Seeing the hidden reservoir: Earth observation and geoinformatics for assessing sand dam impacts in dryland rivers

Sand dams are small water-harvesting structures that store water within the sandy matrix of ephemeral riverbeds. They are widely promoted as nature-based solutions for water security and climate adaptation in drylands. Nonetheless, it remains difficult to systematically assess their environmental and socio-ecological impacts for multiple reasons. This review synthesizes Earth observation and geoinformatics research on sand dams and evaluates how reliably their impacts can be detected from spatial data. A structured literature search and citation tracking identified 11 relevant studies published between 2008 and 2026. Evidence on impacts is dominated by vegetation effects: six studies assess vegetation responses, five report localized greening, higher vegetation vitality, or greater drought resilience, while one finds no average greening. Direct hydrological evidence is less prominent: gravimetric and radar-based approaches could not fully resolve local storage effects, and long-term regional responses remain inconclusive. Geomorphological evidence is limited to one study, while thermal approaches remain largely exploratory. Across these studies, differences in spatial scale, control-site selection, dam maturity, and temporal design constrain comparability and attribution. We develop a methodological taxonomy and propose future research based on time series, Before-After-Control-Impact designs, climatic controls, in-situ validation, multi-sensor integration, automated inventories, and data fusion supported by artificial intelligence.