Numerical Simulation of Winter Precipitation over the Western Himalayas Using a Weather Research and Forecasting Model during 2001–2016

Abstract

In the present study, dynamically downscaled Weather Research and Forecasting (WRF) model simulations of winter (DJF) seasonal precipitation were evaluated over the Western Himalayas (WH) at grey zone configurations (at horizontal resolutions of 15 km (D01) and 5 km (D02)) and further validated using satellite-based (IMERG; 0.1°), observational (IMD; 0.25°), and reanalysis (ERA5; 0.25° and IMDAA; 0.108°) gridded datasets during 2001–2016. The findings demonstrate that both model resolutions (D01 and D02) are effective at representing precipitation characteristics over the Himalayan foothills. Precipitation features over the region, on the other hand, are much clearer and more detailed, with a significant improvement in D02, emphasizing the advantages of higher model grid resolution. Strong correlations and the lowest biases and root mean square errors indicate a closer agreement between model simulations and reanalyses IMDAA and ERA5. Vertical structures of various dynamical and thermodynamical features further confirm the improved and more realistic in WRF simulations with D02. Moreover, the seasonal patterns of upper tropospheric circulation, vertically integrated moisture transport, surface temperature and cloud cover show more realistic simulation in D02 compared to coarser domain D01. The categorical statistics reveal the efficiency of both D01 and D02 in simulating moderate and heavy precipitation events. Overall, our study emphasizes the significance of high-resolution data for simulating precipitation features specifically over complex terrains like WH.

Hydrological Extremes in Western Himalayas-Trends and Their Physical Factors

“…During DJF months, highest amounts of total precipitation are observed during February followed by January and December, respectively. Similar results were reported for winter precipitation amounts at sub-seasonal scale by [1,54].…”

“…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°.…”

“…Collaterally, we also explore the fidelity of the newly developed high resolution IMDAA reanalysis in representing WH precipitation extremes during the summer and winter season. IMDAA's high resolution offers significant potential in better resolution of orography [1,2,54], thus, a relatively better depiction of precipitation extremes is a key possibility. IMDAA's potential in the representation of climatological winter and summer precipitation characteristics over WH has been described thoroughly by [1,2], respectively.…”