Impact of the North Atlantic Oscillation on Middle Eastern climate and streamflow

Interannual to decadal variations in Middle Eastern temperature, precipitation and streamflow reflect the far-field influence of the North Atlantic Oscillation (NAO), a dominant mode of Atlantic sector climate variability. Using a new sea surface temperature (SST) based index of the NAO and available streamflow data from five Middle Eastern rivers, we show that the first principal component of December through March streamflow variability reflects changes in the NAO. However, Middle East rivers have two primary flooding periods. The first is rainfall-driven runoff from December through March, regulated on interannual to decadal timescales by the NAO as reflected in local precipitation and temperature. The second period, from April through June, reflects spring snowmelt and contributes in excess of 50% of annual runoff. This period, known locally as the khamsin, displays no significant NAO connections and a less direct relationship with local climatic factors, suggesting that streamflow variability during this period reflects land-cover change, possibly related to agriculture and hydropower generation, and snowmelt.