Unlocking the Liquid Ledger: Ecological Infrastructure’s role in water security

In South Africa, where water scarcity poses a significant challenge to development, understanding the relationship between land cover within catchments and water resources is pivotal. A recent release in Statistics South Africa’s Natural Capital series, provides a compelling narrative of this relationship, underscoring the vital role of ecological infrastructure in ensuring water security.

In the realm of water management, where knowledge is power, the Sub-national Water Resource Accounts, 2015 to 2021, present a wealth of information for three catchment areas – the Mooi and uMngeni (important sources of water for Pietermartizburg and eThekwini) Catchments and the Breede (an important source of water for Cape Town) Catchment.

Managing Water: A holistic approach

The National Water Act of 1998 underscores the imperative of integrated water resources management, recognizing the multifaceted nature of water-related challenges. Catchment Management Agencies (CMAs) play a pivotal role in overseeing water resources at the catchment level, coordinating efforts to ensure sustainable and equitable water use. CMAs need information at sufficiently disaggregated level to inform management and sustainable use.

Unveiling the Liquid Ledger

The Sub-national Water Resource Accounts offer a comprehensive understanding of water dynamics for an accounting area as a whole and per quaternary catchment, and shed light on the intricate relationship between land cover and water resources.

Water resource accounts are physical accounts of water quantity that describe the water resources within a specific area and time period. These accounts, provide annual estimates of catchment water balances, emphasizing the influence of land cover on water availability.

Insights from the accounts

The Breede Catchment, nestled in the Western Cape, serves as a microcosm of the dynamic nature of water resources. Over the span of six hydrological years, the catchment witnessed fluctuations in water balance, with the lowest recorded during the drought of 2016-2017 and the highest in the 2020-2021. These shifts, driven by variations in precipitation and evaporation levels, underscore the sensitivity of water storage dynamics to climatic conditions.

Similar patterns of variability were echoed in the uMngeni Catchment, where precipitation levels fluctuated over the same period. Despite these fluctuations, the catchment consistently received inter-catchment transfers from the Mooi Catchment, underscoring its reliance on external sources to sustain water resources.

Insights from land cover dis-aggregation

South Africa generally has high evaporation, but the proportion of total evaporation differed across land cover types, with cultivated land exhibiting a higher evaporation rate compared to natural or semi-natural areas in all three sub-accounting areas. For instance, despite cultivated land covering 28.5% of the Breede Catchment, it accounted for a disproportionate share of total evaporation, ranging between 31.3% and 34.7% in different accounting periods.

This influence of land cover on evaporation dynamics, highlights the need to consider land use patterns in water resource management strategies and promotion of water efficient tillage and irrigation practices. Natural or semi-natural areas generally had lower evaporation.

In the uMngeni Catchment and in the Mooi Catchment, built-up and cultivated areas make a proportionally higher contribution to baseflow in those catchments. This may have to do with the slope and partitioning of precipitation on these highly modified areas, and has implications for the quality of water moving to groundwater recharge and baseflow.

Understanding natural spatial variability

Climate and water availability can vary substantially both spatially and temporally. The water resource accounts provide information per quaternary catchment, providing greater understanding of water availability and use in water rich vs water poor parts of the country. Evaporation and surface runoff ratios illustrate precipitation patterns and altered flow characteristics, crucial for storage and downstream flows. Dependency ratios indicate reliance on external sources, while reserved outflow ratios highlight catchments vital for downstream supply. Variability in these water resources, underscores the importance of ecological infrastructure management for sustainable water availability.

Water resource dependency ratio averaged across six hydrological years (2015 to 2021) per quaternary catchment for the;

(a) Breede Catchment,
(b) Mooi Catchment and
(c) uMngeni Catchment sub-accounting areas.

Looking ahead: Towards water security and resilience

The revelation of these intricate relationships between land cover and water resources underscores the importance of ecological infrastructure in ensuring water security. Natural or semi-natural areas within catchments serve as crucial reservoirs of water, supporting surface runoff and infiltration processes that replenish water bodies and sustain downstream ecosystems. Cultivated land, while essential for agricultural production, also plays a role in water retention and recharge, highlighting the need for sustainable land management practices to optimize water resources.

The water resource accounts provide insight into the interlinkages between land, water and ecosystems that ultimately will help safeguard water resources while supporting socio-economic development. By adopting integrated water management approaches and fostering collaboration among stakeholders, South Africa can unlock the full potential of its ecological infrastructure, ensuring a sustainable and prosperous future for generations to come.

Unlocking the potential for ecological infrastructure to contribute to water security in South Africa is the essence of the Ecological Infrastructure for Water Security (EI4WS) Project that SANBI is executing. Funded by the Global Environment Fund (GEF), implemented by the Development Bank of Southern Africa (DBSA), supported by the Department of Forestry, Fisheries and the Environment (DFFE), in partnership with the Department of Water and Sanitation (DWS), Stats SA and others, the sub-national water resource accounts were compiled by the University of KwaZulu-Natal’s Centre for Water Resources Research in collaboration with SANBI.

Aimee Ginsburg
E-mail: a.ginsburg@sanbi.org.za  

To arrange media interviews contact:
Ednah Sekwakwa
E-mail: e.swekwakwa@sanbi.org.za

Felicia Sithole
E-mail: felicias@statssa.gov.za

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