UP-linked study reveals climate-smart water storage strategies adopted by Great Zimbabwe in Middle Ages

A study involving the University of Pretoria (UP), along with academics from Great Zimbabwe University, University of Cambridge in the UK and Aarhus University in Denmark, has revealed how Great Zimbabwe – the largest city in Southern Africa during the Middle Ages – stored water in dhaka pits to overcome severe water scarcity and drought.

Professor Innocent Pikirayi of UP’s Department of Anthropology, Archaeology and Development Studies was part of the research team that discovered how, more than three centuries ago, the community of Great Zimbabwe maintained a stable water supply in a region known for periodic droughts and which is presently water scarce.

The study was conducted in the context of growing water security challenges, currently among the most significant global challenges for human subsistence and environmental health. It highlights the importance of effective strategies in terms of water management and conservation today.

“Though fragmented, the growing body of environmental and archaeological records, when integrated with historical and ethnographic information, paint a new, convincing portrait of Great Zimbabwe: a landscape where human settlement, land and water were intimately linked for a long time and, to some extent, continue to do so,” says Prof Pikirayi. “Springs and rainwater fed an urban population of ruling elites, religious leaders, craftsmen and merchants. Water storage facilities were strategically placed to maximise supply and demand.” 

While the research presents new research findings concerning the site and resource management strategies that supported it to expose their impact and legacies on the present landscape, the disappearance of Great Zimbabwe may be linked to extreme climate conditions associated with drought and arid conditions during the second millennium AD, usually termed the Little Ice Age (1350 – 1850 AD).

Researchers found that the people of Great Zimbabwe devised climate-smart methods for storing and managing water in an area known for experiencing three different climate patterns: a hot, dry season; a warm, wet season; and a friendly, dry winter. A steady water supply was critical for the growing urban society, which required a reliable and safe water supply for its citizens, livestock and agriculture.

Along with researchers from England, Zimbabwe and Denmark, Prof Pikirayi unravelled the mystery in an article published in the journal Anthropocene. The researchers explained how they used remote sensing methods such as LiDAR (Light Detection and Ranging) mapping (which examines the Earth’s surface) to probe several large depressions in the landscape. Locals described these as dhaka pits, used to store water for the once bustling capital of the Shona kingdom, which had a population of between 10  000 and 18 000 residents before the city was abandoned in the 18th century.

The never-before-investigated depressions were originally thought to be sources of clay used for building houses. However, according to Prof Pikirayi, the study shows that the pits must also have been used to store and manage water for the city. There are clear signs, he says, that the depressions have been excavated to assist with the collection of surface water and to retain groundwater seeping from the weathered granite bedrock for use during dry periods.

Using LiDAR mapping, researchers located more dhaka pits than were visible to the eye. These pits were located along streams and rills that drained through Great Zimbabwe’s granite landscape, collecting rainwater from the hills or groundwater where it seeped out. Some of the streams passing through the monumental structures at the foot of the Great Zimbabwe Hill and east of the Great Enclosure and Valley Complexes are still active to this day.

This, combined with the location and construction of the depressions, has convinced researchers that the dhaka pits functioned as a creative system to ensure a stable water supply by storing surface and groundwater that could be used beyond the rainy season and during periods of prolonged aridity. The researchers estimate the pits could store at least 18 000 cubic metres of water at any one time.

They hope that exploring dhaka pits in other areas might also reveal how other medieval communities in the region managed and conserved their water resources.

The article ‘Climate-smart harvesting and storing of water: The legacy of dhaka pits at Great Zimbabwe’ by Innocent Pikirayi, Federica Sulas, Bongumenzi Nxumalo, Munyaradzi Elton Sagiya, David Stott, Søren M Kristiansen, Shadreck Chirikure and Tendai Musindo appears in the journal Anthropocene

Prof Innocent Pikirayi, and Dr Bongumenzi Nxumalo

October 11, 2023

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  • Professor Innocent Pikirayi

    Professor Innocent Pikirayi joined the University of Pretoria (UP) in 2004. He is Deputy Dean of the Faculty of Humanities, where he is responsible for postgraduate education and research. He is a graduate of the University of Zimbabwe.  

    In terms of how his field of research, African archaeology, contributes to the betterment of the world, Prof Pikirayi says: “Archaeology examines cultural and human-induced environmental changes over time, determining trends and patterns, and seeks to make sense of these. It offers a unique perspective on human history and culture, and helps us to understand not only where and when people lived on this planet, but also how they have shaped it and continue to modify it. Such information is important in understanding the current human condition.”

    His research is cross-disciplinary. Prof Pikirayi works with researchers such as Prof Søren Kristiansen of the Department of Geoscience at Aarhus University, Denmark, and Dr Federica Sulas, a geo-archaeologist at Cambridge University’s McDonald Institute for Archaeological Research in the UK.

    Prof Pikirayi is part of an international team of scholars from Africa, Europe and the US that is studying ancient complex societies in sub-Saharan Africa, focusing on the Great Zimbabwe civilisation. The team makes use of approaches in historical ecology, geoarchaeology and conventional archaeology. The collaborative research on Great Zimbabwe goes back to 2015/2016, and focuses on the role of water in socio-political formation. Highlights of this research involve the remapping of ancient and present-day water features on the site using light detection and ranging (LiDAR) mapping, which revealed how the ancient community managed and conserved water resources.

    As far as role models go, Prof Pikirayi points to Peter Storr Garlake (1934 – 2011), an architect, archaeologist and author of the book Great Zimbabwe (Thames and Hudson, 1973). Garlake taught him at undergraduate level and inspired his early career in archaeology. Prof Pikirayi has written a tribute to Garlake.

    As for his early career as a scholar, Prof Pikirayi credits his doctoral supervisor Prof Paul JJ Sinclair as being highly influential, especially his doctoral thesis, ‘Space, time, and social formation: A territorial approach to the archaeology and anthropology of Zimbabwe and Mozambique c 0 – 1700 AD’ (Uppsala University, 1987). He also owes his growth as a senior scholar in archaeology to the numerous interactions and collaborations he has had with Prof Peter Ridgway Schmidt of the University of Florida, who encouraged him to employ locally grounded theories in understanding the African past.

    Prof Pikirayi hopes to become a leading scholar in African archaeology, and use archaeology as an avenue towards other frontiers of knowledge (such as volcanology, plate tectonics, and water and soil sediments) about the origins of Earth.

    “Archaeology is about the human experience and condition over time, so it is important to understand past lifeways and how these have developed to the present day. That is why my research matters,” he says.

    “Such past experiences are also important to us in terms of our broader social and cultural context and how we have shaped the world in the form that we see it, live in it and experience it,” he adds. “Some of the lessons we learn from deep history, which archaeology is part of, hold fundamental clues towards understanding the modern human crisis, such as water scarcity, environment and climate change. Archaeology is the surest way of confirming that humans are changing Earth’s environment at an unprecedented timescale. The very same humans need to put mechanisms in place to halt this. My work at Great Zimbabwe speaks to these broader realities.”

    His advice to school learners or undergraduates who are interested in his field is to realise that archaeology is not primarily about the past but about how the past speaks to the present.

    “Once you understand this, learning archaeological theory and methods become extremely easy. In fact, practising archaeology in the field and in the laboratory becomes a passion.”

    His hobbies include landscape gardening, hiking and mountain climbing. In December 2020, during the pandemic, he scaled Mount Kilimanjaro to Uhuru Peak, the highest summit in Africa.

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  • Dr Bongumenzi Nxumalo

    Dr Bongumenzi Nxumalo completed his undergraduate studies at the University of the Witwatersrand, and has been doing research at the University of Pretoria (UP) since 2020.

    He chose the University as his research base because he is a UP graduate and because of his interest in human-environmental interactions on the landscape. He recognised the potential rewarding synergies and collaborative interdisciplinary efforts of the University’s Department of Anthropology, Archaeology and Development Studies, and its focus on transformation.

    “Apart from my well-established relationship with UP, the main reason for joining UP was centred on representation,” Dr Nxumalo says. “This is based on my engagements with the Department of Anthropology, Archaeology and Development Studies. In terms of transformation and other aspects of equity and diversity, the department engages staff from diverse backgrounds, and I was happy to join a division with this mentality. 

    “This is important to me,” he adds, “because a number of black students have approached me, indicating a strong interest in the discipline but finding it hard to become involved in it because there are not many staff and students who look like them (and who potentially share similar experiences). Perhaps this relates to the absence of black archaeologists in South Africa – that really needs to change. I am a staunch supporter of representation or diversity and other aspects of equity, since we are grappling with decolonisation and calls for the representation of non-European thinkers in the curriculum.”

    Dr Nxumalo’s research focuses on the role of hydrological changes and the demise of southern Africa’s earliest state societies. For example, the rise and demise of Mapungubwe have long been linked to significant climate changes: increased rainfall would have supported intensive agro-pastoral activities and demographic growth, later declining due to the onset of drier conditions. Accordingly, during the Little Ice Age (1300 – 1850 AD), a drier and cooler climate resulted in environmental deterioration, ultimately leading to the abandonment of Mapungubwe. This model is based on archaeological survey records and oral histories, with minimal regional climatic/environmental data. As such, this work has greatly benefitted from geoarchaeological techniques in southern Africa. While the specialisation in geoarchaeology has helped to produce the first local datasets on hydrological changes, optically stimulated luminescence geochronologies and soil micromorphological data in the region – and how these affected past communities – remain unclear.

    Building on these results, ongoing research examines hydrological changes and seismic activity in Mapungubwe using resilience to understand how prehistoric and complex societies in sub-Saharan Africa could have interacted with a changing landscape.

    The research strategy combines geoarchaeological field surveys; geophysical modelling (seismic modelling); laboratory analyses (geochemistry and micromorphology); the study of historical records and modern climatic data; and predictive modelling using geographic information systems, remote sensing and hydrologic engineering centre river analysis system tools. These systems examine the role of hydrological changes in the decline of early state societies in southern Africa. The resulting models from this research offer quantitative and qualitative novel tools to predict human decisions taken on landscape brought about by changing environmental conditions.

    As to why his research matters, Dr Nxumalo says the following: “[My work] characterises the initial phase for developing soil micromorphology records, advanced morphometric analysis and hydrology simulations (geographic information systems, remote sensing and hydrologic engineering centre river analysis modelling) for climate-related issues such as flooding to test and remodel various human-environmental interactions across valley systems in southern Africa. These can help us revise policy development and decision-making processes by informing infrastructural inefficiencies against worsening climatic conditions and sustainable livelihoods.”

    Dr Nxumalo is engaged in field projects that focus on geoarchaeological and geophysical land-surface surveys to model societal developments in the Mapungubwe, Shashe-Limpopo Basin (2021). The proposed research tests the role of seismic activity in the rise and decline of the Mapungubwe state in the middle Limpopo valley. In addition, existing geoarchaeological records (soil chemistry and micromorphological analysis) will be integrated to generate a model for changing environmental conditions and cultural developments in the Mapungubwe landscape.

    A recent highlight for him was receiving funding from the Cambridge-Africa ALBORADA Research Fund and Cambridge Africa, Cambridge University to establish the first geoarchaeology lab in southern Africa. 

    Dr Nxumalo says there are many people who have inspired and influenced his work, both within the discipline and outside of it. He is deeply inspired by the role of Africans in the world’s global past.

    “The representation of Africa, its events and material record were told by non-Africans, which has often led to a negative portrayal and misconceptions of Africa,” he says. “As such, I draw my aspirations from African philosophy, which attempts to define or interpret African identity and culture from the point of view of indigenous Africans and their descendants. The founding fathers of Pan-Africanist thought inspire me greatly, such as Prof Akinwande Soyinka, Kwame Nkrumah, Robert Sobukwe and Ngũgĩ wa Thiong’o, all of whom give voice to African thinkers in the curriculum.” 

    He adds that he is also influenced by several scholars, such as Prof Webber Ndoro, Gilbert Pwiti, Prof Innocent Pikirayi and Dr Ndukuyakhe Ndlovu.

    “All are non-European pioneers of modern archaeological research in southern Africa,” he says. “Internationally, I am inspired by Prof Charles French and Dr Federica Sulas of Cambridge University; they have shaped my journey in geoarchaeology. As one of the very new black African geoarchaeologists in South Africa, it is through this background that my interest in archaeology grew, with the realisation that people like me could study and write about the contributions made by our own people.”

    Dr Nxumalo hopes to establish the first geoarchaeology laboratory in southern Africa.

    He advises school learners or undergraduates who are interested in his field to remember that archaeology is a scarce skill in South Africa, and that it requires intensive reading into different periods that characterise the archaeological record of southern Africa.

    “For example, the Early Stone Age, Middle Stone Age, Late Stone Age as well as the Iron Age,” he explains. “The discipline requires adequate passion and drive for answering questions related to people’s history. However, archaeology is not only about studying the bones of people; several subdisciplines can be studied. These include archaeobotany, geoarchaeology, zooarchaeology, bioarchaeology, maritime archaeology, archaeometallurgy and archaeometry.”  

    As for hobbies and interests, Dr Nxumalo is a huge soccer fan, and regularly plays the sport. He also enjoys being DJ.

    “I support Liverpool (English Premier League), Barcelona (Spanish League) and Mamelodi Sundowns (SA Premier Soccer League),” he says. “I am also a serious consumer of Afrotech music.”

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