Lars Gottschalk

Validation of a distributed hydrological model against spatial observations

In connection with climate change studies a new hydrologic field has evolved - regional hydrological modelling or hydrologic macro modelling, which implies repeated application of a model everywhere within a region using a global set of parameters. The application of a physically based distributed hydrological model ECOMAG to river basins within the NOPEX southern region with this purpose in mind is presented. The model considers the main processes of the land surface hydrological cycle: infiltration, evapotranspiration, heat and water regime of the soil, snowmelt, formation of surface, subsurface and river runoff and groundwater. The spatial integration of small and meso-scale non-homogeneity of the land surface is a central issue both for the definition of fundamental units of the model structure and for determination of representative values for model validation. ECOMAG is based on a uniform hydrological (or landscape) unit representation of the river basin, which reflects topography, soil, vegetation and land use. As a first step the model was calibrated using standard meteorological and hydrological data for 7 years from regular observation networks for three basins. An additional adjustment of the soil parameters was performed using soil moisture and groundwater level data from five small experimental basins. This step was followed by validation of the model against runoff for 14 years from six other drainage basins, and synoptic runoff and evapotranspiration measurements performed during two concentrated field efforts (CFEs) of the NOPEX project in 1994 and 1995. The results are promising and indicate directions for further research.

Energy, Water and Carbon Exchange in a Boreal Forest Landscape - NOPEX Experiences

The role of the land surface in controlling climate is still underestimated and access to information from the boreal-forest zone is instrumental to improve this situation. This motivated the organ ...

Assessing uncertainties in a conceptual water balance model using Bayesian methodology

Abstract Abstract The aim of this study was to estimate the uncertainties in the streamflow simulated by a rainfall–runoff model. Two sources of uncertainties in hydrological modelling were considered: the uncertainties in model parameters and those in model structure. The uncertainties were calculated by Bayesian statistics, and the Metropolis-Hastings algorithm was used to simulate the posterior parameter distribution. The parameter uncertainty calculated by the Metropolis-Hastings algorithm was compared to maximum likelihood estimates which assume that both the parameters and model residuals are normally distributed. The study was performed using the model WASMOD on 25 basins in central Sweden. Confidence intervals in the simulated discharge due to the parameter uncertainty and the total uncertainty were calculated. The results indicate that (a) the Metropolis-Hastings algorithm and the maximum likelihood method give almost identical estimates concerning the parameter uncertainty, and (b) the uncertainties in the simulated streamflow due to the parameter uncertainty are less important than uncertainties originating from other sources for this simple model with fewer parameters.

Distribution of peak flow derived from a distribution of rainfall volume and runoff coefficient, and a unit hydrograph

An expression for the distribution function of peak runoff is derived, combining results of frequency analysis of rainfall volumes with the traditional concepts of runoff coefficients and the unit hydrograph. Rainfall volume, scaled with respect to its duration, is assumed to follow a gamma distribution, whereas for the runoff coefficient a beta distribution is applied. Hydrograph characteristics are considered to be deterministic variables. A closed form analytical expression is achieved when some minor simplifications are made. The approach is tested and validated against data from 17 small Swiss drainage basins, for which unit hydrographs have been determined. The runoff response of these basins is very different in relation to both the distribution of the runoff coefficient and hydrograph characteristics, which is also reflected in the behaviour of the distribution of peak flow. Four main response classes of basins are identified that can be related to the physiography of the basins.

Towards integrated catchment management: increasing the dialogue between scientists, policy‐makers and stakeholders

The aim of the Hydrology for the Environment, Life and Policy (HELP) project is to strengthen the role and inputs of the scientific community in the integrated catchment management process. Water resources management in the 21st century requires a radical reorientation and an effective dialogue between decision‐makers, stakeholders and the scientific water community. This paper offers a skeleton worldview as a starting point for that dialogue by bringing together key issues as identified by water resource experts from different disciplines. Experiences from all over the world demonstrate the need for multistakeholder advocacy and the importance of compromise‐building mechanisms. Water law defines the rules of the game and provides a necessary framework for policy and its execution. However, there must be adequate social acceptance and active compliance, otherwise the formal rules and administrative regulation will not be perceived as legitimate and ultimately could prove ineffective. The challenge now is to create management systems where the formal decision‐makers interact with relevant members of the scientific community, users and other stakeholders for a coordinated approach that successfully orchestrates water uses towards internal compatibility. Integrated water resources management is essential for securing a proper overview of all the activities that depend on the same resource—the precipitation over the basin—and which are internally linked by the mobility of water from the water divide to the river mouth.

Hydrological regionalization of Sweden

ABSTRACT Hydrological regionalization is an important tool for the analysis of the spatial pattern of variations in hydrological phenomena. Regionalization means areal classification, i.e. the ability to attach to some location a label or number which is hydrologically meaningful. With the use of statistical methods, hydrological regions are analogous to areal classes. In this present study, pairwise grouping as well as principal components are applied to Swedish river runoff data in order to analyse the patterns of variation and to delimit regions where hydrological behaviour may be regarded as uniform. Pairwise grouping is the appropriate method to use on a national scale with heterogeneous hydrological regimes. Principal components (empirical orthogonal functions) demand homogeneity but within such regions describe very well the trends and variations.

NOPEX—a northern hemisphere climate processes land surface experiment

The interface between land surfaces and the atmosphere is a key area in climate research, where lack of basic knowledge prevents us from reducing the considerable uncertainties about predicted chan ...

Correlation and covariance of runoff

The application of objective methods for interpolation of stochastic fields is based on the assumption of homogeneity with respect to the correlation function, i.e. only the relative distance between two points is of importance. This is not the case for runoff data which is demonstrated in this paper. Taking into consideration the structure of the river network and the related drainage basin supporting areas theoretical expressions are derived for the correlation function for flow along a river from its outlet and upstream. The results are exact for a rectangular drainage basin. For more complex basin geometry a grid approximation is suggested. The found relations are demonstrated on a real world example with a good agreement between the theoretically calculated correlation functions and empirical data.

Mapping average annual runoff: a hierarchical approach applying a stochastic interpolation scheme

Abstract A novel approach for mapping river runoff is presented. It is based on a disaggregation of the mean annual streamflow measured at the outlet of a basin to estimate water depths on elements of an exact partition of this basin. The developed technique is based on geostatistical interpolation procedures to which a global constraint of water balance has been added. The methodology is illustrated by a case study from a tributary to the Rhône River, France. The results were compared to an established method-the nested approach, and a cross-validation was performed for each mapping technique. The disaggregation approach appears to give the most consistent results. Finally, two gridded maps were derived by applying the disaggregation twice to assess water depth on an increasingly finer grid mesh. The global constraint of water balance was applied to each element of the coarser mesh to give estimates for the finer one.

Interpolation of runoff applying objective methods

The paper treats the problem of interpolating annual runoff from regular streamflow measurements in a regional scale applying objective methods. These methods are adapted to point processes like temperature and precipitation. Modifications are needed to account for the fact that streamflow is an integrated process following the hierarchical structure of river systems. The most straightforward method is therefore to relate the interpolation to the existing river network. For theoretical reasons it is preferable to interpolate the lateral inflow rather than the flow in the river itself. Procedures for the interpolation with the different approaches are developed and discussed. Special attention is put on the question how the equation of continuity can be satisfied. The Laagen drainage basin in southern Norway is used as a test area. The data consist of annual observations of streamflow and digital map information on river networks and drainage basin boundaries.