MNHRZ group: Result of Future Climates and Crop Production Project
Australian dry-land grain farmers are used to dealing with variability in climate, changing commodity and
input prices, and new marketing arrangements. A new challenge facing farmers will be the effects of a
changing climate.
Atmospheric CO2 levels are increasing and this will have an impact not only on the rate at which crops grow
(also called the CO2 fertilisation effect) but also on global, regional and local temperatures and rainfall.
The topic of climate change is controversial and the aim of this short paper is not to convince anyone that
climate change is real or otherwise but to provide information on what the latest science is telling us about
the changes likely in your region. The paper presents a number of results in order to consider the full range of
possible future conditions. The range of future conditions is a function of both future atmospheric CO2 levels
and different climate model outcomes. We believe that the outcomes presented in this paper will be the likely
range in outcomes for your region. We work on the principle that being forewarned allows farmers to make
decisions based on the best available information.
Methods
It is well understood that as the climate warms and CO2 levels in the atmosphere increase the speed at which
crops mature will increase. This means that our crops will flower and fill grain earlier. This may expose crops
in the future to more frost risk but probably more importantly is that dry matter accumulation between the
end of tillering and flowering is reduced which will have a negative effect on yield (there is usually a good
relationship between vegetative growth between the end of tillering and flowering and total grain weight
produced). One practice or adaptation to this change in growth pattern for our crops may be to sow our
crops earlier so that they can still take full opportunity of growth before temperatures start to rise in spring.
Through NAMI (National Adaptation and Mitigation Initiative) the group looked at innovative practices aimed
at reducing the impact of a changing climate, such as earlier sowing times using different maturity types of
wheat. The trial work was undertaken in the region in 2010 and 2011. Using these data we calibrated the
crop model APSIM, we then ran the model from 1961 to 2010, using local climate data and the early 1990s
level of atmospheric CO2, for two varieties of wheat with different maturity (Axe and Yitpi) to provide a
baseline of current yield potential at each of the sowing dates.
We then repeated the model runs but this time to represent future climates (by 2030 and 2050). We used
two Global Circulation Models (GCMs) at two different projected atmospheric CO2 levels to represent possible
future climate outcomes. The two GCMs and CO2 projections were chosen to represent a ‘best case’ outcome
and a ‘worst case’ outcome for (Table 1).
Table 1. The GCMs and projected CO2 levels used in the future climate models by 2030 and 2050.
Future
Best case outcome
Worst case outcome
date
GCM
CO2 projection
GCM
CO2 projection
(ppm)
(ppm)
2030
ECHAM5
451
GFDL2.1
455
2050
ECHAM5
532
GFDL2.1
567
Note: Measured atmospheric CO2 level in the early 1990s was 350ppm; the level in 2011 was 390ppm.
Results
Rainfall
The two models and CO2 projections have different outcomes for rainfall at Tarlee. The best outcome is a
decrease by 2030 of around 2% annually with a similar decrease during the winter growing period; the worst
outcome is around an 18% decrease annually (Table 2). The decrease in rainfall by 2050 is projected to be
more extreme.
46 | T r i a l R e s u l t s 2 0 1 1
Table 2. Percentage change in rainfall from current conditions at Tarlee, 2030 and 2050.
Current
% change from current rainfall
Tarlee
2030
2050
rainfall
Best case
Worst case
Best case
Worst case
mm
ECHAM5 A2
GFDL2.1 A1FI
ECHAM5 A2
GFDL2.1 A1FI
Growing Season
332
-3
-18
-5
-38
Autumn
76
+4
+4
+7
+9
Spring
97
-5
-25
-10
-52
Annual
452
-2
-18
-5
-38
Temperature
Average daily temperatures are projected to rise in the region by between 0.4 and 1.0oC (from the annual
current daily average temperature of 16.5oC) by 2030. By 2050, the average daily temperatures will rise in the
region by between 0.8 and 2.0oC. Winter temperatures will rise by a similar magnitude. This means that, in
the future, the combination of higher temperatures and higher levels of CO2, crops will grow more quickly and
mature earlier.
Evaporation
The annual evaporation rate for the region is, on average, 1805mm per annum. It is expected that by 2030
evaporation rates will increase by up to 3.8%. The increase in evaporation is in part due to the higher
temperatures and will exacerbate the impact of the decline in rainfall and this is taken into consideration in
the yield simulations presented below.
Crop Yield
The expected change in crop yield by 2030 and 2050 for two wheat varieties with different maturity (Axe and
Yitpi) and three sowing dates for the two different GCMs and CO2 projections is listed in Table 3. Despite the
decrease in growing season rainfall there is an increase in yield for both the short and mid season wheat
varieties in the ‘best case’ scenario due to the CO2 fertilisation effect. However, increases in temperature and
decreases in rainfall result in a general decline in potential yield for the ‘worst case’ scenario.
Table 3. Percentage change in yield from average current conditions at Tarlee, by 2030 and 2050.
Wheat maturity
Current
% change from current yield
type and sowing
Tarlee
2030
2050
date
t/ha
Best case
Worst case
Best case
Worst case
ECHAM5 A2
GFDL2.1 A1FI
ECHAM5 A2
GFDL2.1 A1FI
Short
Mid April
2.0
+15
+2
+23
-6
“
Mid May
2.5
+15
-3
+23
-24
“
Mid June
3.3
+10
-18
+15
-51
Mid
Mid April
2.6
+12
-5
+16
-17
“
Mid May
4.2
+7
-19
+10
-51
“
Mid June
4.1
+4
-31
+5
-62
Conclusion: As the climate changes there will be impacts on how crops grow – the main difference from
current conditions will be that crops will mature faster. If the same varieties of crops were still sown by 2030
it is likely that some crop losses could be experienced by 2030, and more extreme losses by 2050 for the
worst case climate outcome. It will be imperative that new varieties are developed which are suited to higher
atmospheric CO2 levels and new climatic conditions. The changes in rainfall patterns in the region will also
require new adaptations to be developed to ensure farming remains productive and viable.
This project is funded by GRDC and the Australian Government's Climate Change Research Program.
47 | T r i a l R e s u l t s 2 0 1 1