When dealing with groundwater resources, a better knowledge of the hydrological processes governing flow
in the unsaturated zone would improve the assessment of the natural aquifer recharge and its vulnerability to contamination.
In North West Europe groundwater from unconfined chalk aquifers constitutes a major water resource, therefore the
need for a good hydrological understanding of the chalk unsaturated zone is essential, as it is the main control for aquifer
recharge. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a
porous matrix with embedded fractures. The case study regards the role of the thick unsaturated zone of the Cretaceous
chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In order to describe the flow
rate that reaches the water table, the kinematic diffusion theory has been applied that treats the unsaturated
water flow equation as a wave equation composed of diffusive and gravitational components. The kinematic diffusion
model has proved to be a convenient method to study groundwater recharge processes in that it was able to provide a
satisfactory fitting both for rising and falling periods of water table fluctuation. It has also proved to give an answer to
the question whether unsaturated flow can be described using the theory of kinematic waves. The answer to the question
depends principally on the status of soil moisture. For higher values of hydraulic Peclet number (increasing saturation),
the pressure wave velocities dominate and the preferential flow paths is provided by the shallow fractures in the vadose
zone. With decreasing values of hydraulic Peclet number (increasing water tension), rapid wave velocities are mostly due
to the diffusion of the flow wave. Diffusive phenomena are provided by matrix and fracture-matrix interaction.
The use of a kinematic wave in this context constitutes a good simplified approach especially in cases when there is a
lack of information concerning the hydraulic properties of the fractures/macropores close to saturation.
Morphological (dry mass, DM; surface area, LA; leaf mass per area, LMA), anatomical (leaf thickness, L), phenological (leaf life span, LL), and physiological (net photosynthetic rate, PN) leaf traits of the evergreen species co-occurring in the Mediterranean maquis developing at Castelporziano (Rome) were tested. The correlation analysis indicated that LMA variation was tightly associated with LL variations: Cistus incanus and Arbutus unedo had a short LL (4±1, summer leaves, and 11±1 months, respectively) and low LMA (153±19 g m-2) values, Quercus ilex, Phillyrea latifolia, and Pistacia lentiscus high LMA (204±7 g m-2) and long LL (22±3 months), Erica arborea, Erica multiflora, and Rosmarinus officinalis a short LL (9±2 months) and an either high (213±29 g m-2, R. officinalis and E. multiflora) or low (115±17 g m-2, E. arborea) LMA. LMA values were significantly (p≤0.05) correlated with PN (r≥0.68). In the tested species, LMA increased in response to the decrease of the total rainfall during the leaf expansion period. LMA variation was due to the unequal variation of DM and LA in the considered species. LMA is thus a good indicator of evergreen maquis species capability to respond to climate change, in particular to total rainfall decrease in the Mediterranean basin. and L. Gratani, L. Varone.
The Green-Ampt (GA) model is widely used in hydrologic studies as a simple, physically-based method to estimate infiltration processes. The accuracy of the model for applications under rainfall conditions (as opposed to initially ponded situations) has not been studied extensively. We compared calculated rainfall infiltration results for various soils obtained using existing GA parameterizations with those obtained by solving the Richards equation for variably saturated flow. Results provided an overview of GA model performance evaluated by means of a root-meansquare-error-based objective function across a large region in GA parameter space as compared to the Richards equation, which showed a need for seeking optimal GA parameters. Subsequent analysis enabled the identification of optimal GA parameters that provided a close fit with the Richards equation. The optimal parameters were found to substantially outperform the standard theoretical parameters, thus improving the utility and accuracy of the GA model for infiltration simulations under rainfall conditions. A sensitivity analyses indicated that the optimal parameters may change for some rainfall scenarios, but are relatively stable for high-intensity rainfall events.
Rain gauges, weather radars, satellite sensors and modelled data from weather centres are used operationally for estimating the spatial-temporal variability of rainfall. However, the associated uncertainties can be very high, especially in poorly equipped regions of the world. Very recently, an innovative method, named SM2RAIN, that uses soil moisture observations to infer rainfall, has been proposed by Brocca et al. (2013) with very promising results when applied with in situ and satellite-derived data. However, a thorough analysis of the physical consistency of the SM2RAIN algorithm has not been carried out yet. In this study, synthetic soil moisture data generated from a physically-based soil water balance model are employed to check the reliability of the assumptions made in the SM2RAIN algorithm. Next, high quality and multiyear in situ soil moisture observations, at different depths (5-30 cm), and rainfall for ten sites across Europe are used for testing the performance of the algorithm, its limitations and applicability range. SM2RAIN shows very high accuracy in the synthetic experiments with a correlation coefficient, R, between synthetically generated and simulated data, at daily time step, higher than 0.940 and an average Bias lower than 4%. When real datasets are used, the agreement between observed and simulated daily rainfall is slightly lower with average R-values equal to 0.87 and 0.85 in the calibration and validation periods, respectively. Overall, the performance is found to be better in humid temperate climates and for sensors installed vertically. Interestingly, algorithms of different complexity in the reproduction of the underlying hydrological processes provide similar results. The average contribution of surface runoff and evapotranspiration components amounts to less than 4% of the total rainfall, while the soil moisture variations (63%) and subsurface drainage (30%) terms provide a much higher contribution. Overall, the SM2RAIN algorithm is found to perform well both in the synthetic and real data experiments, thus offering a new and independent source of data for improving rainfall estimation, and consequently enhancing hydrological, meteorological and climatic studies.
The infrared thermography has been successfully applied as a tool for high resolution imaging in different hydrological studies. This exploratory experimental study aimed at evaluating the possibility of using infrared thermography to determine the diameter of raindrops. Rain samples are collected on a pre-heated acrylic board, which is exposed to rain during an instant, and thermograms are recorded. The area of the thermal stains (''signatures'' of the raindrops) emerging on the board is measured and converted to drop diameters, applying a calibration equation. Diameters of natural raindrops estimated using this technique were compared with laser disdrometer measurements; the Nash-Sutcliffe efficiency coefficient was used for evaluating the match between the resulting histograms of drop size distribution. Results confirm the usefulness of this simple technique for sizing and counting raindrops, although it is unsatisfactory in light rain or drizzle.
In summer 1992 through spring 1994, amphibian abundance and breeding was studied in the pristine temperate forests, typical of central European lowlands. The years 1991, 1992, and 1993 were among the driest in the recent decades, with the spring-summer precipitation 35% lower than the long-term average. In the primeval forests of Białowieża National Park, common frogs Rana temporaria spawned in small (on average, 0.2 ha) ponds (postglacial melt-out hollows) devoid of wood cover and characterised by water pH 5.1-6.0 (as measured in April). Breeding success of frogs, monitored qualitatively in 1993, was rather poor due to pond desiccation. The capture of amphibians on forest grids revealed that densities and seasonal dynamics differed between wet and drier deciduous forests. No amphibians were captured in the mixed coniferous forests during the study. In the wet ash-alder forests, on average, 39 amphibians ha-1 were recorded in late April, 12 ind ha-1 in summer, and 195–222 ind hasup-1 in autumn (September). In those forests, 90% of captured amphibians were common frogs, 6% common toads Bufo bufo, and 4% moor frogs R. arvalis. In the drier oak-lime-hornbeam forests, amphibians appeared in May, and increased in numbers towards summer (19–24 ind ha-1) and autumn (45–71 ind ha-1). Of all amphibians caught in those forests, 43% were common frogs, 38% common toads, and 19% were moor frogs. A majority of amphibians captured in autumn were young of the year. By mid-October, all amphibians had left the forest for their hibernation sites. Comparison of our data collected in very dry years with other available data from Bia∏owie ̋a Primeval Forest (various years between 1955 and 1998) revealed that summer indices of amphibian abundance were strongly positively correlated with rainfall in April-June of the census year and the previous year.
Some studies of responses of plants to elevated concentrations of carbon dioxide (EC) added CO2 only in the daytime, while others supplied CO2 continuously. I tested whether these two methods of EC treatments produced differences in the seed yield of soybeans. Tests were conducted for four growing seasons, using open top chambers, with soybeans rooted in the ground in field plots. One third of the chambers were flushed with air at the current ambient [CO2] (AC), one third had [CO2] 350 µmol mol-1 above ambient during the daytime (ECd), while one third had [CO2] 350 µmol mol-1 above ambient for 24 h per day (ECdn). ECdn increased seed yield by an average of 62 % over the four years compared with the AC treatment, while ECd increased seed yield by 34 %. Higher seed yield for ECdn compared with ECd occurred each year. In comparing years, the relative yield disadvantage of ECd decreased with increasing overall seed yield. On days with high water vapor pressure deficits, soybean canopies with ECd had smaller midday extinction coefficients for photosynthetically active radiation than canopies with ECdn, because of a more vertical leaf orientation. Hence the seed yield of soybean at EC varied depending on whether EC was also provided at night, with much greater yield stimulation for ECdn than for ECd in some years.
It is well known that rainfall causes soil erosion in sloping German vineyards, but little is known about the effect of age of plantation on soil erosion, which is relevant to understand and design sustainable management systems. In the Ruwer-Mosel valley, young (1- to 4-years) and old (35- to 38-years after the plantation) vineyards were selected to assess soil and water losses by using two-paired Gerlach troughs over three years (2013–2015). In the young vineyard, the overland flow was 107 L m–1 and soil loss 1000 g m–1 in the year of the plantation, and decreased drastically over the two subsequent years (19 L m–1; 428 g m–1). In the old vineyard, soil (from 1081 g m–1 to 1308 g m–1) and water (from 67 L m–1 to 102 L m–1) losses were 1.2 and 1.63 times higher, respectively, than in the young vineyard.
The precise rainfall estimate with appropriate spatial and temporal resolutions is a key input to distributed hydrological models. However, networks of rain gauges are often sparsely distributed in developing countries. To overcome such limitations, this study used some of the existing gridded rainfall products to simulate streamflow. Four fridded rainfall products, including APHRODITE, CFSR, PERSIANN, and TRMM, were used as input to the SWAT distributed hydrological model in order to simulate streamflow over the Srepok River Catchment in Vietnam. Besides that, the available rain gauges data were also used for comparison. Amongst the four different datasets, the TRMM and APHRODITE data show their best match to rain gauges data in simulating the daily and monthly streamflow with satisfactory precision in the 2000–2006 period. The result indicates that the TRMM and APHRODITE data have potential applications
in driving hydrological model and water resources management in data-scarce and ungauged areas in Vietnam.
The processing of ombrographic data from 29 meteorological stations of the Czech Hydrometeorological Institute (CHMI), according to the terms of the Universal Soil Loss Equation for calculating long term loss of soil through water erosion, erosion hazard rains and their occurrence have been selected, with their relative amount and erosiveness - R-Factors determined for each month and years. By comparing the value of the time division of the R-Factor in the area of the Czech Republic and in selected areas of the USA it has been demonstrated that this division may be applied in the conditions of the Czech Republic. For the Czech Republic it is recommended to use the average value R = 40 based on the original evaluation.