Climate change or irrigated agriculture &amp;#8211; what drives the water level decline of Lake Urmia?

Stephan Schulz,Christoph Schüth,Elmira Hassanzadeh,Sahand Darehshouri

doi:10.5194/egusphere-egu2020-11448

Abstract

&lt;p&gt;Lake Urmia is one of the largest hypersaline lakes on earth with a unique biodiversity. Over the past two decades the lake water level declined dramatically, threatening the functionality of the lake&amp;#8217;s ecosystems. There is a controversial debate about the reasons for this decline, with either mismanagement of the water resources, or climatic changes assumed to be the main cause.&lt;/p&gt;&lt;p&gt;During this study we gathered an extensive hydro-meteorological data set, information about the reservoirs and the lake bathymetry. This data served for a quantification of the water budget components of Lake Urmia over the last five decades. Interestingly, a comparison of the temporal patterns of the principal natural boundary conditions of streamflow (precipitation and evaporation) with the inflow to the lake revealed that the variability of the inflow can be well explained its natural drivers. With this we can show that variations of Lake Urmia&amp;#8217;s water level during the analyzed period were mainly triggered by climatic changes.&lt;/p&gt;&lt;p&gt;However, under the current climatic conditions agricultural water extraction volumes are significant and often exceed the remaining surface water inflow volumes. This rather simple observation shows that something deeper needs to be dug here. Therefore, we performed a parsimonious hindcast experiment and run a set of development scenarios based on the previously developed water balance. This helped us to better quantify the human impact on the development of the water volume of Lake Urmia. We could show that changes in agricultural water withdrawal would have a significant impact on the lake volume and could either stabilize the lake, or lead to its complete collapse (Schulz et al., 2020).&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Schulz, S., Darehshouri, S., Hassanzadeh, E., Tajrishy, M. and Sch&amp;#252;th, C.: Climate change or irrigated agriculture &amp;#8211; what drives the water level decline of Lake Urmia, Sci. Rep., 10(1), 236, doi:10.1038/s41598-019-57150-y, 2020.&lt;/p&gt;

Highlights

Lake Urmia is one of the largest hypersaline lakes on earth with a unique biodiversity
We could show that in the last decades variation in the volume of Lake Urmia was mainly triggered by changes in climatic conditions, and even without agricultural water extraction the general trend of the lake volume variations would have been the same
Using a parsimonious modeling experiment, we were able to show that agricultural extraction has a massive influence on the resilience of the lake, as it exaggerates the general trend of declining lake volume, especially in the last two decades

Summary

Introduction

Lake Urmia is one of the largest hypersaline lakes on earth with a unique biodiversity. The interannual variability of the lake level has always been high, the extreme decline in the 90 s is a singular event, at least in the last 100 years[11,12] This loss of volume has negative impacts on the lake’s ecosystems, such as a significant reduction of the aquatic habitat accompanied by an increase of salinity to more than 300 gL−1 2, which has caused a severe slowdown of the reproduction rate of Artemia Urmiana[13]. Several studies state that the reduction of surface water inflow due to agricultural extraction predominantly caused the lake level decline[14–22] This was mainly triggered by an uncontrolled growth of the irrigated area, accompanied by the extensive construction of reservoirs, and poor agricultural water use efficiency. Their model results suggest that the influence of the reservoirs (at a storage volume of about 1 km3), the changes in precipitation directly above the lake, and the reduced inflow due to overuse of surface water are responsible for 25%, 10% and 65% of the volume loss, respectively

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Conclusion