**2. Material and methods**

#### **2.1 Data collection**

The bibliographic dataset for this study was selected from two sources, the first one was the data information from Vollmer et al. [7] review paper, and the second was extracting a body of data (December 2021) from the Scopus (https://www.scopus. com) search engine.

The methodology applied in Vollmer et al. [7] was utilized for the systematic review of this document. The authors' investigation resulted in an assortment of 95 indexes in their article. However, for this analysis, only indexes with basin as the geographic

*Reviewing Composite Water and Ecosystem Indexes to Envision Indicators with an Ecohydrology… DOI: http://dx.doi.org/10.5772/intechopen.105162*

scale were selected, deriving the usage of 30 indexes of their research; unfortunately, information of one of them was not found. Since the review paper [7] was published six years ago, an update of the new indexes was necessary. Having this in mind, a search of the latest literature was made, using the Scopus portal, and following Vollmer et al.'s approach [7]. The procedure for the search was using the criteria shown below:


III.The literature review covers the years 2016 to 2021.

IV.Selection of indexes exclusively with basin as geographic scale.


Given that the searching strigs used by Vollmer et al. [7] do not cover completely the ecosystems and ecologic outlook, two more search terms were aggregated (**Figure 1**). The procedure for searching with the new terms was almost the same as the criteria described above, except for numbers I and III (years span: 1980–2021).

The update work altogether with the new subjects connected to ecology, it was made following the PRISMA methodology. The flow diagram (**Figure 2**) displays the identification, screening, and inclusion steps of this process.

## **2.2 Data analysis**

The election of the 76 articles and gathered their respective indexes, resulted in a compilation of data of more than 1000 different indicators. Some of the indicators


#### **Figure 1.**

*Search terms used in the Scopus search engine.*

#### **Figure 2.**

*PRISMA 2020 flow diagram for updated systematic review, which included the new search of the database. Own elaboration with information from [7, 9].*

share a similar context, for example, Pires et al. [10] measure the "burden of water-associated diseases (expressed in DALYs) with comparative risk assessment"; similarly, Cervantes-Jiménez et al. [11] assess the "average disability-adjusted life years (DALYs) due to intestinal disease". Both evaluate problems related to population health due to poor water quality and lack of its treatment, which avoids "access

*Reviewing Composite Water and Ecosystem Indexes to Envision Indicators with an Ecohydrology… DOI: http://dx.doi.org/10.5772/intechopen.105162*

to safe water", another indicator, presented by Perez-Foguet and Garriga [12], and Chidammodzi and Muhandiki [13].

Alternative to this, other authors present a short version of the indicators suggested by an older index, this is the case of Gallego-Ayala and Juízo [14] who took 24 indicators from Hopper [15]. Nonetheless, it also exists the circumstance in which more than one article mentions the same indicator for their index (e.g., channel alteration [16–18]).

An indicator can also be divided into other indicators, so while one author considers a set of aspects, another handles them individually. For instance, heavy metals as one indicator [10, 19–21]; or split it in indicator for chromium, aluminum [22, 23], arsenic [23], mercury [23], lead [23], zinc [23, 24], and iron [23, 25].

Regarding the categories used in the articles to classify the indicators, it is possible to see that some indicators can be put into different classes; to illustrate, population density is grouping in economic factors [26], pressure [27], water demand vulnerability [28], social [11], social development [29], and social and urban activity [30].

Also, it is important to recognize that indicators have neutral, negative, or positive dimensions. It means that some of them measure the state, the impact, or the alternatives to improve the situation. As a final remark in this section, it is to notice that some indicators employed to build an index are index by themselves, namely the environment pressure index (EPI) [22, 31, 32].
