Background Climate
Drought not caused by less rain
In Western Europe we have had a number of dry years in a row. For example, the Union of Water Boards reported last week that the groundwater level in some parts of the eastern and southern Netherlands has not yet fully recovered, despite a wet winter. According to new research published in the scientific journal Nature Geoscience, there appears to be a trend of drier years. It is striking that, according to the researchers, there is not so much less rainfall. The precipitation deficit that occurs mainly in spring is mainly due to more evaporation.
KNMI data shows that the average temperature in the spring has become about 70 degrees warmer since the late 1,5s. The higher temperatures result in more evaporation. Climate models predict that it will rain less in southern Europe in the future, while northern Europe can expect more precipitation. The Netherlands is somewhere in between, which makes forecasting difficult.
Drought trend started 1.000 years ago
A group of European researchers has tried to show how exceptional the drought of recent years is or whether it fits into the normal pattern. The research was done on the basis of the thickness of the growth rings of trees from central Europe. Not only live oaks were used for this, but also oak from old constructions and archaeological finds. In this way we managed to look back more than 2000 years.
Analysis of the growth rings shows that precipitation in Europe varies greatly, but that there has been an increase in the number of dry years in the last 1.000 years. According to the KNMI, current climate models are not yet able to reproduce these variations. This is probably because many factors, such as changes in the ocean, play an important role. The oceans determine the wind above the continent. According to the researchers, the strong warming in the last century has a clear influence on the drought. The tree rings show that the desiccation has been stronger over the past 100 years than in previous periods.
Jurphaas Lugtenburg
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