Sajad Ahmad Hamidi

Climate variability and anthropogenic effects on Lake Urmia water level fluctuations, northwestern Iran

ABSTRACT Lake Urmia, the second largest hyper-saline lake on Earth, has recently experienced a dramatic water-level reduction. This could have been caused by climate change or other anthropogenic effects; however it could also be a part of natural climate variability. To explore the hydroclimate variability effect on the lake water level, two teleconnections were considered for analysis: the Southern Oscillation Index (SOI) and the North Atlantic Oscillation (NAO). Spectral and coherency analyses were used to recognize the frequency components and the relationship between the teleconnections and the lake water-level fluctuations. The results show that the recent water level fall and the rise of water level in 1994–1999 cannot be explained by the natural periodic behavior of Lake Urmia. The inter-decadal water-level oscillations are coherent with NAO and SOI components of such oscillations. The anthropogenic effect on the lake water level was also explored using non-parametric trend analysis. The results show that the lake water level has a positive trend between 1966 and 1995, but the trend is not significant at a 95% confidence level. However, the trend between 1995 and 2009 is negative and it is significant at a 99% confidence interval. This study shows that the very recent fall in water level is due to anthropogenic impacts rather than natural variability. Editor Z.W. Kundzewicz; Associate editor not assigned

Assessment of a 3D Hydrostatic Model (POM) in the Near Field of a Buoyant River Plume in Lake Michigan

River plumes are the major source of nutrients, sediments, and other pollutant into the coastal waters. The predictive capability of a 3D hydrodynamic model (POMGL), a version of the common Princeton Ocean Model (POM), adapted for the Great Lakes, is assessed versus field measurements. The model was applied to simulate the nearshore hydrodynamics as the Grand River plume entering Lake Michigan. A nesting technique was adapted to represent the circulation and thermal structure of the surface river plume with a higher resolution. The model was compared with extensive field studies in the vicinity of Grand Haven. The current predictions showed fairly good agreement with observations, although the thermal structure of the flow especially near the river mouth was not very well represented. The model showed a weak stratification and a mild temperature transition from the plume to the lake water and therefore more diffusion. Application of hydrostatic models in exchange flows (e.g., buoyant river plumes) is recommended with reservations and coupling of these models with near field entrainment or empirical models to consider the nonhydrostatic nature of lake-river interface currents.

Using MODIS remote sensing data for mapping the spatio-temporal variability of water quality and river turbid plume

Fox River is the main source of land-based pollutants that flows into the southern Green Bay of Lake Michigan. Evaluation of water quality is normally based on time consuming and expensive in situ measurements. Remotely sensed data is an efficient alternative for field monitoring because of its spatial and temporal coverage. In this study, remote sensing imagery combined with in situ measurements of water quality were used to estimate an empirical relationship between water surface reflectance and water quality parameters including water turbidity and Total Suspended Sediment (TSS). Surface reflectance values is obtained from MODerate Resolution Imaging Spectroradiometer (MODIS) aboard the Aqua satellite. The empirical equations were derived from data over summers 2011–13 and show high correlation coefficients of equal to 0.83 and 0.87 for TSS and turbidity respectively. The validity of the proposed equations was tested for summer 2014 data. The NRMSE for prediction of measured data by the proposed equations are 0.36 and 0.3 for TSS and turbidity. Remotely sensed data was also used to produce water quality maps to improve our understanding of the spatiotemporal variations of Fox River turbid plume. The proposed approach can be extended to other coastal regions of Great Lakes and provide a framework to study pollution transportation in coastal areas.

A Coupled Empirical-Numerical Model for a Buoyant River Plume in Lake Michigan

A coupling technique is developed to predict the behavior of a buoyant river plume in a lake. The model incorporates a 3D hydrodynamic model (POMGL) and a 3D particle tracking model (Partic3D) for the far-field transport computations. The source conditions for the particle tracking model are obtained from a near-field model derived from the characteristics of the plume analyzed from extensive field studies on the Grand River plume, Lake Michigan. The empirical near-field model was developed to predict the geometry of the plume, dilution, and centerline trajectory near the river mouth, and to provide the concentration and location of the particles to be released in the far field. The coupled empirical-numerical model shows improved predictions in the near field versus the single numerical model. The present results strongly advocate the use of model combinations in order to improve coastal diffusion and transport processes. The primary application of the technique is in recreational water early-warning and forecasting systems that will estimate the immediate and short-term risk of exceeding pathogen indicator concentration criteria in lakes and coastal areas.

Physical Drivers of the Circulation and Thermal Regime Impacting Seasonal Hypoxia in Green Bay, Lake Michigan

The physical processes that drive the circulation and the thermal regime in the bay largely control the duration and persistence of hypoxic conditions in Green Bay. A review of previous studies, existing field data, our own measurements, hydrodynamic modeling, and spectral analyses were used to investigate the effects on the circulation and the thermal regime of the bay by the momentum flux generated by wind, the heat flux across the water surface, the Earth’s rotation, thermal stratification and the topography of the basin. Stratification and circulation are intimately coupled during the summer. Field data show that continuous stratification developed at regions deeper than 15–20 m between late June and September and that surface heat flux is the main driver of stratification. Summertime conditions are initiated by a transition in the dominant wind field shifting from the NE to the SW in late June and remain in a relatively stable state until bay vertical mixing in early September. It is during this stable period that conditions conducive to hypoxia are present. Wind parallel to the axis of the bay induces greater water exchange than wind blowing across the bay. During the stratified season flows in the bottom layers bring cold water from Lake Michigan to Green Bay and surface flows carry warmer water from the bay to Lake Michigan. Knowledge of the general patterns of the circulation and the thermal structure and their variability will be essential in producing longer term projections of future water quality in response to system scale changes.

Multi-decadal and multi-centennial variability in Colorado River streamflow

ABSTRACT A 1240-year-long record of reconstructed annual flows of the Colorado River at Lees Ferry is analysed using singular spectrum analysis and multi-taper method of spectral analysis. Spectral analysis of the 100-year-long recent record of annual flows of Colorado River in the measured and reconstructed forms shows similar oscillations in high- and low-frequency bands. Therefore, the oscillatory components and trends extracted from the reconstructed data are a good representative of inter-annual, multi-decadal, and multi-centennial variability of natural flow in the river. In Colorado River the length of flow data is 1240 years and multi-centennial and multi-decadal oscillatory components can be extracted at a high confidence level. In this research we attempt to find whether the changes in streamflow in the twentieth century are due to an external cause such as climate change or whether they are part of the natural variability of flow observed in the past. The results suggest that there is only a part of the linear trend, caused by climate change or man-made effects, and an important part of that is due to climate variability which is believed to be totally natural. The same line of climate variability is still acting on our planet, and it may have gained new aspects due to the change in atmospheric composition and circulation as a result of anthropogenic effects. This may cause serious limitations to the water sustainability and water availability on the earth.