What are the limitations of flood return period calculations?

Flood return period calculations are limited by their reliance on historical data, assumptions of statistical independence and stationarity.

Flood return period calculations, also known as flood frequency analysis, are a common tool used in hydrology to predict the likelihood of a flood event of a certain size occurring. However, these calculations have several limitations that can affect their accuracy and reliability.

The first limitation is the reliance on historical data. These calculations are based on the analysis of past flood events, which means they are only as good as the data they are based on. If the historical record is short or incomplete, the calculations may not accurately reflect the true flood risk. Additionally, the quality of the data can also be a concern. For instance, older records may not be as reliable or accurate as more recent ones, which can introduce uncertainty into the calculations.

Another limitation is the assumption of statistical independence. This means that each flood event is assumed to be independent of the others, with no influence on the likelihood of future events. However, this is not always the case in reality. For example, a large flood event can alter the physical characteristics of a river, which can affect the likelihood of future floods. Similarly, climatic patterns such as El Niño can lead to periods of increased flood risk.

The assumption of stationarity is another limitation. This means that the calculations assume that the flood risk is constant over time. However, this is not always the case. Climate change, for example, is likely to increase the frequency and severity of flood events in many parts of the world. Changes in land use, such as urbanisation or deforestation, can also affect flood risk.

Finally, flood return period calculations do not take into account the potential impacts of a flood event. They only provide an estimate of the likelihood of a flood of a certain size occurring. They do not provide information on the potential damage or disruption that such a flood could cause. This means that they may not provide a complete picture of the flood risk.

In conclusion, while flood return period calculations are a useful tool in flood risk management, they have several limitations that need to be taken into account.