This paper focuses on a collection of methods that can be used to analyze the water-energy-food (WEF) nexus. We classify these methods as qualitative or quantitative for interdisciplinary and transdisciplinary research approaches. The methods for interdisciplinary research approaches can be used to unify a collection of related variables, visualize the research problem, evaluate the issue, and simulate the system of interest. Qualitative methods are generally used to describe the nexus in the region of interest, and include primary research methods such as Questionnaire Surveys, as well as secondary research methods such as Ontology Engineering and Integrated Maps. Quantitative methods for examining the nexus include Physical Models, Benefit-Cost Analysis (BCA), Integrated Indices, and Optimization Management Models. The authors discuss each of these methods in the following sections, along with accompanying case studies from research sites in Japan and the Philippines. Although the case studies are specific to two regions, these methods could be applicable to other areas, with appropriate calibration.

Dams provide numerous economic benefits and can mitigate the adverse impacts of water variability and extreme climate events. However, such large-scale water infrastructure has also caused significant social and environmental costs, prompting calls for alternative, nature-based solutions. WLE suggests that collections of built and natural infrastructure, combined with participatory management approaches, can support water and food security, while enhancing livelihoods and environmental outcomes.

The summary and the conclusions presented here are based on the results of four case studies, three for drinking water and one for soil and water conservation. The cases were selected from the projects under the Sino-German IESP ("Integriertes Ernaehrungssicherungsprogramm"; Integrated Food Security Programme) in Shandong, People's Republic of China. The aim of the study was to do an economic analysis of the selected cases, in order to answer questions about the sustainability ofthe projects' benefits. The selected drinking water projects include the deep well in Quanziyu village, the big-mouth well in Mawo, and the cisterns in Xiyu. The projects vary in technology, age, and village context (e.g. village size and wealth). The soil and water conservation project covers the whole water catchment area around Mawo village. All projects are located in the county of Pingyi, except for Xiyu, which belongs to Yishui county. In the section A, the main results and conclusions from the drinking water case studies are presented. After a brief introduction, the main findings are explained in general. Next, the situation of each project, as related to costs and water charges, is described in more detail. Finally, an overview of the results from the benefit analysis is given. The section B deals with the main results and conclusions concerning the soil and water conservation project. The results from the financial appraisal of all project components taken together are summarised, before the individual components are described separately.

Irrigation plays a crucial role in enhancing food production, increasing land productivity, and improving the livelihoods of smallholder farmers in Sub-Saharan Africa (SSA). Solar pumps and water harvesting ponds have emerged as promising technologies for sustainable agriculture for smallholders in SSA and beyond. The socio-economic impacts of these systems are less studied in the existing literature. This study examined the agricultural productivity of solar pump and water harvesting irrigation technologies and their impacts on income and food security among smallholder farmers in the Central Rift Valley, Lake Hawassa, and Upper Awash sub-basin areas in Ethiopia. Data were collected from 161 farming households that were selected randomly from woredas where solar pump and water harvesting pond irrigation systems had been implemented. The sample size was determined using the power calculation method. Bio-physical observation and measurements were also conducted at field levels. The benefit–cost ratio (BCR) and net water value (NWV) from the use of solar pump and water harvesting pond irrigations were analyzed to assess the viability of these systems. The household food consumption score (HFCS) and household dietary diversity score (HDDS) were calculated to measure food security, while the revenue from crop production was used to measure crop income. An endogenous switching regression model was applied to address the endogeneity nature of the adoption of the irrigation technologies. The counterfactual analysis, specifically the Average Treatment Effect on the Treated (ATT), was used to evaluate the impacts of the irrigation technologies on income and food security. Results indicate that the ATT of crop income, HFCS, and HDDS are positive and statistically significant, illustrating the role of these irrigation systems in enhancing smallholder farmers’ welfare. Moreover, smallholder farmers’ solar pump irrigation systems were found to be economically viable for few crops, with a BCR greater than 1.0 and an NWV ranging from 0.21 to 1.53 USD/m³. It was also found that bundling agricultural technologies with solar pump irrigation systems leads to enhanced agricultural outputs and welfare. The sustainable adoption and scale-up of these irrigation systems demand addressing technical and financial constraints, as well as input and output market challenges.