Local effects of global climate change on the urban drainage system of Hamburg.

The Hamburg Water Group owns and operates a sewer network with a total length of more than 5,700 km. There has been increasing attention paid to the possible impacts of predicted changes in precipitation patterns on the sewer network infrastructure. The primary objective of the work presented in this paper is an estimation of the hydraulic impacts of climate change on the Hamburg drainage system. As a first step, simulated rainfalls based on the regional climate model REMO were compared and validated with long-term precipitation measurements. In the second step, the hydraulic effects on the sewer network of Hamburg have been analyzed based on simulated long-term rainfall series for the period of 2000-2100. Simulation results show a significant increase in combined sewer overflows by 50% as well as an increase in surcharges of storm sewer manholes. However, there is still a substantial amount of uncertainty resulting from model uncertainty and unknown development of future greenhouse gas emissions. So far, there seems to be no sound basis for the implementation of an overall climate factor for sewer dimensioning for the Hamburg region. Nevertheless, possible effects of climate change should be taken into account within the planning process for major sewer extensions or modifications.

Advances in urban-drainage management and flood protection.

Since the beginning of modern urban drainage in the 19th century, the sole objective has been to get rid of sewage and storm water in the best possible way and design the systems according to accepted standards. In recent decades, advanced methods have been developed not only to refine the design but also especially to enable the assessment of hydraulic performance and pollutant emissions. Consequently, urban drainage has become part of an integrated approach concerning flood protection as well as ecological aspects for whole watersheds. Another major change concerns the management of urban systems: simple structural maintenance has been replaced by interactive operational management and control of the systems in order to make better use of the facilities. Rehabilitation has become a multi-objective task. This paper looks at today's basic principles of urban drainage and tomorrow's potential advances, and deals with their relevance to flood protection.