Spatial and seasonal patterns of temperature lapse rate along elevation transects leading to treelines in different climate regimes of the Himalaya

Abstract

There are growing evidences that indicate the Himalayan region is warming rapidly with more warming in high elevation areas. The elevation-dependent warming (EDW) accelerates the rate of change in mountain ecosystems, including cryosphere, hydrology, biodiversity and socio-economic systems. Here, we present temperature lapse rates (TLRs) based on primary data from 21 stations for three elevation transects leading to treeline (Western Himalaya: WH; Central Himalaya: CH; Eastern Himalaya: EH) representing different climate regimes along the Indian region of Himalayan Arc. TLRs were calculated using high temporal resolution data collected for 2 years (2017–2018) from complex Himalayan terrain. The annual mean TLR increased with decreasing moisture, being markedly higher for dry WH transect (− 0.66 °C/100 m) than at moderately moist CH (− 0.52 °C/100 m) and characteristically moist EH transect (− 0.50 °C/100 m). The One-Way Analysis of Variance (ANOVA) confirms that the TLR varied spatially, declining from West to East across the Himalayan Arc, and significantly differed seasonally. The lowest mean TLRs were found during the winter season (EH: − 0.46 °C/100 m; CH: − 0.40 °C/100 m; WH: − 0.31 °C/100 m). The monthly TLR for EH transect varied within a narrower range (− 0.32 °C/100 m to − 0.54 °C/100 m), than for CH transect (− 0.24 °C/100 m to − 0.68 °C/100 m), and WH transect (− 0.26 °C/100 m to − 0.90 °C/100 m). The lowest monthly TLR occurred in December (− 0.24 °C/100 m to − 0.32 °C/100 m) for all three transects. The relationship of TLR with rainfall and saturation vapor pressure was analyzed for CH transect to find out influence of these factors on seasonal variation in lapse rate. Moisture, snow albedo and reflectance are the factors which largely control the TLR along the elevation transects. The shallow TLR and higher growing season temperature values (9.2 ± 1.8 °C, 10.0 ± 1.4 °C, and 7.8 ± 1.7 °C), than normally found at treelines, may suggest that treeline environment in Himalaya is warming more rapidly than lowland areas. TLR was lowest in December due to reduced albedo and EDW, which influence treeline dynamics, snow and moisture regime, surface energy balance, species distribution, and growing season of alpine vegetation. The findings of this study provide useful insights to re-parameterize the climate models over the Himalayan region. This study facilitates in improving interpolation of air temperature for ecological studies in un-gauged and data-sparse regions, especially for the alpine region of Himalaya where observed data are extremely scarce.