Space-Time Causality Analysis of Regional Impacts of ENSO on Terrestrial and Oceanic Precipitation

Future changes are expected in precipitation under climate change, therefore, changes are projected in the oceanic and terrestrial components. However, it remains poorly elucidated how the El Nino-Southern Oscillation (ENSO) can influence these changes. Therefore, we aimed to perform a space-time causality analysis of regional ENSO impacts on terrestrial and oceanic precipitation by using the Granger causality method as a function of eight temporal lags (lags 1-8). The monthly values of total precipitation obtained using the Lagrangian approach and their respective terrestrial (PLT) and oceanic (PLO) components were used. The analysis was performed for the two regions of western North America (WNA) and eastern South America (ESA) with strong ENSO signals. For the WNA region in winter, the maximum Granger causality was observed in the component of oceanic origin for temporal lags 1 and 2 (3 and 6 months), with a predominance of both positive and negative ENSO conditions. For the ESA region, it was verified that the causality of the ENSO index was maximum for PLT. Temporal lags 2-5 (6-15 months) stood out in winter when there was a marked region of the Granger causality over the La Plata Basin. In autumn, for lags 1-4 (3-12 months), the Granger causality values were predominant in the southern and western areas of ESA and showed a tendency to move northward with an increased temporal lag. Finally, it was shown that high correlation values did not imply the causality of the relationship between the ENSO index and precipitation in the two regions.

Automated summary

Future changes in precipitation under climate change are expected, and this study aimed to investigate the influence of the El Nino-Southern Oscillation (ENSO) on oceanic and terrestrial precipitation. The Granger causality method was used to analyze the ENSO impacts in two regions with strong ENSO signals. The results showed that in winter, the oceanic component had the maximum Granger causality in the western North America region, while the terrestrial component had the maximum causality in the eastern South America region. High correlation values did not imply causality in the relationship between ENSO index and precipitation in the two regions.