The cumulative dry days and
the drought frequency are calculated using the meteorological drought composite
index (CI) based on the data
about daily precipitation and daily average temperature
collected from 90 meteorological stations in Southwest China (Sichuan, Yunnan, Guizhou Province and
Chongqing City) during the time period from 1962 to 2017.Using the wavelet
analysis and linear trend, the temporal and
spatial variation of cumulative dry days and frequency in the span of 56 years
are analyzed in detail. In addition, the atmospheric circulation profiles of the years with
lower and higher value are investigated too using correlation and composition
analysis. The conclusions are
summarized as follows: (1) The overall trend of cumulative dry days and frequency
are gradually decreased, the decade anomaly
between the two is positive correlated from 1960s to 1980s, negative correlated in 1990s and positive correlated
again at the beginning of the 21st century. (2) The duration (the
accumulative dry days) has an inter-annual variation period of 5 years and 9 years, and a decade-wise variation period of 12 years. The drought frequency has an inter-annual variation period of 8 years and a decade-wise variation period of 20 years. (3) The duration
and frequency have the same center area with higher values including the west
Sichuan and the middle and north Yunnan, and the same center area with lower values including
the west of Yunnan, the middle and east
of Guizhou and Chongqing. (4) The relevant circulation analysis indicated it is
to the disadvantage of precipitation in the region if without water vapor and
the uplift dynamics in each of the high, middle and low layers atmospheric circulation.
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