Analysis of dry/wet conditions using the standardized precipitation index and its potential usefulness for drought/flood monitoring in Hunan Province, China

Local dry/wet conditions and extreme rainfall events are of great concern in regional water resource and disaster risk management. Extensive studies have been carried out to investigate the change of dry/wet conditions and the adaptive responses to extreme rainfall events within the context of climate change. However, applicable tools and their usefulness are still not sufficiently studied, and in Hunan Province, a major grain-producing area in China that has been frequently hit by flood and drought, relevant research is even more limited. This paper investigates the spatiotemporal variation of dry/wet conditions and their annual/seasonal trends in Hunan with the standardized precipitation index (SPI) at various time scales. Furthermore, to verify the potential usefulness of SPI for drought/flood monitoring, the correlation between river discharge and SPI at multiple time scales was examined, and the relation between extreme SPI and the occurrence of historical drought/flood events is explored. The results indicate that the upper reaches of the major rivers in Hunan Province have experienced more dry years than the middle and lower reaches over the past 57 years, and the region shows a trend of becoming drier in the spring and autumn seasons and wetter in the summer and winter seasons. We also found a strong correlation between river discharge and SPI series, with the maximum correlation coefficient occurred at the time scale of 2 months. SPI at different time scales may vary in its usefulness in drought/flood monitoring, and this highlights the need for a comprehensive consideration of various time scales when SPI is employed to monitor droughts and floods.     

Study of the temporal and spatial patterns of drought in the Yellow River basin based on SPEI

Drought is one of the severe natural disasters to impact human society and occurs widely and frequently in China,causing considerable damage to the living environment of humans.The Yellow River basin(YRB)of China shows great vulnerability to drought in the major basins;thus,drought monitoring in the YRB is particularly important.Based on monthly data of 124 meteorological stations from 1961 to 2015,the Standardized Precipitation Evapotranspiration Index(SPEI)was used to explore the temporal and spatial patterns of drought in the YRB.The periods and trends of drought were identified by Extreme-point Symmetric Mode Decomposition(ESMD),and the research stages were determined by Bernaola-Galvan Segmentation Algorithm(BGSA).The annual and seasonal variation,frequency and intensity of drought were studied in the YRB.The results indicated that(1)for the past 55 years,the drought in the YRB has increased significantly with a tendency rate of-0.148(10 a)~(-1),in which the area Lanzhou to Hekou was the most vulnerable affected(-0.214(10 a)~(-1));(2)the drought periods(2.9,5,10.2 and 18.3 years)and stages(1961–1996,1997–2002 and 2003–2015)were characterized and detected by ESMD and BGSA;(3)the sequence of drought frequency was summer,spring,autumn and winter with mean values of 71.0%,47.2%,10.2%and 6.9%,respectively;and(4)the sequence of drought intensity was summer,spring,winter and autumn with mean values of 0.93,0.40,0.05 and 0.04,respectively.     

Temporal trends and spatial characteristics of drought and rainfall in arid and semiarid regions of Iran

Drought, a normal recurrent event in arid and semiarid lands such as Iran, is typically of a temporary nature usually leaving little permanent aftermath. In the current study, the rainfall and drought severity time series were analyzed at 10 stations in the eastern half of Iran for the period 1966–2005. The drought severity was computed using the Standardized Precipitation Index (SPI) for a 12‐month timescale. The trend analyses of the data were also performed using the Kendall and Spearman tests. The results of this study showed that the rainfall and drought severity data had high variations to average values in the study period, and these variations increased with increasing aridity towards the south of the study area. The negative serial correlations found in the seasonal and annual rainfall time series were mostly insignificant. The trend tests detected a significant decreasing trend in the spring rainfall series of Birjand station at the rate of 8.56 mm per season per decade and a significant increasing trend in the summer rainfall series of Torbateheydarieh station at the rate of 0.14 mm per season per decade, whereas the rest of the trends were insignificant. Furthermore, the 12‐month values of the standardized precipitation index decreased at all the stations except Zabol during the past four decades. During the study period, all of the stations experienced at least one extreme drought which mainly occurred in the winter season. Copyright © 2011 John Wiley & Sons, Ltd.     

大地电场台站日变幅年度变化趋势分析

为了直观展示大地电场日变幅年度变化趋势,获取多年尺度下数据变化形态及特征,选取2012-2015年,4个地电台网8个存在潮汐地电场变化的地电台站观测数据,进行去除台阶、异常数据及滤波处理,计算地电场日变幅。结果显示：①2012-2013年大多数台站存在春冬低、夏秋高的日变幅趋势性特征;②2014-2015年存在几种不同日变幅年度变化趋势,同时同一台站不同测道间日变幅变化趋势存在差异性,该变化趋势和差异性的存在可能与地下介质结构变化和介质的非均匀性有一定关系。     

The spatial and temporal analysis of dry spells in the Yellow River basin, China

In this research, drought in Yellow River basin has been studied by using dry spells. Three indices, including the maximum length (MxDS), mean length (MDS) and number of dry spells (NDS), and five periods (annual, winter, spring, summer and autumn) are considered. The results show that a south to north gradient for mean MxDS and MDS has been dominantly found in all periods except summer, in which a southwest and southeast to north gradient exists. Mean NDS shows an opposite distribution to that of mean MxDS and MDS. It is surely that the northern part of Yellow River basin, with a higher MxDS and MDS and lower NDS, is much drier than southern part in a regional scale. According to temporal analysis by using the Mann–Kendall trend method, MxDS of most stations show negative but insignificant trends during annual and winter, while the majority of stations show positive trends during spring, summer and autumn. Trends of MDS and NDS dominantly depict positive and negative for most periods, respectively. By comparing the frequency of dry spells during the ENSO events, it can be found that the frequency of intermediate and long dry spells is almost tantamount during the occurrence periods of El Niño and La Niña.     

Summer drought index using SPEI based on 10-day temperature and precipitation data and its application in Zhejiang Province (Southeast China)

Summer drought is one of the main natural disasters in Zhejiang Province, China. To explore the characteristics of summer drought in Zhejiang Province during 1973–2013, the standardized precipitation evapotranspiration index (SPEI) is calculated based on 10-day precipitation and temperature data, and the summer drought index (DI) is defined. The Mann–Kendall test and Sen’s trend test are used to analyze changes of DI and drought area. Temperature is the main effect on changes of summer drought intensity and drought area. Significant increasing trends are observed for drought intensity, drought area, and extreme drought area, and their linear trend rates in northeast Zhejiang Province are larger than that in the southwest Zhejiang Province. DI and drought area time series have significant mutations in 2003. County-average DI and drought area during 2003–2013 are significantly larger than that during 1973–2002. The aforementioned SPEI could quantify, monitor and analyze summer drought onset, extent, and end.     

近40年来南四湖湿地NDVI变化特征及其控制因子分析

利用Landsat系列卫星的MSS、TM和ETM+遥感数据,计算了研究区的归一化植被指数(NDVI),并以此为湿地植被活动的指标,研究1973 2011年间该湿地植被变化特征及年内季节变化特征,揭示植被活动在年内和年际变化的控制因子以及湿地植被对于气候变化、人类活动和极端干旱事件的响应特征.结果表明:(1)近40年来南四湖湿地植被各个季节的变化特征不尽相同.春季NDVI呈现先降低后增加的特征,主要先后受到研究区围垦、渔业养殖等人为活动和气候变化(增温)的影响;夏季和冬季的NDVI呈现显著降低趋势,主要受到围垦、渔业养殖等人类活动的影响;秋季NDVI的变化不显著.(2)年内季节变化方面,湿地植被面积和NDVI都呈现单峰的变化特征,从春季开始增加,在夏季末(全年的第202和205 d)达到最大值,然后开始下降,到冬季降至最低.植被的年内季节变化特征主要受到月均温度的控制.(3)干旱在一定程度上不是湖泊湿地NDVI增加的限制因子.干旱导致湖泊水位下降,滨湖滩地及湖底露出,可能会促进湿地植被生长和植被面积的扩大,使得湿地NDVI增加.     

变化环境下近60年西江流域径流时空演变特征

气候变化叠加人类活动的双重影响下,西江流域的河川径流发生了不同程度的改变,重新认识和掌握变化环境下的径流时空演变规律对流域的科学管理具有重要意义。基于西江流域干支流7个控制性水文站近60年的日径流资料,综合极点对称模态分解法(ESMD)、Mann-Kendall检验、R/S分析、小波分析等方法,从年代、年、季和年内多个时间尺度对径流的时空演变特征进行分析,研究结果表明:年代尺度下,西江流域径流丰枯交替、变化悬殊,1970s与1990s径流丰沛,2010s径流偏枯,降雨影响着径流的丰枯变化,流域上、中游更易发生干旱与洪涝灾害;春、夏、秋、冬季径流振荡周期依次为2～7、15～20、28～29 a,3～5、7～10、20 a,2～3、6～8、12～15 a和3～8、12～15、20 a,均呈现年际与年代的双重周期特征,IMF1的年际振荡在径流变化中占主导地位;受降雨与水库调蓄作用的影响,年、夏、秋季径流呈下降趋势,预测下降变化具有持续性,春、冬季径流整体呈上升趋势。空间内上游的变化趋势更显著;年和季尺度径流在1980年后突变增多,尤其集中于2000—2010年间,人类活动与气候变化是造成西江...     

淮河流域焦岗湖水质参数时空变化及影响因素

焦岗湖是淮河左岸一个天然湖泊,集防洪、灌溉、养殖、旅游等多种功能于一体.利用焦岗湖4个季节水质监测数据,运用Kriging方法,分析焦岗湖水质参数的时空变化及影响因素.结果表明:由于受水文季节变化过程及人类活动等综合影响,焦岗湖水质参数在时间及空间上均存在一定差异.从时间变化来看,夏季透明度较低、秋季较高;溶解氧浓度在春、冬季显著高于夏、秋季;总氮、总磷浓度与高锰酸盐指数均表现为夏季最高、秋季最低.从空间变化来看,4个季节的透明度空间差异较为显著;溶解氧浓度在春、冬季空间分布较为均匀,夏季呈现中心高周围低的变化趋势,秋季则表现为西高东低;总磷浓度春季分布较为均匀,夏、秋及冬季则呈西高东低之势;高锰酸盐指数在春、秋季节呈现东高西低之势,夏季高浓度主要集中在湖区北部,冬季浓度变化不大.     

Changes in the spatial scale of Beijing UHI and urban development

The seasonal and interannual variations of Beijing urban heat island (UHI) are investigated in this paper using the temperature data from 1960 to 2000 at 20 meteorological stations in the Beijing region, and then the relationship between the intensity and spatial scale of UHI and Beijing urbanization indices is analyzed and discussed. Main conclusions are the followings. First, Beijing UHI shows obvious seasonal variations, and it is strongest in winter, next in spring and autumn, and least in summer. The seasonal variation of the UHI mainly occurs in the urban area. The UHI intensity at the center of Beijing is more than 0.8℃ in winter, and only 0.5℃ in summer. Second, the intensity of Beijing HUI exhibits a clear interannual warming trend with its mean growth rate (MGR) being 0.3088℃/10 a. The MGR of HUI is largest in winter, next in spring and autumn, and least in summer, and the urban temperature increase makes a major contribution to the growth of HUI intensity. Third, since the Reform and Opening, the urbanization indices have grown several ten times or even one hundred times, the intensity of HUI has increased dramatically, and its spatial scale also expanded distinctively along with the expansion of urban architectural complexes. Fourth, the interannual variation of urbanization indices is very similar with that of HUI intensity, and their linear correlation coefficients are significant at a more than 0.001 confidence level.     

Research on meteorological thresholds of drought and flood disaster: a case study in the Huai River Basin,China

Together with affected areas of crops from 1978 to 2008, the daily precipitation of 110 stations located in the Huai River Basin during 1959–2008 was used to study the critical conditions when drought and flood occur, based on which the quantitative relationship between the critical condition and the affected area of crops was further studied. Based on the research on the hazard-formative factor of precipitation and the damage degree of crops, the spatial-temporal characteristics of disasters were analyzed, the drought and flood disaster-causing threshold was determined, and the quantitative relationship between the disaster-causing threshold and affected area of crops was established. The results are as the follows: (1) During 1959–2008, extreme precipitation levels were high in the eastern and western part of the Huai River Basin and were low in its central part; the spatial distribution of the coefficient of variation (CV) differed greatly from average extreme precipitation: the series of most stations were located in the central basin, and especially there was a positive trend in Anhui and Henan Provinces. (2) The cumulative precipitation during the disaster period of each station was divided by its mean cumulative precipitation during the same period in 1959–2008 to obtain the disaster-causing threshold, which has shown a good effect on reflecting the actual grade and affected areas in disasters. (3) The relationship among disaster grade, disaster-causing threshold and damage area of crops was established; this threshold can be used as a tool for agricultural disaster assessment and early warning, and can effectively improve the ability to prevent and mitigate disaster in the Huai River Basin. (4) The disaster-causing threshold can be an important input parameter for hazard assessment; other underlying surface indicators can be good supplements for determining the threshold in hazard assessment.     

长江流域历史水旱灾害分析

长江流域有丰富和长期的水旱灾害史料,最早的水灾和旱灾记载有2000余年的历史,经过系统整理和分析的历史水旱灾害资料有1000余年的旱涝型年表和500余年的旱涝分布图集.在以上资料基础上,对长江流域历史水旱灾害的地域分布特性和时间变化规律进行了初步分析:500余年历史水旱灾害的地域分布显示,流域水旱灾害总体特征是水灾重于旱灾,各级水旱灾害频率的地域分布极不均匀,存在着显著的灾害多发和少发地带,它们与自然地理环境、水系特征、气候条件和社会经济条件等因素有关;1000余年旱涝型年表分析表明,长江流域洪涝和干旱频次在时间上的非均匀分布并非完全随机,表现出多种时间尺度的年际变化特征,其中主要表现为约100a上下的大干湿气候期变化及40a左右的小旱涝期振动.     

Comparison of ten notable meteorological drought indices on tracking the effect of drought on streamflow

ABSTRACT

Ten notable meteorological drought indices were compared on tracking the effect of drought on streamflow. A 730-month dataset of precipitation, temperature and evapotranspiration for 88 catchments in Oregon, USA, representing pristine conditions, was used to compute the drought indices. These indices were correlated with the monthly streamflow datasets of the minimum, maximum and mean discharge, and the discharge monthly fluctuation; it was revealed that the 3-month Z-score drought index (Z3) has the best association with the four streamflow variables. The Mann-Kendall trend detection test applied to the latter index time series mainly highlighted a downward trend in the autumn and winter drought magnitude (DM) and an upward trend in the spring and summer DM (p = 0.05). Finally, the Pettitt test indicated an abrupt decline in the annual and autumn DM, which began in 1984 and 1986, respectively.     

Spatiotemporal analysis of climate variability (1971–2010) in spring and summer on the Loess Plateau,China

By using the Variable Infiltration Capacity model with Palmer Drought Severity Index (VIC‐PDSI) model and Standardized Precipitation Index (SPI), spatiotemporal trends of climate variation during the main growing seasons for plants of Loess Plateau between 1971 and 2010 were detected and characterized. The VIC‐PDSI model is established by combining the VIC model with PDSI. The simulation results and the grids system of VIC were applied to substitute for the two‐layer bucket‐type model to do the hydrological accounting, which could improve the physical mechanism of PDSI and expand its application range. Our results suggest that the climate of the study area has experienced a drying and warming trend during the past four decades. Apart from some individual years and regions, there was a perpetuation of water deficit over the Plateau both in spring and summer. The drought frequency increased from southeast to northwest in spring, while the drought frequency decreased from southeast to northwest in summer. The climate in the southern part of the Loess Plateau, accounting for 23.3% of the study region, showed a significant drying and warming trend in spring over the past four decades. The climate variability detected by VIC‐PDSI model shows good agreement with that monitored by SPI. Since a large part of the study region frequently suffered from water shortage during the main growing seasons for plants, people living in such drought‐prone areas should take measures to prevent the negative effects on agricultural production, reforestation, and regional food security caused by drought. Copyright © 2013 John Wiley & Sons, Ltd.     

广东省干旱灾害空间分布特征

利用1956-2005年126个雨量站逐月降水资料,采用标准化降雨指数和经验正交函数分解法,探讨了广东省干旱灾害空间分布规律.结果表明:广东省虽然总体比较湿润,但局部干旱时有发生,且在空间上存在东西差异、南北差异、中部差异的特点;春旱大致呈自西向东、自北向南逐渐加重的趋势;秋旱空间分布特点与春旱相反,由东向西、由南向北逐渐加重;春旱、秋旱在中部地区也有微弱的差异.     

Investigation of spatial and temporal variability of precipitation in Iran over the last half century

Investigation of the precipitation phenomenon as one of the most important meteorological factors directly affecting access to water resources is of paramount importance. In this study, the precipitation concentration index (PCI) was calculated using annual precipitation data from 34 synoptic stations of Iran over a 50-year period (1961–2010). The trend of precipitation and the PCI index were analyzed using the Mann–Kendall test after removing the effect of autocorrelation coefficients in annual and seasonal time scales. The results of zoning the studied index at annual time scale revealed that precipitation concentration follows a similar trend within two 25-year subscales. Furthermore, the PCI index in central and southern regions of the country, including the stations of Kerman, Bandarabbas, Yazd, Zahedan, Shahrekord, Birjand, Bushehr, Ahwaz, and Esfahan indicates a strong irregularity and high concentration in atmospheric precipitations. In annual time scale, none of the studied stations, had shown regular concentration (PCI < 10). Analyzing the trend of PCI index during the period of 1961–2010 witnessed an insignificant increasing (decreasing) trend in 16 (15) stations for winter season, respectively, while it faced a significant negative trend in Dezful, Saghez, and Hamedan stations. Similarly, in spring, Kerman and Ramsar stations exhibited a significant increasing trend in the PCI index, implying significant development of precipitation concentration irregularities in these two stations. In summer, Gorgan station showed a strong and significant irregularity for the PCI index and in autumn, Tabriz and Zahedan (Babolsar) stations experienced a significant increasing (decreasing) trend in the PCI index. At the annual time scale, 50 % of stations experienced an increasing trend in the PCI index. Investigating the changes in the precipitation trend also revealed that in annual time scale, about 58 % of the stations had a decreasing trend. In winter, which is the rainiest season in Iran, about 64 % of stations experienced a decreasing trend in precipitation that caused an increasing trend in PCI index. Comparing the spatial distribution of PCI index within two 25 years sub-periods indicated that the PCI index of the second sub-period increased in the spring time scale that means irregularity of precipitation distribution has been increased. But in the other seasons any significant variations were not observed. Also in the annual time scale the PCI index increased in the second sub-period because of the increasing trend of precipitation.     

青海省东部农业区春季干旱分析及减灾对策

利用青海省东部农业区12个气象站的降水资料，分析了该区降水气候倾向率和近期春季、年降水变化趋势，对春季大气、土壤干旱趋势进行了探讨，并提出了相应的减灾对策。     

The spatial–temporal variation of dry and wet periods in Iran based on comparing SPI and RDI indices

Drought is a natural hazard which can cause harmful effects on water resources. To monitor drought, the use of an indicator and determination of wet and dry period trend seem to have an important role in quantifying the drought analysis. In this paper, in addition to the comparison of Reconnaissance Drought Index (RDI) and Standardized Precipitation Index (SPI), based on the most appropriate probability distribution function, it was tried to examine the trends of dry and wet periods based on the mentioned indices. Accordingly, the meteorological data of 30 synoptic stations in Iran (1960–2014) was used and the trend was analyzed using the Mann–Kendall test by eliminating the effect of any significant autocorrelation coefficients at 95% confidence level (modified Mann–Kendall). Comparing results between the time series of RDI and SPI drought indices based on statistical indicators (RMSE?<?0.434, R²?>?0.819 and T-statistic?<?0.419) in all studied stations revealed that the behavior of the two indices was roughly the same and the difference between them was not significant. The trend analysis results of RDI and SPI indices based on modified Mann–Kendall test showed that the variation of dry and wet periods was decreasing in most of the studied stations (five cases were significant). In addition, the results of the trend line slope of dry and wet periods related to the drought indices in the studied area indicated that the slope was negative for SPI and RDI indices in 70% and 50% of stations, respectively.     

Modelling climate change impacts on hydropower lake inflows and braided rivers in a mountain basin

This study models climate change impacts on the natural flow regime of braided rivers and inflows to hydropower lakes in a New Zealand mountain basin. Flow metrics include the magnitude, frequency, timing and duration of unaltered flows. The TopNet hydrological model was used to simulate impacts in the Upper Waitaki Basin of the South Island for the 1990s, 2040s and 2090s. An average emissions scenario and results from 12 global circulation models were used as input. Indicators of hydrological alteration and Kruskal-Wallis tests were used to evaluate flow differences. Modelled total inflows increase over time for all lakes, with most increases in winter/early spring and small decreases in summer/autumn. High flows generally increase, while low flows decrease. Although these changes may benefit hydropower and floodplain ecology, they may increase flood risk in winter and spring and drought risk in summer and autumn, causing additional challenges managing hydropower operations.

EDITOR M.C. Acreman

ASSOCIATE EDITOR S. Kanae     

Assessment of drought trend and variability in India using wavelet transform

ABSTRACT

This paper presents an analysis of trends in six drought variables at 566 stations across India over the period 1901–2002. Six drought variables were computed using standardized precipitation index (SPI). The Mann-Kendall (MK) trend test and Sen’s slope estimator were used for trend analysis of drought variables. Discrete wavelet transform (DWT) was used to identify the dominant periodic components in trends, whereas the significance of periodic components was examined using continuous wavelet transform (CWT) based global wavelet spectrum (GWS). Our results show an increasing trend in droughts in eastern, northeastern and extreme southern regions, and a decreasing trend in the northern and southern regions of the country. The periodic component influencing the trend was 2–4 years in south, 4–8 years in west, east and northeast, 8–64 years in central parts and 32–128 years in the north; however, most of the periodic components were not statistically significant.