**3. Results**

For the study of climatic oscillations, the ENSO phenomenon was studied through the use of different indices such as El Niño 3/3.4 index, SOI, ONI, and Extended Multivariate ENSO Index (MEI). Only a minority of authors referred to this oscillation

**Figure 1.** *PRISMA flowchart for document selection.*

by means of anomalies in the equatorial eastern Pacific SST [23–26]. On the other hand, the PDO events were measured directly by the original index, except for Mo and Schemm [3] whose study was considered, despite the fact that they contemplate North Pacific SST anomalies. Finally, the AMO oscillation was referred to, in less than 30% of the cases, as North Atlantic SST anomalies. The other 70% of the authors used the AMO index to express their conclusions, and only Ruprich-Robert et al. [27] used the Atlantic Multidecadal Variability (AMV) Index to identify teleconnections.

**Table 1** summarizes the number of articles divided by area of study. What stands out in the table is that the majority of studies reviewed, published from 1984 to 2020, focused in northwestern Mexico or in a region that comprises part of the country or the country as a whole (i.e., subtropical North America or Tex-Mex region). On the other side, northeastern Mexico has been the area with less focused investigations.

Turning now to **Table 2**, an overview of all conclusions reached by the authors is presented by region of the country and by the season of the year. The category "most


#### **Table 1.**

*Studies per region.*

of the territory" includes those authors who referred to Mexico as a whole region, without distinguishing the north, center or south. All 75 articles analyzed in this document, published between 1984 and 2020, are gathered in this table. Also, the cells colored in blue denote that at least one conclusion contained is divergent from the majority of the authors, with majority meaning over 50%. Likewise, cells colored in green signify that two or more conclusions there contained, are divergent from the majority of the authors. Interestingly, although the modes of climate variability cannot fully explain the physical mechanisms that drive extreme events in precipitation patterns [77], most of the authors agree on general conclusions, thus, only a minority of cells is colored.

Furthermore, **Table 3** shows the summary statistics for the percentage of matching and mismatching conclusions. Cells colored in green denote the conclusions repeated by two or less authors, these are referred to as limited information given the lack of sufficient studies to support the conclusion. Cells colored in magenta highlight the conclusions with more than 50% of coincidence. This percentage is obtained by dividing the number of articles that agreed on the condition caused by a specific index, during a specific season, in a specific region, over the total number of articles that addressed the effects of that climatic index for that season and in that region.

From the chart, it can be seen that by far, the most studied SST pattern is ENSO with a total of 158 conclusions driven by different authors. This number is more than twice the sum of the conclusions driven for AMO [34] and PDO [39]. Closer inspection of the table shows that the northern part of the country has received the most attention among different authors; in total, 107 conclusions were reached for this region with the most teleconnections studied during winter [37] and in unspecified season [53], which in most cases means annual conclusions. Conversely, the central and southern regions of Mexico received less attention, with 87 conclusions that were mostly reached for unspecified season or the whole year [44], and for the summer season [28]. Finally, for articles that mentioned the country in general, 39 conclusions were found that were distributed quasi homogeneously in all seasons.

Lastly, **Table 4** provides the results obtained from the systematic review of 75 articles that focused primarily or partially on the study of the teleconnections of interest. Cells colored in magenta show the general conclusions in which more than 50% of the articles agree but at least three authors studied the corresponding phase of the climatic oscillation, in the corresponding region, during the corresponding season.


