## 3 Results
### ESV Analysis
#### 3.2.2 Spatial Variation Analysis of ESV  
In order to analyze the spatial and temporal variation characteristics of the ESV more accurately, based on relevant research [47], we used a 5 km \(\times\) 5 km grid as the primary research unit to reveal the spatial evolution pattern of the ESV in Shaanxi Province. The grid maps of ESV in Shaanxi Province in 1990, 2000, 2010, and 2020 were calculated using ArcGIS 10.8 software. The ESV in the four periods was then separated into five classes using the Natural Jenks method: low, lower, medium, higher, and high. Finally, for 1990, 2000, 2010, and 2020, spatial distribution maps of ESV in Shaanxi Province were obtained (Figure 4). The general regional distribution patterns of high in the south, low in the north, and lowest in the middle can be seen in Figure 4, indicating that the spatial distribution pattern of ESV in Shaanxi Province is largely constant. The southern and central regions of the area \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Ecosystem Service Type**} & \multicolumn{4}{c}{**ESV (\(\times\)10\({}^{8}\) USD)**} & \multicolumn{4}{c}{**Changes Rates (\%)**} \\ \cline{2-10}  & **1990** & **2000** & **2010** & **2020** & **1990–2000** & **2000–2010** & **2010–2020** & **1990–2020** \\ \hline Food production & 181.21 & 181.93 & 176.84 & 174.30 & 0.40 \(\uparrow\) & \(-\)2.80 \(\downarrow\) & \(-\)1.43 \(\downarrow\) & \(-\)3.81 \(\downarrow\) \\ Raw materials & 117.54 & 118.28 & 119.55 & 119.36 & 0.63 \(\uparrow\) & 1.07 \(\uparrow\) & \(-\)0.16 \(\downarrow\) & 1.55 \(\uparrow\) \\ Water supply & \(-\)97.58 & \(-\)99.93 & \(-\)98.71 & \(-\)101.45 & \(-\)2.41 \(\downarrow\) & 1.22 \(\uparrow\) & \(-\)2.77 \(\downarrow\) & \(-\)3.97 \(\downarrow\) \\ Gas regulation & 401.91 & 403.80 & 405.73 & 403.25 & 0.47 \(\uparrow\) & 0.48 \(\uparrow\) & \(-\)0.61 \(\downarrow\) & 0.33 \(\uparrow\) \\ Climate regulation & 891.30 & 896.34 & 914.65 & 91,334 & 0.57 \(\uparrow\) & 2.04 \(\uparrow\) & \(-\)0.14 \(\downarrow\) & 2.47 \(\uparrow\) \\ Environment purification & 281.58 & 281.23 & 281.64 & 277.08 & \(-\)0.12 \(\downarrow\) & 0.15 \(\uparrow\) & \(-\)1.62 \(\downarrow\) & \(-\)1.60 \(\downarrow\) \\ Hydrological regulation & 1036.67 & 1036.93 & 1021.94 & 1006.54 & 0.03 \(\uparrow\) & \(-\)1.45 \(\downarrow\) & \(-\)1.51 \(\downarrow\) & \(-\)2.91 \(\downarrow\) \\ Soil conservation & 423.58 & 425.78 & 431.57 & 430.05 & 0.52 \(\uparrow\) & 1.36 \(\uparrow\) & \(-\)0.35 \(\downarrow\) & 1.53 \(\uparrow\) \\ Nutrient-cycle maintenance & 45.95 & 46.15 & 45.90 & 45.48 & 0.43 \(\uparrow\) & \(-\)0.55 \(\downarrow\) & \(-\)0.91 \(\downarrow\) & \(-\)1.04 \(\downarrow\) \\ Biodiversity maintenance & 356.64 & 358.77 & 366.30 & 366.16 & 0.60 \(\uparrow\) & 2.10 \(\uparrow\) & \(-\)0.04 \(\downarrow\) & 2.67 \(\uparrow\) \\ Aesthetic landscape & 164.00 & 165.60 & 170.80 & 172.38 & 0.98 \(\uparrow\) & 3.14 \(\uparrow\) & 0.93 \(\uparrow\) & 5.11 \(\uparrow\) \\ Total & 3802.82 & 3814.90 & 3836.20 & 3806.50 & 0.32 \(\uparrow\) & 0.56 \(\uparrow\) & \(-\)0.77 \(\downarrow\) & 0.10 \(\uparrow\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Changes in different EVs in Shaanxi Province from 1990 to 2020. Figure 4: Spatial distribution patterns of EVs in Shaanxi Province from 1990 to 2020.  
have more-favorable external environments for plant development due to the elevation and latitude differences in the regions. Grassland and forestland are the most common terrain types in high-value locations, contributing to an increased ESV. The central urban area and the northern part of Shaanxi Province have the highest concentrations of low ESV regions because the central region's urbanization is growing, and the proportion of built-up land is gradually increasing; however, the ESV of built-up land is negative, resulting in a low ESV in the corresponding range. In the northern, low ESV area, the sandy and desert land-use categories predominate, and the ESV is low.