Dynamics of radiocaesium in forests deposited by the Fukushima Daiichi Nuclear Power Plant accident; Long-term monitoring and modelling approaches

Hashimoto, Shoji*; Tanaka, Taku*; Komatsu, Masabumi*; Gonze, M.-A.*; Sakashita, Wataru*; Kurikami, Hiroshi  ; Nishina, Kazuya*; Ota, Masakazu  ; Ohashi, Shinta*; Calmon, P.*; Coppin, F.*; Imamura, Naohiro*; Hayashi, Seiji*; Hirai, Keizo*; Hurtevent, P.*; Koarashi, Jun   ; Manaka, Takuya*; Miura, Satoru*; Shinomiya, Yoshiki*; Shaw, G.*; Thiry, Y.*

We applied modelling approaches to evaluate the past and future dynamics of Cs in forests. In the model inter-comparison exercise using Fukushima data, six models with diverse model structures, processes, parameters and numerical approaches joined this exercise and the performance and uncertainties of the state-of-the-art models were explored. The inter-comparison revealed that, after appropriate calibration, the models reproduced the observed data reliably and the ranges of calculated trajectories were narrow in the early phase after the fallout. However, the envelope of the calculated model end points enlarged in long-term simulations over 50 years after the fallout. The model-inter comparison exercise emphasizes the importance of decadal data for various forest types and repetitive verification/validation processes using holistic, long-term data to improve the models and to update the forecasting capacity of the models.