High resolution WRF simulation of the spatiotemporal variability of precipitation over the Himalaya

Abstract:

The Himalaya enhances and redistributes large-scale precipitation systems associated with winter storms, the Indian monsoon, and other relevant weather systems through the year. The resulting runoff across the Himalaya is depended on by over a billion people in south Asia for energy, agriculture, industry, and human consumption. However, the observation and understanding of regional precipitation patterns are limited on account of sparse in-situ meteorological data and complex topography. Additionally, the region’s extreme elevations pose significant challenges for remotely sensed observation and global reanalyses in accurately representing precipitation. Mesoscale simulations are therefore the best available option to determine precipitation patterns and evaluate water resources in the Himalaya. In this study, the Weather Research and Forecasting (WRF) model has been used to simulate the spatiotemporal distribution of precipitation over High Asia for a single, continuous hydrological year at high resolution (6.7 km). The output is compared to available high-elevation rain gauges along the Himalaya, as well as gridded precipitation estimates from the Tropical Rainfall Measuring Mission (TRMM) and satellite cloud-mask data from the Moderate Resolution Imaging Spectroradiometer (MODIS), to gauge the performance of the model in simulating the full annual range of precipitation systems over the Himalaya.

WRF and TRMM show a similar inter-seasonal cycle of precipitation that appropriately represents climatic influences ranging from extratropical cyclones to the monsoon. Good agreement is also observed in the locations of precipitation maxima in transition months between the two regimes. WRF also compares well to daily in-situ precipitation throughout the year, with correlation coefficients generally at 0.5 and above, but decreasing for stations at increasingly high elevations. Diurnal cycles of precipitation during the monsoon are also similar between WRF and TRMM, with WRF capturing individual mountain/valley circulations not shown by TRMM, but validated by surface stations and MODIS cloud cover. This study demonstrates the strengths and weaknesses of the model in simulating Himalaya precipitation over the course of a year, and improves our understanding of Asia’s water resources.