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Albrecht Weerts

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6 records found

Redressing the balance

Quantifying net intercatchment groundwater flows

Journal article - L.J.E. Bouaziz, L.J.E. Bouaziz, Albrecht Weerts, Albrecht Weerts, Jaap Schellekens, Eric Sprokkereef, Jasper Stam, Hubert Savenije, M. Hrachowitz

Intercatchment groundwater flows (IGFs), defined as groundwater flows across topographic divides, can occur as regional groundwater flows that bypass headwater streams and only drain into the channel further downstream or directly to the sea. However, groundwater flows can also be diverted to adjacent river basins due to geological features (e.g., faults, dipping beds and highly permeable conduits). Even though intercatchment groundwater flows can be a significant part of the water balance, they are often not considered in hydrological studies. Yet, assuming this process to be negligible may introduce misrepresentation of the natural system in hydrological models, for example in regions with complex geological features. The presence of limestone formations in France and Belgium potentially further exacerbates the importance of intercatchment groundwater flows, and thus brings into question the validity of neglecting intercatchment groundwater flows in the Meuse basin. To isolate and quantify the potential relevance of net intercatchment groundwater flows in this study, we propose a three-step approach that relies on the comparison and analysis of (1) observed water balance data within the Budyko framework, (2) results from a suite of different conceptual hydrological models and (3) remote-sensing-based estimates of actual evaporation. The data of 58 catchments in the Meuse basin provide evidence of the likely presence of significant net intercatchment groundwater flows occurring mainly in small headwater catchments underlain by fractured aquifers. The data suggest that the relative importance of net intercatchment groundwater flows is reduced at the scale of the Meuse basin, as regional groundwater flows are mostly expected to be self-contained in large basins. The analysis further suggests that net intercatchment groundwater flow processes vary over the year and that at the scale of the headwaters, net intercatchment groundwater flows can make up a relatively large proportion of the water balance (on average 10 % of mean annual precipitation) and should be accounted for to prevent overestimating actual evaporation rates.@en

Constraining a semi-distributed, conceptual hydrological model on evaporation

A case study for the Kulpawn River Basin, Ghana

Abstract - R.C. Nijzink, Hubert Savenije, M. Hrachowitz, Albrecht Weerts

Hydrological models are typically calibrated on stream flow observations. However, such data are frequently not available. In addition, in many parts of the world not stream flow, but rather evaporation and transpiration are the largest fluxes from hydrological systems. Nevertheless, models trained to evaporation data are rare and typically rely on evaporation estimates that were themselves also derived from models, thereby considerably reducing the robustness of such approaches. In this study, we test the power of alternative approaches to constrain semi-distributed, conceptual models with information on evaporation in the absence of stream flow data. By gradually increasing the constraining information, the analysis is designed in a stepwise way. Both, the models and the relevance of the added information are evaluated for each step. As a first step, a large set of random parameter sets from uniform prior distributions is generated. Subsequently, parameter sets that cannot produce model outputs that satisfy the added constraints are discarded. The information content of these constraints will be gradually increased by making use of the Budyko framework: (1) the model has to reproduce the long-term average actual evaporation of the system, as indicated by the position in the Budyko framework, (2) the model, similarly, has to reproduce the long-term average seasonal variations of actual evaporation, (3) the model has to reproduce the temporal variations of evaporation, e.g. differences between 5-year mean evaporation of different periods, as indicated by different positions in the Budyko framework. As a last step, the model’s temporal dynamics in the root zone moisture content are constrained by comparing it to time series of the NDII (Normalized Difference Infrared Index), which has recently been shown to be a close proxy for plant available water in the root zone and, thus, for transpiration rates ( Sriwongsitanon et al., 2015). The value of the information content of these different constraints to reduce model uncertainty for reproducing the hydrological response of catchments is assessed by comparing the model results of the individual stages to actually observed discharge data in the study catchment. @en

A hydrography upscaling method for scale-invariant parametrization of distributed hydrological models

Journal article - Dirk Eilander, Dirk Eilander, Willem van Verseveld, Dai Yamazaki, Albrecht Weerts, Albrecht Weerts, H.C. Winsemius, H.C. Winsemius, Philip J. Ward

Distributed hydrological models rely on hydrography data such as flow direction, river length, slope and width. For large-scale applications, many of these models still rely on a few flow direction datasets, which are often manually derived. We propose the Iterative Hydrography U ...

Global re-analysis datasets to improve hydrological assessment and snow water equivalent estimation in a sub-Arctic watershed

Journal article - David R. Casson, David R. Casson, Micha Werner, Micha Werner, Albrecht Weerts, Albrecht Weerts, D.P. Solomatine, D.P. Solomatine

Hydrological modelling in the Canadian sub-Arctic is hindered by sparse meteorological and snowpack data. The snow water equivalent (SWE) of the winter snowpack is a key predictor and driver of spring flow, but the use of SWE data in hydrological applications is limited due to high uncertainty. Global re-analysis datasets that provide gridded meteorological and SWE data may be well suited to improve hydrological assessment and snowpack simulation. To investigate representation of hydrological processes and SWE for application in hydropower operations, global re-analysis datasets covering 1979-2014 from the European Union FP7 eartH2Observe project are applied to global and local conceptual hydrological models. The recently developed Multi-Source Weighted-Ensemble Precipitation (MSWEP) and the WATCH Forcing Data applied to ERA-Interim data (WFDEI) are used to simulate snowpack accumulation, spring snowmelt volume and annual streamflow. The GlobSnow-2 SWE product funded by the European Space Agency with daily coverage from 1979 to 2014 is evaluated against in situ SWE measurement over the local watershed. Results demonstrate the successful application of global datasets for streamflow prediction, snowpack accumulation and snowmelt timing in a snowmelt-driven sub-Arctic watershed. The study was unable to demonstrate statistically significant correlations (p/0.05) among the measured snowpack, global hydrological model and GlobSnow-2 SWE compared to snowmelt runoff volume or peak discharge. The GlobSnow-2 product is found to under-predict late-season snowpacks over the study area and shows a premature decline of SWE prior to the true onset of the snowmelt. Of the datasets tested, the MSWEP precipitation results in annual SWE estimates that are better predictors of snowmelt volume and peak discharge than the WFDEI or GlobSnow-2. This study demonstrates the operational and scientific utility of the global re-analysis datasets in the sub-Arctic, although knowledge gaps remain in global satellite-based datasets for snowpack representation, for example the relationship between passive-microwave-measured SWE to snowmelt runoff volume.@en

Water storage capacities in the unsaturated root-zone: a key to estimate root-zone soil moisture from remotely-sensed near-surface soil moisture

Poster - L.J.E. Bouaziz, L.J.E. Bouaziz, S.C. Steele-Dunne, Jaap Schellekens, Albrecht Weerts, Albrecht Weerts, Jasper Stam, Eric Sprokkereef, H.C. Winsemius, H.C. Winsemius, Hubert Savenije, M. Hrachowitz

Estimates of water volumes stored in the root-zone of vegetation are a key element controlling the hydrological response of a catchment. The moisture content of the root-zone regulates the partitioning between drainage and water fluxes and reliable estimates are, therefore, criti ...

Water storage capacities in the unsaturated root-zone: a key to estimate root-zone soil moisture from remotely-sensed near-surface soil moisture

Contributed

1 records found

Bias Correction of Climate Simulations to assess Climate Change Impacts on Low Flows in the Rhine River

Master thesis - A.A.E.A. Ahmed Adil el Tayeb Abdelnour, R. Uijlenhoet, A. Blom, Frederiek Sperna Weiland, Albrecht Weerts

Regional climate model (RCMs) simulations are used in hydrological (climate-change) impact assessment studies. However, RCMs exhibit noticeable deviation from observation, and can show large variation in ensemble projections (biases). The objective of this study is twofold, first to assess the robustness of two high-skill bias-correction methods; empirical quantile mapping (QM), and scaled distribution mapping (SDM) in improving the hydrological modelling of the Rhine River. The second is to assess the potential impacts of climate change on low flows at Lobith based on RCP8.5 scenario. The two correction methods are applied to correct the systematic bias from five climate datasets from the Coordinated Downscaling Experiment in Europe (EURO-CORDEX) covering the Rhine domain, using high resolution gridded datasets (1 km2) spanning from 1979 to 2019. The bias-corrected simulations from the hydrological model provided more accurate discharge estimates than the wet biased simulations, with an average error of less than 100 m3/s at Lobith. The correction methods are also capable of correcting unprecedented temperature and precipitation values, making them useful in climate assessment studies in the Rhine river. However, it appears that the accuracy of the bias correction depends on the parent GCM, performance of the raw RCM and the skill of the hydrological model in estimating discharges at the point of interest. In addition to that, the drizzling effect could not be reduced using these methods. Noticeable climate change impacts at Lobith are found using the bias-corrected projections. These projections suggest that low flows are going to be more frequent and longer in the coming 38 years. Unprecedented discharges (< 700 m3/s) are projected to occur at least 50 times between 2020 - 2060. This is coupled by a decrease in the long-term mean annual flow by 100 m3/s and a slight shift in the seasonality of low flows (2 weeks shift). The general hydrograph at Lobith is set to change due to climate change for the period (2020 – 2060), with relatively higher discharges from early June to end of August followed by relatively lower discharges in the last four months of the year. Water levels are projected to decline in average by 20 cm (early June to the end of August) and increase in average by 30 cm (end of August till to end of December). The study recommends the need of combining bias correction, the feedbacks in the climate system (land use changes) and climate adaptation strategies to study these effects further.