Water footprint of growing vegetables in selected smallholder irrigation schemes in South Africa

Abstract

Crop water footprint (WF) is the volume of fresh water used to produce a certain crop in all the steps in the production line. The CROPWAT model was used to calculate crop evapotranspiration, differentiating green and blue water in Zanyokwe (ZIS), Thabina (TIS) and Tugela Ferry (TFIS) Irrigation Schemes. Green beans had the highest water footprint in all three irrigation schemes with 3 535.7 m³/t in TIS, 2 753 m³/t in TFIS and 2 407.6 m³/t in ZIS. Cabbage had the lowest water footprint. The highest water footprint for growing cabbage was 254.5 m³/t in TFIS, followed by 223.1 m³/t in TIS, and the lowest was 217.8 m³/t in ZIS. Green WF represented the highest percentage of water use at ZIS (50.5%), followed by blue water at 26.5% while grey water constituted 22.9%. At TFIS blue, green and grey water use was 23.1%, 56.7% and 20.2%, respectively. The differences observed in the WF of different crops and different schemes were attributed to the differences in weather and environmental characteristics. Green beans had the highest grey water footprint, i.e., 373 m³/t and the lowest was cabbage with 37 m³/t. Potato, spinach and tomatoes had footprints of 156 m³/t, 214 m³/t and 132 m³/t, respectively. For future research it is necessary to consider the possibility and trade-offs of shifting production of each crop to the places where it is most efficient, and to focus on blue water scarcity in each of the case study locations