Unconfined aquiferAquifer containing unconfined groundwater, that is having a water table and an unsaturated zone.
UnconsolidatedA term used to refer to sediments that are not cemented together.
Unsupervised classificationCategorisation of digital image data by computer processing based solely on the image statistics without availability of training samples or prior knowledge of the area. The classification creates natural groupings in the image values, called spectral clusters or classes. In this fashion, values with similar grey levels are assumed to belong to the same cover type. The analyst must then determine the identity of these spectral clusters.
Upper basin statesCountries located upstream of an international river basin.
Upper LimpopoThe upper portion of the Limpopo catchment, the portion of the river closest to the source.
Upper waters of a riverThe upper portion of the river, closest to the source.
UpstreamIn the direction towards the source of a stream.
Upstream tributaryRiver, brook or stream that flows into another stream, above the location to which you are referring to.
UrbanAn area with an increased density of human-created structures in comparison to the areas surrounding it.
Urban heat islandRefers to the increased temperature in urban areas relative to surrounding rural areas.
UrbanisationThe formation and development of a city or metropolitan area, often due to population growth caused by the movement of people from rural to urban areas.