Modeling Past Episodes of Erosion in the Lake Orūmiye (Urmia) Basin: Analogues for Future Landscape Dynamics

During the Holocene Lake Orūmiye has been subjected to significant changes in climate. These have impacted the surround vegetation and runoff, and erosion rates of the surrounding basin. Shifts in seasonal rainfall from winter to summer dominated patterns have resulted in dramatic changes in the Orūmiye Basin’s vegetation cover from grass to shrub dominated communities. The degree of ground surface exposure to erosion had responded to these changes. Today, as Lake Orūmiye continues to shrink, large areas of lake bottom become exposed to seasonal wind erosion. Seasonal wetting and drying of lake bottom sediment breaks-up crusts that have formed, making them more susceptible to aeolian activity. Past climate and paleoecological analogues indicate that in the future, if global warming becomes a significant factor, increasingly drier conditions will reduce the vegetation cover protecting the landscape surrounding Lake Orūmiye and the unprotected ground surface will be subjected to increased erosion. Sediments will be carried into Lake Orūmiye, joining those already there, providing new, largely unconsolidated materials, which can be easily eroded by wind. These sediments will also accelerate filling of the basin, and shallowing of the lake. The rate of warm season evaporation will increase, as will the length of the drying season, and the annual exposure to aeolian erosion. A model of sediment yield per square kilometer correlated to effective precipitation can be used to predict future erosion rates. The model can be used to reveal past climate-based erosion cycles, and can be validated by radiocarbon dated alluvial records within the Lake Orūmiye Basin. Such a model has been developed in southern Italy and applied to local alluvial sequences and found to have a high degree of correlation with significant changes in seasonal, especially Spring and Summer rainfall. In addition, the model can be calibrated, to take into account human activity. In the Lake Orūmiye Basin, this model can be used to predict the rate of erosion during the coming century resulting from reduced effective precipitation due to increasing global temperature. It is estimated that each degree centigrade increase in regional temperature will result in a ten percent decrease in effective precipitation. The two-degree increase in global temperature projected during the next century should result in a 20% decrease in effective precipitation in the Lake Orūmiye Basin. This decrease in effective precipitation will significantly decrease vegetation cover, increase erosion rates, and the deposition of fresh sediment on the floor of Lake Orūmiye. Increased Aeolian erosion, and dust storms will cause dramatic increases in downwind human respiratory illness and cancer clusters during the coming decades.