Abstract. Climate and land use change (global change) impacts on groundwater systems cannot be studied in isolation. Land use and land cover (LULC) changes have a great impact on the water cycle and contaminant production and transport. Groundwater flow and storage are changing in response not only to climatic changes but also to human impacts on land uses and demands, which will alter the hydrologic cycle and subsequently impact the quantity and quality of regional water systems. Predicting groundwater recharge and discharge conditions under future climate and land use changes is essential for integrated water management and adaptation. In the Mancha Oriental system (MOS), one of the largest groundwater bodies in Spain, the transformation from dry to irrigated lands during the last decades has led to a significant drop of the groundwater table, with the consequent effect on stream-aquifer interaction in the connected Jucar River. Understanding the spatial and temporal distribution of water quantity and water quality is essential for a proper management of the system. On the one hand, streamflow depletion is compromising the dependent ecosystems and the supply to the downstream demands, provoking a complex management issue. On the other hand, the intense use of fertilizer in agriculture is leading to locally high groundwater nitrate concentrations. In this paper we analyze the potential impacts of climate and land use change in the system by using an integrated modeling framework that consists in sequentially coupling a watershed agriculturally based hydrological model (Soil and Water Assessment Tool, SWAT) with a groundwater flow model developed in MODFLOW, and with a nitrate mass-transport model in MT3DMS. SWAT model outputs (mainly groundwater recharge and pumping, considering new irrigation needs under changing evapotranspiration (ET) and precipitation) are used as MODFLOW inputs to simulate changes in groundwater flow and storage and impacts on stream-aquifer interaction. SWAT and MODFLOW outputs (nitrate loads from SWAT, groundwater velocity field from MODFLOW) are used as MT3DMS inputs for assessing the fate and transport of nitrate leached from the topsoil. Three climate change scenarios have been considered, corresponding to three different general circulation models (GCMs) for emission scenario A1B that covers the control period, and short-, medium-and long-term future periods. A multi-temporal analysis of LULC change was carried out, helped by the study of historical trends (from remote-sensing images) and key driving forces to explain LULC transitions. Markov chains and European scenarios and projections were used to quantify trends in the future. The cellular automata technique was applied for stochastic modeling future LULC maps. Simulated values of river discharge, crop yields, groundwater levels and nitrate concentrations fit well to the observed ones. The results show the response of groundwater quantity and quality (nitrate polPublished by Copernicus Publications on behalf of the European Geosc...
Abstract. Climate and land use change (global change) impacts on groundwater systems cannot be studied in isolation, as various and complex interactions in the hydrological cycle take part. Land-use and land-cover (LULC) changes have a great impact on the water cycle and contaminant production and transport. Groundwater flow and storage are changing in response not only to climatic changes but also to human impacts on land uses and demands (global change). Changes in future climate and land uses will alter the hydrologic cycles and subsequently impact the quantity and quality of regional water systems. Predicting the behavior of recharge and discharge conditions under future climatic and land use changes is essential for integrated water management and adaptation. In the Mancha Oriental system in Spain, in the last decades the transformation from dry to irrigated lands has led to a significant drop of the groundwater table in one of the largest groundwater bodies in Spain, with the consequent effect on stream-aquifer interaction in the connected Jucar River. Streamflow depletion is compromising the related ecosystems and the supply to the downstream demands, provoking a complex management issue. The intense use of fertilizer in agriculture is also leading to locally high groundwater nitrate concentrations. Understanding the spatial and temporal distribution of water availability and water quality is essential for a proper management of the system. In this paper we analyze the potential impact of climate and land use change in the system by using an integrated modelling framework consisting of the sequentially coupling of a watershed agriculturally-based hydrological model (SWAT) with the ground-water model MODFLOW and mass-transport model MT3D. SWAT model outputs (mainly groundwater recharge and pumping, considering new irrigation needs under changing ET and precipitation) are used as MODFLOW inputs to simulate changes in groundwater flow and storage and impacts on stream-aquifer interaction. SWAT and MODFLOW outputs (nitrate loads from SWAT, groundwater velocity field from MODFLOW) are used as MT3D inputs for assessing the fate and transport of nitrate leached from the topsoil. Results on river discharge, crop yields, groundwater levels and groundwater nitrate concentrations obtained from simulation fit well to the observed values. Three climate change scenarios have been considered, corresponding to 3 different GCMs for emission scenario A1B, covering the control period, and short, medium and long-term future periods. A multi-temporal analysis of LULC change was carried out, helped by the study of historical trends by remote sensing images and key driving forces to explain LULC transitions. Markov chains and European scenarios and projections have been used to quantify trends in the future. The cellular automata technique was applied for stochastic modeling future LULC maps. The results show the sensitivity of groundwater quantity and quality (nitrate pollution) to climate and land use changes, and the need to implement adaptation measures in order to prevent further groundwater level declines and increasing nitrate concentrations. The sequential modelling chain has been proved to be a valuable assessment and management tool for supporting the development of sustainable management strategies.
ResumenLa expansión espacial incesante de las ciudades, el aumento de la segregación socio-espacial y el aumento del nivel de emisiones afectan severamente al medio ambiente y conforman estructuras emergentes e insustentables. El enfoque de los sistemas complejos, la ecología urbana y la ecología del paisaje nos ayudan comprender algunas de las propiedades de este crecimiento urbano. Para ello, se estudia la dispersión del paisaje urbano de 43 ciudades y conglomerados urbanos chilenos, entre 1993, 2003 y 2011, utilizando distintas métricas del paisaje urbano: fragmentación, elongación y aislamiento, en base a coberturas del Observatorio Urbano (MINVU) y al procesamiento en el programa Fragstat. También, se realiza un escalamiento del tamaño de las ciudades según el nivel de emisiones de CO 2 de manera exploratoria. Los resultados muestran que Santiago presenta los mayores porcentajes de fragmentación y el máximo crecimiento, junto con las ciudades Arica y Calama; la mayor parte experimentan procesos de elongación (Los Ángeles, Chillán e Iquique) y gran parte aumentan su aislamiento (Illapel, San Antonio y Copiapó). Por su parte, el escalamiento de las emisiones presenta un comportamiento sublineal (0,8). Los datos exhiben una alometría heterogénea que dependen estrechamente de la calidad de los datos utilizados, transitando de un modelo de ciudad relativamente compacto a uno difuso y disperso. Los métodos de simulación espacial de la dispersión y de escalamiento pueden servir como proxy para evaluar la sustentabilidad urbana, en la medida que ayudan a determinar la tendencia global de urbanización y pronosticar cómo evolucionarían los sistemas urbanos.Palabras clave: Sustentabilidad urbana, dispersión urbana, sistemas complejos, Fragstat. AbstractIncessant spatial expansion of cities, the increasing socio-spatial segregation, and rising levels of emissions severely affect the underlying environment and generate emerging and unsustainable structures. The approach of complex systems, urban ecology and landscape ecology helps us to understand some of the properties of this urban growth. In order to do this, the urban landscape fragmentation of 43 Chilean urban systems were calculated, between 1993, 2003 and 2011, using landscape metrics: fragmentation, elongation and isolation. Spatial layers of the Urban Observatory (MINVU) were processed in Fragstat program. Also, a scaling of the cities according to the level of CO 2 emissions is carried out in an exploratory way. The results show that Santiago presents the highest percentages of fragmentation and maximum growth, along with the cities Arica and Calama; most of the cities undergo elongation processes and most of them increase their isolation (Illapel, San Antonio and Copiapó). On the other hand, the scaling of the emissions presents sublineal pace (0,8). The data show a heterogeneous allometry that depends very closely on the quality of the data used, moving from a model city relatively compact to a diffuse and disperse one. The spatial simulation methods of urba...
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