Observations of precipitation type using a time-lapse camera in a mountainous region and calculation of the rain/snow proportion based on the critical air temperature

Different types of precipitation significantly affect the associated environmental temperature field. Because of its variability at different altitudes, it is very difficult for researchers to obtain precipitation-type information in mountainous regions. A new precipitation observation method based on time-lapse cameras was used to monitor the precipitation type during the warm season (May–September) of 2012 in the Hulugou River Basin (HRB) of the Qilian Mountains. By georeferencing the camera images, the elevation of the rain/snow boundary for 29 precipitation events was obtained. The critical air temperature (critical air temperature was used to differentiate rain and snow) at rain/snow boundary was calculated through interpolation of observed air temperatures in the HRB at six different altitudes (2,980, 3,382, 3,710, 3,839, 4,166 and 4,496 m). The outcome indicates that from April to July, the elevation of the rain/snow boundary increased from 3,000 to 4,000 m above; subsequently, the elevation of the rain/snow boundary decreased to 3,000 m in October. The daily critical air temperature ranged from 0.0−4.1 °C. Based on the observations of the critical air temperature, the amount of solid precipitation was calculated at different elevations. The results indicated that the proportion of solid precipitation increased from 5.7 to 31.9 % at 3,382–4,496 m during the warm season in the HRB.