Sinking land : Optimal control of subsidence

Land subsidence threatens the living conditions of roughly 1.2 billion people worldwide in deltaic regions characterized by soft top soil. Economic activity in deltaic regions requires lowering the groundwater levels to keep the land sufficiently dry to maintain productivity, which, however, leaves future generations worse off by accelerating subsidence and increasing future costs. The current policymaking is often myopic by ignoring this intertemporal trade-off. This paper provides a model recognizing this trade-off: we integrate the dynamics of land subsidence and groundwater management to derive optimal paths for controlling the groundwater level. Applying our model to the paradigm case of Dutch agricultural peatlands, we find that the welfare costs of ignoring dynamic efficiency can be in the order of 10 percent of the land value. Our results support current proposals to slow down subsidence by increasing the groundwater levels even in the absence of its social benefits such as avoided carbon dioxide emissions.