CN111259306B - Method for measuring and calculating crop coefficient in winter wheat area - Google Patents

Abstract

The invention belongs to the technical field of methods for measuring and calculating crop coefficients, and in particular relates to a method for measuring and calculating regional winter wheat crop coefficients. This method is based on the single crop coefficient method, and combined with the actual situation to improve the single crop coefficient method. Calculation of the crop coefficient, thus to the regional winter wheat crop coefficient map of the present invention. This method proposes the basic recommended values and correction formulas of crop coefficients suitable for China's planting regions, and combines map algebra to propose a regional single crop coefficient method, which is verified by the measured water demand data of winter wheat, in order to solve the transformation of crop coefficients from point to area It provides an effective way to solve difficult problems, and provides technical support for the planning, design and management of farmland water conservancy projects, water allocation between regions, and water allocation across river basins.

Description

A Calculation Method of Regional Crop Coefficient of Winter Wheat

technical field

The invention belongs to the technical field of crop coefficient calculation methods, and in particular relates to a method for measuring and calculating winter wheat regional crop coefficients.

Background technique

Wheat is one of the three major food crops in the world. Winter wheat accounts for 91% of the total wheat production and 90% of the sown area. The level of winter wheat production directly determines the total wheat production in my country, and irrigation is an important guarantee for wheat production. Irrigation water is the main component of agricultural water use. Irrigation water accounts for more than 90% of agricultural water use in my country. Crop water demand is the basis for formulating irrigation systems and an important basis for realizing agricultural water saving. Efficiency matters. Crop water demand is the sum of the water demand for inter-tree evaporation, plant transpiration, plant body composition, photosynthesis and other physiological processes under the conditions of suitable soil moisture, good growth and high yield level. Crop water demand is an important basis for the construction of the water rights system and the formulation of water laws. It is the basic data for the planning and design of farmland water conservancy projects in a country and region. The theoretical basis of operational research and other work is the guarantee for national economic development and decision-making. Therefore, it is very important to accurately determine the water requirement of crops.

The calculation of crop water requirement can be divided into direct method and indirect method. The direct method usually establishes the empirical relationship between the crop water demand and the main influencing factors based on the measured data of the crop water demand. This method has the advantages of simplicity and relatively accurate results. There are usually strict restrictions and cannot be directly applied. The indirect method is to obtain the crop water requirement by multiplying the reference crop evapotranspiration and the crop coefficient. The UN Food and Agriculture Organization volume 56 (FAO56) defines the reference crop evapotranspiration (Reference evapotranspiration, ET ₀ ) as the imaginary reference crop evapotranspiration rate , the crop height is 12cm, the reflectance is constant at 0.23, and the leaf surface resistance is 70s/m, which is similar to the evaporation of green grassland under the conditions of open surface, vigorous growth, complete coverage of the ground, and suitable soil moisture. Currently the most used method is the FAO56PenmanMonteith method based on energy balance and aerodynamic methods recommended by the Food and Agriculture Organization of the United Nations (FAO), also known as the comprehensive method. This method has a good physical basis, a wide range of applications, and does not require regional calibration. Meteorological conditions can be obtained ET ₀ .

The crop coefficient is the ratio of the actual crop water demand ET _c to the reference crop evaporation ET ₀ , the main influencing factors are the biological characteristics of the crop itself, soil moisture factors and cultivation management measures, and it has the interannual stability of the whole growth period, the growth stage Instability and regional characteristics. Crop coefficients are usually obtained through irrigation experiments. In traditional crop coefficient models, linear or nonlinear regression is often used to establish the regression relationship between influencing factors and crop coefficients. However, traditional crop coefficient models do not have a good physical basis and often It represents the point-scale crop coefficient model for irrigation experiments, which is closely related to local meteorology, soil, crops, etc., and cannot be directly applied to other areas without data.

The crop coefficient can also be obtained by the single crop coefficient method and the double crop coefficient method. However, the crop coefficient obtained by the single crop coefficient method and the double crop coefficient method are quite different from the measured value. The recommended value is not tailored for the Chinese region, and it is prone to large errors when used; moreover, the crop coefficient obtained by the single crop coefficient method is still on a point scale, and the spatial representativeness of the crop coefficient is unknown. Due to the large spatial variability of crop coefficients, these point-scale data cannot be directly used for other points, let alone replace the average value on a larger area. Water distribution and cross-basin allocation require crop coefficients and crop water requirements on different scales. Therefore, the water conservancy department has deployed irrigation test stations, central stations and terminal stations nationwide. However, due to limitations in manpower, material and financial resources, it is impossible to limit arrangement of observation sites. Therefore, how to use the limited irrigation test data to "expand" the application and production of more areas without irrigation data from point to area and from the irrigation test station is a difficult problem at present.

Contents of the invention

The current crop coefficient calculation method is based on irrigation experiments, and the crop coefficient empirical formula established through linear or nonlinear regression does not have a good physical basis. The weather, soil, and crops are closely related to other areas without data, and cannot be directly applied in other areas without data; and the crop coefficient recommended by FAO56 single crop coefficient method and double crop coefficient method are not tailored for China. Many studies have shown that the single crop coefficient method In addition, the crop coefficient obtained by the single-crop coefficient method is still point-scale, and the point-scale data cannot be directly used for other points, let alone replace a large area. The average value of the crop coefficient and the spatial representativeness of the crop coefficient are unknown defects and problems. The invention provides a method for measuring and calculating the regional crop coefficient of winter wheat.

The solution adopted by the present invention to solve the technical problems is: a method for measuring and calculating the regional crop coefficient of winter wheat, comprising the following steps:

The first step is to partition the research area, collect meteorological data and water demand data of winter wheat in different partitions in the research area, and divide the whole growth period of winter wheat in different partitions into early growth period, rapid growth period, middle growth period and late growth period;

The second step is to determine the typical climate conditions in the early, middle and late growth stages of each zone, that is, to determine the average measured value of 2m wind speed (u _2(obs) ) and the minimum relative humidity (RH _{min(obs) )} ) The average measured value for many years;

The third step is to carry out winter wheat water demand test according to each division, and determine the initial growth period, middle growth period and late growth period of winter wheat through the ratio of the measured winter wheat water demand ET _c to the reference crop evapotranspiration ET ₀ Crop coefficient measured value K _cini(obs) , K _cmid(obs) , K _cend(obs) ;

The fourth step is to compare the measured values of crop coefficients at different growth stages with the crop coefficients of the FAO56 single crop coefficient method to obtain the relative error between the single crop coefficient method winter wheat crop coefficient and the measured value;

Step 5. If the relative error is large, replace the crop coefficient recommended value of the FAO56 single-crop coefficient method with the average value of the measured value of the winter wheat crop coefficient, and use the measured 2m wind speed and minimum relative humidity in different zones obtained in the first step. Values replace the 2m wind speed and the minimum relative humidity limit values in the FAO56 single crop coefficient method, and the improved expression of the single crop coefficient is obtained,

In formula (1): K _c(obs) represents the multi-year average measured values of crop coefficients at each growth stage, respectively representing the multi-year average measured values of crop coefficients K _cini(obs) , K _cmid(obs) , K _cend(obs) , RH _min(obs) , u _2(obs) represent the minimum relative humidity RH _min and the 2m wind speed u ₂ of the corresponding growth stage, respectively, the multi-year average measured values;

If the relative error is small, use the single crop coefficient method;

The sixth step is to bring the improved single-crop coefficient or the expression of the single-crop coefficient method into the map algebra, and calculate the regional single-crop coefficient method for each pixel of the grid map, and obtain the regional winter wheat crop coefficient map.

In the above-mentioned method for calculating the regional crop coefficient of winter wheat, the calculation method of the single crop coefficient map of the winter wheat region in the sixth step is as follows: first, divide the winter wheat planting area into a grid, and select an appropriate grid size; secondly, the minimum relative humidity and 2m The wind speed raster map is loaded into ArcMap and displayed; finally, with the minimum relative humidity, 2m wind speed raster map and the measured value of crop coefficient as input, the improved single crop coefficient method expression is substituted into the map algebra, and each raster map The improved single-crop coefficient method is used to calculate the pixels, so as to obtain the crop coefficient map.

Beneficial effects of the present invention: the present invention is based on the multi-site winter wheat water demand test, tests the applicability of the FAO56 single crop coefficient method, and improves the single crop coefficient method, and proposes the crop coefficient basic recommendation value and correction formula suitable for China's planting divisions , combined with map algebra, put forward a regional single crop coefficient method, and verify it with the measured water demand data of winter wheat, provide an effective way to solve the problem of crop coefficient transformation from point to area, and provide a basis for the planning, design and management of farmland water conservancy projects, regional Provide technical support for inter-water allocation and cross-basin water allocation.

Description of drawings

Fig. 1 is a technical roadmap of the present invention.

Figure 2 is the calculation flow chart of the regional single crop coefficient method.

Fig. 3 is a distribution map of the winter wheat research area and irrigation test stations of the present invention.

Fig. 4 is the regional winter wheat crop coefficient distribution map of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Embodiment 1: The technical roadmap of the present invention is shown in Figure 1. Firstly, the basic data are processed, and the research area is divided into subregions to determine the typical climate conditions in the early, mid-growth, and late-growth stages of each subregion.

Secondly, according to different divisions, the average value of the measured value of the winter wheat crop coefficient is replaced by the recommended value of the crop coefficient of the FAO56 single crop coefficient method, and the average value of the measured 2m wind speed and the minimum relative humidity of the meteorological stations in different regions is replaced by the 2m value of the FAO56 single crop coefficient method. The defined values of wind speed and minimum relative humidity (2m/s and 45%) are used to obtain the improved single crop coefficient method. It is worth noting that 2m/s and 45% are data under "standard meteorological conditions", which are defined as sub-humid conditions with a minimum relative humidity of 45% and a weak wind of 2m with a wind speed of 2m/s Climate, 45% and 2m/s are the minimum relative humidity and the typical value of 2m wind speed under this specific sub-humid climate condition, simultaneously as the limit value of meteorological condition, it is a static value, and the present invention adopts the 2m of different growth stages of each division The multi-year average measured values of wind speed (u _2(obs) ) and the minimum relative humidity (RH _min(obs) ) are dynamically adjusted to better meet the climatic conditions of each region, which is conducive to improving the calculation accuracy of winter wheat crop coefficients.

Finally, combining the improved mono-crop coefficient method with map algebra, a regional mono-crop coefficient calculation method based on map algebra is proposed, referred to as the regional mono-crop coefficient method. The raster map of winter wheat crop coefficient was obtained by using the regional single crop coefficient method.

The method of the present invention is described in detail below in conjunction with the planting areas and planting conditions of my country's winter wheat.

The first step is to partition the study area. China's winter wheat is mainly distributed in Henan Province, Hebei Province, Shandong Province, Shanxi Province, Shaanxi Province, Anhui Province, Jiangsu Province, Beijing City, and Tianjin City. In combination with the research on China's wheat planting divisions, the present invention divides China's winter wheat planting areas into northern winter wheat areas. The wheat region, the Huanghuai winter wheat region, and the winter wheat region in the middle and lower reaches of the Yangtze River are shown in Figure 3. From Figure 3, it can be seen that the sown area of winter wheat in the three winter wheat regions accounts for 88.0% of the country's total, and the winter wheat production accounts for 91.4% of the country's total.

According to the observation results of irrigation test stations in different regions, the growth period of winter wheat was divided, and the division of winter wheat growth period is shown in Table 1. Since the growth period division of local observation data is different from the four-stage growth period generalized by FAO, it is necessary to transform the growth period. The initial growth stage includes the seedling stage and the greening stage, the rapid growth stage includes the greening stage and the jointing stage, the middle growth stage includes the heading stage and the filling stage, and the late growth stage is the maturity stage.

Table 1 Growth period division of winter wheat

The second and third steps are to determine the typical climate conditions in the early, middle and late growth stages of each subregion, and to determine the multi-year average measured value of 2m wind speed (u _{2 (obs)} ) and the minimum relative humidity (RH _min(obs) ) average measured values for many years; determine the measured values K _cini(obs) , K _cmid(obs) , and K _cend(obs) of winter wheat crop coefficients at the early growth stage, mid-growth stage, and late growth stage, see Table 2.

Table 2 Parameters of measured crop coefficients and typical climate values at each growth stage of winter wheat

The fourth step is to obtain the winter wheat crop coefficient _Kc according to the formula of the FAO56 single-crop coefficient method, and compare the measured value _Kc of the crop coefficient at each growth stage (see Table 2) with the crop coefficient of the FAO56 single-crop coefficient method to obtain the single-crop coefficient The relative error between the winter wheat crop coefficient and the measured value is shown in Table 3.

Table 3 Comparison results of the FAO56 single-crop coefficient method and the measured value of the crop coefficient

Table notes: 1. The winter wheat crop coefficient obtained by the single crop coefficient method; 2. The relative error between the winter wheat crop coefficient obtained by the single crop coefficient method and the measured value, relative error = (crop coefficient obtained by the single crop coefficient method - measured crop coefficient) / Measured crop factor × 100.

It can be seen from Table 3 that the calculated values of the crop coefficients at the seven stations in the early growth stage are all relatively small, and the relative error ranges from -47.0% to 23.5% in the other six stations except Feidong Station in Anhui, which is relatively small (-6.0%) The relative error in the mid-growth period is between -13.3% and 18.0%, among which the calculated values at Huoquan Station in Shanxi, Pingliang Station in Gansu, and Wangwu Station in Shandong are relatively large, while those at other stations are relatively small; the calculated values of crop coefficients at the late growth stage are all relatively small , the relative error range is between -46.1% - 36.5%. It can be seen that the calculation error of winter wheat by FAO56 single crop coefficient method is large. Because the FAO56 single-crop coefficient method has large errors in calculating winter wheat, the single-crop coefficient method was improved.

The fifth step is to replace the recommended crop coefficient value of the FAO56 single crop coefficient method with the average value of the measured value of the winter wheat crop coefficient, and to replace the 2m wind speed and the minimum relative humidity average value measured at different regional meteorological stations in the FAO56 single crop coefficient method. The limiting value of the minimum relative humidity (2m/s and 45%), thereby obtaining an improved single crop coefficient method, as shown in the following formula.

The sixth step is to bring the improved crop coefficient expression into the map algebra, and calculate the regional single crop coefficient method for each pixel of the grid map to obtain the regional winter wheat crop coefficient map.

Combining the improved single-crop coefficient method with map algebra, a regional single-crop coefficient calculation method based on map algebra is proposed, referred to as the regional single-crop coefficient method. The specific process is shown in Figure 2, and the details are as follows:

Firstly, the winter wheat planting area is divided into grids, and the appropriate grid size is selected. In ArcMap10.3, by default, the smaller value of the length and width of the research area is divided by 250 as the grid size, that is, the default grid size is 17.9km*17.9km, which meets the requirements for analyzing the spatial variability of crop coefficients.

Second, load the minimum relative humidity and 2m wind speed raster images into ArcMap for display.

Finally, taking the minimum relative humidity, the 2m wind speed raster map and the measured value of the crop coefficient as input, the improved single crop coefficient method is used as the map algebraic expression, and each pixel of the raster map is single-cropped according to the assignment parameter table 2. The coefficient method is used to calculate the regional winter wheat crop coefficient map, and the calculation flow chart is shown in Figure 2.

With the help of the map algebra of the ArcGIS environment, the calculation of the above-mentioned regional single-crop coefficient method can be realized. As a simple and powerful algebraic language, map algebra can be obtained with the help of the extension module SpatialAnalyst module of the ArcPy Python site package. ArcGIS can be realized by using map algebra. Spatial analysis tools, operators, and various functions to perform geographic analysis.

Using the regional single crop coefficient method, the distribution map of the regional winter wheat crop coefficient is obtained, as shown in Figure 4. It can be seen from Figure 4 that the overall pattern is as follows: the early, middle, late and full growth stages decrease from the Huanghuaihai winter wheat region to the north and the south, and the distribution of crop coefficients shows obvious plate characteristics. It can be seen from Figure 4a that the maximum value of the crop coefficient at the early growth stage appears in the Huanghuaihai winter wheat region (0.687), and the minimum value appears in the northern winter wheat region (0.625). The crop coefficients in each region are constant. It can be seen from Figure 4b that the high-value area of crop coefficient in the mid-growth period appears in the Shandong Peninsula (1.150-1.223) of the Huanghuaihai winter wheat region, and the low-value area appears in the northern part of Hebei, central Shanxi and Guanzhong in the northern winter wheat region (0.958 -1.000). It can be seen from Figure 4c that the high-value area of crop coefficient in the late growth period of winter wheat appears in the Huanghuaihai winter wheat area (0.750-0.857), and the low-value area appears in the winter wheat area of the middle and lower reaches of the Yangtze River (0.621-0.650). It can be seen from Figure 4d that the high value of the crop coefficient in the whole growth period appears in the Huanghuaihai winter wheat region, southern Anhui, and central Hunan (0.900-0.955), and the low value area appears in the southern Shanxi and central Hebei extending from central Shaanxi to the northeast. , Beijing, Tianjin, and western Liaoning (0.763-0.800).

The crop coefficients corresponding to the seven irrigation test stations in the above-mentioned crop coefficient raster map of each growth stage of winter wheat were extracted, and compared with the measured crop coefficients. The difference between the crop coefficient obtained by the regional single crop coefficient method and the measured crop coefficient is shown in Table 4.

Table 4 Comparison of crop coefficients obtained by regional single crop coefficient method and measured crop coefficients

It can be seen from the data in Table 4 that, except for the relative errors of Anhui Feidong Station and Jiangsu Lianshui Station, which are 17.7% and -13.1%, the absolute value of the crop coefficient error in the early growth stage is within 9.3%; Except for Wangwu Station in Shandong Province which is relatively large (13.7%), the absolute values of the relative errors of the other six stations are all less than 5.5%. Except for Huoquan Station in Shanxi Province and Shandong Central Station which are relatively small, the calculation values of the other five stations are all relatively large ; The relative error in the late growth period was between -6.0% and 9.6%. The calculated values at Shanxi Huoquan Station, Shandong Central Station and Anhui Feidong Station were relatively small, while the calculated values of the other four stations’ late growth crop coefficients were relatively large; all irrigation test stations were The relative errors of the growth period were all below 9.0%. Like the late growth period, the calculated values of the crop coefficients in the whole growth period of Shanxi Huoquan Station, Shandong Central Station and Anhui Feidong Station were relatively small, and the other four stations were all relatively large. It is worth noting that the coefficient of fast growing crops is not calculated. It has been verified that the accuracy of the crop coefficient obtained by the regional single crop coefficient method is significantly higher than that of the FAO single crop coefficient method, and it can be used to calculate the spatial distribution map of the crop coefficient.

Embodiment 2: This embodiment provides another method for calculating the crop coefficient of winter wheat, specifically as follows.

The first step is to partition the research area, collect the meteorological data of the irrigation experiment and the water demand experiment of winter wheat in the research area, and divide the whole growth period of winter wheat in different regions into early growth period, rapid growth period, middle growth period and late growth period;

The second step is to determine the typical climate conditions in the early, middle and late growth stages of each zone, that is, to determine the average measured value of 2m wind speed (u _2(obs) ) and the minimum relative humidity (RH _{min(obs) )} ) The average measured value for many years;

The third step is to carry out winter wheat water demand test according to each division, and determine the initial growth period, middle growth period and late growth period of winter wheat through the ratio of the measured winter wheat water demand ET _c to the reference crop evapotranspiration ET ₀ Crop coefficient measured value K _cini(obs) , K _cmid(obs) , K _cend(obs) ;

The fourth step, compare the crop coefficient measured value of crop coefficient with the crop coefficient of FAO56 single crop coefficient method, and obtain the relative error between the winter wheat crop coefficient of single crop coefficient method and the measured value;

The fifth step, the single crop coefficient method If the relative error between the winter wheat crop coefficient and the measured value is small, the single crop coefficient method is directly selected, specifically.

First, according to the characteristics of crop growth, the growth period of crops is generalized into four stages: the early growth period (from the sowing date until the ground coverage reaches 10%), the rapid development period (from the ground coverage of 10% to the effective full coverage of the ground), In the mid-growth period (from effective full coverage to the beginning of maturity) and the late growth period (from the beginning of maturity to harvest or complete senescence), then check FAO56 to determine the recommended crop coefficients under corresponding climate conditions: K _{cini (Tab)} , K _{cmid (Tab)} , K _{cend (Tab)} . Finally, the crop coefficients were corrected according to the climatic conditions in different stages.

(1) Determination of the crop coefficient (K _cini ) in the initial stage of growth

Taking winter wheat as an example, in the early growth stage of winter wheat, soil evaporation is dominant, and the influence of rainfall or irrigation on the crop coefficient needs to be considered. Soil evaporation is divided into two stages. The first stage is the "energy limited" stage, the potential evaporation rate E _so =1.15ET _o , and the duration of the drying process in the first stage is t ₁ =REW/E _so . When the wetting interval time t _w <t ₁ , that is the whole process of the first stage, at this time K _cini ＝E _so /ET _o ＝1.15;

When t _w >t ₁ , that is the second stage, the calculation formula of K _cini is:

In the formula, TEW is the total evaporated water in a drought cycle, mm; REW is the water that can be evaporated in the energy-limited stage, mm; t _w is the average interval of the wetting process, days; t ₁ is the duration of the first stage, days; _Eso is the potential evaporation rate, mm/d.

(2) Determination of mid-term crop coefficient (K _cmid )

When the local climatic conditions are not typical, that is, when the average minimum relative humidity RH≠45%, and the average wind speed u ₂ ≠2.0m/s at 2 meters, the crop coefficient value provided by FAO56 needs to be corrected according to the following formula:

K _cmid ＝K _cmid(tab) +[0.04(u ₂ -2)-0.004(RH _min -45)](h/3) ^0.3

In the formula, K _ctab is the recommended value of mid-term crop coefficient; u ₂ is the wind speed at 2 m in this stage, m/s; RH _min is the average value of the lowest relative humidity in this stage, %, and h is the average height of crops, in m.

(3) Determination of late crop coefficient (K _cend )

When the local climate conditions are not typical, that is, the minimum average relative humidity RH≠45%, and the average wind speed u ₂ ≠2.0m/s at 2 meters, it needs to be corrected according to the following formula:

K _cend ＝K _cend(tab) +[0.04(u ₂ -2)-0.004(RH _min -45)](h/3) ^0.3

In the formula, K _ctab is the late crop coefficient; U ₂ is the daily average wind speed at a height of 2 m in this stage, m/s; RH _min is the average value of the lowest relative humidity in this stage, %, and h is the average height of crops, in m. According to the provisions of FAO56, when the recommended value of late crop coefficient is less than 0.45, no correction is required.

When the minimum relative humidity data is lacking, the following formula can be used for calculation,

In the formula, T _max and T _min are daily maximum temperature and daily minimum temperature.

Substituting the calculation formula of the single crop coefficient method above into the map algebra as an expression, the regional single crop coefficient method is calculated for each pixel of the raster map, and the regional winter wheat crop coefficient map is obtained.

The above descriptions are only preferred embodiments of the present invention, and do not limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. Inside.

Claims (2)

1. a winter wheat regional crop coefficient measuring method is characterized in that: comprise the following steps: The first step is to partition the research area, collect the meteorological data of irrigation experiments in the research area and the water demand data of winter wheat, and divide the whole growth period of winter wheat in different partitions into early growth period, rapid growth period, middle growth period and late growth period; The second step is to determine the typical climate conditions in the early, middle and late growth stages of each zone, that is, to determine the average measured value of 2m wind speed (u _2(obs) ) and the minimum relative humidity (RH _{min(obs) )} ) The average measured value for many years; The third step is to carry out winter wheat water demand test according to each division, and determine the initial growth period, middle growth period and late growth period of winter wheat through the ratio of the measured winter wheat water demand ET _c to the reference crop evapotranspiration ET ₀ Crop coefficient measured value K _cini(obs) , K _cmid(obs) , K _cend(obs) ; The fourth step is to compare the measured values of crop coefficients at different growth stages with the crop coefficients of the FAO56 single crop coefficient method to obtain the relative error between the single crop coefficient method winter wheat crop coefficient and the measured value; Step 5. If the relative error is large, replace the recommended crop coefficient value of the FAO56 single crop coefficient method with the average value of the measured value of the winter wheat crop coefficient, and replace the average value of the 2m wind speed and the minimum relative humidity measured by different regional meteorological stations with the FAO56 single crop In the coefficient method, the 2m wind speed and the minimum relative humidity are defined, and the expression of the improved crop coefficient is obtained,

In the formula: Kc(obs) represents the multi-year average measured value of the crop coefficient in the early growth period, the middle growth period, the late growth period or the whole growth period, and RH _min(obs) and u _2(obs) respectively represent the minimum relative humidity RH _min of the corresponding growth stage and the multi-year average measured value of 2m wind speed _u2 ; If the relative error is small, use the single crop coefficient method; The sixth step is to bring the improved single-crop coefficient expression or single-crop coefficient expression into the map algebra, calculate the regional crop coefficient method for each pixel of the grid map, and obtain the regional winter wheat crop coefficient map. 2. a kind of winter wheat regional crop coefficient calculation method according to claim 1 is characterized in that: in the 6th step, the calculating method of winter wheat regional crop coefficient figure is: Firstly, the winter wheat planting area is divided into grids, and the appropriate grid size is selected; Second, load the minimum relative humidity and 2m wind speed raster images into ArcMap for display; Finally, taking the minimum relative humidity, the 2m wind speed raster map and the measured value of the crop coefficient as input, the improved single-crop coefficient expression or the single-crop coefficient expression is substituted into the map algebra, and each pixel of the raster map is improved. Calculation of the single crop coefficient method to obtain the crop coefficient map.

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