CN117473413A - Compound type dry heat event identification method based on daily drought index - Google Patents
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Abstract
The invention discloses a composite type dry heat event identification method based on a daily drought index, which comprises the following steps: acquiring a cumulative precipitation P value and a daily potential evaporation emission PET value which are 30 days in advance of daily rolling, and constructing cumulative water deficiency sequences of different time scales to obtain a standardized potential evaporation emission index SPEI monitored daily; defining the occurrence of drought events by using the continuous number characteristics of the standardized potential evaporation index monitored day by day; defining the occurrence of an extreme high temperature event by utilizing the event that the daily highest air temperature exceeds the daily high temperature threshold value for 3 consecutive days; when a drought event and an extreme high temperature event occur simultaneously, then a compound dry heat event is considered to occur. The invention realizes the monitoring and identification of the compound type dry heat event by utilizing the daily SPEI index, defines the duration and the severity of the compound type dry heat event, and can quantitatively and comprehensively analyze the characteristics of the compound type dry heat event such as the chronology, the season, the frequency, the duration, the severity and the like in the season.
Description
Technical Field
The invention relates to the technical field of extreme climate identification, in particular to a composite type dry heat event identification method based on a daily drought index.
Background
Global climate warming aggravates instability of the climate system, namely, complex and concurrent extreme climate events formed by interweaving a plurality of events occur, the influence of the complex and concurrent extreme climate events is larger than the sum of the influence caused by single events, wherein the occurrence frequency of complex extreme dry heat events which are simultaneously and co-located in high temperature-drought of inland areas is higher. The relationship between the compound extreme dry heat event and the production and life of people is also more close, is a hot spot problem in the field of extreme climate change research, and is also a compound extreme weather climate event which is most influenced by global climate change.
At present, the monitoring indexes of the compound type dry heat event are not uniform. Most monitoring indexes are based on month precipitation or month drought indexes, and meanwhile, the number of extreme high-temperature events occurring in the month is considered, and the indexes can only reflect the number of compound dry and hot events and cannot reflect the duration, strength and other characteristics, so that related researches are mainly focused on annual frequency change characteristics.
The sensitivity of the composite type dry heat event decreases along with the increase of the time scale, mainly occurs on the time scale of 1-3 months in the season, and the time scale of the composite type dry heat event driven by a high-voltage system is generally several days, so that the prior monitoring method is difficult to describe the characteristics in the season.
On the other hand, for the research of the compound type dry heat event of different areas, different monitoring indexes possibly generate larger difference to the conclusion, so that the compound type dry heat event of the areas is necessary to be comprehensively monitored by combining the drought indexes with better applicability on the area scale, and the uncertainty brought by the evaluation indexes is reduced. Therefore, how to accurately capture the characteristics of time and space in the development process of the composite type dry heat event is a key problem to be solved in order to improve the forecasting and early-warning capability of the composite type dry heat event.
Patent publication (CN 114638526 a) discloses a method of quantitatively evaluating drought-heat wave composite events, in which, although one method of quantitatively evaluating drought, heat wave composite events is pointed out, only image-coupled composite events are employed, and no method of quantifying the severity of composite events is given.
Therefore, the characteristics of time and space in the development process of the composite type dry heat event cannot be accurately captured at present, and the composite type extreme dry heat event cannot be quantitatively identified.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a composite type dry heat event identification method based on a daily drought index, which can identify the characteristics of the starting date, the ending date, the duration, the intensity and the like of the composite type dry heat event and provides practical technical support for monitoring the composite type dry heat event.
The invention is realized by the following technical scheme:
a composite type dry heat event identification method based on a daily drought index comprises the following steps:
acquiring accumulated precipitation P and a daily potential evaporation emission PET value which are rolled every day and advanced for 30 days, and constructing accumulated water deficiency sequences of different time scales to obtain a standardized potential evaporation emission index SPEI monitored daily;
defining the occurrence of drought events using the features of a standardized potential evaporative emission index monitored day by day for consecutive days SPEI < -0.5;
by using the highest temperature T for 3 days max Exceeding the solar high temperature threshold T d Event definition of extreme high temperature events;
when a drought event and an extreme high temperature event occur simultaneously, then a compound dry heat event is considered to occur.
In the technical scheme of the invention, the Penman-Monteth method recommended by the United nations grain and agriculture organization (FAO) is utilized to calculate the daily Potential Evaporation (PET) of a station, and the calculation formula is as follows:
wherein: delta is the slope of saturated water vapor pressure curve (kPa/. Degree.C.), R n Is net radiation (MJ/(m) 2 D)); g is the soil heat flux (MJ/(m) 2 D)), γ is a dry-wet constant (kPa/. Degree.C.), and T is a ground average air temperature (. Degree.C.); u is 2m high wind speed (m/s), and the average wind speed at the meteorological station 10m is converted according to the FAO recommended formula; e, e a E is the actual water vapour pressure (kPa) s Is the average saturated water vapour pressure (kPa).
The accumulated water deficit sequence of different time scales is constructed by utilizing the difference P-PET of accumulated precipitation P and PET which are rolled every day and advanced by 30 days and months:
wherein: p is precipitation, PET is potential evaporation, k is a month time scale (month), and n is the calculated number.
And calculating probability distribution of the accumulated water deficit sequence by adopting a three-parameter log-logistic probability distribution function, carrying out standardization processing on the distribution function, and obtaining a SPEI index monitored day by referring to calculation of a Standardized Potential Evaporation Index (SPEI).
As a preferred definition method of the drought event, the process definition method of the drought event is as follows: the SPEI index has a value of less than-0.5 for 15 consecutive days per day, wherein the drought event process starts on day 1 with a SPEI value of less than-0.5 and ends on day 1 with a SPEI value of less than-0.5 for the last day.
In the technical scheme of the invention, the drought event process end defining method comprises the following steps: and when the SPEI index is greater than or equal to-0.5 in 5 continuous days, ending the drought event process.
As a preferred definition method for the drought event, the severity S of the drought event d Expressed as: during drought events, the sum of the absolute values of the individual daily SPEI indices over the duration of the drought event:
wherein the drought event duration D is the number of days from the beginning to the end of the drought event process.
In the invention, the definition method of the extreme high temperature event is as follows: day maximum temperature T for 3 consecutive days max All exceeding the daily high temperature threshold T d It is believed that an extreme height Wen Shijian occurs,
wherein the daily high temperature threshold is 90% of the daily maximum air temperature of 31 days in the day of the study period and 15 days before and after the day, such as 90% of the daily maximum air temperature of 31 days in the day of 60 given days in 1961-2020 and 15 days before and after the day.
Severity S of the extreme high temperature event h The definition method of (2) is as follows: the cumulative sum of the difference between the maximum daily air temperature and the threshold value of the extreme high temperature process is defined as the severity S of the extreme high temperature event h ：
The method for defining the composite type dry heat event comprises the following steps: when the day SPEI drought index reaches the drought event process starting day standard, and simultaneously exceeds and reaches the extreme high temperature event definition standard, namely, the composite type dry and hot event is considered to occur.
The continuous days D of the composite dry heat event is defined as the number of days continuously reaching the standard, and the severity S is defined as the product of the severity of drought and extreme high temperature events at the time of occurrence of the event:
S＝S d ×S h 。
an alternative composite dry heat event severity S is defined as: severity S of drought event when composite type dry heat event occurs d Normalized values and extreme high temperature eventsSeverity S h Product of normalized values:
S＝S d standardization of ×S h normalization 。
Wherein the severity of the drought event S d The standardized method of (2) is as follows: severity S of all drought events when a composite dry heat event occurs within a given historical interval d Value mapping to [0,1 ]]Standardization is carried out in the interval;
severity S of the extreme high temperature event h The standardized method of (2) is as follows: severity S of all extreme high temperature events when a composite dry heat event occurs within a given history h Value mapping to [0,1 ]]Standardization is performed within the interval.
The invention has the technical effects that:
1. compared with the definition method in the prior art, the method realizes the monitoring and identification of the compound type dry heat event by utilizing the daily SPEI index, defines the duration and the severity of the compound type dry heat event, can quantitatively and comprehensively analyze the characteristics of the compound type dry heat event such as the chronology, the season, the frequency, the duration, the severity and the like in the season, and can provide scientific basis for the monitoring, the forecasting and the early warning of the compound type dry heat event.
2. The invention also has the advantages of adopting image expression compared with the prior art: the method for identifying the compound event by adopting the quantization method quantifies, conforms to the unified measurement standard and statistical method, and has the advantages of more systematic, standard, objective, more accurate and reliable result. Different data of the same quantization index can be directly compared, difference and change trend are judged, comparison is facilitated, quantitative analysis is conducted based on the quantization index, rules are induced, a theoretical model is built, and better induction and summarization are facilitated.
Drawings
FIG. 1 is a graph of cumulative precipitation P values monitored 30 days daily in advance of rolling daily from 5 months in 2010 to 10 months in 2010 in Yunnan Huaning station;
FIG. 2 is a graph of cumulative potential vapor emission PET values monitored 30 days daily in advance of a rolling daily for 5 months in 2010 to 10 months in 2010 of Yunnan Huaning station;
FIG. 3 is a normalized potential evapotranspiration index SPEI plot monitored daily from 5 months 2010 to 10 months 2010 of Yunnan Huaning station;
FIG. 4 is a graph of the daily SPEI index for the most severe periods of drought ranging from 8, 23, 2010, to 9, 22, 2010 of Yunnan Huaning station;
fig. 5 is a sequence diagram of a Yunnan Huaning station, 5 months in 2010 to 10 months in 2010, daily drought index and high temperature event monitoring.
Detailed Description
Embodiments of the technical solutions of the present application will be described in detail below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical solutions of the present application, and thus are only examples, and are not intended to limit the scope of protection of the present application.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the term "comprising" and any variations thereof in the description of the present application and the claims and the description of the figures above is intended to cover non-exclusive inclusion.
Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Those of skill in the art will explicitly and implicitly appreciate that the embodiments described herein may be combined with other embodiments.
The following examples specifically take Yunnan Huaning station as an example to specifically illustrate a composite dry heat event identification method based on a daily drought index.
Table 1 is a table of cumulative precipitation P values monitored 30 days daily ahead of rolling daily for 5 to 10 months in 2010 in Yunnan Huaning station.
Table 1 cumulative precipitation P values monitored 30 days daily in advance by rolling daily for 5 to 10 months in 2010 of Yunnan Huaning station
Fig. 1 is a graph of cumulative precipitation P values monitored 30 days daily ahead of a rolling daily roll from 5 months in 2010 to 10 months in 2010 in Yunnan Huaning station.
Table 2 is the cumulative potential vapor emission PET values monitored 30 days daily ahead of the daily rolling of 5 to 10 months 2010 of Yunnan Huaning station.
Table 2 cumulative potential evaporative PET values monitored 30 days daily in advance with 5 to 10 months daily rolling in the Yunnan Huaning station 2010
Fig. 2 is a graph of cumulative potential vapor emission PET values monitored 30 days daily in advance of a rolling daily roll from 5 months 2010 to 10 months 2010 of Yunnan Huaning station.
The acquisition mode of the potential evaporation emission PET value curve monitored day by day is as follows: the Penman-Monteth method recommended by the United nations grain and agriculture organization (FAO) is utilized to calculate the daily Potential Evaporation (PET) of a site, and the calculation formula is as follows:
wherein: delta is the slope of saturated water vapor pressure curve (kPa/. Degree.C.), R n Is net radiation (MJ/(m) 2 D)); g is the soil heat flux (MJ/(m) 2 D)), γ is a dry-wet constant (kPa/. Degree.C.), and T is a ground average air temperature (. Degree.C.); u is 2m high wind speed (m/s), and is driven by a weather stationThe average wind speed at 10m is converted according to the FAO recommendation formula; e, e a E is the actual water vapour pressure (kPa) s Is the average saturated water vapour pressure (kPa).
The accumulated water deficit sequence of different time scales is constructed by utilizing the difference P-PET of accumulated precipitation P and PET which are rolled every day and advanced by 30 days and months:
wherein: p is precipitation, PET is potential evaporation, k is a month time scale (month), and n is the calculated number.
Table 3 is a statistical table of the normalized latent evaporative index SPEI values monitored daily from 5 months in 2010 to 10 months in 2010 of Yunnan Huaning station.
Table 3 normalized latent evaporative index SPEI values monitored daily 5-10 months from the Yunnan Huaning station 2010
As shown in fig. 3, a standardized potential evaporation index SPEI curve of monitoring from 5 months in 2010 to 10 months in 2010 of Yunnan Huaning station is specifically obtained by obtaining accumulated precipitation P and a daily potential evaporation PET value of 30 days in advance by rolling from 5 months in 2010 to 10 months in 2010 of Yunnan Huaning station, and constructing accumulated water deficiency sequences of different time scales;
and calculating probability distribution of the accumulated water deficit sequence by adopting a three-parameter log-logistic probability distribution function, carrying out standardization processing on the distribution function, and obtaining a SPEI index monitored day by referring to calculation of a Standardized Potential Evaporation Index (SPEI).
The occurrence of drought events is defined by features of the standardized potential evaporative emission index monitored day by day for a succession of days SPEI < -0.5 > timescales.
The process definition method of the drought event comprises the following steps: the SPEI index has a value of less than-0.5 for 15 consecutive days per day, wherein the drought event process starts on day 1 with a SPEI value of less than-0.5 and ends on day 1 with a SPEI value of less than-0.5 for the last day. The drought event process end defining method comprises the following steps: and when the SPEI index is greater than or equal to-0.5 in 5 continuous days, ending the drought event process.
As shown in table 3 and fig. 3, the SPEI index of the Yunnan Huangning station in the period of 5 months from 2010 to 10 months from 2010 is recorded, and as shown in fig. 4 and fig. 4, the SPEI index of the Yunnan Huangning station in the most serious drought degree period of 23 days from 8 months from 2010 to 9 months from 22 days from 2010 is recorded.
Table 4 SPEI index statistics table from 8.2010 to 23.9.22
| Date of day | SPEI value | Date of day | SPEI value | Date of day | SPEI value |
| 8 months and 23 days | -1.87 | 9 months 3 days | -2.11 | Day 9 and 13 | -2.04 |
| 8 months and 24 days | -1.94 | 9 months and 4 days | -2.13 | 9 months and 14 days | -2.09 |
| 8 months 25 days | -1.95 | 9 months and 5 days | -2.05 | 9 months 15 days | -2.09 |
| 8 months and 26 days | -1.98 | 9 months and 6 days | -2.07 | 9 months and 16 days | -2.09 |
| 8 months and 27 days | -2.03 | 9 months and 7 days | -2.05 | 9 month 17 day | -2.07 |
| 8 months and 28 days | -2.03 | 9 months and 8 days | -2.05 | 9 months and 18 days | -2.16 |
| 8 month 29 day | -2.03 | 9 months and 9 days | -2.08 | 9 months and 19 days | -2.22 |
| 8 months and 30 days | -2.05 | 9 months and 10 days | -2.09 | 9 months and 20 days | -2.26 |
| 8 months 31 days | -2.03 | 9 months and 11 days | -1.96 | 9 months 21 days | -2.12 |
| 9 months 1 day | -2.05 | 9 months and 12 days | -1.99 | 9 months and 22 days | -2.02 |
| 9 months and 2 days | -2.08 |
As is clear from table 3 and fig. 3, in the period from 5 months 2010 to 10 months 2010, the number of times of occurrence of drought events was 1, that is, in this period, the value of the SPEI index for 15 or more consecutive days was equal to or less than-0.5, and the SPEI index for 9 to 22 days 10 months was equal to or greater than 5 consecutive days, and it was found that drought events occurred during 5 to 10 months, the drought event course was continued from 5 to 8 days 10 months, and the drought event was ended on 9 days 10 months.
Severity S of the drought event d Expressed as: during drought events, the sum of the absolute values of the individual daily SPEI indices over the duration of the drought event:
wherein the duration D of the drought event is the number of days from the beginning to the end of the drought event process.
Thus, the daily SPEI index, the most serious drought degree period from 8, 23, 2010, 9, 22, 2010, and the drought event severity S can be recorded in table 4 during the continuous drought development period from 5, 2010, 5, 10, 8, 2010 d 63.8.
Further, in the implementation process, the definition method of the extremely high temperature event is as follows: day maximum temperature T for 3 consecutive days max All exceeding the daily high temperature threshold T d An extreme high temperature event is considered to occur, wherein the daily high temperature threshold is 90% of the daily maximum air temperature for a given day of 60 years and for 31 days of 15 days before and after the day of 60 years selected for the study period. The daily high temperature threshold T of Yunnan Huaning station from 8.sup.23.sup.to 9.sup.22.sup.2010 is recorded as in Table 5 d Maximum daily air temperature T max Specific data of (3).
The daily high temperature threshold T is measured for 5 8 month 23 to 9 month 22 days d Maximum daily air temperature T max Statistical table
As is clear from table 5, extremely high temperature events occurred in the days 5 to 7 of 9 and 17 to 22 of 9 in 2010.
Will be spentSeverity S of the extreme high temperature event h The definition method of (2) is as follows: the cumulative sum of the difference between the maximum daily air temperature and the threshold value of the extreme high temperature process is defined as the severity S of the extreme high temperature event h ：
It can be seen that the severity S of extremely high temperature event occurs from 5 at 9 in 2010 to 7 at 9 in 2010 h Severity S of extreme high temperature event at 7.0, 9.2010-17.9.22 h 13.7.
Further, the composite dry heat event definition method comprises the following steps: when the day SPEI drought index reaches the drought event process starting day standard, and simultaneously exceeds and reaches the extreme high temperature event definition standard, namely, the occurrence of the compound dry heat event is considered, so that 2 compound dry heat events can occur from 8 months, 23 days in 2010 to 9 months, 22 days in 2010 of Yunnan Huaning station.
In an alternative embodiment, the composite dry heat event severity S is defined as: the number of sustained days D of a composite dry heat event is defined as the number of days that continuously meet the criteria, and the severity S is defined as the product of the severity of the drought and extreme high temperature event at the time of occurrence of the event:
S＝S d ×S h 。
accordingly, the severity of the compound type dry heat event occurring in the 5 th to the 7 th of the 9 th of 2010 is s= 43.22, and the severity of the compound type dry heat event occurring in the 17 th to the 22 th of the 9 th of 2010 is s= 175.95. However, in this type of embodiment, there are problems of extremely large numerical differences and large degree of dispersion during the calculation, so in an alternative embodiment, when the severity of the composite dry heat event is calculated, S will be d And S is h Respectively normalized, data mapped to [0,1 ]]Interval, and multiplying, in particular the severity S of the drought event d The standardized method of (2) is as follows: 60 years from 1961 to 2020, and when the compound dry heat event occurs, the severity of all drought events S d Value mapping to [0,1 ]]Standardization is carried out in the interval; the poleSeverity S of terminal high temperature event h The standardized method of the (c) is as follows: 60 years from 1961 to 2020, and when the compound dry heat event occurs, the severity S of all extreme high temperature events h Value mapping to [0,1 ]]Standardization is performed within the interval.
Accordingly, the severity of the compound type dry heat event occurring on the days 5 to 9 and 7 of 2010 is s=10.13 (100 times enlarged), and the severity of the compound type dry heat event occurring on the days 17 to 22 of 2010 is s=54.35 (100 times enlarged).
Table 6 also lists the statistics of the composite dry heat events from 5 to 10 months 2010 at Yunnan Huaning station, according to the method of the above example.
Taking Yunnan Huaning station as an example, yunnan Huaning stations from 5 to 10 months 2010 continuously drought, high temperature events with different degrees occur during the period, and the severity of drought is continuously aggravated (as shown in figure 5). The statistics shows that the composite dry heat event process is carried out 13 times in the discovery period, 50 days in total, the main distribution date is shown in table 6, the longest continuous days are 6 days in 7 months 2-7 months 7 days and 9 months 17-9 months 22 days, but the severity degree of the two processes is large. The severity of drought and high temperature events is weaker than that of drought and high temperature events of 7 months 2-7 months 7 days 17-9 months 22 days, and the severity of the compound type dry-heat events is 9.46. And the severity of drought is 0.59 in the period of 9 months 17 to 9 months 22 days along with the continuous development of drought, the severity of high-temperature events is stronger than 0.93, and the severity of compound dry-heat events reaches 54.35.
Table 6 Yunnan Huaning station 2010 5-2010 10 month composite dry heat event statistics
According to the method for identifying the composite type dry heat event based on the daily drought index, which is expressed by the specific embodiment, the daily SPEI index is utilized to realize the monitoring and identification of the composite type dry heat event, the duration and the severity of the composite type dry heat event are defined, the characteristics of the chronology, the season, the frequency in the season, the duration, the severity and the like of the composite type dry heat event can be quantitatively and comprehensively analyzed, and scientific basis can be provided for the monitoring, the forecasting and the early warning of the composite type dry heat event.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced with equivalents; such modifications and substitutions do not depart from the spirit of the technical solutions according to the embodiments of the present invention.
Claims (9)
1. A method for identifying a composite type dry heat event based on a daily drought index is characterized by comprising the following steps of:
acquiring a cumulative precipitation P value and a daily potential evaporation emission PET value which are 30 days in advance of daily rolling, and constructing cumulative water deficiency sequences of different time scales to obtain a standardized potential evaporation emission index SPEI monitored daily;
defining the occurrence of drought events using the features of a standardized potential evaporative emission index monitored day by day for consecutive days SPEI < -0.5;
by using the highest temperature T for 3 days max Exceeding the solar high temperature threshold T d Event definition of extreme high temperature events;
when a drought event and an extreme high temperature event occur simultaneously, then a compound dry heat event is considered to occur.
2. The method for identifying composite type dry heat event based on daily drought index as claimed in claim 1, wherein the process definition method of the drought event is as follows: the SPEI index has a value of less than-0.5 per day for 15 consecutive days,
wherein, the drought event process starts on a date when the SPEI value is less than-0.5 on day 1 and ends on a date when the SPEI value is less than-0.5 on the first day after the last day.
3. The method for identifying composite type dry heat event based on daily drought index as claimed in claim 2, wherein the method for defining the end of drought event process is as follows: and when the SPEI index is greater than or equal to-0.5 in 5 continuous days, ending the drought event process.
4. The method for identifying composite dry heat event based on daily drought index as set forth in any one of claims 1 or 2, wherein the severity of drought event S d Expressed as: during drought events, the sum of the absolute values of the individual daily SPEI indices over the duration of the drought event:
wherein the drought event duration D is the number of days from the beginning to the end of the drought event process.
5. The method for identifying composite type dry heat event based on daily drought index as set forth in claim 1, wherein the method for defining extreme high temperature event is as follows: day maximum temperature T for 3 consecutive days max All exceeding the daily high temperature threshold T d It is believed that an extreme height Wen Shijian occurs,
wherein daily high temperature threshold T d The 90% fraction of the daily maximum air temperature for 31 days, which is the same as the day of the given day of the past year, is calculated for 15 days before and after the day of the given day.
6. The method for identifying composite type dry heat event based on daily drought index as set forth in claim 5, wherein the severity S of said extreme high temperature event h Expressed as: accumulating and S the difference between the maximum daily air temperature and the threshold value for the extremely high temperature process h ：
7. The method for identifying composite type dry heat event based on daily drought index as set forth in claim 6, wherein the method for defining composite type dry heat event is as follows: when the day SPEI drought index reaches the drought event process starting day standard, and simultaneously exceeds and reaches the extreme high temperature event definition standard, namely, the composite type dry and hot event is considered to occur.
8. The method for identifying composite type dry heat event based on daily drought index as set forth in claim 7, wherein the continuous number of days D of composite type dry heat event is defined as the number of days continuously reaching the standard, and the severity S is defined as the severity S of drought event at the time of occurrence of event d And severity of extreme high temperature event S h The product of:
S＝S d ×S h 。
9. the method for identifying composite dry heat event based on a daily drought index as set forth in claim 7 wherein the number of consecutive days D of the composite dry heat event is defined as the number of days continuously reaching the criterion and the severity S is defined as: severity S of drought event when composite type dry heat event occurs d Normalized value and severity of extreme high temperature event S h Product of normalized values:
S＝S d standardization of ×S h normalization 。
Wherein the severity of the drought event S d The standardized method of (2) is as follows: severity S of all drought events when a composite dry heat event occurs within a given historical interval d Value mapping to [0,1 ]]Standardization is carried out in the interval;
severity S of the extreme high temperature event h The standardized method of (2) is as follows: severity S of all extreme high temperature events when a composite dry heat event occurs within a given history h Value mapping to [0,1 ]]Standardization is performed within the interval.
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