Seventh article in a series that discusses the technical aspects of rainfall
Finding a definition for wet spells
As the slow but steady pace of daily rainfall entry and analysis proceeded, so did the horizons on the further importance of the scope of daily rain enlarge.
With the Productive (10mm) and Substantial (25 mm) daily values as a distinct base, further investigation of the history of daily falls, revealed that there are numerous stations countrywide that have recorded wet spells as defined below.

It is a fair assumption that anybody interested in rainfall is aware of groups of very wet days which can occur, even during longer periods of below-normal rainfall. These so-called wet spells have a particular significance for identifying productive rainfall.
Let's take a sample: 22mm, 35.5mm, 11.8mm during 3 consecutive days: almost 70 mm. This is a considerable soak. Back to the reference books! Nothing of any relevance was revealed describing this as a wet spell in a Namibian context. Conventionally, wet spells only refer to unusual to abnormal rain for a district covering weeks, months or even years.
Back to square one! The 600mm isohyet fringes our northern borders. The combined Katima stations pan out in the 580mm range, Gaub Mission in the Tsumeb district (on a north-facing slope) also in the 580mm range with the Kavango rainfall stations hovering slightly below this level. So, if one takes the 600mm figure as a benchmark and takes 10% of this, it creates a new benchmark to provide a definition of a wet spell in the Namibian context.
This benchmark I chose to define as follows: Three consecutive days of Productive and Substantial values totaling 60mm or more. Note that this definition includes at least on Substantial fall (25 mm or more), to ensure sufficient penetration deeper than just a surface soak. Identifying wet spells in a typical Namibian rain season are of major importance for often, it is only these wet spells that determine the general state of grazing, and of animals' ability to survive throughout the year.