*3.1. Analysis of Soil Water Content in Zero Scenario for 2021–2050*

This section compares the obtained seasonal average soil water content results for 2010–2017 (SWAT model) with the results for 2041–2050 for individual climate change projections (RCP 4.5.1, RCP 4.5.2, RCP 4.5.3, RCP 8.5.1, RCP 8.5.2, RCP 8.5.3).

Regardless of the individual climate change projections evaluated, the seasonal average soil water content for the Bystra catchment is projected to decrease between 2041 and 2050 for most seasons compared to 2010–2017 (Table 5).

Lower soil water content will be especially evident for RCP 4.5.1 (MAM, JJA, SON) and RCP 4.5.2 (JJA) where the value of average soil water content may be lower by up to 5.8% compared to the 2010–2017 simulation period. Lower values in the MAM and JJA seasons, especially for the RCP 4.5.1, RCP 4.5.2, RCP 4.5.3 projections, may affect plant growth during the growing season. However, higher soil water content (1.4% higher) was found for the RCP 8.5.1 (JJA), RCP 8.5.2 and RCP 8.5.3 (SON) projections.

Regardless of the regional climate model, the seasonal average soil water content will be lower for climate projections RCP 4.5.1, RCP 4.5.2, RCP 4.5.3 compared to climate projections RCP 8.5.1, RCP 8.5.2, RCP 8.5.3. This is particularly evident when comparing the average annual soil water content results, where, for RCP 4.5.1, RCP 4.5.2, RCP 4.5.3, the average annual soil water content results (2041–2050) are lower between 1.8% and 4.7%, while, for RCP 8.5.1, RCP 8.5.2, RCP 8.5.3, these average annual results are lower between 0.3% and 0.6% compared to the SWAT 2010–2017 model.

The average soil water content by season for 2041–2050 and the SWAT model 2010–2017 is shown in Figure 2 (Figure 2). It shows that the average soil water content decreases throughout the year. The highest soil water values are reached during the winter season of DJF. On the other hand, in spring (MAM), during the growing season period, the average soil water content decreases, maintaining the lowest values in summer (JJA). In autumn (SON), the soil water content increases.

Analyzing the spatial distribution of changes in the average water content in soil in 31 sub-catchments for the simulation period in 2010–2017 in relation to the period 2041–2050 (Figure 3) in the climate forecasts RCP 4.5.1 and RCP 4.5.3, the average water content in the soil will decrease by a few percent points in the Northwest region for most of the projections. In the projections RCP 4.5.1, RCP 4.5.2 and RCP 4.53, a reduced water content in the soil will occur throughout the catchment area, while in the projections RCP 8.5.1, RCP 8.5.2 and RCP 8.5.3, the changes will be small.

#### *3.2. Climate Change Adaptation Scenarios Analysis 1–5 for 2041–2050*

The results presented in Section 3.1 indicate a decrease in soil water content in most seasons during the period 2041–2050 (Table 5, Figure 2). To counteract the negative effects of changes in soil water content, five adaptation scenarios (AS-1, AS-2, AS-3, AS-4, AS-5) were prepared and tested. They were designed to maintain or increase soil water content. The analysis covers the period 2041–2050. Additionally, the impact of adaptation scenarios on total runoff, sediment yield and actual evapotranspiration was compared.

AS-1 of increasing forested areas on soils of complex 6, 7, 8 compared to S-0 for all projections shows a decrease in soil water content for all seasons in the Bystra catchment (Table 6). The soil water content decreases from 4.0% to 4.8% for all seasons.

AS-2, which assumes a forested buffer zone near the Bystra River, shows a slight decrease in soil water content between 2041 and 2050 (Table 6).

AS-3, establishing filter strips, shows no change in soil water content (Table 6).

In AS-4, the application of plowing on arable land—BARL, CANP, CRDY, WWHT was eliminated. This treatment showed a slight increase in soil water content. The increase ranged from 0% to 0.4%. The largest increases occurred in the JJA and SON seasons (Table 6).

AS-5 increased soil organic carbon to 2%. This treatment showed a slight decrease in soil water content. The decrease in soil water content ranged from 0% to 1.4% (Table 6).

Regardless of the GCMs/RMCs and the RCPs evaluated, the results are the same. This means that AS-1 is associated with a greater decrease in soil water content compared to S-0. AS-2 and AS-5 are associated with a decrease of a smaller magnitude compared to AS-1. AS-3 does not predict any significant change in soil water content. In contrast, AS-4 is associated with a small increase in soil water content.

Regardless of the regional climate model, the seasonal average soil water content will be lower under the RCP 4.5 climate change scenario compared to the RCP 8.5 climate change scenario. This is described in more detail in Section 3.1.

Differences in annual average soil water content between AS-2, AS-3, AS-4, AS-5 and S-0 are small. However, for AS-1, the annual average soil water content varies between 296 and 311 mm. In contrast, for S-0, the average annual soil water content is 310–325 mm (Table 6).

AS-1 and AS-2 show a slight decrease for most seasons of total runoff for 2041–2050 compared to S-0 in all climate projections. Changes in total runoff range from 1% (decrease) to 0.3% (increase) (Table 7).

Total runoff in AS-3 did not change (Table 7).

AS-4 shows an increase in total runoff for all seasons in all projections. The increase ranges from 1.3% to 4.7% (Table 7). For climate projection RCP 4.5.1, the increase in total runoff stands out from the other projections in all seasons (above 3%).

In contrast, AS-5 shows a decrease in total runoff for all seasons across all projections. The decrease ranges from 1.0% to 3.9% (Table 7). For climate projections RCP 4.5.1 and RCP 4.5.2, the decrease in total runoff stands out from the other projections in all seasons (above 2%) (Table 7).

Moreover, for total runoff regardless of the GCMs/RMCs and RCPs evaluated, the results are the same. AS-1 and AS-2 have smaller total runoff compared to adaptation S-0. AS-5 has an even smaller total runoff compared to AS-1 and AS-2.

In AS-3, the total runoff does not change. In contrast, AS-4 shows an increase in total runoff compared to all adaptation scenarios.

Regardless of the regional climate model, the average seasonal total runoff will be lower for the RCP 4.5 climate change scenario compared to the RCP 8.5 scenario [8].

Table 8 presents the seasonal sediment yield data (Table 8). AS-1, AS-2, AS-3, AS-4, AS-5 were compared to S-0 for the climate projections. For most adaptation scenarios, there is a reduction in sediment yield from 0% to as much as 73%. The smallest, slight decreases in sediment yield occur in AS-2 compared to S-0. Slightly larger decreases compared to S-0 and AS- 2 occur in AS-1 and AS-5. Large decreases in sediment yield occur in AS-4 (ranging from 6% to 49%). However, the largest occur for AS-3 (over 70%).

For sediment yield, regardless of the GCMs/RMCs and RCPs evaluated, the results are also the same (Table 8).

Regardless of the regional climate model, the seasonal sediment yield will be lower under the RCP 4.5 climate change scenario compared to the RCP 8.5 scenario. Differences in annual sum sediment yields range from 0.54–0.57 t/ha for RCP 4.5 to 0.72–1.00 t/ha for RCP 8.5 in S-0 (Table 8). For AS-4, the annual sum ranges from 0.39–0.40 t/ha for RCP 4.5 to 0.50–0.71 t/ha for RCP 8.5, while for AS-3, the annual sum ranges from 0.15–016 t/ha for RCP 4.5 to 0.20–0.28 t/ha for RCP 8.5.

Table 9 presents data on seasonal actual evapotranspiration (Table 9). The highest evapotranspiration values occur during the MAM and JJA seasons.

AS-1, AS-2, AS-3, AS-4, AS-5 were compared to S-0 for all climate projections. AS-1 shows a decrease in actual evapotranspiration from 1.7% to 1.9% for the MAM season. In contrast, there is an increase between 1.5% and 2.0% for the JJA season.

AS-2 shows little change in actual evapotranspiration (Table 9).

The actual evapotranspiration in AS-3 remains unchanged compared to S-0 (Table 9).

In AS-4, for the MAM and JJA seasons, actual evapotranspiration varies from 1.5% (decrease) to 0.1% (increase) (Table 9) compared to S-0. However, large decreases occur for the SON season (from 3.2% to 4.2%).

In contrast, AS-5 has increases in actual evapotranspiration of 0.7% to 1.7% for the MAM and JJA seasons compared to S-0.

For actual evapotranspiration, regardless of the GCMs/RMCs and RCPs evaluated, the results are the same (Table 9).

Regardless of the regional climate model, seasonal actual evapotranspiration will be similar under the RCP 4.5 climate change scenario compared to the RCP 8.5 scenario [8].

For AS-1, AS-2, AS-3, the annual sum of actual evapotranspiration changes little. However, for AS-4, the annual sum of actual evapotranspiration increases from 1.7% to 3.8% compared to S-0. In contrast, for AS-5, the annual sum decreases from 1.2% to 3.4% (Table 9).

Table 10 shows the percentage sets of changes in soil water content, sediment productivity, total runoff, and actual evapotranspiration under AS-1, AS-2, AS-3, AS-4, AS-5 with respect to S-0 (Table 10). The table was created based on supplementary Material: Figures S1 and S2, for averages of three GCMs/RCMs combinations under two RCP climate change scenarios (RCP 4.5, RCP 8.5).

**Table 10.** Percent summary of changes in soil water content, sediment yield, total runoff and actual evapotranspiration under adaptation scenarios 1–5 (AS-1, AS-2, AS-3, AS-4, AS-5) compared to scenario 0 (S-0) (created from Supplementary Material: Figures S1 and S2), for averages of three GCMs/RCMs combinations under two RCP climate change scenarios (RCP 4.5, RCP 8.5). The summary is for four seasons (DJF, MAM, JJA, SON) in the Bystra catchment. Shaded numbers indicate percentage changes (red indicates % decrease in content, and blue indicates % increase in content). Dark red and dark blue shading indicates large changes, while light red and light blue shading indicates small changes (own study).


#### **4. Discussion**

The results concerning the water content in the soil were compared with the available values of water capacity and the wilting point obtained from the study "Assessment of water retention in soil and the risk of drought based on the water balance of the Lower Silesia Voivodshi", developed in 2013 by the employees of the Department of Soil Science, Erosion and Land Protection, IUNG-PIB in Pulawy [1]. Based on the above-mentioned study, we prepared data on soils in the catchment area of the Bystra River. For a 1.5 m soil profile, the results of the above-mentioned studies are consistent with this publication.

The lowest water content in soil occurs in the summer (JJA), while the highest occurs in the winter (DJF) (Figure 2). For 2041–2050, the largest decreases in soil water content are associated with GCMs/RCMs for RCP 4.5, while small changes occur for RCP 8.5.

The analyzed adaptation scenarios present different results of the influence on the water content in the soil. AS-1 for an increase in forest area on soils of the complex 6, 7, 8 compared to S-0 for all projections shows a reduction in soil water content for all seasons across the entire Bystra catchment (Tables 6 and 10, Figures S1 and S2 in Supplementary Material). The same is true for total runoff. Again, for most seasons, there is a reduction in total runoff (all projections) compared to S-0 (Tables 7 and 10, Figures S1 and S2 in Supplementary Material). Sediment yields for all seasons also decrease (Tables 8 and 10, Figures S1 and S2 in Supplementary Material). In contrast, actual evapotranspiration shows a decrease in the MAM season and an increase in the JJA season (Tables 9 and 10, Figures S1 and S2 in Supplementary Material).

Forests play an important role in absorbing CO2, which is an important factor in reducing the adverse effects of climate change [78]. In addition to absorbing CO2, forest ecosystems can counteract soil erosion and drainage. Within forests, there may be small retention reservoirs, increasing the areas' abundance of water. Forest ecosystems play very important natural, social and productive functions [79]. The results indicate that increasing afforested area in the Bystra catchment has to go beyond the scheme of using soil complexes less favorable for agricultural production, and the areas should be picked with care, focusing on locating forested areas close to catchment borders, so they can slow runoff and help accumulate water at its highest point from the river bed [80].

The large-scale research aimed at estimating the amount of tree stand in the world shows that there are currently 46% fewer trees than before the advent of human civilization [81]. Climate change may affect the condition of forest areas [19] manifested in extreme weather phenomena that begin to lose their anomaly status (hurricanes, droughts). Moreover, the species status of plants and trees may not be flexible enough to adapt to changing climate components (temperature, precipitation, etc.) [82]. Forests therefore should be probably re-designed to cope with changing biotopes. For many years, many concepts regarding forest formation in relation to a changing climate have been considered. These plans are based on the development of actions to reduce the effects of unfavorable phenomena which are occurring now and which may intensify in the future. Another concept will be activities aimed at adapting forest ecosystems to all current and future threats [82].

A program of increasing forest cover is implemented in Poland [83]. According to the report on the condition of forests in Poland in 2020 [84], the level of forest cover in 2020 amounted to 29.6% of the total area of the country. After 2050, the forest cover in Poland is expected to be 33%. The program assumes afforestation of land of low agricultural suitability [85], reflected in AS-1 of this study.

Research using afforestation scenarios was carried out on four sites in Bolivia and Ecuador [86]. They show that the water content in the soil and the total runoff decreased to a varying degree after the application of the forest ecosystem. AS-1 and AS-2 also show a reduction in soil water content (Tables 6 and 10, Figures S1 and S2 in Supplementary Material) and a slight reduction in total runoff (Tables 7 and 10, Figures S1 and S2 in Supplementary Material). Sediment yield also decreased (Tables 8 and 10, Figures S1 and S2 in Supplementary Material). The decrease in soil water content for AS-1 and AS-2 in the Bystra catchment may be caused by increased water uptake by the root system of forest vegetation species.

The afforestation scenario has the potential for further research, in which it is possible to design an appropriate location of forest ecosystems in the Bystra river catchment area, relying not only on the afforestation of soils of complex 6, 7 and 8, but also good tree planting practices in rural areas [87], the use of forested embankment fortifications (also preventing erosion) [72], which would counteract the unfavorable agro-forest checkerboard [88]. The unfavorable location of forest ecosystems near cultivated fields may result in a reduction in the yield of agricultural plants [89,90]. When designing afforestation, one should also take into account the adaptation possibilities of stands to new climatic conditions [82].

Increasing forest cover from 16.34% (S-0) to 19.65% (AS-1) or to 17.37% (AS-2) (Table 4) according to Lambo's forest cover index [91] allows for increased forest retention capacity that, among other things, counteracts the effects of flooding [92]. In addition to increasing

forest cover, equally important is the location of forested areas within the catchment area which has a significant impact on runoff [93].

A buffer zone with a well-developed tree stand, located directly next to watercourses, can prevent the runoff of nutrients and suspensions from agricultural land, contribute to the strengthening of banks and prevent lateral erosion [72,87,94]. A marsh zone forming a belt of wetland and rush vegetation, flooded or boggy for most of the year or all the time, can also be a buffer. Such a zone with well-developed vegetation contributes to the retention of a significant amount of nitrogen and phosphorus from the catchment area, preventing eutrophication of waters [72,95].

AS-3, for the creation of filter strips in a planned management operation on BARL, CANP, CRDY, WWHT arable land, shows no changes in soil water content, total runoff or actual evapotranspiration (Tables 6, 7, 9 and 10, Figures S1 and S2 in Supplementary Material). On the other hand, the filter strips effectively reduce the sediment yield (t/ha) (Tables 8 and 10, Figures S1 and S2 in Supplementary Material). Similar results were obtained in the article describing the use of the filter strips in various scenarios on the example of the catchment area in Thailand [96], where, as a result of their use, the sediment yield was significantly reduced.

Adaptation scenarios involving increasing forest cover, creating buffers next to rivers and creating filter strips can help reduce erosion risk in the 2050 climate horizon in the Bystra catchment by reducing total runoff and decreasing sediment yield.

AS-4, for the cessation of plowing on BARL, CANP, CRDY, WWHT arable land, shows a slight increase (especially in the JJA and SON season) in soil water content (Tables 6 and 10, Figures S1 and S2 in Supplementary Material). The elimination of plowing also shows a significant reduction in sediment yield (t/ha) (Tables 8 and 10, Figures S1 and S2 in Supplementary Material). This may have the effect of reducing soil erosion. However, the total runoff increased, which is induced mainly by the reduction in actual evapotranspiration, especially limited evaporation form the soil surface covered by plant residue mulch (Tables 7, 9 and 10, Figures S1 and S2 in Supplementary Material). Observations by Wawer and Kozyra [97] confirm the prominent role of mulching in preserving soil water by covering the surface of the soil in warm periods.

The discontinuation of plowing is the subject of many articles as well as studies that mention as benefits the reduction in soil erosion, the reduction in surface and subsurface runoff, the reduction in sediment yield, nitrogen yield and phosphorus yield, the increase in soil water content, etc. [76,98–101], which are supported by numerous studies. The abandonment of plowing in the catchment areas in the climate of 2050 also shows a reduction in the sediment yield. On the other hand, the water content in the soil increases. This provides the grounds that new agricultural practices in the coming decades may prevent the negative impact of watershed water deficits from occurring.

Agriculture is closely related to the prevailing climatic conditions, but it also has a large impact on them. The risk of an increase in the frequency of unfavorable climatic conditions in agriculture may result in yield variability from year to year. The reduced amount of water in the soil during plant growth, illustrated in the climate change scenarios (Table 5, Figure 2), will become more frequent and more severe. Other threats will also include droughts, heavy precipitation, erosion [80], floods, landslides and strong winds [102].

AS-5, increasing soil organic carbon to 2%, shows reductions in soil water content, total runoff and sediment yield (Tables 6–8, Figures S1 and S2 in Supplementary Materials). However, actual evapotranspiration increases (Tables 9 and 10, Figures S1 and S2 in Supplementary Materials). In a paper on soil organic carbon changes and their response to climate warming and soil water content changes, a study of the Jinghe catchment in China was described [103]. The study showed that temperature and precipitation will increase by the end of the 21st century under three scenarios—RCP 2.6, RCP 4.5, RCP 8.5—and consequently soil water content will also increase, while organic carbon content will decrease, depending on the climate change scenario. The study also showed that there is a threshold in soil water content that can mediate the loss of soil organic carbon (when the

change in soil water content was lower than the threshold, higher content accelerated the loss of organic carbon, while when the change in soil water content was higher than the threshold, higher content reduced the loss of soil organic carbon) [103]. The mechanism for the decrease in soil organic carbon (despite increased soil water content) due to a warming climate in the future is not fully known [103]. Global studies have found a link between faster CO2 increases in warmer years with less water availability. This demonstrates the importance of warming on the decomposition of soil organic carbon [104]. There are studies in pols on the effect of soil organic matter on soil water management [105]. According to some estimates in the article, increasing soil organic matter by 0.01% increases the amount of organic matter by 480 kg (from 1 hectare of arable soil layer). This corresponds to 278 kg of organic carbon. On the scale of the national area (Poland), this means the sequestration of 11 million tons of CO2 from the entire arable land area of Poland. This represents more than 3% of the total greenhouse gas emissions from the Polish area [77].

A convenient tool for carrying out beneficial changes (afforestation, retention reservoirs, irrigation) in terms of water retention in the landscape is land consolidation on an extended scope [80,106,107]. Several agricultural research centers in Poland deal with the issues of recomposing the rural landscape, including IUNG-PIB in Pulawy. At IUNG-PIB, a broader consolidation formula, called the Composite Development of Rural Areas CDRA [106], was developed, covering extended land consolidation, rural area management and rural development, which are included in addition to classic land consolidation works meant as the transformation of land, water drainage, water supply to farms aimed at improving the conditions for agricultural production on farms [106]. The comprehensive, holistic land consolidation approach remains the most effective way of introducing a wide range of changes in the agricultural landscape, also focusing on water management [106]. Based upon the outcomes of this study, the team plans to simulate a scenario of a fully designed land consolidation with the CDRA scheme as one of the options towards a better holistic water management in rural landscapes.

One of the more recent publications describing the methods of managing water resources and thus counteracting climate change in agriculture for the Polish area is the Code of Good Water Practices in Agriculture, which was commissioned by the Ministry of Agriculture and Rural Development [22]. The Code describes various sustainable and solidarity-based water management practices that can be successfully applied to agriculture in the coming decades in response to an increasing scarcity of water resources. We plan to model the effects of introducing the practices covered by the Code in future studies.

#### **5. Conclusions**

AS-1, AS-2 and AS-5 did not increase the water content of the soil. However, they can help to reduce sediment yield and total runoff. AS-1 and AS-2 have potential for further research using the SWAT model. The research would be aimed at adopting an appropriate strategy for spreading the location of afforestation in the catchment to reduce the adverse effects of climate change. Soil organic carbon sequestration (AS-5) also has potential for further research due to the reduction in negative effects of climate change.

The filter strips in AS-3 contributed to a reduction in sediment yield. Soil water content, total runoff and actual evapotranspiration remained unchanged. The lack of change may be due to suboptimal discretization of the filter strips in the SWAT input files. Further research on this issue will be conducted.

Practices for reducing or eliminating water shortages in soil can be those presented in AS-4 for no-tillage cultivation. Removal of plowing may also contribute to the reduction in sediment yield (t/ha). This may have the effect of reducing soil erosion. However, the positive influence on soil moisture contents throughout the season using the no-till simulation indicated an increase in runoff, which is mainly caused by limiting evaporation from bare soil covered by the mulch of crop residues.

The obtained results cover 150 cm of the soil layer as described by the Polish soilagricultural map, which does fully reflect the conditions for plants, especially during

sawing and in early stages of growth. Further research has to be conducted on discretizing soil hydrology dynamics in the SWAT input configuration to take into consideration the plough horizon as a separate hydrological entity to be modeled.

Higher soil water content, higher total runoff and higher sediment yield for the RCP 8.5 climate change scenario compared to the RCP 4.5 climate change scenario may be related to higher precipitation in 2041–2050 (Badora et al., 2022).

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/w14152288/s1, Figure S1: Summary of changes in soil water content, sediment yield, total runoff and actual evapotranspiration in adaptive scenarios 1–5 (AS-1, AS-2, AS-3, AS-4, AS-5) compared to scenario 0 (S-0), for averages of three GCM/RCM combinations in the RCP 4.5 climate change scenario. The list covers four seasons (DJF, MAM, JJA, SON) in the Bystra catchment area. The first adaptation scenario assumes the growth of afforestation on soils from the agricultural usefulness complex of soil 6–8 (semi-dry, permanent dry, semi-moist, permanently wet). The second adaptation scenario assumes the creation of a forested buffer for the Bystra River and its tributaries. The third adaptation scenario shows one the erosion prevention practices in the river bed, the so-called filter strips. The fourth adaptation scenario assumes the reduction of plowing on agricultural land. The fifth adaptation scenario assumes an increase in soil organic carbon content to 2%. Adaptation scenarios 1–5 are modifications of scenario 0. Scenario 0 only covers climate change in 2041–2050 (own study); Figure S2: Summary of changes in soil water content, sediment yield, total runoff and actual evapotranspiration in adaptive scenarios 1–5 (AS-1, AS-2, AS-3, AS-4, AS-5) compared to scenario 0 (S-0), for averages of three GCM/RCM combinations in the RCP 8.5 climate change scenario. The list covers four seasons (DJF, MAM, JJA, SON) in the Bystra catchment area. The first adaptation scenario assumes the growth of afforestation on soils from the agricultural usefulness complex of soil 6–8 (semi-dry, permanent dry, semi-moist, permanently wet). The second adaptation scenario assumes the creation of a forested buffer for the Bystra River and its tributaries. The third adaptation scenario shows one the erosion prevention practices in the river bed, the so-called filter strips. The fourth adaptation scenario assumes the reduction of plowing on agricultural land. The fifth adaptation scenario assumes an increase in soil organic carbon content to 2%. Adaptation scenarios 1–5 are modifications of scenario 0. Scenario 0 only covers climate change in 2041–2050 (own study).

**Author Contributions:** Conceptualization, D.B. and R.W.; methodology, D.B and R.W.; software, D.B.; validation, D.B., R.W., J.K. and A.N.; formal analysis, B.J. and E.N.; investigation, D.B.; resources, D.B.; data curation, J.K. and A.K.-B.; writing—original draft preparation, D.B.; writing—review and editing, A.N., J.K. and A.K.-B.; visualization, D.B.; supervision, R.W.; project administration, R.W.; funding acquisition, R.W. All authors have read and agreed to the published version of the manuscript.

**Funding:** Research and ACP was funded by Polish Ministry of Agriculture and Rural Development, DC2.0/2021 Programme and B-Ferst project funded by the European commission.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
