Comments on “Evidence for global runoff increase related to climate warming” by Labat

Center for Climatic Research, University of Delaware, Newark, DE 19716-2541, USA
Advances in Water Resources (Impact Factor: 3.42). 12/2005; 28(12):1310-1315. DOI: 10.1016/j.advwatres.2005.04.006


We have examined the evidence presented by Labat et al. and found that (1) their claims for a 4% increase in global runoff arising from a 1 °C increase in air temperature and (2) that their article provides the “first experimental data-based evidence demonstrating the link between the global warming and the intensification of the global hydrological cycle” are not supported by the data presented. Our conclusions are based on the facts that (1) their discharge records exhibit non-climatic influences and trends, (2) their work cannot refute previous studies finding no relation between air temperature and runoff, (3) their conclusions cannot explain relations before 1925, and (4) the statistical significance of their results hinges on a single data point that exerts undue influence on the slope of the regression line. We argue that Labat et al. have not provided sufficient evidence to support their claim for having detected increases in global runoff resulting from climate warming.

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    • "With small secular trends, large interannual variations which may be related to global circulations are observed in continental and global freshwater discharge [17]-[19]. Although some studies suggest that there are detected trends in global streamflows [20], the directions of streamflow trends are still equivocal [21]. At a regional scale, the historical trends in the numerous runoff records have been identified in numerous studies [22], [23] by different statistical tests. "
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    • "In addition to climate variability and change due to the previously mentioned factors, anthropogenic warming of the oceans and atmosphere because of increased greenhouse gas concentrations and the ensuing changes to the hydrologic cycle are topics of serious pursuit. The international scientific community is making strides in understanding the potential warming and its effects on all aspects of climate variability [Intergovernmental Panel on Climate Change (IPCC) 2007], but the impacts on the hydrologic cycle remain debatable and inconclusive (e.g., Cohn and Lins 2005; Legates et al. 2005; Hirsch and Ryberg 2011). Based on analyses of the global mean CO 2 (GMCO2) and annual flood records in the United States, no strong statistical evidence for flood magnitudes increasing with GMCO2 increases were found (Hirsch and Ryberg 2011). "
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    • " scales ) , this approach is nonetheless useful for some applications , in particular to 4 investigate long - term trends . However , one should keep in mind that there are also non - 5 negligible uncertainties in precipitation datasets ( see discussion in Section 8 . 4 and Fig . 6 15e , f ) , and that runoff observations lack in several regions ( Legates et al . 2005 , Peel and 7 McMahon 2006 ) . 8 9 Also land surface models can be used for the estimation of evapotranspiration for 10 instance as part of the GLDAS ( Rodell et al . 2004a ) and GSWP - 2 ( Dirmeyer et al . 2006a ) 11 products . Though evapotranspiration from these products has been less investigated than 12 soil moisture up to now , one"
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    ABSTRACT: Soil moisture is a key variable of the climate system. It constrains plant transpiration and photosynthesis in several regions of the world, with consequent impacts on the water, energy and biogeochemical cycles. Moreover it is a storage component for precipitation and radiation anomalies, inducing persistence in the climate system. Finally, it is involved in a number of feedbacks at the local, regional and global scales, and plays a major role in climate-change projections. In this review, we provide a synthesis of past research on the role of soil moisture for the climate system, based both on modelling and observational studies. We focus on soil moisture–temperature and soil moisture–precipitation feedbacks, and their possible modifications with climate change. We also highlight further impacts of soil moisture on climate, and the state of research regarding the validation of the relevant processes.There are promises for major advances in this research field in coming years thanks to the development of new validation datasets and multi-model initiatives. However, the availability of ground observations continues to be critical in limiting progress and should therefore strongly be fostered at the international level. Exchanges across disciplines will also be essential for bridging current knowledge gaps in this field. This is of key importance given the manifold impacts of soil moisture on climate, and their relevance for climate-change projections. A better understanding and quantification of the relevant processes would significantly help to reduce uncertainties in future-climate scenarios, in particular with regard to changes in climate variability and extreme events, as well as ecosystem and agricultural impacts.
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