Editing Waterlogging severity index (section)

== Signal Definition ==
The waterlogging severity index quantifies the extent and intensity of excess soil moisture saturation in the crop root zone that leads to drainage-related stress on crops. It is expressed as a unitless index or a declared physical unit representing the relative severity of waterlogging conditions. The index captures the canonical base state of excess root-zone saturation, serving as a foundational damage signal in causal models of crop stress and yield reduction.