The atmosphere has to get rid of the extra heating supplied by the eastern tropical Pacific Ocean during an ENSO warm phase event. It does this in certain preferred patterns, which affect temperatures and precipitation in many places around the world. As a result, weather-sensitive human activities, such as agriculture, can be affected. In this part of the lab, we'll examine how closely ENSO parameters are associated with remotely-located agricultural yields. We'll do so by examining the correlation between SOI, and selected wheat yields from agricultural model time series in Australia. View a map of Australia obtained from the National Mapping Division of Geoscience Australia to learn more about the various regions you'll be examining in today's lab.
Most of Australia is semi-arid, and climate conditions are relatively unfavorable for many agricultural crops. Of the major grains, wheat requires the least amount of precipitation to grow, and thus is the most important grain crop in the country. Australia is one of only about five or six countries that produce a significant excess of wheat crop beyond domestic consumption requirements. These few countries supply most of the grain for international trade in wheat. Since ENSO is responsible for a significant portion of the interannual climate variability in parts of Australia, knowledge of ENSO conditions is critical in agricultural decisions in many regions of the country.
Using SOI as an indicator of ENSO conditions, make a scatter plot of annual precipitation amount in the catchment of the River Murray (southeastern Australia) vs SOI (Table 2). The Murray River catchment basin (map obtained from the Murray-Darling Basin Commission) precipitation and discharge data were obtained via personal communications with staff of the Australian Bureau of Meteorology and the Murray-Darling Basin Commission, respectively. Add a linear regression slope, with correlation coefficient and slope equation to the plot. Is the slope positive, negative, or zero? Is there higher rainfall during El Nino or La Nina episodes? Do you think the correlation is statistically significant? Athough the correlation statistics are between the NINO3 index and 10,000 random time series, you may assume that a similar distribution would be obtained for correlations between the SOI and 10,000 random time series. What is the approximate range of lowest to highest annual precipitation amount in this region? Which ENSO state would you think would be more favorable for higher than average wheat yields in this region of Australia?
To facilitate comparison of annual river discharge and annual precipitation in the basin of the River Murray, make a scatter plot of annual natural river discharge (Q) vs annual precipitation (P) (Table 2). [Note that "natural" discharge is computed from actual discharge measurements by attempting to account for all the changes in water amount due to human influences. Examples of these changes including adding back losses such as evaporation in water storage reservoirs, or diversions to agricultural irrigation districts.] Add a linear regression slope, with correlation coefficient and slope equation to the plot. Is the slope positive, negative, or zero? Do you think the correlation is statistically significant? What is the approximate range of lowest to highest annual river amount in this region? How does the ratio of highest to lowest river annual discharge amount compare to that ratio for precipitation in the basin of the River Murray? Does the linear regression line intercept zero for both axes? Why might the Q vs P plot have this feature?
Using SOI as an indicator of ENSO conditions, make a
scatter plot of annual natural river discharge of the River Murray to South
Australia (SA) vs SOI (Table 3). [Note that the River
Murray discharge to South Australia is downstream of the confluence of the
Darling River, and thus includes runoff from the large northern portion of the
catchment, as well as the runoff from the mountain range near the southeast
coast of the country.] Add a linear regression slope, with correlation
coefficient and slope equation to the plot. Is the slope positive, negative, or
zero? Is there higher river discharge during El Nino or La Nina episodes? Do
you think the correlation is statistically significant? Do you think flooding
would be more likely during El Nino or La Nina episodes? Do you think droughts
would be more likely during El Nino or La Nina episodes?
Yields in many regions of Australia have large interannual variations, in large part because of variations in rainfall amount. Make a time-series plot (Yield vs year) for mean annual Wheat Yields per unit area of crop (Tons per hectare) in the state of New South Wales (NSW) in southeastern Australia (Table 4). These data were provided courtesy of Graeme Hammer of the Agricultural Production Systems Research Unit in Australia. How many years have had a Wheat Yield in NSW of less than 1.0 T/ha during the 20th century? How many years have had a Wheat Yield in NSW of less than 1.5 T/ha during the 20th century? Do the years of especially low yield tend to occur in clusters of several years at a time, or do they tend to have higher yields immediately preceeding or following them?
Make a scatter plot of Wheat Yields in NSW vs SOI (Table 4). Do the years of higher yield tend to occur in El Nino or La Nina episodes? Do years of low yield tend to occur in El Nino or La Nina episodes? Add a linear regression slope, with correlation coefficient and slope equation to the plot. Is the slope positive, negative, or zero? Do you think the correlation is statistically significant?
Make a scatter plot of Wheat Yields in Queensland (Qld) in eastern Australia vs SOI (Table 4). Do years of higher yield tend to occur in El Nino or La Nina episodes? Do the years of low yield tend to occur in El Nino or La Nina episodes? Add a linear regression slope, with correlation coefficient and slope equation to the plot. Is the slope positive, negative, or zero? Do you think the correlation is statistically significant?
Make a scatter plot of Wheat Yields in Western Australia (WA) vs SOI (Table 4). Do years of higher yield tend to occur in El Nino or La Nina episodes? Do the years of low yield tend to occur in El Nino or La Nina episodes? Add a linear regression slope, with correlation coefficient and slope equation to the plot. Is the slope positive, negative, or zero? Do you think the correlation is statistically significant?
