Projected changes in drought characteristics over the Western Cape, South Africa

• Published in: Meteorological applications 2020-01, Vol.27 (1), p.n/a
• Main Authors: Naik, Myra, Abiodun, Babatunde J.
• Format: Article
• Language: English
• Subjects: Catchment area; Catchments; Climate change; Drought; Drought characteristics; Drought conditions; Drought index; Drought patterns; Drying; Environmental impact; Evapotranspiration; Evapotranspiration-precipitation relationships; Global warming; Mitigation; Potential evapotranspiration; Precipitation; River catchments; Rivers; Socioeconomic factors; South Africa; Standardized precipitation index; Western Cape
• ISSN: 1350-4827; 1469-8080
• DOI: 10.1002/met.1802

The devastating socioeconomic impacts of recent droughts in the Western Cape have intensified the quest for future drought mitigation measures. While ongoing global warming may increase atmospheric evaporative demand and worsen drought conditions, most studies on drought in the Western Cape have overlooked the role of potential evapotranspiration (PET). The present study examines the role of PET on future drought characteristics, focusing on four river catchments. Two drought indices, the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evapotranspiration Index (SPEI), were analysed. The capability of the Co‐ordinated Regional Downscaling Experiment simulations to reproduce the drought characteristics was evaluated by comparing present‐day climate simulations with observations. The impacts of different global warming levels (GWLs) on the SPI and SPEI projections were assessed using self‐organizing map (SOM) classifications. The results project that a robust drying signal across the Western Cape, but the magnitudes of the projections, which vary across the river catchments, increase with the GWLs. The changes in the drought intensity and frequency are weaker when using the SPI than the SPEI, suggesting that SPI projections may underestimate the influence of global warming on drought because they do not account for the influence of PET. The SOM classification confirms the differences between the two drought indices reveals the drought patterns that are not seen in the drought ensemble means. Nevertheless, the study underscores the need to mitigate future drought impacts over the Western Cape, but with careful consideration on the drought index used in characterizing the droughts. The potential impact of global warming on droughts over the Western Cape is assessed using two drought indices (the Standardized Precipitation Index, SPI; the Standardized Precipitation Evapotranspiration Index, SPEI) with emphasis on the role of potential evapotranspiration. The results suggest a robust future drying over the region. The magnitude of the drying increases with increasing global warming levels. However, a weaker drying is projected with the SPI than with the SPEI, suggesting that SPI projections may underestimate the severity of the future drought over the region.