Variation in rainy season precipitation and associated water vapor transport over the Chinese Loess Plateau during 1961−2012

The variation in rainy season precipitation and its associated atmospheric water vapor transport during 1961 to 2012 over the Chinese Loess Plateau (LP) are examined by using precipitation data from 53 in situ stations and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data. The results show that the rainy season (June to September, hereafter JJAS) precipitation over the LP exhibits strong interannual variability, and the whole LP becomes wetter or drier synchronously, while no significant long-term linear trend is observed. The climatological water vapor transport from the southern boundary, which originates from both the Indian and the East Asian monsoons, dominates the JJAS precipitation over the LP, although the moisture from the western boundary carried by the Westerlies plays a non-negligible role. Quantitatively, the water vapor from the western boundary is similar to 73% of that from the southern boundary. The interannual variability of JJAS precipitation mainly results from the change in water vapor transport from the southern boundary. A positive rainfall anomaly of 100 mm is associated with a positive water vapor transport of similar to 166 (23) kg m(-1) s(-1) from the southern (western) boundary. Both the composite analysis on moisture transport for the wet years and the regression fields of water vapor transport on the precipitation index of the LP feature a cyclone anomaly centered over the northeastern Indian Ocean and an anticyclone anomaly centered over the Pohai region, which strengthen the moisture transport along the southern boundary of the LP, leading to excessive rainfall.