The correlation between mean surface air temperature and altitude is analyzed in this paper based on the annual and monthly mean surface air temperature data from 106 weather stations over the period 1961-2003 across the Qinghai-Tibet Plateau. The results show that temperature variations not only depend on altitude but also latitude, and there is a gradual decrease in temperature with the increasing altitude and latitude. The overall trend for the vertical temperature lapse rate for the whole plateau is approximately linear. Three methods, namely multivariate composite analysis, simple correlation and traditional stepwise regression, were applied to analyze these three correlations. The results assessed with the first method are well matched to those with the latter two methods. The apparent mean annual near-surface lapse rate is -4.8 ℃ /km and the latitudinal effect is -0.87 ℃ /°latitude. In summer, the altitude influences the temperature variations more significantly with a July lapse rate of -4.3℃/km and the effect of latitude is only -0.28℃ /°latitude. In winter, the reverse happens. The temperature decrease is mainly due to the increase in latitude. The mean January lapse rate is -5.0℃/km, while the effect of latitude is -1.51℃ /°latitude. Comparative analysis for pairs of adjacent stations shows that at a small spatial scale the difference in altitude is the dominant factor affecting differences in mean annual near-surface air temperature, aided to some extent bydifferences of latitude. In contrast, the lapse rate in a small area is greater than the overall mean value for the Qinghai-Tibet Plateau （5 to 13℃ /km）. An increasing trend has been detected for the surface lapse rate with increases in altitude. The temperature difference has obvious seasonal variations, and the trends for the southern group of stations （south of 33 o latitude） and for the more northerly group are opposite, mainly because of the differences in seasonal variation at low altitudes. For yearly changes, the tem
Land surface evapotranspiration (ET) is an important part of the hydrologic cycle and energy balances.With the development of remote sensing technology,research on monitoring and estimating of evapotranspiration has made important progress.This paper summarizes advances in measuring and estimating regional evapotranspiration at home and abroad based on traditional methods and remote sensing.This summary includes such methods as Bowen,Gradient,Penman-Monteith,Water Balance,Eddy Correlation,SPAC,Energy Balance and Remote Sensing.Also,the evapotranspiration achievements in the Heihe River Basin are also discussed.Finally,the existing problems in regional evapotranspiration research and future development prospects are also discussed at the conclusion of this paper.
XinPing LuoKeLi WangHao JiangJia SunJuanJuan XuQingLiang ZhuZhaoGuo Li
