Changing seasonality of panarctic tundra vegetation in relationship to climatic variables
Changing seasonality of panarctic tundra vegetation in relationship to climatic variables
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DOI：
10.1088/1748-9326/aa6b0b
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发表时间：
2017-05-01
影响因子：
6.7
通讯作者：
Zhang, Jinlun
中科院分区：
文献类型：
--
作者：
Bhatt, Uma S.;Walker, Donald A.;Zhang, Jinlun
研究了北极苔原植被生产力的潜在气候驱动因素，以了解1982-2015年最大归一化差异植被指数（MaxNDVI）和时间积分NDVI（TI-NDVI）记录的近期绿化和布朗宁趋势。在此期间，夏季海冰继续减少，而海洋热含量增加。夏季温暖指数（SWI）和NDVI的增加在卫星记录上并不均匀。从1982年到1990年代中期，社会工作指数有所上升，从1998年起一直保持相对平稳，直到最近有所回升。虽然MaxNDVI在1982-2015年期间呈现出积极的趋势，但TI-NDVI在1982年至2001年期间有所增加，此后一直下降。对记录的前半部分和后半部分的数据进行了分析，并在空间上比较了变化趋势，重点是生长季节。与1982- 1998年相比，1999-2015年MaxNDVI和TI-NDVI的负趋势更为普遍。生长季内的趋势分析表明，1982-1998年春季海冰减少量大于1999-2015年，而秋季海冰减少量在后期更大。1982-1998年生长季的地表温度趋势为正，1999-2015年5 - 6月为正，7 - 8月为弱负。1982-1998年，春季双周NDVI趋势是积极的和重要的，与春季开放水域增加和可用温暖增加一致。1999-2015年5月和6月上半月的最大NDVI趋势显示出显著的负趋势。需要进一步研究，以确定春季NDVI下降的驱动因素。
Potential climate drivers of Arctic tundra vegetation productivity are investigated to understand recent greening and browning trends documented by maximum normalized difference vegetation index (NDVI) (MaxNDVI) and time-integrated NDVI (TI-NDVI) for 1982-2015. Over this period, summer sea ice has continued to decline while oceanic heat content has increased. The increases in summer warmth index (SWI) and NDVI have not been uniform over the satellite record. SWI increased from 1982 to the mid-1990s and remained relatively flat from 1998 onwards until a recent upturn. While MaxNDVI displays positive trends from 1982-2015, TI-NDVI increased from 1982 until 2001 and has declined since. The data for the first and second halves of the record were analyzed and compared spatially for changing trends with a focus on the growing season. Negative trends for MaxNDVI and TI-NDVI were more common during 1999-2015 compared to 1982-1998.Trend analysis within the growing season reveals that sea ice decline was larger in spring for the 1982-1998 period compared to 1999-2015, while fall sea ice decline was larger in the later period. Land surface temperature trends for the 1982-1998 growing season are positive and for 1999-2015 are positive in May-June but weakly negative in July-August. Spring biweekly NDVI trends are positive and significant for 1982-1998, consistent with increasing open water and increased available warmth in spring. MaxNDVI trends for 1999-2015 display significant negative trends in May and the first half of June.Numerous possible drivers of early growing season NDVI decline coincident with warming temperatures are discussed, including increased standing water, delayed spring snow-melt, winter thaw events, and early snow melt followed by freezing temperatures. Further research is needed to robustly identify drivers of the spring NDVI decline.