Towards a hybrid framework for rainwater harvesting site selection in arid and semi-arid regions

Ibrahim, Safaa Ahmed ORCID: 0000-0003-3079-5898 (2025). Towards a hybrid framework for rainwater harvesting site selection in arid and semi-arid regions. University of Birmingham. Ph.D.

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Abstract

The lack of precipitation and erratic rainfall patterns in arid and semi-arid regions of the world raise concerns about water scarcity. Rainwater harvesting (RWH) is a traditional technique employed to gather and store rainwater for diverse uses such as drinking water and agricultural applications. A number of frameworks, each with its unique set of criteria, have been developed in recent decades to help detect and prioritise locations for rainwater harvesting (RWH), an essential technique not only for the preservation and enhancement of water resources but also as a key component of sustainable integrated watershed management. To rank possible sites, these frameworks were created using what are known as structural criteria (biophysical and socio-economic). While these frameworks are effective in identifying potential sites for RWH, they often do not account for the broader ecological criteria that are essential for the sustainability of the watershed system as a whole. The sustainability of the system, regulatory compliance, climate resilience, biodiversity preservation, water quality improvement, and environmental protection are all dependent on ecological criteria. In this study, this deficiency is addressed by the development of a hybrid framework which combines structural criteria with important ecological criteria. Planning to identify rainwater harvesting sites in arid and semi-arid regions based on various criteria—namely biophysical, socioeconomic, and ecological—is a complex issue especially when including ecological criteria. The first part of this thesis involved a systematic review to identify the gaps in knowledge and the criteria used in existing frameworks. The conducted systematic review is based on the two major databases of Scopus and Engineering Village. Sixty-eight relevant studies were found and critically analysed to identify patterns and unique features in the adopted frameworks. The results of this review reveal that 41% of the frameworks consider both biophysical and socioeconomic criteria, whereas the remaining 59% of the frameworks depend solely on biophysical criteria. The importance of each criterion is encapsulated through a suitability score. The term "scale" is used here to refer to the system or range used to rate or measure how well a site aligns with specific criteria for suitability, whether through a binary indicator (match or no match) or through graded scales of varying levels of detail. The first scale which accounts for 21% of the frameworks uses a binary (0 or 1) indicator of whether the site matches a criterion or not. While the other frameworks use graded scales of differing granularities, with 52% using a low-resolution scale of 1 to 3, 4, or 5. This is followed by a 7% that uses a medium-resolution scale of 1 to 10, and a further 7% using a high-resolution scale of 1 to 100. The remaining 13% of the frameworks did not specify the scale used. Importantly, this part of the thesis concludes that all existing frameworks for selecting RWH sites are solely based on biophysical and/or socioeconomic criteria; ecological impacts, the consideration of which is vital for building RWH systems sustainably, are currently ignored. The latter part of the thesis is to identify the important ecological criteria and their corresponding weights as well as to use a case study to apply the framework. The important ecological criteria have been identified based on additional literature review. The inter-relationships of ecological criteria are complex, with “independent” criteria affecting the “mediator” criteria (e.g. dissolved oxygen, phosphorous concentration) which directly impact ecological standards, i.e. the “dependent” criteria such as the number of aquatic organisms. This study focuses on the key independent criteria of temperature and light, which are prioritised based on findings from the analysis of the literature. These findings have shown temperature and light to be the most influential factors affecting water quality criteria. However, the hybrid framework could easily be expanded to include additional ecological criteria, depending on the region to which it is applied. The framework encompasses independent, mediator and dependent ecological criteria identified from the literature, and the importance of each (represented as weightings in the framework) has been quantified through a robust combination of data analysis and expert opinion. The importance of the ecological criteria inclusion is demonstrated through a case study of Erbil Province in Iraq, where both climate change and human actions have seriously reduced water supplies in the past 20 years. A number of proposed rainwater harvesting sites are assessed via a structural and the new hybrid framework. The results demonstrate that the inclusion of these ecological criteria changes the ranking of the sites. Four different sites for rainwater harvesting (RWH) were chosen within Erbil city, each identified by its specific geographic coordinates. The hybrid framework implemented on these sites encompasses two distinct scenarios. The first scenario incorporates three key components: biophysical, socio-economic, and ecological criteria. In contrast, the second scenario integrates two components: biophysical and socio-economic criteria. For the first scenario, the suitability scores for the sites, listed in sequence from site numbers 1 to 4, are as follows: 1 (2.71), 2 (2.52), 3 (2.13), and 4 (3.31). For the second scenario, the suitability scores for the sites, listed in sequence from site numbers 1 to 4, are as follows: 1 (2.53), 2 (2.62), 3 (2.26), and 4 (3.03).

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):