## 1 Introduction  
Rainfall-runoff relationships are generally simulated using a simplified conceptual model based on physical processes. Conventionally, this process involves the use of a lumped model, which considers the watershed as a homogenous element. The lumped model assumes that the watershed is a single black box that is highly dependent on the reliability of rainfall and runoff data; it suffers from the disadvantage that the temporal and spatial transformations of the rainfall to runoff are not explicitly considered. The development of Geographic Information Systems has facilitated the development of a dynamic model for analyzing the runoff phenomena and has allowed the development of a distributed parameter model that considers the spatial variability of parameters related to the runoff process. It focuses on the spatial variability of the process and explains the physical relationship between the topographic and runoff model parameters by analyzing the runoff. To analyze the runoff event pattern using computational watershed models, the input parameters should be accurately estimated by reflecting the hydrological and hydraulic conditions such as the topographic characteristics, rainfall, and infiltration. However, accurately simulating the rainfall-runoff event is difficult because of the nonlinear characteristics of natural phenomena. One of the distributed parameter models developed to overcome these limitations is the TOPography-based hydrological MODEL (TOPMODEL), which uses the digital elevation model (DEM) [1]. TOPMODEL is semidistributed watershed model and has mainly been applied to hydrologic simulations in mountain basins [2; 3; 4; 5; 6]. TOPMODEL has the advantage in that it can easily separate surface runoff from basal runoff, and a runoff simulation can be performed for a long period. Similarly, the variable infiltration capacity (VIC) model can simulate rainfall-runoff processes and separates surface runoff and baseflow using the concept of three layers [7; 8]. The VIC model simulates both water- and energy-balance equations and considers land-cover type as well as the concept of three soil layers. In contrast, TOPMODEL has a physical basis and focuses on hydrologic processes. Furthermore, the two models employ different infiltration estimation methods. TOPMODEL applies the Green Amp equation, whereas the VIC model uses various empirical methods [9]. [PERSON] and [PERSON] [1] proposed TOPMODEL as a distributed parameter model for a runoff-contributing area. [PERSON] and [PERSON] [10] analyzed the effects of watershed topography on a river runoff using TOPMODEL. The influences of the spatial scale of the DEM, and the topographic characteristics on the hydrological process in TOPMODEL have been studied [11; 12; 13; 14]. [PERSON] et al. [15; 16] analyzed the influence of permeability coefficient based on the DEM resolution. When the DEM resolution is larger, the permeability coefficient accordingly increases, and the variation in the coefficient is smaller. To date, many researchers have pointed out that the topographic index in TOPMODEL is affected by the DEM resolution [17; 18; 19]. They usually demonstrated that high DEM resolutions can yield accurate topographic index estimates [20; 21; 22]. However, the effects of optimized input parameters based on the resolution of topographic data (e.g., effects of changes in DEM grid cell size), as well as the concept of reliable DEM grid cell size resolution on experimental watersheds in TOPMODEL have been rarely studied. In particular, [PERSON] et al. [23] investigated the influence of DEM resolution in TOPMODEL in the Hanjiang River, China, and reported no evident differences in the uncertainty intervals corresponding to different DEM resolutions represented in TOPMODEL. However, uncertainty intervals corresponding to different DEM resolutions depending on changing input parameters in TOPMODEL have not yet been clarified.