Evaluating Winter Precipitation over the Western Himalayas in a High-Resolution Indian Regional Reanalysis Using Multisource Climate Datasets

Abstract

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 that are under-resolved by a sparse gauge network. Additionally, both satellite and gauge precipitation measurements remain subject to systematic errors, typically resulting in underestimation over mountainous terrains. Reanalysis datasets provide prospective alternative but are limited by their resolution, which has so far been too coarse to properly resolve orographic precipitation. In this study, we evaluate and cross compare Indian Monsoon Data Assimilation and Analysis (IMDAA), the first high-resolution (12 km) regional reanalysis over India, with various precipitation products during winter season over WHR. We demonstrate IMDAA’s efficiency in representing winter precipitation characteristics at seasonal, diurnal, 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 the 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 winds. Overall, these findings highlight the potential utility for IMDAA in conducting monitoring and climate change impact assessment studies over the fragile western Himalayan ecosystem.

Hydrological Extremes in Western Himalayas-Trends and Their Physical Factors

“…The regional reanalysis-IMDAA, is a recently released high resolution (12 km) product over the South Asian domain, generated by National Centre for Medium Range Weather Forecasting in collaboration with UK Met Office and IMD using a unified atmospheric model and the four-dimensional variational (4D-Var) data assimilation technique [53]. The dataset provides advantages in better representation of orographic features owing to its high spatial resolution [1,2,54]. Finally, we have also utilized the state-of-the-art global reanalysis ERA5, developed by European Centre for Medium-Range Weather Forecasts [55] available at a resolution of 0.25°Â 0.25°.…”

“…WH is known to be a complex and topographically heterogeneous regime. A wide discrepancy in precipitation patterns is observed among different datasets over this region [1]. Thus, we focus on analyzing precipitation extremes in various datasets to understand how different datasets depict precipitation extremes over the region.…”

“…WH are highly rich in biodiversity and covered with forests, agricultural landscapes, glaciers, wetlands and urbanized land, which underlines the significance of the region. The regional spatiotemporal distribution of precipitation over WH depicts high variability [1,2] which can be partly attributed to influences from the atmosphere-land surface exchange processes over the region, keeping in mind the diverse land surface characteristics and large geographical variability [3,4]. Additionally, complex interplay of regional topography with moist airflow and temperature gradient magnifies this variability further [5][6][7].…”

“…The Indian summer monsoon (ISM), spanning through June-September (JJAS), contributes about 67-75% to the annual precipitation received over WH [2]. These mountainous environments have a significant impact on the spatiotemporal distribution of precipitation [1,9]. Majorly, precipitation over the region during the ISM is contributed by convection followed by an orographically locked system, with Himalayas as barriers forcing moisture-laden southwest monsoon winds to dissipate moisture.…”

“…The region also receives a significant amount of precipitation during the winter season (December to February), primarily through extra-tropical cyclonic systems called Western Disturbances (WD; e.g. [1,13]). WDs, embedded in upper tropospheric sub-tropical westerly jet stream, propagate eastward towards WH carrying moisture mainly from Mediterranean sea, Caspian sea, and Black sea (e.g.…”