Abstract
Anecdotal evidence suggests that the timing and intensity of the Central American Midsummer Drought (MSD) may be changing, while observations from limited meteorological station data and paleoclimate reconstructions show neither significant nor consistent trends in seasonal rainfall. Climate model simulations project robust future drying across the region, but internal variability is expected to dominate until the end of the century. Here we use a high-resolution gridded precipitation dataset to investigate these apparent discrepancies and to quantify the spatiotemporal complexities of the MSD. We detect spatially variable trends in MSD timing, the amount of rainy season precipitation, the number of consecutive and total dry days, and extreme wet events at the local scale. At the regional scale, we find a positive trend in the duration, but not the magnitude of the MSD, which is dominated by spatially heterogeneous trends and interannual variability linked to large-scale modes of ocean-atmosphere circulation. Although the current climate still reflects predominantly internal variability, some Central American communities are already experiencing significant changes in local characteristics of the MSD. A detailed spatiotemporal understanding of MSD trends and variability can contribute to evidence-based adaptation planning and help reduce the vulnerability of Central American communities to both natural rainfall variability and anthropogenic change.
Highlights
Variable precipitation is among the many challenges faced by the millions of families who rely directly on smallholder farming in Central America (PRESANCA-FAO 2011, Van der Zee Arias et al 2012) and is linked to both food insecurity and migration (Lobell et al 2008, Nawrotzki et al 2016)
In agreement with previous studies, our classification identifies a consistent Midsummer Drought (MSD) along the Pacific coastal region but not the Caribbean, where locations experience a single maximum in precipitation or an autumn reduction in rainfall driven by different mechanisms (Magaña et al 1999, Amador et al 2006, Curtis and Gamble 2007, Karnauskas et al 2013, Maurer et al 2017)
We find that MSD onset dates are relatively stable through time across most of the region, in contrast to the end date and duration (figure 2(a))
Summary
Variable precipitation is among the many challenges faced by the millions of families who rely directly on smallholder farming in Central America (PRESANCA-FAO 2011, Van der Zee Arias et al 2012) and is linked to both food insecurity and migration (Lobell et al 2008, Nawrotzki et al 2016). Smallholder farmers have reported changes in the distribution and intensity of rainfall across Central America, resulting in crop losses and reductions in yields for those already contending with pervasive social and economic inequalities (Eakin et al 2014, Pons et al 2016, Hellin et al 2017, de Sousa et al 2018, Harvey et al 2018, Rice 2018, Bellante 2019). During the MSD period, precipitation may decline by up to 40% from the maximum summer rainfall (Magaña et al 1999) and its variable characteristics, including the timing, duration, and magnitude have significant influences on planting dates and crop yields (Hastenrath 1966, Magaña et al 1999, Van der Zee Arias et al 2012, Pons et al 2016). Identifying changes in characteristics of the MSD and in the timing and quantity of rainfall throughout the region is crucial, because it is bound to the livelihoods and food security of many rural communities and is expected to significantly shift by the end of the 21st century in response to anthropogenic modification of the climate system (Rauscher et al 2008, Maurer et al 2017)
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