We know that humans evolved in Africa and then dispersed around the globe, but when they did so, and what routes they took are controversial and poorly understood issues. One of the most important barriers to dispersal is the harsh environment of the Sahara and Arabian deserts. Thus understanding when climate change ameliorated aridity in this region, and the effect this had on human occupation are important issues. Here we outline the use of palaeohydrological mapping to address these questions. Remote sensing and GIS analysis are used to map the paleo rivers and lakes of the Sahara and Arabia. Adjacent catchments that contain paleolakes and form corridors across these deserts are defined and expeditions organized to visit them. Paleolakes are then surveyed for archaeology and fossils and samples collected for luminescence dating and paleoenvironmental analysis. We will describe how this method has been used to define a green corridor across the Sahara and into Arabia during the last interglacial. In this corridor the method successfully located 7 stratified middle and lower stone age sites that date between 30 and 400 ka and revealed  numerous stone tools, a fossil Homo sapiens finger bone dating to~85 ka and footprints dating to 125 ka; thus providing much evidence for human dispersal across these deserts during humid periods.