determination of the effective factors on the water balance of urmia lake basin with a focus on precipitation trends.

Prevention of water loss for the urmia lake due to the drought is environmentally crucial for the lake basin and it seems that, the analysis of the historical process of factors governing the water mass balance equation for the catchment leading to the lake can provide insights on what has to be done. in order to do that, statistical significance for potential breaking points and rate of changes over time points of precipitation and runoff for 25 hydrological basin stations based on the data regarding annual precipitation and annual runoff related to the whole span of the lake basin from 1977 to 2019 has been studied and surveyed using mannkendall test, petit test and sen’s slope estimator. for all hydrological basinstations breaking points have been observed in the water discharge time points from 1993 to 2005 and the decline of water discharge. significant increase in precipitation in the entire urmia catchment area of about 0.16 mm at a indicates its stability during the study period. the annual runoff of the studied basins into lake urmia in the two time periods before and after the discharge drop were estimated at 4.671 and 1.885 billion cubic meters per year, respectively, indicating volume reduction of 2.786 billion cubic meters (59.6%). looking at the lake urmia subbasins annual discharge reduction data, it can be seen that zarrinehroud with the largest share of 34.5% and mahparishai with smallest share of 0.2%, and the rest in between, contribute to the occurrence of draught for lake urmia.