Climate Change Effect on Soil Erosion in Vjosa River Basin

Soil erosion is closely related to climate changes, because changes to temperature and precipitation regimes may alter the erosivity of rainfall. The present study aimed to project future soil erosion phenomena in the Vjosa River Basin (VRB) using climate projections under the Representative Concentrations Pathway (RCP) 4.5 and 8.5 sce - narios. SimCLIM model was used to perform the climate projection for the years 2035 and 2050, based on histori - cal temperature and precipitation data (2000–2015). This investigation was carried out by using Erosion Potential Method EPM to estimate the effects of climate change on soil erosion in Vjosa River Basin, Albania. Results show an increase in average min and max annual temperature for both scenarios RCP4.5 and 8.5 by the end of 2050. The evaluation of the monthly precipitations for all RCPs reveals a likely decrease in summer precipitation, and a slight positive trend of winter precipitation for all time periods up to 2050. An increase in terms of eroded material and specific eroded material was estimated from the results of RCP4.5 and RCP8.5 scenarios. Thus, it can be stated that the study area has and will have a moderate erosion risk under these climate conditions.


INTRODUCTION
These changes can interfere with the quantity and intensity of rainfalls, directly interacting with watershed erosion [Chen et al. 2020]. This can lead to severe erosion in some areas and in a decrease of the phenomena in others. Sediment yields as a result of erosion can affect rivers basins, flow rate, crop productivity and flood prevention safety [Issaka et al. 2017;Lal et al. 2008]. Thus, an estimation of soil erosion in watersheds taking into consideration actual and future climate changes would be of great interest in order to prevent the phenomena. Regardless which scenario is the most accurate, climate changes are expected to highly interfere with erosion. Many authors have been using different methods to perform such estimation in various countries. In Albania, EPM has been previously used to estimate the erosion phenomena in some areas of the country [Marko et al. 2022], but to the best of the author's knowledge, there are no investigations using the EPM to estimate the soil erosion caused by climate changes.
In this study, the investigation of the effect of climate change on soil erosion in the Vjosa river basin was done using the 'Representative Concentration Pathways' (RCP4.5 and 8.5) scenarios. The Representative Concentration Pathways (RCPs) are four greenhouse gas concentration (not emission) trajectories adopted by the IPCC for its Fifth Assessment Report (AR5). The four RCPs, RCP2.6, RCP4.5, RCP6.0, and RCP8.5, are named after a possible range of radiative forcing values in the year 2100 (of 2.6, 4.5, 6.0, and 8.5 W/m 2 , respectively)

Study area
Flowing from the Pindos mountains in Greece and discharging in the southern Albania, the Vjosa river represents one of the longest transboundary rivers in the Balkan area with a total length of 272 km; 80km of Vjosa are located in Greek territory, where it is known as the Aoös (Αώος) River and the other part in Albania. Its basin is calculated to be approximately 6500 km 2 , classified as the second largest river basin in Albania. Moreover, Vjosa is one of the last wild and free flowing rivers in Europe (ref). Shushica, Drino and Bënça are the most important tributaries of the Vjosa River. VRB has a mean elevation of about 855 m a.s.l and a perimeter of about 906.13 km. Furthermore, the Vjosa river has a high biodiversity importance, since it is the natural habitat for many species.

Climate simulation
Scenarios RCP4.5 and RCP8.5 are developed by using SimCLIM4.0 model, where an ensemble of 63 General Circulation Models (GCMs) was used to generate the temperature changes for each RCP, while for the generation of the projections of precipitations an ensemble of 40 GCMs was used.

The erosion potential model EPM
In 1972, Gavrilovic designed a semi-quantitative method to evaluate the erosion coefficient in order to estimate the sediment production and transportation [Gavrilovic, 1988].
The erosion potential model has been used firstly in the Balkan area followed by other countries in Europe and in other continents [Marko et  . Parameters, such as the temperature coefficient, the actual sediment yield, sediment delivery ratio and the annual volume of soil loss, were calculated according to the Gavrilovic method. In order to evaluate the land use coefficient, soil erodibility and active erosion processes, the classification was based on the Zemljic system [Zemljic, 1971].
The equations followed by detailed description of the data set used to evaluate the Erosion Potential Method are shown in Table 2.

Data description and sources
Information gathered from different field surveys and satellite sources were used for the estimation of soil erosion in the Vjosa River Basin.
The CORINE Land Cover (2018) map was used for the evaluation of the land cover coefficient x (data in Table 1). The slope map of the Vjosa River Basin generated by a Digital Elevation Model (DEM) was used to evaluate the mean slope of each sub-basin i m . The coefficient of soil erodibility (y) of the studied area was determined from Geological maps of the Albanian Geological Service.   x -land cover coefficient y -soil erodibility φ -active erosion processes im -the mean slope (%)

RESULTS AND DISCUSSION
Analysis of the Vjosa River Basin land cover map (Figure 2a) showed that the entire surface contains mixed and coniferous forest, agriculture crops, pastures, olive groves, vineyards, irrigated and non-irrigated lands, etc. Moreover, the Vjosa River Basin has high ecological values due to the diversity of areas part of it, and to the presence of rare flora species. The coefficient of land cover for VRB was determined based on the data of Table 1.
Regarding the slope of the study area it was generated by a Digital Elevation Model (DEM), and it was found that it varies from 2% to 28%. The higher slope belongs to the upper part of the VRB, while the low slope to the lower part of the VRB.  The major part of the geology of the Vjosa River Basin belongs to the Ionian zone, which mainly consists in Neocene's deposits (sandstone, siltstone, conglomerate and partly marlstone), Flysch deposits, Karstic calcareous deposits, and ultrabasic rock [Schiemer et al. 2018]. The maps of land cover, slope and geology of the study area are given in Figure 2.
As it can be seen from the graphs the RCP4.5 scenario projects, there is an increase in average monthly temperatures by 2050 at almost all stations of VRB. Figure 3 shows clearly not only the increase of temperature compared to the historical period but also the increase of these values from 2035 to 2050. Permet station has the most significant change on average monthly temperatures for all seasons for the periods 2020-2035 and 2036-2050. The analysis highlighted an increase in average min annual temperature of (+0.5 °C) by 2035, and (+0.8 °C) by 2050. The average max annual temperature is expected to increase (+0.6 °C) by the end of 2050.
A similar increase in average monthly temperatures by 2050 at almost all stations of VRB is projected for the RCP8.5 scenario. Figure 4 shows the increase of average monthly temperature for the periods 2020-2035 and 2036-2050 compared to the historical data. Even in this projection, Permet station shows the most significant change on average monthly temperatures for all seasons. The analysis highlights an increase in average min annual temperature of (+0.7 °C) by In general, RCP4.5 and RCP8.5 project a slight positive trend of winter precipitation for all time periods up to 2050 as it is shown in Figure 5 and 6, respectively. These positive trends may be attributed to higher winter temperatures, resulting in more rainfall than snow.
On the basis of the results and parameters of Vjosa river basin presented above, the EPM method was used for the estimation of the erosion coefficient, the amount of eroded sediment (m 3 /year), and the specific eroded sediment (m 3 / ha/year) for the baseline (2000-2015) and future (2020-2035 and 2036-2050) periods, for the RCP4.5 and 8.5 scenarios. Table 3 presents the results obtained for Vjosa River Basin from the calculations made according the Erosion Potential Method, where the results about the specific eroded sediment were obtained as a report of eroded material and the surface of the VRB expressed in ha.
The results obtained from the use of the EPM model were compared between them in order to quantify the effects of climate change on soil erosion in the Vjosa River Basin. For both scenarios, RCP4.5 and RCP8.5, an increase in terms of eroded material and specific eroded material can be noticed. Specifically, the RCP4.   It is evident that the increase trends are similar in all projections RCPs and periods, with slight differences due to temperature and precipitation changes. Moreover, climate changes affect even other characteristics of the study area which are related to the data set used for this evaluation.

CONCLUSIONS
This investigation has been carried out as the first study using Erosion Potential Method EPM to estimate the effects of climate change on soil erosion in the Vjosa River Basin, Albania. On the basis of historical temperature and precipitation data (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015), the climate projection for the years 2035, and 2050 under RCP4.5 and RCP8.5 scenarios, was performed using SimCLIM model. It was found that all scenarios for the Vjosa River basin suggest that the area is likely to become warmer. The results for RCP4.5 scenario show an increase in average min annual temperature of (+0.8 °C) by 2050, and the average max annual temperature is expected to increase by (+0.6 °C) by the end of 2050.
In turn, the results for RCP8.5 scenario show an increase of (+1.0 °C) by 2050 in average min annual temperature, and (+0.9 °C) by the end of 2050 in the average max annual temperature. The evaluation of the monthly precipitations for all RCPs reveals a likely decrease in summer precipitation, and a slight positive trend of winter precipitation relative to the 2000-2015 period for all time periods up to 2050.
For both scenarios, RCP4.5 and RCP8.5, an increase in terms of eroded material and specific eroded material was estimated. Specifically, RCP4.5 scenario projects an increase of 547.4 m 3 / year and 0.85 m 3 /ha/year by the end of 2050.
Regarding the RCP8.5 scenario, the projection shows an increase of 540.5 m 3 /year 0.84 m 3 / ha/year by the end of 2050. On the basis of the values of the specific eroded sediment, it can be stated that the study area has and will have a moderate erosion risk under this climate conditions.
Finally, considering these results it can be stated that more investigations of the effect of climate change on other areas are necessary for adaption and mitigation measures.