A new study from UKCEH scientists shows that extreme soil moisture droughts in the UK – those lasting 90 days or more - are expected to occur more frequently under climate change. This could have severe implications for farming, water availability and food security.
The research published in Environmental Research Letters reveals that while such severe droughts occurred around once every 16 years in the recent past, they might happen as often as once every three years by the 2060s and 2070s. Even in the current decade and 2030s, they could occur as frequently as once every five or six years. These very low soil moisture levels will mostly occur in summer periods, between June and September in 2020s and 2030s. However, by the 2060s and 2070s, they are expected to extend from May to right through to November, with June through October being especially high risk.
What is different about this study?
While predictions of future UK soil moisture droughts have been made before, this latest study provides a step change in accuracy on the likely severity and duration of them in the absence of appropriate climate change mitigations. This is done by bringing together a unique blend of the latest projections by climate simulations merged with an advanced model of soil water transport, fully calibrated and tested against a UK-wide network of soil moisture measurements.
UKCEH scientist and lead author of the study Dr Magdalena Szczykulska comments, ‘Our analysis provides a particularly exciting translation of the latest predictions of UK climate change into an impact of concern, which is future levels of soil moisture.
"We hope that by predicting the increase in the expected future soil moisture drought frequency and evaluating the impact on individual months, Government and private sector organisations can take action to improve our resilience to this effect of climate change.’
Coauthor Dr Chris Huntingford adds: "The future estimates of climate are based on the latest high-resolution calculations from the Met. Office, which they made available and are outputs from its supercomputer."
Impact on farming
Farmers, growers and water companies may use our analyses to better plan capital infrastructure investments in water storage, such as reservoirs, and more efficient irrigation systems. Planting of less drought prone crops could become a priority, changing what we grow in the UK.
The increased risk of autumn soil moisture drought conditions will affect autumn sown cereals, for instance winter wheat, at the beginning of their foundation phases, potentially reducing yields of these crops.
Grazing land is likely to become much less productive in the response to increased drought conditions during the main spring and summer growing seasons. This, in turn, may increase the price of dairy and meat produce or could force land use change as certain types of farming become less economically viable.
Impact on water availability
Increases in more extreme droughts will reduce water availability also for other industries and consumers. During these hot and dry periods there is likely to be a large increase in consumer demand to keep cool and to water gardens.
Soil moisture droughts, where wilting or ‘brown vegetation’ stops transpiring water, exacerbate extreme high temperatures experienced by the population, making heatwaves more likely.
To combat these impacts, there could be a drive towards deeper rooted perennial plants, shrubs and trees to provide both sustainable food and natural cooling and shade. Accessing deeper soil water reserves can provide drought resilience, as these dry out much more slowly and can be replenished by winter rains.
The results of this work help inform those making climate policy. If we are to avoid much more frequent levels of soil moisture depletion, then global warming would likely need to be constrained to targets such as the Paris 1.5 or 2 degrees threshold.
A unique method
This new study from UKCEH brings together long-term field observations of soil moisture from the UK Cosmic-ray Soil Moisture Observing System (COSMOS-UK) network, the UK's state-of-the-art land surface model, the Joint UK Land Environment Simulator (JULES) and state-of-the-art atmospheric model outputs, the 2.2 km convection-permitting UK Climate Projections (UKCP18).
The JULES model was calibrated with the COSMOS-UK soil moisture observations from 34 field stations across the UK using an advanced data assimilation method. The calibrated model was then forced by the UKCP18 meteorological data to predict future and past soil moisture levels at the 34 COSMOS-UK sites.
The UKCP18 data used here corresponds to a high-emissions future described by the RCP8.5 scenario, which is akin to ‘business as usual’ without large reductions in emissions.
Read the full paper here.