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The short-time heavy rainfall is sudden and easy to cause disaster， which poses a great threat to people's life and property safety.This paper analyzed the spatial and temporal variation characteristics of short-time heavy rainfall （≥20 mm·h-1） in the Sichuan basin and its relationship with geological hazards.The hourly precipitation observation data from high-density regional automatic stations and national stations （1688 stations） was used from 2011 to 2020.The results showed that： （1） The large values of short-time heavy rainfall frequency and rainfall were mainly concentrated in the transition area between high mountains and basins in the southwest and along the Longmen Mountains in the northwest， with more in the west and less in the east overall.（2） The frequency and rainfall were increasing， but the intensity and intensity extremes were decreasing， so the increase in rainfall was caused by the increase in frequency.In the northwestern part of the basin， the frequency and rainfall was the highest， and the interannual variability was the strongest.（3） The short-time heavy rainfall occurred from March to October， one month earlier than in the early 21st century.The frequency peaked in July and was concentrated from 23:00 to 07:00 next day （Beijing Time）， accounting for 56.5% of the whole day.The basin as a whole exhibited a single-peak night rain structure， but the northwestern， northeastern and central parts were bimodal， and the peak time was delayed from south to north.（4） The correlation and composite analysis revealed that the number of geological hazards was highly correlated with the frequency and rainfall of short-time heavy rainfall in the northwest， with correlation coefficients of 0.87 and 0.89， respectively.For the Sichuan basin as a whole， landslides and debris flows showed significant differences between the more frequent and less frequent short-time heavy rainfall.In the northwestern and southwestern parts of the basin， the short-time heavy rainfall had a large impact on various geological hazards.In the northeast， it had an impact on landslides， debris flows and other geological hazards， while in the south， it had an impact on other types of geological hazards.The northwest and northeast had the highest number of geological hazards， accounting for 40.2% and 31.7% of the total， respectively.But the short-time heavy rainfall was more likely to cause casualties in the northwest， and mainly caused direct economic losses and injuries in the northeast.The number of geological hazards in Sichuan basin was increasing， while the economic loss was decreasing， indicating that the disaster prevention and mitigation capacity has been significantly improved.

This study investigates the changes in the drought frequency in 2070–2099 relative to 1970–1999, due to the mean and shape changes of the probability density function (PDF) of the self-calibrated Palmer Drought Severity Index (PDSI), using CMIP5 multi-model historical simulations and projections under the RCP4.5 scenario. For severe droughts defined with PDSIs less than the 10th percentile, it is shown that over 41% of the global land, the increase in the severe drought frequency due to the shape change exacerbates the increase due to the mean change. Over 28% of the global land, the decrease in the drought frequency due to the shape change partially offsets the increase due to the mean change. Over 31% of the global land, the drought frequency increases due to the shape changes, but decreases due to the mean changes. The severe drought frequency due to both PDSI PDF mean and shape changes increases over almost the entire global land. We show that the PDSI standard deviation change is mainly determined by the mean precipitation change, while the PDSI mean change is determined by both mean precipitation and potential evapotranspiration changes. In particular, the PDSI standard deviation increases with the increase in mean precipitation which broadens the PDSI PDF, and thus enhances the severe drought frequency, and vice versa. On the other hand, the PDSI mean decreases with the decrease (increase) in mean precipitation (mean potential evapotranspiration). The difference in the attribution of drought frequency changes to the mean and shape changes over different regions can thus be largely explained by the mean precipitation and potential evapotranspiration changes. We also examine the moderate droughts defined with PDSIs between 10th and 20th percentiles in this study. For the moderate drought frequency, the spatial pattern of its changes due to the PDSI mean changes is similar to that of severe drought but with much smaller magnitudes, while its change in the spatial pattern due to the shape changes differs from severe drought with no significant changes. The moderate drought frequency due to both PDSI PDF mean and shape changes increases over 71% of the global land but decreases over 29% of the land.