Noel Carbajal

A numerical study of the ex-ROFI of the Colorado River

The freshwater discharge of the Colorado River into the Gulf of California has been reduced to negligible quantities since the construction of the Hoover Dam in 1935. These radical anthropogenic changes in the hydrography of the Colorado River Delta had striking repercussions on both physical and biological processes. Using historical river discharge data, the changes in the flow dynamics and hydrographic patterns before and after the drastic freshwater reduction are studied numerically, using a three-dimensional nonlinear shelf model. The results are applied to assess the environmental impact of the reduction of river discharge on the area. Satellite imagery is also used to compare our results with observed fronts.

Simulation of tides, residual flow and energy budget in the Gulf of California

Abstract With the application of a two-dimensional nonlinear hydrodynamical-numerical semi-implicit model, the principal tides M 2 , S 2 , K 2 , N 2 , K 1 , P 1 and O 1 were studied. Energy budgets of the semi-diurnal M 2 and S 2 were calculated separately. The linear sum of these budgets was compared with the tidal energy budget obtained when these two tidal constituents interact. Since a quadratic form for the bottom friction was used, remarkable differences were found. The results show that in the area of the Colorado River delta, the dissipation of tidal energy is very strong. Intense tidal currents were observed in the same region and over the Salsipuedes Sill. Energy budgets calculated for forcing waves of different periods, but of the same amplitude, were used to estimate the principal periods of resonance. Although the topography of the Gulf is very complex, the model reproduced observed sea-surface elevation and current patterns. To study spring tide conditions, the above seven tidal constituents were simulated. Estimates of residual currents reveal the presence of several intense cyclonic and anticyclonic gyres. Over the Salsipuedes Sill, residual currents of the M 2 tide reach values of more than 15 cm s −1 . Horizontal distributions of dissipation rates of tidal energy and of kinetic energy were also obtained.

Tidal current amphidromic system in semi-enclosed basins

Abstract In this paper the behaviour of tidal currents in semi-enclosed basins is examined by treating the Taylor problem and by numerical modeling of the M 2 tide in the North Sea. This study shows that in a large semi-enclosed basin current and nodal (amphidromic) points for a tidal constituent will normally be found. These current amphidromic points (CAPS) can be divided into two groups according to their structure, namely middle CAP and end CAP; the former exists in pairs while the latter exists singularly. The amphidromic systems for current and sea surface elevation are closely connected. Between two elevation amphidromic points (EAPs) there exists one pair of middle CAPS with opposite rotation directions. In real ocean basins, this amphidromic pair is usually separated by a certain distance. The main end CAP appears at the bay head while some end CAPS may occur in small bays of a large basin. Normally, anticlockwise rotation appears at the end CAPS in the northern hemisphere. At CAPs, the current speed is not necessarily zero, but the tidal current ellipse there should reduce to a circle.

Two applications of Taylor's problem solution for finite rectangular semi-enclosed basins

Abstract Taylors problem solution for a finite, rectangular, of constant depth, homogeneous and semi-enclosed basin is applied in two different cases. Bottom friction is taken into account and boundary forcing is specified at the open side. In the first application, current amphidromic points (CAPS) are investigated. In order to achieve this aim, a study of the sensitivity of horizontal distributions of ellipticity to changes in the sea surface elevation designated at the open boundary and to frictional effects was performed. The calculations show that established results for semiinfinite channels, i.e. a pair of current amphidromes related to velocity vectors rotating cyclonically and anticyclonically (middle current amphidromic points, MCAP) and a single current amphidrome near the closed boundary related to velocity vectors rotating cyclonically (closed boundary current amphidromic point, CBCAP), may change radically. A series of experiments made evident that, in the vicinity of open boundaries, a single or a pair of current amphidromes (open boundary current amphidromic point, OBCAP) are also possible. Results of numerical simulations of semi-diurnal tides exhibit multiple ellipticity maxima in embayments situated around the North Sea. In the second application, it will be shown that these structures are reproduced when calculations are carried out for a basin where the open boundary is large in comparison to the length of the embayment.

A criterion to locate regions with anticyclonic tidal current rotation

Abstract The equations of motion written in rotational form, with the rotary components of the velocity R+ (cyclonic) and R− (anticyclonic) and the rotary components of sea surface elevation gradients S+ (cyclonic) and S− (anticyclonic), are applied to investigate a link between sea surface amphidromic system and sense of rotation of tidal currents. It is shown that the assumptions S+=S− or |S+|=|S−| lead to a criterion to locate regions with anticyclonic tidal current rotation from co-tidal and co-range charts. Anticyclonic rotation seems to occur in regions where the gradients of sea surface elevation ζ and phase φζ tend to be parallel, i.e. where ∇ζ×∇φζ=0. It is also shown that this situation takes place in areas where the limits ∇ζ→0 and ∇φζ→0 exist, i.e. where co-tidal and co-range lines are quite separated. Results of numerical modelling of the M2 tide in the North Sea and the Bohai Sea validate this prediction.

Estimation of Total Yearly CO2 Emissions by Wildfires in Mexico during the Period 1999–2010

The phenomenon of wildfires became a global environmental problem which demands estimations of their CO2 emissions. Wildfires have deteriorated the air quality increasingly. Using available information on documented wildfires and a data set of satellite detected hot spots, total yearly emissions of CO2 in Mexico were estimated for the period 1999–2010. A map of the main vegetation groups was used to calculate total areas for every vegetation type. The yearly number of hot spots per vegetation type was calculated. Estimates of emitted CO2 in a wildfire were then accomplished by considering parameters such as: forest fuel load, vegetation type, burning efficiency, and mean burned area. The number of wildfires and total affected areas showed an annual variability. The yearly mean of affected area by a single wildfire varied between 0.2 and 0.3 km2. The total affected area during the period 1999 to 2010 was 86800 km2 which corresponds to 4.3% of the Mexican territory. Total CO2 emissions were approximately 112 Tg. The most affected vegetation types were forest and rainforest.

Bedload Transport of Sediments and Morphodynamics in the Northern Gulf of California

ABSTRACT Hernández-Azcúnaga, L.; Carbajal, N., and Montaño-Ley, Y., 2014. Bedload transport of sediments and morphodynamics in the northern Gulf of California. Huge amounts of sediments have been supplied to the northern Gulf of California in recent geological time. Although water discharge and sediment supply have been suppressed from the Colorado River since about a century, satellite imagery reveals even now a persistently strong mobilization of sediments and the occurrence of marked sea bottom morphological features. To gain information on these processes, we applied a two-dimensional hydrodynamic numerical model to simulate bedload sediment transport caused by the dominant semidiurnal tidal component, M2, in the northern Gulf of California. The resulting transport of sediment encompasses areas of the Colorado River Delta, of the Adair and San Jorge bays, and of the southwestern sector of the study area. The model reproduces longitudinal and transversal bedforms observed in Adair Bay. The residual bedload transport reveals recirculation processes that retain sediments in the Colorado River Delta, and in the bays of Adair and San Jorge. Sediment dynamics occur in areas where tidal currents exceed the threshold velocity, where the incident tidal wave is reflected, and where Poincare waves are generated. This calculated general picture is consistent with satellite images depicting morphological features and mobilization of sediments. The production of bedforms coincides with theoretical predictions on the reflection and diffraction of Kelvin waves at closed boundaries and corners. Sediments mobilization and bedforms in the northern Gulf of California are strongly controlled by tidal dynamics.

Dispersion of atmospheric coarse particulate matter in the San Luis Potosí, Mexico, urban area

Atmospheric pollution in urban areas of Mexico has become a serious problem. The study of spatio-temporal evolution of concentrations of particulate matter is an important issue. A total of 188 samples were randomly collected at 24-hour running time within the period from May 2003 to April 2004 for the San Luis Potosi urban area, located in the central-north part of Mexico, using quartz fiber filters. A series of numerical modeling experiments were conducted for the same period of measurements to investigate particulate matter (PM) concentrations in the above-mentioned urban area. Although there is a considerable annual variability in the atmospheric circulation, the analysis of results indicates preferential seasonal circulation patterns: southwesterly winds during winter and southeasterly during summer. High concentration values of particulate matter were closely associated to local characteristics of the atmospheric circulation. A net transport from the industrial zone into the urban area is one of most important outcomes of the investigation.

Microbial identification of the Nichupte-Bojorquez coastal lagoon in Cancun, Mexico

The microbial community of the Nichupte-Bojorquez lagoon system located in Cancun, Mexico was evaluated using surface-water samples that were collected before and after the hurricane Wilma impacted the area on October 2005. The analysis was done using a culture-independent molecular approach involving Amplified Ribosomal DNA Restriction Analysis, and CLuster ANalysis of Sequences. A total of 61 16S ribosomal RNA genes were differentially selected and screened. The results show a bacterial profile dominated by Cytophaga-Flavobacteria/Flexibacter-Bacteroidetes group; the Bacteroidetes group in particular. The second most abundant group was assigned to the Proteobacteria group and a minor proportion of bacteria that belongs to the Cyanobacteria and Bacilli classes. Our study gives the first insight into the bacterial community adapted to this heavily polluted but occasional oligotrophic coastal lagoon; no substantial differences were, however, found.

Air Quality Deterioration of Urban Areas Caused by Wildfires in a Natural Reservoir Forest of Mexico

Many regions of the world suffer loss of vegetation and reduced air quality due to wildfires. Studies on aerosol emissions by wildfires often discuss the negative effects of atmospheric contaminants from a regional or mesoscale perspective. The occurrence of wildfires reveals that a high percentage takes place close to large urban areas. Very high concentration of pollutants and PM10 particulate matter reach urban zones and millions of inhabitants. These events of high pollutant concentrations are seasonally recurrent. There are many large urban areas in the world that often undergo severe air deterioration due to wildfires smoke. We document the extreme impact of wildfire that occurs in the Protected Area of Flora and Fauna La Primavera located in neighborhood of Guadalajara, a large urban zone in Mexico. The simultaneous emissions of aerosols by 60 wildfires were simulated and compared with observed data. The plume generated by the wildfires reached large areas of the central part of Mexico. The principal characteristics of smog emissions (CO, NO2, and PM10) over the urban area were acceptably reproduced. Observed and modeled CO, PM10, and NO2 data indicated that aerosol plumes generated by the wildfires increased notably the concentrations over the metropolitan zone of Guadalajara.