Impact of water overexploitation on highland lakes of eastern Ethiopia

The eastern Ethiopian highland is endowed with large potential of water resources in terms of rainfall, groundwater and surface water. Yet, due to overpumping of lake water and groundwater and environmental degradation, Lakes Haromaya and Adele have completely dried up. The environmental degradation, due to deforestation and clearing of land for farming, has increased the rate of siltation in the lakes that dramatically decreases the lakes’ volume and surface albedo, which increased the rate of evaporation. The impact of these factors is aggravated due to decreasing net recharge to the lake and the alluvial aquifer. Over the last 35 years, pumping of lake water for irrigation, mainly for subsistence farming, domestic and industrial use shows an increasing trend. Hence, the available water for drinking and industrial purposes decreased drastically. In this research, classical Penman aerodynamic combined energy budget, Penman nomogram methods, conventional soil moisture water balance method and Penman–Monteith model were adopted to estimate free evaporation, actual and potential evapotranspirations. The results indicate that evaporation is the dominant factor for the loss of water and water abstraction is 316% higher than the effective precipitation, which is 110 mm/year. Therefore, overexploitation of the available resources has played an aggravating role for the loss of the lakes in the area. The main cause for such resource depletion is the lack of integrated water resources management strategies. The current water shortage in the area has mainly affected urban residents of Harar, Awoday and Alemaya towns and the surrounding villages, which depend heavily on the two lakes. To alleviate the current crises interbasin water transfer and rainwater harvesting would be possible alternatives besides ameliorating environmental situation of the basin.     

Hydrochemical characterization of complex volcanic aquifers in a continental rifted zone: the Middle Awash basin, Ethiopia

The Middle Awash basin is an arid region in Ethiopia where surface waters are scarce and local communities are dependent on groundwater resources for water supply. The complex hydrogeological system of this basin has been conceptualized. Multivariate statistical analysis of hydrochemical variables and water isotopes were used to study the rock?Cwater interaction, geochemical reaction processes and the hydrological link between aquifers. Groundwaters from aquifers of the high-rainfall plateau bounding the rift are slightly mineralized, as well as depleted in ??¹⁸O and ??D, and contain ³H above 0.8?TU. This suggests a low degree of rock?Cwater interaction and that groundwater is under recharge from heavy rain that falls on surrounding highlands. On the other hand, groundwaters from aquifers of the rift floor are highly mineralized and show slight enrichment in ??¹⁸O and ??D with positive oxygen shift, but contain ³H below 0.8?TU. The positive oxygen shift in rift floor groundwaters may be caused by the isotopic exchange of oxygen between groundwater and aquifer materials during rock?Cwater interaction, whereas the low ³H content could be due to the decay of tritium along relatively long flow paths. The approach utilized in this study may be applicable to understanding hydrogeochemical processes in other complex volcanic terrains.     

Analysis of extreme temperatures for four sites across Peninsular Spain

Statistical analyses regarding climate studies have often used the average temperature as one of the main variables. However, the tails of the respective distributions are also crucial and have become increasingly considered in recent years. As the Intergovernmental Panel on Climate Change in its fourth assessment report (IPCC 2007) states, ??the type, frequency and intensity of extreme events are expected to change as Earth??s climate changes??. In this paper, the focus is on the statistical behaviour of extreme (maximum and minimum) values of temperature, both in winter and summer. Under the framework of the Extreme Value Theory, the methodology of block maxima is employed. The generalised extreme value distribution, allowing for a linear trend in the location parameter, is fitted to data in order to capture the time tendency in the non-stationary processes. We are able to approximate expected values with a determined probability and to identify time trends of such events. Particularly, an increasing time trend in maximum and minimum temperature is generally detected which could be of great concern to public and private sectors.     

The hydrogeology of Adama-Wonji basin and assessment of groundwater level changes in Wonji wetland,Main Ethiopian Rift: results from 2D tomography and electrical sounding methods

Rise of groundwater level becomes an emerging concern at Wonji irrigation field, Main Ethiopian Rift. An integrated study based on geophysical resistivity methods is conducted at Wonji wetland to understand the link between irrigation water and the shallow aquifer system as well as to confirm the current concern of groundwater rise. The study was also intended to improve the uncertainty of understanding the hydrogeology of Wonji wetland including the extent and direction of groundwater–surface water interaction. The vertical and horizontal contacts between the different geological series of the Wonji area are resolved with 2D high-resolution geophysical imaging. Results from both VES and 2D tomography show low resistivity layers under Wonji irrigation field with narrow ranges in resistivity variation which corresponds to a homogeneous saturated layer. The geoelectric sections reveal two fault systems running NW–SE and N–S directions which impede lateral groundwater flow. Furthermore, groundwater is converged towards the Wonji irrigation site strained by these fault systems. The geophysical results show strong link between irrigation water and the shallow unconfined aquifer as well as among the local and regional flow systems.