Nature-based solutions in arid and semi-arid countries: A review of best practices and lessons learned

Arid and semi-arid regions are defined by low annual precipitation, which contributes to chronic water scarcity and frequent severe drought events. In recent years, climate change has exacerbated these challenges, causing more frequent and intense rainfall events, which increase flood risk, particularly in highly urbanized and densely populated areas, followed by prolonged drought periods. To mitigate both water scarcity and flood effects, several nature-based solutions, commonly used in humid areas, have been readapted and implemented in arid and semiarid climates. Specific guidelines and directives for their implementation in these contexts are, however, not available nor well defined. Based on well-established real applications, this work presents a literature review of the most efficient and commonly used nature-based solutions installed in arid and semi-arid areas. The geographical distribution, the main purpose, the structure, and the vegetation chosen in real case studies have been assessed through a systematic analysis of 89 papers. Results highlight frequent use of green roofs, rain gardens, and water harvesting systems in these regions. The findings of this research could serve as a valuable reference for other cities with similar climatic conditions and support the global promotion and adoption of green infrastructure, particularly in arid and semi-arid regions.