Brukerfinansiert klimaberedskap? En beregningsmodell for overvannsgebyr i Oslo

Summary

A stormwater fee for Oslo? A computational approach to user financed climate readiness. Stormwater fee systems constitute a potential policy instrument for user financed climate readiness in Norwegian cities. Stormwater fees can contribute to operation and future maintenance requirements of stormwater networks and wastewater treatment required with climate change. However, stormwater fees calibrated to a property's stormwater runoff has been criticized for being too complex and expensive to compute. In this paper we show how stormwater fees can be computed for a whole city’s built area adjusted to local property run-off conditions. We demonstrate how a property specific fee can be calculated for all properties in Oslo through the combination of detailed landuse maps, a simple but bespoke hydrological model, estimates of current and expected costs of stormwater networks and treatment due to climate change towards 2040. Calculations are carried out in an online web application in Google Earth Engine. The application makes it possible for the property owner to test the effect of different LID measures on run-off and stormwater fees, providing support for the choice of optimal measures and cost savings. We compare the characteristics of the stormwater fee for Oslo with international experiences from other cities and discuss further technical and practical improvements needed to achieve good stormwater management in a future climate. Our work shows that computation costs are not an important argument against introduction of a user differentiated stormwater fee.