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The Okavango Delta is the largest inland delta on Earth, spreading over 15,000 km of the Kalahari sands of Botswana. Though commonly referred to as a delta, it is actually a landlocked wet-fan comprising three active subsystems: permanent, seasonal and intermittent fl oodplains bounded by fossil fl oodplains that mark the coterminous extent of a more extensive wetland during the historical past (Fig. 1). Contemporary perspectives on climate change in this sub-region are dominated by two competing discourses. The fi rst maintains that the current trend in increasing aridity is part of periodic variation within a stable equilibrium and need not be interpreted as sustained deterioration of climatic conditions. The second argues that though periodic variation is evident, close examination of this periodicity reveals a persistent downward trend; a trend that may imply only limited prospects for recovery to the wetter climatic conditions of the historical past. Recent long-term evidence compiled from disparate sources about this sub-region’s climate since the beginning of the 19th century suggests that there is need to question the validity of the stable-equilibrium hypothesis. In this sub-region, oral histories from local people off er an invaluable form of evidence about climate conditions during the historical past. Around 1800 AD, the baYeyi migrated from southern Zambia by canoeing along the Selinda spillway and distributary channels of the Okavango River to settle around Lake Ngami (Fig. 1a) where they had been attracted by the abundant presence of hippo and fi sh. This information suggests high fl oods in the Okavango Delta that were capable of sustaining perennial outfl ow into the Selinda spillway and permanent water presence in Lake Ngami during the fi rst half of the 19th century. The latter is corroborated by archival evidence, with the presence of fi shing boats in the background of Figure 1b pointing to perennial water residence and a productive environment. High productivity is further confi rmed by documented occurrence of widespread peat fi res in this area during the early 1920’s, which suggest substantial papyrus growth capable of sustaining the accumulation of considerable peat deposits. These observations are indicative of a gradual decline in rainfall since the early 19th century: the drying up of the Selinda spillway during the early 1870’s (Stigarnd, 1922), Lake Ngami’s gradual desiccation (Fig. 1b), and virtual disappearance of peat fi res in this environment by the late 1920’s, all confi rm a continuous drying trend (Hamandawana et al, 2005). Though the Lake Ngami’s fl ood régime has been characterized by periodic fl uctuations, the long-term trend suggests that the hydrological system has been unable to revert to the higher fl ood conditions of the historic past. This proposition is supported by simultaneous fl oodplain desiccation in peripheries of the present Delta’s permanent and seasonal swamps. For example, in the east, the Mababe Depression (captured in oral traditions as Lake Mababe) dried during the second half of the 19th century; its infl ow channels from the northwest and southwest ceasing to fl ow by the early 1960’s (Campbell and Child, 1971). In the west, the Thaoge River (described during the 1880’s as reed swamps infested by buff aloes and elephants that had to be hunted from boats (Chapman, 1886)) last fl owed into Lake Ngami around 1883 (Stigarnd, 1922). Since then it has retreated northward to its outfl ow point from the Delta’s permanent swamps by the late 1960’s (Fig. 1a). Given the protracted failure of these emergent fl oodplain environments to periodically recover, as suggested by proponents of quasi-periodic oscillations, it is quite apparent that this sub-region’s climate has become increasingly drier from the beginning of the 19th century to the present. Though human interventions have contributed to fl oodplain desiccation (i.e. papyrus rafts causing vegetation blockages and channel manipulations by colonial authorities), evidence suggests that the sustained decrease in rainfall is the major cause of persistent fl oodplain contraction (Hamandawana et al., in press). While the foregoing examples of oral and documentary evidence provide valuable indicators of the general direction of climate change, additional corroborative

The desiccation of southern Africa’s Okavango Delta:Periodic fluctuation or long-term trend?