Trends in winter fog events in the Terai region of Nepal

Winter fog events of the Indo Gangetic plain (IGP) including the Terai area of Nepal are considered to be one of the important public concerns due to their effect on people's health, transportation, and agriculture. Unlike the IGP area of India, Pakistan and Bangladesh there are only very few fog related studies reported about the Terai region of Nepal. This study is carried out to study the occurrence of fog in the Terai region of Nepal by analysing the historical visibility data from 1980 to 2015 at four airports in the region (Nepalgunj, Bhairahawa, Simara and Biratnagar). It was found that the fog events in the Terai start in the month of November, reach the peak in December/January and end by the end of February. The average number of foggy days ranged from 24 days to 56 days per annum and average number of day-time foggy hours varied from 71 to 169 in the study. Visibility during winter is decreasing at all stations during the study period. The Man Kendall test indicated fog related parameters such as foggy days, foggy hours, dense foggy days, dense foggy hours have increasing trends at least at 0.1 level of statistical significance during the study period. The increasing trend of foggy days and daytime foggy hours may reduce winter crop production and negatively affect the food security of the Terai region of Nepal.