During summertime Saharan heat low, a region of low pressure system, is formed as a result of large solar insolation superimposed with the convergence of west African South westerly monsoon flow and dry north easterly Harmattan flow along the intertropical discontinuity. This region plays significant role in the initiation and development of the West African Monsoon. The Saharan heat low is co-located with region of maximum load of dust aerosol which is known to have impact on the climate. Further the Saharan heat low plays key role in the global circulations including its role in formation of African Easterly Jets and African Easterly Waves. Despite its role in influencing the dynamic and thermodynamics of the region, the Saharan Heat low is not extensively studied partly due to lack of comprehensive data due to the harsh weather conditions of the region. Climate system of the Saharan heat low is a result of different complicated atmospheric and land surface processes most dominantly immense solar input at the surface, large convergence of sensible heat flux from the ground into the atmosphere, and low level cooling by horizontal advection of moisture from the surrounding area. These dynamical and thermodynamical processes take part in transport and redistribution of heat and transport of the moisture in the region. This thesis aims at providing a detailed analysis of the physical processes responsible for the development, maintenance, and decadal variability of the Saharan heat low region. I investigate three specific aspects of the Saharan heat low region. 1. Heat and Moisture Budget: Heat and moisture are drivers of dynamics and thermodynamics of a region. Previous studies presented heat and moisture budget of the Saharan heat Low without attributing to the detailed mechanisms by which heat and moisture is transported from the surrounding area to the Sahara heat low and vice versa. This thesis presents components of heat and moisture budget resulting from mean and transient flows that are responsible for heating/cooling and moistening/drying of the Sahara heat low region. Heat and moisture budget are derived using commonly used reanalyses simulations (ERA-I, NCEP, and MERRA) and comparison of the results between the three reanalyses are made. I investigate the mechanisms responsible for the decadal variability of intensity of the Sahara heat low and provide implications. This work has not been done previously to the best of knowledge. 2. Role of Dust and Water vapor in controlling the radiative flux: Recent studies show that water vapour greenhouse forcing is responsible for intensification of the Saharan heat low and as a consequence recovery of Sahel rainfall. Dust aerosol is known to have impact on the climate through its interaction with radiation. The large dust load in the Sahara heat low makes it important in controlling the variability in the radiative budget of the region. Previous studies have quantified the role of dust and water vapour in the region in controlling day to day variability in the radiative flux in the heat low. There is still uncertainty in the radiative forcing and associated variability partly due to lack of observational data. Furthermore separating the radiative effect of dust from that of water vapour is challenging due to the co-variability of dust and water vapour. This thesis quantifies separate and combined effect of dust and water vapour in controlling the radiative flux of the Saharan heat low using the recently made FENNEC observations of meteorological variables and dust loading. Theoretical experiments are made to study sensitivity of radiative flux to variations in dust and water vapour. 3. Characteristics of convective density currents: Convective down drafting density currents (cold pools) are ubiquitous features of the Saharan Heat low region which are shown to play important role in the transport of moisture and emission of dust in the region. Despite this, the characteristics of these atmospheric processes are not well studied in the Sahara Heat Low. Improving our knowledge of properties of convective density currents is imperative to better understand atmospheric processes within boundary layer of the Saharan heat low and thus improve model simulation performance. Here I provide magnitude, spatial distribution, and seasonal variability of cold pools using data from the Automatic weather Station (AWS) spread over the Sahara desert. I implement a unique identification method which is further verified by satellite observations of cold pool signatures. Once cold pools are identified at all stations, statistical description of the occurrence frequency and distribution are presented. Finally I asses reanalyses model simulation of convection triggered cold pool outflows through comparison with measurements.

This thesis develops an innovative process-based analysis of contemporary model performance of precipitation over southern Africa. This region is typically understudied and not fully understood due to the complexity of various influences and drivers of precipitation. Historical simulations of precipitation are assessed including principal drivers, sources of biases and dominant modes of interannual variability. The South Indian Ocean Convergence Zone (SIOCZ), a large-scale, austral summer rainfall feature extending across southern Africa into the south-west Indian Ocean, is evaluated as the feature of interest in historical simulations. Most CMIP5 models simulate an SIOCZ feature, but are typically too zonally oriented and discontinued between land and the adjacent Indian Ocean. Excessive precipitation over the continent is likely associated with excessively high low-level moisture flux around the Angola Low, which is almost entirely due to model circulation biases. Drivers of precipitation over southern Africa include three dominant moisture flux transport pathways which originate from flow around the SIOHP and SAOHP and monsoon winds. Interannual variability in the SIOCZ is shown by a clear dipole pattern, indicative of a northeast-southwest movement of the SIOCZ. Drivers of this shift are significantly related to the El Niño Southern Oscillation and the subtropical Indian Ocean dipole in observations. However models do not capture these teleconnections well, limiting confidence in model representation of variability. A large majority of the population rely heavily on precipitation over southern Africa for agricultural purposes. Therefore spatial and temporal changes in precipitation are crucial to identify and understand with intentions to ultimately provide useful climate information regarding water security over the region. Key climate change signals over southern Africa are established in this thesis (OND and DJF), in which the dominant regional mechanisms of precipitation change over southern Africa are quantified. Robustness and credibility of these changes are additionally quantified. The most notable projected change in precipitation over southern Africa is the distinct drying signal evident in the pre-summer season (OND). This has the implication of delaying the onset of the rainy season affecting planting and harvesting times. Future projections of the SIOCZ are determined, which indicate a northward shift of approximately 200km. A dipole pattern of precipitation wetting/drying is evident, where wetting occurs to the north of the climatological axis of maximum rainfall, hence implying a northward shift of the ITCZ, consistent with the SIOCZ shift. Using a decomposition method it is established that ΔP's dipole pattern emerges largely from the dynamic component, which holds most uncertainty, particularly over the south-west Indian Ocean. Changes in precipitation over land are not solely driven by dynamical changes but additionally driven by thermodynamic contributions, implying projected changes over land and ocean regions require different approaches. SST patterns of warming over the Indian Ocean corroborate the warmest-get-wetter mechanism driving wetting over the south-west Indian Ocean, which is robust in both key seasons. Coherent model behaviour is understood via across model correlation plots of principal components, whereby patterns of coherent warming patterns are identified. Composite analyses of diagnostic variables across models illustrate patterns driving projected precipitation changes. Drying is more robust over land than over the south-west Indian Ocean. Clear robust drying signal in OND, however magnitude is uncertain. Drivers of uncertainty include SST pattern changes, which modulate atmospheric circulation patterns. Therefore reductions in uncertainty rely on the accurate representation of these processes within climate models to become more robust. There is a desire from both climate scientists and policy-makers to reduce uncertainty in future projections. No one particular methodology is unanimously agreed upon, however one approach is analysed in this thesis. Uncertainties of future precipitation projections are addressed using a process-based model ranking framework. Several metrics most applicable to southern African climate are selected and ranked, which include aspects of both mean state and variability. A sensitivity test via a Monte Carlo approach is performed for various sub-samples of “top” performing models within the CMIP5 model dataset. Uncertainty is significantly reduced when particular sub-sets of “top” performing models are selected, however only for austral summer over the continent. The result has the implication that potential value is established in performing a process-based model ranking over southern Africa. However additional investigation is required before such an approach may become viable and sufficiently credible and robust. Reductions in model spread are additionally established in SIOCZ projections, whereby model processes of change exhibit agreement, despite differing initial SIOCZ conditions. Therefore model process convergence and coherence is established with respect to projected changes in the SIOCZ, irrespective of initial climatology biases.

Research has shown that self-affirmation often leads to more adaptive responses to messages that focus on behaviour-specific, individual threats. However, little is known about the effects of self-affirmation in the context of a multifaceted collective threat, such as climate change. In the current thesis I apply self-affirmation theory to the psychology of climate change. More specifically, I propose that differentially polarized environmental orientations can have an impact on self-affirmation effects. In Chapter 1, I provide a general integration of the self-affirmation literature, the literature on sceptical responses to climate change, and the findings reported in the current thesis. The results from six empirical studies are presented in the following four chapters. In Chapter 2, I present findings that indicated that sceptical responses to climate change information are not always reduced through self-affirmation, but are instead strongly dependent on people's initial levels of rejection of environmental problems. In Chapter 3, I suggest that in the absence of a persuasive threatening message, self-affirmation can serve to validate a person's initial worldviews about environmental issues. In line with this suggestion, results demonstrated that self-affirmation led to more pro-environmental motives among participants with positive ecological worldviews but led to less pro-environmental motives among participants with negative ecological worldviews. In Chapter 4, I examine self-affirmation effects on the acceptance of climate change information. Results showed that self-affirmation promoted perceptions of greater climate change consequences and more self-efficacy among initially sceptical participants. Additionally, self-affirmation reduced pessimism among less sceptical participants. In Chapter 5, I present evidence that showed that self-affirmation resulted in more acceptance of information portraying the UK's contribution to climate change problems among participants with high national identification, while group-affirmation resulted in more information acceptance among participants with low national identification. These effects were only apparent among participants with negative ecological worldviews.

Quantification of flood risk and flood inundation requires accurate numerical simulations, both in terms of the mathematical theory that underpins the methods used and the manner in which the meteorological phenomena that cause flooding are coupled to such systems. Through our research, we have demonstrated how rainfall and infiltration effects can be incorporated into existing flood models in a rigorous and mathematically consistent manner; this approach departs from preceding methods, which neglect terms representing such phenomena in the conservation or balancing of momentum. We demonstrate how the omission of these terms means the solution derived from such models cannot a priori be assumed to be the correct one, which is in contrast to solutions from the extended system we have developed which respect the energetic consistency of the problem. The second issue we address is determining how we can model these meteorological phenomena that lead to flooding, with a specific interest in how existing observation data from rain gauges can be incorporated into our modelling approach. To capture the random nature of the precipitation, we use stochastic processes to model the complex meteorological interactions, and demonstrate how an accurate representation of the precipitation can be built. Given the specific industrial applications we have mind in regards to flood modelling and prediction, there will be a high computational cost associated with any such simulations, and so we consider techniques which can be used to reduce the computational cost whilst maintaining the accuracy of our solutions. Having such an accurate flood model, coupled with a stochastic weather model designed for efficient computational modelling, will enable us to make useful predictions on how future climate change and weather patterns will impact flood risk and flood damage.