Projections of compound wet-warm and dry-warm extreme events in summer over China

Accurate climate projections are essential in China. A quantile delta-mapped spatial disaggregation (QDMSD) has been developed to simulate compound extreme dry-warm (CDDW) and wet-warm (CDWW) events in historical and future summertime. Simulations indicated that the frequencies of CDDW would keep an obvious increase in the historical period. The Niño 3 and Atlantic Multidecadal Oscillation (AMO) indirectly regulate compound extreme events by regulating sea surface temperature anomalies (SSTA) in the western Pacific. In the future period, the growth of compound extremes under SSP5-8.5 surpasses that under SSP2-4.5. Under the SSP2-4.5 scenario, the projected changes in compound extremes may be influenced by SSTA in the northwest Pacific. At 850 hPa, the SSTA may cause a weakening of the geopotential height (GHT) anomalies. The rising of warm-humid air would be hindered by the positive GHT anomalies over Siberia and a weakening of negative GHT anomalies over northwestern Pacific. It is difficult to form precipitation in northwestern China. Therefore, the CDDW will be distributed in northwest China. The correlation between compound extremes and the SSTA in the northwest Pacific will increase under SSP5-8.5. The negative GHT anomalies may occur in the northwest Pacific. Additionally, the positive GHT anomalies will weaken over Siberia. These factors may enhance the upward movement of warm-humid air and moisture convergence, thereby leading to the formation of precipitation. Finally, it would promote the occurrence of CDWW in northeastern, eastern and northern China. These findings are beneficial for policymakers in addressing the risks posed by summertime compound extremes across multiple sectors.