The mid‐summer drought over Mexico and Central America in the 21st century

Abstract

The southern Mexico and Central America (SMCA) region shows a dominant well‐defined precipitation annual cycle. The rainy season usually begins in May and ends in October, with a relatively dry period in July and August known as the mid‐summer drought (MSD); notable exceptions are the Caribbean coast of Honduras and Costa Rica. This MSD phenomenon is expected to be affected as the SMCA experiences an enhanced differential warming between the Pacific and Atlantic Oceans (PO‐AO) towards the end of the 21st century. Previous studies have suggested that this differential warming will induce a strengthening of the westward Caribbean low‐level jet (CLLJ) and that this heightened CLLJ will shift precipitation westwards, falling on the PO instead that within the SMCA region causing a severe drought. In this work we examine this scenario with a new model, the Rossby Center Regional Climate Model (RCA4), for the COordinated Regional climate Downscaling EXperiment (CORDEX) Central America domain, forced with different general circulation models (GCMs) and for different representative concentration paths (RCPs). We consider 25‐year periods as “present conditions” (1981–2005) and “future scenario” (2071–2095), focusing on the “extended summer” season (May–October). Results suggest that in the future the spatial extension of the MSD will decrease and that in certain areas the MSD will be more intense but less frequent compared to present conditions. Also, the oceanic differential warming, the intensification of the CLLJ, and the reduction in regional precipitation in the future scenario, suggested by previous works, were verified in this study.

Regional Climate Change in Southeast Mexico-Yucatan Peninsula, Central America and the Caribbean

“…climate regional factors, such as LLJ [69]. Although AMO shows a positive relation with the precipitation for all three study areas of the region, AMO variability is more than ten years, and it has a low frequency signal [70] that is reflected by the low spread in the data shown in Figure 3.…”

“…The duration of the PDO variability cycle is approximately ten years and, in agreement with the trend, Mexico and the Caribbean show a precipitation increase but CA shows a precipitation decrease. It is important to note that the climate in CA is driven by other climate regional factors, such as LLJ [69]. Although AMO shows a positive relation with the precipitation for all three study areas of the region, AMO variability is more than ten years, and it has a low frequency signal [70] that is reflected by the low spread in the data shown in Figure 3.…”

Projected changes in precipitation and temperature regimes and extremes over the Caribbean and Central America using a multiparameter ensemble of RegCM4

“…(2013) is used, as implemented by Corrales‐Suastegui et al . (2019): when two precipitation peaks are found, separated from each other by 1–3 dry months, the case is defined as an MSD period, otherwise, it is considered as 0 (No‐MSD). The intensity of the MSD is defined as: where MSD i is the intensity of the Mid‐Summer Drought, MSD min is the sum of precipitation for the relatively dry months, MSD max is the sum of the two maximum monthly precipitation peaks and m is the number of dry months between the two maximum peaks.…”

Evaluation of methods to detect and quantify the bimodal precipitation over Central America and Mexico

“…(1999) analysed the climatological characteristics of bimodal precipitation signals over Central America and Mexico to suggest that the changes in sea surface temperatures during summer contribute to the development of bimodal precipitation signals. Other theories include the Caribbean low‐level jet (Magaña and Caetano, 2005; Wang, 2007; Wang and Lee, 2007; Herrera et al ., 2015; Corrales‐Suastegui et al ., 2020), Indian monsoon (Mapes et al ., 2005), vertical wind shear with atmospheric particles (Angeles et al ., 2010), solar declination (Karnauskas et al ., 2013), the El Niño–Southern Oscillation (Peralta‐Hernández et al ., 2008; Rauscher et al ., 2008) and the Madden‐Julian Oscillation (Poleo et al ., 2014; Perdigón‐Morales et al ., 2019; Zhao et al ., 2019; Jury, 2020), and all of these have been shown to potentially contribute to the development of bimodal signals. It is now generally realized that the development of bimodal precipitation on a global scale is not determined by a single factor; it is the result of a combination of several connecting mechanisms, none of which are likely to completely reveal all of the variabilities of bimodal signals.…”