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Fluctuation Data (fluctuation + data)
Selected AbstractsTHE FLUCTUATIONS OF ITALIAN GLACIERS DURING THE LAST CENTURY: A CONTRIBUTION TO KNOWLEDGE ABOUT ALPINE GLACIER CHANGESGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 3 2007MICHELE CITTERIO ABSTRACT. This paper describes the recent evolution of Italian glaciers through an analysis of all available terminus fluctuation data that the authors have entered in a glaciers database (named GLAD) containing 883 records collected on glaciers from 1908 to 2002. Furthermore, a representative subset of data (249 glaciers located in Lombardy) was analysed regarding surface area changes. For the analysis of terminus fluctuations, the glaciers were sorted by size classes according to length. The data showed that during the 20th century Italian Alpine glaciers underwent a generalized retreat, with one distinct and well documented readvance episode that occurred between the 1970s and mid-1980s, and a poorly documented one around the early 1920s. The rates of terminus advance and retreat have changed without significant delays for the larger glaciers with respect to the smaller ones. However, the smaller the glacier, the more limited the advance (if any) during the 1970s and early 1980s. The behaviour of glaciers shorter than 1 km appears to have changed in the last decade, and between 1993 and 2002 they retreated at a very high rate. The analysis of the subset of data led to a quanti-fication of surface reduction of c. 10% from 1992 to 1999 for glaciers in Lombardy. Small glaciers proved to contribute strongly to total area loss: in 1999, 232 glaciers (c. 90% of the total) were smaller than 1 km2, covering 27.2 km2 (less than 30% of the total area), but accounted for 58% of the total loss in area (they had lost 7.4 km2). [source] Recharge, upflux and water table response for shallow water table conditions in southwest FloridaHYDROLOGICAL PROCESSES, Issue 9 2006Fouad H. Jaber Abstract A disproportionate increase or decrease in water table in response to minor water input or drainage is observed in shallow water table conditions inside drainage lysimeters. This increase happens because the capillary fringe of the shallow water table reaches up to or near the surface (Wieringermeer effect). The correlations between water table level changes and rainfall, seepage irrigation, drip irrigation, and drainage were analysed. Correlations with rainfall, seepage irrigation, and drainage were high (R2 ranged from 0·46 to 0·97). Drip irrigation had low correlations due to the low rates of application (R2 ranged from 0·26 to 0·44). Conventional methods of calculating recharge, such as multiplying the specific yield with the water table fluctuations, cannot be used for Wieringermeer effect situations. A method using water balance data and soil moisture at different depths in the lysimeters was developed to estimate recharge and upflux. The recharge results were used to develop the apparent specific yield Sya, which could be used to calculate consequent recharge events from water table fluctuation data. Combining the water table fluctuation relationships developed with the Sya value will allow the prediction of recharge from rainfall and irrigation events without the need for soil moisture equipment. Copyright © 2005 John Wiley & Sons, Ltd. [source] Impact of climate variability on Alpine glaciers in northwestern ItalyINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2007Sandro Calmanti Abstract We analyzed glacier snout fluctuation data in Piedmont and Val d'Aosta (Italy) and studied the impact of climate variability on valley glaciers in the western Italian Alps. The study period covered about 70 years in the 20th century; we focused on the last 50 years where a large number of temperature and precipitation time series are available. Superposed onto a general recession trend, we detected strong oscillations on shorter time scales and we showed that they are significantly correlated with fluctuations in winter precipitation rates and average summer temperatures. On the basis of these results, we constructed a simple lagged-linear empirical stochastic model that explained upto 66% of the variance of the snout fluctuation data. The model produces reliable out-of-sample predictions of the impact of climate variability on the glaciers of the western Alps and it can be used to estimate the average response of Alpine glaciers to different scenarios of climate change, provided the morphology of the individual glaciers does not change completely. Copyright © 2007 Royal Meteorological Society [source] Sustainable use of groundwater for irrigation: a numerical analysis of the subsoil water fluxes,IRRIGATION AND DRAINAGE, Issue 3 2002Mobin-ud-Din Ahmad irrigation; eaux souterraines; surexploitation de l'aquifère; recharge des eaux souterraines; utilisation nette de l'eau souterraine; modélisation au niveau de la parcelle cultivée; le Pakistan Abstract The food-producing regions of the world increasingly rely on irrigation from groundwater resources. Further increases of groundwater use can adversely affect the sustainability of irrigated agriculture and put food security at risk. Sustainability of irrigation at field scale with groundwater is obtained if groundwater recharge is in equilibrium with tubewell extractions and capillary rise. Traditional information on phreatic surface behaviour does not explain the processes causing a phreatic surface to decline or incline. In this study, the physically based numerical model Soil,Water,Atmosphere,Plant (SWAP) was applied to compute soil moisture content and vertical soil water fluxes in the unsaturated zone for the cotton,wheat and rice,wheat cropping system of Punjab, Pakistan. SWAP has been calibrated and verified with in situ measurements of soil moisture content and evapotranspiration fluxes measured by means of the Bowen ratio surface energy balance technique. Accurate data of the soil hydraulic properties are critical for the calibration of the soil moisture distribution. With knowledge of the van Genuchten,Mualem parameters available, SWAP could be applied to assess recharge and capillary rise for most field conditions, including basin irrigation. The results under Pakistani conditions show that deep percolation cannot always be estimated from root zone water balances. An annual recharge of 23.3 cm was computed for the cotton,wheat area. Sustainability of irrigation with groundwater is obtained if a reduction in irrigation with groundwater by 36% is obtained. An annual recharge of 38.9 cm is estimated in rice,wheat systems, and a reduction of 62% in groundwater extraction is required to reach sustainability of groundwater use at field scale. Such information cannot be obtained from classical phreatic surface fluctuation data, and unsaturated zone modelling therefore provides additional insights for groundwater policy making. Copyright © 2002 John Wiley & Sons, Ltd. RÉSUMÉ Les régions de production alimentaire de la planète se servent de plus en plus de l'eau souterraine pour l'irrigation. Ultérieurs accroissements de l'utilisation des eaux souterraines peuvent avoir des répercussions négatives sur l'irrigation agricole soutenable et sur la sécurité alimentaire. Une irrigation soutenable au niveau de la parcelle cultivée en utilisant l'eau souterraine est obtenue si le taux de recharge de cette dernière est en équilibre avec le taux d'extraction des puits et la remontée capillaire. L'information traditionellement disponible concernant l'évolution du niveau phréatique ne permet pas d'expliquer les procès qui causeraient son abaissement ou son accroissement. Cette étude présente les resultats obtenus grâce à l'utilisation d'un modèle numérique appelé Soil,Water,Atmosphere,Plant (SWAP), qui se base sur des principes physiques, avec lequel ont été calculés les taux d'humidité du sol et les flux verticaux d'humidité dans la zone non-saturée du sol pour ce qui concèrne le système de cultivation coton,blé et riz,blé du Pounjab, au Pakistan. SWAP a été calibré et verifié grâce à des mesures in situ du taux d'humidité du sol et des flux d'évapotranspiration quantifiés en appliquant le rapport de Bowen, basé sur le concept du bilan énergétique au niveau du sol. Disposer de données prises concernant les propriétés hydrauliques du sol est essentiel pour calibrer la distribution de l'humidité du sol. Grâce à la connaissance des paramètres de van Genuchten,Mualem disponibles, SWAP a pu être utilisé pour évaluer le taux de recharge et la remontée capillaire en fonction de différentes conditions du terrain, irrigation de bassin incluse. Les résultats sous les conditions Pakistanes montrent que la percolation profonde ne peut pas toujours être estimée par les équilibres hydrologiques de la zone radicale. Une recharge annuelle de 23,3 cm a été estimée pour la zone coton,blé. L'utilisation soutenable de l'eau souterraine pour l'irrigation serait obtenue si on en réduisait l'extraction de 36%. Pour ce qui concerne la zone riz,blé, une recharge annuelle de 38,9 cm a été estimée, et une réduction de 62% de l'extraction de l'eau souterraine serait nécessaire pour une utilisation soutenable de l'eau souterraine à l'échelle de la parcelle cultivée. Ces informations ne peuvent pas être obtenues sur la base des données ordinaires concernant les fluctuations du niveau phréatique; la modélisation représente donc un appui essentiel en matière de prise de décision concernant la gestion de l'eau souterraine. Copyright © 2002 John Wiley & Sons, Ltd. [source] | ||||||||||