 in height, commonly known as “Berlin Walls”.
PMDN I also financed the construction of gabion walls (metal cages filled with rocks) along the downstream river-bank of the Cavaillon watershed to protect the town of Maniche.
The town had experienced significant economic losses, particularly in the agricultural sector, as a result of frequent exposure to flooding.
How Can We Know Whether the Project Was Effective?
After investing US$13.9 million in the infrastructure component of the project, the Haitian government and the IDB wanted to measure the effectiveness of the infrastructure built under PMDN I before contemplating a second phase of the project.
A rigorous evaluation would fulfill two purposes: first, to estimate the benefits of what had been done, and second, to facilitate decision-making regarding the second project phase. However, evaluating infrastructure projects poses three big challenges for evaluators.
First, it is very difficult to find a comparable population exposed to a similar event: that is, to construct a counterfactual.
Second, the infrastructure financed by PMDN I was built to mitigate the effects of natural disasters—random events that cannot be planned or replicated.
Finally, the lack of data intensifies the first two challenges and makes it difficult to establish baselines and follow-ups.
Given these challenges, the PMDN I evaluation team decided to assess the benefits of the infrastructure measures through a cost-benefit analysis in order to evaluate the cost-effectiveness of each infrastructure alternative.
What Methodologies Were Used?
To assess the works to prevent erosion of the canals in the Artibonite watershed, the evaluation team conducted a technical diagnosis of the state of the canals before the project, to establish a baseline before anything new was built. The results showed that the canals would have collapsed within an average duration of five years.
To evaluate the agricultural losses that would result from the destruction of the canals, the team incorporated data in the 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