Distinctive Group

One of the most comprehensive reviews into the science of drought in the UK is now complete. The UK Centre for Ecology & Hydrology (UKCEH) was a major contributor to the report, which will help prioritise future research and management efforts. Hydrologist Jamie Hannaford chats to Water Industry Journal about its significance.

The ‘Review of the research and scientific understanding of drought’ focuses on three themes: the physical processes driving droughts, the impacts of droughts and the management of droughts.

Each theme is further divided into specialist topics, providing an expert review of a specialist area.

What was UKCEH’s primary role in the review?

The Environment Agency commissioned experts from 13 different universities, consultancies and research institutes including the UK Centre for Ecology & Hydrology (UKCEH) to produce the report. Some 20 of the 40 experts who took part were from UKCEH.

Our scientists led the reviews on:

  • past river flow drought trends
  • future river flow projections
  • impacts of drought on water quality
  • impacts of drought on vegetation.

UKCEH also contributed to the review of drought impacts on soils, led by British Geological Survey.

Were you looking at certain timeframes in respect of trends and projections?

The report is primarily a review, so draws from existing published research. Most studies of past trends tend to focus on the last 50 to 60 years (the period of record of most hydrological observations). We did carry out an analysis of trends in seasonal river flows and indicators of extreme low flows, which was focused on the 1965-2021 period. We also took a longer view by using reconstructed datasets which have records of over 120 years.

To answer the question of whether droughts will get more severe in the future, the review draws together many different sets of future projections, but typically these are for the 21st century.

As a general overview, what does the team already know about UK drought patterns and their current / future impact?

For the river flow indicators we assessed, there was a general pattern of increasing flows in northern and western Britain, and a mixed picture in the English lowlands. On rivers within more ‘natural catchments’ i.e. with little human influence, there is a more obvious shift towards lower flows.

Similarly, seasonal patterns generally show consistent increases in autumn and winter, and decreases in spring, and a contrast for summer between increases in the north/west, and a mixed pattern but with some significant decreases in the south.

UKCEH analysis – using the latest Met Office climate projections in order to model future river flows and groundwater levels up to 2080 – shows the UK will see significant increases in the severity of droughts over the coming century.

However, there are still large uncertainties over predictions about future drought events, and how hydrological conditions may vary between regions.

What was UKCEH’s most striking finding for this research?

There are obviously many different headline findings across the different chapters, as it is a very broad topic!

One of the most striking findings from the review of the climatology/hydrology of drought is the apparent disconnect between past trends (which generally show little compelling evidence towards lower river flows or increasing drought severity) and projections for the relatively near future (which all point towards diminishing low flows and worsening droughts).

This presents a challenge for policymakers and decision-makers: should we put more emphasis on observed past trends or highly uncertain future projections?

Unpacking this apparent lack of congruency is an important topic for future research, and necessary to underpin improved long-term drought planning. However, in the meantime, it’s worth underlining that this disagreement does not in any way rule out a role for climate change in impacting droughts – the signal of climate warming is relatively weak and can be obscured by high year-to-year and decade-to-decade variability. The occurrence of droughts, and trends in drought, reflect both underlying warming and climate variability, and it remains a challenge to disentangle them.

Why is the concept of drought in the UK so poorly understood?

Firstly, the UK is, famously, a wet country, and flooding has been very much in the public eye in recent years. Given this, it can be hard to relate to drought as a hazard in the UK, and for many people drought may be more readily associated with much drier parts of the world. However, droughts are a feature of all climate zones, including temperate, maritime environments like the conditions we experience in the UK.

This is because drought is a relative phenomenon. There are numerous definitions of the term ‘drought’, but common to all of them is the fact that there is a significant reduction in precipitation compared to the ‘normal’ conditions for the time of year at that location, sufficient to cause a serious hydrological imbalance.

Furthermore, it can be hard to pin down the onset, duration and termination of a drought event, so it can be difficult to quantify its severity or duration. The infrequency of droughts also means there is limited data and experience of them, which limits society’s ability to predict, prepare and respond.

How quickly is the science catching up?

While the concept of drought in the UK can be difficult to engage with for some, and drought sometimes being seen as a lower priority hazard than flooding, it is clear from the 700-page report that there has been substantial investment in understanding the science of drought.

We do know a lot about drought in the UK, how it has changed in the past and how it is likely to change in future, and we have some understanding of many of the kinds of impacts we are likely to experience during droughts. That said, there are many uncertainties and gaps in our understanding, as highlighted in the reports.

There is a substantial and growing scientific evidence on characterising and quantifying drought risk through drought indicators and indices. A drought indicator can be used to characterise drought, whereas drought index is normally a numerical representation of drought severity for a given indicator. Over the last decade or so, drought indicators have been widely used to assess drought status, or to identify droughts in past hydrological records or future hydrological projections.

Reconciling past observations and future projections remains a key scientific challenge. A priority will be better understanding the past causes of changes in catchments, both climate- and human-driven, and quantifying their relative roles. This will require integration of field observation with climate and hydrological modelling, as well as further statistical and large-sample hydrological approaches. This work is critically dependent on observational datasets.

There have been efforts to improve the observational evidence base: for example, the UK Benchmark Network (UKBN) comprises a subset of gauging stations from the national hydrometric network that are most suited for identification and interpretation of long-term hydrological variability and change. However, major barriers remain, not least information about how human activities (e.g. water withdrawals, land use/cover change) influence droughts, but initiatives are under way to overcome them to provide improved foundations for future studies.

What web-based tools have UKCEH produced to inform decision-making?

Using a wealth of historic and current data, plus the latest weather forecasts and climate models, UKCEH has produced a number of tools that provide information on the past, present or projected hydrological situation in the UK. These enable water companies, regulators and government agencies to better prepare for future droughts in the coming weeks, months, years and decades.

They include:

  • The UK Water Resources Portal brings together a wealth of information on the latest hydrological situation across the UK. It provides the most up-to-date available data on river flows, rainfall, soil moisture and groundwater levels from a local to a national scale, with users able to view measurements in any part of the country by clicking on an interactive map. It has historical data, going back around 50 years for river flows and 100 years for rainfall data.
  • UKCEH Hydrological Outlooks Portal allows users to explore the hydrological forecasts for the next one to three months.
  • Enhanced Future Flows and Groundwater (eFLaG) tool provides projections for rainfall, river flows and groundwater levels in the UK up to the year 2080.
  • The Climate Change Impacts tool provides estimates of the impacts of different climate warming scenarios on river flood peaks across Great Britain up until the 2080s.

What new measurements are included in the FDRI programme?

The national Floods and Droughts Research Infrastructure (FDRI) programme, led by UKCEH and funded by UKRI, will produce extensive new measurements of the whole hydrological cycle (e.g. weather, groundwater, river flow, water quality, land-surface exchange and soils) in several catchments across the country.

Implementation of the infrastructure beings in 2024 aiming to be fully operational by 2028.

This will enable researchers to improve computer models to predict when and where floods and droughts will happen, and their severity. It will comprise a combination of fixed instruments and mobile equipment, such as drones to monitor river flows, which can be deployed to different areas at times of floods and droughts.

Did UKCEH have any input from UK water utilities or regulators for this review?

In addition to their individual reviews, the report authors were joined by representatives from the Environment Agency and UK water companies. This provided an opportunity for the authors to share their work and to ask questions of each other. The group was able to debate both what is known about drought, and the gaps in understanding, both current and future. This report summarises the main themes and findings.

At UKCEH, we integrate water resources monitoring and modelling to enable the water industry, government departments and public bodies to assess and mitigate the impacts of future droughts. Our research identifies environmentally sustainable solutions that meet the increasing, and often competing, demands of users in different sectors, including public water supply, agriculture and food, commerce and industry, and energy.

For example, UKCEH has worked closely with water companies and regulators to deliver new datasets in a way that meets the needs of the sector, including the UK Water Resources Portal and the eFLaG open dataset and related portal, that allows users to access, explore and download these key datasets in user-friendly formats.

Overall, what is the importance of the review – is it definitive in shaping the future of water management in the UK. Or is this just the start?

This is the most comprehensive review of research into drought including its impacts on people and the environment that has been carried out in the UK, and possibly the world.

While there have been reviews of the state of the art in drought, these have never been of the magnitude represented here, nor looked at drought from such a different range of sectoral and disciplinary perspectives. It has drawn together and consolidated the current body of knowledge on drought and highlighted the gaps in our understanding.

As for whether it is definitive, or just the start, that is a big question! The report is certainly very comprehensive and allows us to see the implications of drought on the management of water resources and is important for water companies, water users and regulators. The identification of knowledge gaps also provides a way forward for future research in the area.

However, in many ways it is just a start, as while the review has answered many questions through synthesising this vast knowledge base, it has also opened up many new ones.

The EA is certainly using the report to help shape the future research landscape around drought, and it has also been highly influential for the water industry. It will also help shape the research agenda of the various academic institutions participating.

Here at UKCEH we are using the report’s findings to influence the direction of various ongoing research programmes focused on drought, as discussed below. For example, the review highlights a lack of progress on linking drought indicators through to impacts on people and the environment, and this is something we are actively working on under the project IRIS (details below).

Anything else you’d like to add about your research’s future direction.

We are using the drought review to help shape the direction of research in several drought-related projects and programmes, including:

  • CANARI: we will be delivering new projections of future drought risk for the UK, including tools for better integration of past observations and future projections, as well as understanding the North Atlantic and Arctic drivers of extreme UK droughts.
  • HydroJULES: we are developing integrated climate services to help drought and water resource managers, including platforms for analysis and visualisation of changing drought risk, as well as hydrological status and forecasting tools.
  • IRIS: we are linking drought indicators to ‘on the ground’ impacts on society and the environment, to develop ‘impact-based forecasts’ of drought.

The full report is available at