Tree-ring analysis over western Himalaya and its long-term association with vapor pressure and potential evapotranspiration

Abstract

Multi species tree-ring chronologies of the western Himalaya revealed strong significant negative relationship with potential evapotranspiration (PET) and vapor pressure (VP), and positive with moisture index (MI) and Palmer Drought Severity Index (PDSI) during spring season (March to May). The preliminary study showed that the MI and PDSI particularly in spring season might have a large scale positive association in developing of annual ring-width patterns, whereas PET and VP during the season are found not to be conducive for the trees growth. PET and VP from the beginning of the year 1917 showed strong influence on tree growth. High and low PET/VP might be associated with low and high MI/PDSI of the region. Extremely narrow ring width indices were observed in the year of 1921, 1941, 1953, 1954 and 1985 at most of the tree sites which are under the severe moisture stress condition due to extremely high PET and VP of the region. Also, extremely low PET and VP were found during 1917, 1933 and 1982, reflecting ring-width index above the normal due to enough moisture supply. Thus, the released and suppressed tree growth over the region is probably linked with the high and low MI/PDSI of the region. Loss or accumulation of soil moisture of the region might be precondition before the starting of growing season of the trees. The recent observation also suggests a weakening of VP and PET's influence on tree growth during recent few decades as compared to early period in sliding 31-years windows over western Himalaya. Correlation analysis of PET with MI and VP as well as PDSI for the period 1902–2002 during spring season indicated statistically strong correlation (r=−0.53, 0.82, −0.50) respectively which is highly significant at 0.01% level.