Identification of changes in hydrological drought characteristics from a multi-GCM driven ensemble constrained by observed discharge

Peer reviewedPublisher PD

Extreme regenval en overstromingen in het stroomgebied van de Hupselse Beek

Op 26 en 27 augustus 2010 werd het stroomgebied van de Hupselse Beek getroffen door extreme neerslag: 160 mm in 24 uur (herhalingstijd: meer dan 1.000 jaar). Hierdoor steeg de afvoer in 22 uur van vier naar 5.000 liter per seconde. Door deze stortvloed in detail te onderzoeken, is meer inzicht ontstaan in de werking van stroomgebieden tijdens extreme situaties. Deze informatie kan gebruikt worden om modellen en hoogwatervoorspellingen te verbetere

Anatomy of extraordinary rainfall and flash flood in a Dutch lowland catchment

On 26 August 2010 the eastern part of The Netherlands and the bordering part of Germany were struck by a series of rainfall events lasting for more than a day. Over an area of 740 km2 more than 120 mm of rainfall were observed in 24 h. This extreme event resulted in local flooding of city centres, highways and agricultural fields, and considerable financial loss. In this paper we report on the unprecedented flash flood triggered by this exceptionally heavy rainfall event in the 6.5 km2 Hupsel Brook catchment, which has been the experimental watershed employed by Wageningen University since the 1960s. This study aims to improve our understanding of the dynamics of such lowland flash floods. We present a detailed hydrometeorological analysis of this extreme event, focusing on its synoptic meteorological characteristics, its space-time rainfall dynamics as observed with rain gauges, weather radar and a microwave link, as well as the measured soil moisture, groundwater and discharge response of the catchment. At the Hupsel Brook catchment 160 mm of rainfall was observed in 24 h, corresponding to an estimated return period of well over 1000 years. As a result, discharge at the catchment outlet increased from 4.4 × 10-3 to nearly 5 m3 s-1. Within 7 h discharge rose from 5 × 10-2 to 4.5 m3 s-1. The catchment response can be divided into four phases: (1) soil moisture reservoir filling, (2) groundwater response, (3) surface depression filling and surface runoff and (4) backwater feedback. The first 35 mm of rainfall were stored in the soil without a significant increase in discharge. Relatively dry initial conditions (in comparison to those for past discharge extremes) prevented an even faster and more extreme hydrological response

Carbon–water flux coupling under progressive drought

Water-use efficiency, defined as the ratio of carbon assimilation over evapotranspiration (ET), is a key metric to assess ecosystem functioning in response to environmental conditions. It remains unclear which factors control this ratio during periods of extended water-limitation, and current semi-empirical water-use efficiency models fail to reproduce observed ET dynamics for these periods. Here, we use dry-down events occurring at eddy-covariance flux tower sites in the FLUXNET database as natural experiments to assess if and how decreasing soil-water availability modifies water-use efficiency on ecosystem scale. We demonstrate that an attenuating soil-water availability factor in junction with a previously discovered additive radiation term is necessary to accurately predict ET flux magnitudes and dry-down lengths of these water-limited periods. In an analysis of the attenuation, 20–33% of the observed decline in ET was due to the previously unconsidered soil-water availability effect. We conclude by noting the rates of ET decline differ significantly between FLUXNET sites with tall and short vegetation types and discuss the dependency of this rate on the variability of seasonal dryness

Contribution of water-limited ecoregions to their own supply of rainfall

The occurrence of wet and dry growing seasons in water-limited regions remains poorly understood, partly due to the complex role that these regions play in the genesis of their own rainfall. This limits the predictability of global carbon and water budgets, and hinders the regional management of naturalresources. Using novel satellite observations and atmospheric trajectory modelling, we unravel the origin and immediate drivers of growing-season precipitation, and the extent to which ecoregions themselves contribute to their own supply of rainfall. Results show that persistent anomalies in growing-season precipitation—and subsequent biomass anomalies—are caused by a complex interplay of land and ocean evaporation, air circulation and local atmospheric stability changes. For regions such as the Kalahari and Australia, the volumes of moisture recycling decline in dry years, providing a positive feedback that intensifies dry conditions. However, recycling ratios increase up to40%, pointing to the crucial role of these regions in generating their own supply of rainfall; transpiration in periods of water stress allows vegetation to partly offset the decrease in regional precipitation. Findings highlight the need to adequately represent vegetation–atmosphere feedbacks in models to predict biomass changes and to simulate the fate of water-limited regions in our warming climate

Crossing cultural boundaries : transfer of management knowledge and skills between organisational cultures

The subject of this thesis is the knowledge transfer process through the lens of cultural diversity and cultural awareness, bi-directional transfers between and inside Russian and European organisations, leading to the sustainable creation of values. It is aimed at explaining a variance of functions, which affect the knowledge transfer system and reacting to the research question: “How can management consultants overcome the gaps, barriers and stumbling blocks in the daily operations of the transfer of managerial knowledge and skills in intercultural contexts, in order to provide ensured, sustainable value creation for clients and on behalf of the transmitter organisation”? The study of the literature from Western and Russian perspectives was conducted for revealing the positions of scholars in the related areas, such as the national culture and its dimensions, social environment, organisational culture, roles and styles of the actors in the knowledge transfer process, organisational learning and absorptive capacity. Knowledge management and knowledge transfer processes are designed to manage the generation of knowledge from external and internal resources. For the research an Action Research Methodology and a Mixed Method Research approach was employed. An online survey was conducted to collect and exchange primary data from managers and organisations in Russia, intertwined with a focus group session and in-depth interviews with managers and employees randomly selected from the online survey’s sample. The results of the online surveys were processed by SPSS. For the focus group and in-depth interviews qualitative analyses was conducted. The findings reveal that organisational culture is a dominant factor in the transfer of knowledge and that the Russian national culture has a determinant role in organisations, specifically in the process of knowledge transfer and sustainable creation of values, in both directions

Soil moisture-Temperature Coupling: A multiscale observational Analysis

[1] Land-atmospheric interactions are complex and variable in space and time. On average soil moisture-temperature coupling is expected to be stronger in transition zones between wet and dry climates. During heatwaves anomalously high coupling may be found in areas of soil moisture deficit and high atmospheric demand of water. Here a new approach is applied to satellite andin situobservations towards the characterization of regions of intense soil moisture-temperature coupling, both in terms of climatology and anomalies during heatwaves. The resulting average summertime couplinghot spotsreflect intermediate climatic regions in agreement with previous studies. Results at heatwave-scale suggest a minor role of soil moisture deficit during the heatwave of 2006 in California but an important one in the 2003 event in Western Europe. Progress towards near-real time satellite products may allow the application of the approach to aid prediction and management of warm extremes

Distributed Evaluation of Local Sensitivity Analysis (DELSA), with application to hydrologic models

This is the published version. Copyright 2014 American Geophysical UnionThis paper presents a hybrid local-global sensitivity analysis method termed the Distributed Evaluation of Local Sensitivity Analysis (DELSA), which is used here to identify important and unimportant parameters and evaluate how model parameter importance changes as parameter values change. DELSA uses derivative-based “local” methods to obtain the distribution of parameter sensitivity across the parameter space, which promotes consideration of sensitivity analysis results in the context of simulated dynamics. This work presents DELSA, discusses how it relates to existing methods, and uses two hydrologic test cases to compare its performance with the popular global, variance-based Sobol' method. The first test case is a simple nonlinear reservoir model with two parameters. The second test case involves five alternative “bucket-style” hydrologic models with up to 14 parameters applied to a medium-sized catchment (200 km2) in the Belgian Ardennes. Results show that in both examples, Sobol' and DELSA identify similar important and unimportant parameters, with DELSA enabling more detailed insight at much lower computational cost. For example, in the real-world problem the time delay in runoff is the most important parameter in all models, but DELSA shows that for about 20% of parameter sets it is not important at all and alternative mechanisms and parameters dominate. Moreover, the time delay was identified as important in regions producing poor model fits, whereas other parameters were identified as more important in regions of the parameter space producing better model fits. The ability to understand how parameter importance varies through parameter space is critical to inform decisions about, for example, additional data collection and model development. The ability to perform such analyses with modest computational requirements provides exciting opportunities to evaluate complicated models as well as many alternative models

Does the Normalized Difference Vegetation Index explain spatial and temporal variability in sap velocity in temperate forest ecosystems?

Understanding the link between vegetation characteristics and tree transpiration is a critical need to facilitate satellite-based transpiration estimation. Many studies use the Normalized Difference Vegetation Index (NDVI), a proxy for tree biophysical characteristics, to estimate evapotranspiration. In this study, we investigated the link between sap velocity and 30 m resolution Landsat-derived NDVI for 20 days during 2 contrasting precipitation years in a temperate deciduous forest catchment. Sap velocity was measured in the Attert catchment in Luxembourg in 25 plots of 20×20 m covering three geologies with sensors installed in two to four trees per plot. The results show that, spatially, sap velocity and NDVI were significantly positively correlated in April, i.e. NDVI successfully captured the pattern of sap velocity during the phase of green-up. After green-up, a significant negative correlation was found during half of the studied days. During a dry period, sap velocity was uncorrelated with NDVI but influenced by geology and aspect. In summary, in our study area, the correlation between sap velocity and NDVI was not constant, but varied with phenology and water availability. The same behaviour was found for the Enhanced Vegetation Index (EVI). This suggests that methods using NDVI or EVI to predict small-scale variability in (evapo)transpiration should be carefully applied, and that NDVI and EVI cannot be used to scale sap velocity to stand-level transpiration in temperate forest ecosystems