Estimating rainfall and water balance over the Okavango River Basin for hydrological applications

A historical database for use in rainfall-runoff modeling of the Okavango River Basin in Southwest Africa is presented. The work has relevance for similar data-sparse regions. The parameters of main concern are rainfall and catchment water balance which are key variables for subsequent studies of the hydrological impacts of development and climate change. Rainfall estimates are based on a combination of in-situ gauges and satellite sources. Rain gauge measurements are most extensive from 1955 to 1972, after which they are drastically reduced due to the Angolan civil war. The sensitivity of the rainfall fields to spatial interpolation techniques and the density of gauges was evaluated. Satellite based rainfall estimates for the basin are developed for the period from 1991 onwards, based on the Tropical Rainfall Measuring Mission (TRMM) and Special Sensor Microwave Imager (SSM/I) data sets. The consistency between the gauges and satellite estimates was considered. A methodology was developed to allow calibration of the rainfall-runoff hydrological model against rain gauge data from 1960-1972, with the prerequisite that the model should be driven by satellite derived rainfall products for the 1990s onwards. With the rain gauge data, addition of a single rainfall station (Longa) in regions where stations earlier were lacking was more important than the chosen interpolation method. Comparison of satellite and gauge rainfall outside the basin indicated that the satellite overestimates rainfall by 20%. A non-linear correction was derived used by fitting the rainfall frequency characteristics to those of the historical rainfall data. This satellite rainfall dataset was found satisfactory when using the Pitman rainfall-runoff model (Hughes et al., this issue). Intensive monitoring in the region is recommended to increase accuracy of the comprehensive satellite rainfall estimate calibration procedur

Computer simulation of radio-frequency methane/hydrogen plasmas and their interaction with GaAs Surfaces

The following thesis describes the computer modelling of radio frequency capacitively coupled methane/hydrogen plasmas and the consequences for the reactive ion etching of (100) GaAs surfaces. In addition a range of etching experiments was undertaken over a matrix of pressure, power and methane concentration. The resulting surfaces were investigated using X-ray photoelectron spectroscopy and the results were discussed in terms of physical and chemical models of particle/surface interactions in addition to the predictions for energies, angles and relative fluxes to the substrate of the various plasma species. The model consisted of a Monte Carlo code which followed electrons and ions through the plasma and sheath potentials whilst taking account of collisions with background neutral gas molecules. The ionisation profile output from the electron module was used as input for the ionic module. Momentum scattering interactions of ions with gas molecules were investigated via different models and compared against results given by quantum mechanical code. The interactions were treated as central potential scattering events and the resulting neutral cascades were followed. The resulting predictions for ion energies at the cathode compared well to experimental ion energy distributions and this verified the particular form of the electrical potentials used and their applicability in the particular geometry plasma cell used in the etching experiments. The final code was used to investigate the effect of external plasma parameters on the mass distribution, energy and angles of all species impingent on the electrodes. Comparisons of electron energies in the plasma also agreed favourably with measurements made using a Langmuir electric probe. The surface analysis showed the surfaces all to be depleted in arsenic due to its preferential removal and the resultant Ga:As ratio in the surface was found to be directly linked to the etch rate. The etch rate was determined by the methane flux which was predicted by the code

Extreme rainfall events over southern Africa: influence of Atlantic SST on rainfall variability

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Satellite rainfall retrieval: a climate modelling perspective

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Trends and variability of the start of the wet season over Africa

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Assessment of a climate model to reproduce rainfall variability and extremes over Southern Africa

It is increasingly accepted that any possible climate change will not only have an influence on mean climate but may also significantly alter climatic variability. A change in the distribution and magnitude of extreme rainfall events (associated with changing variability), such as droughts or flooding, may have a far greater impact on human and natural systems than a changing mean. This issue is of particular importance for environmentally vulnerable regions such as southern Africa. The sub-continent is considered especially vulnerable to and ill-equipped (in terms of adaptation) for extreme events, due to a number of factors including extensive poverty, famine, disease and political instability. Rainfall variability and the identification of rainfall extremes is a function of scale, so high spatial and temporal resolution data are preferred to identify extreme events and accurately predict future variability. The majority of previous climate model verification studies have compared model output with observational data at monthly timescales. In this research, the assessment of ability of a state of the art climate model to simulate climate at daily timescales is carried out using satellite-derived rainfall data from the Microwave Infrared Rainfall Algorithm (MIRA). This dataset covers the period from 1993 to 2002 and the whole of southern Africa at a spatial resolution of 0.1° longitude/latitude. This paper concentrates primarily on the ability of the model to simulate the spatial and temporal patterns of present-day rainfall variability over southern Africa and is not intended to discuss possible future changes in climate as these have been documented elsewhere. Simulations of current climate from the UKMeteorological Office Hadley Centre’s climate model, in both regional and global mode, are firstly compared to the MIRA dataset at daily timescales. Secondly, the ability of the model to reproduce daily rainfall extremes is assessed, again by a comparison with extremes from the MIRA dataset. The results suggest that the model reproduces the number and spatial distribution of rainfall extremes with some accuracy, but that mean rainfall and rainfall variability is underestimated (over-estimated) over wet (dry) regions of southern Africa

The way we live from now on : lifestyle and energy consumption

This book section is from Energy 2050 : making the transition to a secure low-carbon energy system: The United Kingdom is committed to reducing its greenhouse gas emissions by at least eighty per cent by 2050, a target that will only be achieved by transforming the way that energy is supplied and used. At the same time there are anxieties about the security of energy provision in terms of European dependency on natural gas and the reliability of electricity supply. This book explores in detail those factors which could help or hinder the attainment of the UK's climate change targets, and how these factors interact with the parallel objective of maintaining a robust and secure energy system. The book is the result of a major national energy research effort by the UK Energy Research Centre, which includes some of the UK's leading energy experts. The results and recommendations are essential reading for policymakers, professionals, researchers, and anyone concerned with achieving large-scale reductions in carbon emissions, both from the UK and internationally. Energy 2050 begins by exploring the evolution of the UK energy system over recent decades: the trends, technologies and environmental impacts related to energy use, and the structures and institutions of governance that have influenced this evolution. It then moves on to changes in energy policy to emphasise decarbonization and resilience, and introduce the approach to scenarios and modelling used in the rest of the book. Later chapters explore different aspects of the uncertainties that may enable or constrain the creation of a low-carbon, resilient UK energy system, related to accelerated technology development, the creation of an infrastructure to support de-centralized energy and microgeneration, to lifestyle and behaviour change, and to public attitudes to wider environmental impacts associated with energy system change

Simulating climate impacts on water resources: experience from the Okavango river, Southern Africa

The Okavango River is one of the largest and most important rivers in Southern Africa. The river rises in Angola, a country that has just emerged from a civil war of three decades. The annual flood pulse of the river feeds the Okavango Delta: one of the most valuable environmental resources of the African continent. The Okavango River water and its ecosystem resources are critically important sources of livelihoods in the basin. Pressures from livelihoods and development are already impacting on the environment and are likely to increase. Moreover, future development will occur against the background of climate variability and change. This chapter describes research conducted under the EU-funded project‘Water and Ecosystem Resources in Regional Development’ (WERRD), whose aims included development of scenario modelling as a tool for integrated water resource management in the Okavango River basin. The impact of climate change scenarios on downstream river flow and flooding in the Okavango Delta are simulated using a suite of hydrological models. The simulated impacts of climate change are sensitive to the choice of GCM and the IPCC SRES greenhouse gas (GHG) emission scenarios. The simulated impacts are considerable larger that those of the selected development scenarios although the uncertainty in the magnitude of future changes remains high