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[1] Precipitable water vapor amounts (PW) determined by Global Positioning System (GPS), radiosonde and operational numerical weather prediction (NWP) system analysis at three stations (Naqu, Gaize, and Deqin) on the Tibetan Plateau are compared. PW measured by water vapor radiometer at Naqu and a low-elevation site, Xian, is used for calibration. The results show that the PW determined by NWP analysis in these regions is comparable with that of the radiosonde measurements but that they both are systematically smaller than those determined by the GPS measurements. The averaged difference of PW between GPS and radiosonde estimates is about 1.75 mm, and that between GPS and NWP analysis can be as large as 7.75 mm. These differences are relatively larger than those reported in the literature because the absolute PW in this region is much smaller. The effect of such large differences on the surface radiation budget is evaluated using a radiation model. The results show that both longwave and shortwave radiative fluxes at the surface determined using the model analysis profiles with the water vapor corrected by the GPS PW are closer to the observations compared with those without water vapor correction. The flux difference at the surface with and without water vapor correction is about 20 W m À2 in the shortwave and 30 W m À2 in the longwave. These differences are much larger than that caused by doubling the concentration of carbon dioxide in the atmosphere in this region.Citation: Liu, J., Z. Sun, H. Liang, X. Xu, and P. Wu (2005), Precipitable water vapor on the Tibetan Plateau estimated by GPS, water vapor radiometer, radiosonde, and numerical weather prediction analysis and its impact on the radiation budget,

Yunnan province is the core region of the drought in the Southwest China, which makes the region become the hot spot in the meteorological research. However, among the various influencing factors of the drought in Yunnan province, the influence of the land use/cover change (LUCC) on the drought has not been quantitatively analyzed. The LUCC in recent decades was first quantitatively analyzed in this study. Given the fact that severe drought in Yunnan province is mainly due to much-less-than-normal precipitation and much-warmer-than-normal surface temperature, this study focused on the future spatiotemporal heterogeneity of the temperature and precipitation, which have great impacts on the drought. Finally, the influencing factors of drought in Yunnan province were simulated with the Weather Research and Forecasting (WRF) model, and the risk of drought was spatially analyzed with the meteorological drought composite index. The results indicate that the large-area forest plays a more important role in alleviating the risk of drought than other vegetation types do. Besides, the changes of the landscape structure resulting from the urban expansion play a significant role in intensifying the risk of drought.

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