The eastward expansion of the climate humidification trend in northwest China and the synergistic influences on the circulation mechanism.

Studies conducted at the beginning of this century revealed a warming and humidification trend in northwest China, which lasted for a short period, with some minor variations. The future trend remains uncertain, with uncertainty over the future duration of warming and humidification trends in the region. In this study, a comprehensive index was constructed to quantitatively characterize the degree of humidity. Using observation data, National Center for Atmospheric Research/National Centers for Environmental Prediction (NCAR/NCEP) reanalysis data, and future scenario prediction data we systematically analyzed the temporal and spatial evolution characteristics of the warming and humidification trend in northwest China and its possible causes. The results showed that the temperature in northwest China has been continuously increasing since 1961, and although there was no obvious precipitation trend from 1961 to 1999, it has been increasing nonlinearly since 2000. The wetness index considers the synergy of evaporation and precipitation, and had the same pattern of variation as precipitation. From a spatial perspective, the temperature has consistently increased throughout the whole northwest region, and the degree of warming has gradually increased. Precipitation displayed a trend of increasing in the west and decreasing in the east, but the area with increased rainfall expanded eastward over almost three climatic periods, and the area experiencing humidification extended across the whole of the northwest. There has been an obvious eastward expansion of climate humidification in northwest China since the start of this century. However, the current extent of climate humidification has not changed the basic climate pattern in northwest China. Over the next 30 years, the humidification trend will likely slow down significantly compared with the last 20 years. The eastward expansion of climate humidification since the start of this century may have resulted from the multi-decadal synergistic influence of westerly wind circulation and monsoon circulation. [ABSTRACT FROM AUTHOR]