**1. Introduction**

Droughts are one of the most threatening natural disasters for human civilization and the ecosystems. Even though there is no universally accepted definition for these phenomena in the scientific literature [1], droughts are characterized by the prolonged absence or pronounced deficiency of precipitation [2]. This negative anomaly in precipitation could be driven by numerous factors, however, changes in SST (sea surface temperature) have shown to be one of the main forces that induce droughts [3]. Moreover, in the late Holocene, three main SST patterns: the Pacific

Decadal Oscillation (PDO), El Niño Southern Oscillation (ENSO), and Atlantic Multidecadal Oscillation (AMO), have been associated to significant changes in precipitation regimes over Mexico [4, 5].

On one side, PDO reflects the monthly variations of Pacific SST north of the 20°N with a periodicity of 15–20 years [6]. The main climatic effects of the PDO are concentrated in the North Pacific and southwestern North America, primarily during the winter season, and can be responsible for up to 50% of the annual precipitation variability [7]. Some authors suggest that during its positive phase, the monsoonal precipitation is reduced in central Mexico [5]. The AMO, on the other side, measures medium-term cycles (20–40 years) of positive and negative detrended anomalies in North Atlantic SST [6, 8]. The AMO variability has been linked with changes of climate and extreme events [8]. During boreal summer, AMO has been associated with intensification of the hurricane season in the Atlantic and droughts in North America [9].

Lastly, ENSO is the most studied climatic oscillation because it affects atmospheric circulation throughout the world [6, 7, 10, 11]. Moreover, several authors consider that ENSO is the most important factor for interannual climatic variation in Mexico [7, 12–15]. ENSO is made up of two phenomena; its oceanic component, El Niño, refers to the positive anomaly of at least 0.5°C in the equatorial Pacific SST for six consecutive months or more [13]. La Niña reflects the opposite. On the other hand, its atmospheric component, the Southern Oscillation Index (SOI), is an air mass equilibrium movement between the Pacific and Indo-Australian areas [10]. Although El Niño and SOI are not perfectly correlated in terms of minor variations, large negative SOI values are associated with warm ONI (Oceanic Niño Index) events [10]. Additionally, the PDO has the potential to act simultaneously with ENSO, and depending on the phasing, it can enhance its effects [16].

Teleconnections are statistical associations between climatic variables perceptible in spatially separated areas [17]. The studies reviewed in this document analyzed the teleconnections between dry periods in México and SST patterns. For this purpose, the majority of authors measured dry periods with precipitation anomalies, which refer to a deviation from the average registered in a determined location. These precipitation anomalies were estimated by numerous methods; some authors used standardized anomalies of monthly, daily, or yearly data; others used the average annual or monthly accumulated precipitation. To define dry periods, other authors used the Standardized Precipitation Index (SPI), whose use was suggested by the World Meteorological Organization [18] as a general recommendation to characterize meteorological drought. Additional indices used were the Palmer Drought Severity Index (PDSI), Tropical Rainfall Index (TRI), and the Outgoing Longwave Radiation Precipitation Index (OPI). Proxy data such as tree ring width and information from ancient sediments was used to estimate dry conditions as well.

Droughts, unlike most natural disasters but like a disease, generally begin before the symptoms appear [19]. Therefore, understanding their causes and expected variations is critical [20]. The potential of forecasting droughts through the study of SST patterns relies in providing time to take mitigation actions. This review paper aims to synthesize the main findings regarding the effects that AMO, ENSO, and PDO can have over dry periods in Mexico. To achieve this goal, the following research questions were addressed.

• RQ1: What are the main conclusions achieved by the majority of studies on the topic?


Moreover, this is the first study that reviews not only the individual but the coupled influences of ENSO, AMO, and PDO over droughts in Mexico. Findings in this review will be useful for local authorities, decision-makers, academics, among others. Furthermore, by identifying the least explored research directions, this review will also help researchers when selecting potential areas of study in the field.
