The Climatology of heat waves in the North West Province, South Africa

Abstract

The overall objective of this dissertation was to develop a heat wave climatology in North West Province (NWP) of South Africa (SA) through analysing maximum temperature and subsequent atmospheric parameters during the heat wave episodes. The main challenge in studying heat wave is the lack of uniform definition. However, in South Africa, the South African Weather Service (SAWS) has defined it as a condition when mean maximum temperatures for the hottest month are exceeded by 5°C and persist for a minimum of three consecutive days. Based on the statistical analysis of maximum temperatures above a station threshold, 25 heat wave events across 13 stations in NWP were identified. The study domain was extended to include the adjacent oceans (10° - 40°S, 0° - 60°E); in order to monitor the evolution of the large- scale circulation as the heat waves develops. The reanalysis of vector winds, humidity, Outgoing Longwave Radiation (OLR), and geopotential heights at 200 hPa, 500 hPa and 850 hPa from NOAA/OAR/ESRL PSD, Boulder Colorado USA through their website at http://www.esrl.noaa.gov/psd were used. Cyclic patterns associated with the recurrence of heat waves in NWP were discovered through the application of spectral analysis. Three signals were identified at different periodicities, namely 12years, 4.8 years, and 2.1 years. These cycles were associated with sunspot activity, El Nino-Southern Oscillation (ENSO), and quasi-biennial oscillation (QBO) respectively. The significant findings that relate large-scale atmospheric circulation and heat waves occurrences were found to include: (i) persistent clear skies over the study area identified by higher OLR values; (ii) existence of strong subsidence as observed from vertical motion patterns and (iii) lower specific humidity and corresponding wind patterns over the South West Indian Ocean (SWIO) and the South Atlantic Ocean (SAO). From this study, the concept and methodology applied in this dissertation should provide the basis for further heat waves scientific research in order to enhance a better understanding about this phenomena. The outcomes derived from this study could be used in various practical applications that include formulating policy developments and several sectoral preparedness and response.