Serving parts of North West London and the Home Counties.

Groundwater levels

Central Region


Central region water levels hydrograph

*The long term average (LTA) has been calculated statistically, using the long term data record for this hydrograph. The respective drought zones are used as operational triggers, and have been derived using the LTA.


Groundwater levels in our Central region are currently in drought zone 2 at the same level as they were at this point in 2018, having crossed into the drought zone in early November 2018. They began the 2018 recession halfway between the drought zone 1 and drought zone 2 triggers. The summer of 2018 was warm and dry, increasing soil moisture deficit (SMD). Higher than average SMD decreases the recharge component from rain, as more water is absorbed by the soil. Groundwater levels declined more quickly than the LTA during 2018. During the autumn, this was primarily due to the high SMD and rainfall pattern. January rainfall was 41 % of the LTA and January effective precipitation was 28 % of the LTA. This means that the last nine months have experienced effective precipitation lower than the LTA. SMD is now slightly higher than the LTA. This will be quickly reduced following the rain and snow in early February, meaning that further precipitation we receive over the coming months is likely to be effective.

If groundwater levels follow the LTA trend, they are likely to increase in February, with the rate and extent of the groundwater recession beyond this being controlled primarily by the rainfall during the month. There are a range of possible scenarios for 2019. A rainfall pattern which is equal to or less than 100 % of the LTA would likely see groundwater levels remain in drought zone 2 through the recharge season, below May 2018 levels but higher than May 2017 levels. Less rainfall (60 % or 80 % scenarios) would not provide significant groundwater level recovery and could result in similar conditions to the recession period of 2017, this summer.