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Cassini detected numerous hydrocarbon seas/lakes in the polar region of Titan and wide areas of sand seas in the tropical region, which initially led to the perception that Titan's tropical region may be too dry for lakes. Yet, a few tropical lakes were possibly seen on Cassini's near-infrared images, while they were not seen by other imaging instruments. This study shows by a lake balance model in combination with a global climate model and global topography map that a few lakes can perennially exist in Titan's tropical drainage basins of Shangri-La, Tui Regio, and Hotei Regio. This is possible because the lakes are fed by precipitation in a huge catchment area, while efficient lake evaporation occurs only in a small area inside of deep topographic depressions. However, tropical lakes may occasionally desiccate due to orbitally forced changes in tropical precipitation.

Plain Language Summary Saturn's largest moon Titan has many hydrocarbon lakes in the moist polar region and dunes in the dry equatorial region. However, one of the imaging instruments of Cassini possibly saw tropical lakes, while other imaging instruments did not. If true, the presence of tropical lakes on Titan is surprising at a glance, as one expects such lakes to disappear soon due to fast evaporation. However, there are enclosed tropical basins on Titan in which methane rainfall can be collected at their bottom. If one keeps track of the precipitation from the whole basin and evaporation from the lake surface, one finds that lakes can stably exist despite the low precipitation rate and high evaporation rate. This is because lake evaporation occurs in a small area compared to total size of the drainage basin. By contrast, standing bodies of liquids sitting on a wide plain have no chance to survive because evaporation occurs everywhere.