Abstract
Changes of the onset dates, end dates, and duration of the rainy season over central Peruvian Andes (Mantaro river basin, MRB) could severely affect water resources management and the main economic activities (e.g., rainfed agriculture, raising cattle, among others). Nonetheless, these changes have not been documented for the Tropical Andes. To asses that, we used daily datasets of observed rainfall during the 1965–2013 period. For this period, the average onset (end) date of the rainy season over the MRB occurs in the pentad 17 (19–23 September) [pentad 57 (7–11 April)]. The duration of the rainy season mainly is modulated by the onset dates due to it has higher variability than end dates. There is a reduction of 3 days/decade in the duration of wet season over the MRB for the last four decades due to the delay of the onset days. Furthermore, El Niño favors late-onset and early end of the rainy season, while La Niña favors early onset and late end of the rainy season in the MRB. Onset dates are related to the propagation of the convective region of the South American Monsoon System (SAMS), from the Caribbean region toward the central Amazon basin. Early (late)-onset days are associated with a southward (northward) shift of the South Atlantic Convergence Zone (SACZ) and weak (strong) convection over equatorial Atlantic that induces the southernmost propagation (eastward shift) of the SAMS.
Highlights
The precipitation plays a vital role in the hydrological cycle, it is one of the climate variables with more attention for climate scientists [1]
Comparing the length of the rainy season in Mantaro river river basin basin (MRB) respect to other regions of South America, such as Amazon basin, we found that the length of the rainy season over the Amazon basin is longer than the rainy season length over MRB
Our findings show that rainy seasons are induced during the southward propagation of convective regions from the Caribbean region toward southern and central Amazon basin between end-September (19–23 September, onset date) and early-April
Summary
The precipitation plays a vital role in the hydrological cycle, it is one of the climate variables with more attention for climate scientists [1]. The SAMS shows a seasonal cycle with an onset during October, a mature phase between December and February, and demise in April [10,13,26]. SAMS onsets start during the austral spring (September-October-November, SON) (Figure 3) when the region of intense convection austral spring (September-October-November, SON) (Figure 3) when the region of intense spreads rapidly from the Caribbean and northwestern South America toward southern Amazon basin convection spreads rapidly from the Caribbean and northwestern South America toward southern and Brazilian highlands in October and southeast Brazil in November [13,26,27,28]
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