The best replacement for intensity is magnitude.

The best alternatives to intensity are rated as following:
★★★★★  magnitude
★★★★★  wavelength
★★★★  loudness
★★★  amplitude
★★★  volume
★★★  frequency
★★  saturation
★★  power
★★  chroma
★★  lg cosmos
★★  duration
★★  low intensity
★★  intimacy
★  intensity
★  intensity level
★  brightness
★  flux
★  high intensity cardio
★  cosmos
★  irradiance
★  low intensity cardio
★  high intensity
★  absorbance
★  volume training
★  dreamstate
  dynamics
  low intensity exercise
  low intensity workouts
  high volume
  value
  amplitude sound
  stimulus frequency
  loudness of sound
  intensity 2

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Speaking about intensity, one probably shouldn't forget about photosynthesis.

Other search terms related to intensity and their ratings are:
★★★★★ photosynthesis
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Google Trends

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intensity
magnitude
wavelength