Robust estimates of climate-induced hydrological change in a temperate mountainous region

A sustainable water resources management depends on sound information about the impacts of climate change. This information is, however, not easily derived because natural runoff variability interferes with the climate change signal. This study presents a procedure that leads to robust estimates of magnitude and Time Of Emergence (TOE) of climate-induced hydrological change that also account for the natural variability contained in the time series. Firstly, natural variability of 189 mesoscale catchments in Switzerland is sampled for 10 ENSEMBLES scenarios for the control (1984-2005) and two scenario periods (near future: 2025-2046, far future: 2074-2095) applying a bootstrap procedure. Then, the sampling distributions of mean monthly runoff are tested for significant differences with the Wilcoxon-Mann-Whitney test and for effect size with Cliff's delta d. Finally, the TOE of a climate change induced hydrological change is determined when at least eight out of the ten hydrological projections significantly differ from natural variability. The results show that the TOE occurs in the near future period except for high-elevated catchments in late summer. The significant hydrological projections in the near future correspond, however, to only minor runoff changes. In the far future, hydrological change is statistically significant and runoff changes are substantial. Temperature change is the most important factor determining hydrological change in this mountainous region. Therefore, hydrological change depends strongly on a catchment's mean elevation. Considering that the hydrological changes are predicted to be robust in the near future highlights the importance of accounting for these changes in water resources planning

In light of seasonal climatic and anthropogenic changes, is the Vaud Canton (Switzerland) vulnerable to water stress by the medium-term?

Observed changes in hydrological processes during the past 20 years in Switzerland are particularly preoccupying as they directly affect water use. In 2003 and 2011, local water shortage episodes occurred. Water withdrawals and supplies had to be restricted, notably in the canton of Vaud (Western Switzerland). These droughts highlighted increasing competition among water users and new water management issues arose. This study explores how hydro-climatic conditions and water needs could evolve by the 2060 horizon and assesses the vulnerability of the canton to water stress under climatic and anthropogenic changes. A daily semi-distributed hydrological model was used to simulate flows. Future changes were derived from Swiss climate scenarios relying on ten regional climate models. Regarding water needs, a population growth scenario was provided by the canton whereas a business-as-usual scenario was considered for irrigation and breeding trends. Currently, catchments in the canton experience moderate water stress from June to August, except in alpine areas. By the medium-term, water needs could reach more than 80% of rivers' total runoff in July and August. This should be due to higher temperatures and a higher ratio of liquid-to-solid precipitation causing more severe low flows. In addition, water needs should significantly increase from April to July, due to higher irrigation (+25%) and urban (+40%) water needs. This study gives a first overview of where and when water tensions are most likely to occur in the canton of Vaud. Highlighting these regional differences supports the development of strategies to cope with water stress that are currently being discussed with the cantonal authorities

Climatic and anthropogenic changes in Western Switzerland: Impacts on water stress

Recent observed hydro-climatic changes in mountainous areas are preoccupying as they may directly affect the capacity to fulfill water needs. The canton of Vaud is representative of this context as it underwent local water shortage episodes during the past decade. Based on an integrated modeling framework, this study explores how hydro-climatic conditions and water needs could evolve in mountain environments and assesses their potential impacts on water stress by the 2060 horizon. Flows were simulated based on a daily semi-distributed hydrological model. Future changes were derived from Swiss climate scenarios based on two regional climate models. Regarding water needs, the authorities of the canton of Vaud provided a population growth scenario while irrigation and breeding trends followed a business-as-usual scenario. Currently, the canton of Vaud experiences moderate water stress from June to August, except in its alpine area where no stress is noted. In the 2060 horizon, water needs could exceed 80% of the rivers' available resources in low- to mid- altitude environments in mid-summer. This should be due to the combination of drier and warmer climate enhancing longer and more severe low flows, and increasing urban (+40%) and irrigation (+25%) water needs. Highlighting regional differences supports the development of sustainable development pathways to reduce water tensions. Based on a quantitative assessment, this study also calls for broader impact studies including water quality issues

Robust estimates of climate-induced hydrological change in a temperate mountainous region

A sustainable water resources management depends on sound information about the impacts of climate change. This information is, however, not easily derived because natural runoff variability interferes with the climate change signal. This study presents a procedure that leads to robust estimates of magnitude and Time Of Emergence (TOE) of climate-induced hydrological change that also account for the natural variability contained in the time series. Firstly, natural variability of 189 mesoscale catchments in Switzerland is sampled for 10 ENSEMBLES scenarios for the control (1984–2005) and two scenario periods (near future: 2025–2046, far future: 2074–2095) applying a bootstrap procedure. Then, the sampling distributions of mean monthly runoff are tested for significant differences with the Wilcoxon-Mann–Whitney test and for effect size with Cliff’s delta d. Finally, the TOE of a climate change induced hydrological change is determined when at least eight out of the ten hydrological projections significantly differ from natural variability. The results show that the TOE occurs in the near future period except for high-elevated catchments in late summer. The significant hydrological projections in the near future correspond, however, to only minor runoff changes. In the far future, hydrological change is statistically significant and runoff changes are substantial. Temperature change is the most important factor determining hydrological change in this mountainous region. Therefore, hydrological change depends strongly on a catchment’s mean elevation. Considering that the hydrological changes are predicted to be robust in the near future highlights the importance of accounting for these changes in water resources planning

Climate change and river flooding. Part 1, Classifying the sensitivity of British catchments

Effective national and regional policy guidance on climate change adaptation relies on robust scientific evidence. This two-part series of papers develops and implements a novel scenario-neutral framework enabling an assessment of the vulnerability of flood flows in British catchments to climatic change, to underpin the development of guidance for the flood management community. In this first part, the sensitivity of the 20-year return period flood peak (RP20) to changes in precipitation (P), temperature (T) and potential evapotranspiration (PE) is systematically assessed for 154 catchments. A sensitivity domain of 4,200 scenarios is applied combining 525 and 8 sets of P and T/PE mean monthly changes, respectively, with seasonality incorporated using a single-phase harmonic function. Using the change factor method, the percentage change in RP20 associated with each scenario of the sensitivity domain is calculated, giving flood response surfaces for each catchment. Using a clustering procedure on the response surfaces, the 154 catchments are divided into nine groups: flood sensitivity types. These sensitivity types show that some catchments are (very) sensitive to changes in P but others buffer the response, while the location of catchments of the same type does not show any strong geographical pattern. These results reflect the range of hydrological processes found in Britain, and demonstrate the potential importance of catchment properties (physical and climatic) in the propagation of change in climate to change in floods, and so in characterising the sensitivity types (covered in the companion paper)

Functional Analysis of the Galactosyltransferases Required for Biosynthesis of d-Galactan I, a Component of the Lipopolysaccharide O1 Antigen of Klebsiella pneumoniae

d-Galactan I is an O-antigenic polymer with the repeat unit structure [→3)-β-d-Galf-(1→3)-α-d-Galp-(1→], that is found in the lipopolysaccharide of Klebsiella pneumoniae O1 and other gram-negative bacteria. A genetic locus containing six genes is responsible for the synthesis and assembly of d-galactan I via an ATP-binding cassette (ABC) transporter-dependent pathway. The galactosyltransferase activities that are required for the processive polymerization of d-galactan I were identified by using in vitro reactions. The activities were determined with endogenous lipid acceptors in membrane preparations from Escherichia coli K-12 expressing individual enzymes (or combinations of enzymes) or in membranes reconstituted with specific lipid acceptors. The d-galactan I polymer is built on a lipid acceptor, undecaprenyl pyrophosphoryl-GlcpNAc, a product of the WecA enzyme that participates in the biosynthesis of enterobacterial common antigen and O-antigenic polysaccharide (O-PS) biosynthesis pathways. This intermediate is directed into d-galactan I biosynthesis by the bifunctional wbbO gene product, which sequentially adds one Galp and one Galf residue from the corresponding UDP-sugars to form a lipid-linked trisaccharide. The two galactosyltransferase activities of WbbO are separable by limiting the UDP-Galf precursor. Galactosyltransferase activity in membranes reconstituted with exogenous lipid-linked trisaccharide acceptor and the known structure of d-galactan I indicate that WbbM catalyzes the subsequent transfer of a single Galp residue to form a lipid-linked tetrasaccharide. Chain extension of the d-galactan I polymer requires WbbM for Galp transferase, together with Galf transferase activity provided by WbbO. Comparison of the biosynthetic pathways for d-galactan I and the polymannose E. coli O9a antigen reveals some interesting features that may reflect a common theme in ABC transporter-dependent O-PS assembly systems

Promoter analysis of the Xanthomonas campestris pv campestris gum operon directing biosynthesis of the xanthan polysaccharide

Katzen F, Becker A, Zorreguieta A, Pühler A, Ielpi L. Promoter analysis of the Xanthomonas campestris pv campestris gum operon directing biosynthesis of the xanthan polysaccharide. Journal of Bacteriology. 1996;178(14):4313-4318.The Xanthomonas campestris gum gene cluster is composed of 12 genes designated gumB, -C, -D, -E, -F, -G, -H, -I, -J, -K, -L, and -M. The transcriptional organization of this gene cluster was analyzed by the construction of gum-lacZ transcriptional fusions in association with plasmid integration mutagenesis. This analysis, coupled with primer extension assays, indicated that the gum region was mainly expressed as an operon from a promoter located upstream of the first gene, gumB