Validity and reliability of drought reporters in estimating soil water content and drought impacts in Central Europe

Authors: BARTOŠOVÁ, L. - Mendel University; FISCHER, M. - Czech Globe - Global Change Research Institute; BALEK, J. - Czech Globe - Global Change Research Institute; BLÁHOVÁ, M. - Mendel University; KUDLÁCKOVÁ,, L. - Mendel University; CHUCHMA, F. - Collaborator; HLAVINKA, P. - Mendel University; MOŽNÝ, M. - Collaborator; ZAHRADNÍCEK, P. - Czech Globe - Global Change Research Institute; WALL, N. - University Of Nebraska; HAYES, M. - University Of Nebraska; HAIN, C. - Nasa Marshall Space Flight Center; Anderson, Martha; WAGNER, W. - Vienna University Of Technology; ŽALUD, Z. - Mendel Biotechnology; TRNKA, M. - Mendel Biotechnology

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2022
Publication Date: 1/10/2022
Citation: Bartošová, L., Fischer, M., Balek, J., Bláhová, M., Kudlácková,, L., Chuchma, F., Hlavinka, P., Možný, M., Zahradnícek, P., Wall, N., Hayes, M., Hain, C., Anderson, M.C., Wagner, W., Žalud, Z., Trnka, M. 2022. Validity and reliability of drought reporters in estimating soil water content and drought impacts in Central Europe. Agricultural and Forest Meteorology. 315:108808. https://doi.org/10.1016/j.agrformet.2022.108808.
DOI: https://doi.org/10.1016/j.agrformet.2022.108808

Interpretive Summary: Numerous drought indices based on modeling or remote sensing have been developed to monitor drought severity, tracking quantities like soil moisture or crop water use (evapotranspiration) as an indicator of plant available water. To relate these indicators to actual impacts experienced on the ground, observer-based reports have proven to an invaluable source of ground truth. This paper compares several drought indicators used in the Czech Drought Monitor System (CzechDM) with farmer reports on soil water content and crop condition and yield collected over the country for the period 2015-2018. The purpose of the comparison was to elucidate the added value of these farmer reports to the complete drought monitoring system, and to quantify the relationships between different drought indicators and realized drought impacts. The study found that reports on local soil moisture conditions agreed well with modeled and remotely sensed soil moisture indicators. Reported impacts on crop yields showed better agreement with an Evaporative Stress Index related to anomalies in remotely sensed crop water use. In combination, the reporter data were found to be a valuable complement to remotely sensed and modeled indicators, serving as a reality check on signals of developing drought and better defining the time of drought onset.

Technical Abstract: Increasing drought has been considered as one of the major threats of climate change in central Europe. In order to provide an objective quantitative tool that represents the current drought situation, the forecast of drought, and links to past events, a Czech Drought Monitor System (CzechDM) was established in 2012. As in many other drought monitoring systems worldwide, the CzechDM uses a set of approaches including meteorological indices, water balance modelling, and remote sensing. However, what makes the CzechDM unique within the international context is the utilization of a network based on voluntary reporters (farmers) who complete an online questionnaire with information about soil water content and the impact of drought on crop yield within their farms on a weekly basis. The results from the questionnaires for individual farms were aggregated over the area of districts and those with a continuous number of reports were further analysed. Reporters’ data about soil water content and drought impacts on crop yield were compared and validated with outputs of the SoilClim model (a core tool of CzechDM) and with other methods for drought monitoring, such as the water balance model (AVISO), a microwave scatterometer based Soil Water Index (SWI), and the land-surface temperature based Evaporative Stress Index (ESI). The number of weekly received reports increased from (on average) of 50 reports in 2015 to 400 reports in 2018 as drought was becoming an obvious issue in agriculture during that period. Soil water content estimated by reporters was significantly correlated (on average r = 0.8) with outputs of the SoilClim model. Conversely, correlation between yield drought impacts estimated by reporters and SoilClim outputs was lower (on average r = 0.4), suggesting that in-situ observations by farmers provide additional insights to drought impacts occurrence. Impact reports were most strongly correlated with the ESI and AVISO indicators, which are more directly related to plant health. Importantly, it was found that farmers reported significant drought impacts on yield earlier in the season than any other methods (models or remote sensing). The main findings are that the drought monitoring provide by the reporters is a useful and reliable part of the CzechDM process and provides additional information about the moisture status and impacts of drought in real time at local scales. We conclude that weekly reports by farmers represent a significant enhancement of drought monitoring and have a potential to further develop automatized approaches combining in-situ, modelling and remote sensing within a data fusion or machine learning framework.