July 2022 was the driest July in England since 1935. Combined with record temperatures, 2022 has a drought comparable to the great drought of 1976, with fears of interruptions in public water supply and low crop yields, especially for fruits and vegetables. But not all droughts are the same and not all farmers are affected by the same type of drought.

For a meteorologist, drought is generally defined as a period of rains significantly below average. However, low rainfall, even for an entire season, does not necessarily mean that the water supply will be low, or that industry or agriculture will suffer, since there may be a lot of water already stored in reservoirs and groundwater.

Of course these reserves are of little help to pastures, cereals and other crops that are entirely fed by rain and are greatly affected when we have a dry spring and summer. The last 12 months have been particularly dry in much of the UK and since May 2021, only October and February have recorded above average rainfall.

Things are even worse if combined with the high temperatures and abundant sun we've seen this year, which increases evaporation and depletes the soils of the water needed for plant growth – the so-called "agricultural drought".

We evaluated the combined impact of low precipitation and warm and sunny weather using the potential soil moisture deficit (PSMD), which is a cumulative measure (in millimeters) of the balance between the inlet of rain in the soil and the potential losses by evaporation and transpiration of plants.

When evaporation exceeds precipitation, the soils become drier and the potential soil moisture deficit increases (it gets drier). When it rains, it slows down. Typically, the deficit begins to increase from late March or early April, peaking in August or September when soils are drier. A potential high soil moisture deficit means that dryland crops such as cereals and grasses will suffer.

In some weather stations, the potential soil moisture deficit in 2022 behaved very similarly to 1976. The deficit began to increase in early March and continued to grow until the end of July.

This contrasts with the last drought in 2018, when spring was wetter and soil drying was delayed. Currently, this deficit is about 350 mm, which is about 50% higher than the average peak between 1981 and 2010. Therefore, for farmers who rely only on rainfall, 2022 looks like it could be as severe an agricultural drought as 1976.

Source: Agrolink