Increased drought effects on the phenology of autumn foliar senescence

Global warming delays the autumn date of foliar senescence (DFS) in recent decades, with implications for growing season length and therefore global carbon storage. However, warming-associated drought in autumn, leading to water limitation, may cause earlier DFS. Using ground observations since 1940s and 34 years of satellite greenness data (1982‒2015) over the Northern Hemisphere (>30°N), we show the increased impact of drought on earlier DFS. Decreased precipitation under warming and weaker drought resistance   shown by various plant functional traits counter the effect of warming on DFS. For example, isohydric plants with strict regulation of water status may drop leaves fast during droughts. We derive an improved set of phenology models based on this influence, and project earlier DFS by the end of the century, particularly at high latitudes (>50°N). Our results limit uncertainties in the later end of plant growth with warming, aiding estimation of C uptake of terrestrial ecosystems.