Water

Water is arguably the single most important climatic factor, since life itself is believed to have originated in water, and water still covers more than 70% of the Earth's surface today. Plants draw on water from three natural sources: atmospheric moisture, precipitation (rain), and soil water. The amount and seasonal timing of rainfall directly shapes what kind of forest can grow in a place — evergreen forests form where heavy rain falls all year round, while sclerophyllous forests (with tough, leathery, drought-resistant leaves) form where heavy winter rain alternates with a dry summer. Water quality matters as much as quantity, especially for aquatic organisms: salinity in different water bodies ranges from around 0.5% in fresh inland water, to 30–35% in typical sea water, up to over 100% in hypersaline lagoons. Based on how much salinity variation they can tolerate, organisms are classed as euryhaline (tolerating a wide salinity range — e.g. marine algae and marine angiosperms) or stenohaline (tolerating only a narrow salinity range — e.g. plants of estuaries, where salinity itself fluctuates least). This same broad-versus-narrow tolerance pattern recurs across several other environmental dimensions too — organisms can be described as stenoecious/euryoecious (habitat/ …