Water availability
Besides the consideration of water introduced by precipitation or condensation, the availability of water throughout a habitat is a fundamental determinant of what plants and animals can adapt locally. The chief water availability parameters are controlled by soil and topography, but deserve discuss as a separate topic due to the importance of water availability. Thus the subject of water availability can be defined by the issues of surface runoff characteristics, downward percolation, water retention in the upper soils,[8]evapotranspiration, groundwater flows and surface water characteristics. At an operational level the key factors are pathways of water availability to plants and storage/timing of water availability to animals. The extreme conditions of aridity or flooding define special habitats, which are respectively deserts or wetlands.