GB/T 20486-2017 in English

Interpretation of the standard for the classification of surface rainfall levels in river basins

I. Background of standard formulation and analysis of technical evolution

The National Standard of the People's Republic of China GB/T 20486-2017 "Surface rainfall levels in river basins" is a revised version of the original standard GB/T 20486-2006. Since its release in 2006, the standard has been widely used across the country, especially in flood forecasting and flood control scheduling.

The main background of this revision includes:

• Adapting to the new needs of business development
• Coordination and unification with GB/T28592-2012 "Precipitation Grade"
• Improving the scientificity and accuracy of surface rainfall calculation methods

II. Comparative analysis of standard frameworks

III. Classification and calculation method of surface rainfall levels

Surface rainfall levels are divided according to the average rainfall in a specific area per unit time, and are mainly divided into six levels: light rain, moderate rain, heavy rain, rainstorm, heavy rainstorm and torrential rain. The 12-hour and 24-hour rainfall amplitude values corresponding to each level are shown in Table 1:

IV. Application and suggestions of area rainfall calculation methods

In practical application, it is recommended to select the appropriate area rainfall calculation method according to the specific topography and distribution of rain gauges in the basin:

1. Arithmetic mean method: It is suitable for small basins with a large number of rain gauges and uniform distribution.
2. Thyssen polygon method: Suitable for medium-sized basins with uneven distribution of rainfall stations, taking into account the control area weight of each rainfall station.
3. Kriging method: Suitable for large basins with complex terrain and uneven spatial distribution of rainfall, and can effectively reflect spatial correlation.