Abstract/Summary

Considerable uncertainties are associated with precipitation characteristics over the western Himalayan region (WHR). These are due to typically small-scale but high intensity storms caused by the complex topography which are under-resolved by a sparse gauge network. Additionally, both satellite and gauge measurements of precipitation remain subject to systematic errors that typically result in underestimation over mountainous terrains. Reanalysis datasets provide a prospective alternative but are limited by their resolution, which has so far been too coarse to properly resolve orographic rainfall. In this study, we evaluate and cross-compare the Indian Monsoon Data Assimilation and Analysis (IMDAA), the first high-resolution (12 km) regional reanalysis over India, against various precipitation products during the winter season over the western Himalayas. We demonstrate the efficiency of IMDAA in representing the characteristics of winter precipitation at seasonal, diurnal and interannual scales, as well as heavy precipitation associated with western disturbances (WDs). IMDAA shows closer agreement to other reanalyses than to gauge-based and satellite products in error and bias analysis. Although depicting higher magnitudes, its fine resolution allows a much closer insight into localized spatial patterns and diurnal cycle, a key advantage over other datasets. Mean winter precipitation over WHR shows a significant decreasing trend in IMDAA, despite no significant trend in the frequency of WDs tracked in either IMDAA or ERA5. The study also exhibits the potential use of IMDAA for characterizing winter atmospheric dynamics, both for climatological studies and during WD activity such as localized valley wind patterns. Overall, these findings highlight the potential utility for IMDAA in carrying out various monitoring and climate change impact assessment studies over the fragile and vulnerable western Himalayan ecosystem.