Global mismatches between drought trends and ecosystem resistance reveal emerging ecosystem vulnerability

Abstract

Ecosystem resistance to drought is widely used to assess vulnerability under climate change, but its decline does not always coincide with worsening drought conditions. In this study, we evaluated the spatial correspondence between long-term changes in ecosystem resistance and drought trends across drought-affected areas of global terrestrial ecosystems, excluding irrigated lands. Using satellite-derived NDVI and SPEI at a spatial resolution of 5 arc-minutes, we evaluated Mann–Kendall trend Z scores for ecosystem resistance and four drought characteristics, namely drought duration, frequency, severity, and intensity, during 2002–2019, and classified their sign combinations into four categories. As a result, declining resistance was observed not only in regions where drought characteristics intensified, but also in regions where drought characteristics weakened. Moreover, even where drought-characteristic trends were non-positive, ecosystem resistance did not consistently show a positive trend. The distribution of the four categories also differed among land-cover types. In addition, comparison of height above nearest drainage suggested that categories associated with declining resistance tended to occur in relatively lower topographic positions. These results suggest that ecosystem resistance cannot be explained by meteorological drying alone, but instead reflects multiple vulnerability types shaped by hydrological conditions and ecosystem-specific sensitivity.