Success in Predictions in Ungauged Basins (PUB) is a challenging problem in Hydrology. In order to apply the physically based distributed runoff models and estimate the runoff from ungauged watersheds, precipitation and other atmospheric data at fine resolution in time and space which can be used as the input data to the models are indispensable. The main objective of this study is to estimate the runoff from ungauged or sparsely gauged watersheds using a Watershed Environmental Hydrology Model coupled with Hydro-Climate Model (WEHY-HCM). In the WEHY-HCM, Regional Hydro-Climate Model (RegHCM) was fully coupled with the Watershed Environmental HYdrology (WEHY) model. RegHCM was utilized for the dynamic downscaling of the historical global reanalysis atmospheric data (NCAR/NCEP) in order to reconstruct historical hydro-climate data over the watersheds at the scale of 3 kilometers. The WEHY model that utilizes upscaled hydrologic conservation equations to account for the effect of heterogeneity within natural watersheds was employed as the hydrological component of the WEHY-HCM. The WEHY-HCM was applied to the Sierra foothills region, encompassing Big Chico Creek (192 km2), Little Chico Creek (78 km2), Upper Butte Creek (407 km2) and Deer Creek (508 km2) watersheds in the northern California.