Systematic Anomalies over Inland Water Bodies of High Mountain Asia in TRMM Precipitation Estimates: No Longer a Problem for the GPM Era?

Two satellite precipitation products (3B42RT and 3B42V7) of the Tropical Rainfall Measuring Mission (TRMM) show systematic overestimation anomalies over inland water bodies in high mountain Asia (HMA). The relative difference (RD) was calculated between precipitation estimates over pixels containing water bodies and over pixels neighboring water bodies. A t-test was employed to check the statistical significance. Results show that ∼53% of the water bodies passed the significance test at the daily scale for the TRMM products on average. Gauge adjustment alleviates the overestimation of 3B42V7 $(\text{mean RD}=20\%)$ compared with 3B42RT $(\text{mean RD}=34\%)$. Liquid water surfaces tend to affect the quality of TRMM Multisatellite Precipitation Analysis more significantly than ice water surfaces due to different passive microwave (MW) emission characteristics. In contrast, Global Precipitation Measurement (GPM) mission products provide more consistent precipitation estimates, with only ∼4% of the water bodies passing the significance test. TRMM-based precipitation estimates are much higher than GPM products over inland water bodies, which is, however, not the case over the land. The improvement is mainly attributed to the unified and updated MW algorithm used in GPM products.