Influence of the Pacific quasi-decadal oscillation on the monsoon precipitation in Nepal

Nepal’s precipitation is uncorrelated with the all-India monsoon precipitation. However, the quasi-decadal variability of precipitation is significant in the Nepal Himalayas but its mechanism has received little attention. Using a set of century-long reanalysis and observations of precipitation, spectral and empirical orthogonal function analyses were conducted to determine the role of the Pacific Quasi-Decadal Oscillation (QDO) in Nepal’s precipitation regime. The dynamical and moisture processes involved in the Pacific QDO of the monsoon precipitation in Nepal were also examined. The monsoon precipitation in Nepal is enhanced when southeasterly moisture fluxes, originated from the Bay of Bengal, divert towards the north and subsequently interact with the southern Himalayan foothills. The redirected moisture fluxes are modulated through the Pacific QDO and are embedded in a propagating global wave 1–2 circulation pattern. However, the modulation exhibits a phase shift of 2 years between the precipitation anomalies in Nepal and the extreme phases of the Pacific QDO. A phase shift of this nature ascribes to the low correlation skill between the Nepal precipitation and traditional monsoon indices, such as those of the El Niño-Southern Oscillation and the all-India precipitation. The lagged relationship between the monsoon precipitation and the Pacific QDO is unique to Nepal, the inclusion of which should improve the predictive ability for the Nepal monsoon.