As the impact of severe weather events intensifies, timely communication becomes critical. The South African Weather Service (SAWS) said its Impact-Based Severe Weather Warning System was designed to alert the public of potential impacts that may result from dangerous weather conditions.
It focuses on communicating the potential impacts of hazardous weather, shifting the focus from describing the weather itself to emphasising the effects it may have.
SAWS uses a colour-coded and numbered risk matrix to determine the warning level.
The colour-coding and the numbering are determined by combining the level of impact with the likelihood of that impact occurring.
“The idea is to warn the public of the looming danger as early as possible so that they can take precautions and ready themselves for such weather events with a view to saving lives and property,” SAWS said.
“Take heed of such warnings and cooperate with disaster management and emergency authorities.”
Elaborating on the Impact-Based Severe Weather Warning System, SAWS forecaster Sihle Dlamini said the service uses three colour codes in the table: yellow, orange, and red.
The Mechanics of the Warning System
Dlamini said looking at the impact, they look at the area.
For example, in Durban, they consider the area’s vulnerability and ask: Is it located in an urban area with drainage systems, or informal housing without drainage systems, or perhaps a rural area with lots of vegetation?
Those places have different impacts in terms of expecting a lot of rainfall.
Dlamini said when looking at impact, you would look if you are expecting minimal, minor, significant or severe impact.
“Again, each area will experience different impacts,” Dlamini said.
For instance, when looking at an area with informal housing, a lean will be towards a higher impact, like a significant impact, based on what is expected in terms of rainfall.
Once the impact (minimal, minor, significant, or severe) has been identified, the focus shifts to the likelihood.
For instance, if a significant impact is expected, what is the likelihood of those significant impacts occurring?
Dlamini said as a forecaster, he determines whether he has a very low likelihood, a low likelihood, a medium likelihood or a high likelihood.
“In terms of the percentages, for a very low likelihood, we have 10% which is quite low. So from that, if I’m sitting on a significant impact, I’ll sit on a Yellow Level 3 warning,” Dlamini said.
“If the other likelihood that we have is low, which is 30% if I’m sitting on significant impact, I will look at a Yellow Level 4 warning.
“For medium likelihood, which is 60% and still sitting on significant impact, I would look at an Orange Level 5 warning.”
Dlamini explained these are still significant impacts.
“If this event or rainfall comes through, I’m expecting a significant impact. But the difference here is the likelihood if I’m much more confident that it’s very low, low, medium or high. Then again, if I’m also sitting on a significant impact, I might be sitting on a likelihood of high, which is 80%, if in that case, I’m much more confident that this impact will occur if this rain comes through.”
Decoding the Weather Warnings
Dlamini said the warning is accompanied by an explanation called an impact table they use in the office. The impact table speaks to areas.
For instance, “if you are looking at a warning that is mostly along the coast, then I might be looking at impacts that are associated with the coast. If I am talking about wind, then I might be looking at the build-up of sand along the coastline and debris. If I’m looking at the interior, in terms of wind, it might be trees falling and dust.”
With severe thunderstorms, SAWS looks at severe or excessive lightning, strong damaging winds, hail (large amounts of small hail or large hail), or heavy downpours. Those are severe thunderstorm details SAWS usually warns people about.