Showing papers in "Physics and Chemistry of The Earth in 2009"

Probabilistic characterization of drought properties through copulas

Abstract: This paper shows an application of copulas to the probabilistic analysis of drought characteristics. Drought occurrences are analyzed by the Standardized Precipitation Index (SPI) computed on the mean areal precipitation, aggregated at 6 months, observed in Sicily between 1921 and 2003. Assuming a drought period as a consecutive number of intervals where SPI values are less than −1, several characteristics are determined, namely: drought length, mean and minimum SPI values, and drought mean areal extent. Results of a preliminary analysis based on Kendall’s correlation and upper tail dependence coefficient, computed on observed and resampled data, show significant dependence properties between almost all the considered pairs. The four-dimensional joint distribution required to correctly model the stochastic structure of variables is determined by resorting to copula approach. This allows flexibility in choosing suitable marginals and dependence structure, and in simplifying the inference procedure as well. Drought return periods are then computed as mean interarrival time, taking into account two drought characteristics at a time by means of the corresponding bivariate marginals of the fitted four-dimensional distribution. Application of the proposed methodology to Sicilian precipitation series shows a good correspondence between empirical and theoretical joint return periods, thus indicating that copulas are adequate to jointly model drought characteristics and to compute exceedance probabilities of drought events.

Going against the flow: A critical analysis of inter-state virtual water trade in the context of India's National River Linking Program

Abstract: Virtual water trade has been promoted as a tool to address national and regional water scarcity. In the context of international (food) trade, this concept has been applied with a view to optimize the flow of commodities considering the water endowments of nations. The concept states that water rich countries should produce and export water intensive commodities (which indirectly carry embedded water needed for producing them) to water scarce countries, thereby enabling the water scarce countries to divert their precious water resources to alternative, higher value uses. While progress has been made on quantifying virtual water flows between countries, there exists little information on virtual water trade within large countries like India. This paper presents the results of two MSc theses which quantify and critically analyze inter-state virtual water flows in India in the context of a large inter-basin transfer plan of the Government of India. Our analysis shows that the existing pattern of inter-state virtual water trade is exacerbating scarcities in already water scarce states and that rather than being dictated by water endowments, virtual water flows are influenced by other factors such as “per capita gross cropped area” and “access to secure markets”. We therefore argue that in order to have a comprehensive understanding of virtual water trade, non-water factors of production need to be taken into consideration.

Potential of using plant extracts for purification of shallow well water in Malawi

Abstract: There has been very little scientific research work into the use of plant extracts to purify groundwater. Research studies on the purification of groundwater have mainly been carried out in developed countries and have focused on water purification systems using aluminium sulphate (a coagulant) and chlorine (a disinfectant). Such systems are expensive and not viable for rural communities due to abject poverty. Shallow well water, which is commonly available throughout Africa, is often grossly contaminated and usually consumed untreated. As a result, water-related diseases kill more than 5 million people every year worldwide. This research was aimed at examining natural plant extracts in order to develop inexpensive ways for rural communities to purify their groundwater. The study involved creating an inventory of plant extracts that have been used for water and wastewater purification. A prioritisation system was derived to select the most suitable extracts, which took into account criteria such as availability, purification potential, yield and cost of extraction. Laboratory trials were undertaken on the most promising plant extracts, namely: Moringa oleifera, Jatropha curcas and Guar gum. The extracts were added to water samples obtained from five shallow wells in Malawi. The trials consisted of jar tests to assess the coagulation potential and the resulting effect on physico-chemical and microbiological parameters such as temperature, pH, turbidity and coliforms. The results showed that the addition of M. oleifera, J. curcas and Guar gum can considerably improve the quality of shallow well water. Turbidity reduction was higher for more turbid water. A reduction efficiency exceeding 90% was achieved by all three extracts on shallow well water that had a turbidity of 49 NTU. A reduction in coliforms was about 80% for all extracts. The pH of the water samples increased with dosage, but remained within acceptable levels for drinking water for all the extracts. Overall, M. oleifera powder produced superior results, followed by Guar gum and lastly J. curcas. There is a need to carry out further more detailed tests, which include toxicity to guarantee the safety of using plant extracts as a coagulant in the purification of drinking water for human consumption.

Rainwater harvesting as an alternative water resource in rural sites in central northern Namibia

Abstract: In this paper, results of the investigations on rainwater harvesting (RWH) in central northern Namibia are described, which are part of the transdisciplinary research project CuveWaters. On the basis of hydrological and technical as well as social and cultural conditions, appropriate solutions for RWH are developed, discussed, and evaluated. The main objective is to analyse their technical and economical feasibility as well as their affordability for future users. In detail, two small-scale RWH systems are examined: roof catchments using corrugated iron roofs as rain collection areas and ground catchments using treated ground surfaces. The current status of local water supply and water use was investigated in the village of Epyeshona. Concepts and techniques of RWH were discussed with the population. Based on the results of these investigations and on the physical conditions, the appropriate RWH design and the required storage capacities could be identified. Local material and labour costs were determined and a dynamic cost analysis was carried out to compare the technological options in terms of amortisation times and prime costs. The feasibility of the RWH systems was assessed in relation to local socio-economic conditions. The calculations reveal that it is economically feasible to apply decentral techniques of RWH in terms of the roof catchment systems. Moreover, the proposed technologies provide comparable benefits to the public water supply. The ground catchment system, however, needs moderate subsidies to obtain the same benchmark.

Assessing the sustainability of the silver-impregnated ceramic pot filter for low-cost household drinking water treatment

Abstract: A low-cost technology to treat water at the household level is the ceramic silver-impregnated pot filter (CSF). The CSF consists of a pot-shaped filter element that is placed in a plastic receptacle. The ceramic pot filter is a promising treatment system to supply safe drinking water especially to people living in rural areas. The focus of this study was to assess the sustainability of a household drinking water treatment system based on five criteria: (i) accessibility, (ii) water quality, (iii) water production, (iv) functionality, and (v) environmental footprint. The removal of Escherichia coli and protozoan (oo)cysts was found to be significant, which was supported by the reduction in diarrhoea cases observed by CSF users in a recent field study. The retention of MS2 bacteriophages as an indicator for virus removal was, however, found to be unsatisfactory. It is therefore recommended that research on virus removal by CSF continues, especially in relation to the colloidal silver application and other potential additives. The criterion of water production was shown to be the limiting factor, because it reduced substantially during treatment of surface water. The fast clogging of the CSF during the first hours of use was caused neither by inorganic nor organic fouling, but by colloidal particles. Two direct effects may be identified from the decreasing flow rate: frequent scrubbing and higher water prices. Frequent scrubbing results in a higher risk of recontamination and breakage. Based on this finding the authors recommend an optimization study to increase the initial flow rate without sacrificing the removal efficiency.

Destructive meteotsunamis along the eastern Adriatic coast: Overview

Abstract: The paper overviews meteotsunami events documented in the Adriatic Sea in the last several decades, by using available eyewitness reports, documented literature, and atmospheric sounding and meteorological reanalysis data available on the web. The source of all documented Adriatic meteotsunamis was examined by assessing the underlying synoptic conditions. It is found that travelling atmospheric disturbances which generate the Adriatic meteotsunamis generally appear under atmospheric conditions documented also for the Balearic meteotsunamis (rissagas). These atmospheric disturbances are commonly generated by a flow over the mountain ridges (Apennines), and keep their energy through the wave-duct mechanism while propagating over a long distance below the unstable layer in the mid-troposphere. However, the Adriatic meteotsunamis may also be generated by a moving convective storm or gravity wave system coupled in the wave-CISK (Conditional Instability of the Second Kind) manner, not documented at other world meteotsunami hot spots. The travelling atmospheric disturbance is resonantly pumping the energy through the Proudman resonance over the wide Adriatic shelf, but other resonances (Greenspan, shelf) are also presumably influencing the strength of the meteotsunami waves, especially in the middle Adriatic, full of elongated islands and with a sloping bathymetry. The generated long ocean waves are hitting funnel-shaped bays or harbours of large amplification factors, resulting in meteotsunami waves with heights up to 6 m at the very end of bays or harbours. Within models the mechanism is fairly well understood, but it is extremely difficult to reproduce these events (and presently almost impossible to forecast) as the meteotsunami generating process is highly variable at both temporal and spatial scales. The final part of the paper discusses the possibilities for further research of the Adriatic meteotsunamis, and meteotsunamis in general, including the basis of a meteotsunami warning system which should be able to capture potentially dangerous travelling atmospheric disturbances in real-time.

Assessing the usefulness of the water poverty index by applying it to a special case: Can one be water poor with high levels of access?

Abstract: Using indices and indicators in assessment of progress of a developing country has two sides. Such indicators offer an easy-to-understand shorthand/synopsis of issues vital for a country’s development. The other side of the coin, however, is that this synopsis may be distorted due to incorrect data or inapplicability of an index or an indicator to a specific case. This paper assesses the applicability of Water Poverty Index for the countries riparian to the Sava sub-basin, a tributary to the Danube river basin and presents the results of its application. At the same time, the paper discusses the concept of water poverty and the appropriateness of its use in the case of Sava River Basin countries by differentiating the economic poverty in some of those countries from sufficient access to and use of water resources in all of them.

Optimization and validation of solid phase micro-extraction (SPME) method for analysis of polycyclic aromatic hydrocarbons in rainwater and stormwater

Abstract: This paper is about development of a simple and rapid solid-phase microextraction (SPME) method coupled with gas chromatography–mass spectrometry (GC–MS) for the quantitative determination of 16 polycyclic aromatic hydrocarbons (PAHs) in rainwater and stormwater samples. In this study the condition of PAHs extractions using SPME was optimized for achieving high enrichment of the analytes from aqueous samples. This condition was optimized by varying the stirring rate, salt concentration, fiber exposure time, sample pH, and sample temperature consecutively. The analysis revealed that optimal operating conditions occurred at condition of 0.5 M of sodium monochloroacetate, 65 °C, pH 7.0, agitation of 720 rpm, and an extraction time of 60 min. A desorption time of 15 min was shown to eliminate carry-over. The satisfactory linearity, detection limits and a high enrichment factor obtained prove that the method is a sensitive tool for trace level measurement. In the next step, the newly developed SPME–GC–MS method was validated for the analysis of PAHs in rainwater and stormwater samples, which resulted in high extraction recoveries from spiked synthetic rainwater and stormwater samples. This corroborates that the method is feasible for analysis of PAHs in real rainwater and stormwater analysis.

Delineation of small reservoirs using radar imagery in a semi-arid environment: A case study in the upper east region of Ghana

Abstract: Small reservoirs serve many people living in semi-arid environments. Water stored in these reservoirs is used to supplement rainfed agriculture, allow for dry season irrigated agriculture and ensure the availability of water for domestic purposes. In order to manage the water effectively for competing uses, the actual storage of these reservoirs needs to be known. Recent attempts to delineate these reservoirs using remote sensing with Landsat imagery have been successful, especially in the upper east region of Ghana, West Africa. This paper shows that radar images (ENVISAT ASAR) can be used to provide similar information all year-round. Radar images have as an important advantage that they are not impaired by cloud cover and thus can be used during the rainy season. Another advantage of radar images is that images taken during night time are usable. The paper compares satellite derived data with field measurements of 21 small reservoirs. Whereas ENVISAT images on the average tend to overestimate the surface areas of small reservoirs, in certain reservoirs these areas are systematically under-estimated due to the shallow tail-ends of reservoirs that tend to have reed vegetation. These cannot be readily distinguished from the surrounding vegetation outside the reservoirs. This paper therefore provides a proof of concept of the monitoring of small reservoir volumes by radar imagery.

A GIS-based decision support system for rainwater harvesting (RHADESS)

Abstract: Rainwater harvesting (RWH) is an unconventional water source that is increasingly adopted in South Africa. Its implementation is promoted by non-governmental organisations and government programmes to alleviate temporal and spatial water scarcity for domestic, crop and livestock production and support the overall water resources management. Unreliable water supply is one of the elements central to the poverty level of rural population. As the potential of RWH to improve water access for drinking and other basic human needs is still untapped, the technique will spread further in the coming decades. Studies on the hydrological impacts of RWH are focused on plot scale and very little is known about its impacts at catchment scale. To integrate RWH into the development and management of water resources in South Africa, there is a need to develop tools and methodologies that not only assist planners with the identification of areas suitable but also quantify the associated hydrological impacts of its wide scale adoption. This paper presents the rainwater harvesting decision support system (RHADESS) that was built to assist decision makers and stakeholders by indicating the suitability of RWH in any selected part of South Africa and quantifying the potential impacts associated with its adoption at catchment scale. RHADESS is GIS-based and uses ArcView 3.3 as a platform to assess the RWH suitability of any given area of South Africa. Results are thereafter exported into an Excel spreadsheet that contains the hydrological impact, as runoff reduction, of different levels of adoption of RWH assessed by using the Pitman model. The decision support system guides the implementation of the following RWH categories: Infield RWH and ex-field RWH and domestic RWH. RHADESS was tested in two selected quaternary catchments C52A and V13D located in the Upper Orange water management area and the Thukela water management area, respectively.

Modelling and observation of biosphere–atmosphere interactions in natural savannah in Burkina Faso, West Africa

Abstract: Savannahs are highly dynamic ecosystems but many of their properties and the related balances of energy, carbon, nitrogen, and water are still poorly understood. A particular scientific issue is the quantification of trace gases emitted from the soil of savannah ecosystems and their interaction with regional and global climate and air chemistry. Therefore it is important to develop and evaluate land-surface models that on the one hand represent vegetation and soil dynamics and on the other hand provide energy and water fluxes in a temporal resolution suitable for the application in climate/air chemistry models. In this paper, we present a consistent coupling between a common land-surface model (OSU) and a widely used biogeochemical model (DNDC) that is a first step for a full coupling of climate/air chemistry and biogeochemical processes. For consistency reasons, both models are linked to a general physiologically based plant model to provide the physical boundary conditions as well as the carbon and nitrogen in- and output variables. Evaluation is carried out with measurements of soil temperature, latent heat flux, soil water content, and soil emission data from two vegetation periods collected at a natural grassland site in Bontioli Nature Reserve, Burkina Faso (Africa). The results demonstrate that simulations of biogeochemical processes based on soil environmental conditions, calculated either with the land-surface model or with the unchanged biogeochemical model, do not differ significantly from each other. The OSU model simulates more realistic day-to-day variation of soil temperature as DNDC but the sensitivity of the biogeochemical simulation to this variation is small. In contrast, the sensitivity to differences in soil water content is high, but simulation results of both models are very similar on the daily scale and hardly depend on spatial soil resolution.

Design flood estimation using model selection criteria

Abstract: The design flood is defined as the discharge value corresponding to an assigned non-exceedance probability, which is usually expressed in terms of the return period. Estimation of the design flood is usually carried out by fitting observed data samples with a suitable probability distribution. The objective of this study is to evaluate if model selection criteria, which are seldom used in hydrological applications, can help identifying the best probability model for this purpose. The study analyzes the performance of three model selection criteria, namely, the Akaike information criterion, the Bayesian information criterion, and the Anderson–Darling criterion. The three methods are compared trough an extensive numerical analysis by using synthetic data samples. The study demonstrates that model selection criteria are a valuable tool for reducing the uncertainty of design flood estimation.

A tool for technical assessment of rural water supply systems in South Africa

Abstract: Water and sanitation services provide a cost-effective solution for alleviating the impact of water-borne diseases. Actually, for water supply projects a top-down approach is followed, giving priority to deliver sufficient quantities of water, increasing its availability by investment in new systems. Little attention is paid to the functioning of these systems on the long-term, and its maintenance and operational constraints. In this paper, a methodology was developed to technically assess water supply systems based on four criteria, namely availability, capacity, continuity and condition. The practicality of the approach is demonstrated by a technical assessment of a number of water supply systems in the Vhembe District in South Africa. The systems consist of piped distribution systems with public standpipes, mostly fed by groundwater. In general, it can be concluded that the performance of the systems, although relatively new, is poor. The availability (criterion 1) of the drinking water is a problem due to poorly constructed boreholes or disagreement on the payment of the operational cost after construction. In most villages the capacity (criterion 2) of the installed infrastructure is sufficient, although storage volume is in some villages too small. The continuity (criterion 3) of the water supply is threatened by disputes about payment of diesel for the pump and maintenance and repair of the pump. Finally, the condition (criterion 4) is poor mostly due to taps at the standpipes which are damaged and require frequent replacement. Despite the simplicity of the proposed assessment methodology, it provides rapid insight in the state of a system and is ideal for bench marking the performance of different systems in different regions. Furthermore, the quantitative measures of the four different criteria allow system operators and planners to rapidly pinpoint the reasons for poor performance and to take the appropriate corrective action. The used weighting factors in this demonstration are arbitrary – different users could adapt them to their own specific situations without invalidating the overall approach to technical assessment suggested in this paper.

Adapting to an innovation: Solar cooking in the urban households of Ouagadougou (Burkina Faso)

Abstract: Most households in Sub-Saharan Africa rely on wood as primary energy source. The availability of wood is decreasing and deforestation is a major ecological problem in Sub-Saharan Africa. The scarcity of wood is demanding for a sustainable solution. The sun seems to provide a good alternative. Solar energy is free, without unhealthy smoke or chances to burns. The idea of using solar energy for cooking is not new: many different techniques have already been tested. Most variants are expensive, and therefore not available for most families in Sub-Saharan Africa. A cheap solar cooking device is the CooKit, a cardboard panel cooker covered with aluminium foil. In the adaptation to the CooKit, as to all innovations, it is important that the users are convinced of the advantages. An important step in the adaptation process is learning how to use the cooking device; the best way to do this is by home practice. Monitoring and evaluating the real use is needed, for it is interesting to know if the CooKit is actually used, and also to find out how women have implemented the new technique in their kitchens. In 2005, the SUPO foundation started a project in Burkina Faso: Programme Energie Solaire Grand-Ouaga (PESGO). The aim of PESGO is to introduce the CooKit in the urban households in Ouagadougou by providing training sessions and home assistance. In this paper, a mid-term review on this small-scale cooking project is presented. The possibilities and challenges of solar cooking are outlined, taking the urban context of Ouagadougou in account. In PESGO, dependence on weather conditions is found to be one of the challenges: if sunrays are blocked by clouds or dust in the air, the cooking will be slowed down. The CooKit cannot replace firewood entirely, and a complementary element has to be found. SUPO is exploring the use of Jatropha oil as a complement to the CooKit. The Jatropha plant is drought tolerant and its fruits contain oil which can be used as fuel substitute. Further research on its use is interesting, because the combination of the CooKit and Jatropha oil seems to have high potential in the kitchens of West-Africa.

AGW as a seismo-ionospheric coupling responsible agent

Abstract: The seismo-ionospheric coupling is one of the hot topics of modern scientific research. The importance to shed more light to this process is connected with the study of ionospheric earthquakes precursors in the ionosphere, monitoring of which could be a further step to the scientifically substantiated solution of the problem of earthquakes warning. The energy transmission channel “from below” in the lithosphere–atmosphere–ionosphere–magnetosphere system is analyzed and atmospheric gravity waves are identified as the most probable energy carriers for the troposphere–ionosphere coupling.

Meteorological tsunamis on the coasts of British Columbia and Washington

Abstract: Tsunami-like sea level oscillations recently recorded by tide gauges located at offshore, as well as sheltered, sites along the coasts of British Columbia (Canada) and Washington State (USA) are identified as meteorological tsunamis. The events resemble seismically generated tsunamis but have an atmospheric, rather than seismic, origin. The event of 9 December 2005 was sufficiently strong to trigger an automatic tsunami alarm, while other events generated oscillations in several ports that were potentially strong enough to cause damage to marine craft. Analysis of coincident 1-min sea level data and high-frequency atmospheric pressure data confirms that the events originated with atmospheric pressure jumps and trains of atmospheric gravity waves with amplitudes of 1.5–3 hPa. The pronounced events of 13 July 2007 and 26 February 2008 are examined in detail. Findings reveal that the first atmospheric pressure event had a propagation speed of 24.7 m/s and an azimuth of 352°; the second event had a speed of 30.6 m/s and an azimuth of 60°. These speeds and directions are in close agreement with high-altitude geostrophic winds (the jet stream) indicating that the atmospheric disturbances generating the tsunami-like sea level oscillations are likely wind-transported perturbations rather than freely propagating atmospheric gravity waves.

A data-based assessment of the dependence of short-duration precipitation on elevation

Abstract: Variability of precipitation with elevation is often related to the presence of an orographic effect interacting with prevailing arrival directions of wet air masses. This effect is commonly recognized to be responsible for the increase with elevation of the annual precipitation amounts measured at the ground level. However, the variability with elevation of heavy rainfall of short duration is poorly investigated in hydrology, despite the importance of short-duration events in hydrological applications. Analyzing a database of 567 time series of annual maximum sub-daily rainfall in northern Italy, we find the relation of extreme precipitation with elevation to be a function of the event duration. In particular, it emerges that the intensity of rainfall decreases with elevation for very short durations (i.e., 1–3 h), while the negative slope of the intensity-elevation regression lines tends to decrease when considering events of longer duration (i.e., 12–24 h), at least in the western part of the alpine chain. A combined use of kriging and regression techniques is then proposed to account for the effect of elevation and longitude in the spatial interpolation of sub-daily rainfalls.

Water balance estimation of a poorly gauged catchment in West Africa using dynamically downscaled meteorological fields and remote sensing information

Abstract: Scientifically sound decisions in sustainable water management are usually based on hydrological modeling which can only be accomplished by meteorological driving information. Especially in regions with weak infrastructure this task is hampered by limited hydro-meteorological information in sufficient spatial and temporal resolution. We investigated three approaches to provide required meteorological fields driving the distributed hydrological model: the results of the mesoscale meteorological model MM5 which are available near real time, the TRMM product 3B42 available with approximately one month delay, and station data available with a delay of one year or more. The study site is the White Volta catchment in the semi-arid environment of West Africa. The results for 2004 show that the meteorological model is able to provide meteorological input data for near real time water balance estimations. In this study the TRMM product does not improve the simulation results. Besides missing important meteorological data, also gridded information on land surface properties (albedo, LAI, etc.) is usually difficult to obtain, albeit it is an essential input for distributed hydrological models. This information is commonly taken from “static” tables depending on the land use. Satellite remote sensing provides worldwide spatially detailed information on land surface properties which is particularly suitable for large regions in remote settings. Therefore the MODIS products for albedo and LAI were processed to annual time series including the identification and replacement of low quality observations by interpolation. The impact using MODIS data on the spatial distribution of water balance variables occurs mainly on local scale. The hydrological simulations using MODIS LAI and albedo values result in higher annual evapotranspiration and lower total discharge sums for 2004. Altogether it is concluded that hydrological decision support systems in regions with weak infrastructure can benefit significantly from the integration of atmospheric modeling and satellite-derived land surface data.

Analysing streamflow variability and water allocation for sustainable management of water resources in the semi-arid Karkheh river basin, Iran

Abstract: This study provides a comprehensive spatio-temporal assessment of the surface water resources of the semi-arid Karkheh basin, Iran, and consequently enables decision makers to work towards a sustainable water development in that region. The analysis is based on the examination of statistical parameters, flow duration characteristics, base flow separation and trend analysis for which data of seven key gauging stations were used for the period of 1961–2001. Additionally, basin level water accounting was carried out for the water year 1993–94. The study shows that observed daily, monthly and annual streamflows are highly variable in space and time within the basin. The streamflows have not been changed significantly at annual scale, but few months have shown significant trends, most notably a decline during May and June and an increase during December and March. The major causes were related to changes in climate, land use and reservoir operations. The study concludes that the water allocations to different sectors were lower than the totally available resources during the study period. However, looking at the high variability of streamflows, changes in climate and land use and ongoing water resources development planning, it will be extremely difficult to meet the demands of all sectors in the future, particularly during dry years.

Policy implications of pollution swapping

Abstract: Pollution swapping can be defined as the increase in one pollutant as a result of a measure introduced to reduce a different pollutant. Although pollution swapping is widely understood it has received relatively little research attention and receives little consideration in agri-environmental policy. Evidence of pollution swapping in constructed wetlands, riparian buffer zones, cover crops, crop residue retention and no-tillage is examined in this paper. These widely used mitigation options are all successful at reducing diffuse pollutants but literature review shows that there is potential for them to increase levels of one or more other pollutants. There is potential for the widespread adoption of mitigation options to result in unexpected increases in some pollutants. There are a number of barriers to the recognition of pollution swapping in agri-environmental legislation including a lack of tools to evaluate the relative impacts of different pollutants, gaps in our knowledge of the impacts of mitigation measures on non-target pollutants and institutional barriers.

Water productivity (WP) in reservoir irrigated schemes in the upper east region (UER) of Ghana

Abstract: Improving water productivity is one important strategy for addressing future water scarcity, which is driven particularly by increasing human population and potential climate and land use changes. Although an understanding of water productivity is required to develop improved water management strategies, little is known about it in irrigated systems of the sub-Saharan Africa. This study assesses the physical crop water productivity at farm and scheme scales for two distinct systems: a medium and small reservoir in semi-arid environment of the Upper East Region in Ghana. The study concludes that water productivity for the study reservoirs is low, and that potential for improvement exists through improved irrigation water management and agronomic practices.

Bioenergy for sustainable development: An African context

Abstract: This paper assesses the sustainability concerns of bioenergy systems against the prevailing and potential long term conditions in Sub-Saharan Africa with a special attention on agricultural and forestry waste, and cultivated bioenergy sources. Existing knowledge and processes about bioenergy systems are brought into a “sustainability framework” to support debate and decisions about the implementation of bioenergy systems in the region. Bioenergy systems have been recommended based on the potential to (i) meet domestic energy demand and reduce fuel importation (ii) diversify rural economies and create employment (iii) reduce poverty, and (iv) provide net energy gains and positive environmental impacts. However, biofuels will compete with food crops for land, labour, capital and entrepreneurial skills. Moreover the environmental benefits of some feedstocks are questionable. These challenges are, however, surmountable. It is concluded that biomass energy production could be an effective way to achieve sustainable development for bioenergy pathways that (i) are less land intensive, (ii) have positive net energy gains and environmental benefits, and (iii) provide local socio-economic benefits. Feasibility evaluations which put these issues into perspective are vital for sustainable application of agricultural and forest based bioenergy systems in Sub-Saharan Africa. Such evaluations should consider the long run potential of biofuels accounting for demographic, economic and technological changes and the related implications.

NDVI–rainfall relationship in the Semliki watershed of the equatorial Nile

Abstract: The use of remotely sensed data to describe, study, monitor and provide greater understanding on watershed’s landscape dynamics have proven to be useful worldwide, especially where timely and reliable ground information are neither available nor accessible like in most of the developing world. This paper, thus presents the first documented relationship between NDVI and rainfall in humid central Africa, and serves as a precursor in the understanding of the interaction between catchment characteristics and water resources of the Semliki region. This study investigates spatial and temporal relationship between NDVI and satellite-derived rainfall. Normalized Difference Vegetation Index (NDVI) time series derived from the NOAA–AVHRR (National Oceanic and Atmospheric Administration–Advanced Very High Resolution Radiometer) satellite data and FEWS satellite-derived rainfall are analyzed. The Semliki watershed (23,621 km2) of the equatorial Nile basin is the study area. Monthly NDVI time series of 21 Semliki’s subcatchments (S3–S23) over 7 years (2001–2007) were processed and extracted with Windisp 5.1 from 10-day NDVI maximum value composite images. At the monthly time step, only 12 subcatchments had weak positive correlation (0.23–0.42) at 5% significance level and the rest were not significantly correlated. Incorporating a 1-month lag effect increased the correlation coefficients between the two variables (0.28–0.68) with 17 subcatchments being significantly correlated at the designated level. The topography within the catchment was found to play a defining role for NDVI values. S15, S16, S18 and S20, the subcatchments covering the Mount Ruwenzori characterized by elevations up to 4862 m above sea level, consistently recorded the lowest values of NDVI over time and no significant correlation could be established between rainfall and NDVI.

Measuring and modeling hydrological processes of sand-storage dams on different spatial scales

Abstract: Sand-storage dams are a successful water harvesting technology in Kenya and a promising solution to ensure water and food security in other semi-arid regions. Assessing the suitability of sand-storage dams for other semi-arid regions requires both a good understanding of the hydrological factors for success of a single dam and the regional effects of a network of dams. Results from a measurement campaign on hydrological processes in the surroundings of a single dam in the Kitui District in Kenya indicated that groundwater levels increase quickly after precipitation. Recession of groundwater levels during the dry season following the rains was more gradual. Based on these results, a groundwater model for a single sand-storage storage dam was developed. As the river banks are important recharge areas for the groundwater stored upstream of the dam, the model showed high sensitivity for parameters like thickness and hydraulic conductivity of the shallow aquifer on the riverbanks and thickness of the sand layer in the riverbed. Parallel to the single dam model, a model for a series of dams was developed. This second model indicated that the inter-dam distance is an important parameter. The distance between dams determined whether influence areas did overlap or that dams behaved as individual structures. When the influence areas did overlap, stored water volume per dam decreased. The results from measurements and modeling confirm that sand-storage dams can effectively increase water availability throughout the dry season. Since measurements and models explain how sand-storage dams successfully modify hydrological systems in semi-arid Kenya, the results can assist in planning introduction of the technology in other regions.

Investigating the water balance of on-farm techniques for improved crop productivity in rainfed systems : A case study of Makanya catchment, Tanzania

Abstract: Water scarcity is a perennial problem in sub-Saharan agricultural systems where extreme rainfall events dominate agricultural seasons. Dry spell occurrences between and during seasons negatively impact on crop yields especially if such dry spells exceed 14 days. The impact of dry spells is felt more at smallholder farming scales where subsistence farming is the only source of livelihood for many households. This paper presents results from on-going research to improve rainfed water productivity in arid and semi-arid regions. The study site is the Makanya catchment in northern Tanzania where rainfall rarely exceeds 400 mm/season. Rainwater alone is not sufficient to support maize which is the preferred crop. The research introduced new soil and water conservation measures to promote water availability into the root zone. The introduced techniques include deep tillage, runoff diversion, fanya juus (infiltration trenches with bunds) and infiltration pits. The research aims at understanding the effectiveness of these interventions in increasing moisture availability within the root zone. Time domain reflectometry (TDR) was used to measure soil moisture twice weekly at 10 cm depth intervals up to depths of 2 m. Soil moisture fluctuated in the range 5–25% of volume with the beginning of the season recording the driest moisture levels and periods after good rainfall/runoff events recording the highest moisture levels. From the field observations made, a spreadsheet model was developed to simulate soil moisture variations during different maize growth stages. The results obtained show that the zones of greatest soil moisture concentrations are those around the trenches and bunds. Soil moisture is least at the centre of the plots. The study confirms the effectiveness of the introduced techniques to help concentrate the little available rainfall into green water flow paths. Indirect benefits from these improved techniques are the creation of fertile and moist zones around the bunds where supplementary food crops (e.g. bananas and cassava) can be grown even in dry seasons.

Water level monitoring using radar remote sensing data: Application to Lake Kivu, central Africa

Abstract: Satellite radar altimetry measures the time required for a pulse to travel from the satellite antenna to the earth’s surface and back to the satellite receiver. Altimetry on inland lakes generally shows some deviation from in situ level measurements. The deviation is attributed to the geographically varying corrections applied to account for atmospheric effects on radar waves. This study was focused on verification of altimetry data for Lake Kivu (2400 km 2 ), a large inland lake between Rwanda and the Democratic Republic of Congo (DRC) and estimating the lake water levels using bathymetric data combined with satellite images. Altimetry data obtained from ENVISAT and ERS-2 satellite missions were compared with water level data from gauging stations for Lake Kivu. Gauge data for Lake Kivu were collected from the stations ELECTROGAZ and Rusizi. ENVISAT and ERS-2 data sets for Lake Kivu are in good agreement with gauge data having R 2 of 0.86 and 0.77, respectively. A combination of the two data sets improved the coefficient of determination to 95% due to the improved temporal resolution of the data sets. The calculated standard deviation for Lake Kivu water levels was 0.642 m and 0.701 m, for ENVISAT and ERS-2 measurements, respectively. The elevation-surface area characteristics derived from bathymetric data in combination with satellite images were used to estimate the lake level gauge. Consequently, the water level of Lake Kivu could be estimated with an RMSE of 0.294 m and an accuracy of ±0.58 m. In situations where gauges become malfunctioning or inaccessible due to damage or extreme meteorological events, the method can be used to ensure data continuity.

Estimating chlorophyll concentration in Lake Malawi from MODIS satellite imagery

Abstract: This paper describes results of research to develop algorithms for estimating chlorophyll-a concentrations in Lake Malawi from MODIS satellite imagery. A procedure relating chlorophyll concentration in Lake Malawi to the atmospherically corrected reflectance ratio of MODIS/AQUA (Ocean Color) bands 9 and 12 (i.e., R443/R551) was established using the SeaWIFS Data Analysis System (SeaDAS) software, and shows a moderate relationship between in situ chlorophyll-a concentration and values obtained from satellite imagery. The results have potential application in monitoring the trophic state of Lake Malawi. Attempts to use Level 1B MODIS/Terra data proved futile because of lack of atmospheric correction in processing the reflectance data. This shows that atmospheric effects have serious impacts on radiant energy, and hence the need for atmospheric correction. This may be described as the correction made to remotely sensed radiance to account for effects related to the intervening atmosphere between the earth’s surface and the satellite sensor, the result being an estimate of spectral reflectance as it would have been measured at ground level.

Low cost thermoformed solar still water purifier for D&E countries

Abstract: Introduction Solar distillation mimics nature’s hydrologic water cycle by purifying water through evaporation (using solar energy) and condensation (rain). It is one of the most basic purification systems available today to obtain high quality drinking water and can remove non-volatile contamination from almost any water source. This low-tech technology should therefore be ideally suited for developing and emerging countries where sun shines in abundance. In the past century numerous designs have been realised with footprints ranging from 0.5 m2 to thousands of square meters. Despite all efforts, this intriguing technology has not been applied widely yet. Among the challenges that remain are: (1) its low yield, (2) obtaining local commitment to operate/maintain large scale systems properly, and (3) relatively high initial investment costs. The objective of this study has been to address challenges 1 and 3 by using standard plastic thermoforming technology to realize a small scale single slope solar still for personal use (2–4 l per day) with adequate efficiency and at low production costs. Materials and methods The solar still consists of two parts: a basin that holds the dirty water and a transparent tilted cover onto which the clean water vapour can condense. The basin has a footprint of 1.34 m2 and is made of a 3 mm thick sheet of black high-density polyethylene (HDPE) which is thermoformed using standard equipment for making fish-ponds. This allows for the incorporation of detailed features, like reinforcements and a clean-water collection gutter, at no extra cost. The transparent cover is made of UV stabilised low-density PE-foil which is under a slope of 10° to transport condensed water droplets to the lower located collection gutter. Throughput and purification performance were evaluated in duplicate at our Bangalore R&D facilities in India, over a short term (5 day) period. Solar radiation was measured using a Pyranometer. The system was loaded with 40 l of laundry rinse water. Results At an average solar radiation of 12.95 MJ/day/m2 the average yield of purified water was 3 l/day. This resulted in a calculated overall system efficiency of 39%. Purification performance (contaminated versus purified water) of the solar still loaded with the most contaminated water source was: Total dissolved solids (TDS) from 2925 ppm to 40 ppm, pH from 9.6 to 5.5, conductivity from 6130 mS/cm to 26 mS/cm, turbidity from 394 NTU to 0.4 NTU, total viable count (TVC) from 314 million cfu/ml to Conclusion Thermoforming allowed for the realisation of a single slope solar still that can sustainably produce high quality drinking water at point of use from waste water with an above average efficiency and at a manufacturing price (in The Netherlands) of below €25-per system. Next step should focus on a long term evaluation (months, instead of days) to access the full potential of the solar still to produce safe drinking water at point of use in an economical and reliable way.

Changes of nitrate concentrations in surface waters influenced by land use in the crystalline complex of the Czech Republic

Abstract: Changes in nitrate pollution in surface waters brought by the construction of tile drainage systems and by conversion of cultivated land to grassland (followed by decrease in fertilizer use) in two districts were examined. The goal was to find out how nitrate concentrations have responded to changes in agricultural management. There were no major changes in land use in the Pelhrimov district after 1990, apart from decrease in mineral fertilizer use. In the Cesky Krumlov district, permanent grassland area increased by 55% (from 228.9 km2 to 353.3 km2) and by 241% (from 5.4 km2 to 13 km2) in the catchments investigated between 1990 and 2000 followed by reduction in use of fertilizers. In these two districts, 31 small catchments where long-term, or repeated, nitrate concentration monitoring was carried out between 1986 and 2005, were analyzed. Trend, regression and factor analyses were conducted on changes in nitrate concentrations, and to assess the impact of several factors on nitrate concentrations in water before and after conversion to grassland. Over the monitoring period 1986–2005, there was a significant decreasing linear trend in N – NO 3 - concentration in surface waters in all catchments in the Cesky Krumlov district. In the Pelhrimov district 3 of 23 catchments showed a significant decreasing trend in nitrate concentrations and 2 a significant increasing trend despite a decrease in mineral nitrogen consumption. The most important environmental factor affecting nitrate pollution was the proportion of ploughed land in the catchment. The greater the share of ploughed land in the catchment, the greater the nitrate contamination of surface water. The proportion of drained land in the catchment after grassing has no markedly influence on nitrate nitrogen concentration.

Two waterfalls do not hear each other. Sand-storage dams, science and sustainable development in Kenya

Abstract: Recent success in economic terms of sand-storage dams in Kenya has stimulated efforts to study options to implement similar techniques on a larger scale in other regions in sub-Saharan Africa. There are several challenges related to developing sand-storage dams. Such systems necessitate addressing issues like ownership, labor investments and siting. This paper discusses experiences in Kitui applying the dimensions of construction planning, hydrological scale and water use. Tensions between stakeholders planning the intervention and benefiting from it are indicated to clarify the questions that need to be answered. It is argued that science can contribute to development interventions aiming at implementing sand-storage techniques elsewhere by narrowing the margin of error in answering relevant questions.