Sars-CoV-2 is spread through contact between people and an understanding of where people are in contact with each other is necessary to prevent its spread. In this paper, the residential building density of Bulawayo was considered a proxy for high density of people. OpenStreetMap (OSM) building data was downloaded and converted from polygon to point data for use in the analysis. World View 2 data was used to visually map those areas where data was missing in OSM. More automated methods were attempted using eCognition however the short turnaround time of the project limited the success of this approach and work in this regard in ongoing. Land use attribute data was joined to the building shape file in order to select only those building which were designated as residential in nature. The residential building density was calculated per hectare and a hot spot analysis of the residential building density determined statistically significant clusters of high density residential buildings. The high density areas are mostly located in the west of the City, where new settlements are being created to accommodate new arrivals to the city. The East is typified by low density housing, largely a legacy of the City’s colonial past. A series of maps which could be printed on A3 paper were produced for the City. The maps displayed both the results of the hot spot analysis and land use and these have been made available to City officials to help in planning their response to the COVID-19 pandemic.
Multi-dwelling fires in informal settlements in South Africa are devastating for residents resulting in loss of life, homes and belongings. The aim of the IRIS-Fire project is to develop innovative methods of assessing and modelling fire risks with the goal of increasing informal settlement fire resilience. This paper outlines a new approach to mapping historic and ongoing fires in informal settlements using satellite imagery. A theoretical informal settlement fire curve for albedo is proposed based on the predicted reflectance of roof materials pre- and post-burn. Landsat OLI imagery in Google Earth Engine is used to map time series of albedo and the method is tested for a pilot site in Masiphumelele, South Africa. Results indicate that the detected albedo time series matches the theoretical informal settlement fire curve to some extent. Further research will investigate using (1) higher spatial resolution satellite data to reduce the impact of the mixed pixel effect, (2) higher temporal resolution satellite imagery such as Sentinel-2 to increase the revisit time and thus increase the number of high quality images, and (3) dark object subtraction to minimise scene noise, (4) use of statistical quality control charts to detect statistically significant change.
Evapotranspiration (ET) is one of the least understood components of the water cycle, particularly in data scarce areas. In a context of climate change, evaluating water vapour fluxes of a particular area is crucial to help understand dynamics in water balance. In data scarce areas, ET modelling becomes vital. The study modelled ET using the Penman-Monteith- Leuning (PML) equation forced by Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and MODIS albedo with ancillary meteorological data from an automatic weather station. The study area is located on the Albany Thicket (AT) biome of South Africa and the dominant plant species is Portulacaria afra. The biggest challenge to the implementation of the PML is the parameterisation of surface and stomatal conductance. We tested the use of volumetric soil water content (fswc), precipitation and equilibrium evaporation ratio (fzhang) and soil drying after precipitation (f) approaches to account for the fraction (f) of evaporation from the soil. ET from the model was validated using an eddy covariance system (EC). Post processing of eddy covariance data was implement using EddyPro software. The fdrying method performed better with a root mean square observations standard deviation ratio (RSR) of 0.97. The results suggest that modelling ET over the AT vegetation is delicate owing to strong vegetation phenological control of the ET process. The convergent evolution of the vegetation has resulted in high plant available water than the model can detect. It is vital to quantify plant available water in order to improve ET modelling in thicket vegetation.
Determining water and carbon fluxes over a vegetated surface is important in a context of global environmental changes and the fluxes help in understanding ecosystem functioning. Pursuant to this, the study measured evapotranspiration (ET) using an eddy covariance (EC) system installed over an intact example of the Albany Thicket (AT) vegetation in the Eastern Cape, South Africa. Environmental constraints to ET were also assessed by examining the response of ET to biotic and abiotic factors. The EC system comprised of an open path Infrared Gas Analyser and Sonic anemometer and an attendant weather station to measure bi-meteorological variables. Post processing of eddy covariance data was conducted using EddyPro software. Quality assessment of fluxes was also performed and rejected and missing data were filled using the method of mean diurnal variations (MDV). Much of the variation in ET was accounted for by the leaf area index (LAI, p < 0.001, 41%) and soil moisture content (SWC, p < 0.001, 32%). Total measured ET during the experiment was greater than total rainfall received owing to the high water storage capacity of the vegetation and the possibility of vegetation accessing ground water. Most of the net radiation was consumed by sensible heat flux and this means that ET in the area is essentially water limited since abundant energy was available to drive turbulent transfers of energy. Understanding the environmental constraints to ET is crucial in predicting the ecosystem response to environmental forces such as climate change.
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