IMPACT OF HEADWATER HYDROLOGICAL DEFICIT ON THE DOWNSTREAM FLOOD‐BASED FARMING SYSTEM IN NORTHERN ETHIOPIA

AbstractFlood‐based farming is a means of improving crop production in rain‐deficit lowlands. Such spate irrigation systems are growing in importance, although the effects of headwater hydrological deficit on downstream flood farming are lacking evidence. This study investigates the impacts of headwater hydrological deficit on the extent of spate‐irrigated agriculture in the Guguf spate system. The length of canals and area of spate‐irrigated agriculture to the right and left of the Guguf River for the 1980s and 2010s were tracked using a global positioning system and mapped in a geographic information system interface, while climate data were collected from National Meteorological Agency. Trends of selected hydroclimatic variables were analysed using linear regression and the Pettitt test. The flash floods have shrunk by 7.36 × 106 m3, as a result of which the length of canals and area of spate‐based farms declined by 1.37 km and 1540 ha, i.e. 35 and 57.5%, respectively, in only three decades. This corresponds to an average withdrawal of −44.0 ha yr‾¹. A single 1 million m3 decline in flash floods caused a 366.4 ha decline in spate‐based farms. Moreover, farm fields located next to the river course are less affected, compared to those at the tail of the scheme. If the current trend continues, there is a high risk that the remaining farms currently receiving floods may find themselves outside of the spate systems. Therefore, we suggest that flood management technologies are needed to optimize the efficiency of soil moisture in the spate system. © 2020 John Wiley & Sons, Ltd.