Water

It is now clear that our climate is changing. The Met Office is 90% certain that human activities are to blame. All but two of the warmest years on record in the UK have occurred since 2000 and the forecasting model used by the Met Office's supercomputer indicates a continuing trend.

At Aberystwyth University, we have modelled the implications of continued warming for water resources in Wales in conjunction with Welsh Water. The results are remarkably consistent, applying the Met Office Hadley Centre's change "scenarios" to computerised riverflow models.

Summers will be drier with lower river levels, causing lower inputs to reservoirs, less dilution of pollution, warmer water temperatures and more evaporation. Fish could be affected by reducing oxygen levels in rivers. Winters will be wetter, with more flooding caused by intense winter depressions, like the one that devastated Cumbria in November 2009.

Even in drier summers, more intense convective storms will cause cloudburst floods. Floods could become 1½ to 2 times more frequent by mid-century.

We have predicted what might happen by using weather predictions from the Met Office's third generation climate model for two of the scenarios created by the Intergovernmental Panel on Climate Change to estimate future greenhouse gas emissions. Predictions based on both the IPCC's A2 (slow economic growth) and B2 (moderate economic growth) scenarios, show it is likely that more extreme flood flows will increase significantly in size by 2080.

Over a year as a whole, water resources will not change much in Wales - though Southeast England could see a 25% reduction. What is important is that water managers will have to deal with an increase in "seasonality", by retaining more winter flows to see us through the summer.

Welsh Water is keeping a watching brief on this: forewarned is forearmed. But shelved plans to expand Elan Valley's Craig Goch reservoir could be revived to serve London and Southeast England.

From around 2040 summer low flows could be 10-20% lower and droughts could be more frequent and double in length beginning from around 2040. Inflows into reservoirs like Llyn Brianne and Crai in South Wales and Aberystwyth's Craig-y-Pistyll could fall by some 25% in summer. Pembrokeshire is more vulnerable: the shortfall in Preseli could be double this.

Even if Copenhagen produces a viable international agreement to limit temperature rise to 2C, Welsh water will be affected. For public water supply, the first strategy is to reduce demand, encourage water conservation, rainwater harvesting, etc. The second is to reduce leakage, followed by raising dams and modifying operating rules.

For floods, hard solutions like dykes can only do so much. They could be raised if society agrees to pay, but soft solutions may be more cost-effective, like improving early warning.

Only a small minority of rivers have warning systems based on computer models, or even simpler systems that use rainfall or riverflow at key locations as indicators of impending floods. The River Dee has all these available and a computer that telephones key sites automatically and warns Flood Officers if it predicts trouble.

The River Rheidol Hydroscheme has a simpler system using the Met Office's weather radar, and the energy company Eon is legally responsible for containing floods by releasing water from the reservoirs ahead of the storm.

The Environment Agency trialled a computerised telephone warning system in 1996 that telephones properties at risk. We need more of this type of approach.

Planting and preserving forests is the focus of numerous carbon-offset schemes. The Forestry Commission has just announced a plan to plant 23,000 hectares of forest annually over the next 40 years and identifies West Wales as a priority area because of the expected increase in severe rainstorms. How this is achieved needs careful consideration of the effects of water resources and river flows.

Trees may reduce flooding, but they also waste water. One engineer proposed that water companies should charge foresters for loss of resources.

The Centre for Ecology and Hydrology at Plynlimon has shown that Hafren Forest now reduces river flow in the Severn some 15% compared with the adjacent moorland catchment. Other research has associated flooding in Newtown with ditches cut to dry out the soil for tree planting. In 1990, the Forestry Commission produced new guidelines banning linking ditches to streams. It is important that private forestry companies follow the same guidelines.

Wales is better placed to cope than many parts of the world; sea level rise will not affect us like the Maldives, nor desertification like much of the Mediterranean.

But we will experience more extreme storms, floods and droughts, and we will need to adjust the management of our water resources to cope with drier summers. We also have the technical expertise to see us through.

But we are not alone, and the impacts on other parts of the world can affect us in many ways, from the food we eat to wars, migration and terrorism. A binding international climate change agreement is sorely needed.

Written by Tony Jones, Emeritus Professor of Hydrology and Water Resources at Aberystwyth University, and Chair of the IGU Commission for Water Sustainability.

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