CN114510824A - Construction method of regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopy and root system - Google Patents
Construction method of regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopy and root system Download PDFInfo
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Abstract
The invention provides a construction method of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots, which comprises the following steps: s1, calculating net radiation, net radiation components and various influence factors through data of the area scale required by the PT-JPL model; s2, estimating the effective root depth Zr of the Chinese regional scale plant based on a Guswa model; s3, coupling the effective root depth Zr of the plants into a PT-JPL three-source evapotranspiration model to construct a regional scale evapotranspiration model synchronously considering vegetation canopy and root depth dynamic change. The model of the invention brings the dynamic vegetation change and the effective root depth of plants into the evapotranspiration calculation and analysis, not only considers the dynamic horizontal change (vegetation coverage) of the vegetation, but also considers the longitudinal change (root depth) of the vegetation change, and has the multi-scale analysis function, low requirements on ground data and aerodynamics, and promotion effect on the improvement of the estimation accuracy of the evapotranspiration and evapotranspiration components of the regional scale.
Description
Technical Field
The invention relates to the technical field of ecological environment monitoring, in particular to a construction method of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots.
Background
When the area scale ET is estimated, air resistance data (such as wind speed, earth surface impedance and vegetation height) are deficient, a physical mechanism is complex, and the coverage factors are numerous, so that the evapotranspiration ET not only depends on energy and water quantity, but also is closely related to various factors such as vegetation physiological processes in the vegetation change process, and the accurate estimation of the evapotranspiration of the area scale is difficult to achieve. In addition, the response of the evapotranspiration process of the regional scale to vegetation change is also greatly different, the physiological difference of different species is huge, and the estimation of the evapotranspiration not only introduces the vegetation type, but also comprehensively considers the common influence of the change of the vegetation in the horizontal direction (canopy coverage) and the change of the vegetation in the longitudinal direction (root depth of the vegetation) on the evapotranspiration.
The PT-JPL model is developed by Fisher ET al, reduces PET (potential evapotranspiration) estimated by Priestley-Taylor to a three-source evapotranspiration model of actual ET based on atmospheric and biological indexes, solves the problem that surface resistance is difficult to obtain due to simplicity and convenience of a calculation process, and enables the PT-JPL model and vegetation characteristics to be comprehensively coupled into reality.
Site observations provide the most reliable information for accurately partitioning the ET. However, since observation sites are sparse, measurement times are inconsistent, and ET partitioning on an area scale is difficult to obtain. The PT-JPL model provides an effective method for simulating ET division. However, the PT-JPL model lacks soil moisture constraints, only relies on the requirements of atmospheric evaporation and transpiration and biophysical factors to represent ground conditions, and is not suitable for complex underlying surface conditions or arid regions. Because at higher atmospheric evapotranspiration demands, soil moisture may not be sufficient to meet the evapotranspiration demand. Previous PT-JPL models use canopy height to characterize the sensitivity of plants to soil moisture, i.e., the higher the canopy height the less sensitive the vegetation is to soil moisture deficiency. However, Zr may be more reflective of the plant's sensitivity to soil moisture than the canopy height, since the plant's water uptake depth varies with Zr. On the one hand, Zr influences the distribution of soil moisture through soil hydraulics, and moisture is transferred from moist soil to dry soil through the root system. On the other hand, Zr affects water, energy and carbon exchange between soil, vegetation and the atmosphere due to the tight coupling between land water, energy and carbon cycles. In addition, Zr is critical to the accurate simulation of many hydrological and biogeochemical models. Therefore, Zr is necessary to be included in the PT-JPL model so as to optimize the characterization of soil moisture on evapotranspiration and improve the model performance of the model.
Although Zr plays an important role in hydrological models and biogeochemical processes, there is still great uncertainty in the distribution and quantification of Zr. The existing model considers Zr in a simplified way. For example, in the Noah-MP mode, Zr is set to 1m for all crop types, regardless of the spatio-temporal variation of Zr. Also, in the Community Land Model (CLM)3.5, soil moisture simulation used fixed Zr. In CLM4-Crop, Zr is also expressed as a static equation. Taking into account the dynamic nature of the plant rooting depth, it is not practical to use a fixed Zr value. But Zr is difficult to parameterize in large scale mode due to lack of observation data. Therefore, we need a model to quantify Zr for each analysis unit and incorporate it into the hydrological model. Guswa (2008) developed a model to balance marginal carbon cost and yield of deep roots to estimate Zr. The model combines carbon constraints and actual water stress with vegetation transpiration through the coupling of a dynamic soil water model. These features make the Guswa model more widely applicable in hydrology.
In the area where the vegetation changes severely, the current model has the problem of low accuracy in quantifying ET and the partition thereof. Therefore, it is necessary to construct a model that comprehensively considers the cooperative variation of vegetation canopy and root system to accurately quantify ET and its partition, and the problem of accuracy of long-time-scale evapotranspiration estimation is not trivial.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a construction method of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots. The invention aims to provide a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and root depths. On the basis of a PT-JPL three-source evapotranspiration model, effective root depth of vegetation is introduced by adding soil moisture influence and combining a Guswa root depth model, and further an area scale evapotranspiration model synchronously considering dynamic changes of a vegetation canopy and a root system is established by combining vegetation canopy data.
The purpose of the invention is realized by the following scheme:
the invention provides a construction method of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots, which comprises the following steps:
s1, calculating the net radiation R through the data of the required area scale of the PT-JPL modelnNet radiation component RnsAnd RncAnd each influencing factor;
s2, estimating the effective root depth Zr of the plant with a preset area scale based on a Guswa model;
s3, evaporating effective root depth Zr in vegetation transpiration T and soil EbThe soil water action in the model is coupled into a PT-JPL three-source evapotranspiration model to construct a regional scale evapotranspiration PT-JPLzr model synchronously considering dynamic changes of vegetation canopy and root depth:
ET＝T+Eb+Ei
in the formula (f)wetRelative surface humidity; f. ofrewIs a soil moisture and soil property constraint; alpha isThe Priestley-Taylor mode coefficient takes a value of 1.26; delta is the temperature-saturated water vapor pressure slope; gamma is a dry-wet table constant, and the value is 0.066; rnsFor surface soil net radiation (W.m)-2) (ii) a G is ground heat flux (W.m)-2)；fg、ftAnd ftrmRespectively green canopy fraction, plant temperature constraint and ecological physiological scalar, ET is evapotranspiration (mm), E isiThe evaporation (mm) was retained for the canopy.
Further, in step S1, the net radiation RnNet radiation component RnsAnd RncThe calculation method of (2) is as follows:
Rn＝Rnshort-Rnlong
wherein R isnIs net radiation, RnshortAnd RnlongRespectively net short wave radiation and net long wave radiation; the calculation method comprises the following steps:
Rnshort＝(1-p)It
Rnlong＝Rld-Rlu
Rlu＝σT4
wherein p is the ground surface albedo, ItIs downward short wave radiation (W.m)-2)，RldIs downward long-wave radiation (W.m)-2)，RluIs upward long-wave radiation (W.m)-2) T is the air temperature (K) and σ is the Stefan Boltzmann constant (5.67X 10)-8W·m-2·K-4)。
Rnc＝Rn-Rns
Wherein R isnsFor net radiation (W.m) to reach the soil surface-2)，RncIs net radiation (W.m) intercepted by the canopy-2)，
Is extinction coefficient, value is 0.6, LAI is leaf area index; source of LAIIn MODIS (MODERATE-resolution Imaging Spectrophotometer) the spatial resolution is 500 meters and the temporal resolution is 8 days (https:// lpdaac. usgs. gov/products/mod15a2hv006 /).
Further, in step S1, calculation of each influence factor
fwet＝RH4
fAPAR＝m1EVI+b1
fIPAR＝m2NDVI+b2
Wherein f iswetRelative surface humidity, fgIs the proportion of green canopy, ftAs a temperature limiting factor, fmIs a water limiting factor, fAPARmaxIs fAPARRH is the relative humidity, TmaxThe maximum air temperature (. degree. C.), ToptIs the optimum growth temperature (DEG C) of vegetation, EVI is the enhanced vegetation index, NDVI is the normalized vegetation index, fAPARIs the PAR coefficient absorbed by the crown, fIPARIs the PAR coefficient intercepted by the crown, the PAR coefficient being the proportion of photosynthetically active radiation, b1＝-0.048，b2＝-0.05，m2＝1，m1＝1.3632。
Further, in step S2, the method for calculating the effective root depth Zr of the plant is as follows:
θp＝θfc-θw
W＝P/PT
wherein, Zr is the effective root depth (cm) of the plant, alpharIs the average depth of rainfall (cm), θpIs effective water content (cm) of plant3·cm-3)，θfcIs the field water holding capacity (cm)3·cm-3)，θwW is the ratio of the average annual precipitation (P, mm) to the potential transpiration rate (PT, mm) for the wilting coefficient;
the calculation formula of A is as follows:
WUE＝GPP/ET
wherein PT represents potential transpiration (mm), γrIs the actual root respiration rate (gCg)-1roots d-1)，
The respiration rate of the root (g Cg) at 20 deg.C-1roots d-1)，TaAir temperature (. degree. C.), Q10As a temperature coefficient, the change in the root respiration rate (g Cg) per 10 ℃ rise in temperature is shown-1roots d-1) Here, take Q10Is 2.0; RLD is root length density, SRL is specific root length, RLD is set to 0.1cm root cm-3soil, SRL set to 1500cm root g-1root, WUE is the ratio of the sum of the primary production values GPP to ET, fGSIs the growing season length fraction based on the leaf area index.
Further, in step S3, frewThe soil moisture and soil property are aboutBundle, the calculation method is as follows:
wherein, thetaobsAs observed value of soil humidity (cm)3·cm-3)，θwTo the wilting coefficient, thetafcIs the field water holding capacity (cm)3·cm-3)。
Further, in step S3, ftrmFor an ecological physiological scalar, the calculation method is as follows:
ftrm＝(1-RH4(1-VWC)(1-RH))fm+(RH4(1-VWC)(1-RH))ftrew
wherein RH is relative humidity, VWC is volume water content (cm)3·cm-3)，fmIs a water limiting factor, ftrewThe sensitivity of vegetation transpiration to soil moisture.
Further, in step S3, ftrewThe calculation method of (2) is as follows:
wherein, thetacrIs a critical soil moisture (cm) limiting ET for soil moisture availability3·cm-3)，θobsAs observed value of soil humidity (cm)3·cm-3)，
The withering coefficient of the surface soil water after the rooting depth of the plants is adjusted, ZrscalarThe root system depth (m) is shown.
Further, in step S3,
wherein the content of the first and second substances,
adjusting the surface soil water withering coefficient theta for the plant rooting depthwTo the wilting coefficient, thetacrIs a critical soil moisture (cm) limiting ET for soil moisture availability3·cm-3) (ii) a p is a limiting factor of soil moisture effectiveness on transpiration, and is mainly related to potential transpiration and water absorption depth (root depth) of plants; thetafcExpressed as the field water capacity (cm)3·cm-3) (ii) a PET stands for latent Evaporation (mm. d)-1) (ii) a a represents Zr vs. thetacrThe weight of the influence is applied, which takes a value of 0.1.
Further, in step S3, EiFor canopy interception evaporation, the calculation method is as follows:
wherein f iswetRelative surface humidity, alpha is a Priestley-Taylor mode coefficient and takes a value of 1.26, delta is a temperature-saturated water vapor pressure slope, gamma is a psychrometric constant and takes a value of 0.066, RncIs net radiation (W.m) intercepted by the canopy-2)。
The invention provides a construction system of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots, which comprises the following steps:
block M1, calculating the net radiation R from the data of the area dimensions required by the PT-JPL modelnNet radiation componentRnsAnd RncAnd each influencing factor;
the module M2 is used for estimating the effective root depth Zr of the plant with a preset area scale based on a Guswa model;
module M3, effective root depth Zr of plant is evaporated in vegetation transpiration T and soil EbThe soil water action in the model is coupled into a PT-JPL three-source evapotranspiration model to construct a regional scale evapotranspiration model synchronously considering vegetation canopy and root depth dynamic changes:
ET＝T+Eb+Ei
in the formula (f)wetRelative surface humidity; f. ofrewIs a soil moisture and soil property constraint; alpha is a prime-Taylor mode coefficient and takes a value of 1.26; delta is the temperature-saturated water vapor pressure slope; gamma is a dry-wet table constant, and the value is 0.066; rnsNet radiation of surface soil; g is ground heat flux; f. ofg、ftAnd ftrmRespectively green canopy fraction, plant temperature constraint and ecological physiological scalar, ET is evapotranspiration, EiEvaporation was trapped for the canopy.
Compared with the prior art, the invention has the following beneficial effects:
1. according to the invention, an area scale evapotranspiration model synchronously considering dynamic changes of the vegetation canopy and the root system is constructed, and ET simulated by the PT-JPL model after the dynamic changes of the vegetation canopy and the root system are synchronously considered, so that the actual evapotranspiration of an area with a large scale can be displayed, the defect of estimating evapotranspiration by the existing method is overcome, and the simulation performance of ET components is obviously improved.
2. The invention constructs a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots, and comprehensively and widely solves the problems of influence of vegetation changes on evapotranspiration and the like by comprehensively considering horizontal and longitudinal changes of vegetation and aboveground and underground characteristics. The method can provide a foundation for hydrological, meteorological and agricultural research in the region, clears the relation between water resource consumption of regional scale and vegetation level and longitudinal change, is used for further analyzing the water resource utilization potential, and discusses the influence of ground change and underground on water resources of large-area ecological restoration engineering (vegetation reconstruction engineering) in arid and semiarid regions.
3. The regional scale transpiration model which synchronously considers the dynamic changes of the vegetation canopy and the root system is constructed as a three-source transpiration model, the physical mechanism of transpiration is raised by one step through the comprehensive consideration of vegetation, and powerful technical and data support is provided for hydrological, meteorological and agricultural researches.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a comparison of simulated evapotranspiration of an unmodified PT-JPL model and a modified PT-JPL model with site observed evapotranspiration, an open square represents the original PT-JPL model, a black dot represents the simulated monthly evapotranspiration of the modified PT-JPL model, the oblique line is a 1:1 line, and the closer to the 1:1 line, the more accurate the representation is;
fig. 2 is a comparison of the ratio of evapotranspiration components (retained evaporation (Ei) and vegetation transpiration (T)) to total Evapotranspiration (ET), and the results can reflect the accuracy of the model in the simulation of the evapotranspiration components. FIG. 2a is the spatial distribution of (T + Ei)/ET for the original PT-JPL model (ranging between 0-1, average (T + Ei)/ET over the entire area of China is 0.48), FIG. 2b is the spatial distribution of (T + Ei)/ET for the modified PT-JPL model (ranging between 0-1, average (T + Ei)/ET over the entire area of China is 0.58), and FIG. 2c is the spatial distribution of (T + Ei)/ET for the GLEAM evapotranspired product (the GLEAM product is currently accepted as a better evapotranspired product, ranging between 0-1, average (T + Ei)/ET over the entire area of China is 0.60).
FIG. 3 is a comparison of the average (T + Ei)/ET values of the original PT-JPL model, the modified PT-JPL model (PT-JPLzr model) and the GLEAM product in different vegetation types.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
The invention provides a regional scale evapotranspiration estimation method synchronously considering dynamic changes of vegetation canopies and roots, which comprises the following steps: (1) estimation of plant effective root depth (Zr); (2) synchronously considering the estimation of the area scale evapotranspiration model of the dynamic changes of the vegetation canopy and the root system: inputting net radiation data of a required region scale by a calculation model; calculating the net radiation component RnsAnd Rnc(ii) a Calculating each influence factor; firstly, adding soil water change into an original PT-JPL model, then coupling Zr into a three-source evapotranspiration model to construct a PT-JPLzr model, and further performing simulated estimation on the evapotranspiration ET; (3) and verifying the simulation effect of the regional scale evapotranspiration model synchronously considering the dynamic changes of the vegetation canopy and the root system. The model of the invention brings the dynamic vegetation change and the effective root depth of plants into the evapotranspiration calculation and analysis, not only considers the dynamic horizontal change (vegetation coverage) of the vegetation, but also considers the longitudinal change (root depth) of the vegetation change, and has the multi-scale analysis function, low requirements on ground data and aerodynamics, and promotion effect on the improvement of the estimation accuracy of the evapotranspiration and evapotranspiration components of the regional scale.
The estimation method of the regional evapotranspiration of the original PT-JPL three-source evapotranspiration model comprises the following steps:
(1) computing the net radiation data for the region scale required for model input
Rn＝Rnshort-Rnlong
Wherein R isnIs net radiation, RnshortAnd RnlongRespectively net short wave radiation and net long wave radiation;
(2) calculating the net radiation component RnsAnd Rnc
Rnc＝Rn-Rns
Wherein R isnsFor net radiation to reach the soil surface, RncIs the net radiation intercepted by the canopy,
is extinction coefficient, value is 0.6, LAI is leaf area index;
(3) calculation of the respective influencing factors
fwet＝RH4
fAPAR＝m1EVI+b1
fIPAR＝m2NDVI+b2
fsm＝RHVPD/β；
Wherein f iswetRelative surface humidity, fgIs the proportion of green canopy, ftIs a temperature limiting factor, fmIs a water limiting factor, fsmIs a soil water limiting factor, fAPARmaxIs fAPARRH is the relative humidity, TmaxThe maximum air temperature (. degree. C.), ToptIs the optimum growth temperature (deg.C) of vegetation, VPD is the saturated water vapor pressure differential (kPa), EVI is the enhanced vegetation index, NDVI is the normalizationIndex of vegetation, beta being fsmSensitivity to VPD, fAPARIs the PAR coefficient absorbed by the crown, fIPARIs the PAR coefficient intercepted by the crown, the PAR coefficient being the proportion of photosynthetically active radiation, b1＝-0.048，b2＝-0.05，m2＝1，m1And beta is a parameter to be optimized, m is more than or equal to 01≤1.4，0≤β≤1；
(4) Simulated estimation of evapotranspiration ET
ET＝Et+Eb+Ei
Wherein E isbEvaporation capacity (mm) of bare soil, EtThe transpiration amount (mm) of vegetation, EiThe canopy retains the evaporation capacity (mm), fwetRelative surface humidity, fgIs the proportion of green canopy, ftIs a temperature limiting factor, fmIs a water limiting factor, fsmIs a soil water limiting factor, G is a soil heat flux (W.m)-2) Alpha is a Priestley-Taylor mode coefficient and takes a value of 1.26, delta is a temperature-saturated water vapor pressure slope, and gamma is a dry-wet table constant and takes a value of 0.066.
The invention provides a regional scale evapotranspiration estimation method synchronously considering dynamic changes of vegetation canopies and roots, which comprises the following steps:
s1, calculating the net radiation R through the data of the required area scale of the PT-JPL modelnNet radiation component RnsAnd RncAnd each influencing factor;
net radiation RnNet radiation component RnsAnd RncThe calculation method of (2) is as follows:
Rn＝Rnshort-Rnlong
wherein R isnIs net radiation, RnshortAnd RnlongNet short wave radiation and net long wave radiation, respectively; the calculation method comprises the following steps:
Rnshort＝(1-p)It
Rnlong＝Rld-Rlu
Rlu＝σT4
wherein p is the ground surface albedo, ItIs downward short wave radiation (W.m)-2)，RldIs downward long-wave radiation (W.m)-2)，RluIs upward long-wave radiation (W.m)-2) T is the air temperature (K) and σ is the Stefan Boltzmann constant (5.67X 10)-8W·m-2·K-4)。
Rnc＝Rn-Rns
Wherein R isnsFor net radiation (W.m) to reach the soil surface-2)，RncIs net radiation (W.m) intercepted by the canopy-2)，
The extinction coefficient is 0.6, LAI is a leaf area index, the LAI is derived from MODIS (modified-resolution Imaging Spectrophotometer), the spatial resolution is 500 meters, and the time resolution is 8 days (https:// lpdaac. usgs. gov/products/mod15a2hv006 /);
the calculation method of each influence factor is as follows:
fwet＝RH4
fAPAR＝m1EVI+b1
fIPAR＝m2NDVI+b2
wherein f iswetRelative surface humidity, fgIs the proportion of green canopy, ftIs a temperature limiting factor, fmIs a water limiting factor, fAPARmaxIs fAPARRH is the relative humidity, TmaxIs the maximum air temperature, ToptIs the optimum growth temperature of vegetation, EVI is the enhanced vegetation index, NDVI is the normalized vegetation index, fAPARIs the PAR coefficient absorbed by the crown, fIPARIs the PAR coefficient intercepted by the crown, the PAR coefficient being the proportion of photosynthetically active radiation, b1＝-0.048，b2＝-0.05，m2＝1，m1＝1.3632。
S2, estimating the effective root depth Zr of the Chinese regional scale plant based on a Guswa model;
the dynamic variation of the effective rooting depth (Zr) of plants was simulated using a carbon cost benefit model (Guswa). The Guswa carbon cost-benefit model is based on the principle that the deeper the root system, the more soil moisture the plant can obtain, so that the plant is protected from long-term water stress during meteorological drought, and the larger total carbon absorption amount is realized. On the other hand, the construction and maintenance of additional roots consumes more carbon. Therefore, there must be an optimal rooting depth so that the marginal carbon gain associated with any additional root systems balances the marginal carbon costs of those root systems.
The calculation method of the effective root depth Zr of the plant is as follows:
θp＝θfc-θw
W＝P/PT
wherein, Zr is the effective root depth (cm) of the plant, alpharThe average rainfall depth is based on the Chinese Meteorological forcing data set (CMFD) 3-hour rainfall data set (mm; the range of values is 0.2-61.7), thetapIs effective water content (cm) of plant3·cm-3)，θfcIs the field water holding capacity (cm)3·cm-3)，θwIs the wilting coefficient (cm)3·cm-3) W is the ratio (in units) of the annual average precipitation (P) to the potential transpiration rate (PT);
the calculation formula of A is as follows:
WUE＝GPP/ET
wherein PT represents potential transpiration (mm), γrAs the actual root respiration rate (g Cg)-1roots d-1)，
The respiration rate of the root at 20 ℃ (g C g)-1roots d-1)，TaAir temperature (. degree. C.), Q10As a temperature coefficient, a change in the root respiration rate per 10 ℃ rise in temperature is shown, where Q is taken10Is 2.0; RLD is root length density (cm root. cm)-3soil), SRL is longer than root (cm root. g)-1root), RLD is set to 0.1cm root cm-3soil, SRL set to 1500cm root g-1root, WUE is the total number of elementary productions GPRatio of P to ET, fGSBased on the growth season length fraction of the leaf area index (LAI, the value range is 0-1), the annual size Zr of 1982 + 2011 is calculated as the dynamic effective rooting depth of plants in China.
S3, evaporating effective root depth Zr in vegetation transpiration T and soil EbThe soil water action in the model is coupled into a PT-JPL three-source evapotranspiration model, and a regional scale evapotranspiration PT-JPLzr model synchronously considering dynamic changes of vegetation canopy and root depth is constructed: ei's algorithm is consistent with original PT-JPL, soil evaporation EhThe calculation method comprises the following steps:
ET＝T+Eb+Ei
wherein f iswetRelative surface humidity, alpha is a Priestley-Taylor mode coefficient and takes a value of 1.26, delta is a temperature-saturated water vapor pressure slope, gamma is a psychrometric constant and takes a value of 0.066, RncIs the net radiation intercepted by the canopy (W.m-2); f. ofrewConstraints for soil moisture and soil properties (dimensionless); rnsFor surface soil net radiation (W.m)-2) (ii) a G is ground heat flux (W.m)-2)；fg、ftAnd ftrmRespectively green canopy fraction, plant temperature constraint and ecological physiological scalar, ET is evapotranspiration, EiFor canopy retention and evaporation, T for vegetation transpiration, EbEvaporating soil;
frewfor soil moisture and soil property constraints, the calculation method is as follows:
wherein, thetaobsAs observed value of soil humidity (cm)3·cm-3)，θwTo the wilting coefficient, thetafcIs the field water capacity.
ftrmIs an ecological physiological scalar, and the calculation method is as follows:
ftrm＝(1-RH4(1-VWC)(1-RH))fm+(RH4(1-VWC)(1-RH))ftrew
wherein RH is relative humidity (%), VWC is volume water content, fmIs a water limiting factor, ftrewThe sensitivity of vegetation transpiration to soil moisture.
ftrewThe calculation method of (2) is as follows:
wherein, thetacrIs the critical soil moisture, θ, of the soil moisture availability limit ETobsAs observed value of soil humidity (cm)3·cm-3)，
The withering coefficient of the surface soil water after the rooting depth of the plants is adjusted, ZrscalarRoot depth Zr of root systemwTo the wilting coefficient, thetacrIs critical soil moisture for which soil moisture availability limits ET; p is a limiting factor of soil moisture effectiveness on transpiration, and is mainly related to potential transpiration and water absorption depth (root depth) of plants; thetafcIs the field water holding capacity (cm)3·cm-3) (ii) a PET stands for latent evaporation (mm); a is a parameter representing Zr vs. thetacrThe weight of the influence is applied, which takes a value of 0.1.
The data sources in the model of the invention are as follows:
the remote sensing data for driving the PT-JPL model comprises: MODIS (MODERATE-resolution Imaging Spectrophotometer) enhanced vegetation index (enhanced vegetation index; EVI; https:// lpdaac. usgs. gov/products/mod13a1v006/), normalized difference vegetation index (normalized difference vegetation index; NDVI; https:// lpdaac. usgs. gov/products/mod13a1v006/), and leaf area index (leaf area index; LAI; https:// lpdaac. usgs. gov/products/mod13a1v006/) were 500 meters in spatial resolution and 8 days in temporal resolution. Vegetation indices between 1982 and 2000 used AVHRR LAI, AVHRR EVI (http:// glcf. umd. edu/data /) and GIMMS NDVI (https:// glam1.gsfc. nasa. gov), with a spatial resolution of 8 km. The AVHRR and MODIS albedo data were used to calculate the regional-scale net radiance in 1982-2000 and 2001-2015, respectively. The original Sinusoid projection of MODIS products is converted into UTM-WGS84 projection by using MRT (MODIS reproduction tool). The data were resampled to 0.1 using a distance square weighting method. albedo (surface albedo) albedo data was used to quantify the net radiance, with a resolution of 0.05 °, derived from the GLASS product, and provided by the national Earth systems science data center (http:// www.geodata.cn/the mathVIEW/GLASS. html). The surface coverage data used in the invention is derived from the surface coverage data of MODIS 2001-2013. These data were resampled to a spatial resolution of 0.1 using an inverse distance weighted average method.
Soil hydraulic characteristic data is provided by a high resolution global soil hydraulic characteristic map (https:// dataverse. harvard. edu/dataset. xhtmlpersisteld ═ doi:10.7910/DVN/UI5 LCE).
The PT-JPL model is driven by using a China regional high space-time resolution earth surface meteorological data set (CMFD) as regional scale meteorological input data. CMFD is from research institute of Qinghai-Tibet plateau of Chinese academy of sciences, and has a data range covering the whole region of China mainland, a spatial resolution of 0.1 degree multiplied by 0.1 degree, and a time length of 1979 to 2015. The data content mainly comprises seven variables of precipitation rate, specific humidity, air temperature, air pressure, full wind speed, downward long wave radiant flux and downward short wave radiant flux. The data set combines data of an observation station of China weather bureau, TRMM satellite precipitation observation data, global water energy conversion earth surface radiation budget (GEWEX-SRB) and a Princeton driving data set. Researchers have confirmed that CMFD is highly accurate and is widely used in hydrological process analysis and model construction. In the invention, CMFD data is used as observation data of an area scale, and a PT-JPL model is driven to simulate area evapotranspiration. The microwave assimilation-based Chinese soil humidity data set is derived from the national Qinghai-Tibet plateau science/third-pole environment data center.
The Evaporation rate of the Global terrestrial evapotranspiration is estimated by GLEAM (Global Land evolution evaporative Model; https:// www.gleam.eu /) using precipitation, soil moisture and vegetation moisture content as limiting conditions, and different components of the Global terrestrial evapotranspiration are calculated: transpiration (Et), soil evaporation (Eb), retention loss (Ei), water Evaporation (EW) and sublimation for a length of 2016 (1980) with a spatial resolution of 0.25 ℃ by 0.25 ℃ (Martens Et al, 2016; Miralles Et al, 2011; Miralles Et al, 2010 b). The verification result based on flux observation data shows that the GLEAM model has better simulation precision in different ecosystems, so ET, Et, Eb and Ei in GLEAM v3.1a are utilized to compare with the performance of the PT-JPL model after the parameters are optimized.
Land use data as used herein is derived from MODIS land use data (https:// lpdaac. usgs. gov/products/mcd12q1v006 /). The MODIS land use types are divided into 17 types according to the definition of the International space biosphere (IGBP) plan, the spatial resolution is 500 meters, the time length is 2001-2013 for 13 years, and the land use types are replaced by the land use types of 2013 every year in 2014 and 2015.
The simulation results of the PT-JPLzr model coupled with the effective root depth of the plant are verified by utilizing observed ET data of 17 vegetation types in China (figure 1), and as can be seen from the figure, black dots (improved PT-JPL model) are closer to 1:1 line, the improved PT-JPL model is proved to have better simulation result on evapotranspiration.
The PT-JPLzr model not only adds the influence of vegetation level dynamic change, but also brings the characteristics of vegetation root longitudinal change into consideration, comprehensively considers the absorption effect of vegetation water consumption on soil moisture, constructs a regional scale evapotranspiration estimation method synchronously considering dynamic changes of vegetation canopy and root system, further comprehensively analyzes the response mechanism of the regional scale evapotranspiration on vegetation change and soil moisture change, optimizes the simulation performance of the model on evapotranspiration components, provides a new idea and a new method for improving the accuracy of evapotranspiration estimation in regions with severe vegetation change on the regional scale, and proves that the optimized model has a good simulation effect.
The original PT-JPL model is combined with soil moisture and vegetation root depth, the constructed PT-JPLzr model comprehensively considers the change of vegetation in the ground, incorporates soil moisture constraint and improves the performance of the model in arid areas and areas with severe vegetation change.
In addition, the proportion of the PT-JPLzr model to the ET components (vegetation transpiration T, soil evaporation Eb and trapped evaporation Ei) simulated by the Original PT-JPL model is greatly improved, as shown in FIGS. 2 and 3, the results of FIG. 2 show that the improved PT-JPLzr model (with a space average of 0.58) is more consistent with the Original PT-JPL model (origin) (with a space average of 0.48) and the (T + Ei)/ET (with a space average of 0.60) of the GLEAM, and in the southern China, the improved PT-JPL model is closer to the GLEAM model and the Original model is smaller in whole. Therefore, the improved PT-JPL model not only improves the simulation performance of the total ET, but also greatly improves the simulation of the ET component. The results in FIG. 3 show that the improved PT-JPL model simulates the evapotranspiration component better than the original model in different vegetation types compared to the GLEAM product.
The constructed PT-JPLzr new model perfects the mechanism of the original model along with the introduction of soil moisture and root depth, so that the proportion of (T + Ei)/ET is increased by 22 percent compared with the original model, and the result of other models is approximate.
A construction system of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots comprises:
module M1, calculating the Net radiation R from the data of the regional scales required by the PT-JPL modelnNet radiation component RnsAnd RncAnd each influencing factor;
the module M2 is used for estimating the effective root depth Zr of the plant with a preset area scale based on a Guswa model;
module M3, effective root depth Zr of plant is evaporated in vegetation transpiration T and soil EbThe soil water action in the model is coupled into a PT-JPL three-source evapotranspiration model to construct a regional scale evapotranspiration model synchronously considering vegetation canopy and root depth dynamic changes:
ET＝T+Eb+Ei
in the formula (f)wetRelative surface humidity; f. ofrewIs a soil moisture and soil property constraint; alpha is a prime-Taylor mode coefficient and takes a value of 1.26; delta is the temperature-saturated water vapor pressure slope; gamma is a dry-wet table constant, and the value is 0.066; rnsNet radiation of surface soil; g is ground heat flux; f. ofg、ftAnd ftrmRespectively green canopy fraction, plant temperature constraint and ecological growthScalar quantity, ET is evapotranspiration, EiEvaporation was trapped for the canopy.
Finally, ET simulated by the PT-JPL model after vegetation canopy and root dynamic changes is synchronously considered, actual evapotranspiration of a full-Chinese-scale area is shown, the defect that evapotranspiration is estimated by the existing method is overcome, and the simulation performance of ET components is remarkably improved. The influence of soil moisture limitation on evapotranspiration is comprehensively considered, the method is more suitable for complex underlying surfaces and arid regions, and scientific support and technical schemes are provided for solving the main technical problems existing in the calculation of the evapotranspiration with large scale at present. The influence of dynamic changes of vegetation canopies and roots on regional evapotranspiration changes is synchronously considered, vegetation level change characteristics and longitudinal change characteristics are simultaneously brought into evapotranspiration calculation and analysis, the effects of different vegetation on evapotranspiration can be comprehensively analyzed, the method also has the advantage of few PT-JPL original model aerodynamic parameters, has low requirements on ground data and aerodynamics, and plays a promoting role in improving the accuracy of estimation of regional scale evapotranspiration. The simulation result of the PT-JPLzr model not only improves the evapotranspiration precision, but also improves the calculation precision of the ET component by 22 percent, thereby realizing that the three-source evapotranspiration model provides a new method for estimating the ET component of various vegetation types in different climatic regions, and providing reference for accurate calculation of the evapotranspiration component of the regional scale.
Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, units provided by the present invention as pure computer readable program code, the system and its various devices, modules, units provided by the present invention can be fully implemented by logically programming method steps in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system and various devices, modules and units thereof provided by the present invention can be regarded as a hardware component, and the devices, modules and units included therein for implementing various functions can also be regarded as structures within the hardware component; means, modules, units for performing the various functions may also be regarded as structures within both software modules and hardware components for performing the method.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A construction method of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots is characterized by comprising the following steps:
s1, calculating the net radiation R through the data of the required area scale of the PT-JPL modelnNet radiation component RnsAnd RncAnd each influencing factor;
s2, estimating the effective root depth Zr of the plant with a preset area scale based on a Guswa model;
s3, evaporating effective root depth Zr in vegetation transpiration T and soil EbThe soil water action in the model is coupled into a PT-JPL three-source evapotranspiration model to construct a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and root depths:
ET＝T+Eb+Ei
in the formula (f)wetRelative surface humidity; f. ofrewIs a soil moisture and soil property constraint; alpha is a prime-Taylor mode coefficient and takes a value of 1.26; delta is the temperature-saturated water vapor pressure slope; gamma is a dry-wet table constant, and the value is 0.066; rnsNet radiation of surface soil; g is ground heat flux; f. ofg、ftAnd ftrmRespectively green canopy fraction, plant temperature constraint and ecological physiological scalar, ET is evapotranspiration, EiTrapping evaporation for the canopy.
2. The method for constructing the regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 1, wherein in the step S1, the net radiation RnNet radiation component RnsAnd RncThe calculation method of (2) is as follows:
Rn＝Rnshort-Rnlong
wherein R isnIs net radiation, RnshortAnd RnlongNet short wave radiation and net long wave radiation, respectively;
Rnc＝Rn-Rns
wherein R isnsFor net radiation to reach the soil surface, RncIs the net radiation intercepted by the canopy,
is extinction coefficient, value 0.6, and LAI is leaf area index.
3. The method for constructing the regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 1, wherein in step S1, each influence factor is calculated
fwet＝RH4
fAPAR＝m1EVI+b1
fIPAR＝m2NDVI+b2
Wherein f iswetRelative surface humidity, fgIs the proportion of green canopy, ftIs a temperature limiting factor, fmIs a water limiting factor, fAPARmaxIs fAPARRH is the relative humidity, TmaxIs the maximum air temperature, ToptIs that the optimum growth temperature EVI of the vegetation is the enhanced vegetation index, NDVI is the normalized vegetation index, fAPARIs the PAR coefficient absorbed by the crown, fIPARIs the PAR coefficient intercepted by the crown, the PAR coefficient being the proportion of photosynthetically active radiation, b1＝-0.048，b2＝-0.05，m2＝1，m1＝1.3632。
4. The method for constructing the regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 1, wherein in the step S2, the calculation method of the effective root depth Zr of the plants is as follows:
θp＝θfc-θw
W＝P/PT
wherein, Zr is the effective root depth of the plant, alpharTo average depth of rainfall, θpIs the effective water content of plant, thetafcFor holding water in the fieldAmount, thetawW is the ratio of the average annual precipitation (P) to the potential transpiration rate (PT) for the wilting coefficient;
the calculation formula of A is as follows:
WUE＝GPP/ET
wherein PT represents potential transpiration, γrIn order to be the actual root breathing rate,
is the root respiration rate at 20 deg.C, TaIs the temperature of air, Q10As a temperature coefficient, a change in the root respiration rate per 10 ℃ rise in temperature is shown, where Q is taken10Is 2.0; RLD is root length density, SRL is specific root length, RLD is set to 0.1, SRL is set to 1500cm root g-1root, WUE is the ratio of the sum of the primary production values GPP to ET, fGSIs the growing season length fraction based on the leaf area index.
5. The method for constructing the regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 1, wherein in the step S3, frewFor soil moisture and soil property constraints, the calculation method is as follows:
wherein, thetaobsAs observed for soil moisture, thetawTo the wilting coefficient, thetafcIs the field water capacity.
6. According to claim 1The method for constructing the regional scale evapotranspiration model synchronously considering the dynamic changes of the vegetation canopy and the root system is characterized in that in the step S3, ftrmFor an ecological physiological scalar, the calculation method is as follows:
ftrm＝(1-RH4(1-VWC)(1-RH))fm+(RH4(1-VWC)(1-RH))ftrew
wherein RH is relative humidity, VWC is volume water content, fmIs a water limiting factor, ftrewThe sensitivity of vegetation transpiration to soil moisture.
7. The method for constructing the regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 6, wherein in the step S3, ftrewThe calculation method of (2) is as follows:
wherein, thetacrIs the critical soil moisture, θ, of the soil moisture availability limit ETobsAs an observed value of the soil moisture,
the withering coefficient of the surface soil water after the rooting depth of the plants is adjusted, ZrscalarIndicates the root system depth evolution.
8. The method for constructing the regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 7, wherein in step S3,
wherein the content of the first and second substances,
adjusting the surface soil water withering coefficient theta for the plant rooting depthwTo the wilting coefficient, thetacrIs critical soil moisture for which soil moisture availability limits ET; p is a limiting factor of soil moisture effectiveness on transpiration, and is mainly related to potential transpiration and water absorption depth (root depth) of plants; thetafcRepresenting the field water capacity; PET represents latent evaporation; a represents Zr vs. thetacrThe weight of the influence is applied, which takes a value of 0.1.
9. The method for constructing the regional-scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots according to claim 1, wherein in the step S3, EiFor canopy interception evaporation, the calculation method is as follows:
wherein f iswetRelative surface humidity, alpha is a Priestley-Taylor mode coefficient and takes a value of 1.26, delta is a temperature-saturated water vapor pressure slope, gamma is a psychrometric constant and takes a value of 0.066, RncIs the net radiation intercepted by the canopy.
10. A construction system of a regional scale evapotranspiration model synchronously considering dynamic changes of vegetation canopies and roots is characterized by comprising the following steps:
block M1, calculating the net radiation R from the data of the area dimensions required by the PT-JPL modelnNet radiation component RnsAnd RncAnd each influencing factor;
a module M2, estimating the effective root depth Zr of the plant with a preset area scale based on a Guswa model;
module M3, passing plant effective root depth Zr through vegetation transpiration T and soil evaporation EbThe soil water action in the model is coupled into a PT-JPL three-source evapotranspiration model to construct a regional scale evapotranspiration model synchronously considering vegetation canopy and root depth dynamic changes:
ET＝T+Eb+Ei
in the formula (f)wetRelative surface humidity; f. ofrewIs a soil moisture and soil property constraint; alpha is a prime-Taylor mode coefficient and takes a value of 1.26; delta is the temperature-saturated water vapor pressure slope; gamma is a dry-wet table constant, and the value is 0.066; rnsNet radiation for surface soil; g is ground heat flux; f. ofg、ftAnd ftrmRespectively green canopy fraction, plant temperature constraint and ecological physiological scalar, ET is evapotranspiration, EiEvaporation was trapped for the canopy.
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