In recent years, shallow lakes in the Lakes Region of Türkiye have dried up, and the water level of Burdur Lake has decreased significantly (Kantarcı, 2008). To understand and explain the changes in wetlands, it is necessary to consider the changes in the rivers that feed the wetland, climate conditions, and other anthropogenic impacts. To ensure the continuity of a lake, the amount of water entering the lake must be equal to or greater than the amount of water leaving the lake (Jones et al., 2001). Factors that cause level changes in lakes are climate change, excessive and conscious use of groundwater for agricultural irrigation, and dams and lakes built on water sources that feed the lake (Du et al., 2001; Legesse and Ayenew, 2006; Kiage et al., 2007; Yıldırım et al., 2011; Yuan et al., 2015; Baydoğan and Sarp, 2016; Soyaslan and Hepdeniz, 2016; Göncü et al., 2017).
The increase in air temperatures due to climate change increases the evaporation rate in the lake, the rivers that feed the lake, and the dams and lakes built on the rivers. The increase in evaporation causes a decrease in the amount of water entering the lake and an increase in the amount of water leaving the lake. As a result, shrinkages in the surface areas of the lakes and decreases in water volume occur (Kantarcı, 2008). According to long-term precipitation data, 75% of the annual total precipitation in the region falls into Burdur Lake. Furthermore, according to long-term evaporation data, an average of 1.34 m of level loss is caused by the water evaporating from the lake’s surface. The lake experienced a level loss of 2.41 m between 1964 and 1975, 10 m between 1975 and 2002, and 3.74 m between 2002 and 2017, resulting in a total level loss of 16.15 m (Beyhan, 2007; Şener and Morova, 2011; Gözükara et al., 2019). It is understood that the level losses are not entirely due to climate change, and other factors also cause level loss.
Excessive and careless agricultural irrigation on the rivers that feed the lake causes a decrease in river flow and a reduction in the amount of water reaching the lake (Kantarcı, 2008; Göncü et al., 2017). With the implementation of agricultural irrigation in the Burdur Basin, there has been a 4% increase in agricultural irrigation areas between 1972 and 2014 and a 1% decrease in total wetland surface area (Göncü et al., 2017; Soyaslan and Hepdeniz, 2017). Also, legal and illegal drilling for agricultural irrigation causes the depletion of underground water. As the underground water decreases, the groundwater is pulled deeper. Until balance is achieved between underground and surface water, it seeps underground through cracks and fissures. This situation causes a decrease in both the river flow and the amount of water reaching the lake (Beyhan et al., 2007).
In low-flow rivers, the amount of water lost through leakage from cracks and crevices due to evaporation and drying up of the riverbed is higher than in high-flow rivers. This significantly reduces the amount of water that reaches the lake (Ataol, 2010; Soyaslan and Hepdeniz, 2016; Göncü et al., 2017). One of the most important of these dams is the Karaçal. The Karaçal Dam is built on the Bozçay River, which is one of the important rivers that feed Burdur Lake. Due to the dam holding back water from the Bozçay, the inflow of water to Burdur Lake has decreased significantly (Ataol, 2010; Atayeter and Yayla, 2021). During episodes of sudden water level and volume decrease in Burdur Lake, measurements taken on the Bozçay and Beydüz streams, which feed the lake, revealed a flow loss of 84% at the Bozçay-Karacal station, 77% at the Bozçay-Yazıköy station, and 38% on the Beydüz stream. This flow loss is attributed to increased water seeping into the ground due to water being drawn from regional wells (Beyhan et al., 2007). The amount of water filtering underground alone will not result in a proportional decrease in river flows. The factor that contributes the most to this reduction is the construction of dams and reservoirs on river tributaries, as a significant portion of the water captured by these structures is not returned to the riverbed.
In addition, population growth is also shown to be another reason for the decrease in lake levels. As the amount of water consumed increases due to the increase in human population, the water level in the dams decreases. Since dams hold back a significant portion of the river until they reach a sufficient fill level, this leads to a decrease in the flow rate of the river and the amount of water reaching the lake.
The Burdur Lake region is characterized by a drought period from 1988–1995, a rainy period from 1995–2003, a drought period from 2006–2008, and a trend towards increased rainfall from 2008–2011 (Beyhan et al., 2007zükara et al., 2019). The drop in lake levels due to loss of flow between 1980 and 1996 was approximately 7.8 m (Beyhan et al., 2007), and the total drop in lake levels from 1964 to 2017 was 16.15 m (Beyhan, 2007; Şener and Morova, 2011; Gözükara et al., 2019). It is estimated that the lake’s water level will fall 25 m below its current level in 2080 (Ataol, 2010). As a result of the drop in water levels, the surface area of Burdur Lake decreased by 40% from 1985 to 2022 (Taş and Akpınar, 2021). The lake shoreline has receded by 11.34 km from the northeast and 1.19 km from the southwest from 1975–2017 (Gözükara et al., 2019).
The present study determined that the loss of volume due to the level decrease between 1985 and 2022 was 32%. Accordingly, the lake has lost 0.9% of its volume every year. It was found that the surface area of Burdur Lake decreased by 40%. Therefore, the lake’s surface area has decreased by approximately 1.1% yearly. As a result of the decrease in volume and the reduction in surface area, the lake has receded 13.20 km from the northeast and 1.3 km from the southwest. While our findings regarding the surface area are consistent with the literature, our findings on volume and lake recession contribute to the literature.
When evaluated in terms of future findings, it is estimated that if the conditions continue according to the same trend, the surface area of Burdur Lake will decrease to zero between 2075 and 2076, and the volume will be depleted between 2109 and 2110, causing the lake to dry up. Although there seems to be a discrepancy between the surface area and volume values, there is no inconsistency. This is because the southwestern part of the lake has a deep and bowl-shaped pit. As the lake loses water over time, the surface area will shrink, and the water mass will finally collect in this bowl-shaped pit. After this stage, the surface area is predicted to shrink, and a deep water mass will remain. Small surface areas and deep water masses have a slower heating and evaporation rate than large surface areas and shallow water masses (Muslu,1993). Therefore, after the water has collected in the basin, the evaporation rate will slow down, and the water sources that feed the lake will not be able to reach the basin. Consequently, precipitation is predicted to be the lake’s only water source. Even in today’s climate conditions, the precipitation rate cannot meet the evaporation rate. As it is also anticipated that temperatures will increase in the coming years, it is predicted that the water inside the basin will gradually decrease from year to year and will be completely depleted between 2109 and 2110.
A significant proportion of the surface area and volume loss in Burdur Lake is attributed to the dams and reservoirs on the main and tributary rivers that feed the lake, as stated by Şener et al. (2005). Other factors include excessive use of groundwater and surface water for agricultural activities and climate change (Du et al., 2001; Legesse and Ayenew, 2006; Beyhan et al., 2007; Kiage et al., 2007; Kantarcı, 2008; Ataol, 2010; Yıldırım et al., 2011; Yuan et al., 2015; Baydoğan and Sarp, 2016; Soyaslan and Hepdeniz, 2016; Göncü et al., 2017).
Lakes and other wetlands are of great ecological, economic, and social importance due to their benefits. As Burdur Lake continues to lose water, the reed beds will dry up, the salinity of the lake water will increase, and numerous species of flora and fauna, including local and migratory bird species, that benefit from the lake in various ways will be adversely affected (Ertuğrul et al., 2017; Gülle, 2021; Öztürk, 2022). In addition, the shrinking of the lake will alter the microclimatic conditions in the lake basin and reduce humidity. This will result in hotter summers and colder winters in the lake area, leading to significant commercial agricultural losses in Burdur and Isparta provinces. This is because the cultivation of economically important species such as rose (Rosa damascena) and lavender (Lavandula sp.) will be negatively affected, and farmers will incur losses. This situation will indirectly affect the cosmetic and healthcare sectors adversely. Therefore, the conservation and restoration of the lake are of great importance, not only from an ecological perspective but also from a socioeconomic perspective.