Seawater intrusion in the coastal aquifers of East and Horn of Africa: A review from a regional perspective

•The first comprehensive regional scale review of seawater intrusion in Eastern Africa.•The extent of SWI varies significantly from location to location in the region.•The hydrogeochemical technique is the most widely used approach for SWI studies.•Kenya and Tanzania's coastal areas are currently the most researched in the region.•In Tanzania, most SWI studies were concentrated in Dar es salaam. As coastal areas continue to experience population and economic growth, there is a need for more holistic understanding of the attendant environmental challenges towards ensuring sustainability. The over 8300km continental coastline stretch of East and Horn of Africa from Sudan to Tanzania is not an exception. A typical challenge associated with coastal areas is seawater intrusion (SWI) into coastal aquifers. Several efforts have been made in understanding this phenomenon and developing management strategies in different parts of the world. This has led to an evolution of different techniques for assessing the extent of seawater intrusion. This paper explores the status and extent of SWI studies in the region, focusing on the trend of techniques and methodologies used in the past 5 years. The findings show that at a regional level, there is more empirical knowledge on SWI in Kenya, Djibouti, and Tanzania while that of Sudan, Eritrea, and Somalia is largely vague for obvious reasons – more studies have been conducted in the former countries. Hydrogeochemical techniques coupled with statistical and analytical tools are the most prevalent approaches. Furthermore, the extents of SWI vary significantly from location to location but rarely extend beyond a few km inland in the region. SWI extent and severity were also shown to vary with seasons in studies covering temporal dimensions. The review shows that more research capacity building is needed especially in countries like Sudan, Somalia, Djibouti and Eritrea. Finally, recommendations on SWI research and management frontiers to explore in the region are suggested. [Display omitted]