Mapping Ephemeral Watering Holes in KAZA

A new  study  by researchers at Duke University and WWF aimed to accurately track the expansion and retraction of small ephemeral water bodies from the wet to dry seasons across the KAZA region. The Kavango-Zambezi Transfrontier Conservation Area, or KAZA, spans a wide variety of ecosystems and is home to many endangered species that travel between and rely on these ephemeral water bodies.

Through detailed study of satellite imagery, more than 650,000 previously unmapped water bodies have now been accurately mapped across one of the richest mammal biodiversity regions in the world.  Quick link to browse water frequency map 

While KAZA is mostly flat land, the region has hundreds of unique features known as omirumba. These omirumba are deeply incised channels through which little water flows downstream. They are a common site for ephemeral watering holes during and after the wet season and host grasses and woody vegetation as well.

Previous work in KAZA focused on habitat loss over time and some small-scale identification of watering holes.

Here, the researches built upon Naidoo et al.’s (2020) small scale water hole mapping by including water body seasonality, expanding the study area, and improving mapping accuracy. Click the button below for more background information on the KAZA landscape, its inhabitants, and habitat change over time.

Ephemeral watering holes are freshwater bodies that expand and contract on short timescales. Across the region, rainfall ranges from 200 mm to 750 mm annually and is highly seasonal. These water bodies fill with rain water during the wet season (September to May) and dry up completely or shrink drastically during the dry season (June to August).

Ephemeral water bodies are found in both the previously mentioned omirumba and in isolation outside the channels.

Many KAZA animals rely on these ephemeral watering holes to support their movement across the landscape, but little is known about them. The motivations for this study were thus twofold: understand the watering holes to better understand large-scale wildlife migrations, and describe the fundamental hydrology of these previously understudied small surface water features.

With the ephemeral water body time series completed, the researchers assessed how climate and landscape factors contribute to the presence, persistence, and size of these seasonal surface water resources which are so pivotal for the movement of migratory wildlife species.

Unsurprisingly, waterholes within omiramba appear to be distinct from waterholes outside omiramba, which tend to be more sparse and uniform with small rounded shapes.

Additionally, they examined attributes from soils, geology, and topography, to climate and soil moisture for a better understanding of watering hole seasonality.

Through data analysis, the researchers found that surface water duration patterns were correlated with precipitation and that soils with higher water retention, like loams, had a longer water duration.

From the wettest time period to the driest, there was a 62% decrease in surface water area across the region.

As we now know, ephemeral watering holes in KAZA are extremely sensitive and highly variable. But why does this matter?

A previous study found that animal movement in the KAZA region may depend as strongly on surface water distributions as it does on other well-known factors such as seasonal changes in vegetation, and the presence of major barriers to wildlife movement (e.g., roads and fences)  (Naidoo et al. 2020) .

With climate change and human development, the future of KAZA points to an increasingly inhospitable environment for wildlife. Climate is expected to become warmer and drier, and with increased human population growth, more water is expected to be diverted from KAZA through new dams and increased agriculture and development.

Less watering holes can lead to less traversable pathways for wildlife within KAZA, threatening animal livelihoods.

With a decrease in more dispersed and isolated water holes across the region, elephants will likely stay closer to permanent water sources. This can lead to an increased risk of starvation as food resources are depleted around the fewer long term water sources where these individuals are forced to congregate.

The new study, “Tracking a Blue Wave of Ephemeral Water Across Arid Southern Africa,” was published November 17, 2022, in the peer-reviewed scientific journal Environmental Research Letters.

Its authors are Danica Schaffer-Smith, Margaret Swift, Allison Killea and Jennifer Swenson of Duke’s Nicholas School of the Environment; Angela Brennan of the World Wildlife Fund-U.S. and the University of British Columbia’s Institute for Resources, Environment and Sustainability; and Robin Naidoo of the World Wildlife Fund-U.S.

You can read the full paper at  https://doi.org/10.1088/1748-9326/ac98d 

Water frequency dataset published  here .