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Variability and distribution of spatial evapotranspiration in semi arid Inner Mongolian grasslands from 2002 to 2011.

Schaffrath D, Bernhofer C - Springerplus (2013)

Bottom Line: Generally, ET equals or exceeds P during the vegetation period, but high precipitation in 2003 clearly exceeded ET in this year indicating a recharge of soil moisture and groundwater.Despite the high interannual and innerannual variations of spatial ET, the study also showed the existence of an intrinsic long-term spatial pattern of ET distribution, which can be explained partly by altitude and longitude (R(2) = 0.49).In conclusion, the results of this research suggest the development of dynamic and productive rangeland management systems according to the inherent variability of rainfall, productivity and ET in order to restore and protect Inner Mongolian grasslands.

View Article: PubMed Central - PubMed

Affiliation: Institute of Hydrology and Meteorology, Technische Universität Dresden, Dresden, Germany ; Professur für Meteorologie, TU Dresden, Fakultät Umweltwissenschaften, PF 1117, 01735 Tharandt, Germany.

ABSTRACT
Grasslands in Inner Mongolia are important for livestock farming while ecosystem functioning and water consumption are dominated by evapotranspiration (ET). In this paper we studied the spatiotemporal distribution and variability of ET and its components in Inner Mongolian grasslands over a period of 10 years, from 2002 to 2011. ET was modelled pixel-wise for more than 3000 1 km(2) pixels with the physically-based hydrological model BROOK90. The model was parameterised from eddy-covariance measurements and daily input was generated from MODIS leaf area index and surface temperatures. Modelled ET was also compared with the ET provided by the MODIS MOD16 ET data. The study showed ET to be highly variable in both time and space in Inner Mongolian grasslands. The mean coefficient of variation of 8-day ET in the study area varied between 25% and 40% and was up to 75% for individual pixels indicating a high innerannual variability of ET. Generally, ET equals or exceeds P during the vegetation period, but high precipitation in 2003 clearly exceeded ET in this year indicating a recharge of soil moisture and groundwater. Despite the high interannual and innerannual variations of spatial ET, the study also showed the existence of an intrinsic long-term spatial pattern of ET distribution, which can be explained partly by altitude and longitude (R(2) = 0.49). In conclusion, the results of this research suggest the development of dynamic and productive rangeland management systems according to the inherent variability of rainfall, productivity and ET in order to restore and protect Inner Mongolian grasslands.

No MeSH data available.


Related in: MedlinePlus

Flowchart of the sources and organisation of model input and parameters for the calculation of spatial ET.
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Fig2: Flowchart of the sources and organisation of model input and parameters for the calculation of spatial ET.

Mentions: A more detailed background on the initial parameterisation of BROOK90 for the grasslands of the study area, validation and simulated results at the experimental field sites of MAGIM are summarised by Vetter et al. (2012) and Schaffrath et al. (2013). This study is based on the initial parameterisation of the model with several modifications for the application in a much larger area. An overview of the organisation of parameters and daily input data are shown in Figure 2. The concept is based on the work of Schaffrath et al. (2013) who calculated ET separately for every 1 km2 pixel of the study area. Individual parameters were used if available (e.g. LAI, latitude, slope and aspect), but some general assumptions were necessary due to limited field data: the same relative root distribution over depth has been used as described for temperate grasslands according to Jackson et al. (1996) and Federer et al. (2003) and one standard soil profile for all pixels was generated, although the analysis of soil texture of more than 30 soil profiles sampled within the study area by the MAGIM project (Wiesmeier et al. 2009 Wiesmeier et al. 2011 Steffens et al. 2011) showed some variations in the partitioning of the material. However, sand is the dominating particle fraction in the soils of the study area and the effect of the variations in texture on ET was found to be relatively small: the entire range of observed texture profiles was simulated to quantify the effect of the variations on ET in a small test area in Vetter et al. (2012). Then, three soil profiles that resulted in the minimum, mean and maximum ET were simulated for the whole study area in 2006 by Schaffrath et al. (2013). The results showed some effects on ET which deviated between −11% and +6% from ET simulated with the soil profile used in this study that is considered representative for the study area as it is resulting in average values of ET (Table 1). Also, since BROOK90 deduces soil water retention and movement from soil texture classes, minor differences are neglected by the model. Individual LAI was taken from the MODIS MOD15 data product (collection 5) and the dates and values of the most significant LAI changes were parameterised during the course of every year. MOD15 LAI is available every 8 days and contains the highest LAI at a pixel during an 8-day observation period. BROOK90 provides 10 supporting points for the annual LAI course. The LAI of DOY (Day of the year) 1 and DOY 366 were set to zero for all pixels. DOY 113 (23 April) and DOY 240 (28 August), which are the start and the end dates of the study period, were linked with the LAI at that time. The remaining six dates were filled with the DOY and LAI of the six most significant LAI-changes. Vegetation height (h, in cm) was roughly estimated (h = 35.5 LAI, R2 = 0.49), based on a relationship between measured vegetation height and LAI data from MAGIM as well as from publications (Fan et al. 2009 Zhang and Zhao 2009). These data were implemented analogously to LAI. Information on latitude was taken from the MODIS coordinates. Individual 1 km values of altitude, aspect, and slope were calculated from the SRTM (Shuttle Radar Topography Mission) data product.Figure 2


Variability and distribution of spatial evapotranspiration in semi arid Inner Mongolian grasslands from 2002 to 2011.

Schaffrath D, Bernhofer C - Springerplus (2013)

Flowchart of the sources and organisation of model input and parameters for the calculation of spatial ET.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4320196&req=5

Fig2: Flowchart of the sources and organisation of model input and parameters for the calculation of spatial ET.
Mentions: A more detailed background on the initial parameterisation of BROOK90 for the grasslands of the study area, validation and simulated results at the experimental field sites of MAGIM are summarised by Vetter et al. (2012) and Schaffrath et al. (2013). This study is based on the initial parameterisation of the model with several modifications for the application in a much larger area. An overview of the organisation of parameters and daily input data are shown in Figure 2. The concept is based on the work of Schaffrath et al. (2013) who calculated ET separately for every 1 km2 pixel of the study area. Individual parameters were used if available (e.g. LAI, latitude, slope and aspect), but some general assumptions were necessary due to limited field data: the same relative root distribution over depth has been used as described for temperate grasslands according to Jackson et al. (1996) and Federer et al. (2003) and one standard soil profile for all pixels was generated, although the analysis of soil texture of more than 30 soil profiles sampled within the study area by the MAGIM project (Wiesmeier et al. 2009 Wiesmeier et al. 2011 Steffens et al. 2011) showed some variations in the partitioning of the material. However, sand is the dominating particle fraction in the soils of the study area and the effect of the variations in texture on ET was found to be relatively small: the entire range of observed texture profiles was simulated to quantify the effect of the variations on ET in a small test area in Vetter et al. (2012). Then, three soil profiles that resulted in the minimum, mean and maximum ET were simulated for the whole study area in 2006 by Schaffrath et al. (2013). The results showed some effects on ET which deviated between −11% and +6% from ET simulated with the soil profile used in this study that is considered representative for the study area as it is resulting in average values of ET (Table 1). Also, since BROOK90 deduces soil water retention and movement from soil texture classes, minor differences are neglected by the model. Individual LAI was taken from the MODIS MOD15 data product (collection 5) and the dates and values of the most significant LAI changes were parameterised during the course of every year. MOD15 LAI is available every 8 days and contains the highest LAI at a pixel during an 8-day observation period. BROOK90 provides 10 supporting points for the annual LAI course. The LAI of DOY (Day of the year) 1 and DOY 366 were set to zero for all pixels. DOY 113 (23 April) and DOY 240 (28 August), which are the start and the end dates of the study period, were linked with the LAI at that time. The remaining six dates were filled with the DOY and LAI of the six most significant LAI-changes. Vegetation height (h, in cm) was roughly estimated (h = 35.5 LAI, R2 = 0.49), based on a relationship between measured vegetation height and LAI data from MAGIM as well as from publications (Fan et al. 2009 Zhang and Zhao 2009). These data were implemented analogously to LAI. Information on latitude was taken from the MODIS coordinates. Individual 1 km values of altitude, aspect, and slope were calculated from the SRTM (Shuttle Radar Topography Mission) data product.Figure 2

Bottom Line: Generally, ET equals or exceeds P during the vegetation period, but high precipitation in 2003 clearly exceeded ET in this year indicating a recharge of soil moisture and groundwater.Despite the high interannual and innerannual variations of spatial ET, the study also showed the existence of an intrinsic long-term spatial pattern of ET distribution, which can be explained partly by altitude and longitude (R(2) = 0.49).In conclusion, the results of this research suggest the development of dynamic and productive rangeland management systems according to the inherent variability of rainfall, productivity and ET in order to restore and protect Inner Mongolian grasslands.

View Article: PubMed Central - PubMed

Affiliation: Institute of Hydrology and Meteorology, Technische Universität Dresden, Dresden, Germany ; Professur für Meteorologie, TU Dresden, Fakultät Umweltwissenschaften, PF 1117, 01735 Tharandt, Germany.

ABSTRACT
Grasslands in Inner Mongolia are important for livestock farming while ecosystem functioning and water consumption are dominated by evapotranspiration (ET). In this paper we studied the spatiotemporal distribution and variability of ET and its components in Inner Mongolian grasslands over a period of 10 years, from 2002 to 2011. ET was modelled pixel-wise for more than 3000 1 km(2) pixels with the physically-based hydrological model BROOK90. The model was parameterised from eddy-covariance measurements and daily input was generated from MODIS leaf area index and surface temperatures. Modelled ET was also compared with the ET provided by the MODIS MOD16 ET data. The study showed ET to be highly variable in both time and space in Inner Mongolian grasslands. The mean coefficient of variation of 8-day ET in the study area varied between 25% and 40% and was up to 75% for individual pixels indicating a high innerannual variability of ET. Generally, ET equals or exceeds P during the vegetation period, but high precipitation in 2003 clearly exceeded ET in this year indicating a recharge of soil moisture and groundwater. Despite the high interannual and innerannual variations of spatial ET, the study also showed the existence of an intrinsic long-term spatial pattern of ET distribution, which can be explained partly by altitude and longitude (R(2) = 0.49). In conclusion, the results of this research suggest the development of dynamic and productive rangeland management systems according to the inherent variability of rainfall, productivity and ET in order to restore and protect Inner Mongolian grasslands.

No MeSH data available.


Related in: MedlinePlus