Human influence on the duration of extreme temperature events in Asia's hotspot regions

Observations and models indicate that human activities exert a considerable impact on the frequency and intensity of extreme temperature events, which are associated with global warming. However, changes in the duration of extreme temperature events and their association with human influence have not been considered in most studies. Thus, the possible relationship between the observed changes in the warm and cold spell duration (WSDI and CSDI) in hotspot regions during 1960–2014 and human influence was investigated based on the NCEP/NCAR reanalysis version 1 and Coupled Model Inter-comparison Project Phase 6 (CMIP6) data. Constraint projection based on these attribution results was also performed. The optimal fingerprinting technique was used to compare observed changes in WSDI and CSDI to simulated changes averaged across eight CMIP6 models. Results show that anthropogenic (ANT) forcing contributed to the observed increase in WSDI in the three hotspot regions (West Asia, South Asia and Southeast Asia), with the majority of the changes being attributed to greenhouse gas forcing. However, a generally weak ANT signal can be observed in the decreasing trend of CSDI and can be detected in South and Southeast Asia. The influence of aerosol forcing remains undetected in either WSDI or CSDI, which differs from the results for frequency and intensity of extreme temperatures. The attribution results revealed that the constrained projection of WSDI is lower than the raw projection for 2015–2100 in West Asia and Southeast Asia. However, no differences in future CSDI changes are found in Southeast Asia between the constrained and raw projections.