Statistical Analyses on the Seasonal Rainfall Trend and Annual Rainfall Variability in Bhutan

Abstract

This study examines the observed seasonal and annual rainfall trend and variability in Bhutan from 1996-2017. Using standard statistical methods, we utilized Mann-Kendall test and Sen's slope estimator to determine the trends in the seasonal rainfall of Bhutan. We analyzed the temporal variability and spatial pattern of rainfall by using the principal component analysis (PCA), Rainfall Anomaly Index (RAI), and Precipitation Concentration Index (PCI). Our results indicate that the summer season contributed to the 73% of the total rainfall in Bhutan while winter season contributed only 1%. Results from the PCI indicate that the rainfall distribution in the northeast part of the country is moderately concentrated while the south to the northwest portion experienced high fluctuation in rainfall distribution. PCA explains the 90.1% of the total variance is linked to the variability of Asian monsoon. The influences of ENSO/La Nina are possible causes for the variability of rainfall in Bhutan though this necessitates more investigations to corroborate.