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

=== 4.3.1 Observed Impacts on Agriculture ===

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AR5 concluded with ''high confidence'' that agricultural production was negatively affected by climate change, with droughts singled out as a major driver of food insecurity. In contrast, evidence of floods on food production was ''limited'' ( [[#Porter--2014|Porter et al., 2014]] ).

Globally, 23% of croplands are irrigated, providing 34% of global calorie production. Of these lands, 68% experience blue water scarcity at the least one month yr –1 and 37% up to five months yr –1 . Such agricultural water scarcity is experienced in mostly drought-prone areas in low-income countries ( [[#Rosa--2020a|Rosa et al., 2020a]] ). Approximately three quarters of the global harvested areas (~454 million hectares) experienced drought-induced yield losses between 1983 and 2009, and the cumulative production losses corresponded to USD 166 billion ( [[#Kim--2019|Kim et al., 2019]] ). Globally, droughts affected both harvested areas and yields, with a reported cereal production loss of 9–10% due to weather extremes between 1964 and 2007. Yield losses were greater by about 7% during recent droughts (1985–2007) due to greater damage—reducing harvested area—compared to losses from earlier droughts (1964–1984), with 8–11% greater losses in high-income countries than in low-income ones ( [[#Lesk--2016|Lesk et al., 2016]] ). Globally, between 1961 and 2006, it has been estimated that 25% yield loss occurred, with yield loss probability increasing by 22% for maize, 9% for rice and 22% for soybean under drought conditions ( [[#Leng--2019|Leng and Hall, 2019]] ). Mean climate and climate extremes are responsible for 20–49% of yield anomalies variance, with 18–45% of this variance attributable to droughts and heatwaves ( [[#Vogel--2019|Vogel et al., 2019]] ). Drought has been singled out as a major driver of yield reductions globally ( ''high confidence'' ) ( [[#Lesk--2016|Lesk et al., 2016]] ; [[#Meng--2016|Meng et al., 2016]] ; [[#Zipper--2016|Zipper et al., 2016]] ; [[#Anderson--2019|Anderson et al., 2019]] ; [[#Leng--2019|Leng and Hall, 2019]] ).

Yields of major crops in semiarid regions, including the Mediterranean, sub-Saharan Africa, South Asia and Australia, are negatively affected by precipitation declines in the absence of irrigation ( [[#Iizumi--2018|Iizumi et al., 2018]] ; [[#Ray--2019|Ray et al., 2019]] ), but this trend is less evident in wetter regions ( [[#Iizumi--2018|Iizumi et al., 2018]] ). Precipitation and temperature changes reduced global mean yields of maize, wheat and soybeans by 4.1, 1.8 and 4.5%, respectively ( [[#Iizumi--2018|Iizumi et al., 2018]] ). Of the global rice yield variability of ~32%, precipitation variability accounted for a larger share in drier South Asia than in wetter East and Southeast Asia ( [[#Ray--2015|Ray et al., 2015]] ). Between 1910 and 2014 agro-climatic conditions became more conducive to maize and soybean yield growth in the American Midwest due to increases in summer precipitation and cooling due to irrigation ( [[#Iizumi--2016|Iizumi and Ramankutty, 2016]] ; [[#Mueller--2016|Mueller et al., 2016]] ) (Box 4.3). In Australia, between 1990 and 2015, the negative effects of reduced precipitation and rising temperature led to yield losses, but yield losses were partly avoided because of elevated CO 2 atmospheric concentration and technological advancements ( [[#Hochman--2017a|Hochman et al., 2017a]] ). Overall, temperature-only effects are stronger in wetter regions like Europe and East and Southeast Asia, and precipitation-only effects are stronger in drier regions ( [[#Iizumi--2018|Iizumi et al., 2018]] ; [[#Ray--2019|Ray et al., 2019]] ) ( ''medium evidence, high agreement'' ). In Asia, the gap between rain-fed and irrigated maize yield widened from 5% in the 1980s to 10% in the 2000s ( [[#Meng--2016|Meng et al., 2016]] ). In North America, yields of maize and soybeans have increased (1958–2007), yet meteorological drought has been associated with 13% of overall yield variability. However, yield variability was not a concern where irrigation is prevalent ( [[#Zipper--2016|Zipper et al., 2016]] ). However, when water scarcity has reduced irrigation, yields have been negatively impacted ( [[#Elias--2016|Elias et al., 2016]] ). In Europe, yields have been affected negatively by droughts ( [[#Beillouin--2020|Beillouin et al., 2020]] ), with losses tripling between 1964 and 2015 ( [[#Brás--2021|Brás et al., 2021]] ). In West Africa, between 2000 and 2009, drought, among other altered climate conditions, led to millet and sorghum yield reductions between 10 and 20% and 5 and 15%, respectively ( [[#Sultan--2019|Sultan et al., 2019]] ). Between 2006 and 2016, droughts contributed to food insecurity and malnutrition in northern, eastern and southern Africa, Asia and the Pacific. In 36% of these nations—mainly in Africa—where severe droughts occurred, undernourishment increased ( [[#Phalkey--2015|Phalkey et al., 2015]] ; [[#Cooper--2019|Cooper et al., 2019]] ). An attribution study showed that anthropogenic emissions increased the chances of October–December droughts over the region by 1.4–4.3 times and resulted in below-average harvests in Zambia and South Africa ( [[#Nangombe--2020|Nangombe et al., 2020]] ). Root crops, a staple in many tropics and subtropical countries, and vegetables are particularly prone to drought, leading to smaller fruits or crop failure ( [[#Daryanto--2017|Daryanto et al., 2017]] ; [[#Bisbis--2018|Bisbis et al., 2018]] ). Livestock production has also been affected by changing seasonality, increasing frequency of drought, rising temperatures and vector-borne diseases and parasites through changes in the overall availability, as well as reduced nutritional value, of forage and feed crops ( [[#Varadan--2014|Varadan and Kumar, 2014]] ; [[#Naqvi--2015|Naqvi et al., 2015]] ; [[#Zougmoré--2016|Zougmoré et al., 2016]] ; [[#Henry--2018|Henry et al., 2018]] ; [[#Godde--2019|Godde et al., 2019]] ) ( ''medium confidence'' ).

Floods have led to harvest failure and crop and fungal contamination ( [[#Liu--2013|Liu et al., 2013]] ; [[#Uyttendaele--2015|Uyttendaele et al., 2015]] ). Globally, between 1980 and 2018, excess soil moisture has reduced rice, maize, soybean and wheat yields between 7 and 12% ( [[#Borgomeo--2020|Borgomeo et al., 2020]] ). Changes in groundwater storage and availability, which are affected by the intensity of irrigated agriculture, also negatively impacted crop yields and cropping patterns ( [[#4.2.6|Section 4.2.6]] , Box 4.3, 4.7.2). Moreover, extreme precipitation can lead to increased surface flooding, waterlogging, soil erosion and susceptibility to salinisation ( ''high confidence'' ). For example, in Bangladesh, in March and April 2017, floods affected 220,000 ha of a nearly harvest-ready summer paddy crop and resulted in almost a 30% year-on-year increase in paddy prices. An attribution study of those pre-monsoon extreme rainfall events in Bangladesh concluded that anthropogenic climate change doubled the likelihood of the extreme rainfall event ( [[#Rimi--2019|Rimi et al., 2019]] ). Moreover, floods, extreme weather events and cyclones have led to animal escapes and infrastructure damage in aquaculture (Beveridge et al., 2018; [[#Islam--2018|Islam and Hoq, 2018]] ; [[#Naskar--2018|Naskar et al., 2018]] ; [[#Lebel--2020|Lebel et al., 2020]] ) (see [[IPCC:Wg2:Chapter:Chapter-5#5.9.1|Section 5.9.1]] ).

Worldwide, the magnitudes of climate-induced water-related hazards and their impact on agriculture are differentiated across populations and genders (Sections 4.3.6; 4.8.3). Evidence shows that hydroclimatic factors pose high food insecurity risks to subsistence farmers, whose first and only source of livelihood is agriculture, and who are situated at low latitudes where the climate is hotter and drier ( [[#Shrestha--2016|Shrestha and Nepal, 2016]] ; [[#Sujakhu--2016|Sujakhu et al., 2016]] ). Historically, they have been the most vulnerable to observed climate-induced hydrological changes ( [[#Savo--2016|Savo et al., 2016]] ). Indigenous and local communities, often heavily reliant on agriculture, have a wealth of knowledge about observed changes. These are important because they shape farmers’ perceptions, which in turn shape the adaptation measures farmers will undertake ( [[#Caretta--2015|Caretta and Börjeson, 2015]] ; [[#Savo--2016|Savo et al., 2016]] ; [[#Sujakhu--2016|Sujakhu et al., 2016]] ; [[#Su--2017|Su et al., 2017]] ) ( [[#4.8.4|Section 4.8.4]] ) ( ''high confidence)'' .

In summary, ongoing climate change in temperate climates has some positive impacts on agricultural production. In subtropical/tropical climates, climate-induced hazards such as floods and droughts negatively impact agricultural production ( ''high confidence'' ). People living in deprivation and Indigenous Peoples have been disproportionally affected. They often rely on rain-fed agriculture in marginal areas with high exposure and high vulnerability to water-related stress and low adaptive capacity ( ''high confidence)'' .

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