Observations for

Onset dates per year
visit site

Equatorial IGAD Countries Historical Onset Date

The Maproom explores historical rainy season onset date based on user-defined definition of onset. The date when the rainy season starts is critical to agriculture planification, in particular for planting.

By enabling the exploration of the history of onset dates, the Maproom allows to understand the spatial and temporal variability of this phenomenon and therefore characterize the risk for a successful agricultural campaign associated with it.

The definition of the onset can be set up in the Control Bar at the top and is looking at a significantly wet event (e.g. 20mm in 3 days) that is not followed by a dry spell (e.g. 7-day dry spell in the following 21 days). The onset date is computed on-the-fly for each year according to the definition, and is expressed in days since an early start date (e.g. Feb. 1st or Aug. 1st). The search for the onset date is made from that early start date and for a certain number of following days (e.g. 60 days). The early start date servers as a reference and should be picked so that it is ahead of the expected onset date. Generally, two rainy seasons are expected in the region: Mar-May and Sep-Dec.

Then the map shows yearly statistics of the onset date: the mean (by default), standard deviation or probability of exceeding a chosen number of days. Clicking on the map will then produce a local yearly time series of onset dates, as well as a table with the actual date (as opposed to days since early start).

Note that if the criteria to define the onset date are not mean within the search period, the analysis will return a missing value. And if the analysis returns 0 (days since the early start), it is likely that the early start date picked is within the rainy season.

Dataset Documentation

Data: UCSB's CHIRPS v2.0 daily precipitation available here at 0.05˚ spatial resolution.


Contact help@iri.columbia.edu with any technical questions or problems with this Map Room.