Monitoring Evapotranspiration to Improve Water Use Efficiency

Water is a key agricultural resource becoming increasingly scarce and valuable due to the growth of human population and climate change. Irrigated agriculture is one of the major consumers of water, which is largely wasted due to inefficient irrigation systems. Monitoring the crops water usage and needs is key to plan an efficient irrigation system. The recent surge in the availability of Satellite imagery and a better understanding of the water cycle bring a disruptive opportunity for an accurate crop monitoring.

At Starlab, we are using cutting-edge remote sensing techniques to monitor evapotranspiration, which is directly related with the amount of water used. Evapotranspiration is estimated at 20 meter spatial resolution from an energy balance model and Sentinel-2&3 optical and thermal imagery from the European Earth Observation Program Copernicus. The method has been recently developed in the framework of the European research project Sen-ET (www.esa-sen4et.org). Figure 1 shows an example of the evapotranspiration map estimated over Baix Ter Basin (north-east Spain) for the 22 of may of 2020. Evapotranspiration can disentangled between the water evaporated from the soil, and the water transpired through leaves and then the water use efficiency can be estimated by the ratio between the transpiration (water actually used by the plant to grow) and evapotranspiration (water used by the plant or the soil) (Bellvert, 2020). Such measure of efficiency allows for irrigation recommendations in order to minimize the water lost through evaporation from the soil.

Figure 1: Example of a map of Evapotranspiration over Baix Ter Basin (north-east Spain) for the 22 May 2020.

The method also provides, as intermediate outputs, biophysical characteristics of the vegetation useful to monitor the crops vegetation, for example the leaf area index (LAI; leaf area per unit of ground surface area; m2/m2), the leaf chlorophyll content and fraction of absorbed photosynthetically active radiation. Figure 2 shows an example of the LAI map.

Figure 2: As in Figure 1 but for Leaf Area Index (LAI).

We have developed a tool to provide at near-real time the daily land surface evapotranspiration and crop vegetation at 20 meter spatial resolution. The tool is available as an interactive web-based platform with at-a-glance views of crops evolution at plot scale and will facilitate informed based irrigation scheduling and ultimately higher water use efficiency.