1. The Effect of ENSO on Precipitation in Atlanta
Steven DiNapoli
EAS 4803 YW
April 22, 2008

2. Introduction Current Atlanta Drought
Projected to continue due to La Niña conditions
Many previous droughts were exacerbated by La Niña (e.g. 1950s, 2000)
Objective of Analysis – Analyze relationship between ENSO and precipitation in Atlanta
Performed correlations on historical ENSO data and monthly precipitation in Atlanta
Hartsfield-Jackson International Airport

3. ENSO Data ONI – Oceanic Niño Index
Measure of 3-month running mean SST anomalies in the Eastern Pacific
Positive Values correspond to El Niño conditions

4. Atlanta Precipitation
Hartsfield-Jackson International Airport
Monthly totals from NCDC
Much more variability than ONI data
Numerous outlier points

5. Correlating the Data (Attempt #1)
[r1, p1] = corrcoef(oni, precip);

6. Problems with Attempt #1
Too much noise in precipitation data
Affected by outside influences (e.g. hurricanes)
Outlier data points
Correlation Coefficient =
Explains less than 0.5% of precipitation variance
p-Value =
Correlation is statistically insignificant
p-value should be less than 0.05
Need to filter noise out of precipitation data
3-month running mean precipitation
ONI values are derived from a 3-month running mean

7. Correlating the Data (Attempt #2)

8. Problems with Attempt #2
Precipitation data still very noisy
Correlation Coefficient =
Still very weak; explains ~1% of the variance
p-value =
Correlation is significant
More filtering still needed
Next attempt correlates average ONI index for each year with total yearly precipitation

9. Visual Analysis of Filtered Data

10. Correlating the Data (Attempt #3)

11. Analysis of Attempt #3 Much less noise in the data
Outlier points removed
Correlation coefficient =
Still weak, but much stronger than before
p-value =
Significance lost due to lack of data points (58 vs. 696)
* Would regional precipitation totals provide a better dataset to correlate with ENSO?

12. Conclusion All major droughts occurred during La Niña
Not all La Niña events lead to drought
The opposite is not always true for El Niño
Correlations were very weak
Data was very noisy
Long-wave synoptic patterns
Hurricanes & convective thunderstorms
La Nina conditions → More hurricanes
Numerous other forcings ignored (e.g. NAO)
Only one station considered

13. Questions?