Abstract
Drought disasters, such as water scarcity and wildfires, are serious natural disasters in Japan that are also affected by climate change. However, as drought generally has widespread impacts and the duration of drought can vary considerably, it is difficult to assess the spatiotemporal characteristics and the climatic causes of drought. Therefore, to identify the drought homogeneous regions and understand climatic causes of regional drought over Japan, this study provides a spatiotemporal analysis for historical droughts patterns and teleconnections associated with global climatic drivers. The trends of meteorological elements, which are the basis of drought index calculation, was first assessed. Then, drought characterized by the Self-calibrating Palmer Drought Severity Index (scPDSI) was investigated. Trends and patterns of drought were identified through the trend-free pre-whitening Mann-Kendall test and distinct empirical orthogonal function. The continuous wavelet transform and cross wavelet transform together with wavelet coherence were utilized to depict the links between drought and global climatic drivers. The results are described as follows: (1) the trends of precipitation were insignificant. However, temperature and potential evapotranspiration increasing trends were detected over Japan; (2) the drought trend over Japan varied seasonally, increasing in spring and summer and decreasing in autumn and winter; (3) two major subregions of drought variabilityâthe western Japan (W region) and most of the northernmost Japan near the Pacific (N region) were identified; (4) wildfires with large burned area were more likely to occur when the scPDSI was less than −1; and (5) the North Atlantic Index (NAOI) showed the strongest coherence connections with Distinguished Principle Components-1 among four climatic drivers. Additionally, Distinguished Principle Components-2 showed stronger coherence connections with NAOI and Arctic Oscillation Index. This study is the first to identify homogeneous regions with distinct drought characteristics over Japan and connect the drought in Japan with the global climatic drivers.
Highlights
Under climate change conditions, especially direct and clear global warming (IPCC, 2014), drought has shown increasing trends in certain regions of the world (Cook et al, 2004; Dai, 2011, 2013; Kogan and Guo, 2016)
Because this paper focuses on the impacts of climatic causes on drought, the distinguished principal components (DPCs) were considered to be dependent variables, while the global climatic drivers were considered to be independent variables
Investigation of the coherence connections between drought and global climatic driving factors is significant for a better understanding of drought
Summary
Especially direct and clear global warming (IPCC, 2014), drought has shown increasing trends in certain regions of the world (Cook et al, 2004; Dai, 2011, 2013; Kogan and Guo, 2016). To further understand the drought characteristics and predict drought events, it is necessary to consider the relationship between drought and global climate drivers (Asong et al, 2018) This type of research has been carried out in different regions. Precipitation Evapotranspiration Index (SPEI) to identify drought patterns over Canada and analysed their teleconnections with global climatic drivers. Their researches have contributed to understanding the causes of drought across the region. Pointed out that the Pacific Decadal Oscillation (PDO) has a certain impact on cyclone-induced precipitation over East Asia These global climatic drivers have already been confirmed to have impacts on hydroclimate in Japan.
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