CHANGING HYDROCLIMATE IN SEMI-ARID NORTHEAST MEXICO SINCE THE LAST GLACIAL MAXIMUM AND POSSIBLE INFLUENCE OF THE MERIDIONAL FLOW OF CARIBBEAN LOW-LEVEL JET
In Mexico, the decadal duration droughts in 1950s and 1990s were consistent with the late 20th century global expansion of drylands. These hydrometeorological extremes have made the rainfed agricultural productions and socioeconomic conditions in rural areas more vulnerable causing the displacement of people through the international border. It has been observed that significant migration has happened from the drier regions of north and central Mexico during the rainfall deficit years, e.g., 1990s and model simulations suggest more frequent and sustained droughts over the next decades. The drought records in Mexico have been generated through instrumental data, tree-rings and the hydroclimate variations registered through the reconstruction of surface processes as well as the changing organic productivity in sedimentary archives collected from lacustrine basins. Some of those have highlighted the role of ocean-atmospheric forcings such as ENSO, PDO, AMOC and ITCZ on the water-scarce intervals, contemporary to the global events of climate change over the glacial and interglacial intervals.
The Caribbean Low-level Jet is an important forcing that brings summer moisture to the semiarid northeast Mexico from the Intra-Americas Sea. It is the eastern zonal winds in lower troposphere along the southern margin of the North Atlantic Subtropical High and splits into two branches over the Caribbean Sea, each with distinctive summer and winter regimes. In the boreal summer, the meridional flow transports moisture for the rainfall deficit regions of northeast Mexico and central US. Its moisture flux agrees well with the precipitation cycle of the Cieneguilla Basin, located at 23°N in western foothills of the Sierra Madre Oriental Mountains. This study evaluated the multi-proxy paleoclimate registers of last 21,000 years from this basin showing the dynamics of near-surface processes such as erosion through runoff, water column salinity through evaporation with respect to Greenland ice core, fluvial discharge into the Carriaco Basin, sea surface temperature in Gulf of Mexico and regional paleoclimate records from US, Mexico and Guatemala to infer the possible influence of Caribbean Low-Level Jet, especially during the wetter deglaciation and drier Holocene in semi-arid northeast Mexico.