An Instantaneous Unit Hydrograph (IUH) represents the direct runoff hydrograph resulting from an instantaneous discharge of 1$\text{ cm}$ of effective rainfall applied uniformly over a catchment at time t = 0. Because rainfall duration approaches zero, the IUH reflects pure catchment routing characteristics without the influence of storm duration. Clark’s Method derives the IUH by routing incremental time-area histograms through a single linear reservoir: $$S = K \cdot O$$ Where $S$ is storage, $K$ is storage attenuation constant, and $O$ is outflow. The routing process follows the Muskingum-based finite difference equation: $$O_2 = C_0 \cdot I_2 + C_1 \cdot O_1$$ Where $I_2$ is area of the time-area segment, and routing coefficients are defined as $C_0 = \frac{\Delta t}{2K + \Delta t}$ and $C_1 = \frac{2K - \Delta t}{2K + \Delta t}.$ In steep Himalayan catchments subject to intense cloudburst events, traditional constant-duration unit hydrographs fail to capture peak attenuati...