Analysis of single-Alter-shielded and unshielded measurements of mixed and solid precipitation from WMO-SPICE Hydrology and Earth System Sciences DOI 10.5194/hess-21-3525-2017 14 July 2017 Precipitation measurements were combined from eight separate precipitation testbeds to create multi-site transfer functions for the correction of unshielded and single-Alter-shielded precipitation gauge measurements. Site-specific errors and more universally applicable corrections were created from these WMO-SPICE measurements. The importance and magnitude of such wind speed corrections were demonstrated. Read more
HESS Opinions: A planetary boundary on freshwater use is misleading Hydrology and Earth System Sciences DOI 10.5194/hess-21-3455-2017 12 July 2017 In 2009, the “planetary boundaries” were introduced. They consist of nine global control variables and corresponding “thresholds which, if crossed, could generate unacceptable environmental change”. The idea has been very successful, but also controversial. This paper picks up the debate with regard to the boundary on “global freshwater use”: it argues that such a boundary is based on mere speculation, and that any exercise of assigning actual numbers is arbitrary, premature, and misleading. Read more
The European 2015 drought from a hydrological perspective Hydrology and Earth System Sciences DOI 10.5194/hess-21-3001-2017 22 June 2017 In 2015 large parts of Europe were affected by a drought. In terms of low flow magnitude, a region around the Czech Republic was most affected, with return periods > 100 yr. In terms of deficit volumes, the drought was particularly severe around S. Germany where the event lasted notably long. Meteorological and hydrological events developed differently in space and time. For an assessment of drought impacts on water resources, hydrological data are required in addition to meteorological indices. Read more
The European 2015 drought from a climatological perspective Hydrology and Earth System Sciences DOI 10.5194/hess-21-1397-2017 8 March 2017 This paper analyses the European summer drought of 2015 from a climatological perspective, including its origin and spatial and temporal development, and how it compares with the 2003 event. It discusses the main contributing factors controlling the occurrence and persistence of the event: temperature and precipitation anomalies, blocking episodes and sea surface temperatures. The results represent the outcome of a collaborative initiative of members of UNESCO’s FRIEND-Water program. Read more
Rapid attribution of the August 2016 flood-inducing extreme precipitation in south Louisiana to climate change Hydrology and Earth System Sciences DOI 10.5194/hess-21-897-2017 14 February 2017 During August 2016, heavy precipitation led to devastating floods in south Louisiana, USA. Here, we analyze the climatological statistics of the precipitation event, as defined by its 3-day total over 12–14 August. Using observational data and high-resolution global coupled model experiments, we find for a comparable event on the central US Gulf Coast an average return period of about 30 years and the odds being increased by at least 1.4 since 1900 due to anthropogenic climate change. Read more
A comprehensive one-dimensional numerical model for solute transport in rivers Hydrology and Earth System Sciences DOI 10.5194/hess-21-99-2017 5 January 2017 In this study a comprehensive model was developed that combines numerical schemes with high-order accuracy for solution of the advection–dispersion equation considering transient storage zones term in rivers. In developing the subjected model (TOASTS), for achieving better accuracy and applicability, irregular-cross sections and unsteady flow regime were considered. For this purpose the QUICK scheme due to its high stability and low approximation error has been used for spatial discretization. Read more
Influence of groundwater on distribution of dwarf wedgemussels (Alasmidonta heterodon) in the upper reaches of the Delaware River, northeastern USA Hydrology and Earth System Sciences DOI 10.5194/hess-20-4323-2016 25 October 2016 The remaining populations of the endangered dwarf wedgemussel (DWM) (Alasmidonta heterodon) in the upper Delaware River, northeastern USA, were thought to be located in areas of substantial groundwater discharge to the river. Physical, thermal, and geophysical methods applied at several spatial scales indicate that DWM are located within or directly downstream of areas of substantial groundwater discharge to the river. DWM may depend on groundwater discharge for their survival. Read more
A thermodynamic formulation of root water uptake Hydrology and Earth System Sciences DOI 10.5194/hess-20-3441-2016 29 August 2016 This theoretical paper describes the energy fluxes and dissipation along the flow paths involved in root water uptake, an approach that is rarely taken. We show that this provides useful additional insights for understanding the biotic and abiotic impediments to root water uptake. This approach shall be applied to explore efficient water uptake strategies and help locate the limiting processes in the complex soil–plant–atmosphere system. Read more
A review of marine geomorphometry, the quantitative study of the seafloor Hydrology and Earth System Sciences DOI 10.5194/hess-20-3207-2016 9 August 2016 Geomorphometry, the science of quantitative terrain characterization, has traditionally focused on the investigation of terrestrial landscapes. More recently, a suite of geomorphometric techniques have been applied to characterize the seafloor. The dynamic, four-dimensional nature of the marine environment and differences in data collection methods cause issues for geomorphometry that are specific to marine applications. This article offers the first review of marine geomorphometry to date. Read more
A post-wildfire response in cave dripwater chemistry Hydrology and Earth System Sciences DOI 10.5194/hess-20-2745-2016 21 July 2016 Our current understanding of wildfires on Earth is filled with knowledge gaps. One reason for this is our poor record of fire in natural archives. We open the possibility for speleothems to be “a missing piece to the fire-puzzle”. We find by effecting surface evaporation and transpiration rates, wildfires can have a multi-year impact on speleothem, forming dripwater hydrology and chemistry. We open a new avenue for speleothems as potential palaeo-fire archives. Read more
Can mussels be used as sentinel organisms for characterization of pollution in urban water systems? Hydrology and Earth System Sciences DOI 10.5194/hess-20-2679-2016 8 July 2016 We assessed if nitrogen stable isotopes in mussels are a suitable indicator, capable of resolving spatial and temporal variability of nutrient pollution in an urban estuary. Our results highlight the value of using stable isotope analysis as an integrative tool to establish an understanding of local processes and pollution levels in theses urban aquatic systems. We suggest that mussels can become a robust tool for the detection of emerging anthropogenic pollutants of concern in urban water systems. Read more
Modeling 25 years of spatio-temporal surface water and inundation dynamics on large river basin scale using time series of Earth observation data Hydrology and Earth System Sciences DOI 10.5194/hess-20-2227-2016 10 June 2016 We statistically modeled surface water extent (SWE) and inundation dynamics from a unique Landsat-based time series (1986–2011) for Australia’s Murray–Darling Basin as a function of river flow and spatially explicit time series of rainfall, evapotranspiration and soil moisture. We present a data-driven and transferable approach that allowed us to model SWE through periods of flooding and drying for 363 floodplain units and to identify local combinations of variables that drive SWE dynamics. Read more
Investigating the impact of land-use land-cover change on Indian summer monsoon daily rainfall and temperature during 1951–2005 using a regional climate model Hydrology and Earth System Sciences DOI 10.5194/hess-20-1765-2016 10 May 2016 Regional climate model (RegCM4) simulations demonstrate that part of the observed decrease in moderate rainfall events during the summer monsoon season over central India from 1951 to 2005 is attributed to anthropogenically induced land-use land-cover change (LULCC). LULCC also partly explains the observed warming trend in the daily mean and maximum temperatures over India. This study demonstrates the importance of LULCC in the context of regional climate change over India. Read more
Coevolution of volcanic catchments in Japan Hydrology and Earth System Sciences DOI 10.5194/hess-20-1133-2016 16 March 2016 We derived indices of landscape properties as well as hydrological response and examined their relation with catchment age and climate. We found significant correlation between drainage density and baseflow index with age, but not with climate. We compared our data with data from volcanic catchments in Oregon and could confirm that baseflow index decreases with time, but also discovered that drainage density seems to stabilize after 2M years, after an initial increase due to landscape incision. Read more
Does the Budyko curve reflect a maximum-power state of hydrological systems? A backward analysis Hydrology and Earth System Sciences DOI 10.5194/hess-20-479-2016 28 January 2016 We derived mathematical formulations of relations between relative wetness and gradients driving run-off and evaporation for a one-box model such that, when conductances are optimized with the maximum power principle, the model leads exactly to a point on the Budyko curve. With dry spells and dynamics in actual evaporation added, the model compared well with catchment observations without calibrating any parameter. The maximum-power principle may thus be used to derive the Budyko curve. Read more
Aggregation in environmental systems – Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments Hydrology and Earth System Sciences DOI 10.5194/hess-20-279-2016 19 January 2016 Catchment mean transit times have been widely inferred from seasonal cycles of environmental tracers in precipitation and streamflow. Here I show that these cycles yield strongly biased estimates of mean transit times in spatially heterogeneous catchments (and, by implication, in real-world catchments). However, I also show that these cycles can be used to reliably estimate the fraction of “young” water in streamflow, meaning water that fell as precipitation less than roughly 2–3 months ago. Read more
Aggregation in environmental systems – Part 2: Catchment mean transit times and young water fractions under hydrologic nonstationarity Hydrology and Earth System Sciences DOI 10.5194/hess-20-299-2016 19 January 2016 Here I show that seasonal tracer cycles yield strongly biased estimates of mean transit times in nonstationary catchments (and, by implication, in real-world catchments). However, they can be used to reliably estimate the fraction of “young” water in streamflow, meaning water that fell as precipitation less than roughly 2–3 months ago. This young water fraction varies systematically between high and low flows and may help in characterizing controls on stream chemistry. Read more
Diagnosing hydrological limitations of a land surface model: application of JULES to a deep-groundwater chalk basin Hydrology and Earth System Sciences DOI 10.5194/hess-20-143-2016 18 January 2016 This paper presents a strategy to diagnose hydrological limitations of a Land Surface Model. It includes the adaptation of the model for hydrological applications and highlights challenges faced while moving towards high resolution modelling. Read more
Regional analysis of groundwater droughts using hydrograph classification Hydrology and Earth System Sciences DOI 10.5194/hess-19-4327-2015 28 October 2015 To improve the design of drought monitoring networks and water resource management during episodes of drought, there is a need for a better understanding of spatial variations in the response of aquifers to major meteorological droughts. This paper is the first to describe a suite of methods to quantify such variations. Using an analysis of groundwater level data for a case study from the UK, the influence of catchment characteristics on the varied response of groundwater to droughts is explored. Read more
Towards observation-based gridded runoff estimates for Europe Hydrology and Earth System Sciences DOI 10.5194/hess-19-2859-2015 22 June 2015 Water storages and fluxes on land are key variables in the earth system. To provide context for local investigations and to understand phenomena that emerge at large spatial scales, information on continental freshwater dynamics is needed. This paper presents a methodology to estimate continental scale runoff on a 0.5° spatial grid, which combines the advantages of in-situ observations with the power of machine learning regression. The resulting runoff estimates compare well with observations. Read more
Large-basin hydrological response to climate model outputs: uncertainty caused by internal atmospheric variability Hydrology and Earth System Sciences DOI 10.5194/hess-19-2737-2015 15 June 2015 Our paper is one of very few studies where the influence of stochastic internal atmospheric variability (IAV) on the hydrological response is analyzed. On the basis of ensemble experiments with GCM and hydrological models, we found, e.g., that averaging over ensemble members filters the stochastic term related to IAV, and that a considerable portion of the simulated trend in annual Lena R. runoff can be explained by the externally forced signal (global SST and SIC changes in our experiments). Read more
Storm type effects on super Clausius–Clapeyron scaling of intense rainstorm properties with air temperature Hydrology and Earth System Sciences DOI 10.5194/hess-19-1753-2015 16 April 2015 We present an empirical study of the rates of increase in precipitation intensity with air temperature using high-resolution 10 min precipitation records in Switzerland. We estimated the scaling rates for lightning (convective) and non-lightning event subsets and show that scaling rates are between 7 and 14%/C for convective rain and that mixing of storm types exaggerates the relations to air temperature. Doubled CC rates reported by other studies are an exception in our data set. Read more
Quantitative high-resolution observations of soil water dynamics in a complicated architecture using time-lapse ground-penetrating radar Hydrology and Earth System Sciences DOI 10.5194/hess-19-1125-2015 2 March 2015 In this study, we analyze a set of high-resolution, surface-based, 2-D Ground-Penetrating Radar (GPR) observations of artificially induced subsurface water dynamics. In particular, we place close scrutiny on the evolution of the capillary fringe in a highly dynamic regime with surface based time-lapse GPR. We thoroughly explain all observed phenomena based on theoretical soil physical considerations and numerical simulations of both subsurface water flow and the expected GPR response. Read more
Global trends in extreme precipitation: climate models versus observations Hydrology and Earth System Sciences DOI 10.5194/hess-19-877-2015 12 February 2015 We present a systematic comparison of changes in historical extreme precipitation in station observations (HadEX2) and 15 climate models from the CMIP5 (as the largest and most recent sets of available observational and modeled datasets), on global and continental scale for 1901-2010, using both parametric (linear regression) and non-parametric (the Mann-Kendall as well as Sen’s slope estimator) methods, taking care to spatially and temporally sample observations and models in comparable ways. Read more
A high-resolution global-scale groundwater model Hydrology and Earth System Sciences DOI 10.5194/hess-19-823-2015 6 February 2015 In this paper we present a high resolution global-scale groundwater model of an upper aquifer. An equilibrium water table at its natural state is contructed. Aquifer parameterization is based on available global-datasets on lithology and conductivity combined with estimated aquifer thickness. The results showed groundwater levels are well simulated for many regions of the world. Simulated flow paths showed the relevance of including lateral groundwater flows in global scale hydrological models. Read more
ERA-Interim/Land: a global land surface reanalysis data set Hydrology and Earth System Sciences DOI 10.5194/hess-19-389-2015 21 January 2015 ERA-Interim/Land is a global land-surface reanalysis covering the period 1979–2010. It describes the evolution of soil moisture, soil temperature and snowpack. ERA-Interim/Land includes a number of parameterization improvements in the land surface scheme with respect to the original ERA-Interim and a precipitation bias correction based on GPCP. A selection of verification results show the added value in representing the terrestrial water cycle and its main land surface storages and fluxes. Read more
Development of a large-sample watershed-scale hydrometeorological data set for the contiguous USA: data set characteristics and assessment of regional variability in hydrologic model performance Hydrology and Earth System Sciences DOI 10.5194/hess-19-209-2015 14 January 2015 The focus of this paper is to (1) present a community dataset of daily forcing and hydrologic response data for 671 unimpaired basins across the contiguous United States that spans a very wide range of hydroclimatic conditions; and (2) provide a calibrated model performance benchmark using a common conceptual snow and hydrologic modeling system. This benchmark provides a reference level of model performance across a very large basin sample and highlights regional variations in performance. Read more
What causes cooling water temperature gradients in a forested stream reach? Hydrology and Earth System Sciences DOI 10.5194/hess-18-5361-2014 20 December 2014 This study demonstrates the processes by which instantaneous longitudinal water temperature gradients may be generated in a stream reach that transitions from moorland to semi-natural forest in the absence of substantial groundwater inflows. Water did not cool as it flowed downstream. Instead, temperature gradients were generated by a combination of reduced rates of heating in the forested reach and advection of cooler (overnight and early morning) water from the upstream moorland catchment. Read more
Dams on Mekong tributaries as significant contributors of hydrological alterations to the Tonle Sap Floodplain in Cambodia Hydrology and Earth System Sciences DOI 10.5194/hess-18-5303-2014 18 December 2014 Hydrological modeling and assessment tools were used to provide evidence of the expected hydrological alterations that hydropower development in the lower Mekong tributaries could bring to the Tonle Sap. The most significant alterations are in terms of water levels during the dry season and rates of water level rise/drop which are crucial for tree seed germination and fish migrations, and therefore major ecological disruptions are likely to follow. Read more
A virtual water network of the Roman world Hydrology and Earth System Sciences DOI 10.5194/hess-18-5025-2014 11 December 2014 Our virtual water network of the Roman World shows that virtual water trade and irrigation provided the Romans with resilience to interannual climate variability. Virtual water trade enabled the Romans to meet food demands from regions with a surplus. Irrigation provided stable water supplies for agriculture, particularly in large river catchments. However, virtual water trade also stimulated urbanization and population growth, which eroded Roman resilience to climate variability over time. Read more
Estimating degree-day factors from MODIS for snowmelt runoff modeling Hydrology and Earth System Sciences DOI 10.5194/hess-18-4773-2014 3 December 2014 In this paper, we propose a new method for estimating the snowmelt degree-day factor (DDFS) directly from MODIS snow covered area and ground-based snow depth data without calibration. Snow density is estimated as the ratio between observed precipitation and changes in the snow volume for days with snow accumulation. DDFS values are estimated as the ratio between changes in the snow water equivalent and difference between the daily temperature and a threshold value for days with snowmelt. Read more
Complex networks for streamflow dynamics Hydrology and Earth System Sciences DOI 10.5194/hess-18-4565-2014 20 November 2014 This study introduces the theory of networks, and in particular complex networks, to examine connections in streamflow dynamics. Monthly streamflow data from a network of 639 stations in the United States are studied. The connections are examined primarily using the concept of clustering coefficient, which quantifies the network’s tendency to cluster. The clustering coefficient analysis is performed with several different threshold levels based on correlations in streamflow between the stations. Read more
Historical impact of water infrastructure on water levels of the Mekong River and the Tonle Sap system Hydrology and Earth System Sciences DOI 10.5194/hess-18-4529-2014 17 November 2014 This paper analyses the historical water levels of the Mekong River and Tonle Sap system by comparing pre- and post-1991 daily observations from six stations along the Mekong mainstream from Chiang Saen (northern Thailand), to Stung Treng (Cambodia), and the Prek Kdam station on the Tonle Sap River. Read more
Analytical approach for predicting fresh water discharge in an estuary based on tidal water level observations Hydrology and Earth System Sciences DOI 10.5194/hess-18-4153-2014 17 October 2014 In this study, the authors investigate the influence of river discharge on tidal wave propagation in the Yangtze estuary with specific attention to residual water level slope. Read more
Integrated assessment of global water scarcity over the 21st century under multiple climate change mitigation policies Hydrology and Earth System Sciences DOI 10.5194/hess-18-2859-2014 6 August 2014 Water scarcity conditions over the 21st century both globally and regionally are assessed in the context of climate change and climate mitigation policies, by estimating both water availability and water demand within the Global Change Assessment Model, a leading community-integrated assessment model of energy, agriculture, climate, and water. Read more
On the future of journal publications in hydrology Hydrology and Earth System Sciences DOI 10.5194/hess-18-2433-2014 27 June 2014 A group of editors from hydrology journals discusses a number of actions to help strengthen publications and research in hydrology as a whole. Read more
Impact of modellers’ decisions on hydrological a priori predictions Hydrology and Earth System Sciences DOI 10.5194/hess-18-2065-2014 4 June 2014 Researchers report the discharge predictions of 10 modellers – using the model of their choice – for the man-made Chicken Creek catchment (6 ha, northeast Germany) and analyse how well they improved their prediction in three steps based on adding information prior to each following step. Read more
A general framework for understanding the response of the water cycle to global warming over land and ocean Hydrology and Earth System Sciences DOI 10.5194/hess-18-1575-2014 6 May 2014 In an attempt to develop a simple framework for local-scale analysis we found that the climate model output shows a remarkably close relation to the long-standing Budyko framework of catchment hydrology. Read more
Ensemble projections of future streamflow droughts in Europe Hydrology and Earth System Sciences DOI 10.5194/hess-18-85-2014 9 January 2014 This paper addresses the issue of future developments in streamflow drought characteristics across Europe. Read more
Quantifying mesoscale soil moisture with the cosmic-ray rover Hydrology and Earth System Sciences DOI 10.5194/hess-17-5097-2013 17 December 2013 This paper explores the challenges and opportunities for mapping soil moisture over large areas using the cosmic-ray rover. Read more
Statistical analysis to characterize transport of nutrients in groundwater near an abandoned feedlot Hydrology and Earth System Sciences DOI 10.5194/hess-17-4897-2013 6 December 2013 Surface water from a lagoon and groundwater samples from 17 wells within and near an abandoned feedlot in northwestern Minnesota, USA, were analyzed for carbon, nutrients, and field parameters. Read more
Rainfall estimation using moving cars as rain gauges – laboratory experiments Hydrology and Earth System Sciences DOI 10.5194/hess-17-4701-2013 28 November 2013 The spatial assessment of short time-step precipitation is a challenging task. Low density of observation networks, as well as the bias in radar rainfall estimation motivated the new idea of exploiting cars as moving rain gauges with windshield wipers or optical sensors as measurement devices. Read more
Inverse streamflow routing Hydrology and Earth System Sciences DOI 10.5194/hess-17-4577-2013 19 November 2013 Here we develop a methodology to invert the routing process, i.e., to derive the spatially distributed runoff from streamflow (e.g., measured at gauge stations) by inverting an arbitrary linear routing model using fixed interval smoothing. Read more
A thermodynamic approach to link self-organization, preferential flow and rainfall–runoff behaviour Hydrology and Earth System Sciences DOI 10.5194/hess-17-4297-2013 1 November 2013 This study investigates whether a thermodynamically optimal hillslope structure can, if existent, serve as a first guess for uncalibrated predictions of rainfall–runoff. Read more
Comparative assessment of predictions in ungauged basins – Part 2: Flood and low flow studies Hydrology and Earth System Sciences DOI 10.5194/hess-17-2637-2013 9 July 2013 The objective of this paper is to assess the performance of methods that predict low flows and flood runoff in ungauged catchments. The aim is to learn from the similarities and differences between catchments in different places, and to interpret the differences in performance in terms of the underlying climate-landscape controls. Read more
Palaeoclimatological perspective on river basin hydrometeorology: case of the Mekong Basin Hydrology and Earth System Sciences DOI 10.5194/hess-17-2069-2013 31 May 2013 Our main aim in this paper is to develop a river basin scale approach for assessing interannual hydrometeorological and discharge variability on long, palaeological, time scales. For the development of the basin-wide approach, we used the Mekong River basin as a case study area, although the approach is also intended to be applicable to other basins. Read more
Reducing cloud obscuration of MODIS snow cover area products by combining spatio-temporal techniques with a probability of snow approach Hydrology and Earth System Sciences DOI 10.5194/hess-17-1809-2013 13 May 2013 This study develops a rule-based, multistep method for removing clouds from MODIS snow cover area images. The methods used include combining images from more than one satellite, time interpolation, spatial interpolation, and estimation of the probability of snow occurrence based on topographic information. Read more
Comparative assessment of predictions in ungauged basins – Part 1: Runoff-hydrograph studies Hydrology and Earth System Sciences DOI 10.5194/hess-17-1783-2013 7 May 2013 The objective of this assessment is to compare studies predicting runoff hydrographs in ungauged catchments. The aim is to learn from the differences and similarities between catchments in different locations, and to interpret the differences in performance in terms of the underlying climate and landscape controls. Read more
Elusive drought: uncertainty in observed trends and short- and long-term CMIP5 projections Hydrology and Earth System Sciences DOI 10.5194/hess-17-1765-2013 7 May 2013 Our results highlight the inherent difficulty of drought quantification and the considerable likelihood range of drought projections, but also indicate regions where drought is consistently found to increase. In other regions, wide likelihood range should not be equated with low drought risk, since potential scenarios include large drought increases in key agricultural and ecosystem regions. Read more
McMaster Mesonet soil moisture dataset: description and spatio-temporal variability analysis Hydrology and Earth System Sciences DOI 10.5194/hess-17-1589-2013 29 April 2013 This paper introduces and describes the hourly, high-resolution soil moisture dataset continuously recorded by the McMaster Mesonet located in the Hamilton-Halton Watershed in Southern Ontario, Canada. Read more