Climate changed rainfalls for urban drainage capacity assessment

Abstract

Guidance on what type of rainfall to use when assessing hydraulic capacity of urban drainage systems under climate change is unclear; focus is mainly on what climate factors to use. Based on a case study in Kalmar, Sweden, this paper compares system performance using two design rainfalls, Block rainfalls and Chicago Design Storm (CDS), and selected observed rainfalls, with two methods of addressing future climate: a constant factor and Delta Change (DC) factors that depend on rainfall intensity. The use of CDS rainfalls presents the maximum hydraulic response, whereas Block rainfalls give lower responses but identify critical durations in the system, which may be useful addressing adaptation actions. Observed rainfalls of target return periods gave similar responses to CDS rainfalls, and can be applied with DC factors to address future changes in both intensity and volume. Differences between the two methods indicate a high dependence related to the maximum factors applied on the rainfalls.

Keywords::

• climate change
• delta change
• design rainfall
• observed rainfall
• rainfall-runoff analysis
• stormwater modelling

Acknowledgements

Thanks to Kalmar Vatten AB, for permission to use the urban drainage model, and to Claes Hernebring (DHI AB), for help with the rainfall statistics for Kalmar.

Additional information

Funding

This work was supported by Länsförsäkringar, through the project “Vattenavledningför en säkerbebyggdmiljö”, which is gratefully acknowledged.