1,721,016 research outputs found
Impact of Climate Variability and Change on Hydrological Extremes of the Upper Blue Nile Basin
No full textOver the recent decades, the world has witnessed frequent and intense hydro-climatic extremes in the form of floods, droughts, heat waves, cyclones and other phenomena in various geographical locations. The scientific community offered substantial attention for the alteration in extremes and possible relations with climate variability and/or change since climate is a key driver to various natural and managed systems. Hydrological cycle and the climate system have close interactions, subsequently local and regional hydrology will bear the immediate consequences of climate variability/change. Changes in hydrological extremes have considerable implications on the planning and management of water resources of a given basin. Accordingly, quantification of possible hydrological impacts due to climate alteration and incorporation of the outcomes in engineering designs and policy formulations is crucial. Recent changes in climate observed as global warming are commonly attributed to anthropogenic activities such as the burning of fossil fuels that increase the concentration of greenhouse gases in the atmosphere. Nevertheless, changes in climate may be due to natural internal processes or external forcings in addition to persistent anthropogenic changes in the composition of the atmosphere or in land use. The most advanced tools such as Global Climate Models (GCMs) are being used to project the future climate and provide information for impact investigators in various aspects of the environment and society. Quantifying the impact of climate change on the future hydrological extremes is undoubtedly important. Nonetheless, prior to such estimations it is wise to retrospectively investigate the historical variability of hydro-climatic extremes to better understand their patterns, causes and effects. This research was aimed at studying the observed climate variability and the impact of future climate change on hydrological extremes of one of the most important river basins in Africa, the upper Blue Nile basin. The importance of this study is guided by the location of the study area which is highly vulnerable to climate variability and change as well as its large discharge contribution to the entire Nile basin system. This study was supported by the readily available data from climate models as well as from selected long-term observations. The study commenced with addressing its first research questions which required assessment of historical patterns and trends in hydro-climatic extremes. This analysis aimed at seeking evidence for a certain pattern in historical records and unravelling whether the recent changes are statistically significant. This analysis provides information on whether certain periods are wet or dry compared to the long-term natural variability. Furthermore, it provides the possibility of separating natural variability patterns from long-term trends in extremes that could be attributed to anthropogenic causes. Long-term records of rainfall extremes, high and low flows from the basin were considered for this analysis. The outcome of this study was that there is an evidence of (multi-) decadal oscillation on hydro-climatic extremes of the basin and a statistically significant negative anomaly period during the 1980s. However, the recent years did not show consistent increasing or decreasing trend. Hence, it is intricate to conclude the recent changes in the extremes on anthropogenic climate change. Alternatively, as a possible cause for the historical variability pattern in the hydro-climatic extremes, large scale atmospheric variables from Pacific and Atlantic Oceans were found to have strong correlations. Identification of the primary causes of the observed variability patterns in the hydro-climatic extremes was conducted making use of lumped conceptual hydrological models and statistical analysis on the simulated results. The hydrological models were used to simulate a long-term time series with the assumption that if changes in catchment behaviour had significant influence on the temporal dynamics of the basins extreme flows, a clear difference would be detected between the simulated and observed variability results. The outcome of the analysis revealed that there is no discernible trend of the difference between the variability pattern of the simulations and that of the observations over time. Additionally there is no perceptible change in the catchment response behaviour between different periods. Hence, the temporal dynamics of extreme flows of the Blue Nile River are much more influenced by (multi-) decadal climate variability rather than the changes in land use or other catchment characteristics. Considering that the basin is one of the data scarce regions and the presence of a multi-decadal oscillation pattern, it was important to assess the effect of the variability patterns on the derivation of flow-duration-frequency (QDF) predictions when short-term data is used. The study showed that the QDF predictions are dependent on the period used for the analysis. For instance, high flow QDF statistics estimated using the 1980s data required bias correction of around 15% to match with the long-term period estimation. A strong correlation was found between temporal variability of high flow extremes and that of large scale atmospheric variables. This relation can be used as an indicator for correcting the bias in the estimation of high flow quantiles that utilized short term data. The final research objective sought to analyse the impact of anthropogenic climate change on the future extremes to determine the potential direction of change by also investigating the influence of different downscaling methods. The results indicated that the choice of downscaling method was an important factor to be considered and that the results based on one downscaling method may not entirely give the full picture. For the upper Blue Nile basin, the chosen downscaling methods agree in projecting mostly decreasing flow for the main rainy season. The reason isboth decreasing rainfall and increasing evapotranspiration at seasonal scale. It is worth mentioning that the uncertainty range obtained in this study can get wider if more GCMs, downscaling methods and hydrological models were used. However, despite this uncertainty, water managers are recommended to take actions that are based on no-regret strategies.status: Publishe
Nexus thinking for sustainable irrigation
No full textOn the 8th International Day of Women & Girls in Science, clean water and sanitation are front and center. Within the framework of the Sustainable Development Goals, the high-level sessions at the United Nations Headquarters in New York will advocate for women in science. Importantly, the agenda also recognizes the role of women in the communities targeted by development programs. On both fronts, observes IWMI Researcher Dr Meron Teferi Taye, “There’s more awareness than before. But on the ground, it’s not always the case that gender mainstreaming has taken place.
Groundwater scarcity and management in the arid areas in East Africa
No full textArid areas in East Africa are characterized by physical water scarcity. The physical water scarcity is further exacerbated by poor water quality (mainly salinity and fluoride) of mainly groundwater sources. Combined physical water scarcity and poor water quality makes the region a hydrogeologically difficult environment. Nevertheless, some viable high-yielding aquifers exist in East Africa. Difficult hydrogeology means that the best practices of reaching rural dwellers, towns, and urban centers require specialized financial, technical, and engineering approaches. The chapter describes the hydrogeology difficulty and the ongoing management strategies and its implications for the Water, Sanitation and Hygiene sector in East Africa arid regions
Hydrologic extremes in a changing climate: a review of extremes in East Africa
Get PDFPurpose: Eastern Africa has a complex hydroclimate and socio-economic context, making it vulnerable to climate change-induced hydrological extremes. This review presents recent research on drivers and typologies of extremes across different geographies and highlights challenges and improvements in forecasting hydrological extremes at various timescales.
Recent Findings: Droughts and floods remain the major challenges of the region. Recently, frequent alterations between droughts and floods have been a common occurrence and concern. Research underlines the heterogeneity of extremes and the impact of climate change as increased intensity and duration of extremes. Moreover, the importance of local and antecedent conditions in changing the characteristics of extremes is emphasized.
Summary: A better understanding of these drivers and how they interact is required. Observational and modeling tools must capture these relationships and extremes on short timescales. Although there are improvements in forecasting these extremes, providing relevant information beyond meteorological variables requires further research
Hydrologic extremes in a changing climate: a review of extremes in East Africa
No full textPurpose: Eastern Africa has a complex hydroclimate and socio-economic context, making it vulnerable to climate change induced hydrological extremes. This review presents recent research on drivers and typologies of extremes across different geographies and highlights challenges and improvements in forecasting hydrological extremes at various timescales.
Recent Findings: Droughts and foods remain the major challenges of the region. Recently, frequent alterations between droughts and foods have been a common occurrence and concern. Research underlines the heterogeneity of extremes and the impact of climate change as increased intensity and duration of extremes. Moreover, the importance of local and antecedent conditions in changing the characteristics of extremes is emphasized.
Summary: A better understanding of these drivers and how they interact is required. Observational and modeling tools must capture these relationships and extremes on short timescales. Although there are improvements in forecasting these extremes, providing relevant information beyond meteorological variables requires further research
Influence of downscaling methods in projecting climate change impact on hydrological extremes of upper Blue Nile basin
No full textMethods from two statistical downscaling categories were used to investigate the impact of climate change on high rainfall and flow extremes of the upper Blue Nile basin. The main downscaling differences considered were on the rainfall variable while a generally similar method was applied for temperature. The applied downscaling methods are a stochastic weather generator, LARS-WG, and an advanced change factor method, the Quantile Perturbation Method (QPM). These were applied on 10 GCM runs and two emission scenarios (A1B and B1). The downscaled rainfall and evapotranspiration were input into a calibrated and validated lumped conceptual model. The future simulations were conducted for 2050s and 2090s horizon and were compared
with 1980–2000 control period. From the results all downscaling methods agree in projecting increase in temperature for both periods. Nevertheless, the change signal on the rainfall was dependent on the climate model and the downscaling method applied. LARS weather generator was good for monthly statistics although caution has to be
15 taken when it is applied for impact analysis dealing with extremes, as it showed a deviation from the extreme value distribution’s tail shape. Contrary, the QPM method was good for extreme cases but only for good quality daily climate model data. The study showed the choice of downscaling method is an important factor to be considered and results based on one downscaling method may not give the full picture. Regardless, the projections on the extreme high flows and the mean main rainy season flow mostly showed a decreasing change signal for both periods. This is either by decreasing rainfall or increasing evapotranspiration depending on the downscaling method.sponsorship: This study has been linked to FRIEND/NILE projects of UNESCO and the Flanders in Trust Fund of the Flemish Government of Belgium. The authors acknowledge meteorological data provision from the National Meteorological Agency in Ethiopia. The study was financially supported by a DBOF scholarship of KU Leuven.status: Publishe
Identifying sources of temporal variability in hydrological extremes of the upper Blue Nile basin
No full textIt is known that changes in catchment runoff variability are a function of changes in climate as well as catchment behavior. For proper management of a certain watershed it is important to have a good understanding of the main causes of variability. Specifically, changes in extreme conditions of water resources are imperative as their consequences are far reaching. This paper attempts to identify the cause of hydrological extremes variability in the upper Blue Nile basin of Ethiopia. A method is proposed to utilize conceptual hydrological models to simulate long term (41 years) hydro-meteorological data and analyse the
outputs using the Quantile Perturbation Method (QPM) specially designed for investigation of the temporal variability of extreme values in time series over multi-annual to (multi-)decadal time scales. Two conceptual hydrological models were calibrated and evaluated for their performance to simulate extreme high flows and changes in these flows for corresponding changes in rainfall conditions. The temporal variability results show similar patterns for simulated and observed extreme flows. This indicates the major influence of climate variability in extreme flows as demonstrated by the rainfall input in the
models. There is no discernible change in the catchment response, e.g. quick runoff coefficient as a function of soil saturation state, between periods of the 1960–1970s, the 1980s and the 1990–2000s, which are attributed to land policy changes. This shows the influence of changes in catchment characteristics is minimal. (Multi-)decadal climate variability is identified as the main cause of temporal variation in hydrological extremes of the Blue Nile basin.sponsorship: DBOF scholarship KU Leuven
FRIEND/Nile basin project of UNESCO & Flanders in Trust Fundstatus: Publishe
Temporal variability of hydro-climatic extremes in the Blue Nile basin
No full textThis paper examines the long term historical changes in frequency and amplitude of hydro-climatic extremes in the Blue Nile basin using the second half of 20th century data. The temporal variability of basin-wide rainfall extremes and river flow extremes from four gauging stations were investigated under the hypothesis of no trend and no persistence in time. Based on quantile anomaly analysis method, decadal variations in extreme daily, monthly and annual quantiles were studied and the periods of statistical significance identified. The analysis showed that high and low river flows and rainfall depths do not vary in time in a fully random way because they have particular variation pattern. Their extremes show significant decadal variations. The 1980s had statistically significant negative anomalies in extremes in comparison with the long term reference period 1964-2009, while the 1960s-1970s and the 1990s-2000s had positive anomalies although less significant. There is neither consistent increasing nor decreasing trend in rainfall and flow extremes of recent years. Therefore, anticipated trends due to global warming could not be identified. Conversely, low flow extremes show an increasing trend during the last decade, which could be related to the effect of water regulation works at the outlet of Lake Tana. Moreover, similar patterns and statistically significant correlations were found between climatic indices representing Pacific and Atlantic oceans and the Blue Nile rainfalls/flow extremes. Changes that occur on the Pacific Ocean appear to be a main driver for the decadal oscillations in climate and related high and low water availability.sponsorship: DBOF scholarship KU Leuven
FRIEND-Nile project of UNESCO & Flanders in Trust fundstatus: Publishe
Bijsturing van de Vlaamse klimaatscenario's voor hydrologische en hydrodynamische impactanalyse inclusief hydrologische extremen
No full textsponsorship: Flemish Environment Agency (VMM) - AOWstatus: Publishe
Statistische analyse nieuwe CMIP5 klimaatmodelruns voor België
No full textsponsorship: Vlaamse Milieumaatschappij – Afdeling Operationeel Waterbeheerstatus: Publishe
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