Quantifying the sourcewater contribution of headwater catchments to the reviving Lake Urmia

Abstract:

The noticeable shrinkage of Lake Urmia in the last two decades has attracted global attention towards the study of water loss causes and the design of a sustainable restoration plan. Determining the source contribution of inflows to the lake (i.e., rainfall, snowmelt, and groundwater) plays an important role in deciphering the distinct contribution of climatic and anthropogenic drivers of the environmental water required for the lake restoration. In this study we explored these issues by simulating the dominant components of water and energy cycles in the 1483 km² Gadarchay River Basin (located in the southwest part of the Lake Urmia) via a 3D distributed subsurface flow model, fully coupled with a land-surface and a particle-tracking model. Given the calibrated model, we investigated the effect of the temporal resolution of climate forcing (i.e., 3, 4, 6, 8, 12, and 24 hours) on the estimated evapotranspiration rate. We also explored the impact of global warming in the form of increase in the temperature and decrease in the precipitation rate on the peakiness and intensity of runoff. The results indicated that the Peyghaleh headwater subbasin (comprising 18.75% of the Gadarchay Basin area) dominates runoff generation through ice melting in winter and spring. In particular, the spatial distribution of snowmelt, cross-validated against remotely-sensed data, significantly controls runoff fluctuations. Also, diurnal fluctuations in downward shortwave radiation witnessed remarkable impacts on the amount of evapotranspiration, i.e., daily instead of hourly data can underestimate estimated evapotranspiration by 30%.

Keywords: Snowmelt, Lake Urmia, Headwater catchment, Source contribution, Water and energy cycle modeling