The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Jan Seibert - One of the best experts on this subject based on the ideXlab platform.

Patrick Willems - One of the best experts on this subject based on the ideXlab platform.

  • uncertainty assessment for Climate Change Impact on intense precipitation how many model runs do we need
    International Journal of Climatology, 2017
    Co-Authors: Parisa Hosseinzadehtalaei, Patrick Willems, Hossein Tabari
    Abstract:

    Precipitation projections are typically obtained from general circulation model (GCM) outputs under different future scenarios, then downscaled for hydrological applications to a watershed or site-specific scale. However, uncertainties in projections are known to be present and need to be quantified. Although GCMs are commonly considered the major contributor of uncertainty for hydrological Impact assessment of Climate Change, other uncertainty sources must be taken into account for a thorough understanding of the hydrological Impact. This study investigates uncertainties related to GCMs, GCM initial conditions and representative concentration pathways (RCPs) and their sensitivity to the selection of GCM runs in order to quantify the Impact of Climate Change on extreme precipitation and intensity/duration/frequency statistics. The results from a large ensemble of 140 CMIP5 GCM runs including 15 GCMs, 3–10 GCM initial conditions and 4 RCPs are analysed. Albeit the choice of GCM is the major contributor (up to 65% for some cases) to intense precipitation Change uncertainty for all return periods (1 year, 10 years) and aggregation levels (1-, 5-, 10-, 15- and 30-day), uncertainties related to the GCM initial conditions and RCPs of up to 38 and 23%, respectively, are found in some cases. The sensitivity analysis reveals that the GCM, RCP and GCM initial condition uncertainties are greatly influenced by the set of Climate model runs considered, especially for more extreme precipitation at finer time scales.

  • Climate Change Impact on river flows and catchment hydrology a comparison of two spatially distributed models
    Hydrological Processes, 2013
    Co-Authors: Thomas Vansteenkiste, Mohsen Tavakoli, Victor Ntegeka, Patrick Willems, Florimond De Smedt, Okke Batelaan
    Abstract:

    Hydrological models have been widely used to assess Changes in stream discharges by Climate Change; however, concern might arise on the accurateness of the model predictions under the Changed conditions particularly during low flow periods. In this study, two spatially distributed hydrological models MIKE SHE and WetSpa, each representing a different model complexity in terms of process description, data needs, parameter space, degree of calibration, were compared in their estimation of the Climate Change Impact on the flow regimes in a medium-sized catchment in Belgium. The fully integrated, physically based MIKE SHE model, comprising a three-dimensional groundwater flow and river model, was applied to better understand the groundwater flow and groundwater–river interactions under Changed Climate conditions. Both models were able to capture the flow dynamics very well with high efficiencies and simulated the flow extremes very accurately. The groundwater heads in MIKE SHE and their seasonal variation had a high model performance. The two models simulated similar Changes to future flows because of climatic Changes. Peak flows were expected to increase or decrease depending, taking the large uncertainty in future Climate trends into account. The model structural uncertainties on these high flow predictions were rather limited. Low flows were expected to reduce because of drier conditions by future Climate Change, indicating elevated low flow risks for Belgium. However, the projected low flow Changes differed significantly over the models and even exceeded the uncertainty by the expected Climate trends. Smaller Impact was predicted by considering the groundwater physics and river interaction in the MIKE SHE model. These Changes to the surface water regimes were verified by the Changes in groundwater heads. Future groundwater conditions also point towards drier conditions with a small decrease in heads for future summer and autumn periods. Projected variations in winter heads depend on the Climate scenario. Copyright © 2012 John Wiley & Sons, Ltd.

  • Climate Change Impact assessment on urban rainfall extremes and urban drainage methods and shortcomings
    Atmospheric Research, 2012
    Co-Authors: Patrick Willems, Karsten Arnbjergnielsen, Jonas Olsson, Vanthanhvan Nguyen
    Abstract:

    Abstract Cities are becoming increasingly vulnerable to flooding because of rapid urbanization, installation of complex infrastructure, and Changes in the precipitation patterns caused by anthropogenic Climate Change. The present paper provides a critical review of the current state-of-the-art methods for assessing the Impacts of Climate Change on precipitation at the urban catchment scale. Downscaling of results from global circulation models or regional Climate models to urban catchment scales are needed because these models are not able to describe accurately the rainfall process at suitable high temporal and spatial resolution for urban drainage studies. The downscaled rainfall results are however highly uncertain, depending on the models and downscaling methods considered. This uncertainty becomes more challenging for rainfall extremes since the properties of these extremes do not automatically reflect those of average precipitation. In this paper, following an overview of some recent advances in the development of innovative methods for assessing the Impacts of Climate Change on urban rainfall extremes as well as on urban hydrology and hydraulics, several existing difficulties and remaining challenges in dealing with this assessment are discussed and further research needs are described.

Christel Prudhomme - One of the best experts on this subject based on the ideXlab platform.

  • derivation of rcm driven potential evapotranspiration for hydrological Climate Change Impact analysis in great britain a comparison of methods and associated uncertainty in future projections
    Hydrology and Earth System Sciences, 2013
    Co-Authors: Christel Prudhomme, Jennifer Williamson
    Abstract:

    Potential evapotranspiration (PET) is the water that would be lost by plants through evaporation and transpi- ration if water was not limited in the soil, and it is commonly used in conceptual hydrological modelling in the calcula- tion of runoff production and hence river discharge. Future Changes of PET are likely to be as important as Changes in precipitation patterns in determining Changes in river flows. However PET is not calculated routinely by Climate mod- els so it must be derived independently when the Impact of Climate Change on river flow is to be assessed. This pa- per compares PET estimates from 12 equations of differ- ent complexity, driven by the Hadley Centre's HadRM3-Q0 model outputs representative of 1961-1990, with MORECS PET, a product used as reference PET in Great Britain. The results show that the FAO56 version of the Penman- Monteith equations reproduces best the spatial and sea- sonal variability of MORECS PET across GB when driven by HadRM3-Q0 estimates of relative humidity, total cloud, wind speed and linearly bias-corrected mean surface tem- perature. This suggests that potential biases in HadRM3-Q0 Climate do not result in significant biases when the physi- cally based FAO56 equations are used. Percentage Changes in PET between the 1961-1990 and 2041-2070 time slices were also calculated for each of the 12 PET equations from HadRM3-Q0. Results show a large variation in the magni- tude (and sometimes direction) of Changes estimated from different PET equations, with Turc, Jensen-Haise and cali- brated Blaney-Criddle methods systematically projecting the largest increases across GB for all months and Priestley- Taylor, Makkink, and Thornthwaite showing the smallest Changes. We recommend the use of the FAO56 equation as, when driven by HadRM3-Q0 Climate data, this best re- produces the reference MORECS PET across Great Britain for the reference period of 1961-1990. Further, the future Changes of PET estimated by FAO56 are within the range of uncertainty defined by the ensemble of 12 PET equations. The Changes show a clear northwest-southeast gradient of PET increase with largest (smallest) Changes in the north- west in January (July and October) respectively. However, the range in magnitude of PET Changes due to the choice of PET method shown in this study for Great Britain sug- gests that PET uncertainty is a challenge facing the assess- ment of Climate Change Impact on hydrology mostly ignored up to now.

  • scenario neutral approach to Climate Change Impact studies application to flood risk
    Journal of Hydrology, 2010
    Co-Authors: Christel Prudhomme, Robert L Wilby, S M Crooks, N S Reynard
    Abstract:

    This paper presents a novel framework for undertaking Climate Change Impact studies, which can be used for testing the robustness of precautionary Climate Change allowances used in engineering design. It is illustrated with respect to fluvial flood risk in the UK. The methodology departs from conventional scenario-led Impact studies because it is based on sensitivity analyses of catchment responses to a plausible range of Climate Changes (rather than the time-varying outcome of individual scenarios), making it scenario-neutral. The method involves separating the Climate Change projections (the hazard) from the catchment responsiveness (the vulnerability) expressed as Changes in peak flows. By combining current understanding of likelihood of the Climate Change hazard with knowledge of the sensitivity of a given catchment, it is possible to evaluate the fraction of Climate model projections that would not be accommodated by specified safety margins. This enables rapid appraisal of existing or new precautionary allowances for a set of Climate Change projections, but also for any new set of Climate Change projections for example arising from a new generation of Climate models as soon as they are available, or when focusing on a different planning time horizon, without the need for undertaking a new Climate Change Impact analysis with the new scenarios. The approach is demonstrated via an assessment of the UK Government’s 20% allowance for Climate Change applied in two contrasting catchments. In these exemplars, the allowance defends against the majority of sampled Climate projections for the 2080s from the IPCC-AR4 GCM and UKCP09 RCM runs but it is still possible to identify a sub-set of regional scenarios that would exceed the 20% threshold.

  • assessing uncertainties in Climate Change Impact analyses on the river flow regimes in the uk part 1 baseline Climate
    Climatic Change, 2009
    Co-Authors: Christel Prudhomme, H N Davies
    Abstract:

    The first part of this paper demonstrated the existence of bias in GCM-derived precipitation series, downscaled using either a statistical technique (here the Statistical Downscaling Model) or dynamical method (here high resolution Regional Climate Model HadRM3) propagating to river flow estimated by a lumped hydrological model. This paper uses the same models and methods for a future time horizon (2080s) and analyses how significant these projected Changes are compared to baseline natural variability in four British catchments. The UKCIP02 scenarios, which are widely used in the UK for Climate Change Impact, are also considered. Results show that GCMs are the largest source of uncertainty in future flows. Uncertainties from downscaling techniques and emission scenarios are of similar magnitude, and generally smaller than GCM uncertainty. For catchments where hydrological modelling uncertainty is smaller than GCM variability for baseline flow, this uncertainty can be ignored for future projections, but might be significant otherwise. Predicted Changes are not always significant compared to baseline variability, less than 50% of projections suggesting a significant Change in monthly flow. Insignificant Changes could occur due to Climate variability alone and thus cannot be attributed to Climate Change, but are often ignored in Climate Change studies and could lead to misleading conclusions. Existing systematic bias in reproducing current Climate does Impact future projections and must, therefore, be considered when interpreting results. Changes in river flow variability, important for water management planning, can be easily assessed from simple resampling techniques applied to both baseline and future time horizons. Assessing future Climate and its potential implication for river flows is a key challenge facing water resource planners. This two-part paper demonstrates that uncertainty due to hydrological and Climate modelling must and can be accounted for to provide sound, scientifically-based advice to decision makers.

Claudia Teutschbein - One of the best experts on this subject based on the ideXlab platform.

A. Jordan - One of the best experts on this subject based on the ideXlab platform.

  • Socio-economic futures in Climate Change Impact assessment: using scenarios as ‘learning machines’
    Global Environmental Change, 2002
    Co-Authors: Frans Berkhout, Julia Hertin, A. Jordan
    Abstract:

    Climate Impact assessment needs to take account of two interrelated processes: socio-economic Change and Climate Change. To date, future Change in socio-economic systems has not been sufficiently integrated with an analysis of Climate Change Impacts. Participative and synthetic scenario approaches offer a means for dealing with critical issues of indeterminacy, innovation, reflexivity and framing in analysing Change in socio-economic systems, paving the way for a coherent way of handling of socio-economic futures in Impact assessment. We argue that scenarios represent heuristic tools that encourage social learning in Climate Impact assessment. The advantages and disadvantages of a scenario-based approach are explored using examples from regional Climate Impact assessment in the UK.