Every night we see weather presenters on television forecasting the outlook for the next few days and week ahead. For the most part, their weather predictions are accurate, but occasionally, unexpected weather events descend on our communities.
In February 2022, southeast Queensland and northern New South Wales endured a ‘rain bomb’ weather event that produced some of the regions’ heaviest rains in years – in fact, it was described as a ‘one in a 100-year event’.
Flooding occurs when heavy and/or continuous rain falls that exceeds the ability of surrounding land to soak up the water. Rivers, creeks and dams carry excess water away but during a flood they are overwhelmed by the sheer volume of water and often, riverbanks are broken leading to inundation of low-lying land.
Let’s explore how numbers and maths are critical for measuring and predicting weather events.
The probability that a given rainfall total accumulated over a given duration will be exceeded in any one year is called the Annual Exceedance Probability (AEP). AEP can be calculated with a simple formula: 100 / x years, where x is the number of years that that a flood occurs, expressed as a percentage. A 1% AEP means there is a one in a 100 chance of a flood in any given year. Similarly, you can easily calculate a 1000-year flood (AEP 0.1%) or a 10-year flood (AEP 10%).
By calculating a ‘probability’ we have a way of measuring the risk of an event happening. The 1% AEP statistic gets a lot of attention because insurance companies use maps to identify areas of risk for 100-year floods when calculating premiums. Planning authorities also use the 1% AEP when issuing building approvals for houses and roads as it is considered an acceptable risk.
In an ideal world we would have many hundreds or thousands of years of measured historic annual rainfall because more rainfall data in a data set produces more accurate predictions. However, given Australia is a relatively young nation, our oldest records only date back 160 to 170 years ago, which is partly why forecasters get predictions wrong.
The Bureau of Meteorology keeps Australian rainfall records and they make ideal data sets for children to practice how to calculate basic statistics. Children can calculate the median, mean and mode rainfalls for months, seasons and years for locations in which they live. They could also create data tables and bar graphs to visually display how rainfall varies with the months and seasons.
ORIGO Education’s Thinking Caps is a sequence of maths investigations designed to foster primary students’ abilities to “think” about mathematics.
Each investigation includes projectable questions to get students solving problems, communicating, reasoning, and understanding the mathematics they are learning and applying it to the world outside the classroom.