During a storm event in a certain period, the rainfall intensity is $3.5 \mathrm{~cm} /$ hour and the $\Phi$ -index is $1.5 \mathrm{~cm} /$ hour. The intensity of effective rainfall (in cm/hour, up to one decimal place) for this period is

During a storm event in a certain period, the rainfall intensity is $3.5 \mathrm{~cm} /$ hour and the $\Phi$ -index is $1.5 \mathrm{~cm} /$ hour. The intensity of effective rainfall (in cm/hour, up to one decimal place) for this period is

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