Radiation index
In this study, we formularised an RI based on different radiation components as follows:
\(\text{RI}=\frac{R_{n}-I}{\text{DSR}},\) (1)
\(R_{n}=\left(DSR+DLR\right)-(USR+ULR)\), (2)
\(I=ULR-DLR,\) (3)
where Rn is the net radiation which indicates the net energy balance of an ecosystem andI the effective radiation which reflects the net heat transmissions within a system through long-wave radiations (Law et al., 2000; Turner et al., 2003; Verma et al., 2014). In theory, the difference between Rn and I can be indicative of the radiation that is absorbed by an ecosystem through photosynthesis. DSR is the downwelling short-wave radiation, also known as global radiation, which is included to normalise Rn and I so that the RI could be applicable in different seasons and regions with variable radiation inputs into a system. DLR, USR and ULR are the downwelling long-wave radiation and upwelling short- and long-wave radiation, respectively (Figure 1).