The study published in SCIENCE CHINA Earth Sciences was conducted by Dr. Zhenzhen Ai and Professor Xin XU from the School of Atmospheric Sciences at Nanjing University, and their collaborators. The researchers conducted a series of numerical experiments for a heavy rainfall event in April 2023 as well as a 13-day rainy episode in July 2023 over the Sichuan Basin in Southwest China. In the control run without OGWD parameterization, the WRF model significantly overestimated the heavy rainfall intensity and presented an eastward location bias. When OGWD parameterization was enabled, the low-level winds in northeastern Sichuan Basin were notably decelerated, reducing the moisture transport and mitigating the rainfall‑intensity overestimation. Meanwhile, the decelerated airflow encountered stronger terrain obstruction. A blocking high was therefore induced, pushing the heavy rain‑generating cyclonic vortex westward and offsetting the eastward position bias of precipitation. For the 13‑day rainy episode in July 2023, batch simulations reveal that, when taking into account the parameterization of OGWD, the mean bias of predicted rainfall is reduced by 27.5%, and the ETS is increased for all intensity levels of rainfall.
This study highlights the vital role of OGWD parameterization in rainfall forecasts in kilometer-scale models, challenging the conventional notion that small-to-mesoscale OGWD can be explicitly resolved by fine-resolution grids. These findings provide an important scientific foundation for operational precipitation forecasting over complex terrain regions. They also suggest that current OGWD parameterization schemes require further improvements, for instance by incorporating non-hydrostatic and moisture-related effects to achieve even greater forecasting accuracy.
See the article:
Ai Z, Xu X, Ji Y, Heng Z, Jiang X. 2026. Orographic gravity wave drag parameterization in kilometer-scale WRF models improves the prediction of rainfall in Southwest China. Science China Earth Sciences, 69(8): 2912–2926, https://doi.org/10.1007/s11430-025-1982-9
Science China Earth Sciences