A study on the spatial variations in stable isotopic composition of precipitation in a semiarid region of Southern India


C. Unnikrishnan Warrier, Isotope Hydrology Division, Centre for Water Resources Development and Management, Kunnamangalam-P.O., Kozhikode-673 571, Kerala, India.

E-mail: warrier@cwrdm.org


The stable isotope analysis of all major rain events from Moinabad (MB), Rajendranagar (RN) and Osmanasagar (OS) reservoir, three closely placed locations in Hyderabad, India, were carried out during the 2005 to 2008 period. The OS station recorded the highest amount of rainfall with an average value of 1000 mm, whereas the MB station recorded the lowest average rainfall of 790 mm. The stable isotope (δ18O) values of the precipitation samples during these period varied from −11.43‰ to −0.03‰ for the MB station, −8.21‰ to 0.54‰ for the RN station and −11.47‰ to 0.72‰ for the OS station. The d-excess of precipitation at the three stations also showed considerable variations and revealed that the precipitation in the region undergoes significant modification through secondary evaporation during its fall. The possible causes for these observed spatial and temporal variations in amount and the isotopic composition of precipitation in a small geographical area within the city were studied. The observed variations may be attributed to the regional scale differences in water budget induced by rapid urbanisation activities in the city coupled with the differences in secondary effects undergone by the falling drops. This study elucidating changes in precipitation patterns in the city and its possible causes may largely help in its water balance calculation. Copyright © 2011 John Wiley & Sons, Ltd.