Annually, various parts of Africa are affected by climate related impacts, such as droughts, flooding etc., to varying degrees of severity. Global and regional hydrological models have recently seen tremendous advances in improved representations of physical processes underpinning these impacts, resulting in better reproductions of observed variables such as streamflow and water extent. As a result, they are increasingly used for predicting socio-economic risks of floods, droughts and water stress in regions around the globe. However, the use of hydroclimatic models for disaster risk reductions in data-sparse regions, while gradually improving, is still limited in comparison.
This session aims to bring together communities working on different strands of African hydrology, climate and other water-related topics, including environmental and food security. We welcome both fundamental and applied research in the areas of hydrological process understanding, flood forecasting and mapping, seasonal forecasting, water resources management, climate impact assessment and societal impacts. Interdisciplinary studies aiming at increasing our understanding of the physical drivers of water-related risks and their impacts in Africa are encouraged. Case studies showcasing practical experiments and innovative solutions in decision making under large uncertainty are welcomed.
vPICO presentations: Thu, 29 Apr
The socioeconomic impacts of changes in climate-related and hydrology-related factors are increasingly acknowledged to affect the on-set of violent conflict. Full consensus upon the general mechanisms linking these factors with conflict is, however, still limited. The absence of full understanding of the non-linearities between all components and the lack of sufficient data make it therefore hard to address violent conflict risk on the long-term.
Although it is neither desirable nor feasible to make exact predictions, projections are a viable means to provide insights into potential future conflict risks and uncertainties thereof. Hence, making different projections is a legitimate way to deal with and understand these uncertainties, since the construction of diverse scenarios delivers insights into possible realizations of the future.
Through machine learning techniques, we (re)assess the major drivers of conflict for the current situation in Africa, which are then applied to project the regions-at-risk following different scenarios. The model shows to accurately reproduce observed historic patterns leading to a high ROC score of 0.91. We show that socio-economic factors are most dominant when projecting conflicts over the African continent. The projections show that there is an overall reduction in conflict risk as a result of increased economic welfare that offsets the adverse impacts of climate change and hydrologic variables. It must be noted, however, that these projections are based on current relations. In case the relations of drivers and conflict change in the future, the resulting regions-at-risk may change too. By identifying the most prominent drivers, conflict risk mitigation measures can be tuned more accurately to reduce the direct and indirect consequences of climate change on the population in Africa. As new and improved data becomes available, the model can be updated for more robust projections of conflict risk in Africa under climate change.
How to cite: de Bruin, S., Hoch, J., von Uexkull, N., Buhaug, H., and Wanders, N.: Projecting conflict risk following the Shared Socioeconomic pathways: what role for water stress and climate?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-101, https://doi.org/10.5194/egusphere-egu21-101, 2021.
The spatial structure of rainfall events over west Africa is not very well understood, and a major limitation for improving this understanding is the generally sparse rain gauge network. This lack of spatial knowledge makes it difficult to describe the state between the rain gauges, something that is important if one wants to determine which locations are likely to have received rainfall and not. Earlier work on estimating correlation structures has been limited by the long distances between rain gauges, which often has been longer than the actual correlation range.
In this talk, we will describe a simple and easily adapted method developed for calculating the decorrelation range in daily rainfall. Thanks to a new, dense daily rain gauge data set from Ghana Met agency, the spatial structure of rainfall for the different phases of the West African monsoon has been investigated. Previous studies have only considered a general decorrelation range, ignoring rainfall intensity as a factor when determining the rainfall extent. For the results presented in this talk, the decorrelation range has been estimated for 4 different rainfall intensities to explore the difference between low and high intensity events. This is analysed separately for each month at a fine spatial scale. Results on the anisotropic, i.e correlation changing with direction, pattern at the subweekly and local scale for several aggregation periods will also be presented.
It is found that the spatial correlation structure of rainfall vary greatly with the intensity of the rainfall event and the phase of the monsoon. In particular, it was determined that the intensity rather than the time of the year had the largest influence at the local scale. The westward propagation of convective systems, a well known phenomena over weekly to monthly time scales, was detected even at short aggregation periods.
How to cite: Israelsson, J., Black, E., Neves, C., Torgbor, F. F., Greatrex, H., Tanu, M., and Lamptey, P. N. L.: A flexible method for determining decorrelation ranges in rainfall applied to Ghana, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2901, https://doi.org/10.5194/egusphere-egu21-2901, 2021.
Evaporation is a major constraining factor of water availability at the land surface which makes its assessment a highly significant prerequisite for application in hydrological, agricultural, climate studies and many other disciplines at various scales. However, its importance and calculation procedures have largely been crafted around and often limited to crop productivity. The overarching consequence of this is inaccurate estimates of evaporation for other land surfaces and particularly for forest systems. Due to limited field evaporation observations attention has been focused on the application of satellite-based products. However, in the case of Africa, and the Miombo ecosystem in particular, the number of flux towers is extremely limited (very few if any) which makes it extremely difficult to evaluate available satellite-based evaporation products. In this study we used the energy balance Bowen ratio approach to estimate field evaporation in a dense Miombo Woodland which we then used to evaluate four energy balance evaporation models. The models evaluated included the MOD16, SEBS, SSEBop and WaPOR. Furthermore, cluster analysis was used to assess the similarity of the models in simulating evaporation. The results show that at daily and dekadal scale the simulated evaporation by the four models significantly varied from field evaporation observations. However, less variations were observed at monthly scale. Furthermore, all four models overestimated evaporation during the dry season (June-September) with RMSE ranges between 0.21 – 0.38 mm.day-1 and 6.64 - 9.91 mm.month-1. Based on the RMSE and biases the MOD16 (RMSE = 6.64 mm.month-1; Bias = 2.04 mm.month-1), SEBS (RMSE = 8.69 mm.month-1; Bias = 5.72 mm.month-1) and WaPOR (RMSE = 7.44 mm.month-1; Bias = 6.67 mm.month-1) ranked higher than the SSEBop (RMSE = 9.91 mm.month-1; Bias = 9.84 mm.month-1) in simulating evaporation in the Miombo Woodland. Three clusters were observed with the SEBS and WaPOR grouped together indicating their close similarity in simulating evaporation in the Miombo ecosystem while the MOD16 and SSEBop were each grouped separately. Results of this study could aid the interpretation of these evaporation models in Miombo Woodland covered basins such as the Zambezi River Basin in Southern Africa. This could help in monitoring basin water availability and ecosystem reactions and feedbacks to climate change and anthropogenic impacts.
How to cite: Zimba, H., Coenders-Gerrits, M., Kawawa, B., Schilperoort, B., Nyambe, I., and H.G. savenije, H.: Do field observations agree with satellite-based evaporation products in the Miombo Woodland of Southern Africa?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3537, https://doi.org/10.5194/egusphere-egu21-3537, 2021.
Agriculture is a key sector in fighting hunger in Sub Saharan Africa. Almost 95% of the agriculture in Africa is rain-fed and smallholder farmers play a crucial role as they produce most of the food consumed by local populations. These characteristics make the SSA agricultural landscape very diverse and particularly vulnerable to weather extremes. The ability of forecasting hydrological variability has increased in recent years due to advancements in the understanding of hydro-climatic processes, growing availability of high-resolution remote sensing datasets, and the increase of computational power, which has promoted the development of high-quality computer-based hydrological models. When adopted in data scarce regions, these models provide new insight into the hydrological budget and in characterizing the hydrological variability of these areas. In this work, we combine the hyper-resolution hydrological model HydroBlocks and the river routing model RAPID to simulate the spatial and temporal heterogeneity of the land surface processes in Malawi at 30 m resolution. The model simulations show high variability of the hydrological variables, particularly soil moisture, across the country. We use these results to further analyse water and food security indicators in the transboundary catchment of Lake Chilwa shared between Malawi and Mozambique. The start and duration of the maize cropping season and the lake level show a large interannual variability which allow us to quantify the weather-related vulnerability of the local smallholder farming system. This work is part of the research activities of the UKRI-GCRF funded project “Building research capacity for sustainable water and food security in drylands of sub-Saharan Africa” (BRECcIA - http://www.gcrf-breccia.com/).
How to cite: Anghileri, D., Vergopolan, N., Gebrechorkos, S., and Sheffield, J.: Hyper-resolution hydrological modelling to assess water and food security in Malawi, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6340, https://doi.org/10.5194/egusphere-egu21-6340, 2021.
Over the last few decades, disasters resulting from natural hazards have often derailed hard-earned development progress. This is especially true in developing countries such as in sub-Saharan Africa which was the object of this study. The majority of disasters in Africa are hydro-meteorological in origin, with droughts affecting the largest number of people and floods occurring frequently along major river systems and in many urban areas. Disasters, however, can be significantly minimised with rigorous understanding of the risk, obtained using scientific risk modelling and through effective institutional and community prevention, mitigation and preparedness. Specifically, this study focuses on the risk assessment due to both Floods and Droughts in 16 countries in Sub-Saharan Africa. The study describes the crucial role of a physically based regional hydrologic model as a common engine to assess drought and flood hazard and their subsequent risk implications on people and economy. The hydrologic simulations are at the basis of the fully probabilistic approach adopted in the study. The study develops risk estimates in both current and future climate conditions, using RCP8.5 projections, paired with socio economic development (i.e., considering population and GDP growth). Results are discussed in terms of impacts on population and different key sectors of the African economy, such as agriculture and infrastructure, while especially focusing on the direct economic losses caused by flood and drought disasters and on the food security implications of drought disasters.
How to cite: Simone, G., Rudari, R., and Rossi, L. and the CIMA, VU and WUR Team: Assessing Floods and Droughts direct impacts in sub-Saharan Africa by using a regional hydrologic model: a fully probabilistic approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7585, https://doi.org/10.5194/egusphere-egu21-7585, 2021.
Lake water balance studies in Ethiopia are commonly conducted for natural conditions without considering the impact of water abstraction. However, hydrological changes are a function of changes caused by human interventions as much as through natural processes. The Lake Tana sub-basin is one of the important basins in Ethiopia as the source of the Blue Nile river and supporter of various livelihoods including considerable number of small-scale farmers. With Ethiopia’s ambitious plan to expand irrigation at different scales to feed the growing population, the Lake Tana sub-basin is one of the selected areas by the federal government for medium scale irrigation. Moreover, the basin is experiencing booming small-scale irrigation users due to initiations by local governments, NGOs and individual farmers. Small-scale community managed irrigation schemes and farmer-led irrigations schemes are common in the basin. While communities are expected to benefit from the expanding irrigation use, there is limited information on how this irrigation expansion impacts the water balance of the sub-basin.
In this study the area under small-scale irrigation is estimated through inventory survey of woredas (districts) that are within the Lake Tana sub-basin and cover the four main tributaries (Gilgel Abay, Ribb, Gumara, and Megech). The inventory from 16 woredas showed more than 30,000 ha is under small-scale irrigation in the Lake Tana sub-basin in 2020. The dominant water source for irrigation is found to be surface water through diversion from rivers and streams. This accounts for 80% of irrigation water source. The other 20% comes from shallow groundwater sources, which are mainly located in the eastern part of the sub-basin in the floodplain in the Fogera area.
This study investigates the current situation of irrigation water abstraction through water abstraction surveys in selected locations in the dry-season and evaluates the impact of water abstraction on the long-term water balance of the sub-basin. Previous studies indicate that Gilgel Abay sub-basin, for instance, shows a decreasing dry season flow in the past decades, which might be associated with dry season water abstraction. The current survey provides the gross diversion of water from rivers to canals in the selected schemes. Preliminary results show large amount of water is being diverted by medium irrigation schemes but also collectively by small-scale irrigation schemes. Continuation of such water abstraction levels will be a concern to the water balance of the sub-basin as it increases losses without productive use and calls for better water management practices.
How to cite: Taye, M. T. and Haile, A. T.: Impacts of human intervention through irrigation on hydrological responses of Lake Tana sub-basin, upper Blue Nile, Ethiopia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9012, https://doi.org/10.5194/egusphere-egu21-9012, 2021.
Burundi is one of the poorest countries in the world with about 65% of the population living below the poverty line and suffering from alarming food insecurity. Its population is highly dependent on rain-fed agriculture, which makes them extremely sensitive to climate variability and extremes for their subsistence. During the last decades, heavy rains, floods, and landslides suffered by Burundi’s population have led to severe famines, death, conflicts, and internal displacement among other fatalities, indicating the high vulnerability of this region to extreme events. Therefore, it is of vital importance to provide detailed information about the potential impacts of climate change in order to enhance adaptation options and preparedness in a country for which little information about climate projections and hydro-climatic impacts is available.
In this work, we investigated the changes in future climate over Burundi projected by a set of 13 regional climate models, for two future periods, under RCP4.5 and RCP8.5. The projections from CORDEX models have been used as forcing climate for the eco-hydrological Soil and Water Integrated Model (SWIM) in order to assess future changes in mean and extreme river discharge and water availability across Burundi.
Our results indicate that unabated climate change will lead to faster and more severe warming over Burundi than the global mean. Precipitation will increase in the north of Burundi despite a possible prolongation of the dry season, and will decrease in the south, with the exception of the months core of the rainy season that show the highest rise along the year and across the country. The increase in the frequency, magnitude, and intensity of extreme climate events (daily temperature, dry and wet events) will characterize the future climate in this region according to CORDEX models.
These changes get translated into increases of discharge in North Burundi across the whole year in all future scenarios and periods (up to 196% in annual streamflow in small catchments and 40% in larger ones), and slight decreases in the south from February to October (up to 7%). The increase of daily and annual extreme river discharges, their probabilities of exceedance, and the decrease in their recurrence intervals implies a higher risk of floods in magnitude and frequency.
These findings indicate the critical importance of adaptation of land and water management to changing hydro-climatic conditions in Burundi to improve food security and support its development.
How to cite: Rivas López, M. R., Liersch, S., and Hattermann, F. F.: Potential hydro-meteorological impacts over Burundi from climate change, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9562, https://doi.org/10.5194/egusphere-egu21-9562, 2021.
Recently, the Global Precipitation Measurement (GPM) satellite constellation measurements combined in the Integrated Multi-satellite Retrievals for GPM (IMERG) algorithm is provided. This GPM-IMERG dataset provides potentially useful precipitation data for regions with a low density of rain gauges. This study is aimed to evaluate the accuracy of the near real-time product (IMERG-E) compared to observed rainfall and its suitability for hydrological modeling over the Ghdat watershed located upstream the city of Marrakech. Several statistical indices have been computed and a hydrological model has been driven with IMERG-E rainfall to estimate its suitability to simulate floods during the period from 2011 to 2018. The following results were obtained: (1) In terms of the precipitation detection capability, the IMERG-E performs better at reproducing the different precipitation statistics at the catchment scale rather than at the pixel scale (2) compared to the rain gauge data, satellite precipitation data overestimates rainfall amounts with a relative Bias of +35.61% (3) The flood events can be simulated with the hydrological model using both the observed and the IMERG-E satellite precipitation data with a Nash–Sutcliffe efficiency coefficient of 0.58 and 0.71, respectively. The results of this study indicate that the GPM-IMERG-E precipitation estimates can be used for flood modeling in semi-arid regions such as Morocco and provide a valuable alternative to ground-based precipitation measurements.
How to cite: Saouabe, T., El Khalki, E. M., Saidi, M. E. M., Najmi, A., Hadri, A., Rachidi, S., Jadoud, M., and Tramblay, Y.: Performance evaluation of the GPM-IMERG product for flood modeling over Moroccan mountainous basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10307, https://doi.org/10.5194/egusphere-egu21-10307, 2021.
This study focus on the catchment of Ambouli wadi which is one of the country’s largest watersheds covering 794 km² (3.5 % of the total area of the Republic of Djibouti). Because of its groundwater resources, this exoreic watershed is of major importance. Indeed, the aquifer is the main source of drinking water supply for the city of Djibouti-city. In addition, this wadi is also responsible for floods causing human suffering and severe economic damages. Despite the importance of the catchment for the development of Djibouti-city, Ambouli wadi has been the subject of few scientific studies. This partly explains the scarcity of rainfall stations and therefore data in this area. Analysis of the spatio-temporal variability of rainfall is required to assess the risk of flooding.
In an arid country like the Republic of Djibouti flash floods are an important concern for the management of water resources systems and risk prevention and protection. The desertic climate of the country is characterized by high levels of temperature and evaporation, and also by very weak and irregular annual rainfall, distributed in two major seasons : a cooler season (from October to March) with high relative humidity and low temperatures comprised between 22°C and 30°C, and a hot and dry season (from June to September).
Rain data were collected from a network of 9 raingauge stations at different time scales, from monthly to hourly. These data are provided by the national meteorological agency (4 stations) and the early warning system of CERD National Research Center (5 stations).
The spatio-temporal variability of rainfall, is characterized using the Standardized Precipitation Index (SPI) and the analysis of rainfall normals over 30 years (1951-1980 and 1961-1990). Long time series data were available from 4 of the 9 stations: (Djibouti-serpent, Djibouti-aeorodrome, Oueah and Arta). At annual scale, the variability is clearly described by a succession of dry and humid years. Also, the monthly rainfall clearly demonstrates the well-known bimodal precipitation regime of east Africa. It shows, two peaks corresponding to the « long rain » and the « short rain » rainy seasons, which correspond to the period of March-April-May and of October-November-December, respectively. On the other hand, we also observe a dry period which is characterized by a rainfall deficit (negative rainfall index for almost all the stations) corresponding to the boreal summer (June to September). Daily data is currently collecting from the Djibouti-aerodrome station (1981-2017) for a better understanding of the precipitation regime. Rainy days are computed from daily data (rainfall > 1 mm) and we find an annual average of 11 wet days with a minimum in 1988 (1 rainy day) and a maximum in 1993 (23 rainy days).
How to cite: Moussa Omar, G., Paturel, J.-E., Salles, C., Mahe, G., and Jalludin, M.: How to assess the vulnerability and the risk of flooding of the most important catchment in the Republic of Djibouti?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12086, https://doi.org/10.5194/egusphere-egu21-12086, 2021.
Rising human populations increase the demand for food and lead to the intensification of agriculture and nitrogen fertilization to sustain productivity. In the tropical montane Mau Forest Complex in Kenya, the annual export of nitrogen from a catchment dominated by smallholder agriculture were reported to almost double those from the native forest. Despite the assumption that this excess nitrogen originates from fertilizer application, there are no studies that provide empirical information on the amount and spatial distribution of nitrogen inputs from smallholder agriculture into these catchments. Given the fact that the Mau Forest complex lost 25% of its forest cover to agriculture and other encroachment activities, such information is essential to better quantify the effect of smallholder farming practices on the nitrogen cycle and its contribution to catchment nitrogen export.
This study aimed at quantifying spatial distribution of fertilizer inputs in a smallholder catchment in the Mau Forest Complex using a household survey (n=185).
Results show that almost all farmers (99.4%) use inorganic fertilizers with an average nitrogen (N) application rate of 41±7.8 kg N ha-1 yr-1 diammonium phosphate (DAP). Among the DAP users, 16% apply in addition 79±3.9 kg N ha-1 yr-1 as NPK fertilizer, and 11% add 29±5.3 kg N ha-1 yr-1 as calcium ammonium nitrate (CAN). Overall, the average nitrogen input from inorganic fertilizers is 64±13.7 kg N ha-1 yr-1. Only 6% of the cropland is fertilized using manure and other farmland residues with 79% of farmers anticipating to increase their inorganic fertilizer application rates in the future.
In conclusion, a future increase in nitrogen application rates on farmland in combination with continued conversion of natural forest to agricultural land raises a concern on whether nitrogen export will increase further, posing a threat to drinking water quality and the health of aquatic ecosystems downstream. To balance the trade-off between food production and the catchment nitrogen balance, there is a need to train farmers on appropriate methods, timing and optimal amounts of fertilizer application to prevent unnecessary losses.
How to cite: Kasebele, M., Jacobs, S., Rufino, M., and Breuer, L.: Nitrogen inputs from smallholder farming in a tropical montane catchment - current state and outlook, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13405, https://doi.org/10.5194/egusphere-egu21-13405, 2021.
Access to water is a critical issue in Sub-Saharan Africa. The objective of our work was to assess spatiotemporal variability in water storage using GRACE satellites in the major aquifers and potential for development. Results show that Total Water Storage (TWS) variability tracked by GRACE satellites is dominated by interannual variability in most aquifer systems driven by dry and wet climate cycles, such as El Nino Southern Oscillation, Indian Ocean Dipole, Pacific Decadal Oscillation and others. Climate cycles result in systems being subjected to droughts or floods, which is challenging for water resources management. Linear trends in TWS were limited to west Africa attributed to land use change and north Africa linked to water use. Variability in storage of some reservoirs and groundwater hydrographs is similar to storage variability from GRACE satellites. Examples of approaches toward sustainable management of water resources include storage of excess flood water for use during droughts in surface reservoirs, conjunctive use of surface water and groundwater, and managed aquifer recharge. Understanding the linkages between climate cycles and water storage should help optimize water management within this framework.
How to cite: Scanlon, B. R., Rateb, A., and Xie, H.: Assessing Water Availability for Development in Africa using GRACE Satellites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16344, https://doi.org/10.5194/egusphere-egu21-16344, 2021.
Groundwater is a resource of increasing prominence in Africa whose potential has still to be developed in full capacity. While it is clear that data gathering is of outmost importance to achieve a certain level of knowledge for many African aquifer systems, Information and Communication Technology may support and boost efficient data management. This way, more technically sound and even community-based decisions may be made. In this context, we attempted to frame the state-of-the-art on the use of digital tools for supporting sustainable groundwater management in the African continent. By means of a comprehensive literature review and performing investigations via a structured questionnaire on ongoing practices at institutional/private sector level, the results allow a clear view on the present level of knowledge and on the diffusion of such tools.
At present the use of digital tools/groundwater numerical models is deemed to be an occasional activity, mostly applied for large engineering projects or basic modelling studies, rarely used for planning and management of the resource. All in all, their use in the period 2000-2020 can be considered low, with a clear difference between North Africa and Sub-Saharan African countries. Digital tools are recognised as needed tools by African institutions at national/regional level. However, skills and capacities are largely missing: the need for capacity building is (extremely) high. Commercial software solutions still dominate the market, while open source ones appear in increasing trend of usage in the last years.
Finally, main barriers in the use of digital tools are: i) scarcity of data, ii) inadequate resources (lack of computing resources), and iii) missing capacities (lack of computing skills). In addition to these, the lack of adequate and well-functioning Internet connection is considered one of the main bottleneck in favouring the spread of new technologies. Capacity building and knowledge transfer has then to be on top of the agenda for a digital groundwater governance in Africa. In particular, training should be directed to favour the use (and re-reuse) of open-source applications and the often huge amount of information and contents available. A generation of experts with a sounding interdisciplinary background should be able, in five to ten years, to properly manage ICT applications.
How to cite: Rossetto, R., Veroli, S., Chekirbane, A., Crestaz, E., and Carmona-Moreno, C.: Framing the state-of-the-art on the use of software for sustainable groundwater resource management in the African continent, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16563, https://doi.org/10.5194/egusphere-egu21-16563, 2021.
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