Diurnal variation of summer rainfall in Tianjin,China

Based on hourly self-recording rain-gauge data,diurnal variation of summer rainfall including hourly rainfall amount,frequency,intensity and different duration rainfall events in Tianjin was analyzed.The results show that the peaks of the accumulated rainfall amount of diurnal different time appear around 17:00 and 02:00,respectively.The variation trends of hourly rainfall intensity and diurnal rainfall amount are consistent,whereas accumulated rainfall frequency is higher from 02:00 to 08:00,followed by a gradual decrease till 11:00 and no significant change from 11:00 to 24:00.Although rainfall amount correlates with both rainfall frequency and intensity significantly(P0.001),its correlation with hourly rainfall intensity is significant,which indicates that the diurnal change of rainfall amount is influenced by rainfall intensity.The rainfall frequency contributes less to diurnal variation of hourly accumulated rainfall amount.Large differences are found in diurnal variation frequency for rainfall events with different durations.The peaks of rainfall events with long duration occur at early morning,while short duration rainfall events often appear in the afternoon,especially for 1—3 hours′ rainfall.