Over 30°C on the bogs of Ireland

[Niall Dollard]

Maximum air temperature readings over 30°C are not all that common in Ireland. Perhaps with a larger reporting network, they are now becoming more frequent.

On July 19th 2016 the temperature reached a max of 30.4°C at Met Éireann's automatic station at Mount Dillon, Co Roscommon. Below is an aerial view of the site and nearby terrain. It is quite an isolated location on flat land mostly consisting of raised bog and some short trees. The raised bogs have/are been worked so you can see a lot of the surrounding land looks dark brown form above.



Link to Google Street Maps : http://goo.gl/maps/cmLTN

On July 19th maxima through much of inland Ireland was about the 28 C mark. (I recorded 28.3°C at my own COL station here in Kilkenny). Other Met Éireann stations nearer to Mount Dillon recorded the following.

Mullingar 27.0°C (45 kms to the SE upwind and at a slightly higher altitude)
Claremorris 28.9°C (60 km to the W downwind)
Athenry 28.4°C (65 km to the SW).

Ordinarily I would have expected a maximum at Mount Dillon similar to that of Claremorris. Between 28 and 29. I wonder though how much an effect the dark bog terrain around Mount Dillon would have on the air temp? Would it have a lower albedo than grassy pasture/leafy trees/cropland ? Enough to lift the temperature by 1.5 C ?

The UHI and concrete effect of places like Heathrow has been often been talked about before but I wonder are the flat, brown bogs of Ireland the most likely hot spots within the country ?

There is precedent. The highest temperature recorded in Ireland in all of the 20th century was at another location surrounded by brown bogs ; 32.5°C at Boora, Co. Offaly on 29th June 1976.

Any visitor to the midlands of Ireland will most likely have seen the bogs stretching for miles ; they make up a considerable proportion of the centre of Ireland and as such I think it is good that Met Éireann have sited at least one of its newer automatic stations at such a site and hopefully we will get to see some more extreme readings.

[Edward Graham]

You're spot on there Niall. I did my Master dissertation at a bog site in the Northern Netherlands and noticed the same effect. I'd need to root out my Monteith and Unsworth book again, but if I remember correctly, the thermal conductivity of peat is very low (the top cm or two can dry out quickly under the summer sun), leading to strong sensible heat fluxes, and hence higher surface air temperatures. I don't doubt the 30.4degC max value at Mount Dillon for any reason - and bogs and peatlands cover some 15-20% of Ireland.

Incidentally, it works in the opposite way too in winter: Lullymore, county Kildara/Offaly (at site of the former peat burning station) holds the 20th century record low temp for Ireland: -18.8C on 2/1/1979, as I'm sure you well know.

All the best
Eddie

[Edward Graham]

Niall,

Here are some soil heat conductivities (from Monteith and Unsworth, p.224, 1990):
Thermal Conductivities (Wm-1K-1) at 40% water content
Sand: 2.2
Clay: 1.58
Peat: 0.29 (increasing to only 0.50 at 80% water content)

i.e. Peat has a poorer conductivity of heat to the order of 3 to 10 times that of sand or clay. In practice, this means we get strong thermal gradients in the top 1 or 2cm of peat, if the top layer is dried out and flat (or frozen), as often happens on the Irish cutaway bogs of the Irish Midlands. Hence, very high surface temperatures result -> and high sensible heat fluxes (in contrast to the more usual much higher latent heat flux over a peat bog).
E.

Reference:
Monteith, J. and Unsworth, M. (1990). Principles of environmental physics (2nd edition), p. 224.

[Niall Dollard]

Thanks Eddie. That backs it up.

Yes I have seen before the many low record temperatures at places like Lullymore and Clonsast Co Offaly. Mount Dillon has recorded many cool nights too, including a rare August air frost (-0.6 on 30th August 2010).