Rapid rewetting is rapidly degrading some of the world’s drylands

Drylands, which cover 40-50% of Earth's terrestrial surface, are increasingly subject to climate extremes and anthropogenic pressures. One phenomenon of concern is rapid rewetting: introduction of large water volumes into previously parched soils following dam construction or for irrigation agriculture. While rewetting may benefit short-term water security or agricultural yields, without proper planning, it can seriously disrupt dryland geomorphological, hydrological and ecological processes, ultimately contributing to land degradation. Using time-series remote sensing and hydrometeorological data, coupled with field observations, we focus on rapid rewetting of two drylands: the Indian Thar Desert and the Sarmiento basin, Patagonia, Argentina. Both regions have seen extensive recent river modification, canal construction, and irrigation expansion, which has radically changed structural and functional landscape connectivity. Some rewetting practices (e.g. flood irrigation) lead to excess surface runoff, and raise local water tables. Downslope topographic lows (e.g. disconnected palaeochannels) commonly serve as receiving basins, locally sustaining new brackish/saline lakes. Additionally, rapid rewetting can increase soil salinisation, destabilize soil structure, exacerbate erosion, and disrupt plant-soil interactions, with implications for landscape resilience. Despite long histories of soil salinisation and land degradation studies in Indian, Argentinian and other drylands, lessons are not being learned. Rather than mitigating climate and population growth threats to water/food security, rapid rewetting is catalysing degradation feedback loops that threaten Land Degradation Neutrality pledges. As the 20th anniversary of the International Year of Deserts and Desertification (2006) approaches, there is an opportunity for a renewed look at geomorphology’s contribution to sustainable dryland water/land management strategies.