End of the hydrological year – 2021/22 was massively too dry in Switzerland – Meteo
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The hydrological year 2021/22 ends on Saturday night. In the past 365 days, it has been far too dry across Switzerland. In many places there was only 60 to 70 percent of the usual annual precipitation, in Geneva it was the fifth driest year ever.
The hydrological year runs from October 1st to September 30th of the following year. The year that is now coming to an end was characterized by long periods of drought, and it was not until September that large amounts of precipitation fell in many places, but this was not able to compensate for the annual deficit.
Sometimes only 60 to 70 percent of the usual precipitation
In the Lake Geneva region, in the Rhone Valley and partly also in Ticino, only 60 to 70 percent of the usual annual precipitation occurs. In Geneva it was the fifth driest year since measurements began, in Locarno the sixth driest. The heavy rainfall in the last days of September was special. This prevented, for example, the past year from being one of the 10 driest in Sitten, Bern and Zurich. The precipitation deficit is lowest in Central and Eastern Switzerland. The meadows there were mostly green even in summer. 98 percent of the usual annual precipitation was measured on the Säntis.
The dry years are long gone
In most places you have to look far back in the statistics to find even drier years. In Geneva, 1921, 1884 and 1906 were even drier, and only 2011 is a bit out of line. In Zurich, the 10 driest years since records began were all recorded before 1950, five even in the 19th century. Only in Ticino have there been various dry years in the 21st century, i.e. 2003 and 2005, but also 2015.
Water balance doesn’t tell everything
The water balance is precipitation minus evaporation equal to runoff. Because the snow in the Alps usually falls as snow in late autumn and only drains off in spring or even in summer, the hydrological year lasts from October to September. This year, however, the water balance shows some special factors. Due to the amount of sunshine and the high temperatures, especially in summer 2022, evaporation was greater than usual. This increased the drought, especially during the summer months. On the other hand, large additional water masses came from the glaciers this summer. Overall, the Swiss glaciers lost 6 percent of their volume over the course of the hydrological year 2021/22. As reported by the Swiss Academy of Sciences, the volume loss of glaciers within a hydrological year has never been as great as it is now. Even in the summer of the century, 2003, the volume loss wasn’t that great.
Little snow, great heat and Sahara dust
In the hydrological year 2021/22 all unfortunate components came together. Snow field in the winter half-year 2021/22, especially before the holidays. When the snow surface was relatively dark in spring, it could melt quickly. And that’s not all: in mid-March, the great Sahara dust event occurred, which further discolored the snow surface. So it was not really surprising that in the spring there was soon an almost complete snowfall. As a result, the glaciers were exposed to the hot summer of 2022 without a layer of snow. These components lead to a record runoff from the glaciers, which were able to somewhat reduce the extreme drought in the glacial runoff areas.
Bleak prospects
This summer, the glaciers were able to compensate for the severe drought. From the middle of this century this will only be the case to a limited extent, since the glaciers will be so small by then that they will no longer be able to adequately compensate for the lack of precipitation.