Summer precipitation characteristics on the southern Tibetan plateau

Abstract

AbstractPrecipitation is an important source of streamflow and a critical parameter in hydrological studies. However, spatiotemporal variation of precipitation in the Tibetan Plateau (TP) has been poorly characterized due to the limited distribution of meteorological stations mostly in the lowlands. In this study, we set‐up rain gauges to study summer precipitation on mountain slopes in three catchments of the southern TP from 2013 to 2016. We studied the precipitation gradients (PGs) averaged during the Indian monsoon season (PGms), as well as daily PGs (PGd) and unit PGs (PGu) under various precipitation intensity grades (PIGs) and subdiurnal precipitation distributions. We also analysed the correlations between the PGs and precipitation amounts under various PIGs. Results showed that the mean PGms, PGd and PGu in the study catchments were 0.0071–0.0082% for monsoon season, 0.11–0.13 mm·100 m−1 d−1 and 2.2–3.1%·100 m−1 for the total (nonintensity‐graded) precipitation, but varied widely under different PIGs. PGms, PGd and PGu were all strongly correlated to precipitation amounts, which were relatively consistent between years but varied between different catchments. In addition, the correlations showed a steep positive slope under fine precipitation but became flat or even negative with increasing PIG. Generally, two distinct precipitation peaks were noted in each of the three catchments: a dispersed peak in the morning, and a stronger but sharper peak at around 18:00 LST; overall, this subdiurnal pattern was temporally stable. The mean precipitation durations of the three catchments were approximately 1.0–1.4 hr (nonintensity‐graded) and increased from <0.5 hr, to <1 hr, 2–5 hr and 6–11 hr for trace, light, moderate and heavy precipitation intensities, respectively. Among the various PG units, both PGd and PGu better represented precipitation at different altitudes than that of PGms. Summer precipitation in the study catchments was influenced more by valley‐scale convection than by large‐scale monsoon circulation.