Simulating the characteristics of droughts in Southern Africa

Includes bibliographical references.Drought is widely considered as one of the most devastating natural disasters in the world. In particular, drought is a big threat in Southern Africa because the economy of most of the population in the region is based on rain-fed agriculture. Previous studies have projected that global warming may enhance the frequency and intensity of droughts over Southern Africa in the future. However, the credibility of this projection depends on the ability of the global and regional climate models (GCMs and RCMs) in simulating the characteristics of drought. This thesis presents the characteristics of the Southern African droughts and evaluates the capability of global and regional climate models in simulating these characteristics. The thesis used a multi-scaled standardized drought index (called standardized precipitation evapo-transpiration index, SPEI) in characterizing droughts at 3- and 12-month scales over Southern Africa. The spatial patterns of the droughts are identified using the principal component analysis (PCA) on the SPEI, while the temporal characteristics of the drought patterns are studied using wavelet analysis. The relationship between each drought pattern and global SSTs (and climate indices) is quantified using correlation analysis and wavelet coherence analysis. The study uses correlation analysis to quantify the capability of the models in simulating the drought patterns

A mechanistic model for long-term immunological outcomes in South African HIV-infected children and adults receiving ART.

Long-term effects of the growing population of HIV-treated people in Southern Africa on individuals and the public health sector at large are not yet understood. This study proposes a novel 'ratio' model that relates CD4+ T-cell counts of HIV-infected individuals to the CD4+ count reference values from healthy populations. We use mixed-effects regression to fit the model to data from 1616 children (median age 4.3 years at ART initiation) and 14,542 adults (median age 36 years at ART initiation). We found that the scaled carrying capacity, maximum CD4+ count relative to an HIV-negative individual of similar age, and baseline scaled CD4+ counts were closer to healthy values in children than in adults. Post-ART initiation, CD4+ growth rate was inversely correlated with baseline CD4+ T-cell counts, and consequently higher in adults than children. Our results highlight the impacts of age on dynamics of the immune system of healthy and HIV-infected individuals