JRC scientists have developed a new index to measure the magnitude of heat waves, in cooperation with colleagues from five research organisations. According to the index projections, under the worst climate scenario of temperature rise nearing 4.8⁰C, extreme heat waves will become the norm by the end of the century. Heat waves like the one that hit Russia in summer 2010, the strongest on record in recent decades, will occur as often as every two years in southern Europe, North and South America, Africa and Indonesia.
The Heat Wave Magnitude Index is the first to allow comparing heat waves over space and time. It takes into account both the duration and intensity of heat waves and can serve as a benchmark for evaluating the impacts of future climate change. Results also show that the percentage of global area affected by heat waves has increased in recent decades, and the probability of occurrence of extreme and very extreme heat waves is projected to increase further in the coming years.
The index is based on an analysis of daily maximum temperatures, which was carried out to classify the strongest heat waves that occurred worldwide during three study periods (1980-1990, 1991-2001 and 2002-2012). In addition, a combination of models is used to project the future occurrence and severity of heat waves, under different scenarios as established in the latest Assessment Report of the Intergovernmental Panel on Climate Change (IPCC).
Taking into account the disastrous effects of the 2003 and 2010 heat wave events in Europe, and those of 2011 and 2012 in the USA, results show that we may be facing a serious risk of adverse impacts over larger and densely populated areas if mitigation strategies for reducing global warming are not implemented.
An extreme heat wave occurred in Russia in the summer of 2010. It had serious impacts on humans and natural ecosystems, it was the strongest recorded globally in recent decades and exceeded in amplitude and spatial extent the previous hottest European summer in 2003. Earlier studies have not succeeded in comparing the magnitude of heat waves across continents and in time. This study introduces a new Heat Wave Magnitude Index (HWMI) that can be compared over space and time. The index is based on the analysis of daily maximum temperature, in order to classify the strongest heat waves that occurred worldwide during the three study periods 1980-1990, 1991-2001 and 2002-2012. In addition, multi-model ensemble outputs from the Intercomparison Project Phase 5 (CMIP5) are used to project future occurrence and severity of heat waves, under different Representative Concentration Pathways (RCP), adopted by the Intergovernmental Panel on Climate Change (IPCC) for its fifth Assessment Report (AR5). Results show that the percentage of global area affected by heat waves has increased in recent decades. Moreover, model predictions reveal an increase in the probability of occurrence of extreme and very extreme heat waves in the coming years: in particular, by the end of this century, under the most severe IPCC AR5 scenario, events of the same severity as that in Russia in the summer of 2010 will become the norm and are projected to occur as often as every two years for regions such as southern Europe, North America, South America, Africa and Indonesia.
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