Hydrology

2.1What is the hydrological cycle?

               The hydrological cycle is defined as the natural circulation of water from the oceans and land surface to the air, air to land, and back to the ocean under solar energy.  

2.2Major components of the hydrological cycle

1)    Precipitation- Mechanism of water movement from the atmosphere to the earth's surface. Rain, sleet, Hail snow and dew are different forms of precipitation. The water which is evaporated from the earth's surface is condensed in the above atmosphere and returns to earth.

2)    Evaporation/Evapotranspiration-The movement of water from the surface to the atmosphere that is changed from liquid to gas. Evaporation is taken place on an abiotic surfaces such as soil, streams, and lakes and leaves the surface.

3)    Surface Water-After all losses water remain on the surface and pour towards the stream. With the saturation of soils, excess water creates floods.

4)    Groundwater- Infiltrated water pour downwards until it meets impermeable rock. This water is trapped so flows laterally very slowly. After a long period of movement, water joins to the streams or oceans. Therefore groundwater table support to recharge streams.

2.2Green water and blue water

2.2.1Green water

             2/3 of precipitation is contributed to the production of biomass defined as green water. Green water has two components such as productive green water and non-productive green water.

              Productive green water is transpiration of plant surfaces. Non-productive green water is evaporation water from soil and interception.

           2.2.2Blue water

                                      1/3 of precipitation is considered blue water. Surface runoff, subsurface runoff, and baseflow are major components of blue water.

               Both green water and blue water can be recycled through the hydrological cycle.

2.2.3The difference between blue water and green water

Green water	Blue water
Invisible water vapors to atmosphere.	Visible liquid water flow moving above and below the groundwater.
Green water cannot be reused.	Bluewater can be reused.
Green water isn’t available for downstream use.	Bluewater is available for downstream use.

          2.3 Greywater

Greywater is wastewater discharge of household. Sinks, toilets, bathtubs, showers, hand washings, and kitchen wastewater are considered as greywater. Greywater also defined as black water. Greywater cannot be reused without proper treatments.

      2.4Relation between stream water and groundwater

           (1)Humid area

                         Groundwater recharges streams.

           (2)Arid area

                            Streams recharge groundwater table after occurring of precipitation.