Unraveling the hydrological dynamics of Lake Urmia: A comprehensive analysis of the impact of climatic changes and agricultural water extraction on lake level decline

Lake Urmia, one of the largest hypersaline lakes on earth, known for its unique biodiversity, has experienced a profound and alarming decline in water levels over the last two decades, posing a huge threat to the lake's complex ecosystems. The causes of this decline are subject to controversy and vary between blaming mismanagement of water resources and attributing it to climate change. In order to find out the reasons for the drying up of Lake Urmia, we have conducted a series of studies to quantify the water balance components of Lake Urmia and analyze their temporal evolution and interaction over the last five decades. These studies encompass various methods, including the development of an improved bathymetric model using remote sensing data (Schröder et al., 2022), laboratory experiments to estimate the evaporation of the dried-up lake bed (Darehshouri et al., 2020, 2023) as well as setting up a water balance model, accompanied by a statistical analysis of lake inflow and meteorological variables (Schulz et al., 2020). Our results show that the fluctuations in the water levels of Lake Urmia during the study period are mainly related to weather conditions. Nevertheless, scenario simulations also revealed that agricultural water extraction, which has even exceeded the residual lake inflow in recent years, is also a decisive factor. The influence of irrigation water withdrawal on the volume of the lake can thus either strengthen the stability of the lake or accelerate its collapse. This differentiated understanding is essential for informed decision-making and sustainable management strategies to preserve or restore the ecological functioning of Lake Urmia. Darehshouri, S., Michelsen, N., Schüth, C., and Schulz, S.: A low‐cost environmental chamber to simulate warm climatic conditions, Vadose Zone Journal, 19, https://doi.org/10.1002/vzj2.20023, 2020. Darehshouri, S., Michelsen, N., Schüth, C., Tajrishy, M., and Schulz, S.: Evaporation from the dried-up lake bed of Lake Urmia, Iran, Science of The Total Environment, 858, 159960, https://doi.org/10.1016/j.scitotenv.2022.159960, 2023. Schröder, T., Hassanzadeh, E., Darehshouri, S., Tajrishy, M., and Schulz, S.: Satellite based lake bed elevation model of Lake Urmia using time series of Landsat imagery, Journal of Great Lakes Research, 48, 1710–1717, https://doi.org/10.1016/j.jglr.2022.08.016, 2022. Schulz, S., Darehshouri, S., Hassanzadeh, E., Tajrishy, M., and Schüth, C.: Climate change or irrigated agriculture – what drives the water level decline of Lake Urmia, Scientific Reports, 10, 236, https://doi.org/10.1038/s41598-019-57150-y, 2020.