In the previous article, I offered a definition in the Namibian context to describe a so-called wet spell. In this article, I discuss certain qualifications to that definition.
In the definition of a wet spell, the overall benchmark is rainfall over 3 consecutive days or more, comprising 60mm across the 3 days, at least, and with one of these days producing a measure of 25mm, at least. This is the basic benchmark from which to consider all appearances of wet spells. This may seem like splitting hairs but in a country as dry as Namibia, often an entire season may depend on one or two wet spells.

As my analysis of measured daily rainfall across all Namibian stations proceeded the extension of the days coupled with a commensurate and appropriate rise in the running total had to be incorporated into an extension of the basic definition.
This depended on an increase in the running total of 20mm for each day, at least. For instance, in the records there are many instances of say, 20 mm, 55mm, one dry day, and then 19mm again. This still qualifies as a wet spell since the total of 94 mm exceeds 20 mm times four (80 mm) and there was one day with more than 25 mm.
On our rainfall scene, from the wettest parts to the edge of the hyper-arid Namib, this appears to be a solid foundation from which to work.
To extract usable and practical information from almost 100 years of rainfall data across as much as 1500 stations, it becomes necessary to incorporate a degree of flexibility. This usually applies to the data from a number of adjacent stations in the same area where the recorded falls at one station may not qualify as a wet spell but corroborating data from the surrounding stations certainly indicate that there was a wet spell in the area during that particular period. The opposite is also true. One single excessively wet day may look like a wet spell but comparing the data of nearby stations for that period, it often becomes clear that the heavy fall was a fluke.
But the flexibility range needs be kept in the wings until a point is reached in that local analysis where the query arises about, say, the 25mm, 18mm, and 12mm range of wet days, or the 20, 24, 15mm set of wet days. In other words, while the initial benchmark remains in place, local values can well be entertained positively when local analyses are made.
Wet spells can also be identified where, over a number of days, the range is dominated by one excessively wet day coupled with two lesser falls: 10mm 55mm and 13mm, for instance. By benchmark standards, this will be noted in the Wet Spell column, but, when an areal analysis is performed, it can become very obvious that the station (a dot on the map) was lucky enough to have had that 55.6. Adjacent stations barely got to a 10mm fall on that day.