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Lake Manyara is a terminal soda lake in the East African Rift System in Northern Tanzania, which provides an important habitat for flora and fauna in the area. Its size also reflects the water availability in the catchment, which is of great importance for local human inhabitants and wildlife. Lake levels naturally fluctuate over the year, but they have been following a shrinking trend in the past decades. The factors that contribute to the shrinkage of the lake have been researched in several studies, but the cause of the shrinkage remained unknown. The aim of this research was to unravel the causes of the shrinkage of Lake Manyara and to discuss management options that best guarantee a sustainable future for the lake. A literature review was carried out to determine which factors contribute to the shrinkage of Lake Manyara. Results strongly suggest that both the use of irrigation water and changes in land use and land cover have neglectable impacts on the shrinkage of the lake. The combination of precipitation and evapotranspiration seems to have a large impact on the size of Lake Manyara. Future rainfall is uncertain because of the East African Climate Paradox, but temperatures in the area will almost certainly increase in the coming decades. Increasing temperatures will lead to increased amounts of evapotranspiration and enhanced periods of droughts. This will almost certainly cause a decreasing size of Lake Manyara in the coming decades, mainly in the dry season. To determine the contribution of gully erosion to the shrinking lake levels, a remote sensing study based on images from Google Earth Pro was performed. Sedimentation in Lake Manyara does occur as a result of gully erosion, but the contribution of sediment load to the shrinkage of the lake is minor when compared to climatological changes. Management strategies that could enhance environmental rehabilitation help to adapt to drought conditions were discussed. It was shown that socioeconomical factors sh

Arid and semi-arid regions are prone to wind erosion due to scarce rainfall and low vegetation cover. As transport of sediment by creep, saltation and suspension can lead to problems affecting the environment, climate and human health, methods to reduce aeolian erosion are continuously being researched. Water harvesting techniques have been applied in dry areas for a long time to reduce wind erosion, by increasing water storage and enhancing vegetation growth. In the Jordanian Badia (desert), Vallerani water harvesting structures have been implemented on an experimental site, but the effect on wind erosion reduction remains unclear. This study aimed to quantify the reduction in wind erosion by integrating a small scale cellular automaton model and a large scale model for Badia conditions with and without water harvesting structures. It also compared different transport equations to assess the uncertainty of the obtained values. The results are promising, as reductions in sediment transport of over 88% were obtained for the plot scale model. Outscaling to suitable areas is similarly promising, as the large scale model determined 60-100% reduction in dust concentration near the surface for areas where water harvesting structures are implemented on a regional scale. The coupling between the models can be optimized through the creation of new, specialized land cover classes with plot scale model values to be implemented in the large scale model. Improvements to the plot scale model can be made to include better vegetation spatial distribution, but field measurements are required to verify the use of model governing equations and validate the modelled sediment fluxes.

The eastern African region continues to be extremely vulnerable to droughts. In Kenya alone, about 50 million people have been affected by droughts since 1983. Rainfall in the region is bi-modal, with the long rains in the boreal spring and the short rains in the boreal autumn. Seasonal forecasts of rainfall are essential to improve drought preparedness and mitigation for water managers and farmers. The aim of this study was to forecast monthly rainfall totals at a set of locations in the equatorial east African region, using an Artificial Neural Network (ANN) called a Long Short-Term Memory (LSTM). The input dataset consisted of seasonal forecasts (SEAS5) of precipitation and temperature from the European Centre for Medium-Range Weather Forecasts (ECMWF) in combination with several climate indices related to the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Madden-Julian Oscillation (MJO). The performance was assessed by means of the WNDI (Weighted Non-Dimensional Index) and the anomaly correlation. Benchmarks for the evaluation included: climatology, precipitation forecasts by SEAS5 and a multi-variate linear model based on the same input data as the LSTM. In addition, the ability of the model to forecasts anomalous seasonal rainfall was assessed based on the 2x2 contingency table and associated scores (hit rate, false alarm rate and Clayton Skill Score). Sensitivity analysis was carried out to evaluate the relative importance of the features in the input dataset. For all lead times, the LSTM outperformed both the linear model and SEAS5 in terms of both anomaly correlation and WNDI, although it is not clear whether or not this is statistically significant. Especially at longer lead times the LSTM shows improved performance relative to SEAS5, due to a good coupling with the climate indices. At a lead time of 4 months and in terms of WNDI and the anomaly correlation, differences in performance between the long rains and the short rains w

Arid regions cover around one third of the Earth’s land surface, including 80% of Jordan. These regions may be suitable for the storage of carbon in their soils, providing environmental and economic benefits. This study was conducted to quantify the potential for soil carbon sequestration in dryland micro-rainwater harvesting (Vallerani) structures. The effect of changing climatic and land management conditions was investigated at the International Centre for Agricultural Research (ICARDA) field site in Al Majidiyya, Jordan. Field data was combined with modelling of carbon stocks using RothC-26.3 to meet this aim. Upscaling of the results and consideration of resultant ecosystem services was completed using the inVEST modelling tools. Results suggest that implementing Vallerani structures can lead to an increase in carbon stocks of 1.75 t/ha at the structure ridge and 4.26 t/ha in the structure furrow over a ten-year period. Upscaling these results shows a sequestration potential of 7.9 ± 0.76 t C at the study site, and almost 3 million tons across the Badia as a whole. Ecosystem service modelling demonstrates a potential economic cost of this sequestration to Jordan of as little as $17/ha, covering a large proportion of the implementation costs, even before benefits from increased food production, habitat improvement and other ecosystem services are considered. These results demonstrate that dryland water harvesting offers the potential for significant carbon sequestration compared to natural conditions. Further work should focus on constraining the economic costs and benefits to further expanding the water harvesting structures, as well as the impact of climate change on these predictions.

Lake Manyara is a terminal lake in northern Tanzania. As a destination of wildlife and part of a national park, it provides a booming tourism industry in the region. The lake also reflects water availability in the catchment used e.g. for agriculture. The catchment experiences a bimodal precipitation pattern, with a long rainy season in March-May and a short rainy season in October-December. Fluctuating lake levels, especially shrinkage of Lake Manyara during dry periods, raise concerns about the (future) water availability and potential disappearance of the lake. Possible mechanisms driving these fluctuations are: land use and land cover changes, sedimentation of the lake, irrigation water abstractions and climate change/drought. The aim of this study was to determine the impact of drought on the dynamics of Lake Manyara. The occurrence of drought over the past century in the Lake Manyara catchment (LMC), the influence of atmospheric teleconnections on LMC rainfall and the impact of drought on Lake Manyara are explored. The occurrence of meteorological drought and characteristics (duration, severity and frequency) was studied using the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) with periods of 3 (short-term droughts) and 12 (long-term droughts) months. A literature study explored the relevant teleconnections influencing East African rainfall: the El Niño-Southern Oscillation, Indian Ocean Dipole, Madden-Julian Oscillation, Southern Annular Mode and North Atlantic Oscillation. Monthly, seasonal, lead-lagged, sliding and partial correlations between rainfall and teleconnections were applied. To determine the impact of drought on Lake Manyara available observations regarding its size were linked with meteorological variables and the drought indices. In general, a drying trend was found in the LMC over the last century. The short rainy season does not show a clear drying or wetting trend. Precipitation of this

Soil erosion by water on steep slope areas is causing a land degradation problem in The West Usambara Mountains in Tanzania resulting in some land becoming unproductive. Traditional agroforestry (AF) practices seemed to have the potential to neutralize these effects maintaining the productivity of the fields and working as a biomass carbon pool, over others soil and water conservation (SWC) measures that have been promoted in the area by the government and private projects for decades like bench terraces. The aim of this thesis is to make a comparison between bench terraces, and traditional AF systems, taking into account three aspects a) effectiveness of soil erosion control, b) carbon sequestration rates, and c) net economic profit. In this study, nine agricultural plots located in the Lushoto district were used as experimental fields. The ACED method was used to quantifies soil loss from sites based on field observations and measurements of visual erosion features. The hillslope version of the revised Morgan, Morgan and Finney water erosion model (hMMF) was used to establish the water erosion patterns. C sequestration was estimated on the base of the biomass carbon and the soil organic carbon (SOC). The biomass was estimated using destructive methods and allometric equations, and the Walkley and Black method was used to determine SOC. Finally, socioeconomic information was collected to characterize its influence on the use of a specific SWC and to estimate the net operating profit of the fields. The results showed that traditional AF and terraced fields are equally effective to control soil erosion, but important differences in terms of carbon sequestration and economic benefits are evident between these two SWC measures. AF fields sequestrate six times more carbon than terraced fields, while terraced fields generate net incomes 2.6 higher than AF fields due to the differences in crop market prices and the inadequate management of AF fields.

The arid and semi-arid regions of Jordan, also known as “Badia”, are said to be increasingly degraded and soil erosion creating large gullies has become a common phenomenon. There are concerns that the rate of gully erosion has increased during the last decades due to enhanced desertification. Bedouin people in the Jordan Badia depend on herding sheep, and enhanced desertification hinders grazing and reduces a key source of income. The Jordanian government deemed it a priority to develop the Badia and reduce the damage of existing gully erosion. The objective of this research is to determine how gullies are initiated and what their progression speed is in the Jordan Badia. A gully growth time lapse of the Wadi al Wala region inside the Jordan Badia has been made in Google Earth Pro and Google Earth Engine to determine gully growth over a period of 15 years. Rangeland Hydrology and Erosion Model (RHEM) is an event-based prediction model for runoff and water erosion that was used for surface runoff quantification. Cipoletti weirs were in addition used to directly measure runoff after events. A finite element model (Hydrus 2D) was used to simulate two-dimensional water movement inside gully channel walls. Initiation of gullies was connected to water velocity and volume, as these factors determined soil detachment and transport. The correlation between critical slope and drainage area determined gully head boundaries but were influenced by obstacles and phenomena on the hillslope. The growth speed was different inside the Wadi al Wala catchment. The lower catchment had an average growth of 6.1%, the middle catchment 4.05% and the high catchment 1.1% in 15 years. The growth did not increase gradually, as the largest rainfall events consisted often for >54% of yearly rainfall, which resulted in enhanced gully growth.

More accurate modelling of aeolian sediment transport in coastal environments is crucial to improving the planning and efficiency around soft coastal protection measures, such as sand nourishments, and a full understanding of the underlying transport mode is key to achieving it. This study aims to contribute to that widely shared purpose by trying to crack the code of the highly dynamically complex aeolian sand streamers. A wide range of different aspects of streamers have been investigated by exploiting an at least as wide a range of different both qualitative and quantitative analytical techniques. Amongst others, this report presents a series of spatiotemporal saltation transport maps as well as one of the first known applications of the non-globalised wavelet transform to time series of transport intensity. In October 2017, saltation intensity records were collected at the beach nearby the Dutch town of Egmond aan Zee using three replicas of the newly developed Saltation Detection System (SDS), while co-located ultrasonic anemometers provided synchronised records of 3-D wind measurements. In addition, time-averaged water levels were measured just off the beach and in two cases surface moisture levels were monitored along a transect parallel to the wind field upwind of the SDS. Four sequential streamer patterns were recognised under intensifying transport conditions, in which spatiotemporal variability in saltation intensity is systematically reduced. Individual streamers were found to to have a typical head-tail structure, coming up quickly, then slowly dwindle. High-intensity streamers were found having lengths of up to 0.5 m, widths of the order of 0.2 m and centre-to-centre spacings of up to 0.5 m. Neither shear velocity nor turbulence kinetic energy provide deterministic relationships for saltation intensity, but a clear, strong response is recognised of saltation intensity to increasing shear velocity. Coupling between the latter two variables is evident on

Inhabitants of drylands often live in below-average conditions of well-being and development. Due to its semi-arid to arid climate, the Jordan Badia is marred by plagues as water scarcity and increasing temperatures which are enhanced by overgrazing and a rapidly growing population. With the impending challenge of freshwater scarcity and the alarming drought records reached in recent years, the uncertainty about the Badia’s future grows aggressively as well as the need for assessing the entity and severity of land degradation processes in the area. The research aims at addressing this need with the aid of remote sensing techniques. Use is made of the satellite-derived land degradation indicators suggested by the United Nations Convention to Combat Desertification (UNCCD) to quantify the portion of degraded land. Moreover, soil and vegetation response to rainfall events are further investigated in this scope. Satellite-derived precipitation, soil moisture and NDVI are analysed in order to unravel soil resilience and its change over time. The assessment performed by the UNCCD shows that 1.3% of the land of Jordan is degraded. Areas in the north-west of the country prove to be the most affected. The pattern of degradation, as defined in this scope, shows to be mainly driven by land cover changes. The long-term analysis of soil moisture and NDVI trends in the Badia shows that soil resilience in drier areas has been partially affected. The implementation of an ecosystem rehabilitation project at Al Majidiyya ICARDA experimental site has proven to be beneficial for the quality of soils. An increased infiltration rate and higher vegetation productivity is observed where rainwater harvesting structures have been implemented.