Spatial and Diurnal Variability of Monsoon Systems Assessed by TRMM Rain Rate Over Indus Basin

The spatiotemporal characteristics of the Asian monsoon over the Indus River basin are studied using the latest near real-time satellite precipitation estimates from the tropical rainfall measuring mission (TRMM) multisatellite precipitation analysis (TMPA). The TMPA data product (3B42RT V7) is used to analyze diurnal variability of the Asian monsoon over the study domain during January 2005 to December 2010. First, the spatiotemporal uncertainty of satellite estimates is systematically characterized by comparison to rain gauge observations using four standard error metrics, i.e., the Pearson correlation coefficient (CC), root-mean-square error (RMSE), mean absolute error (MAE), and relative bias (BIAS). Second, diurnal rainfall variability over selected regions is investigated by comparing rainfall patterns during premonsoon and monsoon seasons. The comparison and evaluation of satellite-based estimates and rain gauge data revealed significant correlation of 0.87 for the stations in the southwest and 0.63 in the northeast monsoon region. The results indicated TMPA underestimates over the intense monsoon region from -8% to -25%, while there is an overestimation over the southern region from 7% to 35%. This study improves understanding on the rainfall diurnal variations captured by the three hourly TMPA products during the April-June (premonsoon) and June-August (monsoon) over the extreme monsoon year 2010 versus the regular periods of 2005-2009 by investigating precipitation mean, frequency, and intensity, as well as the diurnal and semidiurnal cycles. A noticeable bimodal variation during the 2010 season showed an increase in rainfall associated with anomalous atmospheric conditions, causing catastrophic floods in Pakistan.