Rain gauge exposure and siting – identify the correct statement Considering siting and exposure effects on rain-gauge catch, which of the following statements is correct for standard field practice?

Introduction / Context:
Accurate rainfall measurement requires careful gauge siting to avoid wind-induced undercatch and obstruction. Exposure guidelines specify distance from obstacles and mounting height to minimize bias.

Given Data / Assumptions:

• Standard non-recording or recording gauges installed in open terrain.
• Wind effects increase with height and exposure.
• Trees and buildings can shelter or obstruct, altering the catch.

Concept / Approach:
Wind speed increases with height above ground; raindrops are deflected by airflow over the gauge orifice, causing undercatch. Therefore, higher or overly exposed placement typically increases catch deficiency. Good practice places gauges near ground level on level pads, away from obstacles that subtend a small angle (often recommended not exceeding about 30°) at the gauge.

Step-by-Step Solution:
Evaluate (a): Greater exposure/height → more wind → more undercatch → correct.Evaluate (b): Heavier rain produces larger drops less affected by wind; catch generally improves, so (b) is incorrect.Evaluate (c): Recommended obstruction angle limits are typically stricter (≈ 30°), hence 45° is not standard; (c) is incorrect as stated.Evaluate (d): Forest canopies cause interception and turbulence; not ideal → incorrect.

Verification / Alternative check:
Exposure correction studies consistently show increased undercatch with height and wind; siting standards prescribe low, open, and level placements away from tall obstructions.

Why Other Options Are Wrong:

• (b) contradicts empirical undercatch behavior with drop size and intensity.
• (c) uses an overly permissive angle, not aligned with common standards.
• (d) forests are poor sites due to interception and turbulence.
• (e) cannot be correct since several statements are false.

Common Pitfalls:
Mounting gauges on rooftops or hill crests; placing them too close to trees or walls; neglecting wind shielding where appropriate.

Final Answer:
The higher the gauge is installed (above ground or surroundings), the more deficient the rain catch tends to be due to wind effects.