Key findings from the Sub-national Water Resource Accounts, 2015 to 2021

 

The discussion document presents a set of sub-national water resource accounts developed for selected catchments in two Water Management Areas (WMAs), namely the Breede-Olifants WMA that lies largely in the Western Cape province and the Pongola-Mtamvuna WMA that lies largely in the KwaZulu-Natal province. The water resource accounts were compiled for three sub-accounting areas within the two WMAs, namely the Breede Catchment, uMngeni Catchment and Mooi Catchment. These were selected because of their importance for providing water to two major cities in South Africa.

 

The water resource accounts are presented as annual accounts for six hydrological years (accounting periods) from 2015-2016 to 2020-2021 (hydrological years run from October to September the following year).

 

The Sub-national Water Resource Accounts, 2015 to 2021 brings together elements of water accounts and ecosystem accounts, acknowledging connections between the landscapes and ecosystems upon which precipitation occurs and the resulting flows and stores of water that are important for supply to and use by the economy. In essence, this acknowledges the connections between built water infrastructure and ecological infrastructure, as indicated in South Africa’s National Infrastructure Plan 2050 (released in March 2022).

 

Water resource accounts explicitly seek to address the connection between land cover/land use and how water infiltrates, runs off, evaporates, or transpires. Thus, contributing to meet the need for integration of different types of information to inform planners and decision-makers grappling to address complex challenges related water insecurity. Water resource accounts describe the water resources within a specified spatial and temporal water accounting domain, including changes in water storage, the source and quantity of water inflows, water use by different sectors within the domain, and the destination and quantity of water outflows.

 

The purpose of presenting sub-national accounts is to support the evolution of a methodology and output that in the future could be applied at a national level.

Key findings for the Breede Catchment sub-accounting area

1.     Precipitation (as one form of water inflow) into the Breede Catchment sub-accounting area was the lowest in 2016-2017 with 233,3 mm per annum, when the region experienced a drought, but was also low in 2018-2019. Precipitation was the highest in 2020-2021 with 678,5 mm per annum.

2.     Water leaves the catchment through evaporation (which includes transpiration) and outflows of surface water, groundwater and inter-catchment transfers.

3.     The Breede Catchment was largely natural or semi-natural (69,4%), and the remainder was largely cultivated (28,5%) with only 1,8% waterbodies (such as dams for water supply) and 0,3% built-up (urban and mines).

4.     In the Breede Catchment, total evaporation was proportionally higher in cultivated land (the proportion of cultivated land was 28,5% and the proportion of total evaporation on cultivated land was between 31,3% and 34,7% in different accounting periods).

 

Key findings for the uMngeni Catchment sub-accounting area

1.     Precipitation (as one form of water inflow) into the uMngeni Catchment sub-accounting area was the lowest in 2018-2019 with 815,6 mm per annum and also low in 2016-2017 with 819,6 mm. Precipitation was the highest in 2017-2018 with 1 034,0 mm per annum.

2.     Water leaves the catchment through evaporation (which includes transpiration) and outflows of surface water, groundwater and inter-catchment transfers.

3.     The uMngeni Catchment was largely converted to intensively modified land cover being either cultivated (33,5%) or built-up (17,9%). Natural or semi-natural land cover (45,4%) was the lowest proportion of natural or semi-natural land cover compared to the other sub-accounting areas.

4.     Evaporation, in contrast, was not proportional to the area of land cover. In the uMngeni Catchment, total evaporation was proportionally higher in cultivated land (proportion of cultivated land was 33,5% and proportion of total evaporation on cultivated land was between 37,4% in 2018-2019 and 39,3% in 2015-2016).

 

Key findings for the Mooi Catchment sub-accounting area

1.     Precipitation (as one form of water inflow) into the Mooi Catchment sub-accounting area was the lowest in 2019-2020 with 548,3 mm per annum and the highest in 2020-2021 with 915,0 mm per annum.

2.     Water leaves the catchment through evaporation (which includes transpiration) and outflows of surface water, groundwater and inter-catchment transfers.

3.     The Mooi Catchment was largely natural or semi-natural land cover (71,0%), followed by cultivated land (21,8%). The Mooi Catchment had the highest proportion of land that was waterbodies (4,1%) compared with the other sub-accounting areas and 3,1% was built-up areas.

4.     Evaporation, in contrast, was not proportional to the area of land cover. In the Mooi Catchment, total evaporation was proportionally higher in cultivated land (the proportion of cultivated land was 21,8% and the proportion of total evaporation on cultivated land was between 23,3% in 2020-2021 and 24,2% in 2018-2019).