Quantitating the Summer Moisture Sources over Northwest China and Its Annual Variations in Dry and Wet years

Abstract

The Northwest China (NWC) is located in an arid and semi-arid inland region, making its ecosystem highly vulnerable to changes of precipitation. Previous studies have revealed the wetting trend and potential moisture sources of the NWC, while not clearly quantified the moisture (water vapor and precipitation) sources and its interannual variability. Here, by performing and analyzing CAM5.1 simulation for 40 years, with a coupled atmospheric water tracer (AWT) algorithm, we find that the dominant sources of summer moisture over NWC are from terrestrial sources (82% of vapor and 77% of precipitation), i.e. from the North Asia (NA), Europe (EUP), southern Tibetan Plateau (STP), and southeastern China (SEC), rather than the oceanic sources. Due to the influence of synoptic patterns, the precipitation-conversion efficiency of water vapor from the southwestern airflow (STP and SEC) is higher than that from the northwestern airflow (NA and EUP). We also find that despite a general increasing trend in humidification, the fluctuation from relatively dry to wet years still persists in the NWC mainly influenced by the increased transport of moisture from terrestrial sources (NA and STP).