Determining parameters and chronology of a sustainable water harvest system in desert oases; case study Qurayyah, northwest Arabian Peninsula

The arid regions of the world occupy 46% of the total surface area, providing a habitat for 3 billion people. More than 630 million people are directly affected by desertification. Extreme events like droughts and flash floods increase the pressure on plants, animals and above all, humans and their settlements. In the context of a climate change with such far-reaching consequences, historical oases settlements stand out as best practice examples, because their water supply systems must have been adapted to the changing climate during the Holocene to guarantee the viability of the oases and their inhabitants. I will focus on the ancient oasis Qurayyah, located in the northwest of the Arabian Peninsula, a unique example in this context. Recent research has proven that, lacking a groundwater spring, the formation of a permanent settlement in Qurayyah was made possible mainly by surface-water harvesting, with local fracture springs potentially only providing drinking water. First numerical dating results for the water harvesting system from optically stimulated luminescence (OSL) dating of quartz confirm that the system was erected in a period characterized by changing climatic conditions from the Holocene climate optimum to the recent arid phase. This study aims to determine parameters and chronology of this sustainable irrigation system and intends to learn and understand how ancient settlers accomplished the construction of such a highly developed water supply system. To reach this research aim the irrigation system was reconstructed using field mapping and remote sensing techniques. It was shown that the reconstructed irrigation system worked as a flood irrigation system. Dams and channels were built to maximize the flooded area and at the same time to prevent catastrophic flooding under high discharge conditions. Contemporaneous historical irrigation systems in comparable size and complexity are known from Mesopotamia or Egypt. In addition to the system’s reconstruction, a new reverse engineering approach based on palaeobotany was developed for Qurayyah to reconstruct the climate conditions during the time of its operation. Compared to today’s precipitation of 32 mm per year in the research area, our results imply that the irrigation system was constructed in a time of significant climate change, because significantly higher amounts of precipitation would have been necessary to enable the cultivation of olive trees (reference plant for the reverse engineering approach), with a sufficient amount of water.