Spatial and temporal variation of vegetation from 1982 to 2006 over North East Asia and its association with climate variables

Abstract

In order to examine surface changes over East Asia, in response to the climate change, mean NDVI data for the growing seasons (April–October) from 1982 to 2006 were used to examine the spatiotemporal variations in the vegetation. Results indicate that there was a prominent change in the trend of NDVI around the mid‐1990s: a pronounced positive trend over most of the Northeast Asian domain before the mid‐1990s (1982–1996), consistent with findings from other studies and a reverse (or weakened) trend after the mid‐1990s (1997–2006). The reverse trend is evident over the higher‐latitude regions north of 50°N and the eastern Mongolian border area.

Distinct declines in the local vegetation greenness after the mid‐1990s were shown more clearly in seasonal variations of NDVI anomalies. During the springtime (April-May), most area except some northeast parts of Mongolia experienced severe reductions of NDVI after the mid-1990s, which was dominant especially in the higher latitudes of 50°N. Vegetation in the cultivated areas of North China had increased in summertime (June-August), while vegetation in the higher latitudes of 50°N showed a decline trend after the mid-1990s.Decreasing of summertime NDVI was obvious particularly in the south of Mongolia and Inner-Mongolia near the Gobi border. During the autumn (September-October), vegetation reduction after the mid-1990s was great in the northeast Mongolia and east parts of Lake Baikal, while vegetation continuously increased over the other areas.

Possible causes in the vegetation changes were examined with other climate variables. It was suggested that the dominant warming trend during growing season until the mid‐1990s led to the increased NDVI in most North East Asia, especially over the high‐latitude regions. However, after the mid‐1990s, the reverse NDVI trend found primarily in the east of Lake Baikal and the arid and semiarid regions south of 50°N seems to be closely linked to local precipitation changes occurred abruptly in the mid‐1990s despite the continued temperature rise.

Based on the assumption that surface vegetation changes should lead to the radiation energy budget, possible influences of vegetation changes on surface albedo and longwave radiation were examined. It was indicated that change in surface albedo in the clear-sky condition seems to be not directly related to the variation of vegetation but closely associated with changes in soil moisture. On the other hand, clear-sky outgoing longwave radiation at surface showed continuous increasing trend over the whole area with maximum in Mongolia for the whole period, because of increased temperature associated with anthropogenic warming. Overall, influences of surface vegetation changes on the radiation budget over the twenty-year analysis period appeared to be less significant.