Trend Analysis Of Seasonal Precipitation In The Sub-regions Of Hunan Province In Recent 54 Years

Precipitation is a complicated nonlinear atmospheric process,which vary widely in different regions.The regionalization of precipitation is essential to understand the precipitation patterns of the large geographic area.Thus,the detection of precipitation trends in different areas plays an important role in the prediction of precipitation and management of water resources.In this study,the agglomerative hierarchical clustering?AHC?coupled with rotated empirical orthogonal functions?REOF?is applied to form sub-regions based on the seasonal precipitation data of 89meteorological stations in Hunan Province during the period 1960-2013.Then,the method combining the discrete wavelet transform?DWT?,Mann-Kendall?MK?and sequential MK?SQMK?is used to analyze the trend of precipitation change and identify the most dominant periodic components that affected seasonal precipitation trends in each sub-region.In addition,the stepwise variable selection and multiple linear regression are utilized to identify the dominant climate factors in explaining the four different seasonal precipitation changes over Hunan Province.The results are as follows:?1?The first three rotated EOF modes reveal that there are three principal precipitation anomaly sensitive areas that do not overlap each other in different seasonal precipitation over Hunan Province.The three principal precipitation anomaly sensitive areas of winter precipitation are south Hunan,northwest Hunan and central Hunan.The three principal precipitation anomaly sensitive areas of spring precipitation are respectively highlighted in southwest Hunan,north Hunan and south Hunan.The three principal precipitation anomaly sensitive areas of summer precipitation are located in central Hunan,south Hunan and northwest Hunan,respectively.For autumn precipitation,the three principal precipitation anomaly sensitive areas are respectively situated in southwest Hunan,south Hunan and northwest Hunan.?2?Winter precipitation in Hunan can be divided into five homogeneous and distinct regions:northwest Hunan?DJF1?,west-north Hunan?DJF2?,southwest-central Hunan?DJF3?,hilly areas of south Hunan?DJF4?,and mountain areas of south Hunan?DJF5?.Spring precipitation is classified into three sub-regions that cover the north Hunan?MAM1?,southwest-central Hunan?MAM2?and south Hunan?MAM3?.For summer precipitation,the three sub-regions,northwest Hunan?JJA1?,southwest-central Hunan?JJA2?and south Hunan?JJA3?are formed.The three sub-regions of autumn precipitation,namely north Hunan?SON1?,southwest-central Hunan?SON2?and south Hunan?SON3?.The delineated sub-regions for each season shows strongly coherent spatial patterns,all of which are along the strip extending in southwest and northeast direction.?3?The winter precipitation has an increasing trend in each of the five sub-regions,but these trends are different from each other.The southwest-central Hunan,hilly areas of south Hunan and mountainous areas of south Hunan exhibit a statistically significant upward trend.All the original spring precipitation series of three sub-regions show a non-significant downward trend.All the original summer precipitation series of three sub-regions show an increasing trend and the southwest-central Hunan experiences a statistically significant upward trend.The original autumn precipitation series in all sub-regions experience a non-significant downward trend.?4?Results from DWT suggest that the areal mean precipitation series of all sub-regions are decomposed into four detail components?D₁-D₄?,and an approximation component?A₄?.The Results of DWT and sequential MK analyses show that D₁ of seasonal precipitations in all sub-regions is the most dominant periodic mode affecting their observed trends,except for summer precipitation in sub-region JJA3,where D₂ is the most dominant one.Therefore,short-term periodicity?2-4 years?is the most influential in affecting the observed trends of seasonal precipitation over Hunan Province.?5?The precipitation of four different seasons are influenced by the different combinations of climate indices with different time lags,and the variability of seasonal precipitation could be explained by the identified climate indices to some extent.The results indicate that the winter precipitation is affected by Ni?o3,Ni?o3.4 and AO with different time lags.PDO,SOI,DMI and NAO with different time lags affect spring precipitation.Ni?o3,ECS,PDO and AO with different time lags affect summer precipitation.The autumn precipitation is affected by BB and PNA with different time lags.