As compound disasters in which drought and heat waves strike at the same time are increasing worldwide, a study found that the type in which a heat wave starts first and is followed by drought has risen sharply since the early 2000s. Analysts said it is the result of a stronger vicious cycle in which land and atmosphere influence each other and amplify disasters.
A team led by Yea Sang-uk, a professor in the Department of Climate and Energy Systems Engineering at Ewha Womans University (formerly a Hanyang University professor), together with collaborators including the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, published on the 7th in the international journal Science Advances the results of tracking drought–heat wave compound disasters using observational data from 41 regions between 60 degrees north and south latitude from 1980 to 2023.
Many previous related studies analyzed droughts and heat waves using monthly data. But in that case, there was a limitation in determining which of the two started first and how tightly the two phenomena intertwined.
In this study, the researchers used daily data and identified a compound disaster when a heat wave and drought overlapped in space and time for at least one day in the same region. They then divided these compound disasters into a "heat-wave-leading" type, in which a heat wave occurs first and drought follows, and a "drought-leading" type, in which drought begins first and a heat wave accompanies it, and compared the two.
As a result, both types increased over the long term, but there was a clear difference in the pace of increase. Recently, heat-wave-leading compound disasters rose by about 110%, while drought-leading ones increased by about 60%.
In particular, the heat-wave-leading type surged nonlinearly starting in the early 2000s. The rate at which heat-wave-leading compound disasters increase for every 1-degree rise in the global average temperature has become about eight times faster than in the past.
Kim Yong-jun, a researcher at Hanyang University, said at a briefing on the 5th, "In the early 2000s, the global average temperature was about 0.6–0.7 degrees higher than before industrialization," adding, "This means that some extreme phenomena may have already begun to surge even before the '1.5-degree rise' that the international community sees as a key threshold."
The core cause of this phenomenon was identified as land–atmosphere interactions. Simply put, when the ground becomes very hot, the heat is transferred to the atmosphere and warms the air; when the air warms, evaporation becomes more active and soil moisture decreases more quickly. When the land dries out, the cooling effect that originally came from water evaporating weakens. Then the surface heats more easily and the atmosphere gets hotter.
The researchers interpreted that "these land–atmosphere interactions have strengthened since the late 1990s, and with a slight time lag, their aftermath led to a surge since the early 2000s in compound disasters where heat waves pull in drought."
By region, the nonlinear surge of heat-wave-leading compound disasters was most pronounced in the Amazon region of South America. The researchers explained that in regions like the Amazon, where vegetation changes and deforestation are progressing rapidly, land conditions can change significantly, and such changes can strengthen land–atmosphere interactions.
The researchers warned that compound disasters in which a heat wave starts first can pose a more challenging social risk. If soil dries rapidly in a short time after an intense heat wave, damage can grow much faster and more abruptly than during a long-lasting drought. This process can heighten wildfire risk and lead to declines in agricultural productivity and public health crises.
Professor Yea said, "Drought induced by a heat wave is also closely linked to 'flash droughts' that intensify rapidly over a short period. In Korea, the frequency of such flash droughts is also increasing," adding, "There is a need to reassess compound disaster risk management strategies."
References
Science Advances (2026), DOI: https://doi.org/10.1126/sciadv.aea3038