A catastrophe may affect different locations and produce losses that are ra
re and highly correlated in space and time. It may ruin many insurers if th
eir risk exposures are not properly diversified among locations. The multid
imentional distribution of claims from different locations depends on decis
ion variables such as the insurer's coverage at different locations, on spa
tial and temporal characteristics of possible catastrophes and the vulnerab
ility of insured values. As this distribution is analytically intractable,
the most promising approach for managing the exposure of insurance portfoli
os to catastrophic risks requires geo graphically explicit simulations of c
atastrophes. The straightforward use of so-called catastrophe modeling runs
quickly into an extremely large number of "what-if" evaluations. The aim o
f this paper is to develop an approach that integrates catastrophe modeling
with stochastic optimization techniques to support decision making on cove
rages of losses, profits, stability, and survival of insurers. We establish
connections between ruin probability and the maximization of concave risk
functions and we outline numerical experiments.