A catchment area of 140 km² received 120 cm of rainfall in a year. At the outlet of the catchment the flow in the stream draining the catchment was found to have an average rate of 2.0 m³/s for 3 months, 3.0 m³/s for 6 months, and 5.0 m³/s for 3 months. a) What is the runoff coefficient of the catchment? b) If the afforestation of the catchment reduces the runoff coefficient to 0.50, what is the increase in the abstraction from precipitation due to infiltration, evaporation and transpiration, for the same annual rainfall of 120 cm?