## 4 Discussion
This results in higher land surface temperatures, which also influence the rate of drying and evapotranspiration. Therefore, high LST are both a cause and the product in the case of dry periods. A good agreement was found between the spatial distributions of the two indices: for the regions with low SMAI, there are high LST values according to the LSASAF satellite product. However, for periods characterized by precipitation equal to or above the monthly norms, there was not good agreement between the LST spatial distribution and SMAI for the 50 cm soil layer (Figure 5). In such 'wet' periods, LST spatial variability is more closely related to SMAI dynamics in the 20 cm soil layer, but the correspondence is still not satisfactory (Figure 5). This result is consistent with the [PERSON] et al. (2005) ([PERSON] _et al._, 2005) ([PERSON] _et al._, 2005) conclusion that in areas where the surface temperature is controlled by evaporation, and not by thermal inertia, the diurnal amplitude extracted from the infrared observations is not well correlated with the soil moisture. In our study, this finding of [PERSON] et al. (2005) is confirmed on a monthly basis and considering the climatic aspect as well. On the other hand, the reported results indicate that for regional assessment of dry land surface anomalies, more deep root zone layers (about 50 cm) are indicative. The behavior of LST closely corresponds to the drought severity as indicated by SMAI for the whole country in July and August: the lower the SMAI, the higher the LST. Color-coded maps of spatial distribution of the correlation between the anomalies of SMAI and LSASAF LST indicate a strong relationship for the whole region of Bulgaria (correlation coefficient mostly around 0.8, maximum 0.84, Figure 8d,e). For the rest of the growing season, the correlation (above 0.5) is preserved for regions and months where SMA is negative. This indicates that land surface temperature (LSASAF satellite retrievals) can be used as a dry anomaly indicator on a climatic basis. Taking into account that in July and August, the evapotranspiration is limited for the climate regime of Bulgaria, our results are consistent with the findings of [PERSON] et al. (2005), considering that radiation and soil moisture availability are the main drivers of ET at a regional scale ([PERSON] _et al._, 2005). The validation study presented in [PERSON] et al. (2015) [51] exhibits the same conclusions: results from the comparison show an overall good performance over semiarid regions. The main constraint concerning these satellite applications is that MSG LST data are not available for cloudy pixels. The sensitivity of LST to soil moisture and vegetation cover means it is an important component in numerous applications. However, despite their recognized importance in a large number of applications, accurate measurements of surface skin temperatures over continents are not yet available for the whole globe, for clear and cloudy skies, with a time sampling adequate to resolve the diurnal cycle and to analyze synoptic, seasonal, and interannual variability. A contribution in this direction is the GlobTemperature project of ESA's Earth Observation Envelope Programme (2013-2017) that provides global-scale satellite LST data for research and operational user communities. The outcome from the project is the delivery of the first LST datasets via a dedicated data portal in harmonized data format [70; 71]. The GlobTemperature website remains open. The activity continues under the ESA CCI program ([[http://cci.esa.int/lst](http://cci.esa.int/lst)]([http://cci.esa.int/lst](http://cci.esa.int/lst))), which is expected to have LST climate data records (CDRs) with the first passive microwave time series.