The inter-annual variability and the long-term trends in the monsoon rainfall and in two derived climatic parameters, aridity index (I(a)) and moisture index (I(m)), have been examined for the Mahanadi basin using the rainfall and temperature data for the 80-year period (1901-80). The study shows that the basin has experienced a good number of deficit years during the last two decades of the study period. The yearly values of aridity and moisture indices show increase in the aridity conditions over the basin, with the semi-arid type climate in as many as five years during 1965-80. The trend analysis shows that the increasing and decreasing trends in the aridity index and moisture index respectively are statistically significant. The trend in the seasonal rainfall, though negative, is not statistically significant
