*3.4. KE-R Relationships*

The rainfall kinetic energy KE and rainfall intensity *R* are calculated based on Equations (5) and (18), respectively. The KE-*R* relationships of stratiform rain in different seasons are derived in the form of a power function. The fitting results show the KE-*R* relationships satisfy the form of power function KE = *AR*m, in which *A* and m are parameters.

Figure 9 shows that the stronger the rainfall intensity is, the faster the rainfall kinetic energy tends to increase. The exponent of different power functions m varies from 1.45 to 1.82, in order from small to large, spring < autumn < summer. Parameter *A* has similar values in spring (equal to 8.56) and in summer (equal to 8.10), but in autumn the parameter *A* is 5.56. The value of the parameter *A* is closely related to the raindrop spectra [52]. The parameter *A* is also related to the median rainfall intensity *R*m, which results in the decrease of *A* in autumn compared to spring and summer.

**Figure 8.** *Z-R* relationships (*Z* = a*R*b) in three rainfall events. Each rainfall event is selected from different seasons (spring, summer and autumn). (**a**) *Z-R* relationship of a rainfall event in spring, from 19 April to 20 April 2019; (**b**) *Z-R* relationship of a rainfall event in summer, on 3 August 2019; (**c**) *Z-R* relationship of a rainfall event in autumn, on 1 September 2018; the fitted curves are derived based on the power function, which are solid red curves in (**a**–**c**).

**Figure 9.** KE-*R* curves fitted in different seasons. Data of stratiform rain in spring, summer, and autumn are analyzed. (**a**) KE-*R* relationship in spring; (**b**) KE-*R* relationship in summer; (**c**) KE-*R* relationship in autumn. For the error bars in each panel, *R* in the range (0.5, 5) are divided into nine intervals evenly, and error bars are used for each interval. The error bars for each interval are based on the mean value of *R* and KE, with the ±1 Stdev (standard deviation), respectively.

### **4. Discussion**
