water cycle

Source: USGS

We will talk about the process of water cycle (hydrologic cycle): Starting from the water evaporates from ocean, sea, lake, river, trees and other earth surface and lifts up into atmosphere in form of water vapor. Then water vapor condenses as a small drop ( see as cloud from earth). Next when it meet the sastifies condition, the condensed water vapor will fall down to the earth called precipitation (known as snow, or rainfall).

Precipitation comes back onto the earth surface and ocean. The precipitation on earth separates into many parts. Some is intercepted by the trees (1), infiltrate into the ground(2), and runoff into catchment(3).

(1): The interception: the tree obsorbs the water, and it will uptake into atmoshpere also known as evapotranspriration.
(2) The infiltration: When the water infiltrate some amount is stored underground (ground water) and some part will join the stream flow.
(3) Runoff: Water flow into the stream directly join with base flow and another part from ground water. After that water will evaporate into atmosphere again.

All the process endlessly takes place and it is call water cycle. Water cycle is the great nature phnomena which is keep the water balance on the planet. All the amount of water remain constant, yet it change the phase or condtion to gas, liquid, solid or also from fresh to salin water.

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What is return period?

The probability that events such as floods, wind storms or tornadoes will occur is often expressed as a return period. You may hear about that if you are one who learn about environment, hydrology, water resource, climate change and other related. 

Return Period, the inverse of probability (generally expressed in %), it gives the estimated time interval between events of a similar size or intensity.For example, the return period of a flood might be 100 years; otherwise expressed as its probability of ocurring being 1/100, or 1% in any one year. This does not mean that if a flood with such a return period occurs, then the next will occur in about one hundred years' time - instead, it means that, in any given year, there is a 1% chance that it will happen, regardless of when the last similar event was. Or, put differently, it is 10 times less likely to occur than a flood with a return period of 10 years (or a probability of 10%). 

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