Groundwater Recharge Estimation Using WetSpass Modeling in Upper Bilate Catchment, Southern Ethiopia

The study area, upper Bilate catchment, is strongly dependent on groundwater like other rural catchments in the country. The main objective of this work is to quantify the amount of groundwater recharge in upper Bilate catchment. Recharge was estimated using physically based distributed recharge model called WetSpass. As input to the model precipitation, potential evapotranspiration, temperature and wind speed were estimated using data collected from meteorological stations located within the catchment and nearby areas. The physical environmental data including land use, soil type, and groundwater depth were collected from field and existing maps. Slope and topography map were generated from Shuttle Radar Topographic Mission elevation data. Using the model the mean annual recharge of the catchment was found to be 9.4 % of the precipitation whereas the direct runoff was found to be 20 % of the precipitation. The study area is characterized by lower groundwater recharge relative to surface runoff due to the effect of impermeable soils, morphology of the land and land use/land cover of the study area. The western and northern parts of the area are identified as recharging zone and the central and southern part are discharge zone. The groundwater recharge zoning map was validated using base flow separation method and also compared with previous groundwater recharge works of the study area. This study revealed that the groundwater recharge estimation using WetSpass model is reasonable and useful for quantification of annual groundwater recharge with spatial and seasonal variation and also capable in the identification of groundwater recharge zones in the area under study.Keywords: Runoff; Evapotranspiration; Groundwater; WetSpass; Bilate catchment; Ethiopia

Groundwater Based Irrigation and Food Security in Raya-Kobo Valley, Northern Ethiopia

The Raya-Kobo valley is characterized by good groundwater resources potential (excess of 198 Mm3) located in northern Ethiopia. The total area of the valley is approximated to be 3510 Km2. Despite this potential of groundwater, the area has been suffering from droughts. Establishment and expansion of cooperative societies, small business enterprises and irrigation farming were given priority as interventions to address the food security problem in the valley. These interventions were designed and implemented in the last several years by the regional governments administrating the Raya-Kobo valley, and groundwater is used as a source of water for irrigation farming for more than nine to ten years. Nevertheless, food insecurity is still a major problem in the area. The present study has been conducted to investigate the extent of contribution of the groundwater based intervention in the elimination food insecurity. The study was conducted by collecting, analyzing and interpreting all the existing relevant data of the study area. Groundwater potential was compiled from the author’s previous works and recently conducted research works. The impact of the groundwater based irrigation on food security issues was assessed using informal and formal interviews and focus group discussions. Limited area coverage of the irrigated land and the long time taken for the extension works in those drilled productive wells are the major limitations in the Kobo valley that makes the groundwater based irrigation unable to release the farmers of the area from the food insecurity. In Raya valley, besides to these problems, absence of responsible office, failure of pump, and the long time taken for pump maintenance are also the major factors. In Raya-Kobo valley food security is highly related to the availability of water. Irrigating the whole potential irrigable area, increasing and sustaining availability of groundwater and management of the irrigation scheme are vital to eradicate food insecurity from Raya-Kobo valley

Environmental tracers to evaluate groundwater residence times and water quality risk in shallow unconfined aquifers in sub Saharan Africa

In sub-Saharan Africa, shallow aquifer systems are relied on as the main safe and secure water resource available to rural communities. Information on the sustainability and vulnerability of groundwater abstraction is becoming increasingly important as groundwater development increases. As part of the UpGro Consortium Project- Hidden Crisis, 150 hand pumped boreholes (HPBs), ranging between 15 and 101 m depth were investigated to examine the resilience of aquifer systems in the Ethiopian Highlands, and the crystalline basement rocks of Uganda and Malawi. Environmental tracers (chlorofluorocarbons (CFCs), SF6, chloride and the stable isotopes of water), water quality indicators (nitrate and E. coli), and groundwater-level time series data were used to estimate groundwater residence time and recharge at a regional scale (100–10,000 km2) and investigate the risks to water quality and water supply over different timeframes, and geological and climatic environments. Average estimated recharge rates using three different techniques (CFCs, chloride mass balance, water table fluctuation method) were between 30 and 330, 27–110 and 30–170 mm y−1, for sites in Ethiopia, Uganda and Malawi, respectively. These estimates of recharge suggests abstraction from dispersed low-yielding HPBs is sustainable. Comparison of stable isotopes in rainfall and groundwater indicates that there is little evaporation prior to recharge, and recharge events are biased to months with greater rainfall and more intense rainfall events There was a weak correlation between nitrate and CFCs within all three countries, and no correlation between E. coli and CFCs within Ethiopia or Malawi. The presence of E. coli at a large proportion of the sites (Ethiopia = 38%, Uganda = 65% and Malawi = 47%) suggests rapid transit of contaminated surface water into the borehole and its presence in groundwater that has CFC-12 concentrations less than 75 pg kg−1 indicates mixing of very young water with water >40 years old. The rapid transit pathways are most likely associated with damaged HPB headworks and poor construction. In several monitored HPBs, daily drawdown due to pumping, drew the groundwater levels close to the base of the HPB, indicating that these HPBs were located in parts of the aquifer with low permeability, or were poorly designed, offering limited capacity for increased demand. Improved HPB siting and construction, coupled with groundwater level monitoring are required to capitalise on the more resilient groundwater within the shallow aquifers and safeguard adequate and good quality water supply for rural communities

Rainwater harvesting in Modjo watershed, upper Awash River Basin, Ethiopia through remote sensing and fuzzy AHP

All human activities and overall development of this world centre on the essential life substance water. Water supply at many places is augmented mainly through rainwater harvesting (RWH). The study area needs lot of water for agriculture, livestock and human needs especially during the yearly dry season. Although several techniques are in vogue to detect apt RWH sites, their improvement especially for RWH in large sub-catchment regions is much desired. Therefore, RS and GIS techniques already in use are integrated with fuzzy logic to identify and classify sites suitable for RWH in Modjo watershed in central Ethiopia. As a result, potentially acceptable sites in the study area were discerned and categorized as very highly suitable, highly suitable, moderately suitable, low suitable, very low suitable and constraints with 18.1%, 20.9%, 20.3%, 10.6%, 3.1% and 26.9% area, respectively. Thus, the model with geospatial and analytic hierarchy process combination has proved very successful in detecting RWH sites

A review of hydroclimate variability and changes in the Blue Nile Basin, Ethiopia

Understanding the factors that influence hydroclimate variability is crucial for developing sustainable water management strategies in dynamic environments. The Blue Nile Basin, a significant freshwater resource in Africa, is facing challenges related to hydroclimate changes that impact sustainable development. Since the 1970s, the hydroclimate patterns of the region have undergone notable changes, prompting the need for a review of the literature on hydroclimate variability of the basin. Therefore, this study aims to offer a brief overview of the latest literature on hydroclimate variability and changes in the Blue Nile Basin. Based on the review of hydroclimate studies in the basin, it is evident that there have been significant advancements in our understanding of this complex system. However, the review also highlights that there are still areas of research that require further development to provide more comprehensive knowledge of the basin's hydroclimate. The projected intensification of hydroclimate change throughout the 21st century underscores the urgency for continued research efforts. The observed warming trend in the temperature of the basin and the discrepancies amongst research outputs on precipitation changes are important areas that require further investigation. Additionally, the inconsistency in reported changes in the watershed's hydrology and streamflow across the basin emphasizes the need for continued research to understand the factors behind these changes. Overall, this review provides valuable insights into the current state of hydroclimate studies in the basin and highlights the key areas for future research efforts to enhance our understanding of this vital system

Assessment of the impact of rainfall uncertainties on the groundwater recharge estimations of the Tikur-Wuha watershed, rift valley lakes basin, Ethiopia

Spatial recharge estimation uncertainty is directly proportional to uncertainty in input precipitation data Thus, the main objective of this study was to investigate the recharge uncertainty by using improved spatial rainfall observations. The physically based fully distributed hydrological model WetSpa was used to simulate 20,000 possible combinations of parameters for two model setup. The M1 model setup was developed based on the rainfall measurements obtained from rain gauge stations scattered in and around the Tikur-Wuha watershed in Ethiopia, while M2 model setup was developed using bias-corrected satellite rainfall estimates (SREs) based on Climate Hazards Group InfraRed Precipitation (CHIRP) merged with relevant ground station records. The required parameter combinations were generated using Monte Carlo simulation stratified by applying Latin Hypercube Sampling (LHS). One hundred best performing parameter combinations were selected for each model to generate spatial recharge statistics and assess the resulting uncertainty in the recharge estimates. The results revealed that enhanced spatial recharge estimates can be produced through improved CHIRP-based SREs. The long-term mean annual recharge (218.29 mm) in the Tikur-Wuha watershed was estimated. Model parameter calibration performed using discharge measurements obtained from the Wosha rain gauge station located in the subcatchment area of the Tikur-Wuha watershed had a Nash-Sutcliffe efficiency of 0.56. Seventy percent of the watershed showed a coefficient of variation (Cv) < 0.15 for M2, while 90 % of the area exhibited a Cv < 0.15 for M1. Furthermore, the study findings highlighted the importance of improving evapotranspiration data accuracy to reduce the uncertainty of recharge estimates. However, the uncontrolled irrigation water uses and the total recharge coming from the irrigation fields scattered across the Tikur-Wuha watershed were not considered in the study, which is a limitation of the study. Future studies should consider the contribution made by irrigation water to the total recharge of the watershed

Evaluation of a multi-staged bias correction approach on CHIRP and CHIRPS rainfall product: a case study of the Lake Hawassa watershed

A promising future development area to improve the accuracy of satellite rainfall estimates (SREs) is accessing merits from different sources of data through combining algorithms. The main objective of this study is to assess the accuracy and importance of the fused multistage approach of bias correction. Accordingly, two versions of resampled and spatially bias-corrected Climate Hazards Group Infrared Precipitation (CHIRP) estimates were merged with ground measurements using a conditional merging procedure. Results of applied performance measures (i.e. seven) on corrected and merged CHIRP SREs show that the Percent of Detection (POD) and Percent Volume Error (PVE) have improved. Depending on the combination of coupled stations for validation, up to 70 and 50% PVE improvement was achieved at some stations for wet and dry periods, respectively. Moreover, the bias-corrected and conditionally merged CHIRP SREs have outperformed the estimates by resampling CHIRP with station dataset (CHIRPS) over the sparsely populated western part of the watershed. However, the devised method was limited in considering dry-day events during bias correction, which in turn has affected the performance of the bias correction of the CHIRPS product. Finally, future research should concentrate on such methods of fusing to understand the benefits of various approaches and produce more precise rainfall records. HIGHLIGHTS The research provides a fused multi-staged approach for reducing errors in CHIRP and CHIRPS satellite rainfall estimates.; Application of parametric QM for spatial bias correction followed by conditional merging improves the quality of CHIRP SREs.; Bias-corrected and conditionally merged CHIRP estimate outperforms the estimates by CHIRPS.; Incorporating additional ground station records improves the estimates of SREs.

Blue-green water resource availability dynamics in the upper Awash basin, central Ethiopia: implications for agricultural water scarcity assessment

Quantifying and characterizing the spatial distribution of freshwater availability and water scarcity plays an indispensable role in managing water resources in a basin. This study aimed at quantifying green and blue water resource availability using an eco-hydrological model under different land use land cover conditions between 2000–2010 and 2020 in the upper Awash basin, central Ethiopia. Further, the agricultural water scarcity is assessed for dominantly cultivated crops in the basin. The freshwater components such as the green water (GW) flow (∼1041–1240 mm/yr), blue water (BW) flow (277–304 mm/yr), and GW storage (809-872 mm/yr) were observed to be high in the western highlands compared to the central and eastern parts of the basin. The results of GW scarcity indices show low to moderate scarcity for rainfed crops, and moderate to significant BW scarcity for irrigated sugarcane. Integrating GW potential to reduce BW scarcity in the basin is thus crucial

Functionality and resilience of hand-pumped boreholes in sub-Saharan Africa

In sub-Saharan Africa as many as 184 million people rely on hand-pumps. Thus, hand-pumps are, and will remain, a crucial water source in a changing climate, although as many as one in three are non-functional at any time. Drawing on the results of three studies we demonstrate that hand-pumps are resilient and safe, and we examine the physical factors that determine hand-pump functionality. In the first study we analysed the performance of 5196 water points (hand-pumps, motorized boreholes, springs, open-sources) and the success of a proactive maintenance programme during the 2015-16 drought in Ethiopia. Water sources were visited every week for 12 weeks to gather data on access and functionality. The second study, again in Ethiopia, involved monitoring 51 groundwater points (hand-pumps, springs, hand-dug wells) over an 18-month period in 2016. Water sources were equipped with water level loggers and were tested monthly for thermo-tolerant coliforms. All sources were put under considerable strain during the drought. Most demand was placed on motorised boreholes in lowland areas. However, increases in functionality of motorised boreholes, as a result of the maintenance programme, lagged behind those of hand-pumps. Functionality was low for both sources at the on-set of the drought (65% and 75% respectively). Motorised boreholes had longer downtimes due to a lack of appropriate and/or accessible maintenance skills. Water level monitoring showed that hand-pumped boreholes recovered most quickly from daily abstractions. All sources were contaminated with thermo-tolerant coliforms during the rains marking drought cessation but hand-pumped boreholes were least affected. Our results show that hand-pumped boreholes are resilient and less prone to contamination than springs and hand-dug wells. However, like the other sources we studied, hand-pumps had low levels of functionality at the onset of the drought. To better understand the factors affecting functionality we systematically dismantled 150 hand-pumped boreholes in Ethiopia, Uganda and Malawi in 2017. We conducted detailed inspections of hand-pump components and borehole design. Water levels were measured and a pumping test was conducted to measure aquifer yield (transmissivity). In each country specific contextual factors influence functionality. In Ethiopia deep water levels (>60 m) strongly influence functionality. Many hand-pumps operate beyond lift limits (45 m). Aquifer yield is an order of magnitude larger for fully functional hand-pumps than partially functional hand-pumps in Ethiopia. In Uganda many hand-pumps are installed in aquifers with transmissivities close to the minimum required to sustain a hand-pump (c.1 m2/d). The use of galvanized steel components, along with corrosive groundwater, results in high rates of corrosion in Uganda. In all three countries hydrogeology, borehole design and pump condition interact to determine functionality outcomes. Our results reinforce the importance of appropriate borehole siting and design, on-going operation and maintenance and use of appropriate and good quality materials. When supported by responsive and proactive maintenance hand-pumped boreholes, which are less prone to contamination than other shallow groundwater sources, are a resilient water source in a changing climate and are capable of providing water continuously during drought