3.1. Landscape Structure
The structural analysis proved the vast differences between the Czech and Austrian sides of the border (see summary in
Table 1). The total area of each side of the AOI was similar, although not identical, due to the AOI shape (determined by the border buffer). In the end the area on the Czech side (144 000 ha) turned out to be slightly smaller compared to the Austrian side (156 000 ha). Both study areas differ significantly in patch size and shape. The simple patch count suggested differences, with 13 172 patches on the Czech side and 66 788 on the Austrian side. A more informative value for comparing the two AOIs is the patch density, which shows the number of patches relative to the size of the AOI, therefore providing more accurate information when comparing two areas of not identical sizes. In our case, the density of the Czech AOI was 9.1, and the Austrian AOI was 42.8 patches per ha. The largest patch index shows the ratio of the largest patch to the total area with values of 0.37 on the Czech side and 0.11 on the Austrian side.
Another parameter of landscape structure evaluation is the edge characteristics. The total edge is just a plain sum of the edge length in our AOIs; considering the different numbers of patches and different AOI sizes, there are more edges on the Austrian side compared to the Czech side. Edge density is then related to the total areas of each AOI therefore making it more precise for a comparison. The edge density shows a more than 5-fold difference between our Czech area (10.7) and the Austrian area (58.8).
Values of the patch level metrics show the same trends as observed in the densities of patches and edges. The mean patch size in the Czech AOI was 11.0 ha, but it only reached 2.3 in the Austrian one. This was also reflected in the area-weighted mean, which was 57.3 ha for the Czech and only 17.5 ha for the Austrian side. The median plot sizes were 2.26 ha in Czechia and 0.38 ha in Austria. The standard deviations were 22.6 ha (Czechia) and 5.9 ha (Austria), respectively.
Considering the structure of the individual classes of the land cover, we chose categories with the largest proportion of the landscape. We chose arable land, which takes 89.4% of the Czech landscape and 81.0% of the Austrian one. Second, we chose vineyards, which take 3.6% on the Czech side and 5.2% in Austria. Permanent grassland represents 5.5% of the Czech area, yet in Austria, only 2.72%. Another category worth mentioning is the fallow land which takes (sadly) only 0.5% of the Czech agricultural landscape in our AOI but 4.6% of the Austrian (10× more). Another class that is very marginal in Czechia (with 0.5% of the total area) but significant in Austria (with 5.7%) is grass on arable land, which generally indicates animal feed production but on a field instead of a permanent grassland.
From the point of the structure within the chosen classes, we can see similar patterns as we saw with the agricultural landscape as a whole. Focusing on the arable land, we see that the number of patches (7 036 in Czechia versus 18 998 in Austria) and patch density (4.9 patches per ha in the Czech side and 12.2 patches per ha in Austria) are both much larger on the Austrian side. This is then reflected in the other metrics, such as total edge (1 480 km and 7 109 km) or edge density (10.2 vs ). Furthermore, the mean area of the fields in Czechia reached 18.4 ha, and the mean area in Austria 6.6 ha. Other land cover classes follow the trend. Vineyards, permanent grassland, and fallow land have larger total areas on the Austrian side of the AOI than the grass cover on arable land class and arable land. We can see that in Austria the absence of permanent grassland is compensated by growing grass and animal feed in general more temporally on arable land instead of permanent grass cultures. The relative values such as Patch density or edge density are higher in Austria among all the land cover classes. The mean area size is then larger in Czechia within all of the classes.
3.2. Energy Fluxes
From the point of the energy dissipation and functional parameters of the surface, we worked with the same classes as in the structural analysis (all agricultural land, arable land, vineyards, permanent grassland, fallow land and grass cover on arable land). The time series analysis for the dates 18 May 2022, 3 June 2022, 19 June 2022, 21 July 2022, 30 August 2022, 7 September 2022, 23 September 2022 and 25 October 2022 gave the following results. The statistical comparison of the Czech and Austrian sides of the AOI summarises
Figure 2. The graphical explanation is provided in
Figure 3, and
Figure A1 to
Figure A5 in Appendix.
The NDVI on the Czech side had slightly higher values in six out of eight cases with the exceptions of 21 July and 25 October, where the Austrian side had slightly higher median 0.39 vs 0.40 and 0.50 vs 0.51 respectively (
Figure 3). In the class of arable land, we see very similar development (see
Figure A1). Worth pointing out is the plot from 30 August, showing on the Czech side a distinct peak in the area of high values around 0.8 which is absent on the Austrian side. Vineyards on the Czech side appear to have higher NDVI values in the spring compared to Austria, yet this trend is reversed later in the season (
Figure A2. NDVI values are higher in Austria. On the permanent grassland patches, we see more equal results for both sides. However, there is a trend of very low minimum values on the Czech side early (May, June) and late (October) in the season, and the very opposite, especially on the plots from July through the end of September (
Figure A3). Fallow land shows higher NDVI values in all but one case (19 June) on the Austrian side and with a very heterogeneous distribution of values on the Czech side in all of the dates (
Figure A4). In the case of the grass cover on arable land, we see higher average values on the Austrian side till 21 July, when both sides have a quite similar shape and average values. Since 30 August, the land cover on the Czech side has a much narrower range of NDVI values with higher median and average in all the other four cases (
Figure A5).
The NDMI shows a similar pattern logically following the vegetation index. On the same two dates, the NDMI median was slightly higher, the same as we observed with the NDMI, with a very narrow difference (0.02 and 0.05 on 21 July and 0.004 and 0.05 on 25 October, see
Figure 3). On arable land, we see the largest differences in values in June, on 3 June and 19 June, in both cases, with higher values on the Czech side (
Figure A1). The rest of the cases had quite similar NDMI values. In vineyards, we see differences in the appearance of the more outlier values, especially on the Austrian side (
Figure A2). Overall, this class has quite low values of NDMI, with median values ranging between 0.0 and 0.3. The permanent grassland class has a higher NDMI median in Austria in all but one case on 21 July despite outlier low values, especially the dates 30 August, 7 September and 23 September (
Figure A3). The fallow land on the Czech side was reaching more heterogeneous values throughout the whole observed period. In the September and October dates, we also see an increasing difference between the median values with higher values on the Austrian side (
Figure A4). For the grass cover on arable land, the value distribution looks in reverse, with a higher value range on the Austrian side, especially from August to October. There are higher median NDMI values on the Austrian side for the first four cases from 18 May to 21 July; in the four following dates, the medians on the Czech side exceed the Austrian (
Figure A5).
The surface temperature only reached higher median values in Czechia on the first (18 May) and the last (25 October) of our dates. However, we can see more interesting developments in the distribution of temperatures in the agricultural landscape. For example, in the second case (3 June), the median temperature is higher on the Austrian side (32.15 °C vs 32.70 °C), yet we can see more extremely high values on the Czech side, with surface temperatures reaching over 50 °C (
Figure 3). A similar phenomenon also appeared on 23 September, when overall median and mean values were lower in Czechia despite the presence of extremely high values. Solely considering arable land class, we cannot see a dramatic difference from the overall agricultural landscape (
Figure A1). We see extremely high surface temperature values in Czechia on 3 June or 23 September, but we can also see lower
values on the Czech side than in Austria across all cases (best manifested 19 June, 21 July or 7 September). In the patches of vineyards, we see a higher value range in Austria on the first date and 30 August (
Figure A2). On the Czech side, we can see an abundance of low outlier values on September 7. Permanent grassland shows high outlier values, mostly on the Austrian side, with 3 June or 7 September, with some values reaching almost 50 °C. However, median values on those cases on both sides were between 27.7 °C and 30 °C (see
Figure A3). On fallow land, we see distinctly more uniform value distribution on the Austrian side for the first two cases, with the rest of the observed season keeping the trend, however less pronounced (see
Figure A4. The grass cover on arable land has significantly lower values in the first four dates (18 May to 21 July) in Austria and the last two cases (23 September and 25 October). The two dates in the middle (30 August and 7 September) can be characterised by high outlier values on the Austrian side, increasing the median values (for more details, see
Figure A5).
Another parameter that we calculated was albedo. In general, the more vegetation there is on the surface and the more complex it is, the lower albedo values we see. Therefore, high albedo values could suggest dry, bare soil. However, high albedo values could also mean senescent crop areas as they are light in colour and low in moisture. On 18 May, 19 June, 30 August, 7 September and 25 October, we observed more of the extremely high values on the Czech side (see
Figure 3). On the arable land, albedo differs in the first date (18 May) along with the September dates, with both higher occurrences of higher values and overall median (
Figure A1). Albedo values on vineyards were higher in all eight cases throughout the vegetation season (see
Figure A2). On the permanent grassland patches, there are low outlier albedo values most pronounced on 18 May, 30 August or 23 September (
Figure A3). On 3 June, 21 July and 23 September, we found significantly higher albedo values on the Austrian side. As in the surface temperature case, we can see a much higher uniformity of values on the Austrian side. Despite the distribution differences (most shown on 21 July) the median values differ significantly towards the end of the observed period on the three last cases (September and October). The grass cover on arable land class shows more heterogeneous values on the Austrian side, with higher median values at the beginning of the observed period on the Austrian side and lower by the end of it (see
Figure A5).
Evaporative fraction is the fraction of available energy transformed into latent heat. Except for the first and last dates (18 May and 25 October), EF has higher medians and means in all six other cases (3 June 2022, 19 June 2022, 21 July 2022, 30 August 2022, 7 September 2022 and 23 September 2022). The largest difference we can see is on 7 September, with a median of 0.61 on the Czech side and a median of 0.55 on the Austrian side (p < 0.001, see
Figure 3). It is worth mentioning that on the Czech side, despite having higher median values on the dates of 3 June and 23 September, we observe extremely low values in the distribution, and this corresponds to the extremely high-temperature values seen on those same dates. On the arable land, the values of the EF have a similar development (see
Figure A1). In all eight cases, both the high and low outlier values were found on the Czech side. This is more pronounced in the lower values on 3 June and 23 September and in the higher values, for example, on 30 August or 7 September. In all but the first date, the average and median values of the EF are higher in the Czech Republic. The vineyards have varied, with four dates with higher medians on the Czech side and four dates on the Austrian side. The largest difference can be seen directly on the first date when there are higher values of EF on the Austrian side. Nonetheless, the median and average values are lower on this side due to a peak of low values around 0.4. For more details, see
Figure A2). There are very low outliers on the permanent grassland land cover, suggesting some extra dry spots (see
Figure A3). This appears to happen on both sides of the border, however it seems to happen more in Austria. Despite the low-value outliers, EF, in all cases, has average values around 0.8. There is a high heterogeneity of the land cover of the fallow land (see
Figure A4). The larger differences can be found in the first three dates (from 18 May to 19 June) but also on 30 August. The grass on arable land has higher heterogeneity of values on the Czech side on the first three dates and some very low outlier values (see
Figure A5). This distribution changes on 21 July when there is already higher heterogeneity on the Austrian side, and this trend seems to last till the second to last date. The dates 30 August and 7 September have some very low outlier values on the Austrian side, and those are also the only dates with lower average values on the Austrian side.
EF and the latent heat flux have similar development since those two variables are very closely related. The first and last dates have slightly higher median values of latent heat on the Austrian side, and all six of the others have higher median values in Czechia. The September dates (7 September and 23 September) both contain some high outlier values on the Austrian side, however the means in both cases are higher in Czechia (see
Figure 3). The largest median difference occurred on 21 July with values
and
and means
and
. The largest difference in mean values was seen on June 19 with CZ mean of
and
, which makes over
difference in the energy dissipation. What we see in the farmland in general, as well as on the arable land alone, is a higher value heterogeneity on the Czech side. On the arable land, this is even more pronounced, and we see high outlier values along with low outlier values more frequently on the Czech side than on the Austrian side, suggesting more surface heterogeneity (best visible on 19 June or 7 July; for more details, see
Figure A1). On the patches of vineyards, we found higher latent heat median values on the first date, 18 May, and then from 19 June to 7 September, with the letter also having the greatest heterogeneity sticking out, especially with the high extreme LE values. In the early dates we particularly see that arable land has a much higher latent heat flux than vineyards. For example, on 3 June we see on the vineyards median LE values
on the Czech side and
on the Austrian side, however on the arable land the median values are
and
respectively (see
Figure A1 and
Figure A2). The class of permanent grass varies more on the Austrian side, with both high values (on 18 May) and low outlier values (for example, 3 June). In the case of 7 September, we see both at the same time (see
Figure A3). Fallow land has more heterogeneous values of LE such as it had with all the other parameters. Especially on 3 June, 19 June or 7 September, we see a larger range of latent heat values in both high and low extremes on the Czech side (see
Figure A4). The grass on arable land class has some very low outliers of LE on 30 August and 7 September on the Austrian side, as we had seen in the evaporative fraction on this land cover. These two cases also have lower overall median and average values of LE in Austria. All the other dates, and especially the first four of them (between 18 May and 21 July), have higher medians on the Austrian side with more low outlier values on the Czech side. For more details, see
Figure A5.
The sensible heat flux values have the opposite development to the Latent heat flux and Evaporative fraction. In all but the first and the last dates, we see that the sensible heat values are higher on the Czech side. On 3 June and 23 September, Czechia had higher outlier values despite having lower overall median values (see
Figure 3). The fields of arable land show more equality on the Austrian side. The dates 3 June, 30 August or 23 September contain more high extreme values on the Czech side yet again with overall lower median values in all but the first date (18 May). Opposite to the latent heat flux, we see higher median values on the vineyard patches compared to the arable land, especially in the first three cases (see
Figure A1 and
Figure A2). The permanent grass class has significantly lower median values compared to the vineyards, for example, on 3 June, the Czech and Austrian medians are
and
respectively, compared to
and
on vineyards. However, the median values of sensible heat flux are quite low, mainly, the Austrian side shows a great deal of variability with some extreme outlier values reaching almost
, for example, 3 June or 7 September (see
Figure A3). On the fallow land we again see greater heterogeneity on the Czech side with values ranging from 0 to
of the sensible heat flux in two cases (on 18 May and 21 July; see
Figure A4). The grass on arable land has higher heterogeneity and median values on the 30 August and the 7 September. On the other cases, the medians are lower on the Austrian side, with the largest difference on the first date (18 May) with the medians of
and
in the Czech and Austrian side (see
Figure A5).
The last of the energy fluxes is the ground heat flux, which corresponds to the latent heat flux and the sensible heat flux. However, there is a difference in the first date, 18 May. The only case with the higher G median on the Austrian side is the last one (barely by
). In all the other cases, we see higher overall values of the ground heat flux in the agricultural landscape of the two countries (see
Figure 3). Talking solely arable land, the development is quite similar, with all the medians higher on the Austrian side in all cases. On 18 May and on 21 July, the G flux values are quite alike. However, the dates between them (3 June and 19 June) differ significantly between Czechia and Austria. On 30 August and 7 September, the density plots had a similar peak, but we could see more of the low outlier values on the Czech side. For more details, see
Figure A1. The vineyards have relatively high ground heat flux values, steadily growing between 18 May and 21 July to suddenly drop on 30 August and get lower in the dates after. Compared to the ground flux values of the permanent grass cover, for example on 3 June the Czech and Austrian medians for vineyards are
and
respectively and on the permanent grass
and
(see
Figure A2 and
Figure A3). There are higher medians on the Austrian side in the peak vegetation dates on 19 June and 21 July, as well as 7 September. As did the other fluxes, the fallow land patches have a high range of ground heat flux values on the Czech side. This trend is noticeable mostly in the first four dates. However, it continues in the last four cases. The arable land with grass cover has more heterogeneity on the Austrian side with a wide range of values in the first four dates (from 18 May till 21 July), in which the median ground heat flux values on the Austrian side are also significantly lower in all four cases (see
Figure A5).