## 2 Methodology  
### Scope, Literature Search and Inclusion and Exclusion Strategies  
This review focused on past studies conducted on various Japanese plum cultivars (_Prunus salicina_ Lindl.), with clearly and adequately described strategies, methods and technologies for estimating their crop water requirements. The scope includes all global studies conducted in different climates and agroecological zones. There were no restrictions on the articles' publication year to capture the development and advancement of the technology and methods.  
A systematic literature search was undertaken within the Science Direct, Scopus and Web of Science databases to identify relevant studies on estimating the water requirements of various plum cultivars. The key search words included evapotranspiration, water use, water requirements, water consumption, crop coefficients, plum and _Prunus salicina_. The study utilized Boolean operators (OR, AND) to combine the keywords to refine the search using the following query code:TITLE-ABS-KEY ((\"eenaptranspiration\" OR \"water use\" OR \"water requirement\"\" OR \"water consumption\" OR \"crop coefficient\") AND (\"plum\" OR \"prunus salicina\"))._  
A total of 67 articles were collected from Scopus using the query code. These collected articles were thereafter exported into Excel for screening. The number of articles identified, excluded and included were recorded according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement [10], as shown in Figure 1. The inclusion criteria considered for meta-analysis were based on studies (i) published in peer-reviewed journals as full articles, (ii) focusing on the estimation of water requirements of plums using detailed and clearly described strategies, methods and technologies and (iii) providing sufficient data for quantitative analysis. Further, this review excluded (i) studies on Prunus domestic plums, (ii) articles written in languages other than English due to constraints on the resources necessary for translation and therefore analysis, (iii) literature review papers since the paper focused on primary research studies, (iv) conference papers and proceedings and (v) press papers. A total of 18 articles were removed from the records using the listed exclusion criteria.  
The following stage involved examining the titles and abstracts of the remaining articles (n = 48) to check whether the studies had sufficient data and clearly described methods. A total of 21 irrelevant articles were excluded during the title and abstract screening. Of the 28 remaining articles, 14 were unavailable in full-text portable document (pdf) format and were excluded. Full-text-length articles contain detailed information on the study design, data, methodology, results and conclusions. This allows quality assessment to be performed and reduces bias, influenced by limited information. Additional articles (n = 3) were identified with the Google Scholar search engine using a reference list of the remaining articles (n = 14) using the backward reference searching strategy suggested by  
Figure 1: The PRISMA flow diagram shows the selection of considered articles.  
[PERSON] et al. [11]. In total, 17 articles were assessed for eligibility, with all of them meeting the selection criteria.