Interpreting C-band InSAR ground deformation data for large-scale groundwater management in Australia
Pascal Castellazzi, Wolfgang Schmid
Abstract
Three regions across Australia, covering a total of ∼350,000 km2: the Perth basin in Western Australia, Northern New South Wales (Border Rivers, Gwydir, Lower Namoi and Condamine catchments), and Southern New South Wales (Murrumbidgee, Lachlan, Murray and Billabong-Yanco catchments). While presenting the first large-scale InSAR deformation maps over Australia, covering ∼350,000 km2, we explore the value of C-band InSAR ground deformation maps for supporting large-scale aquifer depletion and compaction mapping. The obtention of spatially continuous InSAR ground deformation maps over irrigated agricultural areas (where groundwater depletion typically occurs) implies interpreting the radar phase signal over areas where (1) InSAR coherence is low and/or intermittent and (2) deformation unrelated to aquifer compaction may occur. The study explores how these two factors challenges the interpretability of InSAR data for groundwater management purposes. InSAR signals non-attributable to groundwater storage change occurs in relation to high clay content in surficial soils, unfavourable land cover (low coherence), and cropping activities modifying the soil surface. Clayey soils swell and shrink with climate variability and cropping activities, creating InSAR ground displacement signals in the range ± 20−60 mm/yr, with cropping activities alone contributing up to ∼38 % of this signal. Geomorphological signals corresponding to riverbanks erosion and sediment deposition are observed along ephemeral streams and floodplains. By accounting for non-groundwater deformation sources and via a comparison with in situ groundwater level data, we show a spatial correlation between ground deformation and aquifer storage in five areas, including four in regional Australia.