*3.2. Method*

In this study, a cross-sectional analytical research design was applied to assess the level of consensus among experts in different professions and geographic locations on the proposed indicators to define the UN convention's immeasurable factors. For this purpose, an indicator-based questionnaire was selected as the most appropriate and cost-effective method for collecting primary data from relevant experts to capture potential differences in perspectives based on professional background and location (basin vs non-basin, downstream vs upstream, and specific basin country). The selected approach has been applied in similar previous studies. The questionnaire was developed, distributed, and evaluated based on factors from the UNWC, soliciting responses from five continents, to categorize relevance and acceptability of indicators within the Nile region.

#### 3.2.1. Initial Pool of Indicators

Based on Nile River basin hydrographic specifics and socioeconomic characteristics, 75 potential indicators were identified from previous studies and literature, press releases describing negotiations, and websites of international organizations to describe and measure factors contained within Article 6 of the UNWC (Table S1). The main selection criteria considered for these indicators included the availability, affordability, and feasibility to collect and analyze data; measurability; time bounds; the ability to consider watercourse countries claim; the ability to meet obligatory human rights and environmental rules; and the capacity of the indicators to explain unique features of the basin and basin countries. Also, the monitorability and operational usability was considered. The 75 indicators were categorized under the 7 factors previously described. These indicators were given an identification (I) number from 1 to 75 as shown in Table S1. The descriptions of the indicators were also provided in the table, along with information of the potential data source and timeframe for the data collection.

#### 3.2.2. Questionnaire Development and Distribution

The questionnaire was prepared with a Likert scale of 1–5 representing the following for each indicator: 1. Not important, 2. Less important, 3. Neutral, 4. Moderately important, and 5. Very important. It was distributed via email to a total of 215 experts in Africa, Asia, Europe, North America, and South America, with 150 complete responses collected, following a snowball sampling method. The experts represented five professions: Hydrology/water resources, environmental science, law, socioeconomics, and political science. All experts had an educational background at the master's level or above, and worked in universities, ministries, embassies, regional and international agencies and institutes, nongovernmental organizations, and independent consultants (Figures 2 and 3).

To differentiate potential partialities within, outside, and between countries, experts were also grouped as basin and non-basin professionals. To ensure fair representation of experts across all continents, when we planned three responses from each four professions in the nine basin countries due to the difficulty and time it takes to reach out the questionnaire to experts outside of Africa, two responses per five professions was targeted from at least two countries found in the remaining four continents excluding Antarctica and Australia. Accordingly, 135 and 80 experts were targeted from basin and non-basin countries, respectively. The quota of questionnaires among professions also targeted equality. Apart from basin countries, the choice of representative countries from the four continents were made based on their involvement in international water disputes. For example, from Europe, Belgium and the Netherlands were selected given their experience on the Meuse River. Similarly, the USA had negotiations with Canada and Mexico on the Colombia and Rio Grande Rivers, respectively. Additionally, from the Middle East and Asia, Jordan and Israel (Jordan River), Iran and Iraq (Tigris River), as well as China and India (Mekong River), were selected.

**Figure 2.** Quantity and spatial distribution of the survey.

**Figure 3.** Country, number, and profession composition of experts responded the survey.
