Vanuatu Rainfall (image) University of Texas at Austin Caption Rainfall in the South Pacific (red) varied much more dramatically before the start of the 20th century than after. Rainfall values are first measured annually during the rainy season (November-April) and then averaged over each decade. The blue line indicates actual oxygen isotope values used to determine rainfall values. Credit Jud Partin/University of Texas at Austin Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.