Environmental Studies
- tunnel valley
- turnover time
- type specimen
- U.S. Coast Guard
- unconformity trap
- undertow
- unequal crossing-over
- unicentric distribution
- uniform flow
- unisexual flower
- United States. National Oceanic and Atmospheric Administration
- United States. National Park Service
- Unsaturated Zone
- Uppsala school of phytosociology
- upwelling
- Uranium-lead dating
- urban climate
- vagility
- valency
- valley bulging