Need for integrated solutions
The unexplored rates of land subsidence, its lack of acknowledgement in policy agendas, the divergent interests and the unknown socio-economic consequences of potential management strategies emphasize the need for future scientific attention, societal discussions, and an integrated view on land subsidence. Research by the Water, Climate and Future Deltas hub on land subsidence aims to provide policymakers with action perspectives to accelerate the mitigation of and the adaptation to land subsidence.
Widely unexplored process
We observe that the urgency of land subsidence is increasing in many deltas worldwide and that land subsidence is progressively included in policy agendas as an issue of concern. Despite the increasing urgency, the phenomenon of land subsidence is still widely unexplored and the quantification of past, current and future subsidence rates is complicated by multiple factors, including local land management and soil properties. Currently, quantitative assessments are improving at a local scale and recently two global maps of future subsidence estimates were published (Herrera-Garcia et al., 2021; Nicholls et al., 2021). Despite this uncertainty and especially in combination with sea-level rise, we need to determine the time we still have to adopt management strategies and develop a long-term adaptation plan (Storyline: Pathways of delta development). Future research can help to decrease this uncertainty in planning by improving land subsidence projections.
Unknown long-term effectiveness and socio-economic consequences
Current adaptation and mitigation measures, such as raising land and measures on houses, are often implemented in response to incidents and only patch subsidence problems for a few years before they re-appear or move to neighbouring areas. In addition, measures such as increasing groundwater levels enhance the risk of flooding, burst of land surface and foundation damage at an increasing number of locations. Therefore, new measures are needed that support a long-term perspective on tackling land subsidence. However, the long-term efficiency and socio-economic consequences of these new measures are still unknown, and effective methods to particularly assess the social consequences are lacking. For instance, what are the consequences on livelihoods of reducing groundwater extraction in urban areas or increasing groundwater levels in rural areas?
Furthermore, the many involved interests complicate the implementation of adaptation and mitigation measures to tackle land subsidence. These include economic interests (e.g. of residents, farmers and industries), water management interests to prevent flooding (Storyline: Flood risk management) and drought (Storyline: Drought in deltas), and claims to consider the cultural heritage of the landscape. Dries Hegger, assistant professor of water and climate governance, emphasizes, "A societal discussion on the acceptable risks, effects and costs should therefore begin as soon as possible to develop action perspectives. Such a discussion should include more fundamental debate about the conditions under which subsiding areas can sustain certain societal functions such as housing, agriculture and industrial development". Moreover, future research should focus on how to reconcile measures addressing subsidence with other (national) challenges, such as making agriculture and cities future- and climate-proof, and steering economic development and building construction to decrease their exposure to flooding.
Land subsidence should be part of an integrated water resources management strategy
Integration into policy
To successfully address land subsidence, it needs to be integrated into policy. According to Gilles Erkens, researcher in land subsidence and geomorphology, “Land subsidence should be part of an integrated water resources management strategy which should be linked to flood mitigation". The integration into policy requires adjustments of the current system which is optimized for meeting the short-term interests of involved stakeholders. Creating the required conditions for policymakers to be able to make decisions to step out of this locked-in state is needed to promote the integration of land subsidence into policy.