Investigation of lake drying attributed to climate change

In recent decades, climate change has been of great concern due to its effect on water level and its impact on aquatic ecosystems. Urmia Lake, the largest inland wetland in Iran, has been shrinking. There is a great concern whether it will dry up like the Aral Sea. Therefore, a hydrodynamic model has been developed to simulate the condition of Urmia Lake. The model has been validated using the known annual data on precipitation, evaporation, run off, river discharges and water level which are available for the last 35 years. Different hydrological conditions regarding lake input and output data were tested and water depth was calculated using bathymetry to predict water-level fluctuations in the future. The results predict that the water level will decrease continuously. The lake will be dried up in about 10 years if very dry conditions continue in the region. The drought speed cannot be reduced and there is no potential to develop a water-usage program. Besides, the lake water depth decrease is more slightly, applying alternate wet and dry-period conditions. In some hydrological conditions there is a good potential to consider water development projects. The sensitivity analysis of different parameters indicates that the lake is highly sensitive to river discharges, which implies that the water development project plans will disturb the lake ecosystem if implemented up to 2021 and integrated watershed management plan for the lake can change the condition by regulating the dam output

Ecological Health Assessment of the Surface Sediments of the Coral Reefs of Khark and Kharko Islands (Persian Gulf, Iran)

To assess the ecological risk of the coral reef habitats of Khark and Kharko islands in the Persian Gulf, (Bushehr province), the surface sediment samples were collected from seven stations, in September 2019. The islands have a great ecological value due to the presence of coral reefs. The amounts of potentially toxic elements, sediment texture, total organic matter, total phosphorus and total nitrogen in the sediments were measured by inductively-coupled plasma mass spectrometry, sieve analysis, furnace burning method, spectrophotometer, and Kjeldahl, respectively. The mean concentrations of Al, Fe (%) and Ni, Pb, Zn, V, TP and TN (mg/kg) in the sediments were recorded 0.76±0.53, 0.55±0.35, 35±19, 2.1±1.5, 22±10, 40±25, 0.7±0.3 and 14.7±6.2, respectively. Based on the amount of Ni and Zn enrichment factors (moderate to very sever, respectively), their source around Khark Island could be related to human activities, such as oil industries. Pollution load index (0.06-0.25) showed all stations without pollution. The amount of Ni in stations 1 and 7 were higher than the "range of moderate effect" and "level of possible effects", which indicates the possible biological effects of this element on the benthic organisms. In general, the ecological quality of surface sediments around Kharko was better than Khark Island

Life-cycle simulations of shallow frontal waves and the impact of deformation strain

The life-cycle of shallow frontal waves and the impact of deformation strain on their development is investigated using the idealised version of the Met Office non-hydrostatic Unified Model which includes the same physics and dynamics as the operational forecast model. Frontal wave development occurs in two stages; first, a deformation strain is applied to a front and a positive potential vorticity (PV) strip forms, generated by latent heat release in the frontal updraft; second, as the deformation strain is reduced the PV strip breaks up into individual anomalies. The circulations associated with the PV anomalies cause shallow frontal waves to form. The structure of the simulated frontal waves is consistent with the conceptual model of a frontal cyclone. Deeper frontal waves are simulated if the stability of the atmosphere is reduced. Deformation strain rates of different strengths are applied to the PV strip to determine whether a deformation strain threshold exists above which frontal wave development is suppressed. An objective method of frontal wave activity is defined and frontal wave development was found to be suppressed by deformation strain rates \ge 0.4\times10^{-5}\mbox{s}^{-1}. This value compares well with observed deformation strain rate thresholds and the analytical solution for the minimum deformation strain rate needed to suppress barotropic frontal wave development. The deformation strain rate threshold is dependent on the strength of the PV strip with strong PV strips able to overcome stronger deformation strain rates (leading to frontal wave development) than weaker PV strips

Classifying dynamical forcing mechanisms using a climatology of extratropical cyclones

A climatology of almost 700 extratropical cyclones is compiled by applying an automated feature tracking algorithm to a database of objectively identified cyclonic features. Cyclones are classified according to the relative contributions to the midlevel vertical motion of the forcing from upper and lower levels averaged over the cyclone intensification period (average U/L ratio) and also by the horizontal separation between their upper-level trough and low-level cyclone (tilt). The frequency distribution of the average U/L ratio of the cyclones contains two significant peaks and a long tail at high U/L ratio. Although discrete categories of cyclones have not been identified, the cyclones comprising the peaks and tail have characteristics that have been shown to be consistent with the type A, B, and C cyclones of the threefold classification scheme. Using the thresholds in average U/L ratio determined from the frequency distribution, type A, B, and C cyclones account for 30\%, 38\%, and 32\% of the total number of cyclones respectively. Cyclones with small average U/L ratio are more likely to be developing cyclones (attain a relative vorticity \ge 1.2 \times 10^{-4} \mbox{s}^{-1}) whereas cyclones with large average U/L ratio are more likely to be nondeveloping cyclones (60\% of type A cyclones develop whereas 31\% of type C cyclones develop). Type A cyclogenesis dominates in the development region East of the Rockies and over the gulf stream, type B cyclogenesis dominates in the region off the East coast of the USA, and type C cyclogenesis is more common over the oceans in regions of weaker low-level baroclinicity