Water companies are required to publish drought plans every 5 years. In this they set out what they will do under a set of different drought scenarios to ensure reliability of water supply. These drought plans are then iterated with the Environment Agency to ensure they are defensible, cost effective and sufficiently protective of the environment. This whole process is explained in quite a friendly way here: MaRIUS_Drought_Primer_2017.pdf (aboutdrought.info)
In the drought plans, there are defined ‘trigger levels’ that say how severe the current water supply situation is. These are usually based on reservoir levels or groundwater levels. The level that the water supply situation is in determines what emergency actions the water company may take.
Here is a screenshot from the South East Water (SEW) drought plan. We can see that the different groundwater level triggers are changing cyclically. We can also show a black line with the historic groundwater level over time, starting off in the green area (increased communication around water use), at some point entering the orange area (hosepipe bans) and even at one point close to the red area (non essential use bans). From a water company perspective, this is what a drought looks like, and they will be monitoring these levels carefully to see what state their supplies are in.
Here is another example from the SEW that shows what actions they may take depending on the drought level. We see that when we are in level 1/2/3 the water company can do things like hosepipe bans (temporary use bans) and activate some of their water supplies that might have some environmental impacts (e.g., drawing down a river more than they usually would).
Exactly what are the actions associated with the different levels, and what are the triggers depend on the water company. But all water companies will associate the different levels with different expected return periods (i.e., over a long period of time, how frequently would we expect these things to happen). For example, Thames Water for example expect Level 1 with a return period of 5 years, Level 2 with 10 years, Level 3 with 20 years and Level 4 never.
There isn’t anything particularly controversial about the implementation of a hosepipe ban or droughts in general provided a few things are true:
- The water company has implemented the previous actions that they said they would implement in their drought plan before getting to the point of hosepipe ban (e.g., communication campaign)
- The water supply situation is at the level when a hosepipe ban is warranted (e.g., the groundwater level is within the Level 2 triggers) and that they reached this place through lack of rain and not through operational failures.
- The actions are being implemented as specified (e.g., if the plan says that an abstraction location can increase abstractions from 0.5m3/s->0.75m3/s then the water company should still not be abstracting at 1m3/s), and that these specifications are not being changed at the last minute (e.g., the water company hasn’t petitioned the EA to raise the abstraction level to 1m3/s).
(I should note that I have no data and have done no research on the current drought so cannot say anything about whether these are true or not. Reaching out to water companies is probably the best bet!)
An interesting point is that SEW says in their drought plan that the expected return period of a hosepipe ban is 10 years. This of course depends on our hugely variable rainfall patterns, however it is to interesting note that their last hosepipe ban was in fact 10 years ago.
Whether this drought planning is the most effective way to plan for droughts is a very complicated question, but I would say that in the middle of a drought is not the best time to decide! Whether climate change is impacting a specific drought is also very difficult to answer, although we can say with some confidence that if carbon emissions continue to follow their business as usual trend that they have been following since we started doing carbon emission projections (RCP8.5 tracks cumulative CO2 emissions | PNAS) then the probability of a hosepipe ban occurring is likely to increase. My research shows that, averaged across the UK, a business as usual carbon emissions scenario would likely double the probability of a hosepipe ban by 2050 (The Spatial Dynamics of Droughts and Water Scarcity in England and Wales – Dobson – 2020 – Water Resources Research – Wiley Online Library).
