Recent climatology and trends in surface humidity over India for 1969-2007

Annual and seasonal trends in specific humidity, relative humidity and dry bulb temperature based upon 215 stations across India are studied. The results of trend analysis show evidence of an increase in air moisture content over India during 1969-2007 with more than 90% stations showing increasing trends in specific humidity. Climatological means of specific humidity and relative humidity for the country are 14.1 g/kg and 63.9% respectively and trends are significantly increasing for all periods except for relative humidity in monsoon season. Annual trends in specific humidity, relative humidity and dry bulb temperature are +0.23 g/kg per decade, +0.85% per decade and +0.04° C per decade respectively. Seasonal trends in specific humidity, relative humidity and dry bulb temperature are statistically significant and highest in summer (+0.30 g/kg per decade), winter (+1.49% per decade) and monsoon (+0.11° C per decade) respectively. Spatially, the increasing trends in specific humidity and relative humidity are more coherent over north, northwest, central and southeast India. Spatial patterns of trends in relative humidity and dry bulb temperature are complementary and strongly correlated. Relative humidity trends are consistently decreasing over Jammu and Kashmir and northeast India. Increasing trends in summer season relative humidity and monsoon season dry bulb temperature over large parts of the country contribute significantly to upward trend in human discomfort. The spatial patterns of discomfort index show that the aerial extent of uncomfortable conditions increases both north and westwards as season progresses from summer to monsoon.