The present dissertation focuses on the field of research known as ecohydrology. Although this science, studying the mutual interactions between hydrological cycle and natural ecosystems, has been deeply investigated in recent past, some of its numerous aspects are still relatively unexplored. The main purpose is to investigate the existing scientific literature in order to adapt concepts and models previously developed for some specific ecosystems to the peculiarities of other less explored environments such as those semi-arid within the Mediterranean zone and the wetlands. In particular this study explores an ecohydrological approach to the analysis of water-controlled ecosystems in Mediterranean areas and groundwater dependent ecosystems. Although both are strongly reliant on water availability, these two kinds of environments are deeply different with each other. The most important difference is certainly played by the position of the water table. While on the one hand arid and semiarid ecosystems are usually characterized by a deep aquifer that does not exert any influence on soil water balance, on the other hand, in the case of groundwater dependent ecosystem, the water table position interacts directly with the root zone leading to important feedbacks between hydrological and ecological processes. The existing ecohydrological literature on arid and semiarid ecosystems such as savannas, steppes, deserts and prairies is rather wide, complete and consolidated. In such ecosystems, the soil moisture plays a fundamental role in the mutual links between climatic variations and the pedological and vegetational dynamics. The most common ecohydrological models start from a stochastic differential equation describing the soil water balance, where the unknown quantity, the soil moisture, depends both on spaces and time. Most of the solutions existing in literature are obtained in a probabilistic framework and under steady-state condition; even if this last condition allows the analytical handling of the problem, it has considerably simplified the same problem by subtracting generalities from it. The steady-state hypothesis, appears perfectly applicable in arid and semiarid climatic areas like those of African’s or middle American’s savannas, but it seems to be no more valid in areas with Mediterranean climate, where, notoriously, the wet season foregoes the growing season, recharging water into the soil. This soil moisture stored at the beginning of the growing season has a great importance, especially for deep-rooted vegetation, by enabling survival in absence of rainfalls during the growing season and, however, keeping the water stress low during the first period of the same season. In this thesis, a numerical approach, developed during the triennial graduate school at the University of Palermo, is presented. In particular a non steady numerical ecohydrological model is here proposed to evaluate the soil moisture dynamics and the consequent vegetation response in terms of water stress in Mediterranean areas. Such model is able to reproduce soil moisture probability density function, obtained analytically in previous studies for different climates in steady-state conditions. A first application of this model to the Sicilian river basin of Eleuterio at Lupo (Italy) shows how the model allows to compute the soil moisture time-profile and the vegetation static water stress time-profile in non-steady conditions, resulting able to capture the effects of winter recharge on the soil moisture. One of the possible applications of such model is to investigate the effects of potential climatic changes on vegetational stress in Mediterranean ecosystems. Many recent studies have demonstrated that CO2 increase is driving the climate in Mediterranean areas towards important changes, mainly represented by a temperatures increase and a contemporaneous rainfall reduction. Starting from this premise, the potential responses of vegetation, in terms of plants water stress, to different future scenarios are here investigated, throughout a second application of the model to the same river basin. In recent years great attention has been paid to environments such as riparian zones, peatlands and unsubmerged wetlands, which are considered as fundamental “tanks” of biodiversity and where the water table plays a key role in major ecohydrological processes. Wetlands are groundwater dependent ecosystems, which require access to the water table to maintain their health and vigor. A new fascinating challenge for the scientific community is that to investigate such environments by an ecohydrological approach. The study of the dynamics of interactions between climate, soil and vegetation in groundwater dependent ecosystems requires to couple the water table dynamics with the dynamics of soil moisture in the unsaturated zone. Only few recent frameworks have investigated a probabilistic approach also for the description of soil moisture and water table dynamics in the case of groundwater based ecosystems. In particular two models, the first for the analytical estimation of the water table position and the second for the analysis of the soil moisture dynamics, have been recently developed. Here, it is also presented a validation of the first model, which is the result of its application to three different sites within the Florida Everglades (USA).
La seguente dissertazione verte sul campo di ricerca noto come Ecoidrologia. Sebbene tale scienza, che studia le mutue interazioni fra ciclo idrologico e gli ecosistemi naturali, sia stata recentemente oggetto di svariati studi, alcuni dei suoi numerosi aspetti rimangono tuttavia ancora alquanto inesplorati. L’obiettivo principale della presente tesi è quello di rivisitare la letteratura scientifica esistente sull’argomento, cercando di adattare concetti e modelli sviluppati per certi ecosistemi anche alle peculiarità di altri ambienti meno studiati, come quelli aridi e semiaridi tipici della zona Mediterranea o le cosiddette “wetlands”, zone umide e paludose. In particolare, viene approfondito un approccio ecoidrologico allo studio di quegli ecosistemi controllati dalla risorsa idrica (water-controlled ecosystems) in aree Mediterranee ed a quegli ecosistemi controllati dalla falda acquifera (groundwater dependent ecosystems). Questi due tipi di ambiente sono profondamente diversi fra loro, ma è senz’altro la posizione della falda idrica a giocare un ruolo chiave. Se da un lato infatti, gli ecosistemi aridi e semiaridi sono generalmente caratterizzati da un acquifero cosi profondo da non esercitare alcuna influenza sul bilancio idrico del suolo, dall’altro lato, nel caso di “groundwater dependent ecosystems”, la posizione della falda idrica interagisce con la zona radicale della vegetazione, controllando i più importanti meccanismi di interazione fra processi idrologi ed ecologici. Nel campo delle Ecoidrologia, la letteratura scientifica esistente su ecosistemi aridi e semiaridi come savane o ambienti tropicali risulta essere piuttosto ampia, completa e consolidata. In tali ecosistemi, l’umidità del suolo rappresenta certamente l’anello di congiunzione fra le variazioni climatiche e le dinamiche pedologiche e vegetative. I più comuni modelli ecoidrologici relativi a tali ambienti hanno alla base un equazione stocastica differenziale che descrive il bilancio idrico del suolo, dove l’incognita, rappresentata dall’umidità del suolo, dipende sia dallo spazio che dal tempo. La maggior parte delle soluzioni a tale bilancio sono state ottenute in termini probabilistici è sotto l’ipotesi di stazionarietà. Tale ipotesi però, sebbene consenta la soluzione analitica del problema, semplifica considerevolmente l’analisi togliendo generalità da essa. L’ipotesi di stazionarietà risulta infatti perfettamente applicabile in aree climatiche aride e semiaride come quelle Africane o delle savane del Centro America, mentre sembra essere non più applicabile in quelle aree Mediterranee dove, notoriamente, la stagione umida precede la stagione vegetativa, ricaricando di acqua il suolo. L’acqua immagazzinata all’interno del terreno all’inizio della stagione vegetativa (nota come condizione iniziale di umidità del suolo) ha un ruolo chiave per la vegetazione, specialmente per quella avente un apparato radicale più profondo, garantendone la sopravvivenza anche in assenza di pioggia durante la stagione vegetativa o comunque mantenendo bassi i valori di stress idrico durante la prima fase della stagione stessa. Nella seguente tesi viene presentato un approccio numerico sviluppato durante il corso triennale di Dottorato presso l’Università degli Studi di Palermo. In particolare, viene proposto un modello ecoidrologico numerico non stazionario per la studio delle dinamiche di umidità del suolo e la conseguente risposta della vegetazione in termini di stress idrico. Tale modello è in grado di riprodurre la funzione densità di probabilità di umidità del suolo, ottenuta analiticamente in precedenti studi relativamente a regimi climatici differenti e sotto l’ipotesi di stazionarietà. Attraverso un prima applicazione di tale modello al bacino siciliano dell’Eleuterio al Lupo, viene mostrato come lo stesso modello sia in grado di computare i profili temporali di umidità del suolo e di stress idrico statico per la vegetazione anche in condizioni non stazionarie, tenendo quindi in considerazione gli effetti dovuti alla ricarica invernale di umidità all’interno del terreno. Una delle possibili applicazioni del modello è quella di studiare gli effetti di potenziali cambiamenti climatici sullo stress vegetativo di ecosistemi Mediterranei. Recenti studi hanno infatti dimostrato che l’aumento di CO2 sta gradualmente guidando il clima relativo alle aree Mediterranee verso importanti cambiamenti, principalmente rappresentati da un aumento delle temperature e una contemporanea riduzione delle piogge. Partendo da tale premessa, attraverso un seconda applicazione del modello al bacino dell’Eleuterio al Lupo, vengono analizzati i possibili effetti che diversi scenari futuri potrebbero avere sulla vegetazione in termini di stress idrico. Come precedentemente menzionato, tantissimi sono i lavori che studiano le interazioni fra clima, suolo e vegetazione in ecosistemi aridi e semiaridi controllati dalla risorsa idrica. E svariati approcci analitici ci hanno consentito di ottenere un descrizione probabilistica delle dinamiche di umidità del suolo in tali ecosistemi, partendo dalla conoscenza delle precipitazioni e delle caratteristiche del suolo e della vegetazione. Recentemente grandissima attenzione è stata anche focalizzata sull’importanza di ambienti quali le zone riapariali, le paludi e le zone umide in generale, considerate come un serbatoio di biodiversità fondamentale per la sostenibilità ambientale. In tali aree la posizione della falda idrica gioca un ruolo fondamentale nei maggiori processi eco idrologici e proprio per questo motivo, tali ecosistemi vengono anche definiti groundwater dependent ecosystems. In tali tipi di ambienti, solo pochi lavori in letteratura hanno proposto un approccio probabilistico per lo studio le dinamiche di umidità del suolo e delle falda idrica, analogo al caso degli ecosistemi controllati dalla risorsa idrica. Recentemente sono stati sviluppati due modelli ecoidrologici analitici per groundwater dependent ecosystems, il primo in grado di studiare la posizione della falda idrica e il secondo per lo studio delle dinamiche di umidità del suolo. Nella presente tesi, dopo aver presentato i due modelli, vengono anche mostrati i risultati di una validazione del primo modello, ottenuta mediante una sua applicazione a tre siti all’interno delle Everglades della Florida (USA), aventi dati di campo disponibili.
ECOHYDROLOGICAL MODELLING IN MEDITERRANEAN AREAS AND WETLANDS
PUMO, Dario
2010
Abstract
The present dissertation focuses on the field of research known as ecohydrology. Although this science, studying the mutual interactions between hydrological cycle and natural ecosystems, has been deeply investigated in recent past, some of its numerous aspects are still relatively unexplored. The main purpose is to investigate the existing scientific literature in order to adapt concepts and models previously developed for some specific ecosystems to the peculiarities of other less explored environments such as those semi-arid within the Mediterranean zone and the wetlands. In particular this study explores an ecohydrological approach to the analysis of water-controlled ecosystems in Mediterranean areas and groundwater dependent ecosystems. Although both are strongly reliant on water availability, these two kinds of environments are deeply different with each other. The most important difference is certainly played by the position of the water table. While on the one hand arid and semiarid ecosystems are usually characterized by a deep aquifer that does not exert any influence on soil water balance, on the other hand, in the case of groundwater dependent ecosystem, the water table position interacts directly with the root zone leading to important feedbacks between hydrological and ecological processes. The existing ecohydrological literature on arid and semiarid ecosystems such as savannas, steppes, deserts and prairies is rather wide, complete and consolidated. In such ecosystems, the soil moisture plays a fundamental role in the mutual links between climatic variations and the pedological and vegetational dynamics. The most common ecohydrological models start from a stochastic differential equation describing the soil water balance, where the unknown quantity, the soil moisture, depends both on spaces and time. Most of the solutions existing in literature are obtained in a probabilistic framework and under steady-state condition; even if this last condition allows the analytical handling of the problem, it has considerably simplified the same problem by subtracting generalities from it. The steady-state hypothesis, appears perfectly applicable in arid and semiarid climatic areas like those of African’s or middle American’s savannas, but it seems to be no more valid in areas with Mediterranean climate, where, notoriously, the wet season foregoes the growing season, recharging water into the soil. This soil moisture stored at the beginning of the growing season has a great importance, especially for deep-rooted vegetation, by enabling survival in absence of rainfalls during the growing season and, however, keeping the water stress low during the first period of the same season. In this thesis, a numerical approach, developed during the triennial graduate school at the University of Palermo, is presented. In particular a non steady numerical ecohydrological model is here proposed to evaluate the soil moisture dynamics and the consequent vegetation response in terms of water stress in Mediterranean areas. Such model is able to reproduce soil moisture probability density function, obtained analytically in previous studies for different climates in steady-state conditions. A first application of this model to the Sicilian river basin of Eleuterio at Lupo (Italy) shows how the model allows to compute the soil moisture time-profile and the vegetation static water stress time-profile in non-steady conditions, resulting able to capture the effects of winter recharge on the soil moisture. One of the possible applications of such model is to investigate the effects of potential climatic changes on vegetational stress in Mediterranean ecosystems. Many recent studies have demonstrated that CO2 increase is driving the climate in Mediterranean areas towards important changes, mainly represented by a temperatures increase and a contemporaneous rainfall reduction. Starting from this premise, the potential responses of vegetation, in terms of plants water stress, to different future scenarios are here investigated, throughout a second application of the model to the same river basin. In recent years great attention has been paid to environments such as riparian zones, peatlands and unsubmerged wetlands, which are considered as fundamental “tanks” of biodiversity and where the water table plays a key role in major ecohydrological processes. Wetlands are groundwater dependent ecosystems, which require access to the water table to maintain their health and vigor. A new fascinating challenge for the scientific community is that to investigate such environments by an ecohydrological approach. The study of the dynamics of interactions between climate, soil and vegetation in groundwater dependent ecosystems requires to couple the water table dynamics with the dynamics of soil moisture in the unsaturated zone. Only few recent frameworks have investigated a probabilistic approach also for the description of soil moisture and water table dynamics in the case of groundwater based ecosystems. In particular two models, the first for the analytical estimation of the water table position and the second for the analysis of the soil moisture dynamics, have been recently developed. Here, it is also presented a validation of the first model, which is the result of its application to three different sites within the Florida Everglades (USA).File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14242/82139
URN:NBN:IT:UNIPA-82139