Increasing drought in the recent decades has been observed in the central Himalaya due to decreasing boreal winter and spring precipitation. Spring moisture availability plays a crucial role for vegetation growth, agricultural production, forest productivity and ecosystem functions. Therefore, study on long-term perspective of spring drought variability and its teleconnection to the ocean-atmospheric circulation is a relevant issue. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and University of Erlangen-Nürnberg developed a series of new tree-ring width chronologies of Himalayan spruce (Picea smithiana), a native species in the central and western Himalayas, in the central Himalaya, north-western Nepal.

They aimed to identify the dominant climatic factors limiting radial growth of high-elevation Himalayan spruce and to determine historical drought variations in the central Himalaya. They further wanted to evaluate the teleconnections of spring drought variability with the global climatic drivers. 

Then they presented a new tree-ring chronology of Picea smithiana extending back to 1498 current era, which provides evidence for tree-ring based spring drought variability over the past 289 years (1725–2013) in the central Himalaya.  

They found that radial growth of Himalayan spruce were positively (negatively) related to precipitation (temperature) during the spring season. Further correlations with spring self-calibrating Palmer drought severity index (scPDSI) confirmed that the spring moisture availability was a crucial tree-growth limiting factor in the central Himalaya. 

The dry and wet episodes were generally consistent with previous studies from Himalaya and vicinities. Drought variability in the central Himalaya was mainly associated with disturbances of mid-latitude northwesterlies due to Atlantic Multidecadal Oscillation (AMO).  

Their reconstruction revealed a continuous shift toward drier conditions in the central Himalaya since early 1980s that coincide with continental-scale warming and reduced spring precipitation in the central Himalaya. 

Moreover, the continuous warming and drying climatic conditions could have far-reaching ecological impacts over the Himalayan forests. 

The study entitled "Tree rings reveal recent intensified spring drought in the central Himalaya, Nepal" has been published in Global and Planetary Change. 

Picea smithiana forest in the central Himalaya. (Image by Shankar Panthi)