Scenarios


Irrigation demand by crop and irrigation system

The selected factors of crop and irrigation system are influenced by management decisions while soil texture remains an inherent property of the landscape.

The per hectare irrigation demand of selected crops by irrigation system is shown below. This information is then used to illustrate potential patterns in irrigation demand under two scenarios, 1) A transition to more efficient irrigation systems and 2) An expansion of irrigated area.

Irrigation water required for production of one hectare of selected crop under existing irrigation systems.

Since 95% of blueberries are drip irrigated (AWDM, 2015), it was assumed that the entire irrigated area of blueberries was under drip irrigation and blueberries under sprinkler/traveling gun systems were excluded. Similarly, since 98% of the irrigated area of forage (AWDM, 2015) is under travelling gun system, it was assumed the entire area of irrigated forage was under traveling a gun system and forage under sprinkler systems were excluded [2].

Cranberries and forage are the most water intensive crop requiring 4,600 m^3/ha and 4,200 m^3/ha respectively. Vegetables under both sprinkler and travelling gun irrigation systems have similar and relatively low irrigation demands (2, 200 -2,600 m^3/ha).

This information is used to illustrate potential patterns in irrigation demand under two scenarios, 1) A transition to more efficient irrigation systems and 2) An expansion of irrigated area.


Scenario 1: Transition to more efficient irrigation systems

While 95% of blueberries are drip-irrigated, cranberries and forage are incompatible with drip systems. Potential improvements in forage irrigation efficiency exist in the adoption of small center pivot sprinkler systems. The efficiency of these is 85%; a 20% improvement relative to travelling gun systems which are the dominant irrigation systems for forage crops in the region.

Although vegetable cropping systems are compatible with drip irrigation, the system is not used in Metro Vancouver on a large scale. In order to estimate the relative reductions in irrigation demand that may accompany a transition in vegetable production to a more efficient irrigation system, irrigation demand was calculated for the scenario that all vegetables under travelling gun systems (65% efficient) and sprinkler systems (72% efficiency for handline and overtree solid set systems) were replaced by drip irrigation systems (93% efficient).

Reduction in irrigation demand (m^3) for transition of vegetables on sprinkler and travelling gun systems to drip irrigation system. Estimation based on travelling gun efficiency (65%), handline sprinkler efficiency (72%) and drip efficiency (93%). For average climate year (2010) [2, 16].
In this case, vegetable irrigation demand declined from 5.3 M m^3 per year to 4.0 M m^3 per year (24%) and the overall irrigation demand in Metro Vancouver’s ALR was reduced from 30.0 million m^3 to 28.7 million or by 4%.


Scenario 2: Agricultural Expansion

The AWDM includes a ‘buildout’ scenario that identifies agricultural land in the ALR that could potentially be irrigated in the future, illustrated in the map below.

builout_map
Map of irrigation expansion potential showing irrigated area is use (green) and areas with available irrigation potential (red). (van der Gulik, 2013. fig 11, fig 11)

The AWDM determines potential available irrigation area based on criteria related to the Agricultural Capability Class, the elevation of land and the proximity to water source including; a lake, watercourse, wetland, high productivity aquifer and a water purveyor [16].

Under the applied rules, the AWDM identifies approximately 20, 000 ha of land in Metro Vancouver ALR with the potential for future irrigation. The figure below demonstrates the relative difference in irrigation demand that may result from a complete expansion of irrigated area of the region’s major crops.

Estimated irrigation demand (m^3) for Metro Vancouver with entire buildout area under specified crop and irrigation system. (Calculated as current total irrigation demand for Metro + crop specific irrig demand /ha * buildout area). Estimated demand for vegetables on drip based on efficiency improvements of drip systems relative to sprinkler and travelling gun systems described in scenario 1. Reference line outlines current irrigation demand for Metro Vancouver in average climate year (2010) (AWDM, 2015; van der Gulik, 2015).
Estimated irrigation demand (m^3) for Metro Vancouver with entire buildout area under specified crop and irrigation system. (Calculated as current total irrigation demand for Metro + crop specific irrig demand /ha * buildout area). Estimated demand for vegetables on drip based on efficiency improvements of drip systems relative to sprinkler and travelling gun systems described in scenario 1. Reference line outlines current irrigation demand for Metro Vancouver in average climate year (2010)  [2,16].
A complete expansion of vegetable or blueberry crops is estimated to increase Metro Vancouver’s irrigation demand to 65M-86M m^3 per year, depending on selected irrigation system. In contrast, a complete conversion of potentially irrigated land in the ALR to forage, could yield a total irrigation demand of 120 M m^3. Cranberries were excluded from the scenario due to the limited additional area of peat in the ALR.

While drip irrigation systems are not widely used in vegetable cultivation, estimated demand for vegetables on drip is based on the efficiency improvements of drip systems relative to sprinkler and travelling gun systems (described in Scenario 1).

Photo credit Creative Commons James Isogna

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