What is the main purpose of considering antecedent precipitation in runoff calculations?

The main purpose of considering antecedent precipitation in runoff calculations is to refine peak discharge estimates. Antecedent precipitation refers to the amount of rainfall that has occurred in the days or weeks leading up to a storm event. This prior rainfall can saturate the soil or increase the moisture content, affecting how much additional rainfall will contribute to surface runoff.

When calculating runoff, understanding the previous precipitation helps to better predict how much of the incoming precipitation will either infiltrate into the soil or flow over the surface as runoff. An efficient runoff model takes into account the soil's moisture state before the new rain hits, leading to more accurate predictions of peak discharge during storm events. This is particularly important for infrastructure design, stormwater management, and flood control measures, where anticipating the volume of runoff is crucial for ensuring systems can handle the flow.

The other options do not directly relate to the immediate need for runoff calculations or rely on antecedent precipitation in the same way. Determining soil health, designing irrigation, and assessing flood risks each have varying degrees of connection to precipitation but do not specifically focus on refining runoff calculations in the manner that previous storm data does.