First regional-scale and high-resolution (1 and 6 km) irrigation water data sets obtained from satellite observations

Abstract

Irrigation is widely recognized as the human activity that alters the natural circulation of water on the Earth’s surface the most. It greatly contributes to making the canonical conceptualization of the hydrological cycle incomplete. Nevertheless, irrigation dynamics are still generally unmonitored worldwide, but satellite capabilities have recently proved their suitability for such a purpose.

In this contribution, the first regional-scale and high-resolution data sets of irrigation water use retrieved from satellite data are presented. The products, obtained through the SM-based (Soil-Moisture-based) inversion approach, are an outcome of the Irrigation+ project (https://esairrigationplus.org/) funded by the European Space Agency (ESA). The data have been produced over the Ebro basin (Spain), the Po valley (Italy), and the Murray-Darling basin (Australia) and they are available at: https://zenodo.org/record/7341284#.Y7WHsHbMKUm. The irrigation estimates referring to the Spanish and the Italian pilot areas rely on Sentinel-1 soil moisture obtained through the RT1 (first-order Radiative Transfer) model and are characterized by a spatial resolution of 1 km. A 6 km spatial sampling has been adopted for the Murray-Darling basin; in this case, irrigation water amounts have been retrieved from CYGNSS (CYclone Global Navigation Satellite System) soil moisture. The data sets referring to the European sites cover a time span ranging from January 2016 to July 2020, while irrigation amounts over the Murray-Darling basin are available for the period April 2017 – July 2020. The reliability of the retrieved irrigation estimates has been assessed through comparison against benchmark amounts. Satisfactory performances have been found over the Ebro and the Murray-Darling basins. More in detail, a median value of RMSE, Pearson correlation, r, and BIAS equal to 12.4 mm/14-day, 0.66, and -4.62 mm/14-day, respectively, is found across pilot districts located within the Ebro basin. The analogous results obtained over the Murray-Darling basin are equal to10.54 mm/month, 0.77, and -3.07 mm/month. The evaluation over the Po valley is affected by the limited availability of in-situ reference data for irrigation. This study sheds light on the perspective of building operational systems aimed at monitoring agricultural water use relying on satellite data.