Lag time is the time between rainfall onset and peak discharge; which factors control it?

Lag time is the time between rainfall onset and peak discharge; which factors control it?

• A. Basin size, shape, slope, land cover, and infiltration
• B. Soil type but not basin geometry
• C. Wind speed and solar radiation
• D. Temperature and humidity only

Answer: (D)

Lag time is about how rainfall becomes runoff and moves through the watershed to the outlet. The timing of that peak discharge is controlled by how the basin stores and routes water: its size and shape determine how far and how long water has to travel; slope affects how fast water moves downslope; land cover changes how much rainfall becomes runoff versus evaporates or infiltrates; and infiltration capacity and soil type determine how quickly water can enter the ground versus running over the surface. Antecedent moisture and the characteristics of the rainfall itself (intensity, duration) also shape the response. Temperature and humidity influence evaporation and moisture processes, but they don’t set the timing of the rainfall-to-discharge response. They affect how much water is lost to evaporation or stored, not the fundamental speed at which rainfall translates into a peak flow. So the factors that truly control lag time are the catchment’s physical characteristics and the rainfall characteristics, not atmospheric variables alone.

Lag time is about how rainfall becomes runoff and moves through the watershed to the outlet. The timing of that peak discharge is controlled by how the basin stores and routes water: its size and shape determine how far and how long water has to travel; slope affects how fast water moves downslope; land cover changes how much rainfall becomes runoff versus evaporates or infiltrates; and infiltration capacity and soil type determine how quickly water can enter the ground versus running over the surface. Antecedent moisture and the characteristics of the rainfall itself (intensity, duration) also shape the response.

Temperature and humidity influence evaporation and moisture processes, but they don’t set the timing of the rainfall-to-discharge response. They affect how much water is lost to evaporation or stored, not the fundamental speed at which rainfall translates into a peak flow.

So the factors that truly control lag time are the catchment’s physical characteristics and the rainfall characteristics, not atmospheric variables alone.