In the UK, 2012 was the year of water. Across all seasons, periods of heavy rain dominated, with flooding events seen across the country on a number of occasions. The release of the Met Office’s 2012 records last week has confirmed for the majority of us that, yes, there was nothing average about the amount of rainfall in 2012. The UK national records show that 2012 was the second wettest year since 1910, with a total annual rainfall of 1330.7mm. Over this period, only the year 2000 has been wetter (albeit only 6.6mm so).
The effects that rainfall and flooding events have on ecological systems are huge, and can be long-lasting. Populations and their networks may be uprooted after a flooding event, and the repercussions are likely to be seen throughout communities. Flooding can introduce pollutants to freshwater ecosystems, which are likely to become a long-term detrimental addition to the habitat. Populations or individuals that cannot readily move to unaffected areas are particularly at risk. Trees, for example, will suffer from a lack of oxygen in flooded areas. This is unlikely to be heavily detrimental over a short period, but such short-term flash floods may have arisen through extreme instances of rainfall, which could have other effects on trees, such as decreased stability through the erosion of soil.
Met Office analyses showing increases in both the level of rainfall and the number of extreme rainfall events are therefore alarming. Four of the five wettest years in the UK have occurred since 2000 and longer-term trends show a 5% increase in rainfall from the 1961-1990 average to the 1981-2010 average. The number of extreme rainfall events has become more frequent over time since 1960, and as mentioned above, it is these events that could be most damaging to ecosystems.
The trend towards more extreme rainfall events is now seen worldwide, but its causes are widely unknown. Increasing global temperatures have been hypothesised as a factor, due to the ability for a warmer atmosphere to hold more moisture. Changes in sea surface temperatures from both natural cycles and a reduction in the amount of Arctic ice may be leading to increased levels of rainfall, but further research is required to ascertain their individual effects and exactly how they influence rainfall levels.
Both trends pose a threat to the natural world, and the need to understand their causes and effects fully is vital. This may not be possible in the near-future, and so actions must be taken to improve the resilience of populations and ecosystems across the UK through informed decision-making. As part of the BES’s centenary year celebrations, we will be launching an Ecological Issues focusing on the effects of extreme events on freshwater ecosystems, to be released in June 2013, which will include the effects of flooding.