Evaluating Spatiotemporal Patterns of Drought in Japan from 1960 to 2018

Abstract:

Drought disasters, such as water scarcity and wildfires, are serious natural disasters in Japan that are also affected by climate change. A large-scale water shortage has occurred about once in 10 years in Japan. Additionally, the average annual number of wildfires is 1,255 and the average annual economic loss is 577 million yen in Japan. However, as drought generally has widespread impacts and the duration of drought can vary considerably, it is difficult to comprehensively assess the spatiotemporal characteristics of drought. Therefore, to identify the drought homogeneous regions and further understand regional drought over Japan, this study provides a spatiotemporal analysis for historical droughts patterns over Japan. The trends of meteorological elements (precipitation, temperature, and potential evapotranspiration), which is the basis of drought index calculation, was first assessed. Then, drought characterized by the Self-calibrating Palmer Drought Severity Index (scPDSI) was investigated for the period 1960~2018. Subsequently, trends and patterns of drought were identified through the trend-free pre-whitening Mann-Kendall test (TFPW-MK) and distinct empirical orthogonal function (DEOF). Results indicate that the drought trends over Japan varied seasonally, increasing in spring and summer and decreasing in autumn and winter. Two major subregions of drought variability—the western Japan (W region) and most of the northernmost Japan near the Pacific (N region) were identified. Drought in W region showed a increasing trend, while the trend in N region was decreasing. Further, whether in W region or N region, wildfires with large burned area were more likely to occur when the scPDSI was less than -1, which meant that excess dried-out vegetation provided ample fuel for the wildfires. This study is the first to identify homogeneous regions with distinct drought characteristics over Japan. Also, the results are beneficial for regional drought management over Japan.