Vegetation drought loss probability and disaster-triggering thresholds in Yellow River Basin based on Copula model

Abstract

[Objective] The Yellow River Basin serves as a critical ecological barrier and major agricultural production area in China, characterized by a fragile ecological environment and high sensitivity to climate change. Investigating the response characteristics of vegetation to drought events in this region, quantifying the probability of vegetation loss under different drought scenarios, and identifying the drought thresholds that trigger vegetation loss are of great significance for regional ecological security and sustainable development. [Methods] Based on monthly precipitation and leaf area index(LAI) data from 1982 to 2020, the standardized precipitation index(SPI) was used to identify drought events, and a bivariate Copula-based conditional probability model was constructed to assess vegetation loss probability and inversely identify disaster-triggering thresholds. [Results] 1) LAI was significantly positively correlated with SPI across 94. 3% of the grid cells in the Yellow River Basin, and the optimal cumulative time scale of vegetation response to drought exhibited a pronounced north-south divergence, ranging from 4—9 months in the southern region to over 17 months in the northeastern region. The basin-wide average probability of vegetation loss increased from 52. 0% under mild drought to 67. 7% under extreme drought(LAI ≤ 40 th percentile), with values in the grassland-dominated central and northern areas substantially exceeding those in the forest-and cropland-dominated southeastern areas(by 12% ~18%).(2) Drought thresholds differed markedly among the four vegetation types. The mean SPI required to trigger LAI ≤ 40 th percentile loss was only-0. 70 for grasslands, whereas deciduous broadleaf forests required an SPI as low as-1. 12, indicating a 1. 6-fold difference in drought sensitivity between the two.(3) As the loss level decreased from the 40 th to the 10 th percentile, the proportion of areas with identifiable thresholds declined sharply, suggesting that extreme vegetation loss was predominantly governed by localized drought events in grassland regions. [Conclusion] Vegetation drought vulnerability in the Yellow River Basin is jointly governed by vegetation type and regional moisture availability. Grasslands represent the most drought-prone ecosystem type, and the grassland-dominated central and northern areas constitute priority regions for drought disaster prevention and control. These findings provide a scientific basis for drought risk zoning and management, ecological conservation prioritization, and optimized water resource allocation across the river basin.

Keywords

Yellow River Basin / drought / leaf area index / vegetation loss probability / disaster-triggering threshold / Copula function / vegetation differences / vegetation vulnerability