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COMPARISON OF ACTUAL EVAPOTRANSPIRATION FROM ALEXI AND SOILCLIM MODELS
Jurečka, František ; Hlavinka, Petr ; Lukas, Vojtěch ; Trnka, Miroslav ; Anderson, M. ; Hain, C. ; Balek, Jan ; Bláhová, Monika ; Žalud, Zdeněk
Actual evapotranspiration (ETa) determined by the Atmosphere-land Exchange Inverse (ALEXI) model and water balance model SoilClim was compared for selected districts of the Czech Republic. The ALEXI model uses the land surface temperature (LST) from remote sensing and provides information on ETa and subsequently the surface moisture status. The SoilClim is a dynamic model of watcr content in soil and represents a model based on water balance approach. The current version of the model is able to estimate the value of ETa, as well as soil moisture content in two layers of the soil profile. Investigated period of ETa comparison were years 2014 and 2015. Especially the year 2015 had a special relevance due to the significant summer drought that occurred in CR. Model performance was compared for the period when changes in vegetation are most significant from April to August. Week sums of ETa from both models were compared at the district level for Vysodina, JihomorayskY and Olomouck, regions. The ETa values were generally higher from ALEXI as compared to SoilClim. ALEXI values were in some cases even two or three time higher. Moreover, the seasonal dynamics showed sometimes opposite trends. As this is a pilot testing of ALEXI based ETa in the conditions of Central Europe and show large differences as compared to well established methods, more detailed testing is required prior drawing any general conclusions.
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Towards a combining of remote sensing and in situ evapotranspiration measurements
Fischer, Milan ; Jurečka, František ; Anderson, M. ; Hain, C. ; Pozníková, Gabriela ; Hlavinka, Petr ; Orság, Matěj ; Lukas, V. ; Žalud, Z. ; Trnka, Miroslav
This study provides preliminary results from combining in situ Bowen ratio energy balance (BREB) and\nevapotranspiration (ET) measurements techniques with physically based remote sensing ET estimates determined\nby the Atmosphere-Land Exchange Inverse (ALEXI) model. Evapotranspiration measurements\nand ALEXI estimates were analysed in an agricultural area close to Polkovice, Czech Republic during 2015,\nwhen a drought spell and intensive heatwaves appeared in the country. The BREB system was monitoring a\nwinter wheat (Triticum aestivum L.) field (~26 ha) while the ALEXI pixel (~5 km resolution) covered a wide\nrange of crops, including mainly winter wheat, spring barley, and winter rape. The study results showed that,\nalthough the applied methods work at different spatial scales (field vs. landscape), their combination can provide\nfurther insights into ET at both scales. For instance, such approach can be used to identify whether a specific\necosystem investigated in situ contributes to cooling or warming of the landscape.
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Monitoring of water use, druought and yield impacts of winter wheat using imaginery from satellites
Jurečka, František ; Anderson, M. ; Hlavinka, Petr ; Semerádová, Daniela ; Trnka, Miroslav ; Hain, C. ; Gao, F. ; Yang, Y. ; Žalud, Zdeněk
Remote sensing can be very useful tool for drought monitoring, providing valuable information about yield-limiting moisture conditions and crop response under current climate conditions. In this study the Atmosphere-land Exchange Inverse (ALEXI) model was used. The ALEXI model uses the morning surface temperature (LST) rise and provides information on the surface moisture status. In this paper correlations between yields and satellite indicators of crop water use or evapotranspiration (ET) were studied for the period 2002-2014. Correlations were studied for winter wheat at district scale in Vysocina, Jihomoravsky and Olomoucky regions since winter wheat is one of the traditional and most important crops grown in these regions. The Evaporative Stress Index (ESI) was used for these correlations as an ET-based index. Time series of Pearson correlation coefficient (r) computed between ESI and winter wheat yields at district scale were analysed. Strongest correlations are associated with districts within the Southern Moravian lowlands in Jihomoravsky and Olomoucky region, where frequency of occurrence of severe drought was highest over the period of record. Severe drought resulted in significant yield impacts, particularly in years 2003 and 2012. Correlations tend to be lower over the highlands districts of Vysocina and surroundings. In these districts, yields are more temperature than moisture limited and were more stable over the period of record.
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Use of ESI index for drought monitoring and crop yield forecasting
Jurečka, František ; Anderson, M. ; Hlavinka, Petr ; Hain, C. ; Wayne, D. ; Gao, F. ; Johnson, D. M. ; Otkin, J. ; Žalud, Zdeněk ; Trnka, Miroslav
Remote sensing is already for many years used for various analysis providing limited factors for agriculture production. Drought monitoring, vegetation conditions in the fields and crop\n131 yield forecasting in context of climatic conditions of recent years seem to be crucial. Methods of remote sensing use various wavebands behaving differently under different surfaces and vegetation covers. Remote sensing use many indices for study of vegetation conditions and agriculture landscape and for forecasting yield. In this case, index ESI (Evaporative Stress Index) was used for drought monitoring and yield forecasting. Index ESI is used by ALEXI model (Atmosphere-Land Exchange Inverse model).\n
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