In hydrology and meteorology, isohyets are imaginary contour lines drawn on a map that join locations having equal total rainfall (precipitation) over a specified period. What do isohyets represent?

Introduction / Context:
Iso-lines are foundational tools in environmental mapping. Just as contours depict equal elevation and isobars show equal pressure, isohyets specifically map equal rainfall. Understanding isohyets is essential for catchment delineation, water resources planning, flood studies, and agricultural scheduling.

Given Data / Assumptions:

• The map displays accumulated precipitation over a chosen duration (storm event, month, season, or year).
• Point rainfall data from gauges are spatially interpolated to create continuous lines of equal precipitation.
• The question asks what an isohyet represents.

Concept / Approach:
An isohyet is defined as a line joining points with the same precipitation depth. These lines allow quick visual assessment of spatial variability in rainfall, aiding estimation of areal average rainfall for basins (e.g., by Thiessen polygons, isohyetal method, or arithmetic mean when appropriate).

Step-by-Step Solution:
Identify the iso-term: isohyet → hyetos (rain) + iso (equal).Relate to other iso-lines: isobar (pressure), isotherm (temperature), isohume (humidity), contour (height).Therefore, isohyets represent equal rainfall totals across a mapped region.

Verification / Alternative check:
In areal rainfall estimation, the isohyetal method calculates the weighted average based on areas between successive isohyets, confirming that each line represents a constant precipitation value.

Why Other Options Are Wrong:

• Equal atmospheric pressure: That is an isobar, not an isohyet.
• Equal elevation: Those are topographic contours.
• Equal humidity: Those are isohumes or iso-humidity lines.
• Equal wind speed: These are isotachs.

Common Pitfalls:

• Confusing isohyets with contours or isobars due to similar line maps.
• Assuming isohyets are valid for instantaneous intensity; they are typically drawn for totals over a period.

Final Answer:
Equal rainfall (precipitation depth)