Tucson Summer Thunderstorm (image) University of Arizona Caption In the American Southwest, precipitation during the summer monsoon season provides a significant portion of the annual precipitation. Here lightning strikes over southern Arizona's Tucson Mountains during a 2010 monsoon thunderstorm. Credit Copyright Daniel Griffin, University of Arizona Usage Restrictions This image may only be used to accompany a story about the research described in the release, Monsoon Failure Key to Long Droughts in Southwest 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.