Due to climate change, it is becoming drier in the Netherlands and Europe. There is a possibility that the Atlantic Meridional Overturning Circulation (AMOC) will weaken significantly or even collapse. This will not only make Europe much colder in winter but will also intensify drought. A weaker AMOC causes less precipitation and more evaporation in spring and summer.
AMOC and the weather in Europe
The AMOC transports warm surface water from the tropics towards Europe. This warm water contributes to the mild maritime climate of the Netherlands. Additionally, the warm water evaporates and brings precipitation to our region. Due to climate change, the AMOC is weakening. This changes weather and precipitation patterns, and these changes become stronger as the AMOC further declines. There is also a risk that the Atlantic Ocean circulation collapses. Europe could then cool significantly, with much colder winter months and stronger winter storms. Besides this cooling, there will also be less precipitation over Europe. A new study by KNMI in collaboration with Utrecht University shows that Europe becomes much drier if the AMOC collapses. The Netherlands will also become significantly drier.
Precipitation deficit in the Netherlands
Different future climate conditions were simulated in a climate model. These differ in how much the Earth warms and how much the AMOC decreases. Due to climate change, drought during the dry season in De Bilt increases (figure 1, left). In this study, the dry season is defined as the period in the year when the precipitation deficit on average increases because more water (potentially) evaporates than falls as precipitation. Drought during the dry season increases by about 9 percent compared to the climate around 1900 with a global average warming of 2.9 degrees. Although there is slightly more precipitation, evaporation increases more strongly due to warming, making it on average drier. The months outside the growing season actually become wetter. This trend is visible in observations and also fits the last growing season which was dry.
If the AMOC collapses under climate change, the dry season becomes even drier. Drought then increases not by 9 but by 34 percent (figure 1, right), almost four times as strong. This is mainly due to less precipitation when the AMOC collapses; evaporation changes little. The winter months also become wetter when the AMOC collapses. For the same greenhouse gas emissions, the Earth warms only 1.6 degrees instead of 2.9 degrees due to the AMOC collapse.
All of Europe becomes drier
Throughout Europe, a collapsing AMOC intensifies drought during the dry season (figure 2), mainly due to a decrease in precipitation. In Southern Europe, drought is strongest because temperature and evaporation increase the most. Periods of prolonged drought (longer than 6 months) also occur more frequently.
Societal consequences
This study shows for the first time the hydrological consequences for Europe if the AMOC collapses under further climate change. The strong drought can have major consequences for Dutch and European agriculture with lower yields. For water management in the Netherlands, the collapse of the AMOC also poses greater challenges, with wetter and colder winters alternating with warmer and drier summers. The degree of drought is still very uncertain; the climate model in this study shows relatively strong drought due to climate change compared to other models. The drying effect of the AMOC collapse may therefore also be stronger. It is therefore important to map the effect of an AMOC collapse on the European climate with more and finer models.
