Environmental Fluid Mechanics: Current issues and future outlook.

All forms of life on earth are immersed in natural fluids, such as the air in the atmosphere and the water in surface and underground systems. The knowledge of natural fluids motions is therefore very important and lead to the implementation of a new discipline, termed Environmental Fluid Mechanics (EFM). EFM is the scientific study of naturally occurring fluid flows of air and water on our planet Earth, especially of those flows that affect the environmental quality of air and water. In this chapter EFM is introduced. First commonalities and differences between EFM and its cousin disciplines, such as Fluid Mechanics, Hydraulics and Geophysical Fluid Dynamics, are described pointing out their specific purpose and scales. Second, the concepts of stratification and turbulence, which are two essential ingredients of EFM, are introduced. Third, scales, processes and systems within EFM are presented. The concept of environmental interface is defined introducing the EFM processes occurring across the main four environmental interfaces. The chapter ends with a discussion about the challenges facing EFM scientists in the next decades.