Sensitivity of Microphysics and Planetary Boundary Layer Configurations for Extreme Rain Forecast over the Western Nepal using WRF-ARW Model.

Abstract

The occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends of the range of observed values of the variable is known as extreme, in many cases, a weather or climate event with high impact is also known as extreme. Even though extreme events do not occur often, they can be harmful, can cause great devastation to infrastructures, can affect our economy, and can even cause the loss of life. Monsoon season is a one of the crucial seasons for the precipitating extreme rainfall. Every monsoon affects the environment as well as life style of all living things, causing landslide, floods and affect socioeconomic sector. If the monsoon event could be predicted ahead of event days, we can minimize the loss of property or life. Study of past rainy days shows that all the extreme event were on monsoon season (data taken from 2010 to 2018). In this study WRF (v4.0.3) was used to simulate extreme events to test the sensitivity of the combination of planetary boundary layer physics and microphysics scheme, using initial and boundary condition data from NCEP FNL with 1 0 x1 0 spatial resolution and 6 hourly temporal resolutions. From this study no single scheme combination performs best for all rainfall category. In this study two methods were depicted to overcome a conclusion. Continuous verification shows Thompson-Mynn is best, with result value of RMSE value 68.86. From categorical verification, Skill score test statistics ‘Probability of Detection’ showed Thompson-Mrf, Wdm6-Mynn, and Lin-Mynn best for low, moderate and heavy rainfall category with value 0.671, 0.436, 0.419. ‘Proportion Correct’ showed Morrision-Mynn, Thompson-Mrf and Wdm6-Mynnwas best for low, moderate and heavy rainfall category with the score value 0.336, 0.255, 0.264. ‘False Alarm Ratio’ showed Morrision-Mynn, Morrision-Mrfand Wdm6-Mynn best for low, moderate and heavy rainfall category with value 0.566, 0.559, 0.433. It comes to the point that there must be a different physical combination for different rain category.