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Historical Probability of Seasonal Rainfall Tercile Conditioned on ONI ENSO Definition

This map shows the historical probability of seasonal average rainfall falling within the upper (wet), middle (normal), or bottom (dry) one-third ("tercile") of the 1981-2014 historical distribution given the state of ENSO (El Niño, Neutral, La Niña) during that same season.

Here, the ENSO state for each season is defined according to the Oceanic Niño Index (ONI). It is calculated using Sea Surface Temperature (SST) anomalies, based on centered 30-year base periods updated every 5 years, in the geographical box (170˚W, 5˚S, 120˚W, 5˚N). A season is considered El Niño (La Niña) if it is part of at least 5 consecutive overlapping 3-month long seasons where the ONI is above 0.5˚C (below -0.5˚C). Use the controls on the page to select the region, season, rainfall tercile category of interest, and ENSO state. The analysis reproduces, using same SST dataset, the following definition from NOAA.

Clicking on the map will then display, for the selected point, yearly seasonal rainfall totals time series. The color of the bars depict what ENSO phase it was that year, and the horizontal lines show the historical terciles limits. This allows one to quickly picture what years fell into what ENSO Phase and into what Rainfall Tercile category.

The analysis can also be done on precipitation averaged over a country or its 1st and 2nd administrative boundaries. Use the menu in the top Control Bar to choose at which spatial level you wish to work, then, to select an area, you can either click on the map (layers of the contours of the different administrative levels can be activated for visualization in the Layers control of the map); or select a name in the drop down menu generated accordingly to the spatial level selected. Note that this drop down menu lists only names of areas that are currently in view on the map. Note also that in the case of 2nd level of administration, if the list is too long, it won't show up or update: zoom over the map to make the list shorter.

NB: This is not a forecast. It is based on historical observations of rainfall and SST. However, it would be a good tool for exploring the effect of different ENSO phases on seasonal rainfall.

Reference for ENSO phases definition: V. E. Kousky and R. W. Higgins, 2007: An Alert Classification System for Monitoring and Assessing the ENSO Cycle. Wea. Forecasting, 22, 353–371. doi: http://dx.doi.org/10.1175/WAF987.1

Dataset Documentation

UEA CRU TS3.23 precipitation on a 0.5˚ x 0.5˚ lat/lon grid.
Extended reconstructed sea surface temperature (ERSSTv4).

How to use this interactive map


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