A Nationally Consistent Approach to Assessing Accumulated Rainfall Rarity

Accumulated rainfall totals are an important variable for a range of hydrological applications, including monitoring and forecasting, and long-term planning. A new report has been published which identifies the most appropriate, nationally consistent approach to quantifying return periods of long duration rainfall.

A comparison of the suitability of nine distribution families for estimating the relative rarity of accumulated rainfall periods across the UK provides opportunities to further improve the accuracy of return period estimation in many areas such as the water resource planning and the Hydrological Summary for the UK, and elsewhere.

Whilst distribution families that are commonly applied in extreme value estimation, such as the generalised extreme value, were demonstrated to be suitable in a lot of cases, overall Pearson Type III outperformed all other assessed distributions. Closer inspection of the performance on accumulation periods of 12 months or less provided further support for the suitability of Pearson Type III, as did the strong performance of Pearson Type III across accumulation periods, start months and regions.

Presentation of return level plots for two potentially appropriate distribution families demonstrated the sensitivity of return period estimates to distribution family, and thus the importance of this question. With this in mind, the approaches presented in Eastman et. al. (2021) provide opportunities to further improve the accuracy of return period estimation and uncertainty quantification.

The full report is now available

Figure 1 Northumbrian 12-month accumulation period beginning in October: return period plots for The Pearson Type III (pe3) and Generalised Extreme Value (GEV) distributions, with associated 95% confidence interval bands, and highlighted return periods corresponding to 48.09, 45.83, and 44.56 mm of rainfall per month. Points correspond to the Weibull plotting positions of the observed rainfall accumulation data.

REF: Eastman, MichaelParry, SimonSvensson, CeciliaHannaford, Jamie. 2021. A nationally consistent approach to assessing accumulated rainfall rarity. Wallingford, UK Centre for Ecology & Hydrology, 42pp.

Far reaching influence of MaRIUS research into water risks

By Dr Helen Gavin, Project Manager for MaRIUS

Research from the MaRIUS project is widely recognised as having transformed how water risks are managed by the Government, water suppliers and regulators.

MaRIUS (Managing the risks, impacts and uncertainties of droughts and water scarcity) developed the first national-scale water resource model for England and Wales, triggering a transition in government policy and industry practice. Between 2014 and 2020 MaRIUS research involved new theory, the creation of new datasets and models, validation and demonstration in case studies of how the risk of droughts can be assessed and better managed through system modelling and ‘outcomes-based’ approaches to decision making. To date, four major reports have drawn on its work: ‘Water UK Long Term Planning Framework (2016); the National Infrastructure Commission’s ‘Preparing for a drier future, England’s water infrastructure needs’ (2018); the Committee on Climate Change’s CCRA3 Water Availability study (2018-19) and the Environment Agency’s report ‘Meeting our Future Water Needs: A National Framework for Water Resources’ (2020).

Prof Jim Hall, Principal Investigator (PI) of MaRIUS and Professor of Climate and Environmental Risks at the University of Oxford, is a member of the Prime Minister’s Council of Science and Technology and an Expert Advisor to the National Infrastructure Commission. The project was based at the Environmental Change Institute in Oxford.

“Our research has caused a transition in government policy and industry practice for water resource management in England. It has shown how drought risks can be assessed and better managed through system modelling and ‘outcomes-based’ approaches to decision making.

“We have achieved a significant shift in thinking and practice by the regulators, through interaction over eight years with water companies, the Environment Agency, Ofwat, Defra and the National Infrastructure Commission.”

Professor Jim Hall, University of Oxford

The increasing frequency of droughts and water scarcity in our warming climate, combined with our growing population and increasing demands for supply present huge challenges for national and local government, water suppliers, energy, agriculture, infrastructure, industry and communities.

MaRIUS’s work has provided conceptual frameworks and methodologies that have enabled government and its agencies to address these challenges and has provided data, systems models and other evidence that are transforming policy and practice. The new water resource system simulation model integrates public water supplies with use of water in agriculture, power generation and other industries. It has been used to explore different future scenarios of drought and assess the frequency, duration and severity of water shortages now and in the future. Tools have been developed to explore trade-offs between different aspects of risk and the cost of alternative management plans.

Key to the take-up of MaRIUS’s research was a series of well-managed and effective workshops where potential users sat down with the leading researchers to explore datasets, models and tools in development, sharing their real-world decision-making and communications processes.

“We are continuing to work very closely with the Environment Agency and Ofwat, at their request. We are undertaking joint resilience assessments and exploring the impacts on water resources. We continue to train Environment Agency staff on our model and will transfer this tool to them as they wish to use it to fulfil their regulatory responsibilities.”

Professor Jim Hall, University of Oxford

Groundwater management during droughts and future prospects

A new publication has been released today which explores how our essential groundwater resources are managed during droughts, and against a backdrop of environmental change, what future priorities should be.

The work reports the outputs from a meeting over 50 hydrogeologists from water companies, regulators, consultancies and academia that was held by About Drought in July 2019 in Birmingham. The aim of the meeting was to consider current groundwater drought management practices and identity research needs.

Four key themes are discussed throughout the paper:

  • Joined up definitions of drought
  • Enhanced monitoring
  • Improved modelling of groundwater during droughts
  • Better information sharing

“Managing groundwater supplies subject to drought: perspectives on current status and future priorities from England (UK)” has been published in Hydrogeology Journal and is available to all now.

A Water Strategy for UK Agriculture

Increasing the farming sector’s resilience to drought and water scarcity risks

Water is at the heart of farming and agri-businesses, particularly in eastern England, the east midlands, and south-east, the driest and most water-stressed areas in the UK. Without water most agri-businesses would simply not survive. Irrigated agriculture supplies the UK’s agri-food industry with substantial quantities of high-quality potatoes, fruit and vegetables. But increasing regulation, droughts and a changing climate all threaten the sustainability of this industry and the rural livelihoods it supports. While other sectors and businesses have water strategies, the agriculture sector does need. Agriculture therefore needs a water strategy to ensure that it receives a fair share of the nation’s available water resources.

To address this need researchers at Cranfield University have been working in partnership with the National Farmers Union (NFU), the UK Irrigation Association (UKIA) and other stakeholders to develop a collective vision. The strategy sets out some guiding principles and proposes actions grouped according to the following themes:

  • Manage current and future demand in abstraction ‘hotspots’
  • Address environmental challenges linked to over-abstraction and climate change
  • Build water infrastructure to provide resilience for farming businesses
  • Promote business growth and support multi-sector stakeholder engagement