01.03.2019 | Gottardo Pestalozzi | News WSL
In 2018, Central and Northern Europe – including Switzerland – experienced one of this region's most severe droughts of recent decades. WSL is now analysing its measurements and observations from that summer with a view to improving how droughts are handled.
WSL researchers have started to analyse the events of summer 2018 with regard to drought classification, early detection of drought, early leaf discolouration, lightning-induced forest fires, medium- and long-term effects and public perception.
In some cases that summer, river runoff and lake water levels hit lows never recorded before. Indeed, groundwater levels on the northern side of the Alps had still not recovered by the end of the year. In the agricultural sector, the drought led to significant crop failures, while in many places unusually early discolouration of the leaves on the trees were a sure sign of the heat and the lack of water. WSL measurements showed that water availability in common forest tree species temporarily fell well below the long-term average values.
For decades, forestry, hydrology and biodiversity have been focal areas for the Swiss Federal Institute for Forest, Snow and Landscape Research WSL. Its experience and data series going back many years are helping place the events of summer 2018 in a wider context, allowing sense to be made of them.
13 analyses before summer 2019
The findings from a series of short analyses will contribute to improving drought forecasting and handling, thanks in particular to the further development of the pilot portal drought.ch.
Drought classification
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A1-Historical contextualization of tree damage caused by the 2018 drought
- A2-How extreme? Overall assessment of the 2018 drought
Early detection of drought
- B1-The 2018 drought - how predictable was it?
- B2-Assessing forest vulnerability to drought by intersecting modeled soil water availability (SWA) with remote-sensing derived spectral anomalies
Early leaf discoloration (leaf fall)
- C1-Identification of drought risk zones in current beech stands
- C2-Effects of the drought of summer 2018 and heat on forest canopy greenness
- C3-Analysis of beech litterfall in the drought year 2018
- C4-Droughtindicators: TreeNet meets Sentinel 2
Lightning-induced fires
Medium- and long-term effects
- E1-Rapid survey of the short-term effects of the 2018 drought on beech forests in Switzerland
- E2-Response of European beech and silver fir trees on dry sites to the drought in 2018
- E3Medium-term effects of the drought of summer 2018 on beech individuals with early leaf senescence
Public perception
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Record-low water levels (average runoff over seven days)
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The network TreeNet detects with point dendrometers how much tree stems shrink during dry periods. This so-called tree water deficit (TWD) indicates how much trees are suffering from dry conditions. The higher the value is the more a tree is thirsty. Analyzed were beech, spruce, pine, fir and oak trees. The TWDs are weighted with a species-specific factor in order to account for different TWD amplitudes of different species.
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drought.ch shows the hydrological consequences of droughts. The graph shows the discharges of water bodies in August 2018 (click on file name to animate the image).
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The downy oak (right) is better adapted to summer dryness than the pine (left), because it can still draw water from the ground even in extreme dryness. The pine, on the other hand, must reduce or even stop its photosynthesis. (Photo: Andreas Rigling, WSL)
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The river Töss (Canton Zurich) easily dries out during droughts. The picture was taken on August 4, 2018. Photo: Gottardo Pestalozzi, WSL.
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Due to persistent drought, numerous beech trees in Switzerland changed colour early in the summer of 2018. The year 2019 will show how the lack of water has affected the growth of the tree rings. (Photo: Andreas Rigling, WSL)
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Flash of lightning hitting Pizzo Corgella near Isone in Switzerland. Depending on the situation this might cause a forest fire. Photo: Gottardo Pestalozzi, WSL.
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