Analysing the impact of climate change and land-use change on the water quality of the River Thames

Dr Gianbattista Bussi, Postdoctoral Research Assistant, and Prof Simon Dadson, Associate Professor in Physical Geography, present the results of the POLLCurb project.

Human activities can cause changes in climate and land cover, which affect the water cycle and the water quality of rivers and lakes. These drivers of change, coupled with natural climate variability, lead to alterations in water quality that can have strong repercussions on water supply, ecosystems, navigation, conservation and recreational uses of water.
The River Thames, in Southern England, is a prime example of a river subject to strong human pressure. It is the main source of drinking water for around 14 million people and the recipient of the effluent for around 3 million people. It is also of very high conservation and recreational value for local communities.

In order to study the impact of land-use and land-cover changes over river water quality under a changing climate, the Natural Environment Research Council funded the POLLCurb project (Changes in Urbanisation and its Effects on Water Quantity and Quality from Local to Regional Scale), as part of the Changing Water Cycle programme. The project, which ended in September 2016, was led by the Centre for Ecology and Hydrology in Wallingford and was carried out jointly with the University of Oxford, the University of Bath and the University of Surrey.

As part of the project, Dr Gianbattista Bussi and Prof Simon Dadson, of Oxford University’s School of Geography and the Environment, analysed the joint impact of climate and land-use changes on the sediment transport and water quality at the scale of the River Thames catchment.

The research provided great insights into the sediment dynamic of the River Thames. Sediment dynamics of lowland rivers like the Thames are of vital importance in building resilient strategies to manage environmental change.

The project described the seasonal and inter-annual variability of suspended sediment concentration in Thames, by analysing long-term, intermittent records collected by the Environment Agency since 1974. In particular, the flushing effect, i.e. the increase in sediment load that takes place with the first floods after a dry period, was quantified. This is responsible for increasing the sediment concentration of the Thames by 1.5 – 2 times. A decrease in the flushing effect which began in the 1990s was also observed.

Furthermore, the joint impact of climate change and changes in the extension of arable land was analysed by using a mathematical model called INCA (INtegrated CAtchment model). The results showed that climate and land cover each exert an individual control on sediment transport. The suspended sediment yield of the River Thames is expected to decrease by 4% by the 2030s, although this figure will be strongly affected by the future variations of extreme precipitation and future agricultural practices.

Lastly, the impact of climate change, land management change and waste water treatment strategies on the nutrients and phytoplankton of the river Thames was also assessed. Phytoplankton pose a serious threat to the use of surface waters for water supply purposes. In this project, a river phytoplankton model was employed to evaluate the effects of climate alterations on flow, phosphorus concentration and phytoplankton concentration of the River Thames.

The model demonstrated that an increase in average phytoplankton concentration, especially potentially harmful Cyanobacteria, is highly likely to occur due to climate change. However, an optimal mitigation strategy, which combines reduction of fertiliser and phosphorus removal from wastewater, can help to reduce the phytoplankton concentration, and in some cases, compensate for the effect of rising temperature.

Find out more:

Water use in China’s thermoelectric power sector

New research from Oxford University’s Environmental Change Institute sheds light on China’s water-for-power nexus. Lead author, DPhil student Xiawei Liao, provides an overview of the challenges and trade-offs facing the Chinese energy sector.

Despite being historically managed in isolation, water and energy are two closely interlinked resources. For thermoelectric power plants, water is critical for power production, providing both steam and cooling. Water shortages have caused power curtailments at a number of thermoelectric power plants around the world (Byers et al., 2014), highlighting the critical nature of the water-for-energy nexus, and bringing it to the fore of science and policy debates.

In China, the relationship between water and electricity is a particularly pressing concern. The country is heavily reliant on thermoelectric power, with many plants drawing water from inland waterways vulnerable to water shortages. The vast majority these plants are coal-fired, with coal accounting for over 75% of China’s electricity production (National Statistics Bureau, 2014).

Cooling technology is the key determinant of a coal-fired power plant’s water intensity, defined as water use per unit of electricity produced (Macknick et al., 2012). Water use comprises both water withdrawal and consumption, with water consumption defined as water which is withdrawn from, but not returned to, water bodies (AQUASTAT, 1998).

There are three main types of cooling technology: open-loop, closed-loop and air cooling: the first dissipates heat using running water; the second by recirculating water; while third employs air circulation. Consumptive water use in an open-loop system is around 70–80% lower than a closed-loop cooling system, but the water withdrawal is around 30–60 times higher (WRI, 2015).

Our research, recently published in Global Environmental Change, first quantified the current water use of China’s coal-fired power plants, using plant-level data. We identified two major hot spots for surface water consumption: the Yellow River basin in eastern China, and the Yangtze River basin in southwestern China. Groundwater abstraction for power generation was outlawed in water-stressed Northern China in 2004, but continues to be heavily abstracted, particularly around the North China Plain (Huang-Huai-Hai basin). Reclaimed water is also used in water-scarce North Eastern China, but accounts for a smaller portion of water use overall. In 2014, Chinese coal-fired plants used 0.79 billion m3 of reclaimed water compared to 4.64 and 1.05 billion m3 for surface water and groundwater respectively.


Fig. 1 Water consumption of coal-fired power generation by source.

In order to avoid unsustainable future investments and technology lock-ins, our research also investigated future water use scenarios for China’s thermoelectric power sector.


Fig.2 Annual fresh water withdrawal (left) and consumption (right) by China’s thermoelectric power sector under different scenarios (billion m3).

If no new policies are implemented, China’s demand for water-for-energy – both withdrawn and consumed – is projected to increase to over 280 and 16 billion m3 respectively by 2050; this greatly exceeds the current volumes of 65.2 and 4.64 billion m3 currently used.

Improving energy efficiency, or shifting energy infrastructure to renewable, or low-carbon sources offers scope to reduce water withdrawal by over 50%. Under high-renewable and low-carbon scenarios, concentrated solar power and inland nuclear power would replace coal-fired power as the primary fresh water users. Replacing open-loop with closed-loop cooling systems in the south, and closed-loop cooling systems in the north with air-cooled systems, has potential to cut the power sector’s water withdrawal significantly. However, it may increase water consumption, particularly in the east and central China. While water withdrawal poses less threat to water availability for downstream users, it may cause thermal pollution to the water bodies. Trade-offs between water withdrawal and consumption need to be made.

At a regional level, central and eastern China withdraw the great volume of water for power generation due to the prevalence of open-loop cooling systems. In 2011, China issued its ‘most stringent water policy’ – ‘3 Red Lines’ – setting targets for total water use on a national as well as a regional scale for 2015, 2020 and 2030. Qin et al. (2015) showed that the water use of China’s power sector is likely to exceed its allowances under the ‘3 Red Line’ policy in 2035 on a national scale. Furthermore, we find that the power sector’s water use in the east will exceed its regional quota under all scenarios, unless steps to change cooling technology are taken. The above-mentioned policy is also likely to be violated in central and north China if the business carries as usual.


Fig. 3 Comparison between regional water demands by power sector with water targets set by the ‘3 Red Lines’ policy in 2030. (W-Fresh water withdrawal in 2030; C-Fresh water consumption in 2030; B-Baseline Scenario; HE-High Efficiency Scenario; HR-High Renewable Scenario; LC-Low Carbon Scenario; TC-Technology Change Scenario; IWA-Industrial Water Allowed).

Finally, Chinese electricity generation, and associated water demand, both peak in winter when water availability is especially low. This increases the potential for conflict during this period. In the context of a changing climate, the tension between water demand for power generation is unlikely to decrease. Institutional change and improved policy coherence is required to meet this challenge. The old paradigm, where each sector operated independently, uninformed and unconcerned about its impacts on the others, is no longer sustainable. China must transition to a new paradigm – one embracing a ‘system-of-systems’ approach.

Xiawei Liao is a DPhil student at the Environmental Change Institute supervised by Prof Jim Hall and Prof Nick Ayre. You can find out more about this research in Liao, X., Hall, J.W., Eyre, N. Water use in China’s thermoelectric power sector, Global Environmental Change, Volume 41, November 2016, Pages 142-152.



A framework for drought economics

An economic assessment of drought impacts demands an analytical framework which reflects the unique characteristics of this natural hazard.

New research by the Oxford-led MaRIUS project has developed an innovative framework for drought economics. The framework, which is outlined in a recent paper published in Ecological Economics entitled “The Economic Impacts of Droughts: A Framework for Analysis”, is the result of a collaboration between Dr Jaume Freire González, formerly of Oxford University’s Environmental Change Institute (ECI) and now a researcher at Harvard, Dr Chris Decker, an economist at Oxford’s Centre of Socio-Legal Studies, and Professor Jim Hall, ECI Director and MaRIUS lead.

The research is a key output of the economics work of the MaRIUS (Managing the risks, impacts and uncertainties of droughts and water scarcity) project, which seeks to develop a risk-based approach to decision-making around drought and water scarcity.

The paper argues that, in economic terms, droughts are a specific type of natural hazard, and failure to appreciate the differentiating characteristics of drought can lead to biased estimates of impacts, and poor short-term and long-term management practices.

The authors argue that traditional conceptual frameworks used to assess natural hazards do not adequately capture all of the factors that contribute to the economic impacts of droughts, such as the importance of the level, and composition, of hydraulic capital; the dispersion of economic impacts across different economic activities and agents; the temporality of drought events; and the critical importance of policy-making in shaping the short and long-term economic impacts of droughts. Traditional frameworks also fail to take account of the complex interaction between factors within the domain of decision-making, as well as underlying climate conditions.

The authors propose a new conceptual framework which distinguishes between ‘green’ and ‘blue’ water – the two primary sources of drought-induced economic impact. Green water describes water stored in the top layer of soil and vegetation, while blue water comprises fresh surface water and groundwater. The economic impact of a green and blue water drought is manifest via different mechanisms. Green water availability is largely determined by environmental conditions, particularly climate. The economic impact of a green water drought is felt foremost by the agricultural sector, particularly those reliant on rainfed production. Economic impacts arising from the initial phase of a drought are usually limited to those sectors reliant on green water.

Blue water impacts of drought arise from long-term choices about the water storage, interconnection and production capacity (i.e. hydraulic capital) as well as short-term management decisions regarding the timing, severity and allocation of water restrictions applied to different users.

The new framework provides insights on the drought management policies in the short and long term, and the economic consequences of different actions. By highlighting the trade-offs and choices involved in decision-making, the MaRIUS project hopes this framework will be able to assist policy-makers, regulators, water companies, water users and other stakeholders in managing and responding to drought over the short and long-term.

Citation: Freire-González, J., Decker, C., & Hall, J. W. (2017). The Economic Impacts of Droughts: A Framework for Analysis. Ecological Economics, 132, 196-204.

MaRIUS 2016 Drought Symposium presentations now online

The MaRIUS project hosted its third, annual, international Drought Symposium in Oxford in September. The event was a great success with over 90 attendees from a range of backgrounds.

The Symposium focused on aspects of drought science and drought management, both in the UK and globally. There were presentations and posted from a wide range of drought and water scarcity practitioners, from academia, industry and regulation.

The Symposium focused both on issues in the UK and also across the world, from an impressive array of international speakers who examined the situation in Australia, Europe and America.

Most of the presentations are now available to download as pdf slides from the project website.

Podcasts will be made from some of the talks and these will also be made available (soon hopefully) at the same page.

The speakers and titles of the presentations are as follows:

  • Doug Hunt, Atkins: Water Resource Management in the UK
  • Ian Pemberton, Ofwat: “Moving to a national approach to water management”
  • Mike Morecroft, Natural England: “Effects of drought on UK ecosystems and the implications for nature conservation in a changing climate”
  • Gianba Bussi, University of Oxford: “The impact of droughts on the water quality of the River Thames”
  • Sarah Whatmore and Catharina Landstrom, University of Oxford: “Co-producing knowledge for local drought resilience”
  • Gemma Coxon, University of Bristol: “Drought hydrology on a national scale”
  • Kevin Grecksch, University of Oxford: “Drought Management Practice in the UK – Opportunities to Overcome Innovative Scarcity”
  • Dustin Garrick, University of Oxford: “Transboundary Rivers and Adaptation to Climate Extremes (TRACE): Learning from Severe Droughts”
  • Henny van Lanen, Wageningen University, Netherlands: “Drought indicators – their usefulness for the assessment of drought types, impacts and management”
  • Lee Godden, University of Melbourne, Australia: “Water law and drought in Australia”

Innovation recognized in national flood risk management and modelling competition

Defra awards proposal to tackle flood risk in Cumbria led by Oxford fellow.

A team led by Oxford flood expert Paul Sayers received an innovation prize as part of Defra’s (Department for Environment Food & Rural Affairs) Flood Modelling Competition.

The submission entitled ‘Towards a flood resilient Eden catchment, Cumbria’, developed in collaboration with Horritt Consulting, was among a number of entries recognised for their innovation, with a proposal from JBA Consulting and Lancaster University taking the overall prize.

Defra launched the competition in response to the government’s National Flood Resilience Review that highlighted potential approaches to flood risk, including new techniques and models to assess land use, water flow, natural flood management, meteorological sensitivities, property-level resilience and economic impacts.

The competition – the first of its kind – drew entries from leading groups around the world, all seeking to apply their expertise to the following question:

“If you were responsible for managing the Eden catchment in Cumbria, what  flood risk management approaches would you recommend, and why?”

The Sayers and Horritt submission used the Future Flood Explorer – a model they originally developed to support the UK Climate Change Risk Assessment that uses local model results to support an emulation of the flood risk system (Sayers et al, 2015) – to quantify present and future risks in the catchment and how successful alternative adaptation measures could be in managing it.

The analysis, for the first time, attributed benefits to individual measures when implemented as a broader portfolio response: from natural flood management to traditional defences; from property level measures to flood forecasting and warning.

Paul, a Senior Visiting Fellow at Oxford University’s Environmental Change Institute (ECI) and founder of environmental consultancy Sayers and Partners, noted during the award ceremony that:

‘”Resilience to flooding”’ is not the same as being ‘defended from flooding’. It does mean however using a portfolio of responses to reduce the probability of a flood occurring, limit the exposure should a flood occur and reduce the vulnerability of those that are exposed. A critical barrier to progress in delivering such a portfolio is the lack of credible decision-relevant evidence. This lack of evidence in part reflects the short-comings of traditional modelling approaches that are often too computationally intensive to explore multiple futures and responses at a catchment scale. 

We’ve developed the Future Flood Explorer to fill this evidence gap – the FFE allows us quickly to explore the effectiveness of flood management measures across the whole catchment both now and in the future, under both climate change and population growth scenarios. We can also use the FFE to explore which measures are most effective at managing future risk.’ 

Dr Thérèse Coffey MP, Parliamentary Under-Secretary, Department for Environment, Food and Rural Affairs, herself an Oxford alumnus, hosted the ceremony and remarked at its success. The prize fund was generously supported by United Utilities, Aviva and the Natural Environment Research Council (NERC).

A summary of the submission is available here. If you would like find out more, you can contact Paul directly at