Weatherwatch: soil moisture deficit – how dry are the UK’s thirsty soils?

SMD is the moisture the soil must make up until it is at capacity, with very dry conditions over most of England and Wales When the ground is thoroughly wet, after excess rainwater has run off it is said to be at field capacity.

Meteorologists describe drought in terms of soil moisture deficit (SMD) from field capacity. The SMD is a measure of how thirsty the soil is, expressed as how many millimetres of rain it would take to top it up to field capacity. In southern England, the SMD tends to hover around zero in winter when…