要旨：We study the effect of natural disasters on port level exports. We model the interaction between firms and ports to study how strongly exports from one port are affected by changes in the cost of exporting at neighboring ports. We extend the standard trade model with heterogeneous firms to a multiple port structure where exporting is subject to port specific local transportation costs, port specific fixed export costs and international bilateral trade costs. We show that gravity distortion due to firm heterogeneity is conditional on the comparative advantage at the port level and resulting substitution of exports across ports. We present evidence of the substitution effect using the 2011 Great East Japan Earthquake, indicating that at least 40% of exports was substituted to other ports following the disaster. The substitution effects is strongest in technology intensive product categories, which suggests an interaction between supply chains and domestic trade costs.

要旨：Cities and roads are the fundamental infrastructures that human society has developed. Their organizations are complex phenomena involved with many natural and social factors: business, commerce, transport, politics, diplomacy, culture, landscape, climate, hydrosphere, natural resources, etc. Geographical landscape appears to be the key factor among them, but most previous modelling studies assumed an ideally homogeneous space because of so-called `for the sake of simplicity'. Here we propose a working hypothesis that co-evolving dynamics of cities and roads defined on the space of geographical landscapes reproduce the outline of real-world spatial patterns of them. To examine this hypothesis, using high resolution digital topographic databases, we evaluate the distance between locations on the natural terrains by least cost path analysis, and define a dynamical system of the cites and roads on the evaluated space, and compare the stationary state of the system with a census. In a preliminary work on Hokkaido region in Japan, we found that the integration of the natural geographical factors leads to the emergence of comparable spatial patterns to the real one, while the model also reproduces the regularly spaced, lattice-like pattern of cities as the same as the previous models on an ideally homogeneous space with a homogeneous city-size distribution. This result indicates that the natural landscape factors have important relevance on the spatial distribution of populations.