Create → RTS File for Fractal RainThis routine simulates convective, mesoscale rainfall in a manner that
reproduces many of the scaling properties that have been observed
in radar measurements. Rainfall rates that vary in both space and
time are modeled as the time evolution of a 2D random cascade
(multifractal) with generator processes that are the product of
two independent (stochastic) generator processes, i.e. where X(t) is an Ornstein-Uhlenbeck process with unit variance. In this version, the characteristic time of evolution of both component processes varies with scale according to: so that larger scale processes evolve more slowly and scaling in time is obtained. Here, b is the branching number and H is a scaling exponent in the interval [0,1]. The final result is saved as a grid sequence (RTS file) along with a georeferencing (RTI file) that matches the area spanned by the DEM. Grid values are scaled so as to have the specified maximum rainrate. Note that the spatial scaling assumption for this model and the default parameters have only been checked for radar scales, i.e. 2 to 256 km. Moreover, this is a Lagrangian model in that it evolves in time but does not advect. A more realistic space-time rainfall simulator with advection is planned for a future version of TopoFlow. Reference: Over, T.M. (1995) Modeling Space-Time Rainfall at the Mesoscale Using Random Cascades, PhD Dissertaion, University of Colorado, Boulder. |