Document Type : scientific-research article
Author
University of Sistan and Baluchestan
Abstract
The goal of this paper is to investigate the causes of fluctuations in precipitation and severity of winter droughts in Sistan and Baluchistan province in relation to the teleconnection patterns in the Northern Hemisphere. In this regard, the atmospheric data were collected from meteorological stations in the region to calculate Standard Precipitation Index (SPI) in the winter based on which the intensity and scale of severe winter droughts in the region were determined. The active teleconnection indicators in the Northern Hemisphere during the winter as well as the multivariable Enso index (MEI) were compared with the SPI. It was conducted using correlation tests and multivariate backward stepwise regression models. These patterns explain 55% of variations in SPI and the Scandinavian pattern, which is significantly correlated with the SPI, was identified as the most effective pattern explaining the severity of drought. The hypothesis tests (T, U and Wilcoxon) revealed a significant difference in precipitation during the positive and negative phases of Polar/Eurasian (POL), Scandinavia and tropical Northern Hemisphere (TNH) patterns. The models suggest that with a decrease in each unit of Polar/Eurasian (POL) and Scandinavia patterns, the drought severity surges by 18 and 22 percent, respectively.Based on combinational maps and longitudinal and transverse sections relative to the atmospheric height, the prevailing synoptic patterns in the Northern Hemisphere were investigated along with wet and extremely dry conditions. The results demonstrate a marked shift in the cyclonic paths of rivers and pressure centers concurrent with the rise of droughts in Sistan and Baluchistan in the synoptic scale of the Northern Hemisphere.
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