Jens R. Liebe

Mapping malaria transmission in West and Central Africa

We have produced maps of Plasmodium falciparum malaria transmission in West and Central Africa using the Mapping Malaria Risk in Africa (MARA) database comprising all malaria prevalence surveys in these regions that could be geolocated. The 1846 malaria surveys analysed were carried out during different seasons, and were reported using different age groupings of the human population. To allow comparison between these, we used the Garki malaria transmission model to convert the malaria prevalence data at each of the 976 locations sampled to a single estimate of transmission intensity E, making use of a seasonality model based on Normalized Difference Vegetation Index (NDVI), temperature and rainfall data. We fitted a Bayesian geostatistical model to E using further environmental covariates and applied Bayesian kriging to obtain smooth maps of E and hence of age‐specific prevalence. The product is the first detailed empirical map of variations in malaria transmission intensity that includes Central Africa. It has been validated by expert opinion and in general confirms known patterns of malaria transmission, providing a baseline against which interventions such as insecticide‐treated nets programmes and trends in drug resistance can be evaluated. There is considerable geographical variation in the precision of the model estimates and, in some parts of West Africa, the predictions differ substantially from those of other risk maps. The consequent uncertainties indicate zones where further survey data are needed most urgently. Malaria risk maps based on compilations of heterogeneous survey data are highly sensitive to the analytical methodology.

Determining watershed response in data poor environments with remotely sensed small reservoirs as runoff gauges

In the semiarid regions of Africa, there are many small reservoirs used for irrigation. This study explores the practicality of using small reservoirs as runoff gauges by estimating their water storage changes using remote sensing imagery. A simple rainfall-runoff model is developed by observing the surface area and estimating the volume of eight small reservoirs in the Upper East Region of Ghana and in Togo using Envisat advanced synthetic aperture radar satellite images. The model is based on the Thornthwaite-Mather procedure and the assumption that with increasing precipitation, the contributing watershed area increases exponentially. The model parameters were estimated using the 2005 data and were validated using 2006 data. Although the total rainfall amounts were comparable in these 2 years, the rainfall and reservoir filling patterns were quite different. The model results indicate that the overall impact of the reservoirs largely depends on the ratios of reservoir to watershed areas. For this 2 year study, the reservoirs captured on average 34% of quick flow and 15% of overall runoff.

Suitability and Limitations of ENVISAT ASAR for Monitoring Small Reservoirs in a Semiarid Area

In semiarid regions, thousands of small reservoirs provide the rural population with water, but their storage volumes and hydrological impact are largely unknown. This paper analyzes the suitability of weather-independent radar satellite images for monitoring small reservoir surfaces. The surface areas of three reservoirs were extracted from 21 of 22 ENVISAT Advanced Synthetic Aperture Radar scenes, acquired bimonthly from June 2005 to August 2006. The reservoir surface areas were determined with a quasi-manual classification approach, as stringent classification rules often failed due to the spatial and temporal variability of the backscatter from the water. The land-water contrast is critical for the detection of water bodies. Additionally, wind has a significant impact on the classification results and affects the water surface and the backscattered radar signal (Bragg scattering) above a wind speed threshold of 2.6 mmiddots-1. The analysis of 15 months of wind speed data shows that, on 96% of the days, wind speeds were below the Bragg scattering criterion at the time of night time acquisitions, as opposed to 50% during the morning acquisition time. Night time acquisitions are strongly advisable over day time acquisitions due to lower wind interference. Over the year, radar images are most affected by wind during the onset of the rainy season (May and June). We conclude that radar and optical systems are complimentary. Radar is suitable during the rainy season but is affected by wind and lack of vegetation context during the dry season.

The GLOWA Volta project: Integrated assessment of feedback mechanisms between climate, landuse, and hydrology

Water management issues critical to the Volta Basin are discussed in this paper. An introduction to the Volta Basin and its hydrological characteristics provides the necessary background. Hydropower production for urban areas and irrigation development in rural areas compete for water resources. The paper introduces the GLOWA Volta project and presents details highlighting the project’s integrative approach. In order to address water-policy issues, the GLOWA Volta Project seeks to develop a scientifically sound Decision Support System. The main premise of the GLOWA Volta investigation is that changes in landuse may have important, yet unknown, effects on the hydrological cycle of the basin. To predict future water availability, landuse change, driven by physical and social factors, needs to be predicted as well. In order to illustrate the different ways in which landuse affects the movement of water over the surface and through the atmosphere, three examples are given. The first example treats the indirect and direct effects of changes in soil moisture on the atmospheric circulation. In the second example, the high sensitivity of surface water availability with respect to rainfall is determined. The final example shows the increase in dam building activity in the basin which has a direct but rather limited impact on availability of water resources downstream.

Assessment and Management of Water Resources in Developing, Semi-arid and Arid Regions

Assessing and managing water resources in developing and dryland regions is still fraught with difficulties. The typical tool chain of water resources management starts with the collection of data, subsequently processes and analyses the collected information within the natural and socio-economic setting, and finally generates end products that inform decision-making. However, several of these steps often turn out to be problematic when faced with development issues and severe strains on water resources. Many of these regions are characterised by very complex hydrological systems that often exhibit extreme behaviour, such as strong monsoon seasons or extended drought. Commonly used models and analysis techniques may not represent these processes, or at best they are seldom tested for adequacy and robustness. The complexity of the water cycle contrasts strongly with the poor data availability, which limits the number of analysis techniques and methods available to researchers. Finally, technical solutions should take into account the socio-economic setting in which they will be embedded, and address the need for capacity development to ensure that newly introduced technologies and solutions improve the regional skills in water resources management. This special issue aims to highlight the diversity and complexity of the issues faced in a context of development and resources scarcity. It brings together a collection of papers that

Hydrological parameterization through remote sensing in Volta Basin, West Africa

Abstract Ground‐based hydrological data collection tends to be difficult and costly, especially in developing countries such as Ghana and Burkina Faso where the infrastructure for scientific monitoring is limited. Remote sensing has the potential to fill the gaps in observation networks. The GLOWA Volta Project (GVP) seeks to maximize the information to be gained from satellite imagery by combining remotely sensed data with strategically chosen ground observations. However, there is very limited information about the coupling of remotely sensed data with ground based data over the mixed savanna terrain of West Africa. This paper provides an overview of innovative techniques to measure hydrological parameters as actual evapotranspiration, rainfall, and surface runoff over mixed savanna terrain in a semi‐arid region in West Africa, and their potential use. Evapotranspiration – The Surface Energy Balance Algorithm for Land (SEBAL) was used to calculate sensible heat flux and evapotranspiration through the energy balance. The SEBAL parameterization is an iterative and feedback‐based numerical procedure that deduces the radiation, heat and evaporation fluxes. Along a 1,000 km gradient in the Volta Basin, three scintillometers were installed to measure sensible heat flux over distances comparable to NOAA‐AVHRR pixels, approximately two kilometers. The comparison of sensible heat flux measured from remotely sensed data and scintillometers provide accurate results. This will help to increase the reliability of SEBAL parameterization. Rainfall – Depending on the region within the Volta Basin, up to 90% of the precipitation in originates from squall‐lines. The Tropical Rainfall Measuring Mission (TRMM) imagery provides a valuable tool to monitor such squall lines. However, the TRMM signal should be validated for squall line rainfall. To increase the reliability of space‐based rainfall measurements, TRMM based rainfall rate estimates were calibrated with rainfall measurements from a dense network of rain gauges. Surface Runoff – Remote sensing has limited value in estimating surface runoff. The savanna of West Africa, however, is dotted with a large number of small reservoirs used to supply water for households, cattle, and small scale irrigation. Bathymetry of sixty reservoirs in Ghanas Upper‐East Region produced a very regular correlation between surface area, as observable by satellites, and volumes. By using all‐weather RADAR imagery and the measured surface/volume curves, surface runoff volumes can be monitored throughout the year. These indirect runoff measurements will help researchers to develop surface‐runoff models for the Volta Basin.

Cooperation in Transboundary Water Sharing with Issue Linkage: Game-Theoretical Case Study in the Volta Basin

AbstractThis paper investigates issue linkage of water and energy in transboundary water sharing agreements and evaluates how such issue linkages can enhance the scope of cooperation between upstream and downstream countries. In a case study on transboundary water sharing between Burkina Faso and Ghana, the main upstream and downstream riparians in the Volta Basin, the paper evaluates both the scope and sustainability of such cooperation based on issue linkage. In the framework of a static Stackelberg game with numerical analysis, it is found that the interdependency of countries can lead to efficient and effective solutions regarding water sharing. In the cooperation phase, Ghana has the opportunity to increase its water consumption for agriculture, which is currently restricted, while Burkina Faso benefits from discounted hydropower as a compensation for restricting its water consumption. In such a case, the cooperation is mutually beneficial and stable. However, such interdependency may not be sustaina...

Scope and Sustainability of Cooperation in Transboundary Water Sharing of the Volta River

The paper explores the scope and sustainability of a self-enforcing cooperative agreement in the framework of a game theoretic model, where the upstream and downstream country, Burkina Faso and Ghana respectively in the Volta River Basin, bargain over the level of water abstraction in the upstream. In the model we consider the case where the downstream country, Ghana, offers a discounted price for energy export to the upstream country, Burkina Faso, to restrict its water abstraction rate in the upstream. The paper examines the benefits and sustainability of such self-enforcing cooperative arrangements between Ghana and Burkina Faso given stochastic uncertainty in the river flow. The findings of the paper suggest that at the present condition, the marginal benefit of Burkina Faso from increasing the water abstraction is much higher than that of Ghana’s marginal loss. However, the paper finds that if both countries’ water abstraction rates are at a much higher level, then the marginal loss of Ghana increases phenomenally from similar increase in water abstraction rate by Burkina Faso. Under such circumstances, there is an opportunity for Ghana to provide side payments in terms of discounted export price of power in order to motivate Burkina Faso to restrict water abstraction.

Cooperation in Transboundary Water Sharing Under Climate Change

As multiple countries share a river, the likelihood of a water resource conflict from climate change could be higher between countries. In this paper, we demonstrate how countries can cooperate in transboundary water sharing in a sustainable way, given the impacts of climate change. We illustrate the case of water sharing of the Volta River between the upstream and downstream country, Burkina Faso and Ghana respectively, where the latter country faces a tradeoff of water use between agriculture in the north and production of hydro energy in the south. In the framework of a stochastic Stackelberg differential game, we have shown how the issue of water sharing could be linked to hydropower export that can make water sharing between the countries sustaining in the event of climate change. Our results indicate that during cooperation, Ghana will have an opportunity to increase its water abstraction for agriculture, which has remained largely restricted. We also find that the equilibrium strategies in the long run steady state distribution are stable even with increasing variances of water flow.