Implications of differential effects between 1.5 and 2 °C global warming on temperature and precipitation extremes in China's urban agglomerations

In the context of global warming, urban areas are more vulnerable to extreme weather conditions. In this study, four key temperature and precipitation extreme indices, defined by the Expert Team on Climate Change Detection and Indices, are selected to investigate implications of differential effects of 1.5 and 2 degrees C global warming on extreme weather in China's urban agglomerations (CNUAs). Results indicate that bias-corrected extreme indices derived from downscaled data sets of National Aeronautics and Space Administration (NASA) Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) of 19 Coupled Model Intercomparison Project Phase 5 (CMIP5) models under RCP4.5 scenario [representative concentration pathways (RCP)] can be used to study the effects of global warming on extreme indices in locations of CNUAs. An increase in the global warming from 1.5 to 2 degrees C is likely to exacerbate the intensity of extreme maximum temperature (TXx) and decrease extreme minimum temperature (TNn) in CNUAs. Moreover, additional 0.5 degrees C warming is more likely than not to increase the intensity of total precipitation of very wet days (R95) and maximum 5-day precipitation (Rx5day). For the very extreme events (>1.5 sigma), a global warming increase from 1.5 to 2 degrees C will lead to extra increase in extreme risk for very extreme TXx, R95p and Rx5day by 4.1, 1.8 and 1.0 times, relative to 1986-2005. Thus, it seems that reducing the 2 degrees C global warming level by 0.5 degrees C during the remainder of the 21st century would significantly suppress very extreme heat waves and very extreme wet events in CNUAs. Certainly, the urban heat island and aerosol effects are expected to further enhance such extreme events in the urban areas. The combined influence of global warming and urbanization effects on extreme events needs further study in the future.