The Impact of River Regulation on Downstream Socio-Hydrologic Systems in Ethiopia

In recent years, a renewed interest in large-scale hydraulic interventions has developed, frequently justified by the premise of making the agricultural and energy sectors climate-resilient. Despite this important climate effort, hydraulic interventions are controversial and have far-reaching impacts on river-dependent communities and the environment. Drawing on gis analyses of remote sensing images and qualitative and quantitative empirical evidence from the field, this PhD dissertation focused on the impact of two large dams and one inter-basin water transfer (ibwt) on downstream socio-hydrologic systems (coupled human-water systems) in Ethiopia. The results indicated that (i) downstream hydrogeomorphic systems drastically altered after the implementation of the hydraulic interventions, (ii) small-scale farmer-led irrigation systems more efficiently increased crop productivities than several large-scale irrigation projects, (iii) the newly induced hydrologic regimes strongly altered downstream social interactions due to impeded river crossing and (iv) ill-prepared land redistributions and resettlements left thousands of households with a high risk of impoverishment.

Inundation depth and duration impacts on wetland soils and vegetation : state of knowledge

The following synthesizes studies investigating plant and soil responses to increased inundation in order to support ecosystem restoration efforts related to the alteration of natural wetland hydrodynamics. Specific topics include hydrologic regimes, soil response to inundation, and implications for vegetation communities exposed to increased water depths. Results highlight the important interactions between water, soils, and vegetation that determine the trajectory and fate of wetland ecosystems, including the development of feedback loops related to marsh degradation and subsidence. This report then discusses the knowledge gaps related to implications of inundation depth, timing, and duration within an ecosystem restoration context, identifying opportunities for future research while providing source materials for practitioners developing restoration projects.

Stormwater management by low impact development practices

Due to the effects of climate change, urban and suburban expansion, and urban pollutants on runoff quality and quantity, applying contemporary stormwater management approaches in urban areas have become more critical. Low impact development (LID) practices are environmentally friendly stormwater management methods, seeking to replicate the natural hydrologic regimes in urban areas. They have become popular methods to reduce/prevent adverse stormwater runoff impacts in urban catchments, mainly by improving on-site infiltration or harvesting and reusing runoff. This study introduces LID practices and the importance of using them. Thereafter, the structure, benefits, and limitations of common LID practices are explained to help water resource engineers and urban planners have a better understanding of these practices, and choose the most suitable LID practice based on the needs of the project and features of the site.

Modeling Resilience and Sustainability of Water-Subsidized Systems: An Example from Northwest Costa Rica

Water-subsidized systems are growing in number and maintaining the sustainability of such complex systems presents unique challenges. Interbasin water transfer creates new sociohydrological dynamics that come with tradeoffs and potential regime shifts. The Tempisque-Bebedero watershed in Northwest Costa Rica typifies this class of watershed: Transferred water is used for power generation and irrigated agriculture with significant downstream environmental impacts. To improve and clarify our understanding of the effects of social and biophysical factors on the resilience of such systems, a stylized dynamical systems model was developed, using as a guide the situation in the Tempisque-Bebedero watershed. This model was analyzed to understand the nature of socio-hydrologic regimes that exist in this class of basins and what factors determine these regimes. The model analysis revealed five distinct regimes and different regime shift behaviors dependent on environmental and policy conditions. This work offers insights into other complex socio-hydrologic systems with similar processes.

Impacts of Global Warming of 1.5, 2.0 and 3.0 °C on Hydrologic Regimes in the Northeastern U.S.

Regional climate change impacts show a wide range of variations under different levels of global warming. Watersheds in the northeastern region of the United States (NEUS) are projected to undergo the most severe impacts from climate change in the forms of extreme precipitation events, floods and drought, sea level rise, etc. As such, there is high possibility that hydrologic regimes in the NEUS may be altered in the future, which can be absolutely devastating for managing water resources and ecological balance across different watersheds. In this study, we present a comprehensive impact analysis using different hydrologic indicators across selected watersheds in the NEUS under different thresholds of global temperature increases (1.5, 2.0 and 3.0 °C). Precipitation and temperature projections from fourteen downscaled Global Circulation Models (GCMs) under the representative concentration pathway (RCP) 8.5 greenhouse gas concentration pathway are used as inputs into a distributed hydrological model to obtain future streamflow conditions. Overall, the results indicate that the majority of the selected watersheds will enter a wetter regime, particularly during the months of winter, while flow conditions during late summer and fall indicate a dry future under all three thresholds of temperature increase. The estimation of time of emergence of new hydrological regimes show large uncertainties under 1.5 and 2.0 °C global temperature increases; however, most of the GCM projections show a strong consensus that new hydrological regimes may appear in the NEUS watersheds under 3.0 °C temperature increase.

The Dynamic Factors of Desertification and Their Impact on Ecosystems

Even from the middle of the 19th century desertification was considered a controlled artificial process with anthropic factors as the main cause. Forest treatments applied in tropical forests in an incorrect manner have led to soil degradations and a destabilization of climatic and hydrologic regimes. In these conditions, desertification and its indicators have regressed in regard with agricultural and forestry productivity. This was caused by a non-sustainable management characterised by exploitation anthropic activities realized in an uncontrolled procedure. In 1994, the desertification definition was updated by introducing climatic factors and abusive grazing as consequences of field degradation. The main purpose of this article is to understand the concept of” desertification” and to elaborate a qualitative analysis based on published scientific articles in order to investigate the influence factors that led to the apparition of this phenomenon in Europe, Asia, Latin America and Africa. The scientific objectives consist in analysing the evolution of desertification in different affected regions as well as to analyse the influence factors that led to the ecological destabilization of agricultural and forestry domains through degradation and a reduction of silvo-biologic productivity. The results were based on analysing 74 articles published in specialty agricultural and forestry journals or magazines by institutions or associations of owners, managers of waters and forests, forestry specialists, academicians and ecologists. They have all studied the present problem posed by desertification as well as modern applied methods for rehabilitating ecologic conditions in degraded ecosystems from semi-arid, arid and extremely arid areas.

Impacts of global warming of 1.50C, 2.00C and 3.00C on hydrologic regimes in the northeastern U.S.

Regional climate change impacts show wide range of variations under different levels of global warming. Watersheds in the northeastern region of United States (NEUS) are projected to undergo most severe impacts from climate change in the forms of extreme precipitation events, floods and drought, sea level rise etc. As such, there is high possibility that hydrologic regimes in the NEUS may get altered in the future which can be absolutely devastating for managing water resources and ecological balance across different watersheds. In this study, therefore, we present a comprehensive impact analysis using different hydrologic indicators across selected watersheds in the NEUS under different thresholds of global temperature increases (1.5C, 2.0C and 3.0C). Precipitation and temperature projections from fourteen downscaled GCMs under RCP8.5 greenhouse gas concentration pathway are used as inputs into a distributed hydrological model to obtain future streamflow conditions. Overall, the results indicate that majority of the selected watersheds will enter into a wetter regime particularly during the months of winter while flow conditions during late summer and fall indicate a dry future under all three thresholds of temperature increases. The estimation of time of emergence of new hydrological regimes show large uncertainties under 1.5C and 2.0C global temperature increases, however, most of the GCM projections show strong consensus that new hydrological regimes may appear in the NEUS watersheds under 3.0C temperature increase.