Impacts Of Anthropogenic And Natural Forcing On Historical And Future Changes In Global Precipitation

Precipitation is a crucial part of the water cycle and one of the most direct and critical meteorological factors influenced by climate change.Warming has already changed precipitation patterns,including trend,variability,and intensity,and risen the risk of heavy rainfall,floods,and droughts,which have serious impacts on the social economy and ecosystem.Therefore,assessing the influence from anthropogenic forcing on precipitation changes will help us to understand the patterns of precipitation changes and the mechanisms of their response under global warming,which is essential for defining mitigation and adaptation policies.In this study,we systematically assess the impact of anthropogenic and natural forcing on global land precipitation changes,including mean precipitation,precipitation variability,and extreme precipitation,and evaluate the contributions of different external forcings and their regional differences,based on the results of the latest Coupled Model Intercomparison Project Phase 6(CMIP6)multi-model historical attribution experiment and future scenario estimation experiment.The major conclusions are as following:(1)The GHG-induced precipitation increases by about 20.5 mm/a,while the AAinduced precipitation decreases by ～18.0 mm/a over most global land areas during last100 years(1915-2014),with flattening of the probability distribution functions(PDF).The changes induced by both NAT and LU are relatively little for most of global land areas.Fingerprinting detection shows that signals of GHG and AA are detectable at the global scale since 1990 s,and become detectable at the very likely level(90%)by 2000.However,the time of emergence of the anthropogenic signal vary locally.Both LU and NAT signal are not detectable in most regions.The response of precipitation to climate change show that GHG leads to more warming and increased precipitation,while AA leads to cooling and decreased precipitation.(2)The changes in precipitation due to GHG,AA and all external forcings(ALL)are projected to increase by about 3.0%-24.8%,1.1%-6.9% and 4.2%-31.2%,respectively,across most land areas in the twenty-first century,especially over the midand high latitudes of the Northern Hemisphere(NH)and central Africa.By contrast,the NAT-induced changes are relatively small.The PDF of precipitation will tend to be flattening under the influence of external forcings in the future.Fingerprinting detection shows that the signals of GHG(except for Australia),AA and ALL are detectable over most land areas.The GHG signals are stronger and detected earlier than the AA signals.There are significant regional differences in the response of future precipitation to climate change,with only Europe and South America have correlations between temperature and precipitation under the influence of GHG.(3)The change of precipitation variability shows a global non-uniform distribution.The ALL-and GHG-induced precipitation variability increases over most global land areas,while AA reduces precipitation variability in the mid-and high latitudes of the NH.Precipitation variability due to LU declines over Greenland,Australia,and most of low latitudes,but increases in the mid-and high latitudes of NH.Signals of ALL,GHG,LU,and NAT emerge in 1996,1995,2001,and 2016 in the global and NH,while in 2016,1995,2008,and 2015 in the Southern Hemisphere(SH),respectively.Under the SSP2-4.5 scenario,ALL,GHG,AA,and NAT lead to the change of future precipitation variability far beyond the range of internal climate variability.ALL-,GHG-,and NAT-induced precipitation variability increases over 87.9%,94.0%,and97.6% of global land areas,respectively,and the emergence time is mostly concentrated in the 2020 s.The signal of AA forcing is detectable after 2030 in 50% of global.(4)By the end of the 21 st century,the frequency and intensity of heavy(R95p)and extreme heavy(R99p)precipitation,as well as the maximum continuous rain days(CWD),will increase due to ALL,GHG,AA,and NAT over global land areas.Conversely,the effects of external forcings on future dry days(R1)vary considerably.The frequency and intensity of R1 and maximum consecutive dry days(CDD)increase due to ALL and GHG,while they decrease under NAT.AA is projected to reduce the frequency and intensity of R1,but increase CDD.There are significant regional differences of future extreme precipitation in response to climate change.ALL and GHG will lead to an increased frequency and intensity of R95 p and R99 p,and a reduced frequency of R1 over East Asia(EA),Europe(EU),and North America(NA).In contrast,these forcings will cause a decreased frequency of R95 p and an increased frequency of R1 over South America(SA)and Australia(AU).The R1 intensity attributed to GHG will strengthen in most land areas,while only strengthening over NA,SA,and AU under ALL.AA is predicted to increase the frequency and intensity of R95 p and R99 p,but decrease R1 frequency and intensity over most land areas.The effect of NAT on R95 p and R99 p is minor,while the impact on R1 varies greatly across different regions.ALL,GHG,AA,and NAT are expected to cause a decrease in CWD and an increase in CDD over SA and AU,while causing an increase in CWD and a decrease in CDD over EA,EU,and NA.The distribution and percentage change of daily precipitation intensity in frequency indicate that heavy precipitation events due to external forcings will gradually increase from near(2021-2040)to long term(2081-2100).The most significant impact will be caused by ALL and GHG,followed by AA and NAT.