Abstract
The Free State (FS) and North West (NW) Provinces are often hard hit by droughts with impacts on water availability, farm production and livestock holdings. The South African government declared the two Provinces drought disaster areas in the 2015/2016 hydrological year. This is a major drawback, since both the Provinces play an important role to South African economy as they are a haven to agricultural production and have major water reservoirs in South Africa. This study was undertaken to investigate the historical evolution of drought within the FS and NW Provinces over the past 30 years. The Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) calculated based on monthly meteorological data from 14 weather/climate stations within the FS and NW Provinces were used to explore and characterize variation in drought intensity, duration, frequency and severity in FS and NW Provinces during 1985–2015. Results indicate that there exist localized positive and negative trends with spatial dependence across the selected stations. In particular, about 60% of the weather stations exhibiting a decreasing trend are located in FS Province, suggesting that FS has being experiencing increasing drought during the analyzed period compared to NW Province. Results from the analysis of drought evaluation indicators (DEIs) calculated from SPEI suggest that drought severity and frequency was more pronounced in FS while the intensity of the drought was more in NW Province during 1985–2015. In addition, based on SPEI calculations, moderate drought occurrences increased during 1985–1994 and 1995–2004 periods and decreased thereafter (2005–2015) in both Provinces. Drought classification based on parameters derived from SPEI produced similar results for mild drought occurrences during the same time scales.
Highlights
Extreme Earth systems processes have continued to manifest in terms of natural hazards whose impacts are felt by the entire ecosystem including mankind
Results from the analysis of drought evaluation indicators (DEIs) calculated from Standardized Precipitation Evapotranspiration Index (SPEI) suggest that drought severity and frequency was more pronounced in Free State (FS) while the intensity of the drought was more in North West (NW) Province during 1985–2015
In order to better understand the behavior of the Standardized Precipitation Index (SPI) and SPEI indices across FS and NW Provinces, trends of the DTs were performed for the 14 selected weather stations for the period spanning 1985–2015
Summary
Extreme Earth systems processes have continued to manifest in terms of natural hazards whose impacts are felt by the entire ecosystem including mankind. Drought is one such extreme physical process and is often characterized as a slow-onset natural hazard whose impacts are complex and reverberate through many sectors of the economy such as water resources, agriculture, and natural ecosystems [1,2]. Water 2016, 8, 439 of droughts on the ecosystem and society at large has made drought the subject of numerous studies (e.g., see [3,4,5,6] and references therein). A review by Dracup et al [7]
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