The intensity of insolation depends on

The intensity of insolation is primarily determined by the angle of inclination of the sun's rays, which is directly governed by latitude [1]. As the earth is spherical, the sun's rays strike the surface at different angles depending on the geographical position; equatorial regions receive more direct, vertical rays, while higher latitudes receive oblique rays that spread over a larger area, reducing intensity. While altitude affects temperature [2] and the nature of terrain (slope and aspect) can cause local variations in energy receipt [1], latitude is the fundamental global factor causing large-scale variations in insolation intensity, ranging from approximately 320 Watt/m2 in the tropics to 70 Watt/m2 at the poles. Wind primarily influences surface reflection on water bodies rather than the incoming intensity of solar radiation itself. Therefore, latitude is the most significant factor among the options provided.

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Variability of Insolation at the Surface of the Earth > p. 67
2. [2] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 8: Solar Radiation, Heat Balance and Temperature > Factors Controlling Temperature Distribution > p. 70