In the News

Linking Flood and Drought Data to Water Safety Planning: Part 4

07 December 2018

In Part 3 of this blog series, I briefly discussed how to interpret the suggested datasets, and how to determine if climate conditions are ‘wetter’ or ‘drier’. Two questions remain to be answered, which include identifying those hazards and hazardous events that would be affected by ‘wetter’ or ‘drier’ conditions, and how these conclusions can be incorporated into the WSP process.

1. How do I identify & assess hazards and hazardous events impacting my water utility?

Identifying hazards and hazardous events can be done by, using the WSP teams own knowledge, reviewing the water utility’s current WSP, and through a literature review done by the WSP team. Water utilities may not necessarily need to prepare for those hazards and hazardous events that are associated with ‘wetter’ conditions if their water utility is expected to have ‘drier’ conditions. Hazards and hazardous events should be described using the method below:

After hazards and hazardous events have been described they should be categorised under the physical condition that they may be affected by:

  • hazards affected by wetter conditions
  • hazards affected by drier conditions
  • hazards affected by both wetter and drier conditions
  • hazards unaffected by either wetter or drier conditions

Table 1 shows examples of how previously identified hazards and hazardous events were categorised into the above four categories.

Table 1: Hazards and hazardous events that have been categorised

2. How do I incorporate this into my water safety planning?

After the WSP team has done the analysis to determine if conditions are ‘wetter’ or ‘drier’, these findings need to be incorporated into their WSP. The current risk rating of each hazard and hazardous event has to be known, this can be retrieved from the water utility’s current WSP. Table 2 below indicates the current risk for ‘lower lake and reservoir levels’ which are associated with ‘drier’ conditions.

Table 2: Current Risk Matrix

In order to determine how hazards and hazardous events would be affected by climate change, two matrices were developed, including a ‘likelihood change factor matrix’ and a ‘severity change factor matrix’. These matrices are used to indicate by how much the risk rating and risk score for hazards and hazardous events may change under the influence of climate change. The change factors and their application were developed for the purposes of the guidance document.

Example: the WSP team has completed the analysis, and have determined that their water utility is experiencing an overall ‘drier’ trend. Therefore, they should only consider amending those hazards and hazardous events that are affected by drier conditions. The likelihood and severity for rainfall and temperature for a given hazard and hazardous event are as follows:


Likelihood: 5 out of 12 months had rainfall that exceeded the average/mean.
7 out of 12 months had rainfall that were below the average/mean.
- Severity: mildly dry


Likelihood: 3 out of 12 months had temperatures that exceeded the average/mean.
9 out of 12 months had temperatures that were below the average/mean
- Severity: near normal

Using the above information, the WSP team can determine the change factors for likelihood and severity using the below tables 3 & 4.

Table 3: Likelihood change factor matrix

Table 4: Severity Change factor matrix

The change factors determined using the above matrices should be added to the current risk scores (Table 5).

Table 5: Adding change factors to current likelihood and severity

The new risk score can be put into the WSP risk matrix. This will indicate how the risk score and rating have changed. These change factors should be applied to each hazard and hazardous event affected by the associated physical condition. The risk score has increased from 6 to 9 the hazard and hazardous event (Table 6).

Table 6: New risk rating

The change in the ‘new’ risk score and indicates that the effects of the hazard and hazardous event may have worsened under the physical conditions, and the water utility may have to consider taking action to limit the impact thereof.

« Back to News posted on 07 December 2018 To News Archive »
How much water does it take to...
To grow one kilogram of wheat needs 1300 litres of water - The Water Wheel September/October 2010
How much water does it take to...
To produce one litre of milk requires 1000 litres of water - The Water Wheel Sept/Oct 2010
What's on your mind?
Alone we can do so little, together we can do so much - Helen Keller
How much water does it take to...
One kilogram of maize requires 900 litres of water - The Water Wheel Sept/Oct 2010
What's on your mind?
"Izandla ziyagenzana - People depend on one another, just like the mutual interdependence in the act of hand washing" Zulu parable
What's on your mind?
"Talent wins games, but teamwork and intelligence wins championships" Michael Jordan
Your Water Footprint
Close the tap when shaving or brushing your teeth. You can save up to 45 liters of water!
What's on your mind?
"Ubukulu abubangwa - A man is judged by his actions, not his boasting" Xhosa saying
What's on your mind?
"Action is the foundational key to all success" Pablo Picasso
How much water does it take to...
It takes 4650 litres of water for one steak (300g) - The Water Wheel Sept/Oct 2010
How much water does it take to...
More than 140 litres of water goes into every cup of coffee - The Water Wheel September/October 2010
A dripping tap can waste up to 30 liters of water an hour, wasting 10 000 liters of water per year!

Contact Us

General Contact Details

Tel: +27 (0)21 8802932
Fax: +27 (0)86 5710609

Send us an enquiry »

Subscribe to Newsletter