• Energy Research
• environmental engineering close
• Hyper Article en Ligne close

Upwelling processes bring nutrient-rich waters from the deep ocean to the surface. Areas of upwelling are often associated with high productivity, offering great economic value in terms of fisheries. The sensitivity of spring/summer-time coastal upwelling systems to climate change has recently received a lot of attention. Several studies have suggested that their intensity may increase in the future while other authors have shown decreasing intensity in their equatorward portions. Yet, recent observations do not show robust evidence of this intensification. The Senegalo-Mauritanian upwelling system (SMUS) located at the southern edge of the north Atlantic system (12°N–20°N) and most active in winter/spring has been largely excluded from these studies. Here, the seasonal cycle of the SMUS and its response to climate change is investigated in the database of the Coupled Models Inter comparison Project Phase 5 (CMIP5). Upwelling magnitude and surface signature are characterized by several sea surface temperature and wind stress indices. We highlight the ability of the climate models to reproduce the system, as well as their biases. The simulations suggest that the intensity of the SMUS winter/spring upwelling will moderately decrease in the future, primarily because of a reduction of the wind forcing linked to a northward shift of Azores anticyclone and a more regional modulation of the low pressures found over Northwest Africa. The implications of such an upwelling reduction on the ecosystems and local communities exploiting them remains very uncertain.

Analytical formulae are proposed to describe the first-order temporal evolution of the head in large groundwater systems (such as those found in North Africa or eastern Australia) that are subjected to drastic modifications of their recharge conditions (such as those in Pleistocene and Holocene times). The mathematical model is based on the hydrodynamics of a mixed-aquifer system composed of a confined aquifer connected to an unconfined one with a large storage capacity. The transient behaviour of the head following a sudden change of recharge conditions is computed with Laplace transforms for linear one-dimensional and cylindrical geometries. This transient evolution closely follows an exponential trend exp(−t/τ). The time constant τ is expressed analytically as a function of the various parameters characterizing the system. In many commonly occurring situations, τ depends on only four parameters: the width a c of the main confined aquifer, its transmissivity T c, the integrated storage situated upstream in the unconfined aquifer M = S u a u, and a curvature parameter accounting for convergence/divergence effects. This model is applied to the natural decay of large aquifer basins of the Sahara and Australia following the end of the mid-Holocene humid period. The observed persistence of the resource is discussed on the basis of the time constant estimated with the system parameters. This comparison confirms the role of the upstream water reserve, which is modelled as an unconfined aquifer, and highlights the significant increase of the time constant in case of converging flow.

This study investigates the physical basis of temperature‐index models for three glaciers in contrasting climates: Zongo (16°S, 5050 m, Bolivian Tropics), St Sorlin (45°N, 2760 m, French Alps), and Storglaciären (67°N, 1370 m, northern Sweden). The daily energy fluxes were computed during melt seasons and correlated with each other and with air temperature on and outside the glacier. The relative contribution of each flux to the correlations between temperature and melt energy was assessed. At Zongo, net short‐wave radiation controls the variability of the energy balance and is poorly correlated to temperature. On tropical glaciers, temperature remains low and varies little, melt energy is poorly correlated to temperature, and degree‐day models are not appropriate to simulate daily melting. At the yearly scale, the temperature is better correlated to the mass balance because it integrates the ablation and the accumulation processes over a long time period. At Sorlin, the turbulent sensible heat flux is greater because of higher temperatures, but melt variability is still controlled by short‐wave radiation. Temperature correlates well with melt energy mainly through short‐wave radiation, probably because of diurnal advection of warm air from the valley. At Storglaciären, high correlations between temperature and melt energy result from substantial variability of the sensible and latent heat fluxes (which both supply energy to the glacier), and their good correlations with temperature. In the three climates, long‐wave irradiance is the main source of energy, but its variability is small and poorly correlated to the temperature mainly because cloud emissions dominate its variability.

Natural ventilation performance is one of the key climate control parameters for Canary type greenhouses, which are rapidly expanding along the Atlantic coast in Morocco. The use of insect screens significantly reduces airflow and increases thermal gradients inside the greenhouse. The aim of this study was to analyze the natural ventilation performances in real cultural conditions of a large-scale Canary type tomato greenhouse (1.1 ha) equipped with insect screens on the vent openings. A global energy balance of the greenhouse was used, allowing for the determination of air exchange rates. The greenhouse ventilation performance was compared with those of other greenhouses types and discussed with respect to the improvement of greenhouse vent design, insect screen types, and ridge and crop row orientation. The results confirm the strong dependence of greenhouse ventilation rate on wind speed and ventilation opening location. In addition, results show a significant reduction of the ventilation rate compared with other greenhouse types: the insect screen reduced the greenhouse ventilation rate by 46%, and the tomato rows that were oriented perpendicular to the prevailing air movement through the greenhouse reduced the ventilation rate by 50%. From this analysis, practical improvements are proposed and discussed in the context of protected crop production in the coastal area of Morocco.

Abstract. The repetition of droughts in France has led to a growing demand for irrigation water and consequently to an increase in requests for the construction of small farm dams. Although such dams are small, their accumulation in a basin affects river flows, because the water collected in these small farm dams is used for irrigation and thus does not contribute to river flow. In order to gain more insight into their impact on the annual and monthly discharges, especially during dry years, a small farm dam model was built and connected to a hydrometeorological model. Several scenarios with different volume capacities, filling catchment sizes and filling periods were tested for such dams. The results were analysed in a small basin in western France, where the pressure for building such dams is high, and then extended to the entire country. It was found that, due to the hydrometeorological conditions (mainly low precipitation compared to other regions in France), the development of small farm dams in north-western France would result in greater decreases in river flows and less efficient filling of small farm dams than in other regions. Therefore, such dams might not be as efficient as expected in supplying water to farmers when needed. Moreover, the ability to fill small farm dams is projected to decrease in a context of climate change, despite the uncertainty on the evolution of precipitation, thus worsening the situation.

Abstract. The impact of landuse on stream salinity is difficult to separate from decadal climatic variability, as the decadal scale climatic cycles in ground water and stream hydrology have similar wavelengths to the landuse pattern. These hydrological cycles determine the stream salinity through accumulation or release of salt in the landscape. The Interdecadal Pacific Oscillation (IPO) has been investigated before as an indicator of hydrological and related time series in the southern hemisphere. This study presents a new approach, which uses the rate of change in the IPO, rather than just its absolute value, to define an indicator for the climate component of ambient shallow groundwater tables and corresponding stream salinity. Representative time series of water table and stream salinity indicators are compiled, using an extensive but irregular database covering a very wide geographical area. These are modelled with respect to the IPO and its rate of change to derive climatic indicators. The effect of removing the decadal climatic influence from stream salinity trends is demonstrated.