Abstract
This study was conducted at the Dangishta watershed in the Ethiopian highlands to evaluate irrigation potential from surface and groundwater sources under different farming and water application systems. Daily streamflow and the groundwater table were monitored from 2015 to 2017. Shallow groundwater recharge was estimated using the water table fluctuation method. Automated baseflow separation techniques were used to determine the amount of runoff and baseflow from the total streamflow records. The potential of groundwater and runoff to sustain dry season irrigation (i.e., low flow) was evaluated considering two tillage systems (i.e., conservation agriculture, CA; and conventional tillage, CT), and water application (i.e., drip and overhead) systems for major irrigated crops (i.e., onion, garlic, cabbage, and pepper) grown in the Dangishta watershed. We found that the annual groundwater recharge varied from 320 to 358 mm during the study period, which was about 17% to 22% of the annual rainfall. The annual surface runoff depth ranged from 192 to 268 mm from 2015 to 2017. The results reveal that the maximum seasonal irrigable land from groundwater recharge was observed under CA with drip irrigation (i.e., 2251 and 2992 ha from groundwater recharge and surface runoff, respectively). By comparison, in the CT practice with overhead irrigation, the lowest seasonal irrigable land was observed (i.e., 1746 and 2121 ha from groundwater and surface runoff, respectively). From the low flow analysis, about 199 and 173 ha of one season’s irrigable land could be irrigated using the CA and CT systems, respectively, both with drip irrigation. Similarly, two-season overhead irrigation potential from low flow under CA and CT was found to be about 87 and 76 ha, respectively. The dry season irrigable land using low flow could be increased from 9% to 16% using the CA system for the various vegetables, whereas drip irrigation could increase the irrigable land potential by 56% compared to overhead irrigation. The combined use of groundwater recharge and runoff could sustain up to 94% of the dry season low flow irrigation through the combination of the CA system and drip irrigation. Decision makers must consider the introduction of feasible and affordable technologies to make use of groundwater and direct runoff, to maximize the potential of dry season production through efficient and appropriate CA and water management practices.
Highlights
Agriculture is the main source of livelihoods in Ethiopia [1,2,3,4], where rainfed production is predominantly practiced [5,6]
This study identified the potential irrigable area in the Dangishta watershed from low flow (90 percentile flow), groundwater recharge, and direct runoff
We present the potential of net groundwater recharge, direct runoff, and low flow, and crop evapotranspiration for major vegetables cultivated in the region
Summary
Agriculture is the main source of livelihoods in Ethiopia [1,2,3,4], where rainfed production is predominantly practiced [5,6]. Rainfed agriculture is challenged by climate change and, in particular, prolonged dry seasons and insufficient rainfall during crop production periods, leading to food insecurity in the region [7,8,9]. Due to these challenges, irrigation is an alternative strategy to overcome food shortages [10] and improve the living standards of smallholder farmers in Ethiopia [4,11,12]. In areas where the low flow is minimal but abundant subsurface resources exist, groundwater is an alternative means to sustain dry season irrigation to maximize food production and reduce water scarcity in the region. The irrigation sector is constrained by a lack of irrigation infrastructure and access to irrigation water [19]
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