Great Smoky Mountains National Park (IMAGE) NASA/Goddard Space Flight Center Caption Mid-morning peak in light rainfall appears as clouds and fog at Purchase Knob in the Great Smoky Mountains National Park. Light rainfall is the most reliable and most frequent form of rainfall in the region, contributing 50 to 60 percent of the total precipitation over a year. Light rain is no less than the lifeline of freshwater resources for the landscape's ecosystems. Credit NASA/Barros Usage Restrictions None License Licensed content 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.