Climate change and agricultural production
Projected changes in production
Not all the projected effects of climate change on New Zealand agriculture are bad. Indeed on average there may be relatively little change this century across the country. But extremes, such as drought, may become worse and there are differences in how individual regions are affected.
For an average year later in the century, production is projected to decrease in some dry east coast locations and Northland, and to increase in Southland and the South Island West Coast, although the projected changes averaged over the whole country are small. However, the projected national decrease in production for the driest years during the two future periods considered (2030s and 2080s) is worse than for the driest year in the 1972 – 2002 period.
The EcoClimate report presents projected changes based on the Intergovernmental Panel on Climate Change (IPCC) third and fourth assessment reports. More analysis was completed on the production impacts using the third assessment scenarios due to the earlier timing of the original work and availability of the fourth assessment’s downscaled data.
Figure 7: Projected changes to the frequency of droughts.
The projected driest annual conditions in 2080s under (a) low medium and (b) medium high scenarios for conditions that currently occur on average once every 20 years. For example: In the left hand map Timaru is yellow, meaning that rather than a drought occurring (on average) once every 20 years, the drought could occur between once every 5 years and once every 10 years i.e. 2 to 4 times more frequently than at present.
The report’s key findings are:
• For average years, the projections show no strong increase or decrease during the coming century in production when averaged over the whole country. Projected national dairy production ranges from 96 to 101%, and projected sheep/beef production from 91 to 96% of the 1972–2002 average. See Figures 8, 9, 10 and 11 for projections derived from the Hadley Centre (HadCM2) model. Projections from the fourth assessment downscaling work are shown in Figures 12, 13 and 14.
• Flows in the rivers fed from the Southern Alps in Canterbury and Otago are expected to increase (on average) under most climate change scenarios. Water supply reliability from irrigation systems fed from this source may increase. But it is yet unclear whether the increased water supply will compensate for an increase in demand.
• Agricultural areas in eastern New Zealand outside Canterbury and Otago are likely to face greater shortages of water in future. This includes Northland, Hawke’s Bay and parts of the Tasman and Marlborough regions.
• Compared to 1990, the number of Growing Degree Days (base 5°C) in the 2080s may increase by as much as 500–800 growing degree days for most of the North Island, and for some northern and eastern parts of the South Island (from South Canterbury north). For comparison, currently the average growing degree days exceed 3000 in warmer parts of the North Island.
• Improvements in production are projected for both dairy and sheep/beef in the West Coast and Southland. These regions are likely to remain wetter with a warming climate.
• As the century progresses, the drying of pasture in spring is likely to begin earlier; the projected increase in temperatures and growing degree days may give rise to an earlier start to pasture growth in the late winter or spring. Farmers might choose to bring forward some of their operations in response to the changes, for instance, lambs may be ready for the works earlier than at present.
• Using the Hadley Centre (HadCM2) model, the projected driest years in the 2030s and 2080s are worse for national average production than the worst climatic year between 1971 and 2002. In that worst year, estimated production was 64% of the long-term average for dairy, and 67% of the long-term average for sheep/beef. Under the climate change scenarios, the projected worst years reach only 52% and 50% of the long-term average production for dairy and sheep/beef respectively.
• There is little change between the national average production figures derived from the third and fourth assessment reports. Table 1 below shows national pasture production from areas under high producing pasture in 2002, relative to the median year during the recent period (1989/90).
| Period | Median | Worst |
|---|---|---|
| Recent | Reference | 70.9% |
| 2030–2049 | 100.2% | 51.9% |
| 2080–2099 | 103.1% | 51.7% |
• A decline is projected for dairy and sheep/beef production in an average-year and worst-year production in the east coast (Bay of Plenty, Gisborne, Hawke’s Bay, Wellington, Canterbury), and also for Northland. These projections use the data derived from the Hadley Centre model downscaled from the IPCC third assessment report. Tables 2, 3, 4 and 5 provide a breakdown by region for average and worst years.
• Analysis of the IPCC third assessment report suggests that Hawke’s Bay and Gisborne are particularly vulnerable to increased frequency of successive dry years in the future. However, subsequent modelling based on the IPCC Fourth Assessment Report suggests that Gisborne may not be as badly affected. Changes in El Niño conditions in the future may also influence the impact of climate change.
The projected impacts on dairy production and sheep/beef production, using the Hadley Centre model from the third assessment report are shown in Figures 8, 9, 10 and 11. The average-year and average worst years are shown for the 2030s and the 2080s for both the low-medium and medium-high scenarios. For comparison, relative production projections derived from the fourth assessment report are shown in Figures 12, 13 and 14.
Figure 8: Estimates of average pasture production for the period July 1972–June 2002.
This combines estimated above ground dry matter production with digestibility of herbage for ruminant animals. Areas shown in grey are Land Use Capability Class 8 (Mountain Land) unsuitable for any pastoral use.
Figure 9: Relative production estimates (compared to the 1972–2002 average) based on metabolisable pasture growth estimates, for two agricultural years with unusually dry conditions over parts of New Zealand (1977/78 and 1997/98). Areas shown in grey are Land Use Capability Class 8 (Mountain Land) unsuitable for any pastoral use.
Figure 10: Relative production projections for the 2030s, based on the Hadley model and metabolisable pasture growth estimates. Areas shown in grey are Land Use Capability Class 8 (Mountain Land) unsuitable for any pastoral use.
(Larger image)
Figure 11: Relative production projections for the 2080s, based on the Hadley model and metabolisable pasture growth estimates. Areas shown in grey are Land Use Capability Class 8 (Mountain Land) unsuitable for any pastoral use.
(Larger image)
Figure 12: Relative production estimate (compared to 1989/90; the 1972–2001 median year) based on metabolisable pasture growth estimates for 1977/78. This agricultural year had unusually dry conditions over parts of New Zealand. Areas shown in grey are Land Use Capability Class 8 (Mountain Land) unsuitable for any pastoral use. Note, the index=zero areas on these maps are now coloured white, where previously they were coloured red).
Figure 13: Relative production projections for the period 2030–2049, based on the later IPCC models and metabolisable pasture growth estimates. Note, the index=zero areas on the AR4 maps are now coloured white, where previously they were coloured red).
Figure 14: Relative production projections for the period 2080–2099, based on later IPCC models and metabolisable pasture growth estimates. Note, the index=zero areas on the AR4 maps are now coloured white, where previously they were coloured red).
Table 2: Average projected effect on national export revenue of dairy in an average year.
| Region | 2030s | 2080s | ||
|---|---|---|---|---|
| Low-Medium (h25) | Medium High (h75) | Low-Medium (h25) | Medium High (h75) | |
| Northland | 92% | 88% | 91% | 81% |
| Auckland | 94% | 90% | 94% | 86% |
| Waikato | 98% | 97% | 102% | 101% |
| Bay of Plenty | 90% | 85% | 93% | 83% |
| Gisborne | 72% | 61% | 68% | 48% |
| Hawke’s Bay | 68% | 57% | 63% | 44% |
| Taranaki | 104% | 105% | 108% | 113% |
| Manawatu-Wanganui | 100% | 100% | 102% | 101% |
| Wellington | 86% | 80% | 81% | 69% |
| Tasman | 98% | 97% | 103% | 104% |
| Nelson | 121% | 120% | 103% | 126% |
| Marlborough | 93% | 90% | 98% | 94% |
| West Coast | 104% | 105% | 111% | 116% |
| Canterbury | 93% | 90% | 98% | 96% |
| Otago | 101% | 102% | 105% | 108% |
| Southland | 104% | 105% | 111% | 118% |
| Total | 98% | 96% | 101% | 100% |
Table 3: Average projected effect on national export revenue of dairy in a worst year.
| Region | 2030s | 2080s | ||
|---|---|---|---|---|
| Low-Medium (h25) | Medium High (h75) | Low-Medium (h25) | Medium High (h75) | |
| Northland | 54% | 48% | 53% | 39% |
| Auckland | 39% | 34% | 39% | 29% |
| Waikato | 52% | 49% | 54% | 49% |
| Bay of Plenty | 37% | 29% | 39% | 21% |
| Gisborne | 41% | 27% | 41% | 16% |
| Hawke’s Bay | 47% | 32% | 44% | 19% |
| Taranaki | 63% | 63% | 61% | 57% |
| Manawatu-Wanganui | 47% | 45% | 41% | 34% |
| Wellington | 40% | 33% | 32% | 22% |
| Tasman | 60% | 58% | 61% | 58% |
| Nelson | 76% | 74% | 76% | 66% |
| Marlborough | 64% | 60% | 67% | 61% |
| West Coast | 93% | 95% | 95% | 98% |
| Canterbury | 62% | 58% | 64% | 61% |
| Otago | 75% | 75% | 72% | 72% |
| Southland | 86% | 88% | 88% | 90% |
| Total | 57% | 54% | 57% | 52% |
Table 4: Average projected effect on national export revenue for sheep and beef in an average year.
| Region | 2030s | 2080s | ||
|---|---|---|---|---|
| Low-Medium (h25) | Medium High (h75) | Low-Medium (h25) | Medium High (h75) | |
| Northland | 93% | 88% | 92% | 82% |
| Auckland | 95% | 91% | 94% | 87% |
| Waikato | 100% | 99% | 105% | 105% |
| Bay of Plenty | 89% | 83% | 91% | 81% |
| Gisborne | 70% | 58% | 66% | 46% |
| Hawke’s Bay | 67% | 55% | 61% | 41% |
| Taranaki | 104% | 104% | 108% | 111% |
| Manawatu-Wanganui | 98% | 97% | 101% | 99% |
| Wellington | 81% | 72% | 74% | 57% |
| Tasman | 98% | 97% | 103% | 104% |
| Nelson | 97% | 94% | 97% | 97% |
| Marlborough | 91% | 87% | 97% | 93% |
| West Coast | 104% | 105% | 111% | 116% |
| Canterbury | 87% | 82% | 88% | 79% |
| Otago | 101% | 101% | 106% | 109% |
| Southland | 104% | 106% | 112% | 119% |
| Total | 94% | 91% | 96% | 93% |
Table 5: Average projected effect on national export revenue for sheep and beef in a worst year.
| Region | 2030s | 2080s | ||
|---|---|---|---|---|
| Low-Medium (h25) | Medium High (h75) | Low-Medium (h25) | Medium High (h75) | |
| Northland | 55% | 50% | 55% | 41% |
| Auckland | 46% | 41% | 46% | 38% |
| Waikato | 54% | 52% | 55% | 52% |
| Bay of Plenty | 38% | 31% | 38% | 19% |
| Gisborne | 42% | 27% | 41% | 20% |
| Hawke’s Bay | 40% | 25% | 36% | 15% |
| Taranaki | 63% | 63% | 61% | 57% |
| Manawatu-Wanganui | 47% | 45% | 43% | 38% |
| Wellington | 26% | 18% | 18% | 10% |
| Tasman | 61% | 60% | 62% | 59% |
| Nelson | 61% | 57% | 64% | 58% |
| Marlborough | 65% | 61% | 68% | 63% |
| West Coast | 93% | 95% | 95% | 98% |
| Canterbury | 43% | 38% | 41% | 35% |
| Otago | 75% | 75% | 73% | 72% |
| Southland | 83% | 85% | 84% | 88% |
| Total | 57% | 54% | 56% | 50% |
Key definitions and concepts
Key concepts in the research, the resulting maps and their interpretation are Soil Moisture Deficit (SMD), Growing Degree Days (GDD), and drought.
Growing Degree Days, base 5°C: Growing degree days, base 5°C is a temperature-based parameter for assessing field crop growing requirements. If the average air temperature on a particular day exceeds 5°C, the daily growing degree day value is calculated as the mean daily air temperature minus 5. If the daily mean air temperature does not exceed 5°C, the daily GDD value is set to zero. Growing degree days are added over a set period, in this case July to the following June. As an example, the average annual growing degree day can exceed 3000 in warmer parts of the North Island and can be less than 1000 in cooler higher parts of the South Island. All these values are predicted to change in response to a changing climate.
Soil Moisture Deficit: Soil moisture deficit is a measure of how dry the soil is for plant growth and is also known as the “wilting point deficit” or “potential evapotranspiration deficit” (PED). It is obtained by running a daily “budget” for the amount of moisture in the soil taking into account rainfall (which adds to the daily balance) and evaporation of moisture through a crop or a grass field (which subtracts from the daily balance).
SMD is also known as the “wilting point deficit or potential evapotranspiration deficit”. Once the soil moisture level has reached the wilting point (half of the available water capacity (AWC) of the soil), any continuing period of dry weather is summed at the daily rate of the potential evapotranspiration to give the total deficit. The total deficit values have been estimated from a water balance model which uses inputs of rainfall and potential evapotranspiration, and assumes the AWC of the soil is 150mm.
Drought is a sustained period of high soil moisture deficit. The report defines a drought as having a soil moisture deficit of 200 mm. Severe droughts like those in 1977/78 and 1997/98 have major economic effects and have an estimated soil moisture deficit of 400mm.
While most of the economy recovers from a drought in the next growth year (usually taken from 1 July to 30 June), it is much more difficult to recover from two drought years in a row. The report also calculates the risk of droughts occurring more than once.
The EcoClimate Consortium consists of scientists and researchers from GNS, the New Zealand Centre for Ecological Economics, Motu, AgResearch, NIWA, Infometrics, and Landcare Research.
Figure 1: New Zealand Regional Council Boundaries. Source: Statistics New Zealand
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