Hydrological cycle, also known as Water cycle (Hydro=water), includes ‘water processes’ occurring in a variety of physical environments all around the world. It involves the stages of different types of water movements from one process to another within the cycle. The hydrological cycle involves continuous water movements, which can occur anywhere between the atmosphere, to the bodies of water (oceans, lakes, glaciers, rivers, etc), to the underground rock layers of the earth, and back again - which is why it is known as a ‘cycle’. There are 9 main physical water processes, which can inter-relate in any order, these include:
Evaporation happens when water (in the form of liquid) that is found in the surface of the earth - whether it’s in the form of rainfall, bodies of water (i.e. Oceans, lakes), or even water droplets on vegetation or on any object - returns back to the atmosphere in a gaseous form. For evaporation to eventuate, a reasonable amount of solar heat needs to be present, as well as other influencing factors (i.e. atmospheric pressure, air temperature, among others). As evaporation occurs, moist air is transported around the atmosphere, it cools down and condenses to form clouds. Most evaporation processes come from the Ocean (around 80%), and the rest occurs through the rest of the earth’s waters (including a portion of rainfall), land and vegetation.
It is called precipitation when any water particle leaves the atmosphere (i.e. rainfall from clouds) and hits anywhere onto the surface of the earth, whether it’s a body of water or the ground itself. These particles of water can reach the surface either as water droplets or ice crystals (i.e. snow), depending on the occurring temperature happening at cloud level, or even during its way ‘down’, which can then dissipate in a number of different ways.
Basically condensation occurs when water vapour, in gaseous state, changes to liquid state. The presence of condensation is represented in the form of clouds, fog or dew. This mainly occurs when there is a large concentration of ‘water vapour’ up to its saturation point or when cooling of the air is present during evaporation.
Just as the word implies, percolation is when water infiltrates via gravitational forces through the soil, rocks, and other layers of the earth, into its deeper layers. This water, now referred to as ‘groundwater’, continues moving along to the deeper layers by gravity, which will eventually serve as natural water reservoirs.
This is when water particles accumulate in the surface of the earth’s soil and begins penetrating and filling the pores of the soil into the deeper matrices. The amount and speed of infiltration will directly depend on the porosity and permeability of the soil, as well as the composition, structure and moisture content.
Interception is referred to when the movement of water is blocked or suspended by land ‘obstructions’ such as loose vegetation, stems of plants, branches, leaves, among others, interfering with the water's’ natural flow to reach the soil. Some factors may influence on interception such as the presence of wind, rain, or when the weight of the water stored is greater than the surface tension,
This is a process that occurs to vegetation. Depending on the amount of sunlight and the type of plant, transpiration will be more or less. When plants produce transpiration, the nutrients inside the plant move to the surface leaves and, as they transpire, the plant acquires a cooling effect from the amount of sun exposed. When there is not enough water to be transpired, plants tend to close their ‘stomata’, which are the cells specialised in letting water out. In this case, transpiration continues but at a much slower pace, allowing some of the water to be retained in the plant.
Runoff occurs when water, mainly from rain, underground infiltration and/or surface drainage flow downward and meet a stream, river or lake; which is then carried into the Ocean.
‘Stored water’ can exist, as previously mentioned, in the atmosphere (i.e. snow), on the earth’s surface and underground. Stored water can be found in lakes, oceans, glaciers, underground aquifers, and soil, among others.