There are various explanations for this surprisingly large difference, including hydrological measurement errors, and large-scale abstraction between Mosul and Kut for flood control or other purposes. Based on the available discharge data, mean water yield of the Tigris River appears to exceed Euphrates water yield. No trend can be observed at Mosul, while at Kut the records show a significant negative trend. It should be noted, however, that the data record at Kut exhibits more data gaps and missing values than the discharge record at Mosul, which may bias the trend analysis.