As the world’s population continues to grow at a breakneck speed and the climate crisis increases the likelihood of droughts, the demand for water for irrigation is growing. New research shows how Earth observation data help map the extent water is used for agricultural irrigation, guiding strategies that aim to protect freshwater resources.
It is estimated that irrigated agriculture accounts for about 70 percent of water withdrawn globally from lakes, rivers and aquifers, representing the largest human-induced impact on the water cycle. However, obtaining high-quality global information about the extent and frequency of irrigation is challenging.
Using multi-mission Earth observation data, the research of the Irrigation+ Project, a project within ESA’s EO Science for Society, aims to advance the worldwide mapping and quantification of irrigation in the agricultural sector. The consortium, led by the Hydrology group at the Research Institute of the Geo-Hydrological Protection (CNR-IRPI), has already within two years published 16 peer-reviewed scientific papers, which leverage advanced Earth observation algorithms and techniques for irrigation mapping, quantification and detection.
Animation showing annual water use for irrigation
In the last ten years there has been a substantial improvement in remote sensing techniques for irrigation mapping and quantification. A newly published paper from the project reviews this landscape, highlighting the contribution of the Sentinel-1 and Sentinel-2 satellites of the European Union’s Copernicus Programme [1]. "Tracking irrigation at field scale and estimating irrigation water use, requires high resolution observations, such as those obtained from the Copernicus Sentinel-1 and Sentinel-2 satellites,” says Luca Brocca, of CNR-IRPI, the principle investigator of the Irrigation+ project.
In Europe, irrigation districts tend to be organised in many fields, small in scale relative to a satellite footprint. These fields may grow varying crop types and use different irrigation systems. Furthermore, there may be variability in water use from field to field, largely dependent on the chosen farming practices rather than differences in weather, soil type or crop choice. In this context, the study revealed that high resolution Synthetic Aperture Radar (SAR) data, in combination with optical data and models, seem to provide a new opportunity for mapping and monitoring irrigation at the agricultural field scale.
Microwave radar measurements have the advantage that they are not hindered by weather conditions and are independent of illumination. Microwaves are sensitive to the water content in the soil surface and vegetation, and therefore have the potential to monitor changes in soil moisture as a result of irrigation events. The Copernicus Sentinel-1 mission brings a strong increase in land use mapping methods, by offering data coverage with a time resolution of six days in both ascending and descending geometries, with the two-satellite constellation and a pixel size of 10 × 10 m. According to the paper, there are many approaches to map irrigated areas using the multi-temporal information from Copernicus Sentinel-1 backscatter observations, to detect typical signal variations of irrigated areas. The different methods cover both arid and irrigated regions and sometimes can distinguish between irrigation and rainfall events.
Besides mapping irrigated areas, optical remote sensing can also offer some solutions for estimating irrigation water use. Some of the approaches rely on calculating a crop coefficient and/or exploiting actual evapotranspiration (ETa) estimates from remote sensing, using for example Copernicus Sentinel-2 data. The study concluded, however, that integration of remote sensing and land surface modelling is required for an improved representation of anthropogenic activities, such as irrigation.
Another piece of research in the context of the Irrigation+ project explored the potential for inferring rainfall measurements in the Po River basin, from Copernicus Sentinel-1 data. The most recent publications from the project demonstrate the possibility to accurately estimate the monthly and seasonal water use of irrigated agriculture, using high resolution remote sensing and a novel Hydrological Similar Pixels (HSP) algorithm and by exploiting a soil moisture-based approach [3][4].
The Irrigation+ project led by CNR-IRPI (Italy) collaborates with six other pan-European partners - eLEAF company (Netherlands), KU Leuven (Belgium), Vienna University of Technology (TU Wien, Austria), SPIRE GLOBAL LUXEMBOURG S.A.R.L. (Luxembourg), Universitat Ramon Llull, Observatori de l’Ebre (Spain) and Université Toulouse III Paul Sabatier (France).
About the Copernicus Sentinels
The Copernicus Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to the European Union's Copernicus environmental programme.
The European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites on behalf of the European Union and ensuring the flow of data for the Copernicus services, while the operations of the Copernicus Sentinels have been entrusted to ESA and EUMETSAT.
Did you know that?
Earth observation data from the Copernicus Sentinel satellites are fed into the Copernicus Services. First launched in 2012 with the Land Monitoring and Emergency Management services, these services provide free and open support, in six different thematic areas.
The Copernicus Land Monitoring Service (CLMS) provides geographical information on land cover and its changes, land use, vegetation state, water cycle and Earth's surface energy variables to a broad range of users in Europe and across the World, in the field of environmental terrestrial applications. It supports applications in a variety of domains such as spatial and urban planning, forest management, water management, agriculture and food security, nature conservation and restoration, rural development, ecosystem accounting and mitigation/adaptation to climate change.
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References
[1] Massari, C. et al; Review of Irrigation Information Retrievals from Space and Their Utility for Users. Remote Sens, 2021,13, 4112. doi: https://doi.org/10.3390/rs13204112
[2] Elwan, E. et al; Irrigation Mapping on Two Contrasted Climatic Contexts Using Sentinel-1 and Sentinel-2 Data. Water, 2022,14, 804. doi: https://doi.org/10.3390/w14050804
[3] Brombacher, J. et al; A novel evapotranspiration based irrigation quantification method using the hydrological similar pixels algorithm. Agricultural Water Management, 2022, 267. doi: https://doi.org/10.1016/j.agwat.2022.107602
[4] Dari, J. et al; Irrigation estimates from space: implementation of different approaches to model the evapotranspiration contribution within a soil-moisture-based inversion algorithm. Agricultural Water Management, 2022, 265. doi: https://doi.org/10.1016/j.agwat.2022.107537