An estimation of heat and water balances in the Tibetan plateau

Abstract

A model considering soil-water transportation through vapor and liquid phases under the ground surface has been used for estimating heat and water balances in the Tibetan Autonomous Region of the Tibetan Plateau. The input data is derived from routine meteorological observations in the 14 stations of the Tibetan region. Calculated results were verified by the heat fluxes, and soil-water observation results from JEXAM. Daily variations of the heat fluxes, and seasonal variations of the soil-water content and solar radiation show good or reasonable agreements between the calculated and observed results. Daily and seasonal variations have been estimated for these 14 areas in 1997. Net radiation fluxes show relatively large values (annual mean 55-79 W m-2) over the Plateau where the elevation is above 3000 m. Most (80-90%) of the net radiation is accounted for by sensible heat flux due to low precipitation (e.g., 55 mm in Shiquanhe) in western Tibet (west of about 87° E). Latent heat flux accounts for about 30-50% of the net radiation in east Tibet. From west to east, latent heat flux increases gradually and even exceeds the sensible heat flux in the monsoon season. Latent heat flux (evaporation) is also limited by the relatively low surface temperature because of the high elevation, which indicates why the Plateau serves as the source of several large rivers despite its not so large precipitation. Relatively larger net radiation accompanied with limited evaporation suggests that the Tibetan Plateau plays a role in heating the atmosphere. Calculations have also been conducted for a climatic representative location, Lhasa, from 1979 to 1997. The average of net radiation was 62 W m2 with a sensible heat flux of 38 Wm-2 and a latent heat flux of 24 W m2 for these 19 years. Sensible heat flux peaks in May or June at a range of 54-76 Wm2, and latent heat flux in July or August at 41-83 Wm-2. The variations of annual precipitation are large, hence the annual total difference between the precipitation and evaporation varies from 8 mm in a low precipitation year to 217 mm in a high precipitation year. © 2001 Meteorological Society of Japan.