Abstract
Detailed information about irrigation timing and water use at a high spatial resolution is critical for monitoring and improving agricultural water use efficiency. However, neither statistical surveys nor remote sensing-based approaches can currently accommodate this need. To address this gap, we propose a novel approach based on the TU Wien Sentinel-1 Surface Soil Moisture product, characterized by a spatial sampling of 500 m and a revisit time of 1.5–4 days over Europe. Spatiotemporal patterns of soil moisture are used to identify individual irrigation events and estimate irrigation water amounts. To retrieve the latter, we include formulations of evapotranspiration and drainage losses to account for vertical fluxes, which may significantly influence sub-daily soil moisture variations. The proposed approach was evaluated against field-scale irrigation data reported by farmers at three sites in Germany with heterogeneous field sizes, crop patterns, irrigation systems and management. Our results show that most field-scale irrigation events can be detected using soil moisture information (mean F-score = 0.77). Irrigation estimates, in terms of temporal dynamics as well as spatial patterns, were in agreement with reference data (mean Pearson correlation = 0.64) regardless of field-specific characteristics (e.g., crop type). Hence, the proposed approach has the potential to be applied over large regions with varying cropping systems.
Highlights
IntroductionThe increased evapotranspiration (ET) driven by irrigation has a regional cooling effect on land surface temperature [11,13], potentially masking the full global warming signal on local and regional scales [14]
Large differences are expected if irrigated fields are surrounded by non-irrigated fields, or at least if irrigation does not occur simultaneously in the fields within the spatial window used to compute the areal soil moisture
Distinct soil moisture increases arise from the field-specific irrigation system and/or management practices
Summary
The increased evapotranspiration (ET) driven by irrigation has a regional cooling effect on land surface temperature [11,13], potentially masking the full global warming signal on local and regional scales [14]. Global warming and the expected change of precipitation patterns [15] resulting in a decrease of water availability especially in already water-scarce regions will intensify the need for irrigation [16,17,18]. This complex scenario will be further exacerbated by the increased needs of a more populous world with rising living standards [19]
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