It’s been a long, hot summer
Too much rain and too much sun? Mark Shepherd of ADAS looks at ways the UK can deal with the threat of both droughts and floods after the confused weather over the past year
Water, water, everywhere – time for joy or despair? With the storms and floods of mid-winter, it is hard to believe the UK is a water-poor country. Most people complain about the rain but forget the land is crowded, particularly in the south-east, and consequently there is a pressure on all of the nation’s natural resources – including water. The recent debates during the PR04 review put the water industry in the spotlight just at the time there were warnings of impending drought. Talk of the ‘right type of rain’ to replenish our reservoirs and groundwater might have seemed nonsensical to the general public but the fact is interactions between land management and climate dictate how much of our rainfall can be captured for use by our population.
The year 2003 definitely brought this issue into focus. First, the good news – the UK’s long, dry, hot summer did not lead to water shortages and interruptions to supply (unlike some parts of Europe). It was clear the UK had learned from previous experience. Water companies have sophisticated water resource models and optimise resources. There is annual reporting on both drought plans and water resource plans to the Environment Agency (EA) and Defra and there is close liaison with the local EA offices on a regular basis. The UK also entered 2003 with large reserves of water (full reservoirs and good groundwater levels), which also helped. Then, the bad news – the UK experienced a very dry autumn as many farmers, trying to establish crops in almost dust bowl conditions, will confirm.
This prolonged dry spell lead to a continued decline in reservoir and groundwater levels, reservoirs stocks across the UK fell to below 50% of their capacity and a lack of groundwater recharge led to low aquifer levels.
In December, the EA warned of potential supply problems in 2004. Water companies responded with applications for drought orders and drought permits.
However, since then there has been higher than average rainfall and this has improved the situation, with most reservoirs now close to their normal levels and groundwater recovering. Even previously depleted reservoirs in the south are now nearly full. The recent high rainfall over the winter has restored water resource levels right across the UK.
With close to average rainfall for the rest of the winter and early spring, problems for the summer of 2004, even in the south-east of England, will be minor. So, panic over? Unfortunately not.
The EA has told us a dry spring and autumn could lead to problems in the south and east of England, so there is no room for complacency. With more than 75% of the UK’s land area covered by agricultural activity, the impact of land management on our water resource is large. The solution to dealing with both floods and droughts therefore lies with improved land-use management and a better understanding of the implications for water resources. However, the relationship between rainfall and replenishment of resources is complex. Groundwater recharge depends on the overlying geology and antecedent conditions; reservoir filling depends on run-off rates and local land-use. ADAS has previously worked with water companies to model these links and to calculate the reservoir recharge resulting from different rainfall events based on GIS and modelling of the surrounding geography.
As well as ADAS consultancy activities in water resource management, our research programme has thrown up some interesting questions about the impact of future land management on replenishment of water resources. For example,
my colleague, Professor Roger Sylvester-Bradley, working with Nottingham University, has highlighted the effects of increased wheat yields on water use and aquifer recharge. Wheat is a major crop in eastern England and crops use around 200 litres of water for every 1kg of growth, with little consistent variation amongst varieties. Average yields of modern wheat crops have reached 8t/ha grain, having been little more than 2t/ha 50 years ago. To achieve this, Prof Sylvester-Bradley estimates that of the 600mm rain, which falls annually in eastern UK, wheat must have increased its consumption (for example, evapo-transpiration) from less than 20-50%.
There is still no sign of the progress in wheat yields abating, so we could expect average yields of as much as 12t/ha by 2050, when significantly less than half of the rainfall will be left for other purposes. This is where we need joined-up thinking.
Crop growth has first call on UK rainfall and we need to think about how future agricultural activity will affect recharge. Increased yields through improved productivity is just one consideration, diversification is another.
Short rotation crop (SRC) willow is seen as a biofuel, with plans to increase the area under production. SRC is being grown on our Gleadthorpe Research Centre. Computer models and measurements suggest the soil’s water can be used to a full 3m once the crop has established (year two onwards). If grown on soils with field drains at 1m, the drains tend to run during winter, suggesting the soil has at least reached field capacity to drain depth.
However, on free-draining soils overlying groundwater it is quite conceivable rainfall will only replenish the soil moisture deficit accumulated to 3m, leaving little, if any, for aquifer recharge. Diffuse pollution control may also impact on recharge.
The Water Framework Directive requires us to deal with water quality and quantity issues but I wonder if we are considering the effects on recharge of actions to improve water quality. For example, maintaining green crop cover over winter is advocated as a measure to decrease nitrate leaching. Sowing winter cereals earlier, using cover crops or converting arable land to permanent grass are all practices that will affect drainage volumes. Comments about ‘the right sort of rain’ caused consternation in the popular press. However, there was some truth in the concern. Groundwater recharge will be influenced by the type of rainfall, as well as the amount.
For instance, there is a concern the recent rainfall may lead to flooding rather than groundwater recharge because the intensity means it generates high levels of run-off.
There are so many things to think about – and that is without considering the effects of climate change. There is no doubt it is time for water engineers and policy makers to take a more active role in the debates over Common Agricultural Policy (CAP) reform. Therefore we should all work to ensure farming methods increase water resource security and reduce flood risk rather than the other way around. There are examples of benign farming that integrates wash-lands across the UK but we must all promote these examples of good practice to ensure they become common practice. Drought and water scarcity poses more problems than just availability of supply for water companies.
Low reservoir levels can lead to quality concerns as dilution levels are lower and run-off from adjacent land can lead to increases problems with discoloration, sediment and contamination. Likewise, fluctuations in groundwater levels can mobilise contaminants in the unsaturated zone.
There is also a significant issue associated with the protection of key nature sites. Since the last significant drought of the mid-1990s there has been increased focus of nature protection. English Nature has gained more powers under the CROW Act and this may lead to difficult decisions over the balance between environmental protection and security of supply in relation to drought orders. Integrated catchment management (ICM) is all about landscape management to deliver enhanced water quality, flood and drought mitigation and improved biodiversity. The UK was starting to think along these lines even before the Water Framework Directive. There is no doubt that whereas most would agree with the principles underlying the directive, there is still much to do to actually implement ICM in anger.
All I would ask is that we do not compartmentalise approaches into quality, quantity and biodiversity. ICM should do exactly what it says on the tin – integrate land management approaches to deliver results