Abstract
Agriculture in the Upper Blue Nile (UBN) Basin has recently been incorporating surface water-based irrigation practices in the dry season, the upshots of which rely heavily on seasonal (June, July, August, September) precipitation. Precipitation uncertainty often overshadows the effectiveness of these irrigation schemes. Getting an accurate assessment of JJAS precipitation derived streamflows, and what portion of this water could be used to provide optimal irrigation, could be highly beneficial, especially for local small-scale irrigation projects in data scarce areas like the UBN region. Driven by this, we implemented a local scale groundwater (GW) model in the Quashni River Irrigation (QRI) area (250 ha), located in the Gaita Woreda, Ethiopia, to simulate the vadose zone hydrologic components due to irrigation. Following the simulation from January 2008 to current (baseline), the GW model was used to estimate optimal irrigation releases for the current dry season (October 2020 to May 2021) by identifying the best soil moisture conditions aiming to maximize crop yield. A Modflow-NWT based GW model--forced with reanalysis datasets, i.e. precipitation from MSWEP v1.0 and IMERG, and simulated runoff and streamflow from CREST model is used in this research. The model estimates soil moisture (theta ) and hydraulic head (H), and is calibrated by the hydraulic conductivity (K) and specific yield (S (sub y) ) using in-situ citizen science measurements of H and theta as reference. The citizen science stage measurements on the Quashni River and the main irrigation canal were used to estimate irrigation releases during the baseline period. In the forecast mode (dry season 2020), the model takes as inputs the streamflow and infiltration parameters predicted by CREST, which was forced with the Climate Forecast System (CFS) meteorological variables. The research presented in this study could be beneficial for the QRI area, where local people operate the scheme without rigorous understanding of the impacts of different irrigation releases. This would provide advantages in terms of decision making on optimal irrigation strategies (water amounts and frequency); and hence contribute to water-food security improvement in the area.