A recent scientific paper (reported here on eurekalert) publishes research suggesting a link between decreasing Arctic sea ice and increased snow in the northern hemishphere. More snow in Europe generally means less rain in the south and east of the UK, and more in the north and west.
The research suggests that a decrease in Arctic sea ice has led to increased blocking patterns (long-lived high pressure systems) in the Atlantic. These cause northerly winds to bring very cold air from the Arctic, leading to snow. The researchers link changes in arctic sea ice with changes in atmospheric circulations (a change in the Arctic Oscillation) and atmospheric water content.
Here’s the latest map from the Met Office showing the UK’s Winter rain for Dec 2011- Feb 2012.
Some parts of England received less than 100mm of rain in the winter.
Here’s the anomaly map – again the south and east received between half and 2/3 of their average rain. After a wet December here in Dorchester (96mm) we had 59mm in January and a measly 25mm in February totalling 180mm for Winter.
In the short term, drought orders have been published for Southern England and East Anglia. Given that we have now more or less reached the end of the “recharge” season for water (that is the time when rain stays around rather than being evaporated back into the atmosphere) it seems likely these will be extended beyond the current areas, to those areas now officially At Risk ie South West England, parts of the Midlands and North East England.
There’s already been some media coverage of how this drought is likely to affect wetlands and trees – what about grasslands?
If wet grasslands such as the Culm grasslands of Devon/Cornwall dry out too much their wetland plants, and the wildlife that depend on them, are likely to have a bad year. Dry grasslands such as downland or dry meadows are able to cope better with dry conditions – they just brown off earlier in the year. There’ll be less grazing and hay available for farmers – that drives up the cost of keeping animals, but also the value of those animals, so those two factors should cancel each other out (on a very simplistic level). Dry conditions also mean that undergrazed or abandoned grasslands won’t suffer quite as much as in a normal year as vegetation grows more slowly, including bracken and scrub. A dry sunny spring and summer is also good for sun-loving species like butterflies.
What if this is a sustained change in our weather patterns? That will affect wildlife, as wetlands in the south and east dry out and disappear, while western habitats eg Culm grasslands continue to receive enough rainfall to support them. Apart from the wet grasslands, most grasslands cope pretty well in dry conditions – that’s what they are adapted too – think of the Asian Steppes, African Savannahs or American Prairies. Unimproved and Semi-improved grasslands in the south and east would be more under threat, not so much from the weather itself, but from the disappearance of livestock on which they depend.
In terms of land-use, the UK is already split into the arable east and the pastoral west and this polarisation will only be further developed. Rye-grass, the grass adopted by intensive pastoral agriculture which now covers nearly half of England, depends on a decent amount of rain for it to grow (anyone know how much?). A drier climate could lead to its demise. Forage maize similarly needs a decent rainfall. These could be replaced by grain maize and Alfalfa for animal feed.