Climate change and water abstraction impacts on the long-term variability of water levels in Lake Bracciano (Central Italy): A Random Forest approach

Abstract Study Region Lake Bracciano has been historically used as a strategic water reservoir for the city of Rome (Italy) since ancient times. However, following the severe water crisis of 2017, water abstraction has been completely stopped. Study Focus The relative impact of the various drivers of change (climatological and management) on fluctuations in lake water level is not yet clear. To quantify this impact, we applied the Random Forest (RF) machine learning approach, taking advantage of a century of observations. New Hydrological Insights for the Region Since the late 1990s the monthly variation in lake water levels has doubled, as has variation in monthly abstraction. Increased variation in annual cumulated precipitation and a rise in mean air temperature have also been observed. The RF machine learning approach made it possible to confirm the marginal role of temperature, the increasing role of abstraction during the last two decades (from 24 % to 39 %), and the key role played by the increased precipitation variability. These results highlight the notable prediction and inference capabilities of RF in a complex and partially unknown hydrological context. We conclude by discussing the limits of this approach, which are mainly associated with its capacity to generates scenarios compared to physical based models

Factors controlling the accelerated expansion of Imja Lake, Mount Everest region, Nepal

This study explores the link between area increase of Imja Tsho (Lake) and changes of Imja Glacier (area ∼25km2) under the influence of climate change using multitemporal satellite imagery and local climate data. Between 1962 and 2013, Imja Lake expanded from 0.03±0.01 to 1.35±0.05 km2 at a rate of 0.026±0.001 km2 a-1. The mean glacier-wide flow velocity was 37±30ma-1 during 1992-93 and 23±15ma-1 during 2013-14, indicating a decreasing velocity. A mean elevation change of -1.29±0.71ma-1 was observed over the lower part of the glacier in the period 2001-14, with a rate of -1.06±0.63ma-1 in 2001-08 and -1.56±0.80ma-1 in 2008-14. We conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last few decades. Furthermore, glacier ablation has increased due to increasing maximum temperatures during the post-monsoon months. Decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions.Publisher PDFPeer reviewe

Climate Change Adaptation in a Mediterranean Semi-Arid Catchment: Testing Managed Aquifer Recharge and Increased Surface Reservoir Capacity

Among different uses of freshwater, irrigation is the most impacting groundwater resource, leading to water table depletion and possible seawater intrusion. The unbalance between the availability of water resources and demand is currently exacerbated and could become worse in the near future in accordance with climate change observations and scenarios provided by Intergovernmental Panel on Climate Change (IPCC). In this context, Increasing Maximum Capacity of the surface reservoir (IMC) and Managed Aquifer Recharge (MAR) are adaptation measures that have the potential to enhance water supply systems resiliency. In this paper, a multiple-users and multiple-resources-Water Supply System (WSS) model is implemented to evaluate the effectiveness of these two adaptation strategies in a context of overexploited groundwater under the RCP 4.5 and the RCP 8.5 IPCC scenarios. The presented a case study that is located in the Puglia, a semi-arid region of South Italy characterized by a conspicuous water demand for irrigation. We observed that, although no significant long-term trend affects the proposed precipitation scenarios, the expected temperature increase highly impacts the WSS resources due to the associated increase of water demand for irrigation purposes. Under the RCP 4.5 the MAR scenario results are more effective than the IMC during long term wet periods (typically 5 years) and successfully compensates the impact on the groundwater resources. Differently, under RCP 8.5, due to more persistent dry periods, both adaptation scenarios fail and groundwater resource become exposed to massive sea water intrusion during the second half of the century. We conclude that the MAR scenario is a suitable adaptation strategy to face the expected future changes in climate, although mitigation actions to reduce green-house gases are strongly required

Factors controlling the accelerated expansion of Imja Lake, Mount Everest region, Nepal

This study explores the link between area increase of Imja Tsho (Lake) and changes of Imja Glacier (area: ~25km²) under the influence of climate change using multitemporal satellite imagery and local climate data. Between 1962 and 2013, Imja Lake expanded from 0.03±0.01 to 1.35±0.05 km² at a rate of 0.026±0.001 km² a⁻¹. The mean glacier-wide flow velocity was 37±30ma⁻¹ during 1992–93 and 23±15ma⁻¹ during 2013–14, indicating a decreasing velocity. A mean elevation change of –1.29±0.71ma⁻¹ was observed over the lower part of the glacier in the period 2001–14, with a rate of –1.06±0.63ma⁻¹ in 2001–08 and –1.56±0.80ma⁻¹ in 2008–14. We conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last decades. Furthermore, glacier ablation has increased due to increasing maximum temperatures during the post-monsoon months. Decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions

Pore-scale simulations of concentration tails in heterogeneous porous media

The retention of contaminants in the finest and less-conductive regions of natural aquifer is known to strongly affect the decontamination of polluted aquifers. In fact, contaminant transfer from low to high mobility regions at the back end of a contaminant plume (i.e. back diffusion) is responsible for the long-term release of contaminants during remediation operation. In this paper, we perform pore-scale calculations for the transport of contaminant through heterogeneous porous media composed of low and high mobility regions with two objectives: (i) study the effect of permeability contrast and solute transport conditions on the exchange of solutes between mobile and immobile regions and (ii) estimate the mass of contaminants sequestered in low mobility regions based on concentration breakthrough curves

A Stepwise Modelling Approach to Identifying Structural Features That Control Groundwater Flow in a Folded Carbonate Aquifer System

This paper concerns a stepwise modelling procedure for groundwater flow simulation in a folded and faulted, multilayer carbonate aquifer, which constitutes a source of good quality water for human consumption in the Apennine Range in Central Italy. A perennial river acts as the main natural drain for groundwater while sustaining valuable water-related ecosystems. The spatial distribution of recharge was estimated using the Thornthwaite–Mather method on 60 years of climate data. The system was conceptualized as three main aquifers separated by two locally discontinuous aquitards. Three numerical models were implemented by gradually adding complexity to the model grid: single layer (2D), three layers (quasi-3D) and five layers (fully 3D), using an equivalent porous medium approach, in order to find the best solution with a parsimonious model setting. To overcome dry-cell problems in the fully 3D model, the Newton–Raphson formulation for MODFLOW-2005 was invoked. The calibration results show that a fully 3D model was required to match the observed distribution of aquifer outflow to the river baseflow. The numerical model demonstrated the major impact of folded and faulted geological structures on controlling the flow dynamics in terms of flow direction, water heads and the spatial distribution of the outflows to the river and springs

Impact of Synthetic Porous Medium Geometric Properties on Solute Transport Using Direct 3D Pore-Scale Simulations

Transport processes in porous media have been traditionally studied through the parameterization of macroscale properties, by means of volume-averaging or upscaling methods over a representative elementary volume. The possibility of upscaling results from pore-scale simulations, to obtain volume-averaging properties useful for practical purpose, can enhance the understanding of transport effects that manifest at larger scales. Several studies have been carried out to investigate the impact of the geometric properties of porous media on transport processes for solute species. However, the range of pore-scale geometric properties, which can be investigated, is usually limited to the number of samples acquired from microcomputed tomography images of real porous media. The present study takes advantage of synthetic porous medium generation to propose a systematic analysis of the relationships between geometric features of the porous media and transport processes through direct simulations of fluid flow and advection-diffusion of a non-reactive solute. Numerical simulations are performed with the lattice Boltzmann method on synthetic media generated with a geostatistically based approach. Our findings suggest that the advective transport is primarily affected by the specific surface area and the mean curvature of the porous medium, while the effective diffusion coefficient scales as the inverse of the tortuosity squared. Finally, the possibility of estimating the hydrodynamic dispersion coefficient knowing only the geometric properties of porous media and the applied pressure gradient has been tested, within the range of tested porous media, against advection-diffusion simulations at low Reynolds (<10-1) and Peclet numbers ranging from 101 to 10-2

A Stakeholder Oriented Modelling Framework for the Early Detection of Shortage in Water Supply Systems

Management of water supply systems under shortage conditions due to drought requires computational tools able to relate the past precipitation regime over different time scales to future water resources availability. This work proposes a modelling framework to address the occurrence of shortage for water supply systems whose resource is constituted by natural or artificial reservoirs. The proposed methodology aims at identifying &ldquo;management triggers&rdquo; for possible mitigation measures. Emphasis is given on the use of standardized indices to promote information sharing. The implemented tool is structured into five modules: &ldquo;hydrological&rdquo; module; &ldquo;scenarios&rdquo; module; &ldquo;reservoir&rdquo; module; a module for the evaluation of &ldquo;indices of shortage&rdquo;; and a &ldquo;support to early-warning&rdquo; module. The whole procedure has been applied to three Italian reservoirs. For each water body, a case specific shortage early-warning system, based on standardized precipitation indices has been identified, allowing the implementation of efficient local mitigation measures