where P is precipitation (mm yr−1), H is human water consumption (mm yr−1), and ET is total evapotranspiration (mm yr−1).
2.2.2 Calculation of current vegetation restoration potential
By applying a moving window approach, we used 0.05-degree data to fit the relationship between water resources and vegetation amount in each 0.5-degree grid. GPP was used to characterize vegetation cover. Usually, the increase in GPP is accompanied by water consumption (i.e., ET) \cite{Liang_2019}, as follows:
\(GPP=f\left(ET\right)\) (2)
The above formula reflects the relationship between GPP ( gC m-² yr-1)and ET (mm yr−1), which can also be interpreted as water use efficiency (WUE).
Based on the relationship obtained from the above fitting, when using all of AWR for vegetation growth, we could calculate the GPP that could be supported.
\(GPP'=f\left(AWR\right)\) (3)
and the vegetation restoration potential was defined as the ratio of GPP’ to GPP, which was in the percentage form:
\(Restoration\ potential=\frac{GPP'}{GPP}\times100\%\) (4)
2.2.3 Calculation of vegetation convention potential
We utilized ET data to calculate the median value within each 0.5 grid, and obtained the respective water consumption for different vegetation types. Then, we subtracted the results to get the difference in water consumption of different vegetation (D, mm yr−1). Using all water resources for vegetation conversion, the conversion potential can be calculated by dividing AWR by the calculated difference.