Editing IPCC:AR6/WGI/Chapter-8 (section)

==== 8.4.1.3 Precipitation Amount, Frequency and Intensity ====

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This section assesses projected changes in precipitation at regional scales. Note that changes in precipitation seasonality are assessed in Box 8.2 and that changes in regional monsoons are assessed in [[#8.4.2.4|Section 8.4.2.4]] , where both circulation and rainfall are considered. Further assessments of regional projections of precipitation are presented in Chapters 10, 12 and the Atlas, while a comprehensive assessment of changes in precipitation extremes is provided in Chapter 11.

The AR5 assessed that the contrast of mean precipitation amount between dry and wet regions and seasons is expected to increase over most of the globe as temperatures increase ( ''high confidence'' ), but with large regional variations. Precipitation over the high latitudes, equatorial Pacific Ocean, mid-latitude wet regions, and monsoon regions were assessed as ''likely'' to increase under the RCP8.5 scenario, and in many mid-latitude and subtropical dry regions as ''likely'' to decrease (AR5 Chapters 7, 12, and 14). Extreme precipitation over most mid-latitude land areas and wet tropical regions was assessed as ''very likely'' to become more intense and more frequent.

Geographical patterns of projected precipitation changes show substantial seasonal contrasts and regional differences, including over land (Figure 8.14 and Figure 4.27). Projections for 2081 – 2100 under the SSP2-4.5 scenario suggest increased precipitation over the tropical oceans, north-eastern Africa, the Arabian Peninsula, India, south-eastern Asia and the Polar regions while decreased precipitation is projected mainly over the subtropical regions ( [[IPCC:Wg1:Chapter:Chapter-4#4.5.1.4|Section 4.5.1.4]] ). Precipitation changes contrast regionally in the tropics with wetter wet seasons over South Asia, central Sahel and eastern Africa, but less precipitation over Amazonia and coastal West Africa ( [[#8.4.2.4|Section 8.4.2.4]] ). These large-scale responses are associated with stronger moisture transports in a warmer climate that are modulated by the greater warming over land than ocean, atmospheric circulation responses and land surface feedbacks ( [[#8.2.2|Section 8.2.2]] ). There is agreement across CMIP5 and CMIP6 modelling studies that precipitation increases in wet parts of the atmospheric circulation and decreases in dry parts ( [[#Liu--2013|Liu and Allan, 2013]] ; [[#Kumar--2015|Kumar et al., 2015]] ; [[#Deng--2020|Deng et al., 2020]] ; [[#Schurer--2020|Schurer et al., 2020]] ) although these regions shift with atmospheric circulation changes. The overall pattern is robust across different model scenarios and time horizons ( [[#Tebaldi--2018|Tebaldi and Knutti, 2018]] ), but some deviations from the mean pattern cannot be excluded due to the multiple time scales and non-linear atmospheric or land surface processes involved ( [[#8.5.3|Section 8.5.3]] ). Near-term regional changes in precipitation are more uncertain because of a stronger sensitivity to natural variability ( [[#8.5.2|Section 8.5.2]] ) and non-GHG anthropogenic forcings ( [[IPCC:Wg1:Chapter:Chapter-4#4.4.1.3|Section 4.4.1.3]] and 8.4.3.1).

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[[File:4274eba6c74a1dd9f72d36fd37f4bc65 IPCC_AR6_WGI_Figure_8_14.png]]

'''Figure 8.14 |''' '''Projected long-term relative changes in seasonal mean precipitation.''' Global maps of projected relative changes (%) in seasonal mean of precipitation averaged across available CMIP6 models (number provided at the top right of each panel) in the SSP2-4.5 scenario. All changes are estimated for 2081–2100 relative to the 1995–2014 base period. Uncertainty is represented using the simple approach. No overlay indicates regions with high model agreement, where ≥80% of models agree on sign of change; diagonal lines indicate regions with low model agreement, where &lt;80% of models agree on sign of change. For more information on the simple approach, please refer to the Cross-Chapter Box Atlas.1. Further details on data sources and processing are available in the chapter data table (Table 8.SM.1).

Projected changes in regional precipitation also arise as a response to changes in large-scale atmospheric circulation ( [[#8.2.2.2|Section 8.2.2.2]] and 8.4.2), both in the tropics (Chadwick et al. , 2016b; Byrne et al. , 2018) and extratropics ( [[#Shaw--2019|Shaw, 2019]] ; [[#Oudar--2020b|Oudar et al., 2020b]] ). Despite variability in simulated changes, CMIP5 climate models consistently project large rainfall changes (of varying sign) over considerable proportions of tropical land during the 21st century ( [[#Chadwick--2016b|Chadwick et al., 2016b]] ). Since AR5, some robust responses in large-scale circulation patterns have been identified. For example, and as further assessed in [[#8.4.2|Section 8.4.2]] , CMIP6 models project a northward shift in the tropical rain belt over eastern Africa and the Indian Ocean and a southward shift in the eastern Pacific and Atlantic oceans ( [[#Mamalakis--2021|Mamalakis et al., 2021]] ). A projected strengthening and tightening of the tropical rain belt increases the contrasts between wet and dry tropical weather regimes and seasons. It is less clear how the well understood poleward expansion of the subtropics and mid-latitude storm tracks influences precipitation over subtropical and mid-latitude continents ( [[#8.2.2.2|Section 8.2.2.2]] ).

An ensemble of 31 CMIP6 models under the SSP5-8.5 scenario projects increases precipitation by 10–30% over much of the USA and decreases by 10–40% over Central America and the Caribbean by 2080 – 2099 ( [[#Almazroui--2021|Almazroui et al., 2021]] ). This CMIP6 ensemble also projects an increase in annual precipitation over the southern Arabian Peninsula and a decrease over the northern Arabian Peninsula, as also projected by CMIP3 and CMIP5 models ( [[#Almazroui--2020a|Almazroui et al., 2020a]] ). Annual mean precipitation is projected to increase over South Asia during the 21st century under all scenarios, although the rate of change varies within the region based on 27 CMIP6 models ( [[#Almazroui--2020c|Almazroui et al., 2020c]] ). CMIP6 projections also display a reduction in annual mean precipitation over northern and southern Africa while increases are projected over Central Africa, under the SSP1-2.6, SSP2-4.5 and SSP5-8.5 scenarios ( [[#Almazroui--2020b|Almazroui et al., 2020b]] ). The AR6 ( [[IPCC:Wg1:Chapter:Atlas|Atlas]] assesses that regions where annual mean rainfall is ''likely'' to increase include the Ethiopian Highlands, East, South and North Asia, south-eastern South America, northern Europe, northern and eastern North America, and the Polar Regions. In contrast, regions where annual mean rainfall is ''likely'' to decrease include southern Africa, coastal West Africa, Amazonia, south-western Australia, Central America, south-western South America, and the Mediterranean.

The AR5 identified that high-latitude precipitation increase may lead to an increase in snowfall in the coldest regions and a decrease of snowfall in warmer regions due to a decreased number of freezing days. The fraction of precipitation falling as snow and the duration of snow cover was projected to decrease. Heavy snowfall events globally are not expected to decrease significantly with warming as they occur close to the water freezing point, which will migrate poleward and in altitude ( [[#O’Gorman--2014|O’Gorman, 2014]] ; [[#Turner--2019|Turner et al., 2019]] ). There are only a small number of studies evaluating the implications of this mechanism in specific regions. A study for the north-eastern USA indicates smaller reductions for major snowfall events against the broader decline in snowfall expected from thermodynamic effects ( [[#Bintanja--2017|Bintanja and Andry, 2017]] ). Arctic snowfall is projected to decrease as rainfall makes up more of the precipitation ( [[#Zarzycki--2018|Zarzycki, 2018]] ).

Beyond annual or seasonal mean precipitation amounts, an implication of the parallel intensification of the global water cycle and of the increased residence time of atmospheric water vapour ( [[#8.2.1|Section 8.2.1]] ) is that the distribution of daily and sub-daily precipitation intensities will experience significant changes ( [[#Pendergrass--2014b|Pendergrass and Hartmann, 2014b]] ; [[#Pendergrass--2015|Pendergrass et al., 2015]] ; [[#Bador--2018|Bador et al., 2018]] ; [[#Douville--2021|Douville and John, 2021]] ), with fewer but potentially stronger events ( ''high confidence'' ) ( [[IPCC:Wg1:Chapter:Chapter-4#4.3.3|Section 4.3.3]] ). CMIP6 projections show that in the long-term more drier days but more intense single events of precipitation are expected, regardless of scenario (Figure 8.15). Over almost all land regions, it is ''very likely'' that extreme precipitation will intensify at a rate close to the 7% °C <sup>–1</sup> of global warming, but with large spatial differences (Sections 11.4 and 8.2.3.2). The projected increase in precipitable water is expected to lead to an increase in the highest possible precipitation intensities and an increase in the probability of occurrence of extreme precipitation events on the global scale (Neelin et al., 2017), regardless of how annual-mean precipitation changes ( [[#O’Gorman--2009|O’Gorman and Schneider, 2009]] ; [[#O’Gorman--2015|O’Gorman, 2015]] ). The projected increase in heavy precipitation intensity is also found for daily mean precipitation intensity though at a lower rate ( [[#Pendergrass--2014a|Pendergrass and Hartmann, 2014a]] ).

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[[File:44b811470e377c850a5783ebbff7e125 IPCC_AR6_WGI_Figure_8_15.png]]

'''Figure 8.15 |''' '''Projected long-term relative changes in daily precipitation statistics.''' Global maps of projected seasonal mean relative changes (%) in the number of dry days (i.e., days with less than 1 mm of rain) and daily precipitation intensity (in mm day – 1 , estimated as the mean daily precipitation amount at wet days – for example, days with intensity above 1 mm day – 1 ) averaged across available CMIP6 models (number provided at the top right of each panel) in the SSP1-2.6 '''(a, b)''' , SSP2-4.5 '''(c, d)''' and SSP5-8.5 '''(e, f)''' scenario respectively. Uncertainty is represented using the simple approach. No overlay indicates regions with high model agreement, where ≥80% of models agree on sign of change; diagonal lines indicate regions with low model agreement, where &lt;80% of models agree on sign of change. For more information on the simple approach, please refer to the Cross-Chapter Box Atlas.1. Further details on data sources and processing are available in the chapter data table (Table 8.SM.1).

An increase in the number of dry days is also projected in several regions of the world ( [[#Polade--2014|Polade et al., 2014]] ; [[#Berthou--2019a|Berthou et al., 2019a]] ), which can dominate the annual precipitation change at least in the subtropics ( [[#Polade--2014|Polade et al., 2014]] ; [[#Douville--2021|Douville and John, 2021]] ). These findings are supported by CMIP6 projections showing a widespread increase in daily mean precipitation intensity over land (Figure 8.15b,d,f) as well as an increase in the number of dry days in the subtropics and over Amazonia and Central America (Figure 8.15a,b,c). Such changes in precipitation regimes, as well as the general increase in the frequency and intensity of precipitation extremes ( [[IPCC:Wg1:Chapter:Chapter-11#11.4.5|Section 11.4.5]] ), contribute to an overall increase in precipitation variability ( [[#Polade--2014|Polade et al., 2014]] ; [[#Pendergrass--2017|Pendergrass et al., 2017]] ; [[#Douville--2021|Douville and John, 2021]] ). This is also found in CMIP6 models, which show a stronger increase of interannual variability than in seasonal mean precipitation changes, apart from in the winter extratropics where both quantities increase at the same rate with increasing global warming levels (Figure 8.16).

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[[File:f1c36cb4c37a18ef50999b4d59b8008e IPCC_AR6_WGI_Figure_8_16.png]]

'''Figure 8.16 |''' '''Rate of change in components of water cycle mean and variability across increasing global warming levels.''' Relative change (%) in seasonal mean total precipitable water (grey line), precipitation (red solid lines), runoff (blue solid lines), as well as in standard deviation of precipitation (red dashed lines) and runoff (blue dashed lines) averaged over extratropical land in '''(c)''' summer and '''(d)''' winter, and tropical land in '''(a)''' June–July–August (JJA) and '''(b)''' December–January–February (DJF) as a function of global mean surface temperature for the CMIP6 multi-model mean across the SSP5-8.5 scenario. Extratropical winter refers to DJF for Northern Hemisphere and JJA for Southern Hemisphere (and the reverse for extratropical summer). Each marker indicates a 21-year period centred on consecutive decades between 2015 and 2085 relative to the 1995–2014 base period. Precipitation and runoff variability are estimated by their standard deviation after removing linear trends from each time series. Error bars show the 5–95% confidence interval for the warmest 5°C global warming level. Figure adapted from [[#Pendergrass--2017|Pendergrass et al. (2017)]] and updated with CMIP6 models. Further details on data sources and processing are available in the chapter data table (Table 8.SM.1).

In summary, it is ''virtually certain'' that global precipitation will increase with warming due to increases in GHG concentrations and decreases in air pollution. There is ''high confidence'' that total precipitation will increase in the high latitudes, with a shift from snowfall to rainfall except in the coldest regions and seasons. There is also ''high confidence'' that precipitation will decrease over the Mediterranean, southern Africa, Amazonia, Central America, south-western South America, south-western Australia and coastal West Africa and that monsoon precipitation will increase over South Asia, East Asia and central-eastern Sahel. See ( [[#8.4.2.4|Section 8.4.2.4]] for a more detailed assessment of changes in regional monsoons. Daily mean precipitation intensities, including extremes, are projected to increase over most regions ( ''high confidence'' ). The number of dry days is projected to increase over the subtropics, Amazonia, and Central America ( ''medium confidence'' ). There is ''high confidence'' in an overall increase in precipitation variability over most land areas.

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'''Box 8.2 | Changes in Water Cycle S''' '''easonality'''

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'''Observed changes'''

The AR5 did not highlight observed changes in water cycle seasonality and SRCCL mostly emphasized changes in vegetation seasonality. Since AR5, a number of relevant studies have been published, but often with conflicting results. Based on three ''in situ'' datasets, reduced precipitation seasonality was identified over 62% of the terrestrial ecosystems analysed from 1950 – 2009 (Murray-Tortarolo et al. 2017). In contrast, both ''in situ'' and satellite data show a general increase in the annual range of precipitation from 1979 to 2010, which is dominated by wetter wet seasons ( [[#Chou--2013|Chou et al., 2013]] ). This paradox may be partly explained by a larger aerosol radiative forcing in the middle of the 20th century as well as by internal variability ( [[#Kumar--2015|Kumar et al., 2015]] ; see also Box 8.1). For instance, the ‘long rains’ over East Africa experienced declining trends in the 1980s and 1990s ( [[#Nicholson--2017|Nicholson, 2017]] ), which was linked to anthropogenic aerosols and SST patterns ( [[#Rowell--2015|Rowell et al., 2015]] ), followed by a recent recovery that was linked to internal variability ( [[#Wainwright--2019|Wainwright et al., 2019]] ). Two satellite datasets revealed decreased rainfall seasonality in the tropics but an increased seasonality in the subtropics and mid-latitudes since 1979, without clear attribution ( [[#Marvel--2017|Marvel et al., 2017]] ).

Large differences have been found across seven global precipitation datasets, with no region showing a consistent, statistically significant, positive or negative trend over the last three decades (X. [[#Tan--2020|]] [[#Tan--2020|Tan et al., 2020]] ). Regional studies suggest that observed changes in precipitation seasonality are neither uniform nor stable across the 20th century (X. Li et al. , 2016; [[#Mallakpour--2017|Mallakpour and Villarini, 2017]] ; Sahany et al. , 2018; Deng et al. , 2019) . Since the 1980s, there is growing evidence that contrasts between wet and dry regimes, including seasonality, have increased ( [[#Liu--2013|Liu and Allan, 2013]] ; Polson et al. , 2013; Murray-Tortarolo et al. , 2016; Tapiador et al. , 2016; Gallego et al. , 2017; [[#Polson--2017|Polson and Hegerl, 2017]] ; Barkhordarian et al. , 2018; Lan et al. , 2019; Liang et al. , 2020; Schurer et al., 2020) .

Additional changes in seasonality may manifest in the timing and duration of wet seasons. A later monsoon onset trend was reported throughout India from 1901 to 2013 ( [[#Sahany--2018|Sahany et al., 2018]] ). Conversely, an earlier rainfall onset was implicated in increased springtime rainfall over the Tibetan Plateau in recent decades (W. [[#Zhang--2017|Zhang et al., 2017]] a). Winter and early spring precipitation over the north-western Himalaya for the period 1951 – 2007 shows an increasing trend of daily precipitation extremes in association with enhanced amplitude variations of extratropical synoptic-scale systems known as ‘Western Disturbances’ (Madhura et al. , 2014; Cannon et al. , 2015; Krishnan et al. , 2019) . In China, an earlier onset was observed during 1961-2012 ( [[#Deng--2019|Deng et al., 2019]] ). In the African Sahel, rainfall has been most concentrated in the peak of the rainy season since the end of the 20th century ( [[#Biasutti--2019|Biasutti, 2019]] ). A shift in the seasonality of Sahelian rainfall, including delayed cessation has also been reported ( [[IPCC:Wg1:Chapter:Chapter-10#10.4.2.1|Section 10.4.2.1]] ; [[#Nicholson--2013|Nicholson, 2013]] ; [[#Dunning--2018|Dunning et al., 2018]] ). Over southern Africa, an observed earlier onset (1985 – 2007) is in contrast to a simulated historical and projected future delay in the wet season ( [[#Maidment--2015|Maidment et al., 2015]] ; [[#Dunning--2018|Dunning et al., 2018]] ). An increasingly early onset of the North American monsoon has been observed from 1978 to 2009 (Arias et al. , 2015) . Seasonality changes in the South American monsoon indicate delayed onsets since 1978 (Fu et al. , 2013; Yin et al. , 2014; Arias et al. , 2015; Debortoli et al. , 2015; Arvor et al. , 2017; Giráldez et al. , 2020; Haghtalab et al. , 2020; Correa et al., 2021).

In northern high latitudes, a shorter snow season (X. [[#Zeng--2018|Zeng et al., 2018]] ) is mainly due to an earlier onset of spring snowmelt ( [[#Peng--2013|Peng et al., 2013]] ) which has been attributed to anthropogenic climate change ( [[#Najafi--2016|Najafi et al., 2016]] ). Changes in snow seasonality affect streamflow at the regional scale, with an earlier peak in spring and a possible decrease of low-level flow in summer ( [[#Berghuijs--2014|Berghuijs et al., 2014]] ; [[#Kang--2016|Kang et al., 2016]] ; [[#Dudley--2017|Dudley et al., 2017]] ), while glacier shrinking can also alter the low-level flow in mountain catchments ( [[#Lutz--2014|Lutz et al., 2014]] ; [[#Milner--2017|Milner et al., 2017]] ; [[#Huss--2018|Huss and Hock, 2018]] ). This can be partly ameliorated by water management in regulated catchments ( [[#Arheimer--2017|Arheimer et al., 2017]] ), but not in large river basins such as the Amazon which also shows an increased seasonality of discharge since 1979 ( [[#Liang--2020|Liang et al., 2020]] ).

Increasing aridity contrasts between wet and dry seasons over the late 20th century have been suggested ( [[#Kumar--2015|Kumar et al., 2015]] ), with a human-induced decrease of water availability during the dry season over Europe, western North America, northern Asia, southern South America, Australia and eastern Africa ( [[#Padrón--2020|Padrón et al., 2020]] ). Seasonal contrasts in microwave surface soil moisture measurements have also increased over 1979 – 2016 ( [[#Pan--2019|Pan et al., 2019]] ). Terrestrial water storage variations derived from gravimetric measurements since 2003 show a strong seasonality which is underestimated by global hydrological models ( [[#Scanlon--2019|Scanlon et al., 2019]] ) and whose multi-decadal trends are difficult to interpret given the direct effect of enhanced water use ( [[#Rodell--2018|Rodell et al., 2018]] ; [[#Scanlon--2018|Scanlon et al., 2018]] ).

In summary, there is ''medium confidence'' that the annual range of precipitation has increased since the 1980s, at least in subtropical regions and over the Amazon. There is ''low confidence'' that this increase is due to human influence and that GHG forcing has already altered the timing or duration of wet seasons ''.'' There is ''high confidence'' that the human-induced retreat of the springtime snow cover and melting of glaciers have already contributed to changes in streamflow seasonality in high-latitude and low-elevation mountain catchments, and ''medium confidence'' that human activities have also contributed to an increased seasonality of water availability, including a drier dry season, in the extratropics.

'''Projected changes'''

The AR5 reported with ''high confidence'' that the contrast between wet and dry seasons will generally increase with global warming and that monsoon onset dates will ''likely'' become earlier or show little change, while monsoon retreat dates will ''likely'' be delayed, resulting in a lengthening of the wet season in many regions.

Since AR5, several studies have further documented a projected increase in rainfall seasonality and the understanding of the underlying mechanisms has been improved (Sections 8.2.1 and 8.3.2). CMIP5 models show that the seasonal concentration of annual precipitation will increase over many regions by the end of the 21st century, with robust model agreement in most subtropical regions where an increase in the mean number of dry days was also reported in the RCP8.5 scenario ( [[#Pascale--2016|Pascale et al., 2016]] ). The semi-arid, winter rainfall dominated subtropical climate is projected to shift poleward and eastward, with the equatorward margins replaced by a more arid climate type. However, evolving SST patterns and land – ocean warming contrasts cause more complex responses (Alessandri et al. , 2015; Polade et al. , 2017; Brogli et al. , 2019; Zappa et al. , 2020) . Projections over California show a stronger and shorter wet season ( [[#Polade--2017|Polade et al., 2017]] ; [[#Dong--2019|Dong et al., 2019]] ). Decreases in future winter and spring rainfall are projected over south-western Australia ( [[#Hope--2015|Hope et al., 2015]] ). Central Asia is projected to experience wetter winters, associated with an increase in snow depth in the north-eastern regions (Y. [[#Li--2019|]] [[#Li--2019|Li et al., 2019]] ). Even in a +2°C climate, both extreme precipitation and dryness will increase significantly in the extratropics, amplifying the seasonal precipitation range ( [[#Fujita--2019|Fujita et al., 2019]] ). A single-model study shows that the annual range of precipitation increases globally by 2.6% per 1°C of global warming in stabilized low-warming scenarios (Z. [[#Chen--2020|]] [[#Chen--2020|Chen et al., 2020]] a).

In the tropics, an amplified annual cycle (by about 3–5% °C <sup>–1</sup> ) of global land monsoon hydroclimates (precipitation '','' precipitation minus evaporation ( ''P–E'' ), and runoff) is projected by CMIP5 models under the RCP8.5 scenario, mostly due to a more intense wet season (W. [[#Zhang--2019|]] [[#Zhang--2019|Zhang et al., 2019]] b). A longer rainy season is projected by CMIP6 models over most regional monsoon areas except in the Americas ( [[#Moon--2020|Moon and Ha, 2020]] ). A delayed onset and cessation of the wet season over West Africa and the Sahel ( [[#Dunning--2018|Dunning et al., 2018]] ) and a slightly delayed onset of South Asian monsoon rainfall ( [[#Hasson--2016|Hasson et al., 2016]] ) are projected by CMIP5 models. CMIP5 projections suggest a strengthening of the annual cycle and a lengthening of the dry season in Southern Amazonia (Fu et al. , 2013; Reboita et al. , 2014; Boisier et al. , 2015; Pascale et al. , 2016; [[#Sena--2020|Sena and Magnusdottir, 2020]] ) . This is further verified by the projections from six CMIP6 models ( [[#Moon--2020|Moon and Ha, 2020]] ). A wet season shorter by 5 – 10 days by the end to the 21st century is projected for southern Africa ( [[#Dunning--2018|Dunning et al., 2018]] ).

An increase in streamflow seasonality is projected over several large rivers in the low-mitigation RCP8.5 scenario, but with only small changes in the seasonality timing, except in northern high latitudes due to the earlier but potentially slower snowmelt in a warmer world ( [[#Eisner--2017|Eisner et al., 2017]] ; [[#Musselman--2017|Musselman et al., 2017]] ). At the end of the century in a high-emissions scenario, peak snowmelt timing is projected to occur one month earlier and peak water volume is 79% lower in the eastern USA ( [[#Rhoades--2018|Rhoades et al., 2018]] ). Earlier snowmelt is projected, for example, by 30 days at the end of the 21st century in RCP4.5 for the Sierra Nevada in the western USA (F. [[#Sun--2018|]] [[#Sun--2018|Sun et al., 2018]] ). Sub-seasonal changes in water availability were found in many regions in the RCP8.5 scenario. However, these should be considered with caution given the magnitude of model errors (C.R. [[#Ferguson--2018|]] [[#Ferguson--2018|Ferguson et al., 2018]] ). Increases in the seasonality of water availability has been found to be more pronounced in areas with high atmospheric evaporative demand, giving rise to a pattern of seasonally variable regimes becoming even more variable ( [[#Konapala--2020|Konapala et al., 2020]] ). RCP4.5 and RCP8.5 projections show a pronounced soil drying in summer and autumn over western Europe, and a springtime drying over northern Europe due to an earlier snowmelt ( [[#Ruosteenoja--2018|Ruosteenoja et al., 2018]] ).

A simple relative seasonality metric ( [[#Walsh--1981|Walsh and Lawler, 1981]] ) applied to global projections based on CMIP6 models and SSP scenarios supports previous CMIP5 findings, especially the amplified seasonality of precipitation around the Mediterranean, and across southern Africa, California, southern Australia and the Amazon (Box 8.2, Figure 1). While such changes are not significant in the low-emissions SSP1-2.6 scenario, they are consistent with the increased frequency of dry days projected over the same regions (Figure 8.16). In monsoon regions outside the Americas, rainfall seasonality does not show a significant increase even in high-emissions scenarios. This challenges previous CMIP5 findings based on the difference between maximum and minimum monthly precipitation in a year (W. [[#Zhang--2019|]] [[#Zhang--2019|Zhang et al., 2019]] b) and higher sensitivity to the projected increase in precipitation extremes ( [[IPCC:Wg1:Chapter:Chapter-11#11.4.5|Section 11.4.5]] ). In the northern high latitudes, milder winters are associated with wetter conditions and a decrease in precipitation seasonality.

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[[File:2406f46bb99f532c09f4fe776aaa3b57 IPCC_AR6_WGI_Box_8_2_Figure_1.png]]

'''Box 8.2, Figure 1 |'''

'''Projected long-term changes in precipitation seasonality.''' Global maps of projected changes in precipitation seasonality (simply defined as the sum of the absolute deviations of mean monthly rainfalls from the overall monthly mean, divided by the mean annual rainfall as in [[#Walsh--1981|Walsh and Lawler, 1981]] ) averaged across available CMIP6 models (number provided at the top right of each panel) in the SSP1-2.6 '''(b)''' , SSP2-4.5 '''(c)''' and SSP5-8.5 '''(d)''' scenario respectively. The simulated 1995–2014 climatology is shown in panel '''(a)''' . All changes are estimated in 2081–2100 relative to 1995–2014. Uncertainty is represented using the simple approach. No overlay indicates regions with high model agreement, where ≥80% of models agree on sign of change. Diagonal lines indicate regions with low model agreement, where &lt;80% of models agree on sign of change. For more information on the simple approach, please refer to the Cross-Chapter Box Atlas.1. Further details on data sources and processing are available in the chapter data table (Table 8.SM.1).

In summary, the annual range of precipitation, water availability and streamflow will increase with global warming over subtropical regions and the Amazon ( ''medium confidence'' ), especially around the Mediterranean and across southern Africa ( ''high confidence'' ). The contrast between the wettest and driest month of the year is ''likely'' to increase by 3–5% °C <sup>–1</sup> with global warming in most monsoon regions, in terms of precipitation, water availability (P–E) and runoff ( ''medium confidence'' ). There is ''medium confidence'' that the monsoon season could be delayed in a warmer climate in the Sahel. There is ''high confidence'' of earlier snowmelt.

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