Stoch Environ Res Risk Assess DOI 10.1007/s00477-012-0589-6 ORIGINAL PAPER Analysis of dry/wet conditions using the standardized precipitation index and its potential usefulness for drought/flood monitoring in Hunan Province, China Juan Du • Jian Fang • Wei Xu • Peijun Shi Ó Springer-Verlag 2012 Abstract Local dry/wet conditions and extreme rainfall time scales may vary in its usefulness in drought/flood events are of great concern in regional water resource and monitoring, and this highlights the need for a comprehen- disaster risk management. Extensive studies have been sive consideration of various time scales when SPI is carried out to investigate the change of dry/wet conditions employed to monitor droughts and floods. and the adaptive responses to extreme rainfall events within the context of climate change. However, applicable Keywords Standardized precipitation index Á Drought/ tools and their usefulness are still not sufficiently studied, flood Á Dry/wet conditions Á Hunan Province Á China 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 inves- 1 Introduction tigates the spatiotemporal variation of dry/wet conditions and their annual/seasonal trends in Hunan with the stan- Global climate change, including both gradual and abrupt dardized precipitation index (SPI) at various time scales. changes, has a profound impact on land surface-atmo- Furthermore, to verify the potential usefulness of SPI for sphere interactions and regional social development. On drought/flood monitoring, the correlation between river the one hand, global warming, or gradual climate change, discharge and SPI at multiple time scales was examined, has a significant effect on atmospheric circulation and the and the relation between extreme SPI and the occurrence of hydrological cycle, and it alters the intensity and spatial historical drought/flood events is explored. The results distribution of precipitation (IPCC 2007; Arnell 1999), indicate that the upper reaches of the major rivers in Hunan which in turn changes local dry/wet conditions and affects Province have experienced more dry years than the middle the regional agriculture sector. On the other hand, within and lower reaches over the past 57 years, and the region the context of climate change, change can also occur in the shows a trend of becoming drier in the spring and autumn frequency of extreme weather events (Rosenzweig et al. seasons and wetter in the summer and winter seasons. We 2001), which can induce various meteorological hazards, also found a strong correlation between river discharge and such as floods, droughts and rainstorms. Studies have SPI series, with the maximum correlation coefficient shown that these extreme events appear to have become occurred at the time scale of 2 months. SPI at different more frequent in the middle to lower reaches of the Yangtze River in China (Piao et al. 2010). Despite signif- icant achievements in science and technology and & J. Du Á W. Xu ( ) Á P. Shi improved environmental management in the 20th century, State Key Laboratory of Earth Surface Processes and Resource Ecology, Beijing Normal University, Beijing 100875, China people still continue to suffer from the consequences of e-mail: [email protected] these meteorological hazards worldwide (Krysanova et al. 2008). Climate change is but one symptom of our past J. Du Á J. Fang Á W. Xu Á P. Shi failure to achieve sustainable development amongst many Academy of Disaster Reduction and Emergency Management, Ministry of Civil Affairs & Ministry of Education, the People’s other symptoms (Green 2010). To better understand the Republic of China, Beijing 100875, China recent climatic fluctuations, their manifestation in local 123 Stoch Environ Res Risk Assess places, and to further monitor drought and flood occur- the potential of using SPI as a tool for monitoring flood risk rence, it is worthwhile to investigate the spatiotemporal in the Southern Cordoba Province in Argentina. They variability of local dry/wet conditions. This knowledge will found that SPI satisfactorily explains the development of undoubtedly be useful for improving integrated water conditions leading up to the three main flood events in the resource management. region. However, very few studies have examined the The standardized precipitation index (SPI) is a probabil- capability of SPI to monitor hydrological floods, especially ity-based indicator that depicts the degree to which the the relationship between SPI values at multiple time scales accumulative precipitation of a specific period departs from and monthly river discharges. the average state. The SPI is space-independent and has a Therefore, the main objectives of this study were as sound performance when representing precipitation anom- follows: (1) to apply the SPI to evaluate the spatiotemporal aly (Mckee et al. 1993). Compared with other indices and variability of dry/wet conditions in Hunan Province, China; methods based on physical processes, the palmer drought (2) to examine the relationship between SPI values at severity index (PDSI) for example, SPI is easy to calculate multiple time scales and river discharge; and (3) to thor- and convenient to apply. It requires only precipitation as oughly investigate the potential capability of SPI for input data and escapes the problem of parameter calibration, drought/flood monitoring and management. thus is particularly suitable for drought/flood monitoring in areas where hydrological data is scarce (Yuan and Zhou 2004). Due to its robustness and convenience to use, SPI has 2 Study area and data sources already been widely used to characterize dry and wet con- ditions in many countries and regions, such as the United Hunan Province is an inland province located to the south States (Wu et al. 2007); Canada (Quiring and Papakryiakou of the Yangtze River and is composed of 14 municipalities 2003); Italy (Piccarreta et al. 2004; Vergni and Todisco with a total area of 211, 800 km2, which is 2.21 % of the 2010); Iran (Moradi et al. 2011; Nafarzadegana et al. 2012); total land area of China. Hunan Province is a mountainous Korea (Min et al. 2003; Kim et al. 2009); and China. For region with an elevation descending from south to north example, Bordi et al. (2004) applied SPI to analyze the that varies from 2,079 to 16 m. The annual rainfall is from spatiotemporal variability of dry and wet periods during the 1,300 to 1,600 mm falling mainly from April to September, last 50 years in eastern China. They found that the northern and the annual average temperature is 16–18 °C. part of eastern China had been experiencing dry conditions Hunan Province has a dense hydrological network that more frequently since the 1970s, and they concluded that the can be divided into five main components: the Dongting cycles ranged from 4 to 16 years. Zhai et al. (2010) also used Lake Region, and four major river basins including the SPI and PDSI to investigate the spatial variation and trends of Xiang River Basin, the Zi River Basin, the Yuan River dry and wet conditions in 10 large regions covering the ter- Basin, and the Li River Basin (Fig. 1). Dongting Lake, ritory of China from 1961 to 2005. They found that the fre- which is located in northern Hunan Province, is the second quencies of occurrence of both dry and wet years for the largest fresh water lake in China. The four major rivers whole period were lower for the southern region than for the originate from the mountains, run from south-to north or northwest. In particular, an increasing frequency of wet years west-to east across Hunan Province and flow into the was detected in the upper and lower reaches of the Yangtze Dongting Lake. Hunan is one of the Chinese provinces that River. Zhang et al. (2008) explored the changes of dry/wet frequently suffer from severe flooding and drought disas- episodes in the Pearl River Basin in South China and indi- ters. Affected by the monsoon circulation and complex cated that the Pearl River Basin has become drier during the topography, the temporal and spatial distribution of pre- rainy season and wetter in winter. However, very few rele- cipitation is uneven, with 69 % of the annual precipitation vant studies have been carried out in central China, which is concentrated from April to September (Li et al. 2000), and one of the major grain-producing areas in China, that play an heavy rains always occur in some local areas. indispensable role in ensuring the nation’s food security. The daily precipitation dataset used in this study covers SPI has also been widely used for drought monitoring the period from 1951 to 2007. It was collected from 21 rain and management (e.g., Mckee et al. 1993; Hayes et al. gauge stations in Hunan Province and was provided by the 1999; Cancelliere et al. 2007). National Oceanic and National Climate Center of the China Meteorological Atmospheric Administration (NOAA), especially, has Administration. The distribution of these rain gauge sta- provided the products of successive SPI maps of the United tions is shown in Fig. 1. Daily river discharge data from States (NOAA National Climatic Data Center 2011). five hydrological stations along the Xiang River were Although the SPI was originally developed for drought provided by the Hunan Hydrographic Office. All the sta- detection and monitoring, it can also be applied to indentify tions selected have complete records of rainfall and wetter than normal conditions. Seiler et al. (2002) analyzed streamflows. 123 Stoch Environ Res Risk Assess Fig. 1 Location of Hunan Province and spatial distribution of the rain gauge and hydrological stations 3 Methodology Lloyd-Hughes and Saunders (2002) described the detailed calculation of SPI. The most commonly used 3.1 Calculation of SPI distribution for SPI calculation is the two-parameter gamma distribution with a shape and scale parameter, The SPI was developed by Mckee et al.