19th November 2018Blog

How very high-resolution satellite imagery can stop illegal irrigation and enhance national water security

The use of very high-resolution imagery from Earth Observation (EO) satellites can help national mapping and cadastral authorities improve the monitoring and management of national water resources . This will better protect water supplies whilst combatting illegal irrigation and water abstraction.

The impact of illegal irrigation on water security

Illegal irrigation is one of the main threats to water security and the consequences of illegal water use include:

• A decline in groundwater levels causes rivers, springs and wetlands to dry up resulting in the degradation and loss of water ecosystems.
• Increased salinisation of freshwater leads to the damage of aquatic ecosystems and abandonment of legal wells.
• Water pollution – unlawful irrigation results in poorer quality water which increases the demand for cleansing treatments for domestic water.

The benefits of a regular EO monitoring and management program will identify legal and illegal irrigated areas and crop irrigation requirements. This will focus ground field checks to verify what has been identified by satellite. This helps catch illegal abstractors as well as identify crop stress.

How very-high-resolution satellite imagery can help reduce illegal water irrigation

A comprehensive control programme can be achieved with a small number of satellite image collections throughout the irrigation season.

Crop health can be measured from a satellite using the temporal variability of the Normalised Difference Vegetation Index (NDVI). Simply, an increasing NDVI trend without rain indicates an irrigated crop.

Lower-resolution open-source satellite data cannot provide authorities with the information they need to efficiently and effectively resolve such cases.

NDVI analysis is used to determine irrigation activity which can be performed using open-source 10-metre resolution satellite imagery. However, this low-resolution imagery does not provide sufficient detail to show the difference in vegetation health.

The use of very-high-resolution satellite imagery, for example 80cm resolution pan-sharpened imagery, provides a higher level of detail, making NDVI analysis more definitive which gives national mapping and cadastral authorities a much clearer picture of the condition and treatment of vital water resources.

Satellite imagery and its role in the Gila River Valley dispute

The Gila River Indian community has long contended that non-Indian valley water users are illegally irrigating the river. This violates the 1935 Globe Equity Decree that governs the distribution of water among the community and various other landowners. The Pima Indian population is reliant on the river for its water supply and claims that the illegal irrigation upstream causes the community significant hardship. The community is attempting to resolve the matter through the US District Court, using high resolution satellite imagery to support their claim.

Water security and the importance of very-high-resolution satellite imagery

Water security links to the UN Sustainable Development Goals, and very-high-resolution satellite imagery can support national mapping and cadastral authorities achieve these goals. The Gila River Valley dispute is an example of how this satellite imagery, as part of a national spatial data framework, can be used to help national authorities better monitor and protect critical water supply.

Read our e-Guide, “Why geospatial mapping is important for the well-being of nations”, for more details on very-high-resolution satellite imagery and its role in effective national critical infrastructure management.

To talk to Earth-i about very-high-resolution satellite imagery and national critical infrastructure management, including water resources at the United Nations World Geospatial Information Congress, please contact us on enquiries@earthi.co.uk