Characteristics of Water Vapor Transportation and Budget over the Heihe Drainage Basin

Based on the NCEP/NCAR re-analysis daily mean data from 1948 to 2008,the characteristics of water vapor transportation and budget over the Heihe Drainage Basin were analyzed in this passage.The results showed that,influenced by westerly circulation,Atlantic and Arctic oceans were the main water vapor source over the Heihe Drainage Basin.Water vapor was mainly latitudinally transported from west to east,and the intensity of water vapor exported from east boundary of the Heihe Drainage Basin was greater than that imported from west boundary,the intensity of water vapor imported from north boundary was also greater than that exported from south boundary.In the layer of 700 hPa,convergence and divergence of the southern Heihe Drainage Basin changed seasonally,it is a water vapor divergence area in winter,but a convergence area in summer.The northern Heihe Drainage Basin had no such obvious characteristics all the year round.The annual influent water vapor amount is about 997.3 km3,effluent water vapor amount is about 1046.1 km3,and the net water vapor amount is about 48.8 km3.The net water vapor amount tended to increase since the 1960s.Water vapor in the northern desert area of the Heihe Drainage Basin exported whole year,and it mainly exported from middle and lower atmosphere(surface to 500 hPa).June to September was the water vapor net influent period in the southern mountain area of the Heihe Drainage Basin,and lower atmosphere(surface to 700 hPa) was the main influent layer,middle and upper atmosphere(700 to 300 hPa) was the main enffuent layer.Annual evaporation amount is about 84 km3 according to the atmospheric water balance.