## 3 Results
### Temporal and Spatial Characteristics of the Meteorological Variables  
There were significant spatial heterogeneities in the distribution of the meteorological variables during the period from 2000 to 2018 (Figure 5). The temperature showed an overall increasing trend with a multi-year average rate of 0.03 \({}^{\circ}\)C, while precipitation and radiation decreased, with annual average decreasing rates of 1.46 mm and 4.35 MJ\(\cdot\)m\({}^{-2}\), respectively. Specifically, the temperature reached its peak in 2007 during the study period, with a national average of 7.33 \({}^{\circ}\)C, and then slightly declined, reaching its lowest point in 2012 (5.93 \({}^{\circ}\)C). The spatial distribution pattern is characterized by higher temperatures in the south and lower temperatures in the north. Region II consistently had the highest temperatures during the study period, with a multi-year average of 20.12 \({}^{\circ}\)C, followed by Region I (15.68 \({}^{\circ}\)C), while Region III had lower average temperatures (\(-\)3.24 \({}^{\circ}\)C). Special geographical locations and climate conditions may contribute to this variation, but Region III has shown a noticeable increase in temperatures in recent years, with an average annual increase of 0.04 \({}^{\circ}\)C. At the same time, Regions I, II, and III also exhibit some degree of decreasing trends. Precipitation, on the other hand, displays an overall fluctuating downward trend, reaching its lowest point in 2011 (897.69 mm). The spatial distribution pattern shows that the eastern and southeastern coastal areas receive more abundant rainfall, with a ranking of precipitation amount from highest to lowest in the seven regions as follows: II > I > III > VI > IV > V > VII. The ocean carries moist air into the inland regions, where it meets cold air, leading to rainfall. In contrast, the western regions are located further inland, making it challenging for maritime moisture to reach them. Additionally, these regions have extensive grasslands and deserts, contributing to drier conditions and serving as important factors causing regional differences in precipitation.  
Figure 5: _Cont._Looking at the trend of changes, Region V has an annual precipitation increase rate of 1.70 mm, while the other regions all experience varying degrees of decrease. It is noteworthy that Regions I and IV show more pronounced decreases in precipitation, with annual average decreasing rates of 14.26 mm and 5.48 mm, respectively. Radiation remained consistently high from 2006 to 2009, with the highest annual average occurring in 2006 (11,574.92 MJ\(\cdot\)m\({}^{2}\)) and the lowest in 2016 (11,261.87 MJ\(\cdot\)m\({}^{2}\)). The ranking of annual average radiation values among the seven regions, from highest to lowest, is as follows: III \(>\) VII \(>\) V \(>\) IV \(>\) II \(>\) I \(>\) VI. Regions III and VII consistently have higher multi-year radiation values.  
Furthermore, at the pixel scale, this study found that, in the same region, the trends in precipitation and radiation from 2000 to 2018 were nearly opposite. Areas with increasing precipitation tend to have higher water vapor content in the air, and when sunlight shines, it gets refracted, resulting in less sunlight reaching the surface. Additionally, regions with higher rainfall tend to have thicker cloud cover, which leads to a greater weakening of solar radiation by the atmosphere, partly blocking sunlight. These factors might be significant reasons for the opposite multi-year trends in precipitation and radiation in many areas.