The Botswana High is a prominent mid-tropospheric system that modulates rainfall over subtropical southern Africa, but the capability of a Global Climate Model (GCM) to reproduce it remains unknown. This study examines the capability of a GCM with quasi-uniform resolution (Model Prediction Across Scales, hereafter MPAS) in simulating the characteristics of the Botswana High. The MPAS is applied to simulate the global climate at 240km quasi-uniform resolution over the globe for the period 1980-2010. The model results are validated against gridded observation dataset (Climate Research Unit, CRU), satellite dataset (Global Precipitation Climatology Project, GPCP), and reanalysis datasets (Climate Forecast System Reanalysis, CFSR; the National Oceanic and Atmospheric Administration, NOAA; and the European Centre for Medium-Range Weather Forecasts version 5, ERA5). In general, MPAS replicates all the essential features in the climatology of temperature, rainfall, 500 hPa geopotential height and vertical motion over southern Africa, reproduces the spatial and temporal variation of the Botswana High, and captures the in uence of the Botswana High on droughts and deep convections over the sub-continent. In addition, the model reproduces well the anomalies in vertical motion over subtropical southern Africa during +ve and -ve phases of the Botswana High. However, the model struggles to reproduce the precipitation pattern associated with the positive and native modes of Botswana high. The results of this study have an application in understanding the characteristics of Botswana High and in improving MPAS for seasonal forecasting over southern Africa.

This analysis investigates the relationship between drought and antiretroviral treatment (ART) adherence and retention in HIV care in the Hlabisa sub-district, KwaZulu-Natal, South Africa. Data on drought and ART adherence and retention were collated for the study period 2010–2019. Drought was quantified using the 3-month Standard Precipitation Evapotranspiration Index (SPEI) and Standard Precipitation Index (SPI) from station data. Adherence, proxied by the Medication Possession Ratio (MPR), and retention data were obtained from the public ART programme database. MPR and retention were calculated from individuals aged 15–59 years who initiated ART between January 2010 and December 2018 and visited clinic through February 2019. Between 01 January 2010 and 31 December 2018, 40,714 individuals started ART in the sub-district and made 1,022,760 ART visits. The SPI showed that 2014–2016 were dry years, with partial recovery after 2016 in the wet years. In the period from 2010 to 2012, mean 6-month MPR increased from 0.85 in July 2010 to a high of 0.92 in December 2012. MPR then decreased steadily through 2013 and 2014 to 0.78 by December 2014. The mean proportion retained in care 6 months after starting ART showed similar trends to MPR, increasing from 86.9% in July 2010 to 91.4% in December 2012. Retention then decreased through 2013, with evidence of a pronounced drop in January 2014 when the odds of retention decreased by 30% (OR = 0.70, CI = 0.53–0.92, P = 0.01) relative to the end of 2013. Adherence and retention in care decreased during the drought years.

The Botswana High is an important component of the regional atmospheric circulation during austral spring, summer and autumn. While the high tends to be stronger during El Niño and weaker during La Niña, its direct response to El Niño Southern Oscillation (ENSO) remains unknown. To that end, a variable resolution global climate model (Model Prediction Across Scales version 7, hereafter MPAS) is applied with relatively high resolution (48 km grid spacing) over southern Africa and a coarser resolution (240 km grid spacing) over the rest of the globe for the study period 1980-2010. The rst model experiment uses observed SSTs everywhere during the study period, while the second experiment uses observed SSTs everywhere except over the Paci c Ocean, where monthly climatological SSTs are imposed. The model results were validated against satellite data (Global Precipitation Climatology Project, GPCP), reanalysis datasets (Climate Forecast System Reanalysis, CFSR; European Centre for Medium-Range Weather Forecasts version 5, ERA5). The results of the study show that the MPAS model gives a credible simulation of the temporal variability of the Botswana High, the seasonal rainfall and 500 hPa geopotential heights over southern Africa. In the absence of ENSO forcing, the amplitude of the Botswana High variability reduces but the signal of the variability remains. Hence, this study shows that ENSO enhances the strength of the Botswana High but does not aid in the formation of the Botswana High.

The Botswana High is a prominent mid-tropospheric system that modulates rainfall over subtropical southern Africa, but the capability of a Global Climate Model (GCM) to reproduce it remains unknown. This study examines the capability of a GCM with quasi-uniform resolution (Model Prediction Across Scales, hereafter MPAS) in simulating the characteristics of the Botswana High. The MPAS is applied to simulate the global climate at 240km quasi-uniform resolution over the globe for the period 1980-2010. The model results are validated against gridded observation dataset (Climate Research Unit, CRU), satellite dataset (Global Precipitation Climatology Project, GPCP), and reanalysis datasets (Climate Forecast System Reanalysis, CFSR; the National Oceanic and Atmospheric Administration, NOAA; and the European Centre for Medium-Range Weather Forecasts version 5, ERA5). In general, MPAS replicates all the essential features in the climatology of temperature, rainfall, 500 hPa geopotential height and vertical motion over southern Africa, reproduces the spatial and temporal variation of the Botswana High, and captures the influence of the Botswana High on droughts and deep convections over the sub-continent. In addition, the model reproduces well the anomalies in vertical motion over subtropical southern Africa during +ve and -ve phases of the Botswana High. However, the model struggles to reproduce the precipitation pattern associated with the positive and native modes of Botswana high. The results of this study have an application in understanding the characteristics of Botswana High and in improving MPAS for seasonal forecasting over southern Africa.

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