This paper aims to describe the state of theart of both water harvesting (WH) andsupplemental irrigation (SI) techniques in the temperate and sub-tropical dry lands, especiallyin the countries of WANA that are characterized by a Mediterranean-type climate. In addition,three case studies of water harvesting are presented (see annex). These were selected from the case studies presented at the FAO Expert Consultation Cairo (1994). By sharing with us the success and the failure of these endeavors, the authors of the case studies illustrate many of the points that are made in the text.

African farmers are poorly resourced, highly diverse and aground by poverty traps making them rather impervious to change. As a consequence R4D efforts usually result in benefits but also trade-offs that constraint adoption and change. A typical case is the use of crop residues as mulches or as feedstock. Here we linked a database of household surveys with a dynamic whole farm simulation model, to quantify the diversity of trade-offs from the alternative use of crop residues.