Despite all the rain we've seen during April some parts of UK are still officially in a drought. But how can we have flooding and still be in a drought; and can we really have the wrong type of rain?
The first thing to look at is the definition of a drought – and there are a few of them about depending on the rain-related activity you are considering. Firstly, there is a meteorological drought - a prolonged period with less than average rainfall. Next is an agricultural drought, when the shortage of rainfall occurs during the growing season, with negative consequences on crops – something we experienced in 2011 across some parts of England, which saw their driest spring for over 100 years.
Finally there is a hydrological drought linked with a lack of rainfall during winter and spring, the crucial time of year when groundwater levels are usually replenished. When we hear the word 'drought' being used in the news it is referring to a hydrological drought. And it's not hard to understand why when the last two winters have been unusually dry, in fact since September 2009 there have only been a handful of months with average or above-average rainfall in parts of England, and 2011 was driest year in England and Wales for 90 years. And it is the hydrological drought that impacts most severely on domestic and industrial use, leading to restrictions such as hosepipe bans.
By the middle of April 2012, half of the UK was officially in drought conditions and the Environment Agency suggested that the drought could last into 2013. Their statement went on to explain that 'rain during the spring and summer will help to water crops and gardens; but it is unlikely to improve the underlying drought situation. It's going to take more than a few weeks of rain to undo two years of below-average rainfall.'
So could all this be down to the 'wrong type' of rain? Well, yes and no. The rain couldn't have come soon enough for gardeners and farmers as we move into our growing season but most of this rainwater is taken up by plants or evaporates before it drains into the earth far enough to top up the groundwater. And after a prolonged dry period the ground is dry and compact so, during heavy downpours, most of the water runs off quickly causing flash floods. This rainwater fills up our rivers, causing some to burst their banks, but just runs straight downstream and out to sea, with only a small amount penetrating into the ground and replenishing our groundwater levels. In the UK most of our tap water comes from the groundwater.
April 2012 looks like it will be one of the wettest on record – and some of those rainfall records go back to 1766. But with groundwater levels lower than they were at this time in 1976, it looks like this could be the wettest drought on record.