Abstract
Droughts represent the most complex and damaging type of natural disaster, and they have taken place with increased frequency in China in recent years. Values of the standardized precipitation evapotranspiration index (SPEI) calculated using station-based meteorological data collected from 1961 to 2013 in the middle and lower reaches of the Yangtze River Basin (MLRYRB) are used to monitor droughts. In addition, the SPEI is determined for different timescales (1, 3, 6, and 12 months) to characterize dry or wet conditions in this study area. Moreover, remote sensing methods can cover large areas, and multispectral and temporal observations are provided by satellite sensors. The temperature vegetation dryness index (TVDI) is selected to permit assessment of drought conditions. In addition, the correlation between the SPEI and TVDI values is calculated. The results show that the SPEI values over different timescales reflect complex variations in drought conditions and have been well applied in the MLRYRB. Droughts occurred on an annual basis in 1963, 1966, 1971, 1978, 1979, 1986, 2001, 2011, and 2013, particularly 2011. In addition, the regional average drought frequency in the study area during 1961–2013 is 30%, as determined using the SPEI. An analysis of the correlation between the monthly values of the TVDI and the SPEI-3 shows that a negative relationship exists between the SPEI-3 and the TVDI. That is, smaller TVDI values are associated with greater SPEI-3 values and reduced drought conditions, whereas larger TVDI values are associated with smaller SPEI-3 values and enhanced drought conditions. Therefore, this study of the relationship between the SPEI and the TVDI can provide a basis for government to mitigate the effects of drought.
Highlights
In the context of global warming, extreme weather and climatological events, such as flood and drought, appear to occur more frequently [1,2,3,4,5]
Several drought indices that are calculated using stationbased meteorological data are widely used for monitoring drought evolution. ese indices include the Palmer drought severity index (PDSI), the standardized precipitation index (SPI), and the standardized precipitation evapotranspiration index (SPEI) [16,17,18,19,20]. e PDSI is calculated using a water balance model originally proposed by Palmer [21], and it considers precipitation, the supply of water, and atmospheric evaporative demand in studying wet and dry conditions
According to the methodology described above, the SPEI values of 64 stations calculated for 1961–2013 are averaged to assess dry or wet conditions in the whole MLRYRB, and the regional SPEI is obtained over different timescales (1, 3, 6, and 12 months) using monthly meteorological station-based data for 1961–2013. e SPEI values calculated over different timescales reflect the evolution of wet and dry conditions in different regions of the MLRYRB
Summary
In the context of global warming, extreme weather and climatological events, such as flood and drought, appear to occur more frequently [1,2,3,4,5]. The SPI is calculated using only monthly precipitation data; it largely ignores the mechanisms by which droughts develop. To overcome this problem, Vicente-Serrano et al [24] proposed the SPEI, which is based on precipitation and temperature data [17, 25,26,27]. Erefore, it considers both precipitation and temperature data and combines the sensitivity of the PDSI to changes in evaporation demand with the simplicity of calculation and the multitemporal nature of the SPI [23, 28].
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