Past Climatic Variations in Nepal Himalaya as Reconstructed using Ring-width Chronologies

Abstract:

Taking advantage of the rich diversity of Nepal’s tree species and their distribution over a steep topographical gradient, we carried out a dendroclimatological study in the Himalaya with the objective of identifying the response of various tree species to climate changes and to reconstruct the past hydro-climate of the region. We developed ring-width chronologies dating back to AD 1334 by analyzing tree core samples of Abies spectabilis, Abies pindrow, Betula utilis, Juniperus recurva, Larix griffithiana, Picea smithiana and Tsuga dumosa. We found a significant positive correlation among the chronologies of different species within and between different sites suggesting that common climatic factors limit the growth of these trees, which is a needed basis to produce a climate reconstruction. Response function analysis revealed that pre-monsoon temperature (March-May) had a negative relationship to growth for most of the species, and that tree growth was positively correlated with precipitation of pre-monsoon to monsoon (March-July) in certain sites. In some sites near the treeline, winter climate had significant influence on the growth of the subsequent growing period. The March–May average temperature and precipitation of the past 400 years was reconstructed. The temperature reconstruction identified several periods of warming and cooling; however, it did not show a significant pattern of cooling during the Little Ice Age. Similarly, the reconstructed precipitation showed several wet and dry periods. We tested the correlation between the reconstructed spring temperatures with indexes of sea surface temperature of the equatorial Pacific and extended multivariate ENSO Index, revealing a significant negative correlation with monsoon and post monsoons seasons. This relationship demonstrates that the climate of Nepal Himalaya has spatio-temporal linkages with global scale climatic variability.