Heat and drought, a lethal cocktail


As the increase in the concentration of greenhouse gases in the atmosphere warms the Earth, the global temperature rises and, as a consequence, heat waves increase in duration and intensity . Record temperatures are coming in faster and more furiously than researchers expected. And this raises questions about what to expect in the future.

The fact that temperatures have crossed the threshold much faster than expected could be due to incomplete climate models. In principle, they simulate heat waves and the increase in intensity and probability of extreme heat on a large scale reasonably well. However, at smaller scales, the changes in annual daily maximum temperatures do not follow the same pattern.

The results and observations for some regions , such as the eastern United States and some parts of Asia, allow us to better understand the influence of local factors and natural variability in the local pattern of heat waves.

On the other hand, the balance of moisture, changes in land use and soil moisture must be taken into account to achieve more reliable projections of the coming changes in temperatures.

More mortality, forest fires and crop failure

It is important to anticipate them because persistent heat waves have serious repercussions on ecosystems and societies. Three in particular stand out: excess mortality , forest fires and crop failures .

The summer of 2022 has been the one that has caused the most deaths in Spain in the last 72 years. No fewer than 120,000 people have lost their lives. In fact, 2022 has even surpassed the summer of the pandemic (2020) in deaths. The causes have not yet been fully understood, but undoubtedly the long, intense and recurrent heat waves have had a lot to do with it.

It cannot be denied that the heat suffered has been an absolute record. When on average Spanish summers have had 7 days of heat waves, in 2022 it has had 42. It has been the hottest summer recorded in Spain and 31 provinces have recorded the highest thermal values ​​in their history.

These high temperatures not only kill by the well-known “heat stroke”, but also aggravate pre-existing pathologies, such as cardiovascular, respiratory, pulmonary, renal, gastrointestinal or even neurological diseases. In addition, it must be taken into account that a determining factor in this excess mortality is also the collapse of health care centers.

Spain has led the records of excess mortality (deaths above the average of a country for a given time) throughout Europe, followed at a distance by Germany and Sweden. The daily mortality monitoring system for all causes ( MoMo ), prepared by the Carlos III Health Institute (ISCIII), estimates that in Spain there have been just over 4,700 deaths related to excess temperature between the end of April and early September.

It has, however, been a lethal heat stroke in much of Europe, with absolute records for both heat and deaths in several countries such as the United Kingdom. A similar situation was experienced in the southern summer .

Heat and drought, an explosive mix

If we learned anything from the 2003 drought in Europe it is that when heat and drought combine they amplify their respective impacts on natural ecosystems and have devastating effects. That year, the combination generated a major crisis in the primary productivity of forest ecosystems and the death of more than 100,000 Europeans.

Potsdam Institute for Climate Change Impact Research researcher Efi Rousi and collaborators have identified Europe as a heat wave hotspot . The old continent shows upward trends in these extreme events that are three to four times faster compared to the rest of the northern hemisphere mid-latitudes during the last 42 years.

This accelerated trend is linked to dynamic atmospheric changes that are mainly associated with an increase in the frequency and persistence of double-jet states over Eurasia. The jet stream has a great influence on the climate and on the determination of climatic regions on the planet and the fact that it splits into two currents is something that science is beginning to understand and estimate its repercussions.

Double-jet states are particularly important for western European heat waves, explaining up to 35% of temperature variability. Its upward trend can largely explain the acceleration of heat waves in Western Europe, and about 30% of it in the entire European region.

Certain configurations of the jet stream are linked to thermal extremes in different mid-latitude regions, key regions for grain production. This implies that they can endanger global food security and social stability.

This research, coupled with observations related to the Azores anticyclone and western European drought, advances our ability to assess and anticipate environmental, social, and geopolitical risks under unmitigated climate change.

Author Bio: Ferdinand Valladares is a Research Professor at the Department of Biogeography and Global Change at the National Museum of Natural Sciences (MNCN-CSIC)