Using the Local Drought Data and GRACE/GRACE-FO Data to Characterize the Drought Events in Mainland China from 2002 to 2020  
[PERSON]  
1 School of Architecture and Civil Engineering, Chengdu University, Chengdu 610106, China; [EMAIL_ADDRESS] (L.C. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.L.) 2 School of Geodesy and Geomatics, Wuhan University, Wuhan 430079, China 2  
[PERSON]  
1 School of Architecture and Civil Engineering, Chengdu University, Chengdu 610106, China; [EMAIL_ADDRESS] (L.C. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.L.) [PERSON]  
3 MOE Key Laboratory of Fundamental Physical Quantities Measurement & Hubei Key Laboratory of Gravitation and Quantum Physics, POMF and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China 34 Nanning Survey and Design Institute Group Co., Ltd., Nanning 530022, China; [EMAIL_ADDRESS] 45 School of Civil Engineering and Geomatics, Southwest Petroleum University, Chengdu 610500, China; [EMAIL_ADDRESS] 5  
[PERSON]  
4 Nanning Survey and Design Institute Group Co., Ltd., Nanning 530022, China; [EMAIL_ADDRESS] 4  
[PERSON]  
5 School of Civil Engineering and Geomatics, Southwest Petroleum University, Chengdu 610500, China; [EMAIL_ADDRESS] 5  
[PERSON]  
1 School of Architecture and Civil Engineering, Chengdu University, Chengdu 610106, China; [EMAIL_ADDRESS] (L.C. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.L.) Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
Footnote 11:  
==WARNING: Truncated because of repetitions==
\(-1.19\) & \(-1.02\) & \(-5.24\) & \(86.41\) & \(75.50\) & \(373.60\) \\  & & 200608-200611 & 4 & \(-1.63\) & \(-1.22\) & \(-4.86\) & \(81.89\) & \(74.11\) & \(296.02\) \\  & & 200909-201003 & 7 & \(-1.30\) & \(-1.06\) & \(-7.43\) & \(88.70\) & \(75.04\) & \(527.30\) \\  & & 201108-201110 & 3 & \(-1.24\) & \(-1.09\) & \(-3.28\) & \(73.42\) & \(66.74\) & \(199.95\) \\ \hline \multirow{4}{*}{NE} & \multirow{4}{*}{4} & 200709-200806 & 10 & \(-1.45\) & \(-1.10\) & \(-10.96\) & \(70.00\) & \(64.22\) & \(637.65\) \\  & & 201109-201207 & 11 & \(-1.34\) & \(-1.11\) & \(-12.19\) & \(76.30\) & \(69.52\) & \(761.22\) \\  & & 201506-201510 & 5 & \(-1.04\) & \(-0.99\) & \(-4.97\) & \(80.00\) & \(67.50\) & \(334.20\) \\  & & 20
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In order to maximize the effect of the improved approach, we counted the situation of monthly GRACE-DSI and drought area percentage in the four study regions during the drought events derived from the local drought data. The results are shown in Table 5. Considering that a drought is defined when the GRACE-DSI is less than \(-0.5\), the areas with a grid value less than \(-0.5\) are considered to be in drought, and the grid area is included in the statistics of the drought area. It can be seen from Table 5 that the probability that the monthly GRACE-DSI is below \(-0.8\) is only \(34.68\%\), so it is unreasonable that the threshold of monthly GRACE-DSI was set to \(-0.8\). The threshold for defining the occurrence of a drought proposed by [PERSON] (2017; Table 1) is \(-0.5\); however, the probability that the monthly GRACE-DSI is below \(-0.5\) is only \(66.13\%\). In order to ensure that the most drought events are detected, the detection thresholds need to be cover at least \(90\%\) of the drought events (\(90\%\) criterion adopted was arbitrarily proposed by the authors). We found that the probability that the monthly GRACE-DSI is below \(-0.2\) is \(89.52\%\), and the one that the monthly GRACE-DSI is below \(-0.1\) is \(95.16\%\). The statistical results of the drought area percentage show that the probability is greater than \(90\%\) only when the drought area percentage is less than \(10\%\) (\(94.70\%\)). Therefore, we initially set the threshold of monthly GRACE-DSI and the percentage of drought area to \(-0.2\) and \(10\%\). Subsequently, we determined the most suitable threshold according to the procedure in Section 4.5.