The Mesoamerican mid-summer drought: the impact of its definition on occurrences and recent changes

Abstract

Abstract. The mid-summer drought, veranillo or canícula, is a phenomenon experienced in many areas, including Mexico, Central America, and the Caribbean. It generally is experienced as reduced rainfall in July–August, in the middle of the typical rainy season (May–September). Many past studies have attempted to quantify changes in mid-summer drought characteristics during the recent past or for future climate projections. To do this, objective definitions of a mid-summer drought's occurrence, strength, and duration have been developed by many researchers. In this effort we adopt a recent set of definitions and examine the impact of varying these on the characterization of mid-summer droughts and the detected changes over the past 4 decades. We find the selection of a minimum intensity threshold has a dramatic effect on the results of both the area considered as experiencing a mid-summer drought and the changes detected in the recent historical record. The intensity chosen can affect both the magnitude and direction of changes reported in the recent observed record. Further, we find that the typical mid-summer drought pattern may not be occurring during the time it has historically; whether examining past or future changes or developing improved seasonal forecasts, the non-stationarity of its timing should be accommodated.

Recent Trends in Agriculturally Relevant Climate in Central America

“…Precipitation trends indicate an earlier start to the monsoon, a drier mid-summer drought, and a delay towards October of the second peak of precipitation. Changes in the timing of the mid-summer drought were also found in Maurer et al (2022). In regions and months of signi cant drying over the past 42 years, a stronger positive temperature trend is found, as expected from surface energy balance considerations.…”

Atmospheric circulation types controlling rainfall in the Central American Isthmus

“…Hence, WT5 corresponds with the signal of the MSD, featuring enhanced CLLJ and reduced convection. Furthermore, over the Pacific slopes from the Peninsula de Azuero in Panamá to southern Mexico the contrasts between WT4 and WT5 expected precipitation are the largest is the area with a persistent MSD (Maurer et al ., 2022).…”

How Exceptional Was the 2015–2019 Central American Drought?

“…We subset both data sets to 11-18°N and 93-83°W and only include areas where >75% of annual rainfall occurs between May-October (Figure 1a), which is indicative of areas with both a distinct rainy season and Midsummer Drought (Anderson et al, 2019;Magaña et al, 1999). Our study area approximates other delineations of the CADC (Anderson et al, 2019;Gotlieb et al, 2019;Maurer et al, 2017Maurer et al, , 2022, and does not include much of the Caribbean coast, which is characterized by more annual rainfall, different timing in peak rainfall, a shorter dry season, and a less distinct or absent Midsummer Drought (Alfaro, 2000;Karnauskas & Busalacchi, 2009;Magaña et al, 1999;Martinez et al, 2019;Taylor & Alfaro, 2005). Following McKinnon and Deser (2021) (hereafter MD2021), we transform the GPCC observations with a Box-Cox power transform before fitting the OLEns model to reduce the influence of outliers and to prevent the model from generating negative precipitation amounts (Box & Cox, 1964).…”