Spatial-Temporal Variability of Land Surface Dry Anomalies in Climatic Aspect: Biogeophysical Insight by Meteosat Observations and SVAT Modeling  
[PERSON]  
1 National Institute of Meteorology and Hydrology, 1784 Sofia, Bulgaria; [PERSON](C.G. );  
[PERSON] (P.N. ); [PERSON] (A.K.) 1  
[PERSON]  
1 National Institute of Meteorology and Hydrology, 1784 Sofia, Bulgaria; [PERSON](C.G. );  
[PERSON] (P.N. ); [PERSON] (A.K.) 1  
[PERSON]  
1 National Institute of Meteorology and Hydrology, 1784 Sofia, Bulgaria; [PERSON](C.G. );  
[PERSON] (P.N. ); [PERSON] (A.K.) 1  
[PERSON]  
1 National Institute of Meteorology and Hydrology, 1784 Sofia, Bulgaria; [PERSON](C.G. );  
[PERSON] (P.N. ); [PERSON] (A.K.) 1  
Footnote 1: email: {julia.stoyanova@mete. Although all types of drought originate from precipitation deficiency, it is insufficient to monitor solely this parameter to assess severity and resultant impacts [11]. The relationships between meteorological drought indicators and agricultural/silvicultural drought impacts vary across Europe [12]. The efforts of the scientific community are focused on joint international activities that make use of numerical modeling and satellite data in establishing the synchronized Drought Information System in Europe, Africa, and Latin America [13]. As indicators, the following geophysical indices are recommended to be used: soil moisture anomalies, indicators optimized for characterizing vegetation water stress, and satellite observations and products. Soil moisture, terrestrial vegetation, and atmospheric flows are parts of a complex interacting system, characterized by the presence of many feedback mechanisms between the various components. The strength of the interaction between soil, plants, and atmosphere depends highly on scale, and the incorporation of these relations in a common framework needs an extensive knowledge from different temporal and spatial scales of the land surface-atmosphere interactions [14]. Soil-vegetation-atmosphere feedbacks are particularly important in water-limited ecosystems, where water is the main factor controlling vegetation growth. Therefore, drought as a specific state of the land surface state refers to the 'dry' anomalies of biogeophysical cycling. Soil moisture availability (SMA) to vegetation cover is an important variable for evaluating vegetation transpiration and a key factor in models of ecosystem and carbon cycle processes [15], as well as of energy and water budgets of crop canopies. SMA is a basic parameter in mesoscale atmospheric circulation models [16] and forecasting systems [17; 18]. Since it is the main determinant of plant systems development, SMA might also be used in the current work as an information source for 'warnings' for environmental constraints. The main limitation of SMA calculation is the lack of ground observations of key variables such as soil moisture or evapotranspiration. Approaches that allow obtaining indirect estimates of such land surface parameters are progressively being introduced. The strengths of remotely sensed data lie in providing temporally and spatially continuous information over vegetated surfaces useful for monitoring surface biophysical variables affecting evapotranspiration (ET) [19]. Over the past 50 years, remote sensing has shifted the field away from the reliance on traditional site-based measurements and enabled observations and estimates of key drought-related variables over larger spatial and temporal scales than was previously possible. Nowadays, using satellite-based remote sensing in combination with in situ data is a promising approach for informing Earth surface modeling [20]. A recent review [21] charts the rise of remote sensing for drought monitoring, examining key milestones and technologies for assessing meteorological, agricultural, and hydrological drought events. Agricultural drought (also referred to as soil moisture drought) represents a deficit in soil moisture available to vegetation driven by a precipitation deficit (meteorological drought) [22].