Irrigation

Centre-pivot irrigation is a method of crop irrigation in which equipment rotates around a pivot. A circular area centred on the pivot is irrigated, often creating a circular pattern in crops when viewed from above.

Central pivot irrigation is a form of overhead (sprinkler) irrigation consisting of several segments of pipe (usually galvanized steel or aluminium) joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The system moves in a circular pattern and is fed with water from the pivot point at the centre of the circle. In the current invention the water used to irrigate deserts will be desalinated seawater. The outside set of wheels sets the master pace for the rotation (typically once every three days). The inner sets of wheels are mounted at hubs between two segments and use angle sensors to detect when the bend at the joint exceeds a certain threshold, and thus, the wheels should be rotated to keep the segments aligned. Centre pivots are typically less than 500m in length (circle radius) with the most common size being the standard 400 m machine. In order to achieve uniform application centre pivots require a continuously variable emitter flow rate across the radius of the machine. Nozzle sizes are smallest at in the inner spans to achieve low flow rates and increase with distance from the pivot point.

As explained above 2.5 m of water used to irrigate the world’s hot deserts would likely be lost to evaporation and would end up back in the oceans from whence it came thus having no positive impact on the problem of rising sea levels.

As explained above, the deserts of the world would have to absorb .111 m worth of water for 100 years to overcome sea level rise if that was the only embodiment of this invention addressing the problem of thermal expansion of the oceans, which it is not.

According to the U.S. Geological Survey, for the year 2000, the rate of application of water for irrigation purposes in the U.S. was 2.48 acre-feet (.73 meters). This is about seven times the .111 m annual requirement to prevent sea level rise.
Transpiration is the evaporation of water from the aerial parts of plants, especially leaves but also stems, flowers and roots.

A fully-grown tree may lose several hundred gallons (a few cubic meters) of water through its leaves on a hot, dry day. About 90% of the water that enters a plant's roots is used for this process.

The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced; the transpiration ratio of crops tends to fall between 200 and 1000 (i.e., crop plants transpire 200 to 1000 kg of water for every kg of dry matter produced).

In view of the fact most of the water taken up by a plant is lost by the process of transpiration to the atmosphere and in turn most of this will end up back in the ocean, even though 7 times more water is needed for irrigation purposes than is needed to maintain sea levels – extracting .73 meters of water plus the additional 2.5 meters that will evaporate from the desert will not result in a reduced sea levels but rather will maintain them at, or near, current heights.
Centre Pivot Irrigation systems are used in Saudi Arabia and have demonstrated the viability of irrigating the arid and hyper-arid regions scattered about the globe.

Water is the key to viable desert agriculture. Saudi Arabia has implemented a multifaceted program to provide vast supplies of water necessary and has achieved spectacular growth of its agricultural sector. Land under cultivation has grown from under 400,000 acres (1600 km²) in 1976 to more than 8 million acres (32,000 km²) in 1993.

At the global scale 2,788,000 km² of agricultural land is equipped with irrigation infrastructure as of the year 2000. Compared to this Table 2 shows the world’s hot deserts cover 15,559,000 km². The existing global scale of irrigation therefore needs to be increased by a factor of 5.59 to convert all of the world’s hot deserts to agricultural use.

The process of irrigation is well known and does not form part of this inventive process. It is an objective of the current invention however to irrigate portions or all of the world’s hot deserts for the purposes of growing value-added crops for food, fuel, and fibre and/or building materials. These crops would then sequester significant quantities of CO2 that are causing global warming and would provide sustaining industries as well as nourishment to some the planet’s poorest inhabitants.