Bodunrin et al. (2025) Analyzing the Spatial and Temporal Dynamics of Rainfall and Drought in The Vall River Basin, South Africa

Identification

• Journal: Arid zone journal of engineering technology and environment/Arid Zone Journal of Engineering Technology and Environment
• Year: 2025
• Date: 2025-12-01
• Authors: I. R. Bodunrin, E. K. Onyari
• DOI: 10.63958/azojete/2025/21/04/007

Research Groups

• Department of Civil and Environmental Engineering and Building Sciences, College of Science, Engineering and Technology, University of South Africa, Johannesburg, South Africa.

Short Summary

This study analyzed the spatial and temporal dynamics of rainfall and drought in the Vaal River Basin, South Africa, from 1983 to 2023 using the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI), revealing an intensification of drought frequency and severity, particularly a severe hydrological drought in 2016, driven by climate change.

Objective

• To analyze the temporal and spatial drought patterns and their impacts on water resources and the environment in the Vaal River Basin (South Africa) from 1983 to 2023.
• To utilize SPI and SPEI drought indices to evaluate drought patterns, produce rainfall maps, identify evapotranspiration patterns, and assess the extent of drought effects in the study area.
• To suggest early warning systems for drought occurrence along the Vaal River basin to ensure water availability.

Study Configuration

• Spatial Scale: Vaal River Basin, South Africa (between 26.5°S - 28.5°S, 24°E - 29.5°E), covering parts of Gauteng, Free State, Mpumalanga, Northwest, and Eastern Cape provinces.
• Temporal Scale: 1983 to 2023 (41 years). Drought assessment conducted across multiple timescales (1, 3, 6, 12, 24, and 48 months).

Methodology and Data

• Models used:
  • Standardized Precipitation Index (SPI)
  • Standardized Precipitation Evapotranspiration Index (SPEI)
  • Hargreaves method for Potential Evapotranspiration (PET) estimation
  • Mann-Kendall Trend Test and Sen's Slope estimator for rainfall trend analysis
  • ArcGIS 10.1 for rainfall mapping and study area delineation
  • R for drought index calculations and statistical analysis
• Data sources:
  • Rain gauged data and remotely sensed data
  • Precipitation and temperature records from the South African Weather Service
  • CHIRPS (Climate Hazards Group InfraRed Precipitation with Station data) for precipitation
  • MODIS MOD16A2 for evapotranspiration
  • Data from six meteorological stations, averaged to represent drought severity and duration across the lower, middle, and upper Vaal River basins.

Main Results

• Peak precipitation in the Vaal River Basin occurs during the January to March summer months.
• The annual average evapotranspiration consistently exceeds the annual average precipitation in the Vaal River basin.
• Rainfall showed a downward trend across the Vaal River regions (weak in Lower Vaal, strong in Middle Vaal, moderate in Upper Vaal), although these trends were not statistically significant (p > 0.05).
• 2016 was identified as the hydrologically driest year for the Vaal River based on SPI and SPEI analysis at 12- and 24-month scales, with SPEI-24 reaching -3.20 in the lower Vaal.
• Agricultural droughts were evident in years such as 1983, 1999, 2016, and 2019, particularly at SPEI/SPI-3 and SPEI/SPI-6 timescales.
• Drought frequency and intensity increased markedly after 2013, especially between 2013 and 2018.
• Drought events were more frequent and severe in the middle and upper Vaal regions compared to the lower Vaal.
• SPI and SPEI demonstrated increasing temporal consistency with longer timescales (12- and 24-month scales were most reliable for detecting hydrological droughts), except for SPEI/SPI-1 and SPEI/SPI-48 which did not accurately represent drought in the basin.

Contributions

• Provides a comprehensive spatiotemporal analysis of rainfall variability and drought patterns in the Vaal River Basin over a four-decade period (1983-2023), utilizing both SPI and SPEI indices.
• Highlights the escalating impact of climate change-induced drought in the Vaal area, a vital water resource region for South Africa's agriculture, industry, and domestic use.
• Emphasizes the enhanced capability of SPEI in assessing drought severity by integrating temperature and evapotranspiration, offering a more complete water balance perspective compared to SPI alone.
• Offers crucial insights for informed decision-making, effective water resource management, and the development of early warning systems to build resilience against future drought events in the region.

Funding

Not explicitly mentioned in the paper.

Citation

@article{Bodunrin2025Analyzing,
  author = {Bodunrin, I. R. and Onyari, E. K.},
  title = {Analyzing the Spatial and Temporal Dynamics of Rainfall and Drought in The Vall River Basin, South Africa},
  journal = {Arid zone journal of engineering technology and environment/Arid Zone Journal of Engineering Technology and Environment},
  year = {2025},
  doi = {10.63958/azojete/2025/21/04/007},
  url = {https://doi.org/10.63958/azojete/2025/21/04/007}
}