Landsat-based ET to assess illicit groundwater use: The Ica Valley, Peru

Rapid agricultural development in the Ica Valley of Peru has translated to historic and on-going unsustainable use of groundwater.  Decades of ineffective water resources management threatens the future of agricultural production, requiring an overhaul of water management decisions and actions, particularly for groundwater sustainability.  A key measure of robust groundwater management is an accurate estimate of groundwater use, particularly if groundwater use is thought to exceed regulatory abstraction limits.  In this study, remote sensing estimates of evapotranspiration are combined with precipitation and water use permit databases to quantify groundwater use that exceeds regulatory limits, termed illicit use.  We apply two energy balance approaches, METRIC and SEBAL, combined with gridded climate information to robustly quantify agricultural water use.  Our findings document that illicit groundwater use is approximately twice that of regulation abstraction rates, suggesting current management strategies are failing to mitigate unsustainable groundwater use.  The remote sensing workflow can be applied to quantify groundwater use to inform efficacy of future groundwater management decisions and aid to identify regions for future interventions.