MODEL FOR MULTISCALE DISAGGREGATION OF SPATIAL RAINFALL BASED ON COUPLING METEOROLOGICAL AND SCALING DESCRIPTIONS

The precipitation output of a mesoscale atmospheric numerical model is usually interpreted as the average rainfall intensity over the grid c ell of the model (typically 30x30 km to 60x60 km). However, rainfall e xhibits considerable heterogeneity over subgrid scales (i.e., scales s maller than the grid cell), so it is necessary for hydrologic applicat ions to recreate or simulate the small-scale rainfall variability give n its large-scale average. Rainfall disaggregation is usually done sta tistically. In this paper, a new subgrid scale rainfall disaggregation model is developed. It has the ability to statistically reproduce the rainfall variability at scales unresolved by mesoscale models while b eing conditioned on large-scale rainfall averages and physical propert ies of the prestorm environment. The model is based on two extensively tested hypotheses for midlatitude mesoscale convective systems [Peric a and Foufoula-Georgiou, 1996]: (1) standardized rainfall fluctuations (defined via a wavelet transform) exhibit simple scaling over the mes oscale, and (2) statistical scaling parameters of rainfall fluctuation s relate to the convective available potential energy (CAPE), a measur e of the convective instability of the prestorm environment. Prelimina ry evaluation of the model showed that the model is capable of reconst ructing the small-scale statistical variability of rainfall as well as the fraction of area covered with rain at all analyzed subgrid scales . The performance evaluation was based on comparison of summary statis tics and spatial pattern measures of simulated fields with those of kn own fields observed during the Oklahoma-Kansas Preliminary Regional Ex periment for Storm-Central (PRE-STORM).