Evaporation enhancement drives the European water-budget deficit during multi-year droughts Hydrology and Earth System Sciences DOI 10.5194/hess-26-1527-2022 13 June 2022 Droughts are a creeping disaster, meaning that their onset, duration and recovery are challenging to monitor and forecast. Here, we provide further evidence of an additional challenge of droughts, i.e. the fact that the deficit in water supply during droughts is generally much more than expected based on the observed decline in precipitation. At a European scale we explain this with enhanced evapotranspiration, sustained by higher atmospheric demand for moisture during such dry periods. Read more
Future water temperature of rivers in Switzerland under climate change investigated with physics-based models Hydrology and Earth System Sciences DOI 10.5194/hess-26-1063-2022 16 May 2022 This study presents an extensive study of climate change impacts on river temperature in Switzerland. Results show that, even for low-emission scenarios, water temperature increase will lead to adverse effects for both ecosystems and socio-economic sectors throughout the 21st century. For high-emission scenarios, the effect will worsen. This study also shows that water seasonal warming will be different between the Alpine regions and the lowlands. Finally, efficiency of models is assessed. Read more
Improved representation of agricultural land use and crop management for large-scale hydrological impact simulation in Africa using SWAT+ Hydrology and Earth System Sciences DOI 10.5194/hess-26-71-2022 8 April 2022 We present an approach on how to incorporate crop phenology in a regional hydrological model using decision tables and global datasets of rain-fed and irrigated cropland with the associated cropping calendar and management practices. Results indicate improved temporal patterns of leaf area index (LAI) and evapotranspiration (ET) simulations in comparison with remote sensing data. In addition, the improvement of the cropping season also helps to improve soil erosion estimates in cultivated areas. Read more
Assessing the dependence structure between oceanographic, fluvial, and pluvial flooding drivers along the United States coastline Hydrology and Earth System Sciences DOI 10.5194/hess-25-6203-2021 23 February 2022 We analyse dependences between different flooding drivers around the USA coastline, where the Gulf of Mexico and the southeastern and southwestern coasts are regions of high dependence between flooding drivers. Dependence is higher during the tropical season in the Gulf and at some locations on the East Coast but higher during the extratropical season on the West Coast. The analysis gives new insights on locations, driver combinations, and the time of the year when compound flooding is likely. Read more
Feedback mechanisms between precipitation and dissolution reactions across randomly heterogeneous conductivity fields Hydrology and Earth System Sciences DOI 10.5194/hess-25-5905-2021 26 January 2022 The interplay between dissolution, precipitation and transport is widely encountered in porous media, from CO2 storage to cave formation in carbonate rocks. We show that dissolution occurs along preferential flow paths with high hydraulic conductivity, while precipitation occurs at locations close to yet separated from these flow paths, thus further funneling the flow and changing the probability density function of the transport, as measured on the altered conductivity field at various times. Read more
Relative humidity gradients as a key constraint on terrestrial water and energy fluxes Hydrology and Earth System Sciences DOI 10.5194/hess-25-5175-2021 12 November 2021 Here, we present a novel physically based evaporation model to demonstrate that vertical relative humidity (RH) gradients from the land surface to the atmosphere tend to evolve towards zero due to land–atmosphere equilibration processes. Collapsing RH gradients on daily to yearly timescales indicate an emergent land–atmosphere equilibrium, making it possible to determine evapotranspiration using only meteorological information, independent of land surface conditions and vegetation controls. Read more
From hydraulic root architecture models to macroscopic representations of root hydraulics in soil water flow and land surface models Hydrology and Earth System Sciences DOI 10.5194/hess-25-4835-2021 20 October 2021 Root water uptake is an important process in the terrestrial water cycle. How this process depends on soil water content, root distributions, and root properties is a soil–root hydraulic problem. We compare different approaches to implementing root hydraulics in macroscopic soil water flow and land surface models. Read more
Rainbow color map distorts and misleads research in hydrology – guidance for better visualizations and science communication Hydrology and Earth System Sciences DOI 10.5194/hess-25-4549-2021 4 October 2021 We found with a scientific paper survey (~ 1000 papers) that 45 % of the papers used rainbow color maps or red–green visualizations. Those rainbow visualizations, although attracting the media’s attention, will not be accessible for up to 10 % of people due to color vision deficiency. The rainbow color map distorts and misleads scientific communication. The study gives guidance on how to avoid, improve and trust color and how the flaws of the rainbow color map should be communicated in science. Read more
Nonstationary weather and water extremes: a review of methods for their detection, attribution, and management Hydrology and Earth System Sciences DOI 10.5194/hess-25-3897-2021 20 August 2021 Weather and water extremes have devastating effects each year. One of the principal challenges for society is understanding how extremes are likely to evolve under the influence of changes in climate, land cover, and other human impacts. This paper provides a review of the methods and challenges associated with the detection, attribution, management, and projection of nonstationary weather and water extremes. Read more
Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology Hydrology and Earth System Sciences DOI 10.5194/hess-25-1849-2021 19 May 2021 This article examines future changes in land cover and hydrological cycling across the interior of western Canada under climate conditions projected for the 21st century. Key insights into the mechanisms and interactions of Earth system and hydrological process responses are presented, and this understanding is used together with model application to provide a synthesis of future change. This has allowed more scientifically informed projections than have hitherto been available. Read more
Do small and large floods have the same drivers of change? A regional attribution analysis in Europe Hydrology and Earth System Sciences DOI 10.5194/hess-25-1347-2021 26 April 2021 Recent studies have shown evidence of increasing and decreasing trends for average floods and flood quantiles across Europe. Studies attributing observed changes in flood peaks to their drivers have mostly focused on the average flood behaviour, without distinguishing small and large floods. This paper proposes a new framework for attributing flood changes to potential drivers, as a function of return period (T), in a regional context. Read more
Vapor plumes in a tropical wet forest: spotting the invisible evaporation Hydrology and Earth System Sciences DOI 10.5194/hess-25-619-2021 3 March 2021 Forest evaporation exports a vast amount of water vapor from land ecosystems into the atmosphere. This work describes the formation process of vapor plumes in a tropical wet forest as evidence of evaporation processes happening during rain events. Read more
Intercomparison of freshwater fluxes over ocean and investigations into water budget closure Hydrology and Earth System Sciences DOI 10.5194/hess-25-121-2021 27 January 2021 The net exchange of water between the surface and atmosphere is mainly determined by the freshwater flux: the difference between evaporation ( E ) and precipitation ( P ), or E−P . Although there is consensus among modelers that with a warming climate E−P will increase, evidence from satellite data is still not conclusive, mainly due to sensor calibration issues. We here investigate the degree of correspondence among six recent satellite-based climate data records and ERA5 reanalysis E−P data. Read more
New flood frequency estimates for the largest river in Norway based on the combination of short and long time series Hydrology and Earth System Sciences DOI 10.5194/hess-24-5595-2020 24 December 2020 We combine systematic, historical, and paleo information to obtain flood information from the last 10 300 years for the Glomma River in Norway. We identify periods with increased flood activity (4000–2000 years ago and the recent 1000 years) that correspond broadly to periods with low summer temperatures and glacier growth. The design floods in Glomma were more than 20 % higher during the 18th century than today. We suggest that trends in flood variability are linked to snow in late spring. Read more
The pulse of a montane ecosystem: coupling between daily cycles in solar flux, snowmelt, transpiration, groundwater, and streamflow at Sagehen Creek and Independence Creek, Sierra Nevada, USA Hydrology and Earth System Sciences DOI 10.5194/hess-24-5095-2020 7 December 2020 Streams and groundwaters often show daily cycles in response to snowmelt and evapotranspiration. These typically have a roughly 6 h time lag, which is often interpreted as a travel-time lag. Here we show that it is instead primarily a phase lag that arises because aquifers integrate their inputs over time. We further show how these cycles shift seasonally, mirroring the springtime retreat of snow cover to higher elevations and the seasonal advance and retreat of photosynthetic activity. Read more
Ionic aluminium concentrations exceed thresholds for aquatic health in Nova Scotian rivers, even during conditions of high dissolved organic carbon and low flow Hydrology and Earth System Sciences DOI 10.5194/hess-24-4763-2020 10 November 2020 Wild salmon numbers in Nova Scotia, Canada, have been plummeting in recent decades. In 2014, we launched an ionic aluminium monitoring program in Nova Scotia to see if this toxic element was a threat to salmon populations. We found that all 10 monitored rivers had ionic aluminium concentrations that exceeded the threshold for aquatic health. Our results demonstrate that elevated aluminium still threatens aquatic ecosystems and that delays in recovery from acid rain remains a critical issue. Read more
Hydrology and water resources management in ancient India Hydrology and Earth System Sciences DOI 10.5194/hess-24-4691-2020 5 November 2020 Like in all ancient civilisations, the need to manage water propelled the growth of hydrological science in ancient India also. In this paper, we provide some fascinating glimpses into the hydrological, hydraulic, and related engineering knowledge that existed in ancient India, as discussed in contemporary literature and recent explorations and findings. Many interesting dimensions of early scientific endeavours emerge as we investigate deeper into ancient texts, including Indian mythology. Read more
In situ measurements of soil and plant water isotopes: a review of approaches, practical considerations and a vision for the future Hydrology and Earth System Sciences DOI 10.5194/hess-24-4413-2020 13 October 2020 Water isotopes are a scientific tool that can be used to identify sources of water and answer questions such as From which soil depths do plants take up water?, which are highly relevant under changing climatic conditions. In the past, the measurement of water isotopes required tremendous effort. In the last decade methods have advanced and can now be applied in the field. Herein, we review the current status of direct field measurements of water isotopes and discuss future applications. Read more
Revisiting the global hydrological cycle: is it intensifying? Hydrology and Earth System Sciences DOI 10.5194/hess-24-3899-2020 20 August 2020 We overview and retrieve a great amount of global hydroclimatic data sets. We improve the quantification of the global hydrological cycle, its variability and its uncertainties through the surge of newly available data sets. We test (but do not confirm) established climatological hypotheses, according to which the hydrological cycle should be intensifying due to global warming. We outline a stochastic view of hydroclimate, which provides a reliable means of dealing with its variability. Read more
Survival of the Qaidam mega-lake system under mid-Pliocene climates and itsrestoration under future climates Hydrology and Earth System Sciences DOI 10.5194/hess-24-3835-2020 11 August 2020 During the Pliocene, the Qaidam Basin on the Tibetan Plateau contained a mega-lake system. During the Pleistocene, it disappeared almost completely. Today, hyperarid climates prevail in the low-altitude parts of the basin. This study reveals that today’s mean water balance of the Qaidam Basin is nearly zero and is positive during warmer, less dry years. The results explain how the mega-lake system could survive for a long time in the past and could eventually be restored in the future. Read more