Understanding Rainfall Measurement Units
📌 Rainfall measurement units are typically expressed in millimeters (mm), representing the depth (thickness) of the rain that falls over a specific area, not volume (like liters or cubic meters).
💧 A rainfall depth of 5 mm over one hectare ($10,000 \text{ m}^2$) equates to a total collected volume of 50 cubic meters ($50 \text{ m}^3$).
📏 While volume is calculated as Depth $\times$ Area, the standard unit for reporting rainfall intensity remains $\text{mm}$ (thickness).

Installation Requirements for Rain Gauges (Ombrometer)
📐 The opening of the rain gauge must be installed at a minimum height of 120 cm from the ground level.
🚫 The gauge must be placed in an open field, avoiding any obstructions like trees, buildings, or overhangs that could shield it from direct rainfall.
🧺 Simple setups often involve placing the gauge within a fenced enclosure (like a $1.5 \text{ meter}$ high box) to prevent interference or tampering.

DIY Rainfall Calculation Using Simple Tools
🛠️ If an official ombrometer is unavailable, simple containers like cans or buckets can be used, provided the cross-sectional area ($\pi r^2$) of the opening is accurately known.
📐 Example calculation: If a container with a diameter of $15 \text{ cm}$ (radius $r = 7.5 \text{ cm}$) collects $100 \text{ ml}$ of water:
- Cross-sectional area $\approx 176.6 \text{ cm}^2$.
- Volume collected $= 100 \text{ ml} = 100 \text{ cm}^3 = 100 \times 10^3 \text{ mm}^3$.
- The resulting rainfall depth (height) is calculated by dividing the volume by the area: $\text{Depth} = \frac{100 \times 10^3 \text{ mm}^3}{176.6 \text{ cm}^2}$.
- This results in a rainfall depth of approximately $6 \text{ mm}$.

Key Points & Insights
➡️ The critical factor in rainfall measurement is determining the depth of water (in mm) that fell, regardless of the collection vessel's shape.
➡️ Accurate placement of the gauge is non-negotiable; it must avoid shelter to represent the true rainfall over the catchment area.
➡️ It is possible to estimate rainfall depth accurately using simple household items (like a can) if the radius/diameter of the opening and the volume collected (in ml) are measured precisely.

📸 Video summarized with SummaryTube.com on Nov 16, 2025, 07:47 UTC