The Niwot Ridge and Green Lakes Valley (NWT) long-term ecological research (LTER) site collects environmental observations spanning both alpine and subalpine regimes. The first observations began in 1952 and have since expanded to nearly 300 available datasets over an area of 99 km2 within the north-central Colorado Rocky Mountains that include hydrological (n = 101), biological (n = 79), biogeochemical (n = 62), and geographical (n = 56) observations. The NWT LTER database is well suited to support hydrologic investigations that require long-term and interdisciplinary data sets. Experimentation and data collection at the NWT LTER are designed to characterize ecological responses of high-mountain environments to changes in climate, nutrients, and water availability. In addition to the continuation of the many legacy NWT datasets, expansion of the breadth and utility of the NWT LTER database is driven by new initiatives including (a) a catchment-scale sensor network of soil moisture, temperature, humidity, and snow-depth observations to understand hydrologic connectivity and (b) snow-albedo alteration experiments using black carbon to evaluate the effects of snow-disappearance on ecosystems. Together, these observational and experimental datasets provide a substantial foundation for hydrologic studies seeking to understand and predict changes to catchment and local-scale process interactions.

Improving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where and why changes occur is essential for adapting and mitigating human behaviors. In this context, long-term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 10 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 meter tall tower (a combined ecosystem-atmosphere station; ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere-atmosphere exchanges of carbon, water, and energy. In addition to field infrastructures, the KCS has also been the focus of numerous high resolution multi-spectral LiDAR measurements. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi-, trans-, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists and social scientists, and many others bringing their knowledge and experience to the site. The combination of long-term monitoring, shorter-term research projects, and large-scale experiments, including manipulations of climate and various forest management practices have contributed much to our understanding of the boreal landscapes functioning, while also supporting the development of models and guidelines for research, policy and management.

This study presents the results of a long-term paired catchment experiment in south central Chile (mean annual precipitation = 2,500 mm, 5% falling in summer, mean annual temperature = 10 °C) in which fast-growing plantations of exotic Eucalyptus spp. were clearcut and replaced with native temperate rainforest species as part of an ecological restoration project. Precipitation, streamflow, and vegetation were measured starting in 2006 in four small (3 to 5 ha) catchments with Eucalyptus globulus plantations and native riparian buffers in the Valdivian Coastal Reserve. In 2011, the 12-yr-old Eucalyptus plantations were harvested in three catchments, and the clearcut area was planted with native trees (Nothofagus dombeyi), and diverse native forest species regenerated vigorously. In the restoration period (2011 to 2019), annual streamflow increased in average by 21 – 73% compared to the 2006-2010 pre-treatment period, and as much as 100% in wet years and by more than 150% in fall and summer of some years. Streamflow was 50 to 100% lower than before treatment in two dry summers (2014-2015. Base flow increased by 28 to 87% during the restoration period (2011 to 2019) compared to the pre-treatment period, and remained elevated in later years despite low summer precipitation. Streamflow increases persisted through the first decade of restoration. Overall, these findings indicate that removal of Eucalyptus plantations immediately increased streamflow, and native forest restoration gradually restored deep soil moisture reservoirs that sustain base flow during dry periods, and these flows showed steady positive values in the last three years contributing to water provision ecosystem services. The results of this study are relevant to efforts to restore native forest ecosystems on land currently intensively managed fast-growing forest plantations. They also provide useful information to inform policy and decision-making related to options for climate change mitigation under a drying trend in South-central Chile. To our knowledge this study is the first to test streamflow response to native forest restoration in former fast-growing Eucalyptus forest plantations.

In this study, we introduce datasets that include both hydrological and meteorological records at the Nučice experimental catchment (0.53 km2) which is representative for an intensively farmed landscape in the Czech Republic. The Nučice experimental catchment was established in 2011 for the observation of rainfall-runoff processes, soil erosion processes, and water balance of a cultivated landscape. The average altitude is 401 m a.s.l., the mean land slope is 3.9%, and the climate is humid continental (mean annual temperature 7.9 °C, annual precipitation 630 mm). The catchment is drained by an artificially straightened stream and consists of three fields covering over 95 % of the area which are managed by two different farmers. The typical crops are winter wheat, rapeseed, and alfalfa. The installed equipment includes a standard meteorological station, several rain gauges distributed across the basin, and an H-flume that monitors stream discharge, water turbidity, and basic water quality indicators. Additionally, the groundwater level and soil water content at various depths near the stream are recorded. Recently, large-scale soil moisture monitoring efforts have been introduced with the installation of two cosmic-ray soil moisture sensors. The datasets consist of measured precipitation, air temperature, stream discharge, and soil moisture and are available online for public use. The cross seasonal, open access runoff generation datasets at this small-scale agricultural catchment will benefit not only hydrologists but also local farmers.

The present dataset is related to the Arc-Isère long-term environmental research part of the Rhône Basin Long Term Environmental Research Observatory. This alpine watershed located in the French Alps is characterized by high Suspended Particulate Matter (SPM) in very anthropogenized valleys. Suspended Sediment Concentrations (SSC) naturally observed in the river are very high, ranging from a few tens of milligrams per litre at low flow to tens of grams per litre during major natural hydrological events (floods, debris flows) or river dam hydraulic flushes. One research objective related to this site aims at better understanding the SSC dynamics along the river using a system of nested watersheds (Arvan, Arc, and Isère) in order to access to both temporal and spatial dynamics. Studies using this dataset are on the quantification of fine sediment fluxes but also on the related morphological changes due to fine sediment deposition or resuspension. Additionally, the observatory database can support studies on contaminants (either dissolved or particulate contaminant). Six hydro sedimentary stations monitor SSC with high frequency via turbidity sensors associated to automatic samplers. Discharge is measured via classical water level measurements and a rating curve. The oldest station (Grenoble-campus) started recording data from 2006 while others hydro-sedimentary stations were built from 2009 to 2011. Data are available in an online data website called “Base de Données des Observatoires en Hydrologie” (Hydrological observatory database, https://bdoh.irstea.fr/ARC-ISERE/) with DOI references for each site. The hydrological and sediment transport time series are stored, managed and made available to a wide community in order to be used at their full extent. This database is used as a data exchange tool for both scientists and operational end-users and as an online tool to compute integrated fluxes.

Headwater forest ecosystems of the western U.S. generate a large portion of the dissolved organic matter (DOM) transported across North America. Land cover changes that alter forest structure and forest species composition affect the quantity and composition of DOM transferred to aquatic ecosystems. Clear-cut harvesting effects ~1% of the forest area of North America annually, leaving most forests in varying stages of successional regrowth, and the total area of old-growth forest decreasing. The consequences of this widespread management practice on watershed carbon cycling remain unknown. We investigated the role of land cover change from old-growth subalpine forest to lodgepole pine dominated second-growth on the character and reactivity of DOM hillslope exports. We evaluated inputs of DOM from litter leachates and export of DOM collected at the base of trenched hillslopes during a three-year period (2016-2018) at the Fraser Experimental Forest in northcentral Colorado, USA. Dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were higher in lateral subsurface flow draining old- versus secondary-growth forest. Fluorescence spectroscopy showed that the DOM exported from the old-growth forest was more heterogeneous and aromatic and that proteinaceous, microbially processed DOM components were more prevalent in the second-growth forest. Biological oxygen demand (BOD) assays revealed much lower microbial metabolism of both DOM inputs from litter leachate and subsurface exports from old-growth forest. Old-growth and second-growth forests are co-mingled in managed ecosystems, and our findings demonstrate that the influence of species composition on DOM inputs can affect the reactivity of DOM transferred from terrestrial to aquatic ecosystems.

Watershed description:The watershed is underlain by Oligocene tuffaceous and fossiliferous sandstone bedrock, rich in calcite, and clay-rich (Smectite) soils overlie a thick saprolite (Baille et al., 2007). BCI ranges in elevation from 26m asl to 167 m asl, is fully forested, with what has been characterized as a lowland seasonal tropical forest, with a mix of deciduous and evergreen trees. Annual rainfall averages 2,580 mm, with strong seasonality: the dry season is from December to May. BCI is one of the most intensively studied area of the global tropics because of the century-long presence of a research station and ongoing scientific investigation focused mainly on terrestrial forest ecology, entomology, animal behavior and related fields. The Lutz Creek data improve our understanding of basic hydrological processes and inform our ongoing research into the complex terrestrial ecosystems of the island and the region [bibliography below]. BCI is also home to the first of what is now a global network of more than 70 forest research plots known as the Forest Global Earth Observatory (ForestGEO, see https://forestgeo.si.edu/ ). ForestGEO is dedicated to advancing long-term study of the world’s forests to strengthen science capacity in an era of rapidly changing landscapes and climate to understand and predict forest dynamics

Beasley Lake Watershed is an agriculturally influenced drainage basin in western Mississippi that has been intensively studied for 25 years. As part of the USDA Conservation Effects Assessment Project (CEAP), the watershed has archived hydrology, precipitation, and water quality data in order to measure the effects of multiple USDA Natural Resources Conservation Service conservation practices on lake water quality. The long-term database is available to researchers using a web-based application, Sustaining the Earth’s Watersheds, Agricultural Research Data System (STEWARDS). STEWARDS is a GIS-based data retrieval application that encompasses spatial and temporal data collected from multiple sites within the watershed. This data note describes information located in the STEWARDS Beasley Lake Watershed database, including hydrology, precipitation, and water quality data. This information is valuable to researchers and agencies beyond the USDA as an available and useful database to improve the understanding of how land-use practices affect the water quality of shallow lake systems.

The 20 km² Galabre catchment belongs to the French network of critical zone observatories. It is representative of the sedimentary geology and meteorological forcing found in Mediterranean and mountainous areas. Due to the presence of highly erodible and sloping badlands of various lithologies, the site was instrumented in 2007 to understand the dynamics of suspended sediments (SS) in such areas. Two meteorological stations including measurements of air temperature, wind speed and direction, air moisture, rainfall intensity, raindrop size and velocity distribution are installed both in the upper and lower part of the catchment. At the catchment outlet, a gauging station records the water level, temperature and the turbidity (10 min. time-step). Water and sediment samples are collected automatically to estimate SS concentration-turbidity relationships, providing SS fluxes quantifications with known uncertainties. The sediment samples are further characterized by measuring their particle size distributions (PSD) and by applying a low-cost sediment fingerprinting approach using spectrocolorimetric tracers. Thus, the contributions of badlands on different lithologies to total SS flux are quantified at a high temporal resolution providing the opportunity to better analyze the links between meteorological forcing variability and watershed hydrosedimentary response. The set of measurements was extended to the dissolved phase in 2017. Both the river electrical conductivity and its major ion concentrations are measured each week and every three hours during storm events. This allows progress in understanding both the origin of the water during the events and the partitioning between particulate and dissolved fluxes in the critical zone.

The main objective of this study was to use an uncertainty version of a widely used monthly time step, semi-distributed model (the Pitman model) to explore the equifinalities in the way in which the main hydrological processes are simulated and any identifiable linkages with uncertainties in the available observational data. The study area is the Zambezi River basin and 18 gauged sub-basins have been included in the analyses. Unfortunately, it is not generally possible to quantify some of the observational uncertainties in such a data scarce area and mostly we are limited to identifying where these data are clearly deficient (i.e. erroneous or non-representative). The overall conclusion is that the equifinalities in the model are hugely dominant in terms of the uncertainties in the relative occurrence of different runoff generating processes, although water use uncertainties in the semi-arid parts of the basin can contribute to these uncertainties. The identification of landscape features that suggest the occurrence of saturation excess surface runoff provides some information to constrain the model. Improved independent estimates of groundwater recharge is also identified as a key source of observational data that would help a great deal in constraining the model parameter space and therefore reducing some of the model equifinality.

The Shenandoah Watershed Study (established in 1979) and the Virginia Trout Stream Sensitivity Study (established in 1987) serve to increase understanding of hydrological and biogeochemical changes in western Virginia mountain streams that occur in response to acidic deposition and other ecosystem stressors. The SWAS-VTSSS program has evolved over its 40+ year history to consist of a temporally robust and spatially stratified monitoring framework. Currently stream water is sampled bi-hourly during high-flow events at 3 sites and weekly at 4 sites within Shenandoah National Park (SHEN), and quarterly at 72 sites and on an approximately decadal frequency at ~ 450 sites within the wider western Virginia Appalachian region. Stream water is evaluated for pH, acid neutralizing capacity (ANC), base cations (calcium, magnesium, sodium and potassium ion), acid anions (sulfate, nitrate and chloride), silica and ammonium, with a subset of samples evaluated for monomeric aluminum and dissolved organic carbon. Hourly stream discharge (4 sites) and in-situ measurements of conductivity, water and air temperature (3 sites) are also measured within SHEN. Here we provide an overview and timeline of the SWAS-VTSSS stream water monitoring program, summarize the field and laboratory methods, describe the water chemistry and hydrologic data sets, and document major watershed disturbances that have occurred during the program history. Website links and instructions are provided to access the stream chemistry and time-series monitoring data in open-access federal databases. The purpose of this publication is to promote awareness of these unique, long-term data sets for wider use in catchment studies. The water chemistry and hydrologic data can be used to investigate a wide range of biogeochemical research questions and provide key inputs for models of these headwater stream ecosystems. SWAS-VTSSS is an ongoing program and quality assured data sets are uploaded to the databases annually.

Internal erosion is one of the most common causes of failure in hydraulic engineering structures, such as embankments and levees. It also plays a vital role in the geohazards (such as landslides and sinkhole developments) and more importantly, the earth landscape evolution, which has a broad environmental and ecosystem impacts. The groundwater seepage is multi-directional, and its multi-dimensional nature could affect the initiation and the progression of internal erosion. With a newly developed apparatus, we carry out nine internal erosion experiments under five different seepage directions. The results reveal that the critical hydraulic gradient increases as the seepage direction varies from the horizontal to the vertical. After a global erosion is triggered, preferential erosion paths distribute randomly from the bottom to the top of the specimen. If the seepage direction is not vertical, small preferential erosion paths merge into a large erosion corridor, in which the loss of fine particles is significant but negligible outside. Results of experiments manifest that the erosion is heterogeneous and three-dimensional, even in the unidirectional seepage flow. The particles are rapidly eroded at the early stage of the erosion, indicating a high erosion rate. With the erosion time increasing, the particle loss slows down and even ceases if the time is long enough. The erosion rate increases if the seepage direction approaches a vertical direction. Overall, the erosion rate approximately decreases with erosion time exponentially. We proposed exponential equations to illustrate the variation of the erosion rate in the erosion process.

Evapotranspiration (ET) plays an important role in integrated water resource planning, development and management. This process is particularly relevant in semiarid regions. The aim of the present study is to compare the actual spatial and temporal evapotranspiration (ETa) patterns and temporal trends in two semiarid forests, one in Brazil (Aiuaba) and the other in Spain (Valladolid). We used the Surface Energy Balance Algorithm for Land (SEBAL) to assess the effect of climatic variation in both areas. In the Brazilian semiarid forest, Caatinga is the main vegetation, while it is stone pine in Spain. For this purpose, 69 Landsat-5 and 42 Landsat-8 images (1995 – 2019) were used. The Mann-Kendall test was applied to assess the occurrence of trends in precipitation, temperature and potential evapotranspiration data; and the Temporal Stability Index (TSI) to know which areas have greater seasonal ETa. The annual amplitude of the potential evapotranspiration (ET0) is the same in both areas, however, the Caatinga values are higher. In the Caatinga forest, when ET0 presents its highest values throughout the year, ETa presents the lowest, and vice versa. In the Pinares forest, ETa follows the ET0 dynamics during the year, and the difference between ET0 and ETa is maximum during the summer. The Caatinga forest showed a greater spatial variation of ETa than the Pinares forest as well as a greater extension with lower temporal stability of ETa than the Pinares forest. Both the Caatinga forest and the Pinares forest showed significant annual trends of increase for ET0 and ETa: 3.5 mm and 2.2 mm, and 7.0 mm and 3.9 mm, respectively.

Evaporation is the key to the basin’s water cycle. Agricultural irrigation has resulted in a significant variation of regional potential evaporation (Epen). The spatiotemporal variation of Epen and the influencing factors in the natural, agricultural, and desert areas in different developmental stages of irrigation in the Heihe River Basin (HRB) from 1970 to 2017 are comparatively analyzed in this study. This work focused on the correction effect of irrigation on the variation of Epen. The agricultural water consumption in HRB significantly varied around 1998 due to the agricultural development and water policy. Under the influence of irrigation, the annual variation of Epen in the agricultural, natural, and desert areas was significantly different. From 1970 to 1998, the annual trend slope of Epen in the natural area only reduced by 1 mm decade-1, while that in the agricultural area significantly decreased by 39 mm decade-1. After the implementation of water-saving irrigation, the Epen in the natural and agricultural areas increased by 11 and 54 mm decade-1, respectively, from 1998 to 2017. In contrast with the natural and agricultural areas, Epen in the desert area decreased by 80 mm decade-1 from 1970 to 1998 and continuously decreased by 41 mm decade-1 from 1998 to 2017. However, the regulatory effect of irrigation on Epen in the desert area started to manifest due to the expansion of the cultivated land area in the desert area from 2010 to 2017. Irrigation has a significant regulatory effect on the variation of Epen in HRB. The regulatory effect is mainly reflected on the aerodynamic term (Eaero). The analytical results of the main meteorological factors affecting Epen in different regions indicated that the main meteorological factors influencing the variation of Epen in each region are the wind speed 2 m above the surface (U2) and the water vapor pressure difference (VPD).

Ice reserve estimates is a fundamental prerequisite for the water resources management, the upper Indus river basin (UIB) possesses the most abundant mid-latitude ice resources outside the poles. However, the ice reserve estimates remain unclear due to limited accessibility. We validated the critical parameters of the GlabTop2 model through ground-penetrating radar (GPR) measured ice thickness, compared the plots and profiles of the GPR-measured ice bed elevation versus GlabTop2-estimated results, integrated with GlabTop, Volta model, and the inverse distance weighted (IDW) interpolated results on various sized glaciers, a reasonable parametric scheme (τ =120 kPa and f = 0.8) of GlabTop2 was selected to apply on vast amounts of glaciers in the UIB region. GlabTop2 estimates indicated that the ice thickness of the UIB was varying from 0 to 488.1 m, with an average value of 74.4 m. Significant spatial heterogeneity exists in the sub-basins, Shyok, Shigar, and Hunza high-altitude sub-catchments own the most abundant ice reserve, less quantity was stored in the Western Himalaya and Hindukush ranges, which accounts for a small proportion (11.3% and 6.9%, respectively). A total of 1269.7 km3 ice volume can be converted to 1142.7 km3 water resources, and it can supply at least 16.1 y for the Besham hydrological station as runoff without considering the glacier process and other variables. The UIB relies on the glacier melting of the midstream because they are keeping in a self-sufficient state, in contrast, it will be up against water shortage in the future evenly, especially for the upper reaches and downstream area. Our estimates will provide the baseline information for water resources planning and management of the Indus river.

Subalpine forests are hydrologically important to the function and health of mountain basins. Identifying the specific water sources and the proportions used by subalpine forests is necessary to understand potential impacts to these forests under a changing climate. The recent ‘Two Water Worlds’ hypothesis suggests that trees can favour tightly bound soil water instead of readily available free-flowing soil water. Little is known about the specific sources of water used by subalpine trees Abies lasiocarpa (Subalpine fir) and Picea engelmannii (Engelmann spruce) in the Canadian Rocky Mountains. In this study, stable water isotope (δ18O and δ2H) samples were obtained from Subalpine fir and Engelmann spruce trees at three points of the growing season in combination with water sources available at time of sampling (snow, bound soil water, saturated soil water, precipitation). Using the Bayesian Mixing Model, MixSIAR, relative source water proportions were calculated. In the drought summer examined, there was a net loss of water via evapotranspiration from the system. Results highlighted the importance of tightly bound soil water to subalpine forests, providing insights of future health under sustained years of drought and net loss in summer growing seasons. This work builds upon concepts from the ‘Two Water Worlds’ hypothesis, showing that subalpine trees can draw from different water sources depending on season and availability. In our case, water use was largely driven by a tension gradient within the soil allowing trees to utilize tightly bound soil water and saturated soil water at differing points of the growing season.

Long-term experimental watershed studies have significantly influenced our global understanding of hydrological processes. The discovery and characterization of how stream water quantity and quality respond to a changing environment (e.g., land use change and acidic deposition) has only been possible due to the establishment of catchments devoted to long-term study. One such catchment is the Fernow Experimental Forest (FEF) located in the headwaters of the Appalachian Mountains in West Virginia, a region that provides essential freshwater ecosystem services to eastern and mid-western USA communities. Established in 1934, the FEF is among the earliest experimental watershed studies in the Eastern USA that continues to address emergent challenges to forest ecosystems, including climate change and other threats to forest health. This data note summarizes some of the seminal findings from more than 50 years of hydrologic research in the FEF. During the first few decades, research at the FEF focused on the relationship between forest management and hydrological processes – especially those related to the overall water balance. Later, research efforts included the examination of interactions between hydrology and soil erosion, biogeochemistry, N-saturation, and acid deposition. Hydro-climatologic and water quality datasets from long-term measurements and data from short-duration studies are publicly available to provide new insights and foster collaborations that will continue to advance our understanding of hydrology in forested headwater catchments. As a result of its rich history of research and abundance of long-term data, the FEF is uniquely positioned to continue to advance understanding of forest ecosystems in a time of unprecedented change.

It is widely recognized that multi-year drought can induce changes in catchment hydrological behaviors. However, at present, our understanding about multi-year, drought-induced changes in catchment hydrological behaviors and its driving factors at the process level is still very limited. This study proposed a new approach using a data assimilation technique with a process-based hydrological model to detect multi-year drought-induced changes in catchment hydrological behaviors and to identify driving factors for the changes in an unimpaired Australian catchment (Wee Jasper) which experienced prolonged drought from 1997 to 2009. Modelling experiments demonstrated that the multi-year drought caused a significant change in the catchment rainfall-runoff relationship, indicated by significant step changes in the estimated time-variant hydrological parameters SC (indicating catchment active water storage capacity) and C (reflecting catchment evapotranspiration dynamics), whose average values increased 23.4% and 10.2%, respectively, due to drought. The change in the rainfall-runoff relationship identified by the data assimilation method is consistent with that arrived at by a statistical examination. The proposed method provides insights about the drivers of the changes in the rainfall-runoff relationship at the processes level. Declining groundwater and deep soil moisture depleted by persistent evapotranspiration of deep-rooted woody vegetation during drought are the main driving factors for the catchment behaviors change in the Wee Jasper catchment. The new method proposed in this study was found to be an effective technique for detecting both the change of hydrological behaviors induced by prolonged drought and its driving factors at the process level.