## 5 Conclusions  
This study used multi-source data, such as meteorological stations and remote sensing, and the Cubist algorithm to establish the mISDI dataset of the HHHP from 2001 to 2020. The spatial and temporal distributions of drought events and the impact of drought events on CWUE changes were analyzed. The results are summarized as follows.  
1. The mISDI dataset in the HHHP was established, and the June data were taken as an example to establish a drought index model suitable for the HHHP. SPI03, SOSA, VSWI, AWC, DEM, LON, LAT, and YEAR were selected as independent variables, and scPDSI was a dependent variable.
2. Five drought events were identified using the run theory. The first drought event had the highest intensity (\(-1.925\)) and the longest drought duration (18 months) and was considered as the most severe of all the drought events. However, the gradual decline in the mISDI over the 2001-2020 period indicated a trend of worsening drought conditions in most areas of Shandong Province and in the northeastern part of Henan Province. The recent short-term droughts alternating with wet periods was consistent with an increase in climate variability related to climate change. Further studies are needed to determine if the rapid alternation between droughts and wet periods will continue. Drought had an enhanced effect on the CWUE of the HHHP, and the enhancement of the CWUE in the eastern hilly area was more significant.
3. Using the most severe drought event during the study period as an example, the correlation between drought and the CWUE was studied. The study found that there was a three-month lag period and a significant positive correlation between the response to drought and the CWUE, which was related to the irrigation habits of the HHHP. The areas with significant correlations were dominated by plains with the flattest terrain in the entire area.  
In general, the mISDI has high accuracy in the comprehensive drought index model in the HHHP and has been effectively verified in the monitoring of drought events. From the response results of the CWUE and drought, the conclusions can also be verified by previous studies; however, the conclusions are more precise than those of previous studies. The relationship between multiple influencing factors of the WUE requires special attention. In future research, we plan to compare different regions of the country, explore the impact of drought on the WUE in different LATs and LONs, climatic zones, and biomes and try to reveal the underlying mechanism of drought and the WUE.  
Conceptualization, W.W. and J.L.; methodology, J.L. and W.W.; formal analysis, W.W., H.Q., W.X., C.Z., Y.T. and Z.H.; writing--original draft preparation, J.L. and W.W.; writing--review and editing, J.L. and W.W.; visualization, W.W. and J.L.; project administration, J.L.; funding acquisition, J.L. All authors have read and agreed to the published version of the manuscript. This research was financially supported by the Natural Science Foundation of Anhui Province (grant No. 2108085 MD29) and in part by the National Natural Science Foundation of China (grant No. 41571400).  
Data Availability Statement: The data used to support the findings of this study area are available from the corresponding author upon request via email.  
The authors declare that they have no conflict of interest.