Biotite weathering in granite is known to induce micro-crack propagation. Conversely, fracture propagation exposes fresh surfaces to percolating fluids and enhances fluid flow, which accelerates chemical weathering. These feedback mechanisms between weathering, microcracks and larger fractures remain under-explored. To bridge this gap, a weathering-induced damage model is coupled with a cohesive fracture model to study the joint effects of topographic, tectonic, and weathering stresses in granite. Weathering is simulated over 250 years in sinusoidal topographies. Numerical results suggest that without pre-fracturing, horizontal tectonic stresses are needed to trigger weathering. Under tensile horizontal tectonic stress, simulations indicate that weathering advances vertically beneath the valleys, consistent with field observations. High-compression tectonic stresses transmit forces through valley bottoms and side slopes, which provides the mechanism for surface-parallel fracturing, and weathering regions spreading laterally beneath both the valleys and ridges, in conformity with fractures observed parallel to the surface and slightly dipping. Simulations also indicate that the presence of a valley incision enhances the mechanism of mode-I fracture propagation under tensile horizontal tectonic stress, but does not significantly impact the mixed-mode fracture propagation sub-parallel to the surface under compressive horizontal tectonic stress.