Intensified seasonal droughts and carryover effects amplify negative growth anomalies in Eurasian grasslands during the past four decades

Eurasian grasslands, among the ecosystems most vulnerable to climate change, have experienced an increasing frequency of negative extreme anomalies in vegetation growth (NEGs) in recent decades, significantly impairing their ecosystem services. Despite their ecological importance, the mechanisms driving NEGs across Eurasian grasslands remain inadequately understood. As annual ecosystems with shallow root systems that respond rapidly to climate fluctuations, grasslands require seasonal-resolution analyses that integrate both immediate and lagged effects of extreme climate events, along with the trans-seasonal growth legacy effects of previous vegetation conditions on subsequent NEGs. To address these gaps, we implemented a comprehensive multifactor coincidence analysis spanning 1982 to 2018, using long-term satellite observations and climate time series to assess these complex interactions. Our results showed that NEGs occurred approximately three times more often at seasonal than annual timescales. Specifically, spring cold extremes dominated spring NEGs over 47% of the study area, while preseason droughts drove summer and autumn NEGs in 55% and 40% of the region, with these drought effects further intensified by preseason NEGs. Notably, the spatial extent of spring NEGs driven by cold extremes shrank from 47% (1982–1996) to 39% (2004–2018), as drought conditions emerged as a more influential factor. Concurrently, the carryover effects from preseason vegetation anomalies on summer and autumn NEGs strengthened substantially over time. These findings underscore the seasonal variability of the drivers of NEGs and highlight the crucial role of biological carryover effects in shaping Eurasian grassland dynamics, offering new insights for ecosystem management and climate adaptation strategies in these important yet vulnerable regions. • Drivers of negative extreme growth (NEGs) in Eurasian grasslands were investigated. • A framework linking exogenous, endogenous processes, and seasonal NEGs was proposed. • Cold dominate spring NEGs, but droughts' influence increased over past four decades. • Preseason droughts and NEGs drive summer/autumn NEGs, with the latter intensified.