boundaries, or it didn’t the last time I looked.

Saturday 15 April 2017 – Dry spell hangs on despite overnight rain

 

Figure 1 – Data courtesy of the Met Office

The dry spell and absolute, or ‘meteorological’ drought as it’s known these days is just hanging on despite some overnight rain across the country (fig 1). St James Park in London last had >0.1 mm of rain 17 days ago, but as always the rainfall data in the SYNOP data can be omitted or the observation missing at times. Linton-on-Ouse in the Vale of York got away without any overnight rain, as did a few other stations including Exeter as far as I can tell (fig 2). Please post a comment if you know any different.

Figure 2

Figure 3

As far as I know, St James Park only reports 24 hour rainfall totals at 06 UTC each day, and it’s rarely missed so far this year. The accumulation for 2017 is currently standing at 135.2 mm (5.32″) for the last three and a half months. Looking more closely the last real rain was 7.2 mm on the 23rd of March, so I make it, barring an instrument malfunction, they’ve had 0.2 mm of rain in the last 22 days (fig 4). I’ve got a strong feeling that they won’t get away with it tomorrow, although Exeter might just get away with a trace.

Figure 4

 

The drought in the southeast

Figure 1 – Consecutive dry days (13 April 2017)

The overnight rain in some places put an end to any possible drought across the country, but as far as I can see both Wattisham in Suffolk, and St James Park in London have now gone 15 consecutive days with less than 0.2 mm of rain in any day, so are technically in drought, and when I say drought, that’s the old-fashioned meteorological type. It might not last very long though, because the GFS is forecasting rain from a cold front moving south during Friday, which might scupper the drought before it even gets going. Looking beyond Friday though, the same model predicts anticyclonic conditions returning and persisting till at least the 21st, so we could be in for a very dry April in some parts.

Dry start to April continues…

Here are the number of consecutive dry days (<0.2 mm) across the southern half of the British Isles I’ve compiled from SYNOP reports. This is my best shot, some sites have missing observations, some have missing rainfall reports, and I have noticed that the AWS the Met Office employ are very sensitive and have a preponderance to push out a 0.2 mm report, when a trace or 0.1 mm might have been more appropriate. I reckon that’s the case at many stations, take Exeter Airport for example, some very good radiation nights in the last week could easily knock up 0.2 mm of dew in the gauge, and as this count is for days with less than 0.2 mm each day, so the total gets zeroed, and we have a count of 3 days instead of 8 or more.

The dry spell of early April 2017

The above plotted chart (fig 1) is of rainfall totals for stations since the 28th of March 2017. They show how dry it’s been recently in all areas, but particularly in eastern counties. The figures are as close as I can estimate them from the SYNOP data I download from OGIMET so don’t get upset if I get one or two of them wrong. I would prefer to use the 06-06 UTC totals because then you don’t have to do any maths or guess-work, but since the good old Met Office refuses to make NCM climate data available for the UK, this will just have to suffice. I estimate an 00-00 UTC total from the 6 and 12 hourly totals in the observations. I do this because not all countries, in particular the Irish publish their 06-06 totals. This is further complicated by missing rainfall reports from observations, or just plain missing observations. Why do government agencies such as the Met Office deliberately hide daily climate data that they collect on our behalf?

I was going to mention the word drought in the title, or rather meteorological drought, which as far as I know is still a period of 15 consecutive days with less than 0.2 mm of precipitation, but that can get rather complicated so I just called it a dry spell! Nevertheless, we are very close to meteorological drought conditions, in whats proved to be an exceptional start to April, and the latest NWP does seem to suggest that pressure will remain fairly high across the south, and especially the southwest, with anticyclones never that far away. Who knows, it may rival the April of 1938 but it will have to go some to beat that month, perhaps this article has already jinxed that possibility.

If anyone reading this in Scotland feels left out I can tag on a chart for the northern half of the UK without too much problem, just let me know.

Dry spell across the UK continues

Figure 1

The 365 day running totals of daily precipitation totals are below average in eight out of the nine regions (fig 1) across the UK. In England and Wales the accumulation over the last 365 days is 94.7% of the long-term average (fig 2). Not overly low of course, but many reservoirs in the south and west of the UK are well below 100%, where at this time of the year they usually are.

Figure 2

But it’s in Northern Ireland were anomalies are at their lowest at only 81.5% of the long-term average (fig 3), and probably the lowest they’ve been in the Province since 2004 (fig 3).

Figure 3

Here’s a closer look at the last year in more detail (fig 4). So rainfall totals dropped from September in what was a very anticyclonic Autumn and anticyclonic Winter.

Figure 4

NIWater don’t seem too worried about the reservoir levels (currently at 87%) there though (fig 5).

Figure 5

Let me know if I’ve screwed up with any of my UKP rainfall stats that I download from the Met Office website.

Rainfall in last six months well below average

Figure 1 – Data courtesy of the Met Office

In the last six months the Southeast of England has seen only around two-thirds the amount of rainfall that it usually receives. Below average rainfall is not just confined to the Southeast though, anomalies are low across all regions of the United Kingdom, after what has been a generally quiet anticyclonic Autumn and Winter up until now. The 2016-17 period (July 1 – January 31) in the southeast, is the 7th lowest total for this period (ignoring the 1930-31 incomplete period) since the UKP data series began in 1931.

Figure 2 – Data courtesy of the Met Office

We get water from the river Exe in the part of Devon that we live, but the nearest reservoir to us, Wimbleball, isn’t looking too good at just 57.7% full at the end of January.

At the moment the level of water in their two reservoirs in Sussex, that to me act like giant rainfall gauges for the whole county, aren’t too low but at this time of year they should I’m sure, be closer to 100%.

Reservoir levels and rainfall this Winter

It never fails to amaze me what you can find with a bit of digging on the Internet. I was looking for reservoir levels from around the country and although most Water Companies do maintain a web page to indicate what kind of reserves they currently had, a number didn’t, notably Welsh, Northumbria and Yorkshire Water. But all of them, well at least the ones in England, are required to upload monthly situation reports of the state of the reservoirs that they oversee and maintain to the www.gov.uk website. The next couple of images (fig 1 & 2) are one’s that I’ve copied out of one of those situation reports, and show some climate graphics that the Met Office generate on behalf of these private companies – I wonder who pays for it? Silly question, we do of course.

Figure 1 – Courtesy of the EA and the NCIC at the Met Office

I realise that it’s been dry in the southwest over the last year, but the values on the maps (fig 1) did take me by surprise. The next graphic is also very informative splitting England and Wales into a series of weekly rainfall maps (fig 2) which at a glance show you what’s going on across the country. The question that immediately springs to my mind, is why aren’t they available in the climate pages of the Met Office website? The statistics look like they are generated from Weather Radar images, very nice.

Figure 2 – Courtesy of the EA and Met Office

Theses are the reservoir levels from some of the Water companies around the country.

Anglian Water

Figure 3 – Anglian Water

Poor graphic with little precision (fig 3) – water levels look fairly respectable for one of the driest regions in the UK though.

Southern Water

Figure 4 – Courtesy of Southern Water

Nice graph, perfick as Pa Larkin would have said (fig 4). Bewl Water reservoir is the largest stretch of open water in the South East of England, so 58% full in mid-January is not great news for the southeast if the tendency for anticyclonic weather persists into the summer.

South West Water

Great website, and an even more perfect graph (fig 5). Reservoirs are just like giant rainfall gauges really, and why statistics aren’t used more for climatological studies I just don’t know, lets face it many have been there since Victorian times. We meter what goes down the pipe and out of the reservoir, and we continually measure the depth of water in so know fairly accurately what’s coming in from the surrounding hills. In many ways they’re a much better ‘gauge’ (pardon the pun) than a five-inch copper gauge will ever be, because the catchment area of the reservoir is so vast, which should make them more representative and sensitive to each passing shower. I suppose the big unknown is how much water is lost to evaporation, especially in the summer.

Looking at this graph (fig 5), I’m slightly worried about the chances of a drought this year in the southwest, although our water here in the part of mid-Devon that I live is extracted out of the River Exe, which in the last 14 years has never let us down, or should that be left us dry.

Northwest Water

Figure 6 – Courtesy of United Utilities

A basic table of general reservoir levels grouped into regional areas and updated weekly. It wouldn’t have killed them I would have thought, to have produced a 12 month graph of those weekly values for each region to make a visit to their web page a little more worthwhile. It’s interesting to note that after the devastating heavy rains of last Winter, some regions are at less than 70% capacity.

Welsh Water

Figure 7 – Courtesy of Welsh Water

Perhaps it’s because they’ve got so much of the stuff, they don’t feel the need to let people how much they’ve got, or perhaps they don’t know themselves. I can’t find any information on their website about reservoir levels, let me know if you do.

Yorkshire Water

Figure 8 – Yorkshire Water

Similarly to Welsh Water, Yorkshire Water think they have no need to inform anyone how much water that are storing up on our behalf, or they simply just have too many reservoirs to bother. I can’t find any information on their website about reservoir levels either, let me know if you do.

Northumbrian Water

Figure 9 – Northumbrian Water

The one thing that strikes me as I knock out this article, is that the more water you receive and the more reservoirs that you seem to have as a water company, the less you care about letting people know exactly what you actually have in them. That’s just out-of-date thinking and has to change eventually I would have thought, because freshwater is a scarce resource.

Scottish Water

Figure 10 – Scottish Water

In Scotland it appears that Scottish Water (don’t you just love their logo) defer all the monitoring of rivers, lochs and reservoirs to Scottish Environment Protection Agency [SEPA], which is not a bad idea. Having lived in Scotland for a number of years, I know a lot of drinking water is extracted from rivers rather than reservoirs. I don’t know for sure but a lot of water away from the central belt must come from freshwater lochs. Glasgow must surely take water from Loch Lomond, and I wonder where Inverness gets its drinking water from?

The SEPA site is just great, you can monitor just about any river or body of water from this one site. It’s very similar in fact to the Environment Agency in England and Wales, but as far as the EA site goes it’s just for monitoring river levels in the event of flooding and not reservoir levels.