Abstract
Abstract. The Fukushima Daiichi nuclear power plant (FDNPP) accident in March 2011 resulted in the fallout of significant quantities of radiocesium over the Fukushima region. After reaching the soil surface, radiocesium is quickly bound to fine soil particles. Thereafter, rainfall and snowmelt run-off events transfer particle-bound radiocesium downstream. Characterizing the precipitation regime of the fallout-impacted region is thus important for understanding post-deposition radiocesium dynamics. Accordingly, 10 min (1995–2015) and daily precipitation data (1977–2015) from 42 meteorological stations within a 100 km radius of the FDNPP were analyzed. Monthly rainfall erosivity maps were developed to depict the spatial heterogeneity of rainfall erosivity for catchments entirely contained within this radius. The mean average precipitation in the region surrounding the FDNPP is 1420 mm yr−1 (SD 235) with a mean rainfall erosivity of 3696 MJ mm ha−1 h−1 yr−1 (SD 1327). Tropical cyclones contribute 22 % of the precipitation (422 mm yr−1) and 40 % of the rainfall erosivity (1462 MJ mm ha−1 h−1 yr−1 (SD 637)). The majority of precipitation (60 %) and rainfall erosivity (82 %) occurs between June and October. At a regional scale, rainfall erosivity increases from the north to the south during July and August, the most erosive months. For the remainder of the year, this gradient occurs mostly from northwest to southeast. Relief features strongly influence the spatial distribution of rainfall erosivity at a smaller scale, with the coastal plains and coastal mountain range having greater rainfall erosivity than the inland Abukuma River valley. Understanding these patterns, particularly their spatial and temporal (both inter- and intraannual) variation, is important for contextualizing soil and particle-bound radiocesium transfers in the Fukushima region. Moreover, understanding the impact of tropical cyclones will be important for managing sediment and sediment-bound contaminant transfers in regions impacted by these events.
Highlights
In March 2011, the Great Tohuku earthquake triggered a giant tsunami that resulted in the release of the largest amount of radioactive material since Chernobyl from the Fukushima Daiichi nuclear power plant (FDNPP) (Chino et al, 2011; Thakur et al, 2013)
Between 1977 and 2015, regional mean annual precipitation ranged from 869 mm in 1984 to 1844 mm in 2006 (Fig. 3a) with a coefficient of variation (CV) of 15 %
This interannual variation in precipitation was maintained over a longer period (Fig. 4), with a mean annual precipitation for the long-term stations (126 yr) of 1159 mm yr−1 (SD 187 mm) with a 16 % CV
Summary
In March 2011, the Great Tohuku earthquake triggered a giant tsunami that resulted in the release of the largest amount of radioactive material since Chernobyl from the Fukushima Daiichi nuclear power plant (FDNPP) (Chino et al, 2011; Thakur et al, 2013). Laceby et al.: Rainfall erosivity in subtropical catchments (Fukushima, Japan)
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