Making Groundwater visible: Drought in England and Wales and the role of Groundwater
Drought occurs when a water shortage is severe enough to cause real hardship or consequences.
One of the most significant impacts of climate breakdown we are seeing today is the increased volatility of our weather. Records are being broken on all fronts, and we are facing increasing flood and drought extremes.
In this blog, I will suggest ways to understand better the role of groundwater in drought and the implications for how we predict and manage water resources.
What do we mean by drought?
Traditionally, the concept of drought is related to a certain number of days without rainfall, but more recently, regulatory bodies such as the Environment Agency (EA) have been monitoring various indicators (such as rainfall, river flows, groundwater levels, reservoir storage, ecology and public water supplies) and are deciding the level of drought based on more of a ‘balanced scorecard’ approach.
They use four stages to describe and manage their response:
- Prolonged dry weather
- Drought
- Severe drought
- Recovering from drought
The drought update from the Environment Agency on 4th September 2026 showed that 71% of England was officially in drought after record low rainfall and exceptionally high temperatures.
The EA defines the types of drought as follows:
- Agricultural drought – when there isn’t enough rainfall and moisture in soils to support crop production or farming practices such as spray irrigation.
- Environmental drought – when lack of rainfall has a detrimental impact on the environment and ecology.
- Water supply drought – when lack of rainfall leads to concerns from water companies about supplies for their customers.
These definitions focus on where the impact occurs, but the surface and subsurface conditions for each type are very different, so there is also merit in focusing on what source of water we are short of. A more useful analysis is achieved by considering soils, groundwater and surface water as three separate, connected but highly independent systems.
Therefore, I suggest it is useful to distinguish between:
- Meteorological drought, which has the soonest direct impact on soils and growing conditions for plants and wildlife.
- Surface water drought, which results in insufficient water in rivers and lakes to meet normal needs.
- Groundwater drought, which results in a reduction in baseflows in rivers and problems maintaining normal abstractions for water supply.
The role of groundwater in drought
This approach reveals that we are suffering from serious and widespread meteorological and surface water drought, but in most parts of the country we have groundwater levels close to normal due to good recharge and replenishment of our aquifers last winter. This contrasts with the situation experienced in 1976, when dry conditions the previous winter led to extremely low groundwater levels.
Considering groundwater separately helps demonstrate that this year in many places, groundwater resources are helping us compensate for the meteorological and surface water drought conditions, enabling us to consider more long-term effects. We have not experienced a national groundwater drought this year; however, groundwater has been a critical resource. Increased abstraction has met some of the increased demand during the periods of meteorological and surface water drought.
Why winter rainfall matters for groundwater
Groundwater is our largest freshwater resource, but serious summer drought has not been a groundwater issue so much as a groundwater solution. It is important to make groundwater visible because storage varies seasonally and can become seriously depleted if resources are not managed longer term. In particular, it is important to look at what may happen next summer.
Groundwater is what keeps the rivers flowing between rainfall events by providing base flow from aquifers. Flows recede slowly over many weeks as groundwater levels fall due to lack of rainfall to recharge them. In fact, it is not rainfall as such but ‘effective rainfall’ that counts (effective rainfall is how much rainfall is left after evapotranspiration). The indicative graph below shows that effective rainfall is expected to be low in the summer, so a shortage of rainfall has the least effect on groundwater recharge if it happens in the summer:
The graph below shows the typical long-term average recharge rates for the Thames basin, illustrating the typical seasonal distribution of groundwater recharge in the Chalk, our main aquifer in Britain (derived from Mansour M M, Hughes A G. 2017. Summary of results for national scale recharge modelling under conditions of predicted climate change. British Geological Survey Commissioned Report, OR/17/026). Clearly, it will be winter rainfall that has the most effect on groundwater:
The main groundwater recharge season is between November and March. With only around 6% of the recharge on average occurring during May to August, you can see that this summer drought can only have had very limited effect on groundwater. By contrast, with about 71% of the recharge usually expected during December to March, even losing one month of recharge during this period could have three times the impact of a drought lasting all four summer months.
Lessons from the 1976 drought
To contrast this with 1975, winter rainfall was the lowest recorded since 1879/80 at 50% of the average for November-April (Rodda & Marsh, 2011), and this low rainfall meant an 80% reduction in recharge. Comparing rainfall totals, March to August 1976 experienced just 52% of average rainfall for that period, whereas March to August this year experienced 67% of the long-term average. Our summer drought was so severe, particularly due to July rainfall only achieving 10% of the average for that month, and the reason this did not affect groundwater too much was that we typically only expect 0.7% of our annual groundwater recharge that month.
The longer-term seasonal storage gives groundwater a vital role in our water supplies and in sustaining our water habitats and ecology, and abstraction also helps mitigate groundwater flood risk as well as provide our largest national freshwater resource.
Looking ahead: what happens this winter?
Looking ahead to the winter, it is illustrative to recall 2023, when October rainfall led to some of the most rapid groundwater rises on record. As we reported at that time, this transformed groundwater conditions from below average to exceptionally high, leading to groundwater flood risk as seen in our forecast below for Chalton on the South Downs:
The critical question for our water resources, flood risk and drought vulnerability next year will be: “What will happen to groundwater recharge this winter?” Given a super El Niño on top of our rapidly changing climate, both flood and drought risk deserve increased attention for hydrogeologists this year. Making groundwater visible and remembering “a flood is a resource in the wrong place” can help give England a stronger foundation for future water resources planning and flood resilience.
Bio Note
Mark is a groundwater scientist, hydrologist and Chartered Geologist and the founder and Chief Executive of GeoSmart Information, a flood and climate risk data and analytics specialist based in Shrewsbury. Mark has been working on catchment problems for over 39 years and specialises in flood risk assessment and management, particularly on the role of groundwater and associated drought and water resources in a rapidly changing climate.
GeoSmart publishes flood risk maps and data and applies machine learning coupled with groundwater and surface water models to predict groundwater, surface water and river flooding and drought likelihood and to forecast water resources, sewer and drain infiltration and CSO spills.
