Use of canopy coefficients obtained from satellite data to estimate evapotranspiration over high mountain Mediterranean watersheds

This work explores the dynamics of the water consumed by the vegetation in two Mediterranean watersheds of Sierra Nevada Mountains (Southern Spain). This region has experienced an increase in the demand of water in the last years due to the growth of irrigated areas, and a new water resources plan is required. The evapotranspiration (ET) of irrigated horticultural crops and natural communities were monitored for the hydrological years 2013/14 and 2014/15, using an approach based on the concept of reference evapotranspiration (ETo) and canopy coefficients derived from the computation of vegetation indices (VIs), which we will call the VI-ETo approach. A set of Landsat-8 and MODIS images has been used as remote input data. The results were used for the spatial analysis of water consumption in terms of the main land cover types in the area. The annual runoff obtained with a simple surface water balance, using the ET values estimated by the VI-ETo approach, was comparable to that obtained by the HBV (Hydrologiska Byrans Vattenbalansavdelning) model, a precipitation-runoff generation model that reproduces the observed river discharge at the outlet of the watershed.</p

Vertical variation in the amplitude of the seasonal isotopic content of rainfall as a tool to jointly estimate the groundwater recharge zone and transit times in the Ordesa and Monte Perdido National Park aquifer system, north-eastern Spain

The time series of stable water isotope composition relative to meteorological stations and springs located in the high mountainous zone of the Ordesa and Monte Perdido National Park are analyzed in order to study how the seasonal isotopic content of precipitation propagates through the hydrogeological system in terms of the aquifer recharge zone elevation and transit time. The amplitude of the seasonal isotopic composition of precipitation and the mean isotopic content in rainfall vary along a vertical transect, with altitudinal slopes for d18O of 0.9‰/km for seasonal amplitude and - 2.2‰/km for isotopic content. The main recharge zone elevation for the sampled springs is between 1950 and 2600 m·a.s.l. The water transit time for the sampled springs ranges from 1.1 to 4.5 yr, with an average value of 1.85 yr and a standard deviation of 0.8 yr. The hydrological system tends to behave as a mixing reservoir.Peer ReviewedPostprint (author's final draft

Structure of a complex carbonate aquifer by magnetic, gravity and TDEM prospecting in the Jaén area, Southern Spain

Knowledge of aquifer geometry is essential for efficient and sustainable groundwater management, particularly in carbonate aquifers due to uncertainties inherent to karstic systems. The geological structure and hydrogeological continuity of Los Chotos-Sazadilla-Los Nacimientos and La Serreta-Gante-Cabeza Montosa carbonate aquifers (Jaén; SE Spain) have been established through structural measurements, geophysical prospecting –magnetic, gravity and time-domain electromagnetics (TDEM)– and the study of piezometric levels. Yet the scarce hydrogeological data, the complexity of the tectonic structure and the presence of Plio-Quaternary rocks covering the highly permeable carbonate rocks make it difficult to establish a robust conceptual hydrogeological model of the aquifer. This study focuses on an area where hydrogeological disconnection between the two aquifers was traditionally assumed, given the diapiric emplacement of low permeable rocks between them. The new geophysical data demonstrate connection between aquifers that implies greater groundwater reserves than previously supposed. This field example supports the suitability of the combined use of electromagnetic methods with gravity and magnetic research that have been poorly combined up to recent times for hydrogeological studies

Contribution of isotopic research techniques to characterize highmountain-Mediterranean karst aquifers: The Port del Comte (Eastern Pyrenees) aquifer.

Water resources in high mountain karst aquifers are usually characterized by high rainfall, recharge and discharge that leads to the sustainability of the downstream ecosystems. Nevertheless, these hydrological systems are vulnerable to the global change impact. The mean transit time (MTT) is a key parameter to describe the behavior of these hydrologic systems and also to assess their vulnerability. This work is focused on estimating MTT by using water stable isotopes in the framework of high-mountain karst systems with a very thick unsaturated zone (USZ). To this end, it is adapted to alpine zones an existing methodology that combines in a row a semi-distributed rainfall-runoff model used to estimate recharge time series, and a lumped-parameter model to obtain through a convolution integral. The methodology has been applied to the Port del Comte Massif (PCM) hydrological system (Southeastern Pyrenees, NE Spain), a karst aquifer system with an overlying1000 m thick USZ. Six catchment areas corresponding to most important springs of the system are considered. The obtained results show that hydrologically the behavior of the system can be described by an exponential flow model (EM), with MTT ranging between 1.9 and 2.9 years. These values are shorter than those obtained by considering a constant recharge rate along time, which is the easiest and most applied aquifer recharge hypothesis when estimating through lumped-parameter models. This methodology can be useful to improve the characterization and understanding of other high mountain karst aquifers with an overlying thick USZ that are common in many alpine zones elsewhere the globe

Changes in water level, land use, and hydrological budget in a semi-permanent playa lake, Southwest Spain

Medina playa lake, a Ramsar site in western Andalusia, is a brackish lowland lake of 120 ha with an average depth of 1 m. Water flows into Medina from its 1,748-ha watershed, but the hydrology of the lake has not previously been studied. This paper describes the application of a water budget model on a monthly scale over a 6- year period, based on a conceptual hydrological model, and considers different future scenarios after calibration to improve the understanding of the lake’s hydrological functioning. Climatic vari- ables from a nearby weather station and observa- tional data (water-level evolution) were used to develop the model. Comparison of measured and predicted values demonstrated that each model component provided a reasonable output with a realistic interaction among the components. The model was then used to explore the potential consequences of land-use changes. Irrigation of olive groves would significantly reduce both the hydroperiod (becoming dry 15% of the time) and the average depth of the lake (water level <0.5 m 40% of the time). On the other hand, removal of an artificial overflow would double the average flooded surface area during high-water periods. The simulated water balance demonstrates that the catchment outputs are dominated by lake evaporation and surface outflow from the lake system to a creek. Discrepancies between pre- dicted and observed water levels identify key ar- eas of uncertainty for future empirical research. The study provides an improved basis for future hydrological management of the catchment and demonstrates the wider utility of this methodology in simulating this kind of system. This methodol- ogy provides a realistic appraisal of potential land- use management practices on a catchment-wide scale and allows predictions of the consequences of climate changePeer reviewe

Structure of a complex carbonate aquifer by magnetic, gravity and TDEM prospecting: Los Chotos-Sazadilla-Los Nacimientos (Jaén, Southern Spain)

Knowledge of aquifer geometry is essential for efficient and sustainable groundwater management, particularly in carbonate aquifers due to uncertainties inherent to karstic systems. The geological structure and hydraulic connection of the Los Chotos-Sazadilla-Los Nacimientos and the La Serreta-Gante-Cabeza Montosa carbonate aquifers (S of Jaén; Spain) have been established through structural measurements, geophysical prospecting ―magnetic, gravity and TDEM― and the study of piezometric levels. Yet the scarce hydrogeological data, the complexity of the tectonic structure and the presence of Plio-Quaternary rocks covering the highly permeable carbonate rocks make it difficult to establish a robust conceptual hydrogeological model of the aquifer. This study focuses on an area where hydraulic disconnection between the two aquifers was traditionally assumed, given the diapiric emplacement of low-permeable rocks between them. The new geophysical data demonstrate connection between aquifers that implies greater groundwater reserves than previously supposed. This field example supports the suitability of the combined use of electromagnetic methods with gravity and magnetic research that have been poorly combined up to recent for hydrogeological studies

Epikarst mapping by remote sensing

Epikarst – the shallow, surficial part of a karstic massif – has a significant influence on the spatio-temporal variability of recharge and the hydrodynamic functioning of many karst aquifers. In the Mediterranean morphoclimatic zone, the average thickness of a well-developed epikarst is around ten metres, but the spatial patterns of its degree of development are very heterogeneous due to the complex interaction of a number of different factors such as lithology, fracturing, weathering, soil and vegetation. In addition, direct field observation is difficult because good outcropping conditions are restricted to particular locations, some areas are not accessible and the size of the study area is often too large for exhaustive field surveys. Satellite-based remote sensing, however, provides a complete coverage of an entire area with spectral resolutions that detect variability in features that can define image textures related to the development of the epikarst. This paper describes a quantitative methodology for epikarst mapping using satellite images and field data. The proposed method comprises an unsupervised classification to define the spectral signature of each of three epikarst development categories in a high-resolution satellite image followed by a supervised classification of the terrain into one of the three categories on a low spatial resolution scale. The training areas in the field are assigned to the three categories by a panel of experts using the Delphi method. Geophysical data are used for validation to overcome any bias that may be introduced by the panel. The proposed methodology has been applied to the Sierra de las Nieves karstic aquifer (Málaga, southern Spain). The outcome is a map of estimated epikarst development that is an approximation to reality and which can be improved as more experimental data become available.Eulogio Pardo-Igúzquiza, Peter A. Dowd, Ana Ruiz-Constán, Sergio Martos-Rosillo, Juan A. Luque-Espinar, Víctor Rodríguez-Galiano, Antonio Pedrer

Correlation of the seasonal isotopic amplitude of precipitation with annual evaporation and altitude in alpine regions

Abstract The time series of stable water isotope composition relative to IAEA-GNIP meteorological stations located in alpine zones are analyzed in order to study how the amplitude of the seasonal isotopic composition of precipitation (Aδ) varies along a vertical transect. A clear relationship between Aδ and local evaporation is obtained, with slopes of â 0.87 â °/100 mm/yr and â 7.3 â °/100 mm/yr for Aδ18O and Aδ2H, respectively. When all sampling points of the vertical transect receive the same moisture sources, then a linear relationship between Aδ and elevation is obtained, with vertical gradients of 0.16 â °/100 mm/yr and 1.46 â °/100 mm/yr for Aδ18O and Aδ2H, respectively.Published27-376A. Monitoraggio ambientale, sicurezza e territorioJCR Journalrestricte

Vertical variation in the amplitude of the seasonal isotopic content of rainfall as a tool to jointly estimate the groundwater recharge zone and transit times in the Ordesa and Monte Perdido National Park aquifer system, north-eastern Spain

The time series of stable water isotope composition relative to meteorological stations and springs located in the high mountainous zone of the Ordesa and Monte Perdido National Park are analyzed in order to study how the seasonal isotopic content of precipitation propagates through the hydrogeological system in terms of the aquifer recharge zone elevation and transit time. The amplitude of the seasonal isotopic composition of precipitation and the mean isotopic content in rainfall vary along a vertical transect, with altitudinal slopes for d18O of 0.9‰/km for seasonal amplitude and - 2.2‰/km for isotopic content. The main recharge zone elevation for the sampled springs is between 1950 and 2600 m·a.s.l. The water transit time for the sampled springs ranges from 1.1 to 4.5 yr, with an average value of 1.85 yr and a standard deviation of 0.8 yr. The hydrological system tends to behave as a mixing reservoir.Peer Reviewe

Snowmelt as a determinant factor in the hydrogeological behaviour of high mountain karst aquifers: The Garcés karst system, Central Pyrenees (Spain)

International audienceTime series of environmental tracers (groundwater stable isotope composition, electrical conductivity and temperature) and concentration breakthrough curves of artificial tracers (uranine, eosine, amino-G and naphtionate) have been analyzed to characterize fast preferential and slow matrix in-transit recharge flows in the Paleocene-Eocene limestone aquifer of the Ordesa and Monte Perdido National Park, an alpine karst system drained by a water table cave, a rare hydrological feature in high mountain karst systems with similar characteristics. Snowmelt favors the areal recharge of the system. This process is reflected in the large proportion of groundwater flowing through the connected porosity structure of the karst aquifer, which amounts the 75% of the total system water discharge. From the perspective of water resources recovery, the water capacity of the fissured-porous zone (matrix) represents 99% of the total karst system storage. The volume associated to the karst conduits is very small. The estimated mean travel times are 9 days for conduits and 475 days for connected porosity. These short travel times reveal high vulnerability of the karst system to pollutants in broad sense and a great impact of climate change on the associated water resources