Synoptic variation of stable isotopes in precipitation and ground level vapour in a humid tropical region, Kerala, India

The controlling factors of spatio-temporal variation in delta O-18 and delta D composition of rainwater and the rain-vapour interaction in the southern, middle and northern regions of Kerala, India, are presented. The isotopic distribution (delta O-18) of rainfall ranged between 0 and -6 parts per thousand during January to September and between -6 to -12 parts per thousand during October to December. The rain during post-monsoon season has significant contribution to recycled vapour. Evaporation from falling raindrops is significant despite high relative humidity. The sudden isotopic depletion of ground level vapour from baseline isotopic composition is due to interaction and isotopic exchange with falling raindrops.