ABSTRACT There are growing concerns on compound dry and hot extremes (CDHEs) amidst global warming. This paper formulates the total derivative of the probability of CDHEs to elaborate on the role of precipitation in future CDHEs. Specifically, the probability of CDHEs is mathematically derived from the joint distribution of standardised precipitation index (SPI) and standardised temperature index (STI); and then the total derivative is used to quantify the contributions of mean value of SPI, standard deviation of SPI, correlation coefficient between SPI and STI, mean value of STI and standard deviation of STI. For the Shared Socioeconomic Pathways 585 of the Coupled Model Intercomparison Project Phase 6, the probability ratio of CDHEs is investigated for the future period from 2015 to 2099 over the near past period from 1950 to 2014. The results show that the probability ratio of CDHEs in the future period over the historical period is expected to be increased by 2.79 (90% confidence interval (CI): 1.71 to 4.14) owing to the mean value of STI. The contributions are respectively, −0.19 (90% CI: −1.54 to 1.77) for the mean value of SPI, −0.07 (90% CI: −0.47 to −0.32) for the correlation coefficient between STI and SPI, 0.20 (90% CI: 0.05 to 0.33) for the standard deviation of SPI and −0.02 (90% CI: −0.06 to 0.03) for the standard deviation of STI. While the rising temperature is inevitably the primary driver of increasing CDHEs, precipitation is observed to be a key modulator that can possibly mitigate future CDHEs.
Zhao et al. (Fri,) studied this question.