Een snelle kosten-effectiviteitsanalyse voor het Deltaprogramma IJsselmeergebied: wat zijn de kosten en veiligheidsbaten van wel of niet meestijgen met de zeespiegel en extra zoetwaterbuffer?

Changes in the climate will have a major impact on the Dutch economy and environment. According to official Dutch climate scenario’s, at the end of the century the sea level will have increased by between 35 and 85 cm. This paper investigates major policy options for the IJsselmeer-area to ensure safety against flooding and various options to increase the freshwater stock. It is concluded that the costs to ensure safety and to protect the citizens, economy and the environment are substantial, that installing massive pumps results in major savings and that in the short run the fresh water stock can be tripled at very low costs (25 million euro). In contrast to the suggestion by the second Dutch Delta Commission, the water level in the IJsselmeer need not rise in line with the sea level The costs of raising dikes and safety benefits were calculated using the model Diqe-Opt. In addition, also all kinds of secondary costs and benefits were investigated, like the effects of changing the water level for the environment, shipping, agriculture and historic monuments built on long wooden piles. The effects on the environment were incorporated in several different ways. One approach was to estimate the costs to prevent environmental damage. For biodiversity, the shallow parts of the IJsselmeer are the most important. These can be protected against a rising water level by constructing a sand barrier. An alternative option is to purchase agricultural land and to use this for environmental purposes. In addition to these cost estimates, also the effects on biodiversity without any additional policy measures were investigated. This was measured in two different ways: the extent to which legal environmental protection standards were met and the score in biodiversity points. According to this cost-effectiveness analysis le 5.5), the option to install giant pumps at the Afsluitdijk is billions of euro cheaper than letting the water level rise with the sea level. This holds also when the differences in fresh water buffer are taken into account. Another conclusion of this analysis was that with limited investments (about 25 million euro), the fresh water buffer in the IJsselmeer-region could be tripled in about a decade.