To analyze the characteristics of drought and flood variations in Quanzhou during recent 55 years, the standardized precipitation index (SPI) and Empirical Orthogonal Function (EOF) and Rotated Empirical Orthogonal Function (REOF) were calculated by using the monthly precipitation data from 6 meteorological bureaus across Quanzhou for 1960-2014. Results showed that: 1) During 1960-2014, the drought and flood showed Periodic variation characteristics in Quanzhou, the specific period of frequent drought was 1963-1972, 1977-1986 and 2009-2011, and the specific period of frequent flood was 1961-1962, 1972-1975, 1990-1992 and 1997-2007; the drought and flood did not have significant tendency of variation in Spring and Summer, and the drought and flood showed a non-significant downward trend in Autumn and Winter. 2) The drought and flood variation had relatively consistent trend in Quanzhou, but there was a big difference on the northwest mountainous area, the middle semi-mountainous area and the southeast coast area in some periods. 3) The precipitation cell and distribution in every season were Nan’an and Anxi, but there was a big difference in rainfall less area: it was Yongchun and Dehua in Spring, Chongwu and Jinjiang in Summer, Chongwu in Autumn, Dehua and Chongwu in Winter.
The loss caused by meteorological disasters is huge, and in meteorological disasters, the effects of droughts and floods are the most serious [
At present, the commonly used indicators of droughts and floods include precipitation anomaly (Pa), Palmer drought index (PDSI), soil relative humidity index, standardized precipitation index (SPI), Z index, and integrated meteorological drought index (CI). Many scholars at home and abroad have comparatively analyzed the effects of different indexes on monitoring drought events. The SPI index based on precipitation data not only has the advantages of simple calculation and multiple time scales, but also can compare droughts and floods in different spaces and has good stability. In extreme cases, it is superior to the widely used Z index in the country and has been widely used in drought monitoring [
The data used by the Institute is the monthly precipitation data from 6 regular weather stations in Quanzhou during 1960-2014. In order to ensure the integrity and continuity of the data, the monthly precipitation data from Anxi Station in January, August, and August in January 1968 and January 1971 were used to interpolate the monthly precipitation data from the Nan’an Station with the best correlation.
The Standardized Precipitation Index (SPI) was proposed by McKee et al. [
S P I = S t − ( c 2 t + c 1 ) t + c 0 [ ( d 3 t + d 2 ) t + d 1 ] t + 1.0 (1)
In the formula, t = ln 1 g ( x ) 2 , g ( x ) is the probability distribution of precipitation associated with the Γ function; x is the sample of precipitation; S is the positive and negative coefficient of probability density.
When g ( x ) > 0.5 , S = 1; when g ( x ) ≤ 0.5 , S = −1. g ( x ) is calculated from the probability density integral formula of the Γ distribution function:
g ( x ) = 1 β α Γ ( α ) 0 ∫ 0 x x α − 1 e − x β d x , x > 0 (2)
In the formula, α and β are the shape parameters and scale parameters of the Γ distribution function, respectively. c 0 , c 1 , c 2 and d 1 , d 2 , d 3 are the calculation parameters of the simplified approximate solution formula for the conversion of the Γ distribution function to the cumulative frequency, where c 0 = 2.515517, c 1 = 0.802853, c 2 = 0.010328, d 1 = 1.432788, d 2 = 0.189269, d 3 = 0.001308.
SPI has the characteristics of multiple time scales (1, 3, 6, 12, 24, 48 months, etc.). For example, the SPI of December time scale represents the standard deviation of December precipitation. The SPI of 3 months time scale in December represents the standard deviation of precipitation in October-December. The December 12-month time scale SPI represents the standard deviation of January-December precipitation. This article mainly analyzes the 12-month and 3-month time scale SPI. Because 12-month time scale SPI can more clearly reflect the stage changes of drought and flood, and 3-month time scale SPI can reflect the seasonal drought, it is closely related to agricultural drought. The drought classification was graded according to the drought level criteria such as Mckee [
The empirical orthogonal function (EOF) and the rotational empirical orthogonal function (REOF) can convert the original multiple related indexes to a few new and independent comprehensive indexes without losing or losing the original information. Therefore, EOF was used to process the SPI sequences of each station, and the overall trend of drought and flood changes over time and the spatial distribution of drought and flood were analyzed. By rotating the EOF feature vector (REOF) and redistributing the variance, the principal components have more separation, and the rotative factor load vector is obtained. Each vector represents the spatial correlation distribution structure. The larger the value is, the better the correlation is, and the closer to 0 is the irrelevance, so that the results of the principal component analysis can be better explained and the area of the drought and flood is divided.
The multi-time scale characteristics of SPI can realize the monitoring of different types of droughts and floods. Synthetic application of SPI at each time scale can comprehensively monitor and evaluate droughts and floods.
SPI Value Range | Drought and Flood Level |
---|---|
SPI ≤−2.0 | Extremely drought |
−2.0 < SPI ≤−1.5 | Heavy drought |
−1.5< SPI ≤−1.0 | Drought |
−1.0 < SPI < 1.0 | normal |
1.5 > SPI ≥ 1.0 | Waterlog |
2.0 > SPI ≥ 1.5 | Heavy Waterlog |
SPI ≥ 2.0 | Extremely Waterlog |
reflection on the underlying soil moisture, river runoff, groundwater level and reservoir water storage capacity. The characteristics of long-term changes in drought and flood can be clearly reflected.
Taking 1963 as an example, we can see in
The interannual change of SPI can reflect the specific time period of drought and flood. As can be seen from the monthly changes in SPI12 in
Related studies have shown that the time scale of 3 months SPI can be used to analyze seasonal drought, and can better represent the agricultural drought conditions [
Spring: During the period of 1960-2014, droughts and floods in Quanzhou City were characterized by periodical changes, and droughts dominated from 1960 to 1971. There were 4 spring droughts, with an average of once every 3 years. From 1980 to 1990, the rainstorm was dominant, and there were 5 spring floods, occurring about every 2 years. SPI values were relatively stable between 1972-1979 and 1991-2014. The main years of spring drought occurred in 1963-1964, 1968, 1971, 1991, 1995, 2011 and 2014. The spring drought in 1971 was the most serious and the SPI value reached −1.90. In 1973, 1980, 1983-1984, 1990 and 2000, the year of spring floods, especially in the history of the most recent year in 1973, the SPI value reached 2.11. Calculating the linear tendency of SPI3 in spring is only 0.005/10a, indicating that from the long-term trend, there is no change in spring drought and flood in Quanzhou.
Summer: Quanzhou experienced frequent droughts and floods in the summer between 1963-1973 and 1988-2008. The main summer drought years were 1967, 1978, 1988, 1991 and 2003-2004. The main summer disaster years were 1963, 1965, 1972-1973, 1993, 1997, 2000, 2006 and 2008. The summer drought in the past 55 years was the highest in 2003, the SPI value was −1.96, the summer flood was the highest in 2006, and the SPI value was 2.17. The linear tendency of the summer SPI3 calculation was only 0.008 times per year, indicating that the
long-term change trend showed that there was no change in summer drought and flood in Quanzhou.
Autumn: The autumn drought in Quanzhou in the 1960s and the 1980s was relatively frequent. In the late 1990s and early 21st century, autumn quails frequently occurred, with an average of every 1 - 2 years. The main autumn drought years were 1963, 1965, 1967, 1982, 1986, 1993 and 2014. The main autumn disaster years were 1961, 1975, 1990, 1999-2000, 2002-2003 and 2005. Autumn drought was the most serious in 1986, with an SPI value of −1.66. The most serious locust plague occurred in autumn in 1990, and the SPI value reached 2.17. Calculating the linear trend rate of SPI3 in the autumn was 0.08/10a, indicating that from the long-term trend, the autumn drought in Quanzhou showed a weaker trend, but the reduction trend was not obvious.
Winter: During the period of 1960-2014, droughts and floods changed frequently in winter in Quanzhou City. Winter drought was more common in the early 1980s, and winter floods occurred frequently in the early 21st century. The winter drought mainly occurred in 1962, 1964, 1983-1985, 1995 and 2003-2004. Winter floods mainly occurred in 1963, 1974, 1982, 1986, 1997, 2000, 2002, 2006 and 2011-2012. The year with the least precipitation in winter occurred in 1962. The SPI3 value was −2.06, the most precipitation year appeared in 2011, and the SPI3 value was 2.03. Calculating the linear trend rate of SPI3 in winter was 0.092/10a, indicating that the winter drought in Quanzhou City showed a weaker trend of reduction, while winter precipitation slightly increased, but the trend was not significant.
The analysis of SPI12 using orthogonal empirical function (EOF) shows that the first two eigenvectors explain 90.9% of the total variance. After the third eigenvector, the contribution of the variance of each vector is smaller. Therefore, this article only analyzes the first two feature vectors.
second type of drought and flood distribution in Quanzhou, namely the northwest-southeast difference type. This is mainly due to the environmental factors such as geographical location and special terrain in Quanzhou, such as the northwest mountainous region is in the windward slope of the Daiyun Mountains, and the southeastern part of the coast is in the leeward slope of the Taiwan Mountains.
The first two EOF eigenvectors of SPI12 in Quanzhou were rotated by the maximum variance for factor analysis to further analyze the spatial distribution characteristics of drought and flood in Quanzhou. The absolute value large value region (|feature vector| > 0.8) of the first orthogonal spatial module (REOF) decomposition of the first space module (
Whether it is EOF or REOF, Yongchun is always the center point. The overall distribution of EOF and REOF is consistent.
The EOF analysis was performed on SPI3 at each site in Quanzhou to obtain the distribution of the first feature vector for each season (
spatial distribution of drought and flood in each season, and their components are all positive. This shows that Quanzhou’s precipitation in each season has a good spatial consistency. The precipitation centers of the various seasons are distributed in Nanan and Anxi areas, but the areas where the precipitation is relatively small are slightly different: Spring in Yongchun, Dehua area; summer in Chongwu, Jinjiang area; autumn in Chongwu; winter in Dehua and Chongwu. This indicates that the occurrence of rainstorms in Quanzhou in the past 55 years is similar, but the occurrence of drought in different seasons is quite different.
1) Droughts and floods in Quanzhou are characterized by periodical changes. There were 22 droughts and 17 rainstorms in Quanzhou during the period from 1960 to 2014. The specific time periods for frequent drought events were 1963-1972, 1977-1986, and 2009-2011. The specific time periods of frequent rainstorm events were 1961-1962, 1972-1975, 1990-1992 and 1997-2007. The drought in Quanzhou generally showed a weaker trend, and precipitation increased slightly, but the trend was not significant.
2) During the period from 1960 to 2014, there was no change in droughts and floods in spring and summer in Quanzhou, but the drought in autumn and winter was decreasing, but the trend was not obvious. The spring drought occurred frequently between 1960 and 1971, and the spring flood was concentrated in 1980-1990. Summer droughts and floods were frequent between 1963-1973 and 1988-2008. The autumn drought was more common in the 1960s and 1980s, and the autumn monk occurred frequently in the late 1990s and early 2000s. Winter droughts and floods changed frequently between 1960 and 2014. Winter droughts occurred at the beginning of the 1980s and winters occurred frequently at the beginning of the 21st century.
3) The drought and flood changes in Quanzhou have a relatively uniform trend, but they also show some differences in certain periods, which are mainly represented by the large differences in the northern mountainous area, the middle semi-mountainous area, and the southeastern coastal area. There is no obvious trend of droughts and floods in the mountainous areas in the middle and the northwest, but the drought conditions in the southeastern coastal areas have eased.
4) The precipitation in each season in Quanzhou has a good spatial consistency. The precipitation centers are in the Nanan and Anxi areas, and there are significant differences in the areas with less rainfall: spring in Yongchun and Dehua; summer in Chongwu and Jinjiang; autumn in Chongwu; winter in Dehua and Chongwu.
The authors declare no conflicts of interest regarding the publication of this paper.
Liu, D.H., You, J.F., Xie, Q.J., Huang, Y.Y. and Tong, H.J. (2018) Spatial and Temporal Characteristics of Drought and Flood in Quanzhou Based on Standardized Precipitation Index (SPI) in Recent 55 Years. Journal of Geoscience and Environment Protection, 6, 25-37. https://doi.org/10.4236/gep.2018.68003