Editing IPCC:AR6/WGI/Chapter-4 (section)

==== 4.3.1.2 Precipitation ====

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The AR5 assessed from CMIP5 projections that global mean precipitation over the 21st century will increase by more than 0.05 mm day <sup>–1</sup> (about 2% of global precipitation) and 0.15 mm day <sup>–1</sup> (about 5% of global precipitation) under the RCP2.6 and RCP8.5 scenarios, respectively ( [[#Collins--2013|Collins et al., 2013]] ). These changes are generally in line with those from the CMIP6 simulations following SSP1-2.6 and SSP5-8.5 (Table 4.3).

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'''Table''' '''4.3 |''' '''CMIP6 precipitation anomalies (%) relative to averages over 1995–2014 for selected future periods, regions and SSPs.''' Displayed are the multi-model averages across the individual models and, in parentheses, the 5 '''–''' 95% ranges. Also shown are land precipitation anomalies at the time when global increase in GSAT relative to 1850–1900 exceeds 1.5°C, 2.0°C, 3.0°C, and 4.0°C, and the percentage of simulations for which such exceedances are true (to the right of the parentheses). Here, the time of GSAT exceedance is determined as the first year at which 21-year running averages of GSAT exceed the given threshold. Land precipitation percent anomalies are then computed as 21-year averages about the year of the first GSAT crossing. The numbers of models used are indicated in Figure 4.4.

{| class="wikitable"
|-
| colspan="2"| '''Time Period and Region'''

| '''SSP1-1.9 (%)'''

| '''SSP1-2.6 (%)'''

| '''SSP2-4.5 (%)'''

| '''SSP3-7.0 (%)'''

| '''SSP5-8.5 (%)'''

|-
| rowspan="3"| '''Land'''

| 2021–2040

| 2.4 (0.7, 4.1)

| 2.0 (–0.6, 3.6)

| 1.5 (–0.4, 3.6)

| 1.2 (–1.0, 3.4)

| 1.7 (–0.1, 4.1)

|-
| 2041–2060

| 2.7 (0.6, 5.0)

| 2.8 (–0.4, 5.2)

| 2.7 (0.3, 5.2)

| 2.5 (–0.8, 5.1)

| 3.7 (–0.1, 6.9)

|-
| 2081–2100

| 2.4 (–0.2, 4.7)

| 3.3 (0.0, 6.6)

| 4.6 (1.5, 8.3)

| 5.8 (0.5, 9.6)

| 8.3 (0.9, 12.9)

|-
| '''Global'''

| 2081–2100

| 2.0 (0.4, 4.2)

| 2.9 (1.0, 5.2)

| 4.0 (2.3, 6.7)

| 4.7 (2.3, 8.2)

| 6.5 (3.4, 10.9)

|-
| '''Ocean'''

| 2081–2100

| 1.9 (0.6, 4.1)

| 2.8 (1.1, 5.4)

| 3.8 (2.0, 6.8)

| 4.4 (2.1, 7.9)

| 6.0 (2.9, 10.5)

|-
| rowspan="4"| '''Land'''

| ∆T &gt; 1.5°C

| 2.0 (0.6, 4.4) 55

| 1.7 (–2.0, 6.9) 87

| 1.7 (–2.9, 6.2) 100

| 1.5 (–3.9, 6.6) 100

| 1.5 (–3.5, 6.4) 100

|-
| ∆T &gt; 2.0°C

| 3.8 (2.4, 5.8) 36

| 2.2 (–2.0, 4.6) 58

| 2.8 (–2.2, 8.1) 97

| 2.4 (–4.4, 7.7) 100

| 2.8 (–2.8, 8.3) 100

|-
| ∆T &gt; 3.0°C

| – (–, –) 0

| – (–, –) 0

| 4.9 (1.5, 9.6) 54

| 4.3 (–4.4, 11.5) 97

| 4.9 (–2.6, 11.0) 100

|-
| ∆T &gt; 4.0°C

| – (–, –) 0

| – (–, –) 0

| 4.2 (1.3, 6.3) 9

| 5.1 (–2.5, 11.1) 57

| 6.4 (–3.4, 15.0) 85

|}

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[[File:cb61dbfb90e415dbe28bdb48631401f0 IPCC_AR6_WGI_Figure_4_4.png]]

'''Figure''' '''4.4 |''' '''CMIP6 annual mean precipitation changes (%) from historical and scenario simulations. (a)''' Northern Hemisphere extratropics (30°N–90°N). '''(b)''' North Atlantic subtropics (5°N–30°N, 80°W–0°). Changes are relative to 1995–2014 averages. Displayed are multi-model averages and, in parentheses, 5–95% ranges. The numbers inside each panel are the number of model simulations. Results are derived from concentration-driven simulations. Further details on data sources and processing are available in the chapter data table (Table 4.SM.1).

Unlike AR5, our focus here is on land rather than global precipitation because land precipitation has greater societal relevance. These are displayed as percent changes relative to 1995–2014 (Figure 4.2b). Based on these results, we conclude that global land precipitation is larger during the period 2081–2100 than during the period 1995–2014, under all scenarios considered here ( ''high confidence'' ) (Table 4.3). Global land precipitation for 2081–2100, relative to 1995–2014, shows a 5–95% range of –0.2 to +4.7% under SSP1-1.9 and 0.9–12.9% under SSP5-8.5, respectively. The corresponding ranges under the other emissions scenarios are 0.0–6.6% (SSP1-2.6), 1.5–8.3% (SSP2-4.5), and 0.5–9.6% (SSP3-7.0). A detailed assessment of hydrological sensitivity, or change in precipitation per degree warming, can be found in [[IPCC:Wg1:Chapter:Chapter-8|Chapter 8]] (Section 8.2.1).

For scenarios where unanimity across all of the model simulations that GSAT change relative to 1850–1900 rises above 1.5°C (SSP2-4.5, SSP3-7.0, or SSP5-8.5), the ensemble-mean change in global land precipitation from 1850–1900 until the time of exceedance is on average about 1.6%. For scenarios with unanimous global warming above 2.0°C (SSP3-7.0, or SSP5-8.5) and 3.0°C (SSP5-8.5), the ensemble-mean increase in global land precipitation for those models that do exceed 2.0°C and 3.0°C is on average about 2.6% and 4.9%, respectively. On average under SSP1-1.9 and SSP1-2.6, the global land precipitation change for simulations where global warming exceeds 1.5°C and 2.0°C will be about 1.9% and 3.0%, respectively.

Relative to 1995–2014, and across all of the scenarios considered here, CMIP6 models show greater increases in precipitation over land than either globally or over the ocean (Table 4.3; ''high confidence'' ). Over the Northern Hemisphere (NH) extratropics, the 5–95% changes in precipitation over land between 1995–2014 and 2021–2040, 2041–2060, and 2081–2100, following SSP5-8.5, are 0.6–4.9%, 1.5–8.8%, and 4.7–17.2%, respectively (Figure 4.4). At the other end of scenario spectrum, SSP1-1.9, the corresponding changes are 0.6–5.4%, 0.6–7.3%, and 0.2–7.7%, respectively. By contrast, over the North Atlantic subtropics, precipitation decreases by about 10% following SSP3-7.0 and SSP5-8. There is no change in subtropical precipitation in the North Atlantic following SSP1-1.9, SSP1-2.6, or SSP2-4.5 ( ''high confidence'' ); thereby highlighting the potential limitations of pattern scaling for regional hydrological changes (Section 8.5.3). The reasons for the opposing changes in these two regions are assessed in Chapter 8.

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