Estimating outdoor water use allowing for the possible impacts of climate change

Makwiza, Chikondi (2018-03)

Thesis (PhD)--Stellenbosch University, 2018.


ENGLISH ABSTRACT: Climate change may stress water supply systems due to both diminishing water resources and rising climate driven water use. Reducing the sensitivity of residential outdoor water use to climatic factors is desirable for climate change adaptation. Outdoor water use is also attractive for achieving water savings, because outdoor use is more elastic than indoor use. This study was aimed at estimating residential outdoor water use for the purpose of estimating how it would be impacted by climate change. A conceptual model was formulated to derive irrigation water use for vegetated areas around the home from climate variables. The model was based on the modification and adaptation of an existing residential end-use model for outdoor water demand to include climate change parameters. The resulting irrigation water end-use model is suitable for assessing water use for specific vegetation types maintained around the home. Application of the model to the case of leafy vegetables grown in the backyard garden was demonstrated in this study. The growth of vegetables in backyard gardens is often linked to nutritional food security in developing countries, stressing the importance of research to better understand the impacts of climate change on water use for garden irrigation. In this research study, outdoor water use events were studied using sound recorded at outdoor taps. The automatic detection algorithm applied to the recorded sound signals performed reasonably well with precision and recall rates of at least 80%. Diurnal water use patterns derived at the outdoor tap revealed time periods of peak water use. An exploratory analysis of water billing records for the city of Lilongwe showed that water use increased with plot size, similar to previously reported research in southern Africa. Summer peaking factors also increased with plot size. In a follow-up study, panel linear regression analysis was used to create an empirical relationship between household water use and the independent variables: plot size and theoretical irrigation requirements. Predictions for ensemble averages of temperature and rainfall projections for 2050 showed an increase of 1.5% in annual water use under the low emissions scenario and 2.3% under the high emissions scenario. Finally, the performance of temperature and rainfall as independent variables in water use regression models was compared to the use of theoretical irrigation requirements. Empirical analysis of a residential water use dataset for 12 North American cities showed that the transformation of temperature and rainfall to irrigation requirements, using a suitable set of parameter values, improved the performance of the water use regression models. The results of this study show that garden irrigation will increase due to climate change, but the increase is relatively small compared to the expected population growth and urbanisation in many parts of Africa. The impact of climate on expected water use was examined using simple and effective techniques that were employed at relatively low cost. Water utilities and planners could employ the methods and tools reported on here to better plan for the additional expected increase in outdoor water use resulting from climate change.

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