H1 Microclimatic spatio-temporal variability

1.4.1.1 Air Temperature

During growing season, morning, afternoon and evening, air temperature under the PV panels was significantly cooler than the gap by 1.2-2.2 °C (p < 0.001; Figure 1.2). Overall, in the morning the mean air temperature along the transect was cooler (16.4 °C) compared to the afternoon and evening metrics which were similar throughout (20.1 °C and 20.2 °C, respectively), with p < 0.001 among the three times of day. The difference between the minimum air temperatures under and at the gap was similar (less than 1 °C; Table 1 in SI.1) with under warmer in the morning and the afternoon. The maximum air temperatures in the morning and in the evening, showed a 3.5-4 °C difference between under and gap (warmer throughout the day). The difference was at its peak during the afternoon, with the gap exceeding the under by 10 °C (Table 1 in SI.1).

During non-growing season, mean air temperature increased by 3 °C throughout the day (p < 0.001). The minimum and the maximum air temperatures between under and gap were similar (less than 0.5 °C difference; Table 1 in SI.1) with under slightly cooler and gap slightly warmer in the morning and afternoon, respectively. The overall trend along the transect was different to the growing season, with temperatures gradually cooling down, up until the northern panel edge and gradually warming up by ~3 °C along the gap, especially in the afternoon and evening periods (Figure 1.2).

Figure 1.2: Air temperature metrics spatial distribution of the means, in three times of the day during growing and non-growing season along the five linear transects. Blue shaded area illustrating the standard error of the mean.

1.4.1.2 Soil Temperature

Growing and non-growing season soil temperatures along the transect demonstrated a similar pattern compared to air temperatures, but with the soil remaining cooler than the air and the transitions from under to the gap being sharper at each time period (Figure 1.2

and Figure 1.3). During the growing season, soil temperature under the PV panels was cooler throughout the day compared with the gap (p < 0.001). Further, soil temperatures demonstrated sudden increases at the northern panels’ edges, which in the evening reached 5 °C (p < 0.001). The differences between the minimum temperatures under and the gap ranged from 1.3 °C in the morning to 2.4 °C in the evening, while the maximum temperatures ranged from 3.2 °C in the morning to 8.8 °C in the evening. In the afternoon the difference between the maximum soil temperatures were minor (0.3 °C; gap warmer) and between the minimum soil temperatures the difference was 2 °C (gap warmer; Table 2 in SI.1).

During the non-growing season, morning and afternoon soil temperature trends along the transects were more similar with slightly warmer soils in the afternoon (Figure 1.3). Soil temperatures along the transect were gradually increasing from morning to afternoon and afternoon to evening (15.2 °C, 16.4 °C and 17.3 °C respectively). Morning and afternoon mean under and at the gap were the same, 9.2 °C, with gap’s minimum and maximum values warmer by 1 °C in the afternoon (Table 2 in SI.1). Soil temperature mean increased gradually at the northern panel edge, (breaking points at 3.75 m-5.25 m along the transect; alike the air temperature). Both soil temperature means under and at the gap in the evening were ~1 °C warner compared with the morning and afternoon temperatures (p < 0.001). There was a sudden increase of the minimum soil temperatures in the evening of 7 °C (was ~2.5 °C in the morning and the afternoon) while the maximum temperature was increasing by 1 °C from the morning to the evening (Table 2 in SI.1).

Figure 1.3: Soil temperature metrics spatial distribution of the means, in three times of the day during growing and non-growing season along the five linear transects. Blue shaded area illustrating the standard error of the mean.

1.4.1.3 Soil moisture

Soil moisture demonstrated the greatest small-scale variations of all the examined microclimatic variables (Figure 1.4). This was notable under the panels regardless of season or time of the day. Further, there were sharp and significant fluctuations under the panels from one point to another (p < 0.001), while at the gap the most significant change occurred at the last sampling point (southern panel edge). Despite these small-scale variations, during growing season, under was on average moister than the gap regardless time of day (p < 0.001). Further an abrupt transition between under and the gap was evident at sampling point 4.5 m (northern panel edge). During the non-growing season, the gap demonstrated a reversed trend with distance along the transect; the soil moisture decreased towards the southern panel edge. Overall, the section of the transect under the PV panels was drier compared to the gap (p < 0.001).

Figure 1.4: Soil moisture metrics spatial distribution of the means, in three times of the day during growing and non-growing season along the five linear transects. Blue shaded area illustrating the standard error of the mean.

1.4.1.4 PAR

PAR increased over a short distance at the northern panel edge and reduced over a short distance at the southern edge (Figure 1.5). Further, PAR, was constantly lower under the PV panels compared to the gap, regardless of time of day, during growing and non- growing season (p < 0.001). The maximum difference between under and gap, was in the afternoon of the growing season were the gap reached 975 μmol mˉ² sˉ¹ and under received just 218 μmol mˉ² sˉ¹ (p < 0.001; Table 3 in SI.1). PAR in the morning and evening of the growing season demonstrated similar magnitudes and were significantly different to the afternoon (p < 0.001). The standard error of the mean was higher in the afternoon during both seasons for both under and gap.

Figure 1.5: PAR metrics spatial distribution of the means, in three times of the day during growing and non-growing season along the five linear transects. Blue shaded area illustrating the standard error of the mean.

1.4.1.5 Precipitation and Evaporation from an open water system

Precipitation differed significantly between growing and non-growing season along the transect (p < 0.001). Further, the spatio-temporal interaction (season and distance) showed evidence of significance with p < 0.05. Over the entire sampling period, under and gap precipitation differed significantly, with precipitation under the panels being always lower (p < 0.001) with a different distribution at each period tested (Figure 1.6). In addition, smoother transitions from one sampling point to the next, were observed during the growing season compared to out of season (Figure 1.6), with maximum precipitation deriving from 9 m along the transect (statistically different to both under and gap sampling points along the transect; p < 0.001). At the northern panel edge, precipitation demonstrated a steep rise, from under to the gap, with this sudden increase being sharper during non-growing season. The Tukey pairwise analysis illustrated a

statistical significance of those sampling points at the northern panel edge compared with the other under and at the gap (p < 0.05).

Evaporation did not illustrate a statistically significant spatial and/or temporal variation. However, during the non-growing season, there were some sudden spikes especially at 2.25 m, 8.25 m and 11.25 m along the transect (Figure 1.6). On the other hand, during growing season, the amount of the evaporation under the panels was gradually increasing towards the gap.

Figure 1.6: Precipitation and evaporation spatial distribution of the means during growing and non-growing season along the five linear transects. Shaded area illustrating the standard error of the mean.