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Climate projections and trend analysis of historical data suggest that precipitation and temperature changes can dramatically alter the supply of and the demand for water in the human- and eco-systems. Moreover, anthropogenic landscape changes are occurring at unprecedented scales and rates given the societal needs for various (and often competing) ecosystem goods and services (food, energy, and water). How stable or resilient are the human- and eco- systems to climatic and anthropogenic perturbations remain a major societal concern. Of these concerns, hydrologic cycle changes, water resources availability and related management rank among the highest because of their importance in regulating human and ecological sustainability and climate feedbacks. Attempts at re-constructing the most basic components of the continental-scale hydrologic cycle of the past century are already stirring scientific controversy.

Scope of the project: Exploring the impact of climate change and anthropogenic landscape changes on all aspects of the water cycle is well beyond the scope of a single project. The goal of this research program is on the overall impact of such changes on rainfall (the source of water) and concomitant replenishment of usable water supplies (e.g. ground- and streamwater) given their high priority to any future water resource planning. Even within this restricted scope, the barriers to scientific progress are numerous necessitating an interdisciplinary approach that combines principles from eco-hydrology, hydraulics and fluid mechanics, soil physics, plant physiology, stochastic processes, dynamical systems theory, and water resources management. This project aims to build a network of researchers with complementary talents to begin progress on these fronts. Moreover, this network of researchers will be actively engaged in preparing the next generation of international scientists (via graduate student exchanges) who will be trained to approach such 'interdisciplinary' societal problems and progress on them by adopting 'trans-disciplinary' approaches now emerging from complex systems science, dynamical systems theory, and stochastic processes.

To pursue such an ambitious goal, the project is divided into three working packages (WP). The intent of these working packages is not to provide a comprehensive 'plug-and-play' model for water resources managers or a set of 'modular products' to be implemented in climate systems community models. Rather, it is 'biased' towards pressing scientific and management problems that require (at minimum) a combination of 'diagnostic' and 'prognostic' framework to progress on them.

WPA: Precipitation and Water Distribution

Objectives: The probabilistic representation of precipitation and river flows are nowadays affected by the need to account for non-stationarity due to climatic shifts. Because of the major uncertainties produced by climate change on the hydrologic cycle , it is essential to include, in the frequency analysis of the extreme events, a reproduction of the phenomena at the scale of interest, which is typically the basin scale. The transfer of climatologic information at finer scale claims the use of robust and objective criteria that accounts for the different spatial effects produced by the forcing, depending on the different physiographic soil and vegetation characteristics of the study domain. To define the relations that induce the variability of the hydrologic processes from basin to basin, objective statistical methods and empirical procedure were widely used in the past, even if very often they have a limited validity in space, according to merely geographical assumptions. The need to face climatic anomalies by building future probabilistic scenarios characterized by unsteady phenomena is currently giving acceleration to the research of causative and non-empirical relation between climate forcing, physical basin structure and hydrological processes. However, within the domain of such research, it is imperative to confront three challenges: 1) the collection of new information about watershed characteristics, lacking especially for the Mediterranean region; 2) the development of methods for catchment classification, aimed at identifying physiographic and climatic macro-region; 3) the improvement of the statistical and geomorphoclimatic analysis of the relation between characteristics discharge and basin descriptors.

Description of work: The main purpose here is linking the spatial variability of hydrological variable at different spatial scale (local, basin, regional and national scale) by defining methodological standards for the characterization of physical and hydrological parameters (WPA1). A twofold method is proposed: 1) the basins characteristics will be investigated with classification procedures partially or fully unsupervised, for addressing a rational subdivision according to different physical-climatic environment, with the aim of defining homogeneous regional units that can be used to assess the design flows in ungauged basins (WPA2); 2) research on the statistical link between basin descriptors and observations preserving the cross-scale information flow that is most pertinent to preserving the non-linearities in the phase-space of the observations. By mean of the “downward approach” (method used to investigate a variable at a broader scale starting from information provided at finer scales) the results obtained at a local and basin scale would be transferred to a regional scale, climate change forcing acts as a forcing (WPA3 and WPA4).

The specific Scientific highlights and research achievements are described later.

WPB: Feedbacks to Precipitation

Objectives: The coupling between soil moisture, land-surface fluxes of heat and water vapor, and the initiation of convective rainfall remains an open research problem, which has recently attracted a lot of attention. The complexity of this problem mainly resides in the large number of interacting processes occurring within the soil-plant-atmosphere system that vary over a wide range of space and time scales. Below ground and surface processes involve the dynamics of water movement from the soil into the atmosphere (rooting system, plant hydrodynamics, and stomatal regulation dictating water movement from the roots and out of the stomata as water vapor after phase transition), the canopy aerodynamics (affecting the transport of heat and water vapor from the canopy into the atmospheric boundary layer or ABL), and the partitioning of net radiation into latent and sensible heat fluxes, thereby influencing skin temperature and directly impacting the dynamics of mean air temperature and water vapor concentration in the ABL. On the other hand, the ABL, with its unique coexistence of mechanically- and thermally- generated turbulence, acts as an integrator of these surface processes with larger length and slowly evolving synoptic scale processes impacting mass and heat entrainment. The dynamics of these land-surface fluxes and soil-plant-atmosphere variables control the simultaneous growth of the convective boundary layer and lifting condensation level (LCL) and thus their crossing - a necessary condition for the triggering of convective rainfall. Even in the most idealized cases, any exploration of the feedback mechanisms between soil moisture and convective-rainfall triggers must account, at minimum, for all these pathways at the appropriate scales. To do so, small scale processes, such as root water uptake, must be spatially up-scaled, and fast processes, such as entrainment turbulent fluxes, must be temporally averaged in such a way that the dynamics of each process is still preserved and the coupling between them can be properly investigated.

Description of work: The primary objective of this WP is to explore via model calculations and data analysis how anthropogenic land use changes impact convective rainfall triggers and drainage starting from the rooting zone (as a surrogate for water recharge). To achieve this objective, two tasks must be completed: 1) couple an ABL dynamics model with a detailed soil-plant model that resolves both - the microscopic and macroscopic soil moisture dynamics (WPB1); and 2) conduct model calculations to assess how various land-use conversion scenarios (e.g. forest to agriculture or conversely) impact triggers of convective rainfall and water drainage from the routing zone. The ABL dynamics model should be sufficiently realistic to provide reasonable estimates of entrainment fluxes, which brings water vapor and heat from synoptic scale conditions to ABL state variables and consequently to boundary layer growth and lifting condensation levels (WPB2). The soil-plant model should be able to simulate root water uptake mechanistically and capture vegetation responses to water stress, including soil moisture modulations of the Bowen ratio in a manner consistent with what is known about the soil-plant hydraulic system (WPB3 and WPB4).

The specific Scientific highlights and research achievements are described later.

WPC: Implications to Water Resources Management

Objectives: Computing a correct water balance in Alpine environments is difficult because the storage occurs typically under a both liquid and solid (snow and ice) form. The different physics and thermodynamics of such water bodies clearly speak for a need of appropriate models, e.g., either physically based or lumped depending on the time scale targeted by the investigation (WPC1). Because runoff in this case is a function of melting, appropriate either energy balance or temperature indexes approaches must be used to compute the ablation. Eventually this is also function of how snow redistributes on glaciers because of the wind action. River runoff becomes thus availables and fluctuates typically over several time scales, e.g. synoptic due to night and day temperature differences, week time scale depending on local weather phenomena, and annual according to seasonality. Therefore, redistribution among water uses and the environment must be done again accounting for the interactions occurring at the different scales and for a number of scenarios about climate and land use changes. Particularly, stochastic optimization models are of importance if water allocation has to be treated in probabilistic terms.

Description of work: Either distributed or lumped catchment scale models will be used to investigate the effects of climatic and landscape changes. The modelling approach is based on using RCMs climate scenarios (regional scale) as inputs. The catchment response models will provide the water availability scenarios at the basin and local scale. In particular, the sensitivy of the catchment scale model to the spatial variability of highly local processes (point scale) will be studied to evaluate their relevance on the water resources management (WPC1). The long term allocation of the available water resource at the basin scale will be achieved by means of nonlinear optimisation models appositely developed and investigated to optimise the redistribution of water among users on an economical basis. The novelty in this type of approach is the introduction of non-conventional water users, i.e. the environment, which may concur with other conventional users (e.g., hydropower, irrigation, etc.) in the competition for the use of the resource. Fundamental in this respect is the definition of appropriate marginal benefit functions able to quantify the equivalent economical return made by the environment. A number of marginal benefit functions for environmental water uses will be explored and tested. Particularly, competitions between conventional and nonconventional users will be addressed either in a deterministic (e.g., known inputs, WPC2) or in a stochastic (statistically known inputs, WPC4) fashion in order to mathematically study the water redistribution among the users at the optimum and analyse the corresponding sensitivity to changes in the inputs. The achieved knowledge about the water cycle will be applied to projected scenarios of climatic forcing and then used to assess the impacts on water demand, estimating the available water resource and investing new techniques for the optimization of its allocation and management (WPC3).

The specific Scientific highlights and research achievements are described later.

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