Warming in the Tibetan Plateau: Possible influences of the changes in surface water vapor

Abstract

The Tibetan Plateau has warmed most rapidly during the winter months in the latter half of the 20th century. Changes in surface specific humidity and their effect on changes in downward longwave radiation (DLR) at the surface are examined to evaluate the pattern of seasonal warming at different elevations over the plateau between 1961 and 2000. We use observed seasonal changes in specific humidity to calculate the changes in DLR over the Tibetan Plateau. We find that increases in surface humidity during winter and spring months produce relatively large increases in DLR when the specific humidity is 2.5 g/kg or less, which usually occurs during the colder months and at higher altitudes. These increases in surface water vapor and the related changes in DLR appear to be part of the reason for the prominent winter warming trend observed over the plateau between 1961 and 2000.