Impact of Climate Change on Wheat Megaenvironments

CIMMYT develops improved wheat germ-plasm for use in developing and emerging countries, which grow wheat on about 110 million ha (Lantican et al., 2005). To address the needs of these diverse wheat growing areas, CIMMYT uses the concept of megaenvironments (MEs) (Rajaram et al., 1994) to target germplasm development. A ME is defined as a broad, not necessarily contiguous, area occurring in more than one country and frequently transcontinental, defined by similar biotic and abiotic stresses, cropping system requirements, consumer preferences, and, for convenience, by a volume of production. The MEs to which wheat breeding stations participating in IWIN are assigned are given in Fig. 7.1 (Hodson and White, 2007a). Germplasm generated for a given ME is useful throughout it, accommodating major stresses, although it does not necessarily show good adaptation to all significant secondary stresses. The definitions for these MEs are based primarily on moisture regime (irrigated versus rainfed) and growth habit and, related to this, temperature (spring versus facultative versus winter). The wheat area in developing countries was assigned to twelve MEs, of which ME1-ME6 are classified as spring

Winter

Spring

Hill ME2 Hm ME3 ME4 ME5 HP ME6

Facultative ME7

Winter

ME10 ME11 ME12

Fig. 7.1. CIMMYT defined wheat production and breeding targeted mega-environments (MEs).

wheat environments, ME7-ME9 as facultative and ME10-ME12 as winter wheat environments. Since every ME corresponds to a unique combination of these parameters, each one tends to be associated with a characteristic set of abiotic and biotic stresses (Braun et al., 1996).

Hodson and White (2007a) expanded the criteria to classify wheat MEs by introducing additional geospatial data and discussed the impacts of global climate change on wheat (Hodson and White, 2007b). Table 7.2 summarizes the expected impact of climate change on the various MEs. The greatest impact is expected in ME1-ME5, which include subtropical to tropical spring wheat regions. An estimated 9 million ha of wheat in these regions currently experience yield losses due to heat stresses (Lillemo et al., 2005). Typically heat-stressed environments are classified as ME5, with subdivisions for predominantly humid or dry conditions (ME5A and ME5B). Wheat regions already at the limit for heat tolerance, for example in the Eastern Gangetic Plains of Nepal, India and Bangladesh, are most likely to suffer and may see substantial area reductions. Similarly, under warming, large areas of ME1 will transition to ME5, as illustrated by Hodson and White (Chapter 13, this volume, Fig. 13.3). Positive impacts for ME1, however, are anticipated from CO2-driven increases in productivity, accompanied by increased water-use efficiency.

High elevation, high rainfall environments (ME2A) will experience reductions in area as the elevation band providing suitable temperatures for wheat is displaced upwards. An agroclimatic study on Ethiopia (White et al., 2001) concluded that the current wheat area is largely delimited by high temperature and that warming would greatly reduce the area suitable for wheat. If heat tolerance of currently grown cultivars could be enhanced by 2°C, the wheat area in the periphery of the highlands could be nearly doubled. For the acid soil area in Brazil (ME3) rising temperatures will further increase the stress to be similar to ME5. The most severe negative impact from global climate change is expected for ME4. Drought and heat are often associated, and this combination of warming and water deficits may result in low-rainfall ME4 areas becoming unsuitable for wheat production. For temperature increases up to 2°C this trend may be partially offset by CO2-driven increases in productivity and water-use efficiency.

Cool high-latitude spring wheat areas above 45°N in ME6 of Kazakhstan, Siberia, China, the USA and Canada may benefit from the affects of global climate change. Warmer temperatures should allow earlier sowing and reduce chances of late-season frost. Some areas may convert to more productive winter wheats (ME10-ME12) as risk of cold-induced winter-kill declines. This is already happening in Russia, where in traditional spring wheat areas more winter than spring wheat is grown today (A.I. Morgounov, Turkey, 2009, personal communication). An expansion into areas further north is also likely (Ortiz et al., 2008). Due to the low temperatures throughout ME6, beneficial effects of CO2 on productivity and water-use efficiency are likely.

Regions where facultative wheat (ME7-ME9), which is intermediate to spring and winter wheats, predominates should become more suitable for autumn- to winter-sown spring wheats as risk of cold damage decreases. Some ME7 areas will grow culti-vars adapted to ME1. The effect on yield potential in these environments is more uncertain, but since the growing season will be shortened, this may open new options for crop diversification.

Table 7.3 provides estimates for the average effect of increasing temperatures on grain yields of wheat, maize and rice. Data are extracted from Easterling et al. (2007). In high-latitude regions, yield of all three cereals will increase, or remain unchanged, if adaptation measures are taken, such as cultivar change, change in sowing date and shift from rainfed to irrigated systems. Without such measures, yields will decline slightly for all three crops in the 3-5°C temperature increase scenario. In low-latitude sites, where nearly all of the wheat, rice and maize in developing countries is produced, without adaptation measures grain yield is estimated to decrease for all three crops with rising temperatures. Yield reductions vary from

Table 7.2. Classification of mega-environments (MEs) used by the CIMMYT Global Maize Program and the CIMMYT Global Wheat Program using qualitative (ME1-ME12) and geospatial criteria (ME1-ME6).

Latitude (N and S)

Wheat area (million ha)

Criteriaa

Temperature regimeb

Sowing time

Major biotic and abiotic stresses0

Representative Change in ME due to climate change and conse-locations/regions quences for germplasm development"

Spring wheat

32.0

Low rainfall irrigated; coolest quarter (3 consecutive months) mean minimum temperature > 3°C, < 11°C

High rainfall in summer; wettest quarter mean minimum temperature

> 3°C, < 16°C; wettest quarter (3 consecutive wettest months) precipitation > 250 mm; elevation > 1400 m

High rainfall in winter; coolest quarter mean minimum temperature

High rainfall and acid soil (pH < 5.2); climate as in ME2

Temperate Autumn

Lodging, SR, LR, YR, KB, Alternaria spp.

Temperate Autumn

Lodging, sprouting, SR, LR, YR, KB, Alternaría spp., Septoria spp., PM, RDC, BYD

Temperate Autumn As for ME2A

Temperate Autumn

As for ME2A + acid soils

Yaqui Valley, N - Rising temperatures result in large areas evolving

Mexico; to ME5; N - Reduced precipitation in subtropical

Indus Valley, regions restricts irrigation; supplementary irrigation

Pakistan; results in temporary drought periods requiring

Gangetic germplasm with high yield and tolerance to drought

Valley, India; (adapted to ME1 and ME4); P - Reduced irrigation

Nile Valley, due to impact of elevated CO2 on water-use

Egypt efficiency; N - Increased insect problems

Highlands East N - Rising temperatures result in some areas evolving

Africa and to ME5; N - Reduced precipitation results in areas

Mexico, Andes evolving to ME4

Mediterranean U - Changes in precipitation patterns in areas will have coast, Caspian variable effects; N - Frequency of climate extremes Sea over years increase requiring germplasm with high yield potential, wide spectrum of disease resistance and tolerance to drought

Passo Fundo, N - Rising temperatures result in large areas evolving Brazil to ME5; U - Changes in precipitation patterns in areas will have variable effects

Continued

Latitude Wheat area Temperature Sowing

ME (N and S) (million ha) Criteria2 regimeb time

4A <40° 10.0 Low rainfall, winter rainfall Temperate Autumn dominant; coolest quarter mean minimum temperature > 3°C,

< 11 °C; wettest quarter precipitation > 100 mm,

4B <40° 5.8 Low rainfall, summer Temperate Autumn rainfall dominant; coolest quarter mean minimum temperature

> 3°C, < 11°C; wettest quarter precipitation

4C < 40° 5.8 Mostly residual moisture; Hot Autumn coolest quarter mean minimum temperature

> 12°C, < 18°C; wettest quarter precipitation

5A <40° 3.9 High rainfall/irrigated, Hot Autumn humid; coolest quarter mean minimum temperature > 11°C,

5B <40° 3.2 Irrigated, low humidity; Hot Autumn coolest quarter mean minimum temperature

Major biotic and Representative Change in ME due to climate change and conse-abiotic stresses0 locations/regions quences for germplasm development"

Drought, Septoria spp.,YR, LR, SR, RDC, hessian fly, sawfly, sunn pest

Settat, Morocco; N - Rising temperatures exacerbate water deficits,

Aleppo, Syria; either further reducing yields or making production

Diyarbakir, uneconomical; P - Reduced water deficits through

Turkey impact of elevated CO, on water-use efficiency

Drought, Septoria spp., LR, SR, Fusarium spp.

Marcos Juarez, N - Changes in precipitation patterns likely to increase Argentina drought risk

Drought, heat in Indore, India seedling stage and grain fill, SR

U - Changes in precipitation patterns in areas \ variable effects

I have

Heat, sprouting, Eastern Gangetic N - Rising temperatures result in large areas becoming Helmintho- Plains in Nepal, unsuitable for wheat cropping systems and sporium spp., India, agronomy practices allowing early sowing of wheat

Fusarium spp., Bangladesh; paramount; N - Increasing biotic stress; U -in Brazil, Bolivia Londrina, Elevated C02 may increase water-use efficiency, but and Paraguay Brazil the same mechanism implies increased canopy wheat blast temperature, which would be likely to exacerbate heat stress

Heat, SR, LR Gezira, Sudan; N - Rising temperatures result in large areas becoming Kano, Nigeria unsuitable for wheat; N - Increasing biotic stress; U - Elevated C02 may increase water-use efficiency, but the same mechanism implies increased canopy temperature, which would be likely to exacerbate heat stress

>45° 11.0 Moderate rainfall/summer dominant; high latitude 45°N; coolest quarter mean minimum temperature < -13°C; warmest quarter mean minimum temperature > 9°C

Facultative wheat

Irrigated

Moderate cold

Autumn

Irrigated, often only supplementary irrigation

Moderate cold

Autumn

> 600 mm rainfall; medium cold

Moderate cold

Autumn

> 600 mm rainfall

Moderate Autumn cold tan spot, Hessian fly, FHB, photoperiod sensitivity

Siberia; Harbin, China

P - Rising temperatures allow wheat production in higher latitudes so wheat area expansion likely; P -Lengthening growing season permits marginal areas to become productive; P - Reduced risk of winter-kill allows conversion to more productive winter wheat

Henan, China

Turkey; Iran; Central Asia; Afghanistan

YR, Septoria spp., PM, FHB, RDC, photoperiod sensitivity

Chilian, Chile

Transitional zones and Trace, Turkey

U - Reduced cold stress allows growing autumn-sown spring wheat, possibly reducing yield potential but shortening growing season offering more options for diversifying cropping systems; P - Reduced irrigation due to impact of elevated C02 on water-use efficiency

U - Reduced cold stress allows growing autumn-sown spring wheat, possibly reducing yield potential but shortening growing season offering more options for diversifying cropping systems; P - Reduced irrigation due to impact of elevated C02 on water-use efficiency; N - Supplementary irrigation with temporary exposure to drought requires germplasm that is adapted to ME7 and ME9

U - Reduced cold stress allows growing spring wheat, possibly reducing yield potential but shortening growing season; U - Increasing biotic stress

U - Changes in precipitation patterns in areas will have variable effects; N - Frequency of climate extremes overyears increase requiring germplasm with high yield potential, wide spectrum of disease resistance and tolerance to drought

Continued

Table 7.2. Continued

Latitude Wheat area

(N and S) (million ha) Criteria2

Temperature Sowing regime"

time

Low rainfall < 400 mm, Moderate winter/spring rainfall cold dominant

Autumn

Winter wheat

Irrigated

Severe cold Autumn

Often supplementary Severe cold Autumn irrigation

Area in less High rainfall/irrigated, developed long season countries insignificant

Area in less High rainfall/irrigated, developed short season countries insignificant

Severe cold Autumn

Severe cold Autumn

Major biotic and Representative Change in ME due to climate change and conse-abiotic stresses0 locations/regions quences forgermplasm development"

Drought, cold, heat West and Central U - Reduced cold stress allows growing spring wheat, at grain fill, YR, Asia; North possibly reducing yield potential but shortening

CB, LR, SR, Africa (mainly growing season; U - Changes in precipitation sunnpest, RDC, non-dwarf patterns in areas will have variable effects; P -

nematodes cultivars grown) Reduced water deficits through impact of elevated

C02 on water-use efficiency; N - Rising temperatures exacerbate water deficits, either further reducing yields or making production uneconomical

Winter-kill, YR, LR, Beijing, China P - Warmer winters reduce severity of winter-kill, PM, BYD increasing yields; N - Warmer spring and summer hasten grain filling; P - Reduced irrigation due to impact of elevated CO, on water-use efficiency

Winter-kill, YR, SR, BYD, CB, LS, RDC, sunnpest, Nem

Turkey; Iran; Central Asia

Central and Western Europe; Northwest USA

P - Warmer winters reduce severity of winter-kill, increasing yields; N - Warmer spring and summer hasten grain filling; P - Reduced irrigation due to impact of elevated C02 on water-use efficiency

P - Warmer winters reduce severity of winter-kill

Winter-kill, sprouting, LR, SR, PM, FHB, Septoria spp., BYD

South-east

Europe, North Korea, China

P - Warmer winters reduce severity of winter-kill

Low rainfall between 300 Severe cold Autumn Winter-kill,

Ankara, Turkey; P - Warmer winters reduce severity of winter-kill; P -

and 450 mm drought, heat during grain fill, zinc deficiency, YR, SR, CB, sunnpest, Nem, RDC

West and Central Asia (in Turkey and Iran mainly non-dwarf varieties grown); China

Reduced water deficits through impact of elevated CO2 on water-use efficiency; N - Increased frequency of years with severe drought; N - Increased insect problems a Moisture regime refers to rainfall just before and during the crop cycle. High, > 500 mm; low, < 500 mm. b Temperature regime: hot, mean temperature of the coolest month > 17.5°C; cold, < 5.0°C.

c Biotic stresses: BYD, barley yellow dwarf; CB, common bunt; FHB, Fusarium head blight; KB, Karnal bunt; LR, leaf or brown rust; LS, loose smut = root lesion nematodes; PM, powdery mildew; RDC, root disease complex; SR, stem or black rust; YR, stripe or yellow rust. d Change in ME: N, negative; P, positive; U, unknown (adopted from Hodson and White, 2007b).

Ustilago tritic; Nem, cereal cyst and

Table 7.3. Average sensitivity of cereal yield (expressed as % increase (+) or decrease (-) of current yields) to temperature increase for maize, wheat and rice derived from 69 papers. Sites were assigned as either low latitude or mid- to high latitude and the experiments were classified as either with (+) or without (-) adaptation measures to compensate for temperature increase (see Easterling etal., 2007 for complete list of references).

Mid- to high-latitude sites Low-latitude sites

Temperature increase (°C) Temperature increase (°C)

Table 7.3. Average sensitivity of cereal yield (expressed as % increase (+) or decrease (-) of current yields) to temperature increase for maize, wheat and rice derived from 69 papers. Sites were assigned as either low latitude or mid- to high latitude and the experiments were classified as either with (+) or without (-) adaptation measures to compensate for temperature increase (see Easterling etal., 2007 for complete list of references).

Mid- to high-latitude sites Low-latitude sites

Temperature increase (°C) Temperature increase (°C)

Crop

Adaptation measuresa

1-2

2-3

3-5

1-2

2-3

3-5

Wheat

+

20

18

5

7

-14

-25

-

5

5

-18

-4

-24

-40

Difference

15

13

23

11

10

15

Maize

+

10

0

0

6

0

-10

-

0

-3

-9

-7

-20

-35

Difference

10

3

9

13

20

25

Rice

+

7

20

6

10

15

0

-

0

5

-9

-2

-8

-20

Difference

7

15

15

12

23

20

a Adaptation measures in these studies were changes in sowing date, changes in cultivar, and shifts from rainfed to irrigated conditions. Studies span a range of precipitation changes and CO2 concentrations, and obviously vary in how they represent future changes in climate variability.

a Adaptation measures in these studies were changes in sowing date, changes in cultivar, and shifts from rainfed to irrigated conditions. Studies span a range of precipitation changes and CO2 concentrations, and obviously vary in how they represent future changes in climate variability.

2% for rice when temperatures increase by 2°C to 40% for wheat, should temperatures increase by 5°C. With adaptation measures, an increase of up to 2°C will raise yield of all three cereal crops. A 5°C temperature increase has no effect on rice yields, but will reduce maize yields on average by 10% and wheat yields by 25%. For the three crops in all three temperature scenarios, adaptation measures will increase yield on average by 10-25% compared to yield without adaptation measures.

A disadvantage of the static definition of the ME is that it does not take into account the fact that MEs tend to shift from year to year and fluctuate in weather patterns. In particular this is important for locations in ME2 (high rainfall spring wheat) and ME4 (rainfed spring wheat low rainfall) but also ME1 (irrigated) and ME5 (irrigated high temperature). The frequency with which ME2 or ME4 conditions are experienced varies between locations. Climate change may bring an increased intensity and frequency of storms, drought and flooding, weather extremes, altered hydrological cycles, and precipitation (Ortiz et al., 2008). Such climate vulnerability will threaten the sustainability of farming systems, particu larly in the developing world. Widely adapted, stress-tolerant cultivars, coupled with sustainable crops and natural resource management will provide means for farmers to cope with climate change and benefit consumers worldwide.

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