## 3 Results
### Comparative Analyses of Soil Moisture Anomalies Versus Land Surface Temperature Anomalies
#### 3.3.1 Site-Scale Correlation Analyses
It is demonstrated that in March, the highest correlation is present at 100 cm soil depth. This is due to the very low SMAI anomalies in deep soil layers that correspond to low LST variations in March when the vegetation cover is still at an early stage and insolation is still moderate. The selected stations in the NC and SW regions, Kneza and Blagoevgrad, respectively, are located in valleys that determine a specific microclimate. A positive relation in Kneza, although very low (r = 0.03), appears in June. For Blagoevgrad, which is in a mountain valley, low correlation in March (respectively low Pearson's r) is obtained. Further evaluation of the relation between SMA anomalies and LST anomalies is performed using the linear regression technique. Mean monthly anomalies from March to October are calculated on the basis of a 12-year period (towards 2007-2018) including the whole region of Bulgaria. SMAI anomalies at different soil layers of 50 and 100 cm were derived. In addition, the mean SMAI for the whole root zone (including 5, 20, 50, and 100 cm soil layers) is considered. Negative linear regression models are estimated to fit the sample distributions for each month with a high level of significance, \(\alpha\) = 0.00 (indicated on the graphs, Figure 6). Using information for the whole region of Bulgaria, the linear regression models confirm the results from site-scale correlation analyses. The correlation of anomalies is minimal in June, still around moderate values, r = \(-\)0.45 (Figure 6a). This is the period of full vegetation cover and maximum precipitation for Bulgaria and is related to the high values of SMA and an undisturbed evaporative cooling effect of the land surface. A strong negative relationship between SMAI and LST anomalies is observed in July and August, with correlation coefficients around \(-\)0.70 (Figure 6b,c). These are the periods with the most limited rain quantities for the climate of the country, leading to a decrease in the available soil moisture to the vegetation, which restricts evapotranspiration cooling of the vegetated land surface. With strong insolation at the beginning of this period and the following cumulative effects, land surface temperature can increase significantly (above 45 \({}^{\circ}\)C). The values of anomalies of the SMAI and LST indices vary, being in a narrow range during spring and becoming largest for July and August (Figure 6). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Station** & **Soil Layer, cm** & **March** & **April** & **May** & **Jun** & **Jul** & **Aug** & **Sep** & **Oct** \\ \hline \multirow{4}{*}{Dobrich, NE} & 20 & \(-\)0.68 & \(-\)0.59 & \(-\)0.84 & \(-\)0.38 & \(-\)0.78 & \(-\)0.83 & 0.09 & \(-\)0.59 \\ \cline{2-10}  & 50 & \(-\)0.73 & \(-\)0.38 & \(-\)0.88 & \(-\)0.59 & \(-\)0.78 & \(-\)0.80 & \(-\)0.41 & \(-\)0.40 \\ \cline{2-10}  & 100 & \(-\)0.82 & \(-\)0.44 & \(-\)0.61 & \(-\)0.60 & \(-\)0.62 & \(-\)0.77 & \(-\)0.57 & \(-\)0.27 \\ \hline \multirow{4}{*}{Rasgrad, NC} & 20 & \(-\)0.36 & \(-\)0.84 & \(-\)0.79 & \(-\)0.64 & \(-\)0.62 & \(-\)0.43 & \(-\)0.3 & \(-\)0.46 \\ \cline{2-10}  & 50 & \(-\)0.42 & \(-\)0.85 & \(-\)0.73 & \(-\)0.74 & \(-\)0.74 & \(-\)0.83 & \(-\)0.22 & \(-\)0.05 \\ \cline{2-10}  & 100 & \(-\)0.41 & \(-\)0.85 & \(-\)0.69 & \(-\)0.67 & \(-\)0.63 & \(-\)0.74 & \(-\)0.59 & 0.09 \\ \hline \multirow{4}{*}{Kneza, NW} & 20 & \(-\)0.72 & \(-\)0.76 & \(-\)0.76 & \(-\)0.12 & \(-\)0.85 & \(-\)0.54 & \(-\)0.65 & \(-\)0.51 \\ \cline{2-10}  & 50 & \(-\)0.59 & \(-\)0.39 & \(-\)0.81 & \(-\)0.21 & \(-\)0.93 & \(-\)0.82 & \(-\)0.73 & \(-\)0.44 \\ \cline{2-10}  & 100 & \(-\)0.7 & \(-\)0.38 & \(-\)0.91 & 0.03 & \(-\)0.83 & \(-\)0.94 & \(-\)0.71 & \(-It is demonstrated in Figure 6 that a larger correlation, i.e., a stronger relationship between higher warm anomalies of LST and stronger dry anomalies of SMAI occur in the summer months.