South East Rivers Trust (& the Wandle Trust)

Water, water everywhere… or is it?


By 2050, the South East of England will need to find at least an additional 1 billion litres of water per day to meet demand in the region. That is about a fifth of the water used in the region today, and equivalent to the water use of 7 million people per day.  Demand for water will exceed supply by 2030.

This is due to a combination of different factors. Some of it is because of the expected growth in population (even if personal water consumption is reduced). Some because water companies are trying to ensure that they have enough water available to continue supply even during more significant drought periods. Finally, climate change will affect when water is available, and how much. Unsustainable abstractions need to be reduced in order to avoid our rivers and wetlands being damaged beyond repair.

Climate change will reduce summer flows and could reduce groundwater recharge in some areas.

Effects of climate change on the UK are often summed up as “warmer, wetter winters and drier, hotter summers”. By 2050, 16-25% less summer rainfall will be the norm, with winter increases of 10-15%. These figures, while significant, are only averages. Extreme events such as droughts and intense rainfall events will become much more common and have been occurring more frequently already.  

It’s expected that summer river flows will decrease, while winter flows will increase – and extreme events on either end of the spectrum will be more common. Some groundwater-fed rivers may be more resilient as they rely on (increasing) winter rainfall recharging the groundwater body, but parts of the chalk aquifer in the South East have been estimated to be particularly vulnerable and likely to decline. Recharge periods – the time in the winter where plants don’t take up so much water and more reaches the groundwater – have already reduced and will shorten further in the future as temperatures rise and allow vegetation to grow earlier and for longer.

A “wetland” and “stream” in Kent, both bone dry due to water scarcity.

This means that shorter droughts in the winter could have much more impact on water supply from groundwater sources. This would lead to similar situations like the drought during 2004-2006 when low winter rainfall over consecutive years saw groundwater levels decline, as well as levels in Bewl reservoir drop to the lowest on record.

The summer of 2018 has become emblematic for what climate change could look like. While the temperatures that occurred in this year had a 1 in 10 year chance of occurring at the time, by 2050 they will likely occur one out of two years . By 2080, these extreme conditions could become normal and be experienced almost every year (MetOffice 2018).  Restrictions on water use will be twice as likely to occur (on a national level) than they were in the past, unless additional precautions are taken. In a water scarce area such as South East England, this could have serious impacts on humans and ecosystems alike.

Droughts and Water Scarcity are not the same.

There are different definitions of drought, but their main characteristic is that they mean less water is available than normal. Currently, for example, the 3 months leading up to June 2020 have been classified as “severely dry”, while the 3 months leading up to April 2020 were “moderately wet”. This is when compared to the long-term rainfall trends in those months.

Droughts can start with a rainfall deficit, that then starts to affect flows in rivers as they receive less runoff, or agriculture as plants have too little water available to continue growing. This happened in 2018, when hot, dry weather reduced yields of wheat and barley.

This can lead to a public water supply drought, where not enough water is available to supply the required amounts of drinking water. In this case, additional steps need to be taken by water companies to ensure they can continue supply. Not all droughts are the same, and they don’t affect all regions in the same way. Winter droughts, especially over consecutive years, have high impacts on groundwater resources that rely on winter rainfall for recharge, and can impact reservoir recovery. While summer droughts affect smaller, rainfall fed catchments much more and have a higher impact on agriculture. That’s why some areas might be experiencing drought conditions, while at the same time others are not.

In the future, drought and flooding at the same time (as we saw in 2019) could become more common, where groundwater levels were still low but summer rainstorms caused flooding across large areas without replenishing supplies.

Agricultural drought causes reduced crop yeald.

Water scarcity is a long-term imbalance in the demand for water and how much is available. This is calculated by looking at how much water is usually used in an area, compared to how much freshwater (i.e. rainfall minus evapotranspiration) is provided. Even in regions with comparatively a lot of water, water scarcity can occur if demand is high.

A ‘warning threshold’ is set when about 20% of freshwater resources are abstracted, and at 40%, an area is classified as severely water stressed. Analysis by the World Resource Institute showed that in the Thames River Basin, 52% of available resource are abstracted, while it is 35% in the South East. This amount of abstraction is impacting how our ecosystems can function, because enough water needs to remain in rivers and groundwater to allow them to function normally and support the wide range of ecosystems that rely on them. If more water is abstracted, it is unlikely that they will be able to resist this stress. Additionally, this makes an area less resilient to extreme events such as droughts – if a high proportion of water is used already, there is little flexibility for more abstraction.

What is happening to address this?

A key focus is to reduce the amount of water that is wasted by inefficient use and leakage, which makes up 21% of water use nationally.

Personal water consumption in the UK is 141 litres per day, per person on average. This is higher than similar European countries such as Germany, which uses 121 litres per day. Water companies have committed to working with their customers to reduce consumption, and to reach a national target of 110 litres per day on average across the country by 2050. Some water companies have chosen to be more ambitious and have shown success, including Southern Water’s metering programme which has reduced water consumption significantly to 129 litres per person, per day.

The Water Retail Market – that allows business customers to choose their supplier based on the best offer, rather than be bound to a specific company because of their location – is meant to increase water efficiency for businesses supplied by water companies. However, this is currently not happening sufficiently, and much more needs to be done to help businesses become more efficient, which will also help them save costs as well as carbon.

On top of this, water companies are looking at investing in more infrastructure to connect areas with unused supplies to those that need them, as well as providing more storage capacity and finding new sources of water. But there is one more asset that it is crucial for them to invest in.

The supply-demand balance of the environment.

Water abstraction needs to take account of the impacts it has on the environment, so ensuring that rivers and wetlands are resilient is a key part of being able to guarantee water supply. In some cases, this simply means only abstracting limited amounts of water. Other times, it can include restoring channels to be more natural and reducing the impact of the additional pressures.

But our ecosystems are not just reliant on water, they are a key factor in its availability in the first place. Headwater wetlands store water and provide flows to small streams, that in turn feed the main rivers from which water is taken, but they have often been drained and lost their function. They can also improve water quality by retaining sediment and nutrients that would otherwise need to be cleaned at treatment plants (and have impact on wildlife on the way). Meandering channels slow the flows down and so provide not only flood benefits, but also a longer availability of the water resource at the abstraction point. Healthy soils and grasslands on chalk allow consistent recharge without the risk of nutrient and pesticide leaching into the groundwater body – a type of pollution that affects most groundwater bodies used for drinking water supply. Converting conifer plantations to chalk grassland can double the volume of water that infiltrates and drains towards the groundwater by reducing the amount held in canopies and taken up by tree roots.

All these elements of our landscape – the natural assets that we rely on – are what we need to protect and invest in to ensure a future that is resilient to the pressures of climate change and the additional need for water. Our water doesn’t just come from our tap. It comes from the streams draining agricultural land, from the grassland covering the South Downs, from the slow-moving clay river winding its way through the Weald – and it’s important that we protect them.

A beautiful area of wet woodland in the headwaters of the Beult.

PROWATER, a European partnership project funded by the European Regional Development Fund, is investigating how ecosystem-based adaptation measures such as soil management and wetland restoration can be used to increase the resilience of our water resources to climate change. You can find out more about the project HERE.

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