HYDRO

HYDRO aims at an improved understanding of the mechanisms and impact of global change and in particular climate change on the water cycle, providing the driving data for an assessment (through the other SPs) of the impact on water quality and availability, as well as soil functions. This affords an ideal opportunity to bring together innovative methods in generating climate and rainfall scenarios to drive an integrated surface-subsurface model. This synergy has not previously been realised and will provide much needed understanding of the role of precipitation variability on the key biogeochemical processes in soils and sediments (FLUXES, BIOGEOCHEM), how these influence water quality and quantity (COMPUTE) and how these relationships may change under perturbations of climate and land-use (TREND).

Downscaling of global climate change models (WP H1) is required 1) as input for the numerical system models which are validated at the catchment scale (WP H2) and 2) to assess the impact of climate change in the future (TREND). Water budgeting (WP H2) at the catchment scale is needed for the quantification of solute and pollutant fluxes in the water cycle (FLUX, BIOGEOCHEM) and for the basis of numerical modelling (COMPUTE). Rainfall and potential evapotranspiration time series will be combined with integrated surface-subsurface numerical models in COMPUTE to examine the potential impacts of a number of climate and land-use perturbations on soil functioning and water quality (TREND, FLUXES) and how future monitoring strategies that should be adopted (MONITOR).

WP H1 The problems of scale and resolution in Global Climate Model (GCM) outputs are well known [1] and a number of methods of downscaling have been developed, including modification of observed rainfall, dynamical downscaling, and statistical downscaling linked to rainfall modelling 2. However, the balance of state of the art in downscaling has perhaps recently moved from statistical downscaling to dynamical downscaling using Regional Climate Models (RCMs). The main, perceived drawback with the use of RCMs is the relatively short time series available. However, this shortcoming can be addressed by combination with stochastic rainfall modelling. Extension of the RCM time-series may be achieved with a high degree of reliability using methodology such as the Neyman-Scott Rectangular Pulses model [2]^;

[3], so that very long (e.g. 10,000 year) daily rainfall series may be generated for statistical analysis of impacts in a modelling framework [4]. In WP H1, state-of-the-art climate projections from both the Hadley Centre and Max Planck Institute models will be assessed and output will be downscaled and corrected to produce specialist rainfall variables including extremes.

The role of rainfall variability on soil functioning and water quality is the key issue for river basin management under current and future climates. Three aspects are of particular importance: 1) inter-annual variability; 2) rainfall regime or seasonality; and 3) daily and sub-daily extremes. WP H1 aims to further develop existing rainfall modelling techniques to better represent convective and frontal rainfall processes [5], low-frequency features such as variations caused by the North Atlantic Oscillation [6], inter-annual and seasonal variability and daily/sub-daily extremes ^{3;

[7]}. The rainfall and potential evapotranspiration time series resulting from WP1 will be combined with numerical models in COMPUTE to examine the impacts of a number of climate and land-use perturbations on soil functioning (BIOGEOCHEM) and water quality (TREND, FLUXES).

WP H2 aims to establish detailed water budgets for the selected catchments. Works to be carried out in order to assess the detailed water budget of the catchment are threefold: characterization of the aquifer system (geology, natural and artificial boundaries), and quantitative assessment of the water input and outflow from the system groundwater flow and velocity, permeability, storage capacity, etc). Natural and artificial inputs and outputs will be quantified and documented WP H2, to serve as basic elements for the studies conducted in BASIN, FLUXES, and the deterministic modelling in COMPUTE.

To provide suitable rainfall and potential evapotranspiration scenarios for present and future climates to support the development and application of models of soil functioning at a range of space and time scales, the scenarios will:

Description of work

Characterization of the systems for a valid conceptualisation of the water fluxes through the system. Determination of the geological structure of the system, its natural or artificial boundaries, and the characteristics of the unsaturated layers (hydraulic properties of a wide range of samples requiring long equilibration times for establishing relations between water content and suction for instance; dedicated task of partner UHAGx for the Brévilles site) and aquifer layers (permeability, storage coefficient) that determine the direction of the groundwater flow, its velocity and its storage capacity. Collecting these data require field work such as detailed geological mapping, borehole drillings, geophysical investigations or remote sensing that lead to the identification of the structure of the aquifer system. Piezometric campaigns involving precise (centimetric) levelling will be conducted to assess flow direction and thus determine recharge area and zones of outflow. Aquifer parameters will be determined by pumping tests, slug test or tracer experiments (dedicated task of partner HGULg for the Brévilles site). The partners from UT and UPD focus on an alpine catchment and an alluvial plane catchment, respectively. Emphasis is posed on runoff generation, since surface-subsurface water interaction is addressed by the other partners in this WP. The former catchment is located in the Adige river basin while the latter is one of the catchments feeding the Venice lagoon. Characterization, which is oriented to runoff production, will be performed with available data and no additional fieldworks are programmed.
Quantitative assessment of the water input to the system: Water input to the system may be natural or artificial. Besides precipitations (rain and snow), natural inputs may also involve leakage from rivers, infiltration from pond or lakes, run-off. Artificial input to the aquifer system may imply return flow from irrigation, leakage from network, injection through wells. All these inputs will be detailed and quantified, including whenever necessary and possible, data mining.
Quantitative assessment of the water outflows from the system: full inventory of natural outputs such as springs - that need to be precisely located, gauged and monitored -, rivers - to which groundwater contribution may be assessed through differential gauging and geochemical studies -, lakes, connection between aquifers, evaporation. Determination of artificial outputs, i.e. withdrawals from wells, either measured or estimated through consideration of i) agricultural use knowing the type of crops grown and their periods of growth, ii) the type of pump itself and its pumping depth can give an estimate of the maximal discharge rate, and thus the extracted volume provided that the hours of functioning are known. UT and UPD will collect existing data on water discharge at the selected control-sections together with all the relevant data (rainfall, snow, temperature ectc.).

[1] Kilsby C.G., Cowpertwait P.S.P., O'Connell P.E. and Jones P.D. (1998): Predicting rainfall statistics in England and Wales using atmospheric circulation variables.- Int. J. Climatol., 18, 523-539.

[2] Cowpertwait, P.S.P., Kilsby, C.G. and O'Connell, P.E. (2002): A space-time Neyman-Scott model of rainfall: Empirical analysis of extremes.- Water Resour. Res., 38: 1131.

[3] Fowler, H.J., Kilsby, C.G., O'Connell, P.E. (2000): A stochastic rainfall model for the assessment of regional water resource systems under changed climatic conditions.- Hydrol. Earth Sys. Sci., 4: 261-280.

[4] Fowler, H.J., Kilsby, C.G., and O’Connell, P.E. (2003): Modeling the impacts of climatic change and variability on the reliability, resilience and vulnerability of a water resource system. Water Resources Research, 39(8), 1222..

[5] Cowpertwait, P.S.P. and O’Connell, P.E. (1997): A Regionalised Neyman-Scott Model of Rainfall with Convective and Stratiform Cells.- Hydrol. Earth Sys. Sci., 1: 71-80.

[6] Fowler H.J., and Kilsby, C.G. (2002): Precipitation and the North Atlantic Oscillation: A study of climatic variability in northern England.- Int. J. Climatol., 22: 843-866.

[7] Fowler, H.J. and Kilsby, C.G. (2003): A regional frequency analysis of United Kingdom extreme rainfall from 1961 to 2000. International Journal of Climatology, 23(11), 1313-1334.