Assessing carbon stock change for effective Nature-based Solutions implementation allocation: A framework

Mapping and assessing the carbon stock change (CSC) in urban areas can support the allocation of Nature-based Solutions (NbS) to mitigate climate change and advance urban sustainability. However, an effective framework concerning historical CSC and future simulation to support the allocation of NbS implementation is lacking. To fill this gap, we proposed a framework and applied it in the Zhejiang coastal region based on the assessment of historical (from 1990 to 2020) and predicted future (2030) CSC and local context analysis of urban and ecosystem challenges. Over the past three decades, the Zhejiang coastal region has experienced a considerable C stock loss of 20.34 Tg, predominantly owing to fast urbanization. The severest C stock reduction occurred from 2000 to 2010, with a slowdown in the following decade. Even so, more effective spatial management policies are urgent to mitigate further C stock depletion. Our framework identified 50.51% of the study area as the allocation area for NbS implementations where current and future C sequestration demand existed. Within the allocation area, six NbS types identified from literature were allocated or co-allocated, leading to eight tailored NbS implementations to tackle specific urban and ecosystem challenges of each location. The most widely allocated NbS implementations were "NbS1 × NbS2 × NbS3" and "NbS2 × NbS4", covering 42.86% and 34.69% of the allocation area. NbS2 covered nearly the entire allocation area (98.80%), with its primary role of habitat preservation and to control urban expansion. The proposed framework can be adapted to support various planning decisions regarding the prioritization and spatial allocation of NbS.