Abstract
This work provides an assessment of the two most intense seasonal droughts that occurred over the Balsas River Basin (BRB) in the period 1980–2017. The detection of the drought events was performed using the 6 month scale standardized precipitation–evapotranspiration index (SPEI-6) and the 6 month standardized precipitation index (SPI-6) in October. Both indices were quite similar during the studied period, highlighting the larger contribution of precipitation deficits vs. temperature excess to the drought occurrence in the basin. The origin of the atmospheric water arriving to the BRB (1 May 1980–31 October 2017) was investigated by using a Lagrangian diagnosis method. The BRB receives moisture from the Caribbean Sea and the rest of the tropical Atlantic, the Gulf of Mexico, the eastern north Pacific and from three terrestrial evaporative sources: the region north of BRB, the south of BRB and the BRB itself. The terrestrial evaporative source of the BRB itself is by far the main moisture source. The two most intense drought events that occurred in the studied period were selected for further analysis. During the severe drought of 2005, the summertime sea surface temperature (SST) soared over the Caribbean Sea, extending eastward into a large swathe of tropical North Atlantic, which was accompanied by the record to date of hurricane activity. This heating generated a Rossby wave response with westward propagating anticyclonic/cyclonic gyres in the upper/lower troposphere. A cyclonic low-level circulation developed over the Gulf of Mexico and prevented the moisture from arriving to the BRB, with a consequent deficit in precipitation. Additionally, subsidence also prevented convection in most of the months of this drought period. During the extreme drought event of 1982, the Inter Tropical Convergence Zone (ITCZ) remained southern and stronger than the climatological mean over the eastern tropical Pacific, producing an intense regional Hadley circulation. The descent branch of this cell inhibited the development of convection over the BRB, although the moisture sources increased their contributions; however, these were bounded to the lower levels by a strong trade wind inversion.
Highlights
Numerous severe drought events have been witnessed around the world during the last decades [1], such as the 2007–2009 drought in the Fertile Crescent [2], the 2010 Amazon drought [3], the long drought of the first decade of the current century in Australia [4] or the2011 record-setting Texas drought [5]
It is widely accepted that dry conditions prevail in the southern part of Mexico top-seven drought events occurred during El Niño - Southern Oscillation (ENSO) warm phases (1982, 1987, 1994, 1997, 2009) being three of them during strong El Niño years
Sent the accumulated monthly anomalies of the water vapor supplied by these three moisture sources (BRB: blue, southern BRB (SOUTH): pink and Caribbean Sea (CAR): red; black solid lines in Figure 5a) for the severe and the extreme drought events that occurred in the period 1980–2017
Summary
Numerous severe drought events have been witnessed around the world during the last decades [1], such as the 2007–2009 drought in the Fertile Crescent [2], the 2010 Amazon drought [3], the long drought of the first decade of the current century in Australia [4] or the. To investigate the relative importance of moistening in the BRB, we take advantage of the use of the Lagrangian dispersion model FLEXPART (flexible particle dispersion model) [26,27] This Lagrangian approach allows us to determine large-scale water vapor advection by tracking evaporation minus precipitation (E–P) from a region forwards or backwards in time, thereby facilitating the determination of the source–receptor relationships of water. The BRB has an extension of 116,436 km2 [17], and it is the most important Pacific slope river in the country, supplying water to big conurbation areas such as Puebla, Tlaxcala and Cuernavaca-Cuautla, among others. Basin for the period from 1980–2017 from the University of East Anglia Climate Research Unit (CRU) database [15]
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