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 hydrographs. 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 1, just above the drought zone 2 curve. Significant recovery of Chalk groundwater levels last winter meant that they began the 2018 recession mid-way between drought zone 1 and drought zone 2. The summer of 2018 has been warm and dry, particularly through June and July, whilst August and September have experienced cooler temperatures and more unsettled conditions, albeit with continued lengthy dry spells. For the June to September period inclusive, rainfall was 57 % of the LTA in Central region. Despite the fact that October has been wetter, receiving 84 % of the LTA rainfall, effective precipitation was 42 % of the LTA. This means that the last 6 months have experienced effective precipitation lower than the LTA. The results have been a recession faster than the LTA and that soil moisture deficit (SMD) has remained higher than the LTA. Higher than average SMD decreases the recharge component from rain, as more water is absorbed by the soil; this may impact the recharge pattern over the coming months.

According to the LTA, groundwater levels are likely to continue to decline until December, with the rate and extent of the groundwater recession being controlled primarily by the rainfall during November and December. There are a range of possible scenarios for the next 12 months. If we receive continued rainfall which is equal to the LTA, we are likely to dip briefly into drought zone 2 but recover to a position approximately halfway between drought zone 1 and drought zone 2 by the summer of 2019, slightly above current levels. Drier conditions would not provide the recharge required for groundwater levels to rise out of the drought zone during the recharge period of 2018/2019. Very low rainfall (60 % of LTA or less) could result in groundwater levels starting the 2019 recession period approximately halfway between drought zone 2 and drought zone 3, with likely further decline through the summer and autumn.