基于NDVI的云南省2009-2010年干旱遗产效应研究

气候变化正导致干旱事件发生的强度、频度显著改变,极端气候事件发生的不确定性直接影响陆地生态系统关键生态过程。我国西南地区在2009-2010年发生百年一遇的极端干旱,目前关于植被生长在长时间尺度对此次干旱事件的响应尚不明确。以云南省为研究区,基于多年Normalized difference vegetation index(NDVI)影像数据以及长时间序列气象资料对此次极端事件的干旱遗产效应开展研究,分析了干旱遗产效应的持续时间以及不同植被类型的响应差异。结果表明:1)云南省植被生长在极端干旱事件发生后受到的抑制时间大约持续1-2年,受影响区域主要集中在遭遇降水严重减少的地区;2)海拔2000 m附近为植被对干旱响应最为敏感的区域,海拔高于4000 m的植被生长几乎未受到干旱影响;3)较之草地和农田,森林植被受到的抑制作用更为强烈。研究揭示了极端干旱对云南省植被生长造成的影响,为该地区未来应对极端干旱并有效开展植被恢复提供理论依据。

The drought legacy effects of 2009-2010 based on NDVI in Yunnan Province

Climate change is leading to significant variations in the intensity and frequency of drought events. The compositions, structures, functions as well as the processes of terrestrial ecosystems are directly affected by the uncertainty of extreme climate events. In 2009-2010, the southwestern China, an area that contains multiple types of fragile ecosystems and was frequently hit by drought events, experienced a once-in-a-hundred-year extreme drought. Over the past decade, large efforts have been made to evaluate the recovery of vegetation after drought, however, the responses of vegetation growth to this extreme drought event on a long-term time scale is still unclear. In this study, using multi-year normalized difference vegetation index(NDVI) data, ecosystem type data, digital elevation model(DEM) and meteorological datasets, we found a climate factor to predict vegetation growth based on linear regression model. Then the duration and the spatial variation of legacy effects of 2009-2010 extreme drought in Yunnan Province in southwestern China were determined, and the responses of diverse vegetation types on the extreme drought event were analyzed. The results showed that 1) the inhibition of vegetation growth occurred about 1-2 years in Yunnan Province after the extreme drought event, especially in areas where precipitation experienced a severe reduction. The mean deviation between observed NDVI and predicted NDVI in whole research area in 2010 and 2011 were -0.0404 and -0.0330, respectively, and the deviations were more evident in grid points with a significantly positive relationship between climate factors and vegetation growth, 2) The most sensitive area of vegetation response to drought event was around 2000 m above sea level. The magnitude of negative drought legacy effects showed an increasing trend along the elevational gradients at altitudes lower than 2000 m and a decreasing trend at altitudes between 2000 m and 4000 m. At altitudes higher than 4000 m, the vegetation growth was almost unaffected. 3) Compared with grassland and farmland, the inhibition of forest vegetation was stronger and longer lasting, suggesting a weaker drought resilience of forest under dryer conditions. Our study revealed the negative impacts of extreme drought on the growth of vegetation in Yunnan Province and provided a theoretical basis for coping with extreme drought and restoring vegetation effectively in the future. More in-situ observation data are needed to improve the understanding of drought legacy effects and predict trajectories of terrestrial ecosystems in response to a warmer and drier climate in Yunnan Province and southwestern China.