Variability of Summer Atmospheric Moisture Flux and Its Effect on Precipitation over East China

Using the in-situ precipitation and NCEP/NCAR daily reanalysis data, we found by studies of change of moisture flux and its effect that the northward water vapor transport represented by moisture flux in East China tends to retreat southward, and the eastward water vapor transport tends to weaken with weakening of the intensity of moisture flux. The north boundary of meridional moisture ux (50 kg m-1s1) retreats 2.8 degrees in latitude per decade during 1968-2003. The weakening of water vapor transport implies the weakening and southward retreat of East Asian monsoon, which leads to the tendency of decrease in moisture flux convergence over North China and the middle and lower reaches of the Yellow River, and the tendency of decrease in precipitation over those regions, but on the contrary the enhanced water vapor transport convergence over the middle and lower reaches of the Yangtze River implies the tendency of increase in precipitation to some extent. Indeed the long-term variability of precipitation in East China has a close relation with that of atmospheric moisture flux.