Many studies have reported that daytime warming advances the end of the vegetation growing season (EOS) in arid and semi-arid ecosystems in the northern middle latitudes. This finding, however, seems to contradict the fact that low temperature constrains alpine vegetation activity. Using EOS from 1982 to 2015 retrieved from satellite observations, we show that daytime warming could facilitate a delay in EOS on the Tibetan Plateau, the world's largest and highest alpine region, with a dry and cold climate. Our analysis revealed a positive partial correlation (REOS-Tmax) between EOS and preseason mean daily maximum temperature (Tmax) on 57 % of the Plateau in wetter years, but on only 41 % of it in drier years. At a regional level, REOS-Tmax was 0.69 (P < 0.05, t-test) during wetter years and -0.56 (P = 0.11) during drier years, indicating that daytime warming could directly delay EOS on the Plateau. On the other hand, we found a positive partial correlation (REOS-Prec) between EOS and preseason cumulative precipitation on 62 % of the Plateau during warmer years, but on only 47 % during colder years. At a regional level, REOS-Prec was 0.68 (P < 0.05) during warmer years and - 0.28 (P = 0.46) during colder years. Moreover, REOS-Prec increased on 60 % of the Plateau under increasing Tmax during 1982-2015, suggesting that daytime warming facilitates a delay in EOS on the Tibetan Plateau by regulating the effect of precipitation on EOS. Thus, to improve autumn phenology models in this region, researchers should consider the interactive effects of temperature and precipitation on EOS.
Keywords: Alpine ecosystem; Autumn phenology; Climate change; Normalized Difference Vegetation Index; Precipitation; Temperature.
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