---
title: "Chinese Rainfall"
canonical: "https://help.innovyze.com/space/infodrainage2021v1/16548143/Chinese%20Rainfall"
format: markdown
---
For Chinese conduit design, the regulation recommends the rational method, so every city has a rainfall intensity formula with same form :

![image](media://860a0560-845b-4a0c-ab25-e5ecbd522b1a)

Keifer & Chu (1957) design rainfall (also called as Chicago Rainfall) describes how to generate a design rainfall using that intensity formula.

> ⚠️ This method may not be available for your region. For more information, refer to the [Regionalisation](https://help-innovyze.atlassian.net/wiki/spaces/infodrainage2021v1/pages/16548015) topic.

![image](media://76e0690f-564d-4f22-a9ad-b774e744832e)

The fields specific to Chinese Rainfall generation are listed below:

### Return Period

Period, in years, between events of the same intensity or of a greater intensity than this storm.

### Calculation of A

Select method of specifying value of A:

- Calculated - A is calculated from a, C and return period values
- User - A is user defined

### A (Calculated)

A is calculated as:

a(1 + Clog<sub>10</sub>P)

Where P is return period.

### A (User)

User defined equation constant.

### a

Equation constant, used in calculation of A when calculation of A is set to Calculated

### C

Equation constant, used in calculation of A when calculation of A is set to Calculated

### r

The portion of the duration of the event occurring before the peak

r Value Examples

|  |  |  |  |
| --- | --- | --- | --- |
| place | r(times) | area | r(times) |
| Chicago | 0.375(83) | Beijing | 0.355(57) |
| Soviet | 0.35(—) | Shanghai | 0.367(80) |
| Japan | 0.50(1050) | North china | 0.3-0.4(483) |
| Most Chinese city | 0.3-0.4(—) | Wuhan | 0.3-0.4(—) |

### b

User defined equation constant.

### n

User defined equation constant.


## Intensity and Rainfall Calculation

The duration for the design rainfall is > Macro (inline-media-image)



Instantaneous intensity before peak is > Macro (inline-media-image)

, corresponding duration is > Macro (inline-media-image)

, and cumulative depth is > Macro (inline-media-image)

.

Instantaneous Intensity after peak is > Macro (inline-media-image)

, corresponding duration is > Macro (inline-media-image)

, and cumulative depth is > Macro (inline-media-image)

.


Total rainfall depth > Macro (inline-media-image)




Set > Macro (inline-media-image)

, the peak time ratio is r (which has a range of 0-1),  then > Macro (inline-media-image)

.


Assume the density formula is > Macro (inline-media-image)




In China, A = a(1 + log<sub>10</sub> P) where P is the return period and a is a constant.


the instantaneous intensity before > Macro (inline-media-image)

 and after peak > Macro (inline-media-image)

 are:

![image](media://b6bb7628-41de-4b38-a748-bd481379c81e)

![image](media://2b0b2f7e-fe1e-4bbf-947d-11b56c398124)


So > Macro (inline-media-image)

 and > Macro (inline-media-image)

are calculated as follows:


> Macro (inline-media-image)

> Macro (inline-media-image)




> Macro (inline-media-image)

> Macro (inline-media-image)




From the above two equations, the cumulative rainfall depth is produced ad shown below:

![image](media://22c1315f-9d35-4247-a16d-d4d7d0bb8632)


The cumulative rainfall is calculated by following equations：

> Macro (inline-media-image)

> Macro (inline-media-image)




> Macro (inline-media-image)

> Macro (inline-media-image)




where

![image](media://7a6de1f6-03d9-4158-8cb7-7c7fdb1cfa70)

#### Reference on Chicago rainfall

C.J. Keifer, H.H. Chu, synthetic storm pattern for drainage design, proc paper 1332. ASCE. Aug. 1957.