Not only was 2023 characterized by unprecedentedly high temperatures but also by excessive droughts in many parts of the world as well as floods in other areas. The World Meteorological Organization (WMO) has now presented its third report on the status of global water resources. According to the report, 2023 was the driest year compared to the previous 33 years, putting it in first place followed by 2021 and 2015. "The year 2023 was indeed much drier than we had expected," said Professor Robert Reinecke of Johannes Gutenberg University Mainz (JGU). Reinecke heads the Earth System Modeling group at JGU's Institute of Geography and contributed to the report.
The third State of Global Water Resources report takes an even more detailed look at what is happening to the Earth's water cycle than the first two reports. In particular, the information has been extended to include the storage capacity of lakes and other types of water reservoirs, including that of the planet's cryosphere, i.e., water locked up in solid form such as snow and glaciers. The additional data and models analyzing this data thus provide more precise insights into the current situation. The results for 2023 continue to exhibit significant deviations from the typical values of the past as recorded for the reference period 1991 to 2020. "More than 50 percent of catchment areas show deviations from this reference period," said Reinecke. The water discharge rates of rivers, which is one of the main indicators of water resources, were predominantly below normal. As a result, the WHO report registers unparalleled low water levels in the Mississippi and Amazon basins. Moreover, extremely low volumes of water in the form of snow meant that less water was made available in spring, resulting in lower discharge of water – an effect particularly to European rivers. "The worldwide loss of glacier volume, equivalent to 600 gigatons of water according to the latest WMO report, is alarming," emphasized Reinecke. "It is the greatest loss we have witnessed in the past five decades."
Globally, 2023 was either too dry or too wet
In some cases, the report documents the recovery of groundwater levels, as in South Africa, for instance. At the same time, groundwater availability in North America and Europe decreased significantly due to longer drought periods. "However, we can assume that the results for Central Europe in 2024 will turn out to be somewhat better," anticipated Reinecke. In terms of soil moisture levels, there was a severe drought in North and South America, while in other countries – including New Zealand and Russia – moisture levels were far above normal.
According to Professor Robert Reinecke, the report's key finding is that there were, again, considerable divergences from normal conditions all over the globe. "It was either too dry or too wet – and neither is encouraging. We have to expect both extremes more frequently as global temperatures continue to rise." 2023 was the hottest year on record, with temperatures 1.45 degrees Celsius above the pre-industrial average.
It was in collaboration with Dr. Hannes Müller Schmied, a researcher at Goethe University Frankfurt and the Senckenberg Biodiversity and Climate Research Center (SBiK-F), both located in Frankfurt am Main, and the Global Runoff Database Center (GRDC) in Koblenz that Reinecke was able to make a major contribution to the 2023 WHO report. Together, they supplied modeling results and worked on the corresponding methodology. Reinecke's Earth System Modeling group at Mainz University focused on the methods used to analyze groundwater data. To better understand the effects of climate change on groundwater status, the Mainz team is at present compiling a set of worldwide data.
The research project was a joint effort of the Rhine-Main Universities (RMU) alliance.
