GC: n
CT: The concept of green and blue water is relatively new1. When precipitation reaches land, it takes either green or blue water pathways. The water that is stored in the unsaturated soil layer forms the green water resource and the water that is stored in the rivers, streams, surface-water bodies and groundwater forms the blue water resources. Problems such as water scarcity and water security are changing the way we understand, use, and manage green and blue water resources for food production and ecosystems. One of the recommendations to alleviate water scarcity is to reduce consumptive water use in the agriculture sector3. However, understanding water use in crop production by source (rain water or irrigation water from surface and groundwater) is vital for water resource management. Information on how much of direct rain water (green water) and how much of non-rain water (blue water) in the form of irrigation is being productively used is critical for efficient management of water resources. However, such information is not readily available.
By definition, crop or vegetation evapotranspiration (ET) comes from green water sources (i.e., from the water consumed by the vegetation from the root zone soil moisture and soil evaporation from the unsaturated soil surface). However, when vegetation falls short of green water sources, they are often supplied with or have the ability to extract blue water resources (such as irrigation from rivers, reservoirs, or groundwater). While doing so, blue water is converted to green water before it is lost as ET.
S: NCBI – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5522464/ (last access: 5 December 2017)
N: 1. – green (adj): Old English grene, Northumbrian groene “green, of the color of living plants,” in reference to plants, “growing, living, vigorous,” also figurative, of a plant, “freshly cut,” of wood, “unseasoned” earlier groeni, from Proto-Germanic *gronja– (source also of Old Saxon grani, Old Frisian grene, Old Norse grænn, Danish grøn, Dutch groen, Old High German gruoni, German grün), from PIE root *ghre-“grow” (see grass), through sense of “color of growing plants.”
– water (n): Old English wæter, from Proto-Germanic *watar (cognates: Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, Old Norse vatn, Gothic wato “water”), from PIE *wod-or, from root *wed- (1) “water, wet” (cognates: Hittite watar, Sanskrit udrah, Greek hydor, Old Church Slavonic and Russian voda, Lithuanian vanduo, Old Prussian wundan, Gaelic uisge “water;” Latin unda “wave”).
2. Environmental Science. In water resource management: water that is directly derived from rainfall and used by plants or stored in the soil.
3. The term virtual water was first defined in 1998.
It is the volume of water required for making a product and the water used in the production chain.
Virtual water is comprised of 3 different components:
- Green water;
- Blue water;
- Grey water.
Different kinds of ‘coloured water’ (green, blue, grey and black-which is not virtual water) are classified based on where they are found in nature or the level of contamination of wastewater.
- Green water is the soil moisture from precipitation, used by plants via transpiration. It is part of the evapotranspiration flux in the hydrologic cycle.
- Blue water is the freshwater: surface and groundwater. It is stored in lakes, streams groundwater, glaciers and snow.
- Grey water is polluted water which was not in contact with faecal matter.
S: 1. OED – https://goo.gl/U5WwZu; https://goo.gl/wWNh4t (last access: 5 December 2017). 2. OD – http://www.goo.gl/RciWBc (5 December 2017). 3. WN – http://www.goo.gl/Lqi62n (last access: 5 December 2017).
SYN:
S:
CR: grey hydrogen, water footprint.
