Tuesday, 8 January 2019
Hall 4 (Phoenix Convention Center - West and North Buildings)
Although the link between droughts and heatwaves is widely acknowledged, how climate change affects this link remains uncertain. Here we assess human-induced changes in U.S. summertime drought-heatwave interaction that may yield more such compound events using a coupled climate model simulation (CESM1), subjected to respective Year-1850 and Year-2000 radiative forcings. Our results reveal a strong dependency of heatwaves on soil moisture variability in water-limited regions of the Southern Plans and Southwest U.S.; while in energy-limited regions of the North/Northeast U.S., heatwaves are insensitive to drought severity. Applying a statistical model based on pair copula constructions, we find anthropogenic warming leads to enhanced soil moisture–temperature coupling in moisture-limited areas, and consequently amplified intensity and increased likelihood of heatwaves during severe droughts over the South and West U.S.. This strengthened coupling can explain a substantial fraction of rising temperature extremes related to the long-term climate change, thereby highlighting an increased role of land–atmosphere feedback in the development of hotter droughts in a warmer climate. To contrast, coupling effects remain weak and largely unchanged in energy-limited regions, thereby yielding no appreciable contribution to heatwave intensification over the North/Northeast U.S., apart from the long-term warming effects.
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