Biodiversity threat index: methodology and application for Emerald network sites under catastrophic flood conditions

Abstract

Purpose. To develop and apply the Biodiversity Threat Index (BTI) as a quantitative tool for prioritizing post-disaster restoration of Emerald Network sites under conditions of limited field data availability.
Method. The BTI integrates five normalised indicators: flood coverage (F, w = 0.30), number of protected bird species under Bern Convention Resolution No. 6 (B, w = 0.22), number of habitat types under Resolution No. 4 (H, w = 0.18), other protected species (S, w = 0.12), and the normalised weighted flood impact area accounting for ecosystem vulnerability (W, w = 0.18). All indicators were normalised by min–max scaling. Weights were assigned by expert judgement and tested by ±10% sensitivity variation. The index was applied to 11 Emerald Network sites of the steppe biogeographical region affected by the catastrophic flood caused by the Kakhovka Dam failure on 6 June 2023. Flood extent was assessed using a satellite-derived flood mask based on Sentinel-2, Landsat-9, and Sentinel-1 data processed in Google Earth Engine.
Findings. Three sites received a critical threat class (BTI ≥ 0.70): Black Sea Biosphere Reserve (0.945), Dnipro-Bug Estuary (0.789), and Biloberezhzhia Sviatoslava National Nature Park (0.705), while the Lower Dnipro site (0.687) belonged to the high threat class. The Black Sea Biosphere Reserve ranked first because of the highest concentration of protected biodiversity features (180), despite not having the maximum flood percentage (80.5%). Sensitivity analysis confirmed the robustness of the index: the ranking of the top four sites remained unchanged under ±10% weight variation.
Theoretical significance. The study contributes to the development of an integrated methodological framework for biodiversity-risk assessment in protected areas affected by catastrophic events by combining spatial flood indicators with species, habitat, and ecosystem-vulnerability characteristics.
Practical significance. The proposed index can be used to support post-disaster management, restoration prioritization, and allocation of limited conservation resources for Emerald Network sites where field verification is constrained or impossible.
Scientific novelty. The study proposes a reproducible quantitative index that moves beyond simple flood-area ranking and enables integrated prioritization of Emerald Network sites on the basis of both physical impact and conservation value.
Future research. The BTI relies on Emerald Network Standard Data Forms and remotely sensed flood estimates; therefore, it reflects the documented conservation value of sites rather than direct post-disaster field observations. Further research should refine the ecosystem-vulnerability component and test the method on other types of environmental disasters and in other regions.