Cornelis, Wim M.Verbist, KoenAraya, TesfayOpolot, EmmanuelWildemeersch, Jasmien C.J.Al-Barri, Bashar2023-04-112023-04-112021Cornelis, W. M., Verbist, K., Araya, T., Opolot, E., Wildemeersch, J. C., & Al‐Barri, B. (2021). Fully coupled surface–subsurface hydrological modeling to optimize ancient water harvesting techniques. Handbook of Water Harvesting and Conservation: Case Studies and Application Examples, 49-64.https://onlinelibrary.wiley.com/doi/abs/10.1002/9781119776017.ch4https://nru.uncst.go.ug/handle/123456789/8435Worldwide, but particularly in drylands, water scarcity has become a major limitation to crop production and to delivering ecosystemservices in general. Likewise, in many regions rainfall is becoming more erratic, with later and shorter rainy seasons, more and longer dry spells, and fewer rainy days (Sillmann et al. 2013), even in cases when total rainfall is increasing (Wu et al. 2013; Greve et al. 2014). This might be linked to anthropogenic climate change (Rockström and Falkenmark 2015). It results in a higher frequency of particularly agricultural droughts – shortage of available water for plant growth – which generally occur more often than meteorological droughts, i.e. shortage of precipitation (Wani et al. 2009). In order to improve food and water security, water harvesting in its broadest sense should be an entry-point activity to enhance crop production through sustainable/ ecological intensification. On a larger scale it contributes to regreening of the landscape, through crops, grasses, shrubs, or trees, hence rendering ecosystem services for society (Stroosnijder 2009). In a broad sense,water harvesting refers to retaining rainwater by in situ and ex situ practices (Dile et al. 2013; Cornelis 2014). In situ practices capture and store water where it falls, whereas ex situ practices collect water from a larger area and convey it to fields for immediate use or to storage systems for later use. Various examples are given elsewhere within this book.enHydrological ModelingWater Harvesting TechniquesBook chapter