Rainfall intensities play a crucial role in shaping the characteristics of a hydrograph, including its overall shape, peak discharge, lag time, and base flow.

A hydrograph is a visual representation that illustrates the discharge of a river over time. The components of the hydrograph—its shape, peak discharge, lag time, and base flow—are all susceptible to variations in rainfall intensity.

When rainfall intensity is high, the hydrograph typically displays a steep rising limb, indicating a rapid increase in river discharge. This steepness occurs because the ground saturates quickly, resulting in a significant amount of surface runoff. Consequently, the peak discharge, which represents the maximum rate of river flow, is also likely to be elevated due to the large volume of water entering the river system in a short timeframe.

In contrast, when rainfall intensity is low, the rising limb of the hydrograph is less steep. In such cases, the ground has a greater capacity to absorb the rainfall, leading to slower surface runoff. As a result, the peak discharge tends to be lower, reflecting the smaller volume of water that enters the river system.

Additionally, the lag time—the interval between peak rainfall and peak discharge—is influenced by rainfall intensity. High-intensity rainfall often leads to a shorter lag time because the ground saturates rapidly, allowing water to flow quickly into the river. Conversely, low-intensity rainfall can result in a longer lag time, as the ground absorbs the rainfall more effectively, causing a delay in the flow to the river.

Finally, the base flow, which represents the river’s normal day-to-day discharge, can also be impacted by rainfall intensity. High-intensity rainfall may cause a temporary increase in base flow as the ground becomes saturated and excess water flows into the river. In contrast, low-intensity rainfall is less likely to significantly alter the base flow, as the ground is able to absorb most of the precipitation.