Hamburg's groundwater supply seems secure

Does Hamburg have to fear for its drinking water supply? Even now, the city cannot satisfy its consumption from its own sources alone, but also pumps water from the surrounding area. Will this trend be intensified by persistent dry phases, such as one that lasted for weeks from March to April this year? The municipal water supplier Hamburg Wasser has been looking for answers to these questions - and published them in its latest water report.

The good news: You don't have to worry about the amount of new groundwater in the Hanseatic city, said Hamburg Water Managing Director Ingo Hannemann on Wednesday when the report was presented. Every year, around 1.1 billion cubic meters of new groundwater are created in the areas where Hamburg pumps water.

About 200 million cubic meters of this would be needed for the water supply of the metropolis, for companies and agriculture, explained Hannemann. This corresponds to about one fifth of the consumption compared to the newly created groundwater. This is exactly the value that experts consider sustainable use. Because groundwater is also used to feed streams and rivers, which could dry up if people take too much water.

Overall, the water supply in Hamburg is not endangered by climate change and rising temperatures in the long term, said Daniel Petry from the industry association of water suppliers DVGW, who compared the effects of current climate projections on the water balance.

Accordingly, a decline in groundwater recharge is not to be expected in northern and north-eastern Germany by the end of the century due to increasing precipitation. Because rising temperatures ensure that the air contains more water. "In terms of trend, the vast majority of forecasts predict constant to slightly increasing groundwater recharge rates up to 2100," said Petry.

To speak of "everything is fine" is still the wrong way, emphasized Hamburg-Wasser boss Ingo Hannemann. Because, as Petry also made clear, all forecasts currently assume that the number of extreme weather events will increase - and they can become a problem for water suppliers.

The published water report also states that the year 2022 has already shown the associated effects. Because long dry phases, heat records and a wet winter showed a mixed balance of the hydrological year.

In Hamburg, the hydrological year that has now come to an end - the period from November to October of the following year is considered - was average compared to the past 30 years, said Hannemann. However, the precipitation fell very differently.

While the extremely rainy month of February brought almost three times as much precipitation as usual with 153 millimeters, March with only 18 millimeters of precipitation was a good 70 percent below the long-term average. "That led to dry soil layers very early on," he said.

The summer was then hot again – on ten days with temperatures of more than 30 degrees. In July, a new record value of 40.1 degrees was measured in the Neuwiedenthal district. "Compared to the previous year, the heat was less constant," said Hannemann. Nevertheless, between June and the end of August, the top 30 centimeters of the soil dried out completely. Only heavy rainfall in September would have brought relief.

Despite record temperatures, the people of Hamburg – as far as peak consumption is concerned – held back in the summer. On no day was a total consumption of more than 400,000 cubic meters determined, said Hannemann. In the summer of last year, this value was exceeded on six days, and in 2020 even on 20 days.

"We believe that the general change in energy consumption plays a role," said Hannemann. In addition, the dry spring may have played a part. "If you already have a dry lawn in May, don't start watering it in June to make it green again."

Nevertheless, Hannemann expects that the days with peak loads could become a problem for the water suppliers. "We have to assume that there will be more days with temperatures above 30 degrees." When the taps are turned on everywhere in Hamburg to fill pools or water flowers, the water network reaches its limits. You have to prepare for this in the long term.

The water for Hamburg comes exclusively from groundwater wells. The sustainable use of this resource is all the more important, said Hannemann and called for more transparency, also with regard to the withdrawals of other consumers such as agriculture. "Sustainable groundwater protection is only possible if we have transparency."

For the present report, Hamburg's water supplier systematically evaluated consumption data from its customers, data from its own climate stations and groundwater storage tanks, as well as reports from the German Weather Service (DWD) and compared them with measured values ​​from previous decades. “We need to know as precisely as possible how water resources and their use are developing and what impact climate change may have in the future. This is an essential prerequisite for the strategic orientation of our company," said Hannemann.