Ocean Evaporation and Precipitation

Abstract

In view of the threat of global climate change , the proper understanding of the intensity of the hydrological cycle and of its development over time is one of the most important challenges of the century, at least in the area of the geosciences. The hydrological cycle can essentially be summarized to be the evaporation of moisture in one location, offset by precipitation elsewhere. The rate of evaporation exceeds the rate of precipitation over the oceans, which are therefore a net source of moisture; this moisture is then transported to the landmasses, which are a net sink for moisture, where precipitation exceeds evapotranspiration. In consequence, surface runoff enters rivers and other watercourses, which discharge into the ocean, thereby completing the cycle. Taken as a whole, the hydrological cycle is characterized by the evaporation of about half a million cubic kilometers of water per year, the bulk of which (86%) is from the ocean, with only 14% originating in the continents. The vast majority of the water that evaporates from the oceans (90%) is precipitated back into them, while the remaining 10% is transported to the continents, where it precipitates. About two-thirds of this precipitation is recycled over the continents and only one-third runs off directly into the oceans. Ultimately, despite the small continental recycled component, all the water used in natural ecosystems and in human activity originates in the oceans. Because societies depend for their continued existence on the security of water resources, it is extremely important to understand the processes that govern the evaporation of water from the oceans (in the domain of oceanography), the transport of moisture in the atmosphere (meteorology), and the effects of these processes on the hydrological cycle (hydrology), all within the context of the current paradigm of global climate change.