Global Estimation of the Synergies and Trade-offs among
Climate Policies and SDGs in terms of Water Sector
気候政策が水に関するSDG目標へ与えるグローバルな影響

Yukiko HIRABAYASHI, Besse Andi RIMBA, Shibaura Institute of Technology
Taikan OKI, Masahide KIGUCHI, The University of Tokyo
Naota HANASAKI, Ai ZHIPIN, National Institute for Environmental Studies
Toshichika Iizumi, Noriko NOZAKI, Wonsik KIM, National Institute for AgroEnvironmental Sciences

18 October 2023, Tokyo, Japan

Background
IPCC SR 1.5
SPM Fig.4• Climate change mitigation and adaptation
measures are expected to have significant
synergies with efforts to achieve the Sustainable
Development Goals (SDGs); however, trade-offs
are also a concern.
• SDG 6 (water) exhibits the greatest trade-offs
through energy demand and land use.
✓ The assessment of past IPCC reports aremainly based on a qualitative review✓ IPCC SR Land (2019) assess the qualitative
effects of biofuel production✓ The integrated assessment model lacks
consideration of water resource constraints,drought, and flooding.
• Quantitative effects of climate actions(mitigation & adaptation) to SDG targets2There is great synergy between mitigation and adaptation
measures to improve vulnerability to fluvial flooding••••

Low emission scenario can reducethe deterioration of the SDG
indicator by up to 50% by 2100
compared to the high emission
scenario, with mitigation measures
having greater synergy.
Adaptation measures can reducethe deterioration of indicators by19%.
With financial support from outside
their own countries, exposure toflooding in low-income countries
can be reduced from current levels.
More ambitious flood control
measures are also important toachieve flood exposure indicators in
low-income countries to levels
similar to those in developedcountries.
Tanoue et al., Nature Climate Change, 2021

Changes in SDG 1.5.1 (poverty) and SDG 11.5 (urban) indicators (flood exposed
population per 100,000) for fluvial flooding. Standard adaptation: a country protects
up to if costs is lower than benefits; maximum adaptation: a country adapts whenadaptation is effective regardless of costs of the additional protection.

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Neglecting water use sustainability could increase century-end global
BECCS potential via irrigation by 60-71%, compared to a mere 5-6%
when considering it
Maximum feasible amount of BECCS with sustainable irrigation

Sustainable irrigation increases BECCS maximum feasible volume by only 5-6%.
→Refute the optimism of conventional irrigation to increase BECCS production.
Ai, Hanasaki, et al., Nature Sustainability, 2021

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Mitigation has a positive impact on small farmers’ productivity (SDG2)• Small farmers’ productivity at the end of the century under the low emission scenario (ssp126) is52.7% higher than under the high emission scenario (ssp585). →Mitigation has synergy to SDG2.
• The irrigation adoption rate in low-income countries in water scarce areas is 37% for small-scale
farmers and 42% for non-small-scale farmers.

• 5% increase in the irrigation adoption, the small farmers’ productivity can increase by 10% evenssp585. → importance of narrowing the gap in irrigation adoption rates in low-income countries
Change in annual agricultural output perhousehold from current irrigated area

(%)

(%)

Change in annual agricultural output
per household from current climate

Nozaki et al. (2023),
Environ Res Commun.

SSP126

SSP585

SSP126

SSP585Global ex. high income
Middle to low income

Low income
Middle to high income5In addition to mitigation, carbon storage in agriculturallands is expected to have synergies in increasing crop
yields and improving water quality••

Agricultural land management canincrease global cropland soil carbon
by 12.78 billion tC (11.55-14.05billion tC).
This amount of carbon could
increase crop production by 38.25
million tons (22.88-5.748 million
tons), reduce the global averagetemperature increase by 0.030°C(0.019-0.041°C), and save 5.82
million tons N (3.89-7.14 milliontons N) in nitrogen fertilizer inputs.

Iizumi T, Hosokawa N, Wagai R Soil carbon-food synergy: sizable
contributions of small-scale farmers CABI Agric Biosci 2 43 (2021).
https://doi.org/10.1186/s43170-021-00063-6

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Promoting BECCS relying on too much water use may
prevent a reduction in the disparity in the rate of irrigation• If energy crops were fully irrigated, theadoption by small farmers

increase in water withdrawal would be
3,929 km3 per year. This increase inwater withdrawal is equivalent to 4,001
km3 of total global water withdrawal in2010.
• In Asia and Africa, this would require 20
to 21 times more water than would beneeded if competition with other wateruses were avoided, and there is clearly noroom for increasing the rate of irrigation
adoption by small farmers.

Nozaki N et al. Environ Res Lett (2023)

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Weather-related Disaster Risk and Tipping
Climate change will increase the risk of weather-related disasters

Flooding in Rojana Industrial
Estate, Thailand (Oct-Nov 2011)
タイ、ロジャナ工業団地の浸水
Source：MLIT

Increase in heavy
rainfall, flooding,extreme temperature
大雨・河川洪水
極端な高温の増加

mentions qualitative impact of TE for the first time
＋ AR6The higher, the greater the probability of occurrence.

Sea Level Rise（m）

Catastrophic Effects of Tipping Element (TE)1.5

IPCC AR6 WGI Fig.SPM.8

10.5

If tipping occurs
Most megacities are located along the coast

1950

2000 2020 2050

2100

TE: Geophysical critical phenomena: irreversible changes
that occur when a certain threshold (tipping) is exceeded 8What happens if tipping should occur?
Collapse of icesheet,increased fresh
water supply

irreversible risk

If the instability of ice sheets such as inwestern Antarctic continues, the upper
limit could reach 15 m or more.

87

SLR・AMOC stoppage

6Up to about 1 m by 2100 under
SSP-RCP climate scenarios?

ssp1-2.6

Irreversible ocean
cycle change
AMOC etc.
※AMOC：Atlantic Meridional Overturning Circulation

ssp5-8.5

Climate？

IPCC AR6 WGI Fig.SPM.8

SRL in2300 (m)54321

What happens if tipping should occur?
Collapse of icesheet,increased freshwater supply

irreversible risk
SLR・AMOC stoppage

Likely loss of much of Japan's coastline+ Combined with river flooding, typhoons, etc.?
+7m due to the collapse of the Greenland ice sheet

Climate？

TokyoNagoya?
Irreversible ocean
cycle change
AMOC etc.
※AMOC：Atlantic Meridional Overturning Circulation

Courtesy: Shinjiro Kanae

10What happens if tipping should occur?
Collapse of icesheet,increased fresh
water supply

irreversible risk
SLR・AMOC stoppage
Climate？

?

Impact on atmospheric-mediatedweather hazards is unknown.

• Younger Dryas period（12,800–11,700 years ago）
✓ Weakening of the African and Asian monsoons
アフリカモンスーン・アジアモンスーンの弱化✓ Strengthening of Southern Hemisphere monsoon system
南半球のモンスーンシステムの強化✓ Drying of meso-America and Europe
メソ-アメリカとヨーロッパの乾燥化✓ Wetting of the mid-latitude North America
北米の中緯度の湿潤化
Younger Dryas Event

AMOC weakening, 2×CO2

Irreversible ocean
cycle change
AMOC etc.
※AMOC：Atlantic Meridional Overturning Circulation

Dry
乾燥化

IPCC AR6 WGI Fig.8.27

Wet
湿潤化

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Summary• There is great synergy between mitigation and adaptation measures to improvevulnerability to fluvial flooding, water quality and water resources.
• For SDG targets on water, synergies from climate policies significantly outweigh tradeoffs, and should be actively pursued with consideration regarding areas/items of trade-off
concern.
• Promoting BECCS relying on too much water use may prevent a reduction in the disparity
in the rate of irrigation adoption by small farmers.
• The countries with the largest synergies and trade-offs are mainly developing countries in
Asia and Africa, suggesting the importance of international support for adaptation
measures.
• If our climate goes beyond a tipping point, this might lead to catastrophic changes.
✓ Disastrous sea level rises ranging from several meters to as much as ten meters.
✓ Slowing or cessation of the Atlantic Meridional Ocean Circulation (AMOC) due to the
freshwater supply from melting ice sheets may impact on climate.
• A rapid transition to a low-carbon society is imperative in reducing the likelihood of suchcatastrophic tipping element.
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