Wastewater Forum Archive

WASTEWATER RESEARCH AND INDUSTRY SUPPORT FORUM

Report on a one-day MET Office conference 14th June 2001

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Climate Change and the Water Environment

Introduction
The Met Office hosted this conference for invited delegates to present the work of its dedicated climate division – the Hadley Centre - and to examine the key impacts of climate change in Britain on urban and rural flooding, water resources, asset management and aquatic environments.

The conference was organised in three elements. The morning was devoted primarily to presentations focussed on the science; the afternoon to three, brief, presentations on impacts followed by a workshop session with feedback.

This brief overview summarises the position with regard to temperature and rainfall and have largely ignored changes in CO2. This is simply because the focus of the Forum interest is on changes in patterns and intensity of rainfall and drought rather than the atmospheric drivers – interesting though they are.

Climate change -Science
The conference was opened by Dr John Murlis, EA Chief Scientist. He presented data evidencing climate change and also identified potential impacts. The following copies of some of the figures presented in the various presentations show both observed long term data and future projections.

The increase in global temperatures shown by this figure can be attributed to a combination of:-

• natural variability;
• volcanic and solar activity;
• human activity

Dr Geoff Jenkins (Hadley centre) later showed that temperature trends in the Northern Hemisphere over the 1 000 years 1000-1999 were downwards until 1950 with a significant upward rise in the last 50 years. This recent increase cannot be explained by natural variability (including solar/volcanic activity). The addition of human activity to natural variability gives good agreement. The 0.40C rise over the last 50 years is mainly due to human activity. The figure below shows the temperature rise in Central England over relative to the period 1772-1900. Note the rise in the later half of the 20th Century.

These two figures show the predictions for summer temperature increase °C and rainfall decrease (%) over the British Isles by 2050.

Note from these figures that, although overall rainfall shows little change over the total length of record, there have been significant changes in seasonal rainfall over the last 60 years. The following figure shows predicted changes (%) in UK Winter rainfall by the 2080’s.

Dr Jonathan Gregory (Hadley Centre) discussed the uncertainties in prediction. He attributed these to:-

• uncertainty in climate predictions due to natural variability;
• uncertainty in climate models.

The following figure illustrates the extent of uncertainty in predictions of summer rain shown on an earlier figure.

In summary:-

• Large natural variability of UK climate;
• Ongoing research leading to better prediction over next 5-10 years;
• Uncertainty in long-term climate change due to future greenhouse gas emissions and understanding and modelling of climate;
• Next challenge: quantify this uncertainty for risk assessment;
• Current uncertainty over magnitudes of uncertainty but no uncertainty about overall conclusions.

Climate change – Impacts
Professor Nigel Arnell (University of Southampton) talked about the impact of climate change on water resources. He quoted from the (soon to be published) Third Assessment report of the Intergovernmental Panel on Climate Change (IPCC):

• Most of the observed increase in global temperature over the last 50 years is due to human activities;
• We can see the impacts of climate change on some ecosystems and “hydrological” systems;
• It is difficult to see the effects of climate change on hydrology and water resources, for many reasons;
• Impacts of climate change depend on the degree of climate change and the way the system is managed: it is impossible to generalise;
• Efficient adaptation requires the use of flexible management techniques.

The conclusions were:

• Climate change is likely to have an observable effect on British river flows (and recharge) over the next few decades…along with other changes;
• We have much of the “technology” in place to estimate these potential effects, but need more work on the definition of scenarios;
• Efficient response to climate change needs adaptive management techniques and methods – including ways of estimating risk.

John Firth (Severn Trent Water) said that his company considered climate change to be “The most important environmental issue affecting the company” and saw particular impact on the urban drainage system (sewers and treatment plants) - “It’s not all about water resources!”

The potential impacts are seen as affecting customers, river water quality, and causing both operational and asset maintenance problems.

Customer impacts:

• Increased foul and surface water flooding of properties;
• Increased ‘floodcare’ payments;
• Increase in customer complaints;
• Blight and insurance;
• Increased OPEX and CAPEX.

Pollution impacts:

• Increased frequency of operation of CSO’s with increased volumes discharged;
• Increased build up of pollutants in (longer) dry spells with flush out from surface water sewers;
• Greater impact on watercourses – reduced flows and already under stress;
• Aesthetic concerns;
• Increased OPEX and CAPEX

Severn Trent carried out a research project with the Met Office to examine the changes in frequency and intensity of short period rainfall events. The results from that project were:

• Climate models simulated short period rainfall;
• No significant trend in hourly data;
• Possible to establish relationships between different durations of extreme rainfall;
• The frequency of extreme rainfall events is expected to increase;
• 1 hour rainfall amounts for return periods of 2-50 years are typically 20-40% higher by 2080;
• 1 hour rainfall amounts for return periods of 2 to 5 years are predicted to increase by – 15-20% by 2020, 20-25% by 2050, and 25-35% by 2080.

Subsequently, the recently established UKWIR project on Climate change and the design of sewerage systems was outlined. The project involves HR Wallingford, Met Office, Montgomery Watson and Imperial College. The project objectives include:

• the application of similar methods used for Severn Trent, but across the whole of the UK and up to the end of the 21st Century;
• Duration range 15 mins to 12 hours;
• Return period range 1 year to 100 years;
• Identify changes to rainfall patterns across UK between FSR and FEH;
• Generate revised rainfall sequences and storm profiles;
• · Identify whether recent designs are adequate for the future.