Abstract
Eswatini, as the rest of southern Africa, is being frequented by drought over the last decade, and modelling experts are predicting that drought years will become more and severe. The expected increase in extreme climatic events makes the use of drought indices essential for drought monitoring and early warning. To enable Eswatini to better prepare, analyse and respond to drought, this study analysed the use of Normalised Difference Vegetation Index (NDVI) and Standard Precipitation Index (SPI) for near-real-time drought monitoring through the development of a model for drought severity. Meteorological stations across all agro-ecological zones with data for the period 1986–2017 were selected for analysis. The SPI computation was achieved through DrinC software. Primary NDVI data sources were CHIRPS gridded rainfall dataset and the MODIS NDVI CMG data. Results of the 3-month SPI indicated that moderate droughts were experienced in 1990/1991, 2005/2006, 2011/2012, 2012/2013 and 2015/2016. The Highveld and Middleveld had the lowest drought occurrence percentage of 3.3%, whereas the likelihood of having a moderate, severe and extreme drought was higher in the Lowveld. The study determined a positive correlation between the SPI and the NDVI at 3-month time scale, and a value of Y (drought severity) greater than 0.54 indicated a significant dry spell and could be used as a drought trigger threshold for early warning. The combined use of NDVI and SPI was deemed capable of providing a near-real-time indicator for drought conditions allowing planners to provide timely information for drought preparedness, mitigation and response planning, thereby helping to lower the eventual drought relief costs, protect food security and reduce the humanitarian impact on the population.
Highlights
Eswatini, as the rest of southern Africa, is being frequented by drought over the last decade
This study analysed the use of Normalised Difference Vegetation Index (NDVI) and Standard Precipitation Index (SPI) for near-realtime drought monitoring in Eswatini
Similar research by Hayes et al (1999) found out that because of the SPI versatility, it can be calculated on any timescale, thereby giving it the ability to monitor drought conditions
Summary
As the rest of southern Africa, is being frequented by drought over the last decade. The Eswatini Vulnerability Assessment reports have indicated that yields, especially in the Lowveld, can be reduced by over 50% during drought years, thereby affecting the overall country food security situation. This reduction in agriculture production, especially for the maize (the staple crop), results in the government importing grain and the UN and non-governmental organisations providing 20% – 30% of the population with food aid. The extent of the food aid distributed as well as imports needed requires effective and timely planning by the government and stakeholders, ensuring that the required food is available on time and the populace does not go hungry This makes the aspect of drought monitoring and early warning critical
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