Historical Onset and Cessation Date

The maproom explores historical rainy season onset and cessation dates based on user-defined definitions. 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 and cessation 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 actual date is the first wet day of the wet event. 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. Nov 1^st). 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 serves as a reference and should be picked so that it is ahead of the expected onset date.

The default definition of the cessation date is the first date after March 1 ^st in 60 days when the soil water balance falls below 5mm for a period of 3 days.

Then the map shows yearly statistics of the onset or cessation 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 and cessation dates, as well as a table with the actual date (as opposed to days since early start); and a probability of exceeding graph.

Note that if the criteria to define the onset or cessation date are not met 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

Reconstructed rainfall on a 0.0375˚ x 0.0375˚ lat/lon grid (about 4km) from Zambia Meteorological Department. The time series (1981 to 2020) were created by combining quality-controlled station observations in DGM’s archive with satellite rainfall estimates.

How to use this interactive map

The Plots Range controls define the range of the vertical axis of the time series and the horizontal axis of the probability of exceeding graph. Blanking the boxes will set the range to the extrema of graph in view.

Helpdesks

Contact info@zmd.gov.zm with any technical questions or problems with this Map Room.