cost-benefit analysis from a household survey conducted in 2012 for another IDB operation in the same area.
This was crucial for establishing a counterfactual scenario that demonstrated that all three Berlin Walls built by the project helped prevent agricultural losses and generated a positive net present value ranging from US$22 million to US$32 million, where the investment costs on the Berlin Walls ranged from US$1.9 million to US$3.8 million.
The cost-benefit analysis used to evaluate the impact of the gabion walls built in the area of Maniche was more challenging. The team aimed to compare expected annual economic losses caused by floods before the project (ex-ante) with projected losses after the project (ex-post).
A direct comparison of the effects of two similar climate events before and after the project was not possible because – fortunately – no significant climate event occurred in the direct aftermath of the construction work.
Instead, the team created loss curves specifically built for the Cavaillon watershed by establishing the relationship between expected annual economic losses caused by floods and the annual probability of flooding for both pre- and post-project scenarios.
The post-project scenario was created under the assumption that the new infrastructure would provide protection against flood events having a return period (or probability of occurrence) ranging from less than once every year (for small floods which, on average, occur every year or less) to once every ten years (for larger floods which, on average, occur once every ten years).
The main challenge here was the scarcity of concrete data on the effects of climate events on households. To overcome this problem, the project team conducted a survey inquiring about households’ assets, as well as the height of water levels that those surveyed had witnessed in their homes during specific historical flood events. With this information, the team was able to create a map visualizing the reported water levels and the exposed economic assets.
To estimate how often extreme rains occur in Haiti, the team used data collected by the National Water Resource Service (Service National des Ressources d’Eau – SNRE) and the National Center for Meteorology (Centre National de Météorologie – CNM).
Despite avoiding annual economic losses in the Cavaillon watershed, which were estimated to be around US$500,000, the analysis found that the flood mitigation infrastructure yielded a negative net present value of US$2.2 million.
This means that the costs of this portion of the project exceeded the benefits. The construction of the Berlin and gabion walls yielded a positive net present value.
What Did We Learn from the Evaluation?
The two methodologies that were developed and used to measure ex-post the impact of the downstream riverbank protection works built as part of PMDN I were then used ex-ante to identify and objectively prioritize the best opportunities to mitigate flooding and erosion in Haiti in the project’s second phase (PMDN II).
This marks a significant improvement in the design of natural disaster and risk management programs in Haiti, where cost-benefit analyses in the past were typically conducted only after the infrastructure in which to invest had already been selected.
The evaluation of PMDN I thus contributed to the IDB’s goal to improve policymaking in natural disaster risk management in Haiti.
This story is one of the project stories included in the Development Effectiveness Overview, an annual publication that highlights the lessons learned from IDB projects and evaluations.
About the Authors:
Sebastien Gachot is an impact evaluation consultant in the Environment, Rural Development and Disaster Risk Management Division in the IDB office in Port au Prince, Haiti.
Gines Suárez is a disaster risk specialist in the Environment, Rural Development and Disaster Risk Management Division in the IDB office in El Salvador.
Bruno Jacquet is a rural development specialist in the Environment, Rural Development and Disaster Risk Management Division in the IDB