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The goal of limiting the use of natural resources and combatting climate change has led to the improvement of agricultural techniques and the development of some Carbon Dioxide Removal (CDR) techniques, given their proficiency to sequester carbon from the atmospheric CO2 and to store it in more stable forms within oceans, plants, soil, or other terrestrial environments. Among them, Enhanced Weathering (EW) is regarded as one of the most promising. This consists of amending soils with silicate minerals, such as olivine, so as to speed up the weathering process that naturally occurs in soils. This work aims to couple a model for the resolution of the agro-hydrological balance in the active soil layer of croplands (i.e., WATNEEDS model) and a dynamic mass balance model that explores ecohydrological, biogeochemical, and olivine dissolution dynamics, also estimating carbon sequestration rates (i.e., EW model). This latter is composed of different interacting components and takes into account important processes, such as the cation exchange.From the operational point of view, the EW model is fed by rainfall data, and the outputs of the soil water balance (i.e., infiltration, evapotranspiration, leaching, and runoff rates) estimated by the WATNEEDS at the global scale at a 5 arcminute resolution. In this study, a regional application of both models is proposed to explore EW efficiency in various cropland areas in Sicily (Italy), the largest island of the Mediterranean basin, which is considered a hot spot of climate change. The methodological approach will be developed and tested for four different crops (i.e., olive and citrus groves, vineyards, and fruit trees) that are particularly widespread and profitable in the selected region. Apart from facing climate change, the goal of this study is also to preserve water, thus selecting the most suitable irrigation strategies in the context of a changing climate and olivine amendment prescription. This study may also provide a tool to decision-makers for an actual future application of EW, which can be valid for Sicily and for other parts of the world with similar climatic conditions, soil, and vegetation.

Enhanced weathering (EW) is a promising strategy for carbon sequestration, but several open questions remain regarding the actual rates of dissolution in conditions of natural hydroclimatic variability in comparison to laboratory experiments. In this context, models play a pivotal role, as they allow exploring and predicting EW dynamics under different environmental conditions. Here a comprehensive hydro-biogeochemical model has been applied to four cropland case studies (i.e., Sicily and the Padan plain in Italy and California and Iowa in the USA) characterized by different rainfall seasonality, vegetation (i.e., wheat for Sicily and California and corn for the Padan plain and Iowa), and soil type to explore their influence on dissolution rates. The results reveal that rainfall seasonality and irrigation when applied are crucial in determining EW and carbon sequestration dynamics, given their effect on hydrological fluxes, soil pH and weathering rate. The carbon sequestration rate was found to be strongly affected also by the background weathering flux, which is one of the main factors controlling soil pH before the olivine amendment. Regarding the US case studies, Iowa sequesters the greatest amount of CO2 if compared to California (4.20 and 2.21 kg ha−1 yr−1, respectively), and the same happens for Sicily with respect to the Padan plain (0.62 and 0.39 kg ha−1 yr−1, respectively). These low carbon sequestration values suggest that an in-depth analysis at the global scale is required to assess EW efficacy for carbon sequestration.

Steep landscapes maintain predominantly planar hillslopes over a range of spatial scales. These hillslopes are bounded at a typical angle, beyond which shallow landslides or slope failures remove the excess sediment influx. The evolution of such steep topographies with threshold hillslopes is well approximated by the eikonal equation, which is well-known in problems of geometry, optics, and mechanics. According to this approximation, hillslopes meet upstream to construct a network of sharp ridges and join downstream at the boundary to produce a complementary valley network. We find a good agreement between the proposed approximation and the spatial organization of landscapes with a dominant control of landslide erosion and negligible fluvial erosion. We also show that the eikonal approximation can be utilized to reconstruct the landscapes with threshold hillslopes where fluvial erosion sets the downstream free boundary.

The impacts of climate change, mainly due to the use of fossil fuels, have been rising over the last decades. To address this problem, the scientific community is currently making a big effort, coming up with several solutions aiming to reduce greenhouse gas emissions or to sequester the carbon within the atmospheric CO2.In this context, Enhanced chemical weathering is included in the group of carbon sequestration technologies. These techniques involve removing CO2 from the atmosphere and storing the carbon within it in the oceans, terrestrial environments or geologic formations. The natural chemical weathering is the main process of soil formation, since it is the ensemble of the chemical/biochemical reactions leading to the alteration of primary minerals, thus to the formation of secondary minerals. The Enhanced chemical weathering consists of increasing the natural weathering reaction rates, by adding some highly reactive minerals to the soil. It is widely known that weathering rates are higher under warm and humid climate conditions and high soil acidity.The present study evaluates the effects of Forsterite, a common silicate mineral also known as Mg-olivine, on soil carbon sequestration. This mineral is recognized by many studies as the best solution for Enhanced weathering applications since it is available in many parts of the world and its reaction rates with CO2 are much higher than those of other minerals. In this study, a model simulating the dynamics of the biogeochemistry of a soil treated with olivine under different climate scenarios is presented. The model is forced by a stochastic rainfall, simulated as a marked Poisson process, and puts together the ecohydrology and the biogeochemistry. Plants influence the whole system with their evapotranspiration, nutrients uptake (Na+, Ca2+ and Mg2+) and the addition of organic matter to the soil. Biogeochemistry involves all the aspects of the model related to the cycle of the dissolved ions (H+, Na+, Ca2+ and Mg2+), litter decomposition and the chemical reaction of olivine with CO2.Running the model under different climate scenarios highlights that the highest olivine weathering rates are assessed under wet conditions. This happens because high soil moisture leads to higher reactive surface areas of particles and higher dissolution rates. This aspect is emphasized from the fact that soil pH is lower in humid than in dry environments and weathering reaction rates are higher in acid conditions since hydrogen ions are the reactants of many weathering reactions. The study also attempts to evaluate the economic feasibility of the intervention in agricultural fields. Apart from the costs of performing this kind of intervention, some benefits should be taken into account. More specifically, spreading olivine on agricultural fields leads to an increase of Na+, Ca2+ and Mg2+ concentrations, thus a certain amount of olivine can replace the addition of fertilizers. Therefore, this study proposes a natural solution for facing climate change problems and presents a model that could be used as a decision support system in land management.

Enhanced weathering (EW) is one of the most promising technologies for sequestering atmospheric carbon. It consists on accelerating the chemical weathering fluxes naturally occurring in soils, by means of the addition of silicate minerals (i.e., forsterite), used as amendments, to the soil. If crushed into micrometer-sized particles, these minerals are characterized by high dissolution rates, that may be further improved under high soil water content and low pH conditions. Before actually applying EW technique at the global scale for carbon sequestration, an in-depth characterization of weathering and carbon sequestration rates, under different environmental conditions, is needed, also looking at correlated beneficial/detrimental effects. In this context, modeling approaches may play a pivotal role, since they allow to achieve this goal without affording costs required by laboratory and field experiments. The present study describes the application of a dynamic mass balance model connecting ecohydrological, biogeochemical and olivine dissolution dynamics. The model is composed of four connected components and is solved through an explicit system of eight mass balance total differential equations and an implicit one having 22 algebraic equations.In this study, the model is applied to two sites in Italy (i.e., Sicily, in the south and the Padan plain, in the north) and two in the USA (i.e., California, in the south-west and Iowa, in the north-central area). The most common crops for the case studies, i.e., wheat for Sicily and California and corn for the Padan plain and Iowa are here considered, along with the most frequent soil types, namely the clay loam for Sicily and California and the silty clay loam for the Padan plain and Iowa. Maps of lithological composition of bedrocks and spatial distributions of soil pH have been also used to calibrate the background weathering flux, responsible of the H+ consume from all the minerals naturally present in the soil. Apart from deriving the most suitable locations, among those presented, providing the highest weathering and carbon sequestration rates, these simulations allow to assess the role of different climate, crop and soil types on EW dynamics, in perspective to find the combination that maximizes the CO2 sequestration.

Incipient valley formation in mountainous landscapes is often associated with their presence at a regular spacing under diverse hydroclimatic forcings. Here we provide a formal linear stability theory for a landscape evolution model (LEM) representing the action of tectonic uplift, diffusive soil creep, and detachment-limited fluvial erosion. For configurations dominated by only one horizontal length scale, a single dimensionless quantity characterizes the overall system dynamics based on model parameters and boundary conditions. The stability analysis is conducted for smooth and symmetric hillslopes along a long mountain ridge to study the impact of the erosion law form on regular first-order valley formation. The results provide the critical condition when smooth landscapes become unstable and give rise to a characteristic length scale for incipient valleys, which is related to the scaling exponents that couple fluvial erosion to the specific drainage area and the local slope. The valley spacing at first instability is uniquely related to the ratio of the scaling exponents and expands logarithmically with an increase in this ratio. We find compelling evidence of sediment transport by diffusive creep and fluvial erosion coupled with the specific drainage area equation as a sufficient mechanism for first-order valley formation. We finally show that the predictions of the linear stability analysis conform with the results of numerical simulations for different degrees of nonlinearity in the erosion law and agree well with topographic data from a natural landscape.

Enhanced weathering (EW) is one of the most promising negative emissions technologies urgently needed to limit global warming to at least below 2 °C, a goal recently reaffirmed at the UN Global Climate Change conference (i.e., COP26). EW relies on the accelerated dissolution of crushed silicate rocks applied to soils and is considered a sustainable solution requiring limited technology. While EW has a high theoretical potential of sequestering CO2, research is still needed to provide accurate estimates of carbon (C) sequestration when applying different silicate materials across distinct climates and major soil types in combination with a variety of plants. Here we elaborate on fundamental advances that must be addressed before EW can be extensively adopted. These include identifying the most suitable environmental conditions, improving estimates of field dissolution rates and efficacy of CO2 removal, and identifying alternative sources of silicate materials to meet future EW demands. We conclude with considerations on the necessity of integrated modeling–experimental approaches to better coordinate future field experiments and measurements of CO2 removal, as well as on the importance of seamlessly coordinating EW with cropland and forest management.

Aiming at facing climate change, some CDR (Carbon Dioxide Removal) techniques are currently studied given their capability to sequester carbon from the atmospheric CO2 and to store it within oceans, plants, soil, or other terrestrial environments. Among them, Enhanced Weathering (EW), that acts in speeding up the chemical weathering naturally occurring in soils through the amendments of highly reactive silicate minerals, is referred to as one of the most promising. Hot and humid climates provide the best conditions for EW, since reactions are faster at high temperature, high soil water content and low soil pH. This study presents a dynamic mass balance model that explores ecohydrological, biogeochemical and olivine dissolution dynamics. Through the application of this model, which is composed of different interconnected components, it is possible to explore the role of hydrological processes on olivine dissolution and, therefore, to compute carbon sequestration rates. The model is coupled with a spatially distributed crop specific agro-hydrological model named WATNEEDS, able to solve the soil water balance at the global scale at a 5 arcminute resolution. Input of rainfall data, along with the outputs components of the soil water balance (i.e., infiltration, evapotranspiration, leaching and runoff rates) for each crop, estimated the WATNEEDS are used as input in estimating EW yields at large scale. Here a current application at the regional scale for agriculture, is proposed to explore EW yields in various cropland areas in Italy. The spatial extension of the study area, i.e., the whole Italian territory, allows to explore the EW dynamics under different climate conditions and crop and soil types, defining the importance of such factors in the EW dynamics. This allows to extract olivine dissolution dynamics in places characterized by significant differences in terms of rainfall seasonality, crop phenology, soil type and composition. A future enhancement of this study may be the application of the EW model at the global scale, so as to provide a tool to decision makers for an actual future application of EW.

Enhanced Weathering (EW) is a promising strategy for carbon sequestration, but several open questions remain regarding the actual rates of dissolution in conditions of natural hydroclimatic variability in comparison to laboratory experiments. In this context, models play a pivotal role, as they allow exploring and predicting EW dynamics under different environmental conditions. Here a comprehensive hydro-biogeochemical model has been applied to four cropland case studies (i.e., Sicily and the Padan plain in Italy and California and Iowa in the USA) characterized by different rainfall seasonality, vegetation (i.e., wheat for Sicily and California and corn for Padan plain and Iowa), and soil type to explore their influence on dissolution rates. The results reveal that rainfall seasonality, and irrigation when applied, are crucial in determining EW and carbon sequestration dynamics, given their effect on hydrological fluxes, soil pH, and weathering rate. The carbon sequestration rate was found to be strongly affected also by the pre-EW soil pH, which is one of the main factors controlling soil pH before the olivine amendment. In the analyzed case studies, Iowa and Sicily sequester the greatest amount of CO2 (4.20 and 0.62 kg ha-1 y-1, respectively), as compared to California and the Padan plain (2.21 and 0.39 kg ha-1 y-1, respectively). These low carbon sequestration values suggest that an in-depth analysis at the global scale is required to assess EW efficacy for carbon sequestration.

With the aim to face climate change, some NCS (Natural Climate Solutions) are currently studied given their capability to sequester carbon from the atmospheric CO2, by means of some natural processes, and to store it within oceans, plants, soil, or other terrestrial environments. Among all the existing NCS, Enhanced Weathering (EW) acts in speeding up the chemical weathering that naturally occurs in soils. This is achieved by amending soils with crushed highly reactive silicate minerals, such as forsterite, better known as olivine. In general, EW reactions are faster at high temperature and soil water content and low soil pH, demonstrating that the most suitable places in the world to apply this technique are those characterized by hot and humid climates. Vegetation has a positive effect for EW reactions, given its acidifying action on soil water, due to the displacement of H+ ions consequent to the uptake of cations used as nutrients (i.e., Mg2+, Ca2+ and K+). Furthermore, it has been demonstrated that olivine dissolution leads to the increase of the above-listed nutrients concentration in soil water, resulting in a fertilizing effect for plants. For these reasons, various studies affirm that it may be realistic to apply EW technique in forested or cultivated areas, but only after reliably quantifying its carbon sequestration rate and other beneficial/detrimental effects. This study presents a dynamic mass balance model that explores ecohydrological, biogeochemical and olivine dissolution dynamics. The model allows to explore the role of hydrological processes on long term olivine dissolution and, therefore, to compute carbon sequestration and the increase of nutrients in soil water upon olivine dissolution. The model is composed of different interconnected components and the resulting scheme consists of an explicit system of eight mass balance total differential equations and an implicit part with 22 algebraic equations in as many unknown variables. The main purpose of the present study is to apply the model to two different sites in Italy (i.e., Sicily, in the south and the Padan plain, in the north) and two other sites in the USA (i.e., California, in the south-west and Iowa, in the north-central area). Furthermore, crops that are very common and occupy a huge area in correspondence of the considered sites, namely the wheat crop for Sicily and California and the corn crop for Padan plain and Iowa, are here taken into account. This allows to explore the EW dynamics under different climate conditions and crop and soil types, with the aim to assess the importance of such factors in the EW application. This study could be helpful for decision makers to identify which parts of the globe, among those presented, are more suitable for amending soil with olivine, in perspective to put EW into practice.

As photovoltaic power is expanding rapidly worldwide, it is imperative to assess its promise under future climate scenarios. While a great deal of research has been devoted to trends of mean solar radiation, less attention has been paid to its intermittent character, a key challenge when compounded with uncertainties related to climate variability. Using both satellite data and climate model outputs, here we characterize solar radiation intermittency to assess future photovoltaic reliability. We find that the relation between the future power supply and long-term trends of mean solar radiation is highly nonlinear, thus making power reliability more sensitive to the fluctuations of mean solar radiation in regions where insolation is the highest. Our results highlight how reliability analysis must account simultaneously for the mean and intermittency of solar inputs when assessing the impacts of climate change on photovoltaics., Comment: 19 pages, 10 figures, 1 table

Irrigation agriculture is the most important user of the global freshwater resources worldwide, which makes it one of the key actors conditioning sustainable development and water security. The anticipated future climate change, population growth, and rapidly rising global demand for food will likely lead to agricultural expansion by allowing the development of irrigated areas. This together with the fact that irrigated crops are approximately four times more profitable than rainfed crops will place much additional pressure on water resources in the next years. Therefore, it is of vital importance to devise solutions that minimize the negative impacts of agricultural expansion, particularly on biodiversity and water use, so as to help us achieve environmental and economic sustainability. To realize such an ambition, quantifying irrigation water withdrawal at different spatio-temporal scales is essential. Global Hydrological Models (GHM) are often used to produce irrigation water withdrawal estimates. Yet GHMs questionably rely on several uncertain estimates of irrigated areas, crop evapotranspiration processes, precipitation and irrigation efficiency, which are the four main inputs in the structure of GHMs. Here we show that, once basic uncertainties regarding these estimates are properly integrated into the calculations, the point-based irrigation water withdrawal estimates actually correspond to uncertainty intervals that span several orders of magnitude already at the grid cell level. Our approach is based on the concept of “sensitivity auditing”, a practice of process-oriented skepticism towards mathematical models. The numerical results suggest that current estimates of global irrigation water withdrawals are spuriously accurate due to their neglect of several ambiguities/uncertainties, and thus need to be re-assessed. Our analysis highlights that models of global irrigation water demands need to better integrate uncertainties, both technical and epistemological, so as to avoid misguiding the development of strategies intended to help ensure water and food security.

Enhanced weathering (EW) is a promising negative-emission technology that artificially accelerates the dissolution of natural minerals, promotes biomass growth, and alleviates the acidification of soils and natural waters. EW aims to increase the alkalinity of natural waters (alkalinization) to promote a transfer of CO2 from the atmosphere to the water. Here we provide a quantification of the alkalinization carbon-capture efficiency (ACE) as a function of the water chemistry. ACE can be used for any alkaline mineral in various natural waters. We show that ACE strongly depends on the water pH, with a sharp transition from minimum to maximum in a narrow interval of pH values. We also quantify ACE in three compartments of the land-to-ocean aquatic continuum: the world topsoils, the lakes of an acid-sensitive area, and the global surface ocean. The results reveal that the efficiency of terrestrial EW varies markedly, from 0 to 100 %, with a significant trade-off in acidic conditions between carbon-capture efficiency and enhanced chemical dissolution. The efficiency is more stable in the ocean, with a typical value of around 80 % and a latitudinal pattern driven by differences in seawater temperature and salinity. Our results point to the importance of an integrated hydrological and biogeochemical theory to assess the fate of the weathering products across the aquatic continuum from land to ocean.

Ecohydrology is a fast-growing branch of science at the interface of ecology and geophysics, studying the interaction between soil, water, vegetation, microbiome, atmosphere, climate, and human society. This textbook gathers the fundamentals of hydrology, ecology, environmental engineering, agronomy, and atmospheric science to provide a rigorous yet accessible description of the tools necessary for the mathematical modelling of water, energy, carbon, and nutrient transport within the soil-plant-atmosphere continuum. By focusing on the dynamics at multiple time scales, from the diurnal scale in the soil-plant-atmospheric system, to long-term stochastic dynamics of water availability responsible for ecological patterns and environmental fluctuations, it explains the impact of hydroclimatic variability on vegetation and soil microbial systems through biogeochemical cycles and ecosystems under different socioeconomical pressures. It is aimed at advanced students, researchers and professionals in hydrology, ecology, Earth science, environmental engineering, environmental science, agronomy, and atmospheric science.

Anthropogenic emissions of CO2 must soon approach net zero to stabilize the global mean temperature. Although several international agreements have advocated for coordinated climate actions, their implementation has remained below expectations. One of the main challenges of international cooperation is the different degrees of socio-political acceptance of decarbonization.In this contribution, we interrogate a minimalistic model of the coupled human-natural system representing the impact of such socio-political acceptance on investments in clean energy and the path to net-zero emissions. Despite its simplicity, the model can reproduce complex interactions between human and natural systems, and it can disentangle the effects of climate policies from those of socio-political acceptance on the path to net zero. Although perfect coordination remains unlikely, as clean energy investments are limited by myopic economic strategies and a policy system that promotes free-riding, more realistic decentralized cooperation with partial efforts from each actor could still lead to significant emissions cuts.Since the socio-political feedback on the path to net zero could influence the trajectories of the Earth System for decades to centuries and beyond, climate models need to incorporate better the dynamical bi-directional interactions between socio-political groups and the environment. Our model represents a first step for incorporating this feedback in describing complex coupled human and natural systems.

Soil salinization represents one of the most widespread forms of land degradation worldwide, posing an enormous threat to food security, sustainable development, and ecosystem resilience across a w...

To mitigate global warming, a noticeable research effort is being devoted to NCS (Natural Climate Solutions) as means to reduce greenhouse gas emissions or sequester carbon within the oceans or terrestrial environments by exploiting natural processes. Enhanced weathering is a NCS that aims to increase the weathering reaction rates of silicate minerals, by amending soils with crushed reactive minerals. Various studies have shown that this technique is favored by hot and humid climates (i.e., tropical ecosystems), since weathering reactions are mostly effective under high temperature and soil moisture. Despite olivine dissolution dynamics in laboratory conditions are quite well known, understanding and modeling them in field is still a challenge. Indeed, apart from some pot experiments involving soils of agricultural fields, only few weathering models are available. Given the urgency of the problem, models play a very important role for extrapolating results of laboratory and field experiments in both time and space, as well as for quantifying the impact of hydroclimatic fluctuations on the involved biogeochemical processes.The present study explores the role of hydrological processes on long-term Forsterite dissolution, a highly reactive silicate mineral also known as Mg-olivine or simply olivine. Toward this goal, we present a novel dynamic mass balance model coupling ecohydrological and biogeochemical dynamics, including mineral dissolution. Results under different climate scenarios highlight that hydrological fluctuations lead to hysteretic patterns of weathering rate with soil moisture, meaning that the process maintains a memory of past events (i.e., dry or wet periods). The model allows to explore the twofold role of organic matter on enhanced weathering; indeed, while its decomposition is a source of CO2, organic matter also increases the soil CEC, thus buffering changes in soil pH. Carbon sequestration and nutrients availability due to enhanced weathering are quantified, in this study, as a function of MAP (Mean Annual Precipitation). Average CO2 that reacts with olivine can exceed 40 t ha-1 y-1 for MAP higher than 2000 mm, condition that is always reached in the tropics. This CO2 can be found as dissolved in soil water in the form of bicarbonate (HCO3-) and carbonate (CO32-) ions and will be leached away from the domain, eventually reaching the ocean. In presence of tropical climate olivine application also leads to an increase of soil pH and nutrients availability, especially calcium and magnesium, which in turn can enhance plant productivity. This study paves the way for a potential integration of enhanced weathering in agroecosystem management practices, especially in humid tropical regions since these are characterized by high MAP and temperature.

Natural climate solutions are attracting considerable research effort with the aim of reducing greenhouse gas emissions or sequestering carbon within the oceans or terrestrial environments. In this context, enhanced weathering can be a powerful means of increasing the natural weathering reaction rates, by adding some highly reactive minerals to the soil. The present study evaluates the effects of hydrologic fluctuations on Forsterite dissolution, a silicate mineral also known as Mg-olivine. This mineral is available in many parts of the world and its reaction rates with CO2 are much higher than those of other minerals. Toward this goal, we developed a mathematical model coupling biogeochemical and ecohydrological aspects of a soil treated with olivine. The model can be forced with a stochastic rainfall, in order to understand the role of hydrological processes on long-term enhanced weathering dynamics. The results under different climate scenarios quantify the dependence of weathering rates on wetness. High soil water contents are linked to higher reactive surface area and lower pH levels, resulting in higher dissolution rates. The weathering rate shows a hysteretic behavior with respect to soil moisture since its variability does not immediately lead to a change in weathering rate. Plants play a relevant role in this context since they may further increase the weathering rate by releasing H+ ions in soil water. In addition, we explore the twofold role of organic matter on enhanced weathering; while its decomposition is a source of CO2, organic matter also increases the soil CEC, thus buffering changes in soil pH. In conclusion, by shedding light on the interaction between olivine dissolution and ecohydrological processes, this study paves the way for the inclusion of enhanced weathering in agroecosystem management practices.

Because of the large carbon sequestration potential, reforestation and afforestation (R&A) are among the most prominent natural climate solutions. However, while their effectiveness is well established for wet tropics, it is often argued that R&A are less advantageous or even detrimental at higher latitudes, where the reduction of forest albedo (the amount of reflected solar radiation by a surface) tends to nullify or even overcome the carbon benefits. Here, we carefully analyze the situation for R&A at midlatitudes, where the warming effects due to vegetation albedo are regarded to be almost balanced by the cooling effects from an increased carbon storage. Using both satellite data and atmospheric boundary-layer models, we show that by including cloud–albedo effects due to land–atmosphere interactions, the R&A cooling at midlatitudes becomes prevalent. This points to a much greater potential of R&A for wet temperate regions than previously considered.

Alkalinization of natural waters by the dissolution of natural or artificial minerals is a promising solution to sequester atmospheric CO$_2$ and counteract acidification. Here we address the alkal...