CSIR NET Dec 2015 Q111: Sedimentology

Erosivity refers to the potential of rainfall to cause soil erosion, and it depends strongly on rainfall intensity (amount of rain per unit time), not merely on total annual rainfall amount, because higher-intensity rain delivers greater kinetic energy per unit time, producing more splash and sheet erosion. Place A receives 1200 mm/year spread over 6 months, giving an average intensity of about 1200/6 = 200 mm/month. Place B receives 1000 mm/year concentrated into just 2 months, giving an average intensity of about 1000/2 = 500 mm/month. Despite B's lower total annual rainfall, its much higher rainfall intensity (concentrated over a shorter period) gives it substantially greater erosivity than A, matching option 3.

Option 1 (equal at both places) ignores the large difference in rainfall intensity resulting from the very different durations over which each location's rainfall is distributed. Option 2 (higher at A than B) is incorrect and reverses the relationship; A's rainfall is spread over a much longer period (6 months) and thus has lower intensity than B's. Option 3 is correct: B's rainfall, concentrated into just 2 months, has more than double the intensity of A's, giving it higher erosivity despite lower total annual rainfall. Option 4 (erosivity is unrelated to rainfall) contradicts the fundamental definition of erosivity, which is explicitly derived from rainfall characteristics (particularly intensity).