Data and code from: Spatial selection undermines flood protection in U.S. wetland markets

Wetland mitigation markets aim to offset environmental damage by allowing developers to purchase credits from previously restored wetlands. We test whether wetland credits traded in these markets offer equivalent flood protection benefits. Using newly developed, high-resolution estimates of wetland flood protection for 915 wetland markets within the continental U.S., we document a likely decline in flood-protective value due to wetland loss over the 1985 to 2021 period. Consistent with standard models of urban economic geography, wetlands lost to development exist near prior developed areas and therefore provide relatively high levels of downstream flood protection compared to wetlands created in compensation--on average 4.1 times as much, though in some cases up to 78 times. We document a high concentration of lost flood protection in Florida. While wetland markets may succeed in preserving total wetland acreage, they may systematically fail to preserve downstream flood protection services. More generally, this suggests that designing environmental markets to preserve complex bundles of spatially heterogeneous ecosystem services while still allowing meaningful compliance flexibility may be challenging.

湿地缓解交易市场（Wetland Mitigation Markets）通过允许开发者从已完成修复的湿地购买信用额度，以此抵消开发活动造成的环境损害。本研究旨在检验此类市场中流通的湿地信用额度是否具备等价的防洪效益。本研究依托针对美国本土915个湿地市场开发的新型高分辨率湿地防洪效益评估数据集，发现1985年至2021年间，湿地流失导致的防洪价值呈现显著下降趋势。结合城市经济地理学的标准模型框架，因开发活动流失的湿地多位于已开发区域周边，相较于作为补偿性新建的湿地，其可为下游提供更高水平的防洪保护——平均为补偿新建湿地的4.1倍，部分案例中最高可达78倍。研究同时观测到，防洪效益流失的情况在佛罗里达州呈现高度集中的特征。尽管湿地缓解市场或可实现湿地总面积的保有目标，却可能系统性地无法保障下游防洪服务的有效留存。从更广泛的学术视角来看，本研究结果提示：若要在保留合理合规灵活性的同时，设计出能够保护空间异质性生态系统服务复合体的环境市场，仍存在不小的挑战。