A 2021 meta-analysis in the Proceedings of the National Academy of Sciences (PNAS) analyzed 18 studies on natural sounds and health outcomes. Water sounds, which include rain, showed the strongest positive affect improvement of all natural sound categories tested (d = 1.63, representing a 184% improvement in exposed groups). Stress and annoyance decreased significantly (d = -0.60).
Proverbio et al. (2018) found that rain sounds boosted arithmetic performance compared to silence in 50 university students, with extroverts showing greater benefit, consistent with arousal theory.
Rain's broadband spectral profile approximates pink noise (-3 dB/octave), connecting it indirectly to the noise color evidence base for ADHD. No ADHD-specific rain study exists. The benefit likely comes from broadband masking properties and the steady-state temporal character that prevents auditory habituation.