Establishment of numerical beach-litter hindcast/forecast models: An application to Goto Islands, Japan Shin’ichiro Kako a,⇑ , Atsuhiko Isobe a , Shinya Magome b , Hirofumi Hinata c , Satoquo Seino d , Azusa Kojima e a Center for Marine Environmental Studies, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan b Sanyo Techno Marine, Inc., 1-3-17, Nihonbashi Horidome-cho, Chuo-ku, Tokyo 103-0012, Japan c National Institute for Land and Infrastructure Management, 3-1-1 Nagase, Yokosuka, Kanagawa 239-0826, Japan d Urban and Environmental Engineering, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan e Japan Environment Action Network, 3-4-12 Minami-cho, Kokubunji, Tokyo 185-0021, Japan article info Keywords: East China Sea Two-way particle tracking model Beach survey Inverse method Web camera Beach-litter hindcast/forecast abstract This study attempts to establish a system for hindcasting/forecasting the quantity of litter reaching a beach using an ocean circulation model, a two-way particle tracking model (PTM) to find litter sources, and an inverse method to compute litter outflows at each source. Twelve actual beach survey results, and satellite and forecasted wind data were also used. The quantity of beach litter was hindcasted/forecasted using a forward in-time PTM with the surface currents computed in the ocean circulation model driven by satellite-derived/forecasted wind data. Outflows obtained using the inverse method was given for each source in the model. The time series of the hindcasted/forecasted quantity of beach litter were found consistent with the quantity of beach litter determined from sequential webcam images of the actual beach. The accuracy of the model, however, is reduced drastically by intense winds such as typhoons which disturb drifting litter motion. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction One of the most serious problems facing the marine environ- ment worldwide is beach litter (e.g., Derraik, 2002), which arises from land-based sources such as industry, domestic sewage, and public negligence as well as from vessels, including accidental losses and illegal dumping at sea (Velander and Mocogni, 1998). Recently, Kako et al. (2010a) established a beach litter monitoring method using webcams, which took sequential photos of a beach littered by debris once every 90 min over a one and half year per- iod in the Goto Islands, Japan (Fig. 1(a) and (b)). These photos were converted into a time series of the litter-covered area as an index of the quantity of litter on the beach. The camera monitored the quantity of beach litter sequentially reasonably well, showing that the quantity does not increase monotonically in-time, but largely fluctuates over a time scale of a few months (shown later in Fig. 5). A natural consequence of this research is the idea of fore- casting the fluctuations in the quantity of litter so that beach litter is cleaned up efficiently, which is the primary aim of the present study. Before describing this litter forecasting research, we briefly mention our previous studies with respect to beach litter in the Goto Islands, where a large amount of litter originating from unspecified sources is washed ashore on various beaches (Fig. 1(c)). In particular, two previous studies provide us with a technical background for forecasting beach litter in the Goto Is- lands. One of these was beach surveys carried out on a beach in the Goto Islands (Seino et al., 2009; Kako et al., 2010b; Section 2.1). The other is a numerical particle tracking model (hereinafter referred to as the PTM experiment) in which both an inverse esti- mate of litter sources and a hindcast of the behavior of litter are carried out (Isobe et al., 2009; Kako et al., 2010b; Sections 2.2 and 2.3). 2. Technical background provided by previous studies 2.1. Beach surveys To investigate the quantity, composition and type of items of beach litter washed ashore on Hassakubana beach (Fig. 1(b)) in the Goto Islands, beach surveys were carried out every 2 months from September 2007 through September 2009 (13 surveys in to- tal; see Table 1 for dates; Seino et al., 2009; Kako et al. 2010b). A few tens of citizens and researchers took part in each beach survey, and beach litter (plastic-bottle cap, disposable lighter, polystyrene buoys and so forth) on the 350-m long beach was all retrieved and counted in the course of 2 days. In the present study, we regard the 0025-326X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2010.10.011 ⇑ Corresponding author. Tel./fax: +81 89 927 8182. E-mail address: kako@dpc.ehime-u.ac.jp (S. Kako). Marine Pollution Bulletin 62 (2011) 293–302 Contents lists available at ScienceDirect Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul