The climate of Namaqualand in the nineteenth century

Abstract

Southern African climatic change research is hampered by a lack of long-term historical data sets. This paper aims to extend the historical climate record for southern Africa to the semi-arid area of Namaqualand in the Northern Cape province of South Africa. This is achieved through extensive archival research, making use of historical documentary sources such as missionary journals and letters, traveller's writings and government reports and letters. References to precipitation and other climatic conditions have been extracted and categorised, providing a proxy precipitation data set for Namaqualand for the nineteenth century. Notwithstanding problems of data accuracy and interpretation the reconstruction enables the detection of severe and extreme periods. Measured meteorological data, available from the late 1870s, was compared to the data set derived from documentary sources in order to ascertain the accuracy of the data set and monthly rainfall data has been used to identify seasonal anomalies. Confidence ratings on derived dry and wet periods, where appropriate, have been assigned to each year. The study extends the geographical area of existing research and extracts the major periods of drought and climatic stress, from the growing body of historical climate research. The most widespread drought periods affecting the southern and eastern Cape, Namaqualand and the Kalahari were

Recent trends in the climate of Namaqualand, a megadiverse arid region of South Africa

“…14 The strong inter-annual variability in rainfall in Namaqualand has been noted in previous studies 19,54 but no trend in the frequency of drought and wet periods has been observed. 17 Recent evidence suggests that El Nino Southern Oscillation (ENSO) modulates rainfall in the region with El Nino (La Nina) years being associated with higher (lower) than normal rainfall amounts in May, June and July. 55 During ENSO events, the rain-bearing systems are larger in extent and are located further north, while during La Nina Southern Oscillation (LNSO), events are smaller and located further south.…”

“…Peak rainfall amounts occur over the Kamiesberg Mountains as a result of the orographic effect. 17 More than 60% of the rainfall occurs during the winter months between May and September as a result of the cold, westerly fronts from the southern oceans. 35 Coastal lows are also common in winter.…”

“…36 Namaqualand is prone to droughts, which usually span a few successive years. 17,19 Annual average temperatures for the study area are relatively mild throughout the year and range from 13 °C to 21 °C, owing to the cold Benguela Current off the west coast of Namaqualand. 31 Mean annual temperatures are highest inland of the west coast increasing northwards, while the escarpment and high lying areas experience cooler temperatures.…”

“…36 With the exception of the coastal belt, the region experiences a large annual and diurnal range in temperatures. 17 Occasional frosts occur in the high lying areas of the escarpment and central plateau.…”

“…To date, only three studies have investigated the historical climate of the Namaqualand, [17][18][19] all of which focused specifically on changes in rainfall. Various palaeoclimate studies in the winter rainfall zone of South Africa [20][21][22][23] have also contributed to the understanding of the long-term changes in climate in Namaqualand.…”