Studies on stable isotopic composition of daily rainfall from Kozhikode, Kerala, India.

The stable isotopic compositions of all major daily rain fall samples (n = 113) collected from Kozhikode station in Kerala, India, for the year 2010 representing the pre-monsoon, southwest and northeast monsoon seasons are examined. The isotopic variations δ(18)O, δ(2)H and d-excess in daily rainfall ranged from δ(18)O: -4.4 to 2 ‰, δ(2)H: -25.3 to 13.8 ‰, and d-excess: -2.4 to 15.3 ‰; δ(18)O: -9.7 to -0.6 ‰, δ(2)H: -61.7 to 5.3 ‰, and d-excess 5.8 to 17.4 ‰; δ(18)O -11.3 to -1.4 ‰, δ(2)H: -75.3 to 0.9 ‰, and d-excess: 8.8 to 21.3 ‰ during the pre-, southwest and northeast monsoon periods, respectively. Thus, daily rainfall events during two monsoon periods had a distinct range of isotopic variations. The daily rain events within the two monsoon seasons also exhibited periodic variations. The isotopic composition of rain events during pre-monsoon and a few low-intensity events during the southwest monsoon period had imprints of secondary evaporation. This study analysing the stable isotopic characteristics of individual rain events in southern India, which is influenced by dual monsoon rainfall, will aid in a better understanding of its mechanism.