## 4 Discussion
### Differences in Sensitivity to Precipitation across Seasons  
The impact of precipitation on vegetation can vary significantly depending on plant growth phases [74] and plant species. For example, desert trees were shown to use more water accumulated in winter than desert shrubs [75]. Precipitation frequency and sensitivity to it decrease in spring and winter, as cold climate conditions with less precipitation slow down the growth of plants. In summer, sufficient precipitation and radiation supported the vegetation carbon sink, reducing the sensitivity of plant communities to frequency changes.  
For shrubland, when the frequency of small to heavy precipitation decreases in summer for shrubs, GPP and their sensitivity also decreases. Only the sensitivity to trace precipitation increases. This suggests that substantial precipitation is needed to ensure shrub growth when the temperature is favorable. An increased frequency of trace precipitation during summer can hinder shrub growth. In autumn, while the frequency of precipitation continues to decline, and GPP rises, sensitivity decreases. From September to November, as temperatures gradually drop, arid conditions become more suitable for shrub growth.  
In winter, precipitation frequency declined or remained stable, and sensitivity increased in all vegetation areas. This may be explained by the fact that, on the one hand, as vegetation witness and GPP values drop in winter in environments such as cropland, grassland, and barren land, changes in precipitation cannot promote GPP growth; on the other hand, vegetation in evergreen forests needs large precipitation amounts to penetrate through the soil and improve soil water content. The seasonal divergence of water availability [76] may explain why sensitivity increased with precipitation frequency in summer. A previous study showed that during midsummer, many plants use water that originated during winter [77], implying that winter precipitation may play an important role in regulating growing season dynamics, particularly in the context of the shifting seasonal precipitation inputs projected to occur with climate change [78].  
In this study, shrubland showed strong seasonal sensitivity diversity, possibly because of solar radiation, precipitation intensity, and temperature, shrub drought, and plant mortality. Another reason may be that vegetation growing in arid areas all year round is adapted to drought conditions; for example, shrubland tends to use water accumulated in winter to support recovery and development during times with less precipitation. The little variation in vegetation sensitivity may also be related to the number of bud banks, which ensure the stability of vegetation growth during drought [79; 80]. Strong evapotranspiration and low precipitation intensity in barren land converge to cause lesser plant productivity than in other land cover types and GPP sensitivity to precipitation frequency unresponsiveness until GPP exceeded the threshold at which vegetation could be recovered. The sensitivity of vegetation to large and heavy precipitation is almost unchanged, especially in forests, grassland, and barren land. The forest ecosystem is relatively stable, and precipitation events will not impact GPP in the short term. The grassland has stronger root systems where water could not easily be saturated into soil. The measurement of the resistance of vegetation to precipitation changes should also consider topography and soil hydraulic characteristics, and whether the decrease in precipitation frequency leads to the duration of soil available water below the withering point is also an important factor that cannot be ignored. Alternatively, it is possible that the continuous increase of potential evaporation caused by global warming also weakened the role of precipitation frequency in the aridity change on a regional scale [81].