## 4 Discussion  
The main contributions of this study are twofold. First, we conducted a targeted study on the CWUE and obtained the relationship between cultivated land and drought in the HHHP from the perspective of the WUE, which has never been reported in previous studies. This study provides a scientific basis for the production and development of food safety in China. Second, this study systematically conducted a spatiotemporal analysis of drought in the HHHP from the two aspects of drought events and drought trends, which provided a reference for drought prevention and disaster prevention in the HHHP. This study explored the spatial and temporal distributions of droughts in the HHHP and the sensitivity of the CWUE to drought anomalies. Five drought events were identified using the run theory. The results showed that the duration of recent droughts was short, but their frequency increased. Moreover, the period of change from soaked to parched gradually shortened. The recent short-term droughts alternating with wet periods are consistent with an increase in climate variability related to climate change [50]. Recently, [PERSON] et al. [51] developed a method to identify small-scale extreme flash drought events. Therefore, for future research, we could combine this method to expand the study of drought events in the HHHP. [PERSON] et al. [7] previously divided the global ecosystem into arid and humid ecosystems and concluded that droughts had a positive or negative impact on the WUEs of both ecosystems. Although the effects of drought on the WUE have been shown to be region- and biome-dependent, at the spatial scale, dividing ecosystems into arid and humid ecosystems is not sufficiently specific. [PERSON] et al. [6] analyzed the spatial-temporal changes of the annual WUE in different regions and its response to drought depends on the vegetation types and administrative divisions. However, a differential analysis of the response of the same vegetation type to droughts in different regions has not been conducted. Further research [23] considered the southwest region as the study area and found that the responses of the WUEs of forests, shrublands, and other ecosystems to droughts vary with the drought severity. In summary, the current research on the relationship between droughts and the WUE has led to different conclusions owing to differences in the scales of the study area and the calculation model used for the WUE. Therefore, the present study indicated that the smaller the study area, the more helpful it is to determine the relationship between the WUE and drought. Thus, we suggest that the discussion of the relationship between drought and the WUE should start at a small scale. This study took the HHHP as the research area, selected the cultivated land ecosystem as the research object and explored the spatiotemporal relationship between the CWUE and drought. In addition to the precise spatial scale, the accurate division of time periods was also the focus of the follow-up research on the CWUE in this study. For example, the vegetation growing season can be used as a criterion for the time scale division. Many studies have examined the time-lag effects of drought on the WUE [24; 46; 52]. Some researchers believe that the impact of droughts on the WUE has a lag effect of approximately four months, and this effect exists in 70.87% of the global vegetation areas. For shrubs and sparse vegetation, the lag effect of droughts on the WUE is short (1-4 months) [24]. Owing to the vegetation sparseness of cultivated land, the time-lag effects of drought on the CWUE in the HHHP obtained in this study were in agreement with results obtained previously [24]. Moreover, this study clearly concluded that there was a lag period of three months in the response of the CWUE to drought. This may be related to the fact that the cultivated land in this area is mainly irrigated.