Quantifying the impacts of human water use and climate variations on recent drying of Lake Urmia basin: the value of different sets of spaceborne and in-situ data for calibrating a hydrological model

Abstract

Abstract. During the last decades, the endorheic Lake Urmia basin in northwestern Iran has suffered from decreased precipitation, groundwater levels and a very strong reduction in the volume and more recently also in the extent of Lake Urmia.Human water use has exacerbated the desiccating impact of climatic variations. This study quantifies the contribution of human water use to the reduction of inflow into Lake Urmia, to the loss of lake water volume and to the loss of groundwater and total water storage in the entire Lake Urmia basin during [2003][2004][2005][2006][2007][2008][2009][2010][2011][2012][2013]. To this end, the WaterGAP Global Hydrology Model (WGHM) 15 was manually calibrated specifically for the basin against multiple in-situ and spaceborne data, and the best-performing calibration variant was run with or without taking into account water use. Observation data encompass remote-sensing based time series of annual irrigated area in the basin from MODIS, monthly total water storage anomaly (TWSA) from GRACE satellites and monthly lake volume. In-situ observations include time series of annual inflow into the lake and basin averages of groundwater level variations based on 284 wells. In addition, local estimates of sectoral water withdrawals in 2009 and 20 return flow fractions were utilized. Four calibration variants were set up in which the number of considered observation types was increased in a stepwise fashion. The best fit to each and all observations is achieved if the maximum amount of observations is used for calibration. Calibration against GRACE TWSA improves simulated inflow into Lake Urmia but still overestimates it by 90%; it results in an overestimation of lake volume loss, underestimation of groundwater loss and a shifted seasonality of groundwater storage. Lake and groundwater dynamics can only be simulated well if calibration against 25 groundwater levels leads to adjusting the fractions of human water use from groundwater and surface water. According to our study, human water use was the reason for 50% of the total basin water loss of about 10 km 3 during 2003-2013, for 40% of the Lake Urmia water loss of about 8 km 3 and for up to 90% of the groundwater loss. Lake inflow was 40% less than it would have been without human water use. We found that even without human water use, Lake Urmia would not have recovered from the significant loss of lake water volume caused by the drought year 2008. These findings may serve to support water 30 management in the basin and more specifically Lake Urmia restoration plans.Hydrol. Earth Syst. Sci. Discuss., https://doi

Introductory Chapter: Lake Urmia - A Witness to the Simultaneous Effects of Human Activities, Climate Change, and Global Warming

“…The reduction in rainfall along with decreasing groundwater tables and a rising population in the basin will likely exert growing pressure to continue diverting stream flow before it reaches Lake Urmia. Over the last two decades, it was sharply dried and its surface reduced about 80% from 2003 [5]. The water table of Lake Urmia was decreased severely in recent years which caused serious socio-environmental consequences [4].…”

“…Hosseini-Moghari using spatial and hydrology and in situ data assessed the contribution of human acts to the decline of inflow water for the lake, the groundwater table reduction, and water storage in the lake reservoir [5]. They found that 50% of the total basin water loss is due to sectorial management of water resources in the region.…”

Meeting agricultural and environmental water demand in endorheic irrigated river basins: A simulation-optimization approach applied to the Urmia Lake basin in Iran

“…Overuse of irrigation in the basin coupled with a recent drought has resulted in decreased environmental flows to Lake Urmia and led to continued shrinking of the lake (Hosseini-Moghari et al, 2018;Moshir Panahi et al, 2020;Schulz et al, 2020). As such, environmental flow requirements for Urmia lake are in direct competition with agricultural water demand.…”

System dynamics applied to water management in lakes*

“…Hosseini‐Moghari et al . (2018) quantified the effect of human water use in reducing the inflow into Urmia Lake. They discovered that even if human water use were eliminated completely, Urmia Lake would have a significant loss of water caused by drought.…”