Anatomy of an extended drought in part of the Eastern Cape Province, South Africa

The city of Grahamstown in the Eastern Cape Province of South Africa has been experiencing an extended period of below average rainfall for more than 7 years. The public perception of this drought is that it could be a consequence of climate change and represents the new ‘normal’ for this area. This study looks at this drought in the context of daily rainfall records extending back to the start of the 20^th century. The rainfall data are analysed in several ways to determine if this drought is really exceptional and to try and identify any unique characteristics of the recent drought period. The analyses are all relatively simple non-statistical methods, largely because statistical trend tests are considered by the author to frequently suggest results that are more artifacts of the data analysis methods than real, particularly in data sets that show cyclical trends (frequently shown to be one of the key characteristics of South African rainfall data).  

A relatively simple analysis using the cumulative departure of monthly rainfall totals from the calendar month means shows a systematic downward slope since 2014 (Figure 1). However, there was a similar general downward trend between 1940 and 1960, as well as between 1980 and 1990, suggesting that, from this perspective, the current period is not exceptional. A comparative analysis using a similarly long rainfall record for a farm located in a drier area, but only 20 km from the city, shows a relatively different pattern of historical rainfall variations.

Other types of analysis using different rainfall characteristics show different things. The rainfall data for over 120 years are also used to force a hydrological model to generate simulated streamflow, groundwater recharge and soil moisture storage to further investigate the drought characteristics from a broader perspective than simply the rainfall data themselves. The rainfall data are also used to simulate the performance of a domestic rainwater storage tank to investigate the feasibility of using household level interventions to mitigate against deficiencies in the municipal water supply.