@article{19369, abstract = {Monitoring and estimating mountain snowpack mass over regional scales is still a challenge because of the inadequacy of observational networks in capturing spatiotemporal variability, and limitations in remotely sensed retrievals. Recent work using C-band synthetic aperture radar (SAR) backscatter data from the Sentinel-1 satellite mission has shown good promise for tracking mountain snow depth over specific northern hemisphere ranges, although the broader potential is still unknown. Here, we extend the new Sentinel-1 based modeling framework beyond the northern hemisphere by only utilizing globally available input data, and evaluate different model parametrization and model performance over the Chilean and Argentine Andes mountains, which contain the largest mountain snowpack in the southern hemisphere. The accuracy of Sentinel-1 snow depth estimates is evaluated against an extensive in situ network available for the region. Satellite-retrieved snow depth is found to have poorer performance across the Andes than observed for northern hemisphere mountain ranges because of greater sensitivity to evergreen forest cover and shallower snowpacks. The algorithm does offer some skill but performance is variable and site-dependent. Algorithm performance is best over regions with limited evergreen forest cover (<15%) and snow depths greater than 0.75 m, although the retrievals over-estimate snow depth across most sites. Systemic errors for specific snow classes and across different snow depths are shown, highlighting specific areas in need of further investigation and development.}, author = {Bulovic, N. and Johnson, F. and Lievens, H. and Shaw, Thomas and Mcphee, J. and Gascoin, S. and Demuzere, M. and Mcintyre, N.}, issn = {1944-7973}, journal = {Water Resources Research}, number = {2}, publisher = {Wiley}, title = {{Evaluating the performance of sentinel-1 SAR derived snow depth retrievals over the extratropical Andes cordillera}}, doi = {10.1029/2024WR037766}, volume = {61}, year = {2025}, } @article{22438, abstract = {The topography of a landscape regulates the spatial distribution of water and energy fluxes, which are main drivers of vegetation and soil carbon and nutrient dynamics. Despite the recognized role of topography in mediating such processes, quantifying and predicting the spatial distribution of carbon and nutrient fluxes and stocks in highly heterogeneous landscapes remains challenging. The main limitations stem from the prevalence of largely decoupled modeling approaches which fail to concurrently account for ecohydrological and biogeochemical processes as well as the lack of adequate frameworks describing the links among topography, water and energy balances, and soil biogeochemical dynamics. Here, we extend the capabilities of the mechanistic ecohydrological model Tethys-Chloris-Biogeochemistry (T&C-BG) by including a soil carbon and nutrient routing module in the distributed model version. The newly developed T&C-BG-2D model is validated against long-term hydrological and biogeochemical measurements from the Hafren catchment in Wales (UK) and the Erlenbach catchment in the Swiss pre-Alps. The model successfully captures carbon and nutrient concentrations and dynamics in these catchments, with relative differences between simulated and observed median values of between −4% and −0.3% for dissolved organic carbon, and between 1% and 20% for ammonia. A sensitivity analysis in the Erlenbach basin suggests that elevation explains over 80% of the observed spatial patterns, followed by topographic wetness index (12.6%), aspect (2.9%), and curvature (2.1%). These findings underscore topography's critical role in shaping water, carbon, and nutrient dynamics, which cannot be reflected in plot-scale simulations neglecting spatial interactions and topographic effects.}, author = {Lian, Taiqi and Fatichi, Simone and Stähli, Manfred and Bonetti, Sara}, issn = {1944-7973}, journal = {Water Resources Research}, number = {10}, publisher = {American Geophysical Union}, title = {{Assessing spatial patterns of carbon and nutrient dynamics in catchments of complex topography}}, doi = {10.1029/2025wr040260}, volume = {61}, year = {2025}, } @article{22553, abstract = {Tidal freshwater marshes are threatened by seawater intrusion globally due to freshwater discharge reduction and sea-level rise. However, terrestrial nitrate (NO3−) transport responding to seawater intrusion remains poorly understood in tidal marshes. After validation against laboratory experiments, numerical simulations were conducted to analyze seawater intrusion effects on terrestrial NO3− transport and transformation in tidal marsh aquifers. Results reveal that seawater intrusion noticeably affects NO3− transport from the marsh aquifer to the tidal creek. Seawater intrusion results in an upper saline plume and a saltwater wedge within the aquifer, which markedly narrows the discharge outlet width of the NO3− plume and intensifies the peak NO3− flux across the creek bank. Consequently, both the NO3− removal efficiency and total nitrogen gas load to the creek decrease substantially after seawater intrusion. This is because the reduction of the transit time and the mixing zone width of the NO3− plume after seawater intrusion weakens denitrification. Sensitivity analyses indicate that the difference of the NO3− removal efficiency before and after seawater intrusion depends on soil properties. A larger unsaturated flow effect, saturated hydraulic conductivity or effective porosity leads to a greater difference of the NO3− removal efficiency before and after seawater intrusion. The predicted decrease of the NO3− removal efficiency after seawater intrusion is consistent with existing field data.}, author = {Luo, Zhaoyang and Kong, Jun and Yu, Xiayang and Gao, Chao and Barry, D. A. and Fatichi, Simone}, issn = {1944-7973}, journal = {Water Resources Research}, number = {9}, publisher = {American Geophysical Union}, title = {{Seawater intrusion inhibits nitrate removal in tidal marsh aquifers}}, doi = {10.1029/2024wr038107}, volume = {60}, year = {2024}, } @article{14487, abstract = {High Mountain Asia (HMA) is among the most vulnerable water towers globally and yet future projections of water availability in and from its high-mountain catchments remain uncertain, as their hydrologic response to ongoing environmental changes is complex. Mechanistic modeling approaches incorporating cryospheric, hydrological, and vegetation processes in high spatial, temporal, and physical detail have never been applied for high-elevation catchments of HMA. We use a land surface model at high spatial and temporal resolution (100 m and hourly) to simulate the coupled dynamics of energy, water, and vegetation for the 350 km2 Langtang catchment (Nepal). We compare our model outputs for one hydrological year against a large set of observations to gain insight into the partitioning of the water balance at the subseasonal scale and across elevation bands. During the simulated hydrological year, we find that evapotranspiration is a key component of the total water balance, as it causes about the equivalent of 20% of all the available precipitation or 154% of the water production from glacier melt in the basin to return directly to the atmosphere. The depletion of the cryospheric water budget is dominated by snow melt, but at high elevations is primarily dictated by snow and ice sublimation. Snow sublimation is the dominant vapor flux (49%) at the catchment scale, accounting for the equivalent of 11% of snowfall, 17% of snowmelt, and 75% of ice melt, respectively. We conclude that simulations should consider sublimation and other evaporative fluxes explicitly, as otherwise water balance estimates can be ill-quantified.}, author = {Buri, Pascal and Fatichi, Simone and Shaw, Thomas and Miles, Evan S. and Mccarthy, Michael and Fyffe, Catriona Louise and Fugger, Stefan and Ren, Shaoting and Kneib, Marin and Jouberton, Achille and Steiner, Jakob and Fujita, Koji and Pellicciotti, Francesca}, issn = {1944-7973}, journal = {Water Resources Research}, number = {10}, publisher = {Wiley}, title = {{Land surface modeling in the Himalayas: On the importance of evaporative fluxes for the water balance of a high-elevation catchment}}, doi = {10.1029/2022WR033841}, volume = {59}, year = {2023}, } @article{22505, abstract = {High Mountain Asia (HMA) is among the most vulnerable water towers globally and yet future projections of water availability in and from its high-mountain catchments remain uncertain, as their hydrologic response to ongoing environmental changes is complex. Mechanistic modeling approaches incorporating cryospheric, hydrological, and vegetation processes in high spatial, temporal, and physical detail have never been applied for high-elevation catchments of HMA. We use a land surface model at high spatial and temporal resolution (100 m and hourly) to simulate the coupled dynamics of energy, water, and vegetation for the 350 km2 Langtang catchment (Nepal). We compare our model outputs for one hydrological year against a large set of observations to gain insight into the partitioning of the water balance at the subseasonal scale and across elevation bands. During the simulated hydrological year, we find that evapotranspiration is a key component of the total water balance, as it causes about the equivalent of 20% of all the available precipitation or 154% of the water production from glacier melt in the basin to return directly to the atmosphere. The depletion of the cryospheric water budget is dominated by snow melt, but at high elevations is primarily dictated by snow and ice sublimation. Snow sublimation is the dominant vapor flux (49%) at the catchment scale, accounting for the equivalent of 11% of snowfall, 17% of snowmelt, and 75% of ice melt, respectively. We conclude that simulations should consider sublimation and other evaporative fluxes explicitly, as otherwise water balance estimates can be ill-quantified.}, author = {Buri, Pascal and Fatichi, Simone and Shaw, Thomas E. and Miles, Evan S. and McCarthy, Michael J. and Fyffe, Catriona L. and Fugger, Stefan and Ren, Shaoting and Kneib, Marin and Jouberton, Achille and Steiner, Jakob and Fujita, Koji and Pellicciotti, Francesca}, issn = {1944-7973}, journal = {Water Resources Research}, number = {10}, publisher = {American Geophysical Union}, title = {{Land surface modeling in the himalayas: on the importance of evaporative fluxes for the water balance of a high‐elevation catchment}}, doi = {10.1029/2022wr033841}, volume = {59}, year = {2023}, } @article{22554, abstract = {Investigating modifications in the hydrological cycle is essential to understand the impacts of climate change on ecosystems. This study assesses the change in the velocity of the water cycle over land at the global scale, whereas previous studies have mostly focused on changes in the atmospheric water cycle. The hydrological acceleration is quantified by a decrease in average residence time (RT) of water in the first meter of soil. The soil water RT is shown to be sensitive to the soil texture and seasonality of hydroclimatic variables. Despite substantial local variability, most of the RTs are in the range of 50–300 days. The global mean soil water RT declined at a rate of −2.30 and −0.36 days decade−1 (−1.6 to 1.0 days decade−1 the range of nine models) from 2001 to 2020 as measured by reanalysis and CMIP6 simulations for the historical scenario, respectively, which corresponds to −6.8 and −1.1 days °C−1 when expressed per degree of global warming over land. This acceleration is projected to continue at a rate of −1.35 days decade−1 (−3.4 to 0.0 days decade−1 the range of nine models) or −2.2 days °C−1 during the period 2015–2100 under the most extreme emission scenario: SSP 585. Changes in precipitation dominantly drive the acceleration of the terrestrial water cycle compared to changes in evapotranspiration. Rising temperatures and increasing carbon dioxide have opposite effects on the speed of the terrestrial water cycle with compensatory roles keeping RT relatively unchanged in the absence of PR trends.}, author = {Wang, Y. and Meili, N. and Fatichi, Simone}, issn = {1944-7973}, journal = {Water Resources Research}, number = {8}, publisher = {American Geophysical Union}, title = {{Evidence and controls of the acceleration of the hydrological cycle over land}}, doi = {10.1029/2022wr033970}, volume = {59}, year = {2023}, } @article{22515, abstract = {Hydrological, ecohydrological, and terrestrial biosphere models depend on pedotransferfunctions for computing soil hydraulic parameters based on easily measurable variables, such as soil texturaland physical properties. Several pedotransfer functions have been derived in the last few decades, providingdivergent estimates of soil hydraulic parameters. In this study, we quantify how uncertainties embedded inusing different pedotransfer functions propagate to ecosystem dynamics, including simulated hydrologicalfluxes and vegetation response to water availability. Using a state-of-the-art ecohydrological model applied at79 sites worldwide, we show that uncertainties related to pedotransfer functions can affect both hydrologicaland vegetation dynamics. Uncertainties in evapotranspiration, plant productivity, and vegetation structure,quantified as leaf area, are in the order of ∼10% at annual time scales. Runoff and groundwater rechargeuncertainties are one order of magnitude larger. All uncertainties are largely amplified when small-scaletopography is taken into account in a distributed domain, especially for water-limited ecosystems with lowpermeability soils. Overall, pedotransfer function related uncertainties for a given soil type are higher thanuncertainties across soil types in both hydrological and ecosystem dynamics. The magnitude of uncertainties isclimate-dependent but not soil type-dependent. Evapotranspiration, vegetation structure, and plant productivityuncertainties are higher in water-limited semiarid climates, whereas groundwater recharge uncertainties arehigher in climates where potential evapotranspiration is comparable to precipitation.}, author = {Paschalis, Athanasios and Bonetti, Sara and Guo, Yanran and Fatichi, Simone}, issn = {1944-7973}, journal = {Water Resources Research}, number = {9}, publisher = {American Geophysical Union}, title = {{On the uncertainty induced by pedotransfer functions in terrestrial biosphere modeling}}, doi = {10.1029/2021wr031871}, volume = {58}, year = {2022}, } @article{22452, abstract = {Model fidelity and accuracy in process representations have been the crux of scientific hydrological modeling, creating a pressing need for a better linkage between the development of hydrological models and the growing number of data sources and measurement techniques. Improved representation of process dynamics in hydrological models can provide new insights into complex hydrological systems and point out less understood natural phenomena that need further investigation. This special issue includes contributions that offer potential solutions and strategies to improve and test the representation of hydrological processes. We have organized the special issue contributions into four topical categories: (a) Beyond streamflow, which looks into the power of complementary data sources in addition to traditionally used streamflow for process inference. (b) Challenge of subsurface hydrology, that reflects on lesser understood processes under the surface and their impact on the model structure. (c) Evaporation in hydrological modeling, linking ecological aspects to the hydrological functioning of the natural system. Finally, (d) top down vs. bottom up modeling approaches, relied upon for process representation analysis. The special issue and our reflection on the contributions present a snapshot of ongoing efforts for integrating new concepts, knowledge, and data in process representation in hydrological models.}, author = {Guse, Björn and Fatichi, Simone and Gharari, Shervan and Melsen, Lieke A.}, issn = {1944-7973}, journal = {Water Resources Research}, number = {11}, publisher = {American Geophysical Union}, title = {{Advancing process representation in hydrological models: Integrating new concepts, knowledge, and data}}, doi = {10.1029/2021wr030661}, volume = {57}, year = {2021}, } @article{12594, abstract = {Information about end-of-winter spatial distribution of snow depth is important for seasonal forecasts of spring/summer streamflow in high-mountain regions. Nevertheless, such information typically relies upon extrapolation from a sparse network of observations at low elevations. Here, we test the potential of high-resolution snow depth data derived from optical stereophotogrammetry of Pléiades satellites for improving the representation of snow depth initial conditions (SDICs) in a glacio-hydrological model and assess potential improvements in the skill of snowmelt and streamflow simulations in a high-elevation Andean catchment. We calibrate model parameters controlling glacier mass balance and snow cover evolution using ground-based and satellite observations, and consider the relative importance of accurate estimates of SDICs compared to model parameters and forcings. We find that Pléiades SDICs improve the simulation of snow-covered area, glacier mass balance, and monthly streamflow compared to alternative SDICs based upon extrapolation of meteorological variables or statistical methods to estimate SDICs based upon topography. Model simulations are found to be sensitive to SDICs in the early spring (up to 48% variability in modeled streamflow compared to the best estimate model), and to temperature gradients in all months that control albedo and melt rates over a large elevation range (>2,400 m). As such, appropriately characterizing the distribution of total snow volume with elevation is important for reproducing total streamflow and the proportions of snowmelt. Therefore, optical stereo-photogrammetry offers an advantage for obtaining SDICs that aid both the timing and magnitude of streamflow simulations, process representation (e.g., snow cover evolution) and has the potential for large spatial domains.}, author = {Shaw, Thomas E. and Caro, Alexis and Mendoza, Pablo and Ayala, Álvaro and Pellicciotti, Francesca and Gascoin, Simon and McPhee, James}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {8}, publisher = {American Geophysical Union}, title = {{The utility of optical satellite winter snow depths for initializing a glacio‐hydrological model of a High‐Elevation, Andean catchment}}, doi = {10.1029/2020wr027188}, volume = {56}, year = {2020}, } @article{12598, abstract = {Obtaining detailed information about high mountain snowpacks is often limited by insufficient ground-based observations and uncertainty in the (re)distribution of solid precipitation. We utilize high-resolution optical images from Pléiades satellites to generate a snow depth map, at a spatial resolution of 4 m, for a high mountain catchment of central Chile. Results are negatively biased (median difference of −0.22 m) when compared against observations from a terrestrial Light Detection And Ranging scan, though replicate general snow depth variability well. Additionally, the Pléiades dataset is subject to data gaps (17% of total pixels), negative values for shallow snow (12%), and noise on slopes >40–50° (2%). We correct and filter the Pléiades snow depths using surface classification techniques of snow-free areas and a random forest model for data gap filling. Snow depths (with an estimated error of ~0.36 m) average 1.66 m and relate well to topographical parameters such as elevation and northness in a similar way to previous studies. However, estimations of snow depth based upon topography (TOPO) or physically based modeling (DBSM) cannot resolve localized processes (i.e., avalanching or wind scouring) that are detected by Pléiades, even when forced with locally calibrated data. Comparing these alternative model approaches to corrected Pléiades snow depths reveals total snow volume differences between −28% (DBSM) and +54% (TOPO) for the catchment and large differences across most elevation bands. Pléiades represents an important contribution to understanding snow accumulation at sparsely monitored catchments, though ideally requires a careful systematic validation procedure to identify catchment-scale biases and errors in the snow depth derivation.}, author = {Shaw, Thomas E. and Gascoin, Simon and Mendoza, Pablo A. and Pellicciotti, Francesca and McPhee, James}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {2}, publisher = {American Geophysical Union}, title = {{Snow depth patterns in a high mountain Andean catchment from satellite optical tristereoscopic remote sensing}}, doi = {10.1029/2019wr024880}, volume = {56}, year = {2020}, } @article{22458, abstract = {Groundwater can have a critical role in sustaining the functioning of natural ecosystems during droughts, especially in dry and seasonally dry climates. However, the response to droughts of ecosystems embedded in urban areas is not well known. This study investigates how different scenarios of groundwater availability control the water balance and vegetation productivity of two urban reserves hosting native vegetation in the Melbourne metropolitan area, Australia. Using a mechanistic ecohydrological model supported by field observations, long-term simulations were run to explore the impact of groundwater flow on water, carbon, and energy fluxes under present climatic conditions, including the Millennium Drought (2001–2009), and in response to perturbations in key environmental variables (air temperature, atmospheric CO2 concentrations, and rainfall). It was found that the presence of a water table and its capillary fringe within the root depths supports ecosystem transpiration and vegetation productivity. The effects of declining groundwater were found to be more severe in predominantly sandy soils because of the lower water holding capacity, identifying that the water status of vegetation differs significantly depending on soil type. Differences in rooting strategies and groundwater availability also had a pivotal role in helping plants soften the impacts of increased air temperature (Ta) and make use of higher atmospheric CO2 concentrations. Increased Ta strongly affected evapotranspiration, enhancing the competition for water between different vegetation types. These results provide quantitative insights of how vegetation responds to groundwater depletion and climate variability, highlighting the essential role of groundwater resources in urban ecosystems characterized by seasonally dry climates.}, author = {Marchionni, V. and Daly, E. and Manoli, G. and Tapper, N. J. and Walker, J. P. and Fatichi, Simone}, issn = {1944-7973}, journal = {Water Resources Research}, number = {5}, publisher = {American Geophysical Union}, title = {{Groundwater buffers drought effects and climate variability in urban reserves}}, doi = {10.1029/2019wr026192}, volume = {56}, year = {2020}, } @article{22565, abstract = {Solutes in rivers often come from multiple sources, notably precipitation (above) and generation from the subsurface (below). The question of which source is more influential in shaping the dynamics of solute concentration cannot be easily addressed due to the general lack of input data. An analysis of solute concentrations and their dependence on discharge across 585 catchments in nine countries leads us to hypothesize that both the timing and the vertical distribution of the solute generation are important drivers of solute export dynamics at the catchment scale. We test this hypothesis running synthetic experiments with a tracer-aided distributed hydrological model. The results reveal that the depth of solute generation is the most important control of the concentration-discharge (C-Q) relation for a number of solutes. Such relation shows that C-Q patterns of solute export vary from dilution (Ca2+, Mg2+, K+, Na+, and Cl−) to weakly enriching (dissolved organic carbon). The timing of the input imposes a signature on temporal dynamics, most evident for nutrients, and adds uncertainty in the exponent of the C-Q relation.}, author = {Botter, M. and Li, L. and Hartmann, J. and Burlando, P. and Fatichi, Simone}, issn = {1944-7973}, journal = {Water Resources Research}, number = {8}, publisher = {American Geophysical Union}, title = {{Depth of solute generation is a dominant control on concentration‐discharge relations}}, doi = {10.1029/2019wr026695}, volume = {56}, year = {2020}, } @article{12600, abstract = {The snow cover dynamics of High Mountain Asia are usually assessed at spatial resolutions of 250 m or greater, but this scale is too coarse to clearly represent the rugged topography common to the region. Higher-resolution measurement of snow-covered area often results in biased sampling due to cloud cover and deep shadows. We therefore develop a Normalized Difference Snow Index-based workflow to delineate snow lines from Landsat Thematic Mapper/Enhanced Thematic Mapper+ imagery and apply it to the upper Langtang Valley in Nepal, processing 194 scenes spanning 1999 to 2013. For each scene, we determine the spatial distribution of snow line altitudes (SLAs) with respect to aspect and across six subcatchments. Our results show that the mean SLA exhibits distinct seasonal behavior based on aspect and subcatchment position. We find that SLA dynamics respond to spatial and seasonal trade-offs in precipitation, temperature, and solar radiation, which act as primary controls. We identify two SLA spatial gradients, which we attribute to the effect of spatially variable precipitation. Our results also reveal that aspect-related SLA differences vary seasonally and are influenced by solar radiation. In terms of seasonal dominant controls, we demonstrate that the snow line is controlled by snow precipitation in winter, melt in premonsoon, a combination of both in postmonsoon, and temperature in monsoon, explaining to a large extent the spatial and seasonal variability of the SLA in the upper Langtang Valley. We conclude that while SLA and snow-covered area are complementary metrics, the SLA has a strong potential for understanding local-scale snow cover dynamics and their controlling mechanisms.}, author = {Girona‐Mata, Marc and Miles, Evan S. and Ragettli, Silvan and Pellicciotti, Francesca}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {8}, pages = {6754--6772}, publisher = {American Geophysical Union}, title = {{High‐resolution snowline delineation from Landsat imagery to infer snow cover controls in a Himalayan catchment}}, doi = {10.1029/2019wr024935}, volume = {55}, year = {2019}, } @article{12605, abstract = {Snow depth patterns over glaciers are controlled by precipitation, snow redistribution due to wind and avalanches, and the exchange of energy with the atmosphere that determines snow ablation. While many studies have advanced the understanding of ablation processes, less is known about winter snow patterns and their variability over glaciers. We analyze snow depth on Haut Glacier d'Arolla, Switzerland, in the two winter seasons 2006–2007 and 2010–2011 to (1) understand whether snow depth over an alpine glacier at the end of the accumulation season exhibits a behavior similar to the one observed on single slopes and vegetated areas; and (2) investigate the snow pattern consistency over the two accumulation seasons. We perform this analysis on a data set of high-resolution lidar-derived snow depth using variograms and fractal parameters. Our first main result is that snow depth patterns on the glacier exhibit a multiscale behavior, with a scale break around 20 m after which the fractal dimension increases, indicating more autocorrelated structure before the scale break than after. Second, this behavior is consistent over the two years, with fractal parameters and their spatial variability almost constant in the two seasons. We also show that snow depth patterns exhibit a distinct behavior in the glacier tongue and the upper catchment, with longer correlation distances on the tongue in the direction of the main winds, suggesting spatial distinctions that are likely induced by different processes and that should be taken into account when extrapolating snow depth from limited samples.}, author = {Clemenzi, I. and Pellicciotti, Francesca and Burlando, P.}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {10}, pages = {7929--7945}, publisher = {American Geophysical Union}, title = {{Snow depth structure, fractal behavior, and interannual consistency over Haut Glacier d'Arolla, Switzerland}}, doi = {10.1029/2017wr021606}, volume = {54}, year = {2018}, } @article{22481, abstract = {Water transit times and flow pathways are crucial elements in characterizing catchment hydrologic response. Understanding their variability in space and time sheds light on the link between discharge formation and water quality at the catchment scale. Here, we introduce a novel modeling framework to explore water transport mechanisms using the Hafren catchment in Wales (UK) as a case study. We show that a fully distributed hydrological model coupled with a transport component for conservative tracers is useful in analyzing how hydrometeorological conditions and spatial heterogeneity may affect water transit times and age distributions in a real catchment. We use the model to track the paths of water parcels that entered the catchment as rainfall over 2 years, labeling each day of rain individually. There is a reasonable agreement between tracer simulations and observations, suggesting that dynamic transit time distributions (TTDs) both forward and backward in time can be approximated using a high spatial and temporal resolution hydrochemical model, without assuming a priori any transit and storage selection functions at the catchment scale. TTDs are quantified for the modeled internal dynamics of the study catchment. TTDs conditional on a given rainfall time are mostly correlated to the season in which the rain event occurs, whereas TTDs conditional on a given exit time are mostly affected by catchment wetness. When TTDs for individual rainfall events are re‐scaled as functions of cumulative discharge, they collapse around a single common distribution, suggesting a potential characteristic catchment function.}, author = {Remondi, Federica and Kirchner, James W. and Burlando, Paolo and Fatichi, Simone}, issn = {1944-7973}, journal = {Water Resources Research}, number = {4}, pages = {3081--3099}, publisher = {American Geophysical Union}, title = {{Water flux tracking with a distributed hydrological model to quantify controls on the spatio-temporal variability of transit time distributions}}, doi = {10.1002/2017wr021689}, volume = {54}, year = {2018}, } @article{22455, abstract = {While the claim that water-carbon interactions result in spatially coherent vegetation patterning is rarely disputed in many arid and semiarid regions, the significance of the detailed water pathways and other high frequency variability remain an open question. How the short temporal scale meteorological fluctuations form the long-term spatial variability of available soil water in complex terrains due to the various hydrological, land surface, and vegetation dynamic feedbacks frames the scope of the work here. Knowledge of the detailed mechanistic feedbacks among soil, plants, and the atmosphere will lead to advances in our understanding of plant water availability in arid and semiarid ecosystems and will provide insights for future model development concerning vegetation pattern formation. In this study, quantitative estimates of water fluxes and vegetation productivity are provided for a semiarid ecosystem with established vegetation bands on hillslopes using numerical simulations. A state-of-the-science process based ecohydrological model is used, which resolves hydrological and plant physiological processes at the relevant space and time scales, for relatively small periods (e.g., decades) of mature ecosystems (i.e., spatially static vegetation distribution). To unfold the mechanisms that shape the spatial distribution of soil moisture, plant productivity and the relevant surface/subsurface and atmospheric water fluxes, idealized hillslope numerical experiments are constructed, where the effects of soil type, slope steepness, and overland flow accumulation area are quantified. Those mechanisms are also simulated in the presence of complex topography features on landscapes. The main results are (a) short temporal scale meteorological variability and accurate representation of the scales at which each ecohydrological process operates are crucial for the estimation of the spatial variability of soil water availability to the plant root zone; (b) water fluxes such as evapotranspiration, infiltration, runoff-run-on, and subsurface soil water movement have a dynamic short temporal scale behavior that determines the long-term spatial organization of plant soil water availability in ecosystems with established vegetation patterns; and (c) hypotheses concerning the hydrological responses that can lead to vegetation pattern formation have to accommodate realistic and physically based representations of the fast dynamics of key ecohydrological fluxes.}, author = {Paschalis, Athanasios and Katul, Gabriel G. and Fatichi, Simone and Manoli, Gabriele and Molnar, Peter}, issn = {1944-7973}, journal = {Water Resources Research}, number = {3}, pages = {2259--2278}, publisher = {American Geophysical Union}, title = {{Matching ecohydrological processes and scales of banded vegetation patterns in semiarid catchments}}, doi = {10.1002/2015wr017679}, volume = {52}, year = {2016}, } @article{22495, abstract = {An expression that separates biotic and abiotic controls on the temporal dynamics of the soilmoisture spatial coefficient of variation C v(h) was explored via numerical simulations using a mechanisticecohydrological model, Tethys-Chloris. Continuous soil moisture spatiotemporal dynamics at an exemplaryhillslope domain were computed for six case studies characterized by different climate and vegetationcover and for three configurations of soil properties. It was shown that abiotic controls largely exceed theirbiotic counterparts in wet climates. Biotic controls on C v(h) were found to be more pronounced in Mediter-ranean climates. The relation between Cv(h) and spatial mean soil moisture h was found to be unique in wetlocations, regardless of the soil properties. For the case of homogeneous soil texture, hysteretic cyclesbetween C v(h) and h were observed in all Mediterranean climate locations considered here and to a lesserextent in a deciduous temperate forest. Heterogeneity in soil properties increased C v(h) to values commen-surate with field observations and weakened signatures of hysteresis at all of the studied locations. Thisfinding highlights the role of site-specific heterogeneities in hiding or even eliminating the signature ofclimatic and biotic controls on C v(h), thereby offering a new perspective on causes of confounding resultsreported across field experiments.}, author = {Fatichi, Simone and Katul, Gabriel G. and Ivanov, Valeriy Y. and Pappas, Christoforos and Paschalis, Athanasios and Consolo, Ada and Kim, Jongho and Burlando, Paolo}, issn = {1944-7973}, journal = {Water Resources Research}, number = {5}, pages = {3505--3524}, publisher = {American Geophysical Union}, title = {{Abiotic and biotic controls of soil moisture spatiotemporal variability and the occurrence of hysteresis}}, doi = {10.1002/2014wr016102}, volume = {51}, year = {2015}, } @article{22512, abstract = {Extreme rainfall events are the major driver of shallow landslide occurrences in mountainous and steep terrain regions around the world. Subsurface hydrology has a dominant role on the initiation of rainfall-induced shallow landslides, since changes in the soil water content affect significantly the soil shear strength. Rainfall infiltration produces an increase of soil water potential, which is followed by a rapid drop in apparent cohesion. Especially on steep slopes of shallow soils, this loss of shear strength can lead to failure even in unsaturated conditions before positive water pressures are developed. We present HYDROlisthisis, a process-based model, fully distributed in space with fine time resolution, in order to investigate the interactions between surface and subsurface hydrology and shallow landslides initiation. Fundamental elements of the approach are the dependence of shear strength on the three-dimensional (3-D) field of soil water potential, as well as the temporal evolution of soil water potential during the wetting and drying phases. Specifically, 3-D variably saturated flow conditions, including soil hydraulic hysteresis and preferential flow phenomena, are simulated for the subsurface flow, coupled with a surface runoff routine based on the kinematic wave approximation. The geotechnical component of the model is based on a multidimensional limit equilibrium analysis, which takes into account the basic principles of unsaturated soil mechanics. A series of numerical simulations were carried out with various boundary conditions and using different hydrological and geotechnical components. Boundary conditions in terms of distributed soil depth were generated using both empirical and process-based models. The effect of including preferential flow and soil hydraulic hysteresis was tested together with the replacement of the infinite slope assumption with the multidimensional limit equilibrium analysis. The results show that boundary conditions play a crucial role in the model performance and that the introduced hydrological (preferential flow and soil hydraulic hysteresis) and geotechnical components (multidimensional limit equilibrium analysis) significantly improve predictive capabilities in the presented case study.}, author = {Anagnostopoulos, Grigorios G. and Fatichi, Simone and Burlando, Paolo}, issn = {1944-7973}, journal = {Water Resources Research}, number = {9}, pages = {7501--7523}, publisher = {American Geophysical Union}, title = {{An advanced process-based distributed model for the investigation of rainfall-induced landslides: The effect of process representation and boundary conditions}}, doi = {10.1002/2015wr016909}, volume = {51}, year = {2015}, } @article{12637, abstract = {The performance of glaciohydrological models which simulate catchment response to climate variability depends to a large degree on the data used to force the models. The forcing data become increasingly important in high-elevation, glacierized catchments where the interplay between extreme topography, climate, and the cryosphere is complex. It is challenging to generate a reliable forcing data set that captures this spatial heterogeneity. In this paper, we analyze the results of a 1 year field campaign focusing on air temperature and precipitation observations in the Langtang valley in the Nepalese Himalayas. We use the observed time series to characterize both temperature lapse rates (LRs) and precipitation gradients (PGs). We study their spatial and temporal variability, and we attempt to identify possible controlling factors. We show that very clear LRs exist in the valley and that there are strong seasonal differences related to the water vapor content in the atmosphere. Results also show that the LRs are generally shallower than the commonly used environmental lapse rates. The analysis of the precipitation observations reveals that there is great variability in precipitation over short horizontal distances. A uniform valley wide PG cannot be established, and several scale-dependent mechanisms may explain our observations. We complete our analysis by showing the impact of the observed LRs and PGs on the outputs of the TOPKAPI-ETH glaciohydrological model. We conclude that LRs and PGs have a very large impact on the water balance composition and that short-term monitoring campaigns have the potential to improve model quality considerably.}, author = {Immerzeel, W. W. and Petersen, L. and Ragettli, S. and Pellicciotti, Francesca}, issn = {1944-7973}, journal = {Water Resources Research}, keywords = {Water Science and Technology}, number = {3}, pages = {2212--2226}, publisher = {American Geophysical Union}, title = {{The importance of observed gradients of air temperature and precipitation for modeling runoff from a glacierized watershed in the Nepalese Himalayas}}, doi = {10.1002/2013wr014506}, volume = {50}, year = {2014}, } @article{22547, abstract = {Interannual variability of precipitation can influence components of the hydrological budget, affecting them directly and indirectly through adjustments in vegetation structure and function. We investigate the effects of fluctuations of annual precipitation on ecohydrological dynamics. Specifically, we use the advanced weather generator, AWE‐GEN, to simulate 200 years of hourly meteorological forcing obtained by imposing four types of precipitation annual process with identical long‐term mean. The generated time series force a mechanistic ecohydrological model, Tethys‐Chloris. Simulations with perturbed precipitation variability are performed for four locations characterized by different vegetation cover and climate. The results indicate that long‐term transpiration (T) and evapotranspiration (ET) fluxes as well as vegetation productivity expressed as Gross Primary Production (GPP) and Aboveground Net Primary Production (ANPP) are essentially unaffected by the imposed climate fluctuations. This finding supports the hypothesis of a relative insensitivity, except for water‐limited environments, of interannual evapotranspiration and vegetation productivity to annual climatic fluctuations, which are mostly reflected in the fluxes of deep leakage and runoff. The occurrence of short periods of favorable meteorological conditions randomly taking place within the year was found to be a better explanatory variable for interannual variability of ET and ANPP than average annual or growing season conditions. The results indicated that local, single‐site sensitivities are considerably smaller than those observed across climatic and vegetation spatial gradients and thus an important role of ecosystem reorganization in modifying ANPP and ET sensitivity in a changing climate is recognized.}, author = {Fatichi, Simone and Ivanov, Valeriy Y.}, issn = {1944-7973}, journal = {Water Resources Research}, number = {4}, pages = {3275--3294}, publisher = {American Geophysical Union}, title = {{Interannual variability of evapotranspiration and vegetation productivity}}, doi = {10.1002/2013wr015044}, volume = {50}, year = {2014}, }