Abstract
Large-scale climate oscillations, particularly the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO), have widespread influences on climate systems across the Tibetan Plateau (TP). It is understudied how the temporal changes in AMO and PDO affected growth of vegetation through modifying the local climatic factors in different areas across the TP. We used the AMO and PDO indices, gridded growing season mean temperature (TGS), cumulative precipitation (PGS), and normalized difference vegetation index (NDVIGS) data from 1982 to 2015 to investigate the temporal trends of these variables and the correlations of the TGS and PGS with each of the AMO and PDO indices as well as their correlations with the NDVIGS. The results showed that the warming of the TGS over the TP and the increases of the PGS in western, central, and northeastern areas of the TP may have been related to an increase of the AMO index and a decrease of the PDO index. Combining those relationships with the spatial patterns of the TGS-NDVIGS and PGS-NDVIGS correlations suggested that the changes of the AMO and PDO may have indirectly increased the NDVIGS in the central and northeastern areas of the TP by increasing TGS and PGS, in most parts of the southwestern TP by increasing PGS, and in the eastern and south-central regions of the TP by increasing TGS. In contrast, the decrease of the NDVIGS in some areas of the southeastern and southwestern TP may have been associated with a negative effect of warming as a result of changes in the AMO and PDO. These results highlight the indirect impacts of changes in large-scale climate oscillations on the growth of vegetation through modification of local climatic factors across the TP, and they suggest the substantial spatial heterogeneity of these impacts largely depends on the responses of vegetation to local climatic factors.
Highlights
The Tibetan Plateau (TP), known as the roof of the world, is the largest and highest highland in the world, with an average elevation of over 4,000 m and an area of about 2.5 × 106 km2 (Tang et al, 2009)
In 93.4% of all pixels, PGS values were positively correlated with Atlantic Multidecadal Oscillation (AMO) indices, and the positive correlations were significant in 24.4% of the pixels, most of which were distributed in the northeastern and central portion of the TP and in the region between 84 and 90°E (Figure 1B)
We investigated the impacts of temporal changes of the AMO and Pacific Decadal Oscillation (PDO) on local climate characteristics and subsequently on the growth of vegetation across the TP during the period 1982–2015
Summary
The Tibetan Plateau (TP), known as the roof of the world, is the largest and highest highland in the world, with an average elevation of over 4,000 m and an area of about 2.5 × 106 km (Tang et al, 2009). Most precipitation that falls on the vegetated portion of the TP during the growing season is attributable to the South Asian Summer Monsoon (SASM) (Conroy and Overpeck, 2011), while a recent study claimed 63% water vapor of TP precipitation is provided by local moisture recycling (Curio et al, 2015) Both the AMO and SASM are controlled by sea surface temperature (SST) over the North Pacific region [e.g., the Pacific Decadal Oscillation (PDO)] through alternating SST of the tropical Indian Ocean and by the thermal contrast between the TP and tropical Indian Ocean (Li and Yanai, 1996; Krishnamurthy and Krishnamurthy, 2014). The changes of the AMO and PDO may have major impacts on climate over areas of the TP where the growth of vegetation is sensitive to climate change
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