Surfaces with no drainage: Reconnaissance assessment of the hydrogeologic significance of pockmarks in African drylands

Abstract This study presents a reconnaissance investigation into the occurrence, typology, and hydrogeologic significance of pockmarks in African drylands. These unique geomorphic depressions, characterized by poorly developed or disconnected drainage networks, occur on a surface covering more than 10 million km 2 of the continent. Despite their widespread presence, pockmarks remain understudied in hydrogeology and their significance in local groundwater security is rarely investigated. Using an integrated methodology that combines remote sensing, digital elevation models, literature review, and field isotope hydrological investigations, this study identifies and classifies five major pockmark types. Evidence from the isotope hydrology study in Ethiopia reveals their vital role in focused groundwater recharge, temporary surface water storage, and promoting the occurrence of perched groundwater systems in otherwise groundwater-scarce environments. The depressions are shown to be critical for supporting biodiversity, ecosystem services, and water security in arid and semi-arid regions. This study highlights the hydrogeologic significance of these features and calls for an increased hydrogeological investigation.