Recharge variability and sensitivity to climate: The example of Gidabo River Basin, Main Ethiopian Rift

AbstractStudy regionGidabo River Basin, located in the south eastern Main Ethiopian Rift (MER).Study focusThe focus is to characterize the spatial and temporal variability of groundwater recharge, identify the drivers that govern its distribution, and to improve the understanding of its sensitivity to precipitation and temperature in the MER by applying the semi-distributed hydrological model, Soil and Water Assessment Tool (SWAT).New hydrological insights for the regionThe average annual recharge for 1998–2010 reveals a remarkable decrease from the highland (410mm/year) towards the rift floor (25mm/year). Both the spatial and temporal recharge variability is mainly controlled by the climate. In the rift floor, recharge is found to occur only when annual precipitation exceeds a threshold of approximately 800mm. A sensitivity analysis reveals that annual recharge is very sensitive to variations in precipitation and moderately sensitive to temperature changes. The relative sensitivity increases from the highland to the rift floor across the watershed. Increases in both precipitation and temperature, as suggested by climate change projections for Ethiopia, appear to have an overall positive impact on recharge in the majority of the catchment. These findings have implications also for other catchments where recharge is spatially nonuniform and provide a basis for further investigations into the assessment of groundwater resources and their vulnerability to climate change at the watershed and sub-watershed scale

A baseline appraisal of water-dependant ecosystem services, the roles they play within desakota livelihood systems and their potential sensitivity to climate change

This report forms part of a larger research programme on 'Reinterpreting the Urban-Rural Continuum', which conceptualises and investigates current knowledge and research gaps concerning 'the role that ecosystems services play in the livelihoods of the poor in regions undergoing rapid change'. The report aims to conduct a baseline appraisal of water-dependant ecosystem services, the roles they play within desakota livelihood systems and their potential sensitivity to climate change. The appraisal is conducted at three spatial scales: global, regional (four consortia areas), and meso scale (case studies within the four regions). At all three scales of analysis water resources form the interweaving theme because water provides a vital provisioning service for people, supports all other ecosystem processes and because water resources are forecast to be severely affected under climate change scenarios. This report, combined with an Endnote library of over 1100 scientific papers, provides an annotated bibliography of water-dependant ecosystem services, the roles they play within desakota livelihood systems and their potential sensitivity to climate change. After an introductory, section, Section 2 of the report defines water-related ecosystem services and how these are affected by human activities. Current knowledge and research gaps are then explored in relation to global scale climate and related hydrological changes (e.g. floods, droughts, flow regimes) (section 3). The report then discusses the impacts of climate changes on the ESPA regions, emphasising potential responses of biomes to the combined effects of climate change and human activities (particularly land use and management), and how these effects coupled with water store and flow regime manipulation by humans may affect the functioning of catchments and their ecosystem services (section 4). Finally, at the meso-scale, case studies are presented from within the ESPA regions to illustrate the close coupling of human activities and catchment performance in the context of environmental change (section 5). At the end of each section, research needs are identified and justified. These research needs are then amalgamated in section 6

Modeling Spatial Soil Water Dynamics in a Tropical Floodplain, East Africa

Analyzing the spatial and temporal distribution of soil moisture is critical for ecohydrological processes and for sustainable water management studies in wetlands. The characterization of soil moisture dynamics and its influencing factors in agriculturally used wetlands pose a challenge in data-scarce regions such as East Africa. High resolution and good-quality time series soil moisture data are rarely available and gaps are frequent due to measurement constraints and device malfunctioning. Soil water models that integrate meteorological conditions and soil water storage may significantly overcome limitations due to data gaps at a point scale. The purpose of this study was to evaluate if the Hydrus-1D model would adequately simulate soil water dynamics at different hydrological zones of a tropical floodplain in Tanzania, to determine controlling factors for wet and dry periods and to assess soil water availability. The zones of the Kilombero floodplain were segmented as riparian, middle, and fringe along a defined transect. The model was satisfactorily calibrated (coefficient of determination; R2 = 0.54–0.92, root mean square error; RMSE = 0.02–0.11) on a plot scale using measured soil moisture content at soil depths of 10, 20, 30, and 40 cm. Satisfying statistical measures (R2 = 0.36–0.89, RMSE = 0.03–0.13) were obtained when calibrations for one plot were validated with measured soil moisture for another plot within the same hydrological zone. Results show the transferability of the calibrated Hydrus-1D model to predict soil moisture for other plots with similar hydrological conditions. Soil water storage increased towards the riparian zone, at 262.8 mm/a while actual evapotranspiration was highest (1043.9 mm/a) at the fringe. Overbank flow, precipitation, and groundwater control soil moisture dynamics at the riparian and middle zone, while at the fringe zone, rainfall and lateral flow from mountains control soil moisture during the long rainy seasons. In the dry and short rainy seasons, rainfall, soil properties, and atmospheric demands control soil moisture dynamics at the riparian and middle zone. In addition to these factors, depths to groundwater level control soil moisture variability at the fringe zone. Our results support a better understanding of groundwater-soil water interaction, and provide references for wetland conservation and sustainable agricultural water management

Multi-scale modeling of water resources in a tropical inland valley and a tropical floodplain catchment in East Africa

This study investigated the dynamics of hydrological processes at the wetland-catchment scale through field scale-based analysis, point scale modeling using Hydrus-1D model along a floodplain transect in Tanzania and wetland-catchment modeling with SWAT model in an inland valley in Uganda. The impact of different land use management options and the projected climate change on the water resources of the inland valley were also evaluated using a hydrological response unit (HRU)-based (ArcSWAT2012) and a grid-based setup (SWATgrid) of the SWAT model. The inland valley is located in Namulonge, central Uganda, and it is one of the headwater catchments of Lake Kyoga basin. The inland valley catchment covers an area of 31 km2 with a wetland area of 4.5 km2. The floodplain is located in Kilombero district, Southern Tanzania and the catchment area is 40,240 km2 and the study area in a wetland is 96 km2. Both sites reflect the prevailing diversity of wetland attributes and uses. Monitoring of hydro-meteorological data for both sites was conducted for two hydrological consecutive years of 2015 and 2016. The cross–section of the wetland transect was subdivided into three major hydrological positions defined as riparian zone, middle, and fringe. Hydrological instrumentation and data collection for soil moisture, soil properties, depth to shallow groundwater was conducted along these hydrological positions for both wetland systems. In addition, there was data mining from other sources. Following the field-based analysis at a wetland scale in the inland valley, the spatial and temporal variability in soil moisture increased significantly (p In the Kilombero floodplain, Hydrus-1D model was successfully calibrated (R2 = 0.54–0.92, RMSE = 0.02–0.11 cm3/cm3) using measured soil moisture content. Satisfying statistical measures (R2 = 0.36–0.89, RMSE = 0.03–0.13 cm3/cm3) were obtained when calibrations for one plot were validated with measured soil moisture for another plot within the same hydrological zone, indicating the transferability of the calibrated Hydrus-1D. The hydrological regimes correlated with the hydrological positions in the floodplain. Soil moisture dynamics is controlled by overbank flow, precipitation, and groundwater control at the riparian and middle zone, while it is controlled by rainfall and lateral flow from mountains at the fringe during the long rainy seasons. In the dry and short rainy seasons, rainfall, soil properties, and atmospheric demands control soil moisture dynamics at the riparian and middle zone. For the wetland-catchment scale hydrological modeling in the inland valley, good model performance was achieved from the calibration and validation of daily discharge (R2 and NSE > 0.7) for both model setups (ArcSWAT2012 and SWATgrid). The annual water balance indicates that 849.5 mm representing 65% of precipitation is lost via evapotranspiration. Surface runoff (77.9 mm) and lateral flow (86.5 mm) are the highest contributors to stream flow. Four land use management options were developed in addition to the current land use system, with different water resources conservation levels (Conservation, Slope conservation, Protection of the headwater catchment, and Exploitation). There is a strong relationship between the first three management options with decreasing surface runoff, annual discharge and water yield while the fourth option will increase annual discharge and total water yield. The future climate change in the inland valley was analyzed using climate scenarios RCP4.5 and 8.5 of six GCM-RCM models from the CORDEX-Africa project. Compared to the reference period of 1976-2005, a general increase in temperature of +0.9 0C to +1.9 0C over the period of 2021-2050 is projected by the model ensemble. A mixed change signal in annual precipitation (-30 to 43.9%) is projected among the six climatic models. However, on average, the models show an increase in annual precipitation of +7.4% and +21.8% under RCP4.5 and 8.5, respectively. The application of the climate model ensembles in SWAT showed future discharge change similar to the projected precipitation change. The six climate models showed uncertainty in the annual discharge change ranging from -44 to 149% although on average, the climate models project an increase of +16% and +29% under RCP4.5 and 8.5, respectively. Wet and dry seasons are expected to get wetter and drier, respectively in the future. Compared to land use management options, climate change will have a dominant impact on the water resources in inland valleys. Adoption of Conservation, Slope conservation and protection of the headwater catchment options will significantly reduce the impacts of climate change on the total water yield and surface runoff and increase evapotranspiration and water availability in the inland valley

Assessing the impacts of climate and land use and land cover change on the freshwater availability in the Brahmaputra River basin

AbstractStudy Region: Brahmaputra River basin in South Asia.Study Focus: The Soil and Water Assessment Tool was used to evaluate sensitivities and patterns in freshwater availability due to projected climate and land use changes in the Brahmaputra basin. The daily observed discharge at Bahadurabad station in Bangladesh was used to calibrate and validate the model and analyze uncertainties with a sequential uncertainty fitting algorithm. The sensitivities and impacts of projected climate and land use changes on basin hydrological components were simulated for the A1B and A2 scenarios and analyzed relative to a baseline scenario of 1988–2004.New hydrological insights for the region: Basin average annual ET was found to be sensitive to changes in CO2 concentration and temperature, while total water yield, streamflow, and groundwater recharge were sensitive to changes in precipitation. The basin hydrological components were predicted to increase with seasonal variability in response to climate and land use change scenarios. Strong increasing trends were predicted for total water yield, streamflow, and groundwater recharge, indicating exacerbation of flooding potential during August–October, but strong decreasing trends were predicted, indicating exacerbation of drought potential during May–July of the 21st century. The model has potential to facilitate strategic decision making through scenario generation integrating climate change adaptation and hazard mitigation policies to ensure optimized allocation of water resources under a variable and changing climate

Groundwater recharge prediction for broad scale irrigation modelling: a case study in the M.I.A-main canal irrigated areas

Determining the water balance is a vital element in water resource management. This is particularly important for arid and semi-arid regions in Australia where surface water resources such as rivers and rainfalls are less available. Consumption of water is the highest for agricultural purposes in Australia. Due to the importance of conserving water resources in the background of agriculture and climate it is necessary to quantify the water incoming to the system and water outgoing from the system. For this reason, it is required to estimate the amount of groundwater recharge. The project deals with recharge within irrigated areas. The study area chosen is a group of irrigation districts, geographically located within the Murrumbidgee Irrigation Areas (MIA). The MIA is situated in southern-central New South Wales. The study area and the MIA come under semi-arid environment. Agriculture is prevalent in the MIA. The irrigation districts under the study area receive irrigation water diversions from the Main Canal which inturn is diverted from the Murrumbidgee River. This report describes the application of a newly developed recharge optimisation method for arriving at prediction parameters specific to the study area for estimating groundwater recharge from an irrigated area. The method is developed leading from AWRA-R irrigation model which is developed by Commonwealth Scientific and Industrial Research Organisation (CSIRO). The irrigation model has two components in it: Diversions modelling module and Recharge estimation module. The diversions module is built in order to estimate irrigation diversions to agricultural farms at a river basin scale. It is simple, can be calibrated and run for long-term simulations quickly. It is designed to generate estimations of diversions even under circumstances of parsimonious data availability. Recharge module, the other component, is a modified form of Overbank flood recharge (OFR) method to estimate groundwater recharge for a given district. The AWRA-R irrigation model is applied to the study area and simulated results for groundwater recharge are obtained. These results are further optimised based on factors that influence recharge dominantly in the study area. Simulations are run by varying the input parameters to the irrigation model thus obtaining 840 trial recharge estimations. These recharge values are fitted against a set of collated recharge estimates from previous studies and researches done within the MIA and the lower Murrumbidgee by means of root-mean-square error analysis. The simulation recharge outputs that give the closed fit to the collated data are accepted to be the recharge estimates specific to the study area. The input parameters, Kc and soilCap, applied for that simulation are determined to be prediction parameters, the values of which are 7.78E-07m/sec and 0.105m respectively. The prediction parameters, thus deduced, have been used to estimate recharge for years 1970-2012. From the results of simulated recharge, it is observed that there are several years with no recharge while the maximum recharge is 79.49mm in the year of 1991

Hydrological Modeling of the Effect of the Transition From Flood to Drip Irrigation on Groundwater Recharge Using Multi-Objective Calibration

[EN] The replacement of flood-irrigation systems by drip-irrigation technology has been widely promoted with the aim of a more sustainable use of freshwater resources in irrigated agriculture. However, evidence for an irrigation efficiency paradox emphasizes the need to improve our understanding of the impacts of irrigation transformations on water resources. Here, we developed a distributed hydrological modeling approach to investigate the spatiotemporal effect of flood and drip irrigation on groundwater recharge. The approach recognizes differences in the water balance resulting from the localized application of water in surface drip-irrigated fields and the more extensive application of water in flood irrigation. The approach was applied to the semi-arid Mediterranean region of Valencia (Spain) and calibrated using a multi-objective framework. Multiple process scales were addressed within the framework by considering the annual evaporative index, monthly groundwater level dynamics, and daily soil moisture dynamics. Daily simulations from 1994 to 2015 suggested that, in our hydroclimatic conditions, (a) annual recharge is strongly related to annual rainfall, which had a four times higher impact on recharge than the type of irrigation practice, (b) flood-irrigated recharge tends to exceed drip-irrigated recharge by 10% at annual time scales, (c) however, recharge response to a particular precipitation event is smaller in flood irrigation than in drip irrigation, and (d) 8¿18 rainfall events could generate more than half of the annual recharge in drip and flood irrigation, respectively. Our results highlight the importance of understanding the hydrological dynamics under different irrigation practices for supporting irrigation infrastructure policies.The authors thank the Coop Research Program on ¿Sustainability in Food Value Chains¿ of the ETH Zurich World Food System Center and the ETH Zurich Foundation for supporting this project. The Coop Research Program is supported by the Coop Sustainability Fund. The authors also acknowledge the financial support from the Spanish Ministry of Science and Innovation through the research project TETISCHANGE (RTI2018-093717-B-100). This work was additionally supported by the ADAPTAMED research project funded by the Spanish Ministry of Science and Innovation (RTI2018-101483-B-I00) with European FEDER funds. The support of Andreas Scheidegger (Eawag) for statistical questions is also acknowledgedPool, S.; Francés, F.; Garcia-Prats, A.; Puertes, C.; Pulido-Velazquez, M.; Sanchis Ibor, C.; Schirmer, M.... (2021). Hydrological Modeling of the Effect of the Transition From Flood to Drip Irrigation on Groundwater Recharge Using Multi-Objective Calibration. Water Resources Research. 57(8):1-19. https://doi.org/10.1029/2021WR029677S11957

Integrated Hydrological Modeling for Water Resources Management of Heeia Coastal Wetland in Hawaii.

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017

Impact of grassland conversion to forest on groundwater recharge in the Nebraska Sand Hills

Study region: Nebraska National Forest in the High Plains Aquifer, Nebraska Sand Hills, U.S.A. Study focus: This research aimed to investigate the effects of grassland conversions to forest on recharge rates in a century-old experimental forest. The DiffeRential Evolution Adaptive Metropolis (DREAMZS) global optimization algorithm was used to calibrate the effective soil hydraulic parameters from observed soil moisture contents for 220 cm deep uniform soil profiles. The historical recharge rates were then estimated by applying the numerical model HYDRUS 1-D for simulation of two plots representing grasslands and dense pine forest conditions. New hydrological insights: The results indicate that conversion from grasslands to dense pine forests led to vegetation induced changes in soil hydraulic properties, increased rooting depth, and greater leaf area index, which together altered the water budget considerably. The impacts of land use change, expressed in percent of gross precipitation, include a 7% increase in interception associated with an increase in leaf area index, a nearly 10% increase in actual evapotranspiration, and an overall reduction of groundwater recharge by nearly 17%. Simulated average annual recharge rates decreased from 9.65 cm yr−1 in the grassland to 0.07 cm yr−1 in the pine plot. These outcomes highlight the significance of the grassland ecology for water resources, particularly groundwater recharge, in the Nebraska Sand Hills and the overall sustainability and vitality of the High Plains Aquifer