Thermal Regions Classification System (IMAGE) UK Centre for Ecology & Hydrology Caption Lakes with similar seasonal patterns of surface water temperatures are grouped together in a thermal region. The range in terms of relative temperature is from frigid, to cool, to temperate, to warm, to hot. Tropical Hot, in red, on and around the Equator, is the hottest of the nine thermal regions. Credit Maberly et. al 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.