Evaluating adaptation measures for reducing flood risk: A case study in the city of Colombo, Sri Lanka

Abstract Many cities around the world face frequent problems with flooding, which is expected to get worse due to anthropogenic climate change and further urbanization. To tackle these problems often local infrastructural adaptation measures are proposed. In this study a chain of state-of-the-art models is presented that can be used to evaluate the benefits of such measures. Also, a method is presented to calculate the costs of not responding to a changing environment that is slowly aggravating floods. These methods are applied to a case study in the city of Colombo in Sri Lanka. Colombo faces problems with floods that are expected to get worse by further wetland reduction and climate change. Several local measures (infrastructural interventions) are proposed to tackle that problem. This paper shows a method to quantify the expected reduction in future flood damages resulting from the proposed measures, and compares the risk reduction to the proposed measure costs. This is done by creating probabilistic inundation depth maps using a 1D2D hydrodynamic model. A detailed flood damage model and socio-economic development scenarios are then applied to estimate damage with and without the measures. An economic analysis is done to demonstrate the benefits of the measures, which can be used by decision makers. Additionally, calculations are carried out of future flood risk increases when wetland reduction in Colombo continues. In this case, the effect of stopping wetland encroachment is found to be larger than the effect of the structural adaptation measures.

[1]  Bruno Merz,et al.  Review article "Assessment of economic flood damage" , 2010 .

[2]  Bruno Merz,et al.  A Probabilistic Modelling System for Assessing Flood Risks , 2006 .

[3]  M. A. Mian.  Project Economics and Decision Analysis , 2011 .

[4]  Sebastiaan N. Jonkman,et al.  Integrated Hydrodynamic and Economic Modelling of Flood Damage in The Netherlands , 2008 .

[5]  Stefan Beissel,et al.  Foundations of Decision Making , 2016 .

[6]  T. Porter,et al.  Trust in Numbers , 2020 .

[7]  Dennis Wagenaar,et al.  Multi-variable flood damage modelling with limited data using supervised learning approaches , 2017 .

[8]  Jim W. Hall,et al.  National-scale Assessment of Current and Future Flood Risk in England and Wales , 2005 .

[9]  Stephanie E. Chang,et al.  HAZUS-MH Flood Loss Estimation Methodology. II. Damage and Loss Assessment , 2006 .

[10]  Stefan Lüdtke,et al.  Regional and Temporal Transferability of Multivariable Flood Damage Models , 2018 .

[11]  Dennis J. Parker,et al.  Evaluating flood damages: guidance and recommendations on principles and methods executive summary , 2007 .

[12]  P. Hougaard.  A class of multivanate failure time distributions , 1986 .

[13]  Jeroen C. J. H. Aerts,et al.  Accounting for risk aversion, income distribution and social welfare in cost‐benefit analysis for flood risk management , 2017 .

[14]  K. Emanuel,et al.  Evaluating Flood Resilience Strategies for Coastal Megacities , 2014, Science.

[15]  Albert S. Chen,et al.  From hazard to impact: flood damage assessment tools for mega cities , 2016, Natural Hazards.

[16]  J. Chatterton,et al.  The Benefits of Flood and Coastal Risk Management: A Handbook of Assessment Techniques , 2005 .

[17]  F. Diermanse,et al.  Towards risk-based assessment of flood defences in The Netherlands: An operational framework , 2012 .

[18]  Ana Deletic,et al.  Assessment of Urban Pluvial Flood Risk and Efficiency of Adaptation Options Through Simulations – A New Generation of Urban Planning Tools , 2017 .

[19]  K. M. de Bruijn,et al.  Uncertainty in flood damage estimates and its potential effect on investment decisions , 2015 .

[20]  Dennis Wagenaar,et al.  Development of damage functions for flood risk assessment in the city of Colombo (Sri Lanka) , 2018 .

[21]  Bruno Merz,et al.  Multi-variate flood damage assessment: a tree-based data-mining approach , 2013 .

[22]  J. Aerts,et al.  Flood risk assessment for delta mega-cities: a case study of Jakarta , 2014, Natural Hazards.

[23]  K. Riahi,et al.  The roads ahead: Narratives for shared socioeconomic pathways describing world futures in the 21st century , 2017 .

[24]  J. Kind,et al.  Economically efficient flood protection standards for the Netherlands , 2014 .