Observations for


Probability of Monthly Averages (in a Season) Rainfall Tercile Conditioned on IOD

This map shows the historical probability (given in percentile) of seasonal average monthly rainfall falling within the upper (wet), middle (normal), or bottom (dry) one-third ("tercile") of the 1983-2014 historical distribution in Tanzania given the Terciles of IOD (Postive, Neutral, Negative) during that same season.

The IOD is defined as the difference between SST anomalies of a West box average (50E-70E, 10S-10N) and an East box average (90E-110E, 10S-0N). Anomalies are computed for and with respect to the period of rainfall data availability (1983-2014). The IOD is categorized in 3 Tercile classes and the positive tercile indicates warmer SST conditions in the West compared to the East.

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

While the IOD is often referred to as a distinct feature of climate variability, a similar pattern of sea surface temperature variations on the Indian Ocean often occurs as a response to ENSO in the Pacific Ocean. That is, the two phenomena are often related. As a result, one should expect similar impacts of El Niño (La Niña) phase and Positive (Negative) IOD to climate in Eastern and Southern Africa. Therefore, this Maproom doesn't exhibit an independent feature that comes on top of the information that is displayed by the ENSO Maprooms, but rather complementary information that can help intricate the delicate cases when ENSO and IOD could be out of sync at some critical seasons.

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

Dataset Documentation

Reconstructed rainfall over land areas on a 0.0375˚ x 0.0375˚ lat/lon grid. The rainfall time series (1983 to present) were created by combining quality-controlled station observations with satellite rainfall estimates.

How to use this interactive map


Contact massam.victor@gmail.com with any questions about or problems with this Map Room.