Study of the Characteristics of Atmospheric Water Resources and Hydrometeor Precipitation Efficiency over the Liupan Shan Area

To develop atmospheric water resources reasonably over the Liupan Shan area based on precipitation enhancement techniques, it is necessary to first understand the influence of the water vapor field and topography on local precipitation, the characteristics of water resources in the air, and the hydrometeor precipitation efficiency of clouds in typical precipitation processes over this area. On the basis of the high spatial and temporal resolution reanalysis dataset issued by ECMWF (European Centre for Medium-Range Weather Forecasts) and MODIS (moderate resolution imaging spectrometer) data, the features of water vapor transport, the convergence and ascending motion of water vapor flux forced by topography, and the orographic cloud characteristics were investigated using statistical analysis methods. Moreover, during several precipitation events with stratus clouds embedded in convective systems moving from west to east in the summer of 2016 and 2017, the hydrometeor precipitation efficiency was calculated on the basis of the simulation results of the WRF model and ERA5 reanalysis dataset. The results are as follows. In the eastern part of Northwest China, abundant atmospheric precipitable water and strong water vapor transport are observed over the Liupan Shan area. Under the influence of the Asian monsoon, abundant water vapor is transported by the southerly wind to this mountain area in summer, thereby making it a high relative humidity zone. The CF (cloud fraction) reaches 70% over the Liupan Shan in the afternoons of spring, summer, and autumn. Moreover, CWP (cloud water path) and optical thickness (COT) in summer are considerably larger than those over the surrounding areas. The dynamic field caused by topography has a considerable impact on summer precipitation. Obvious convergence and ascending motion of water vapor flux forced by topography occurs in the process with daily precipitation exceeding 5 mm. Furthermore, when the convergence and ascending motion are more intense, the corresponding rainfall intensity is stronger. In typical precipitation systems in summer, the average hydrometeor precipitation efficiency is approximately 48.1% and a considerable amount of hydrometeor in the air does not undergo precipitation. Therefore, in terms of water conservation, the Liupan Shan area has relatively abundant atmospheric water resources; however, precipitation in summer is insufficient, which indicates that potential exists for developing atmospheric water resources in this area.