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Tipping bucket rain gauges (TBRs) have been, and apparently will continue to be one of the most widely used pieces of equipment for rainfall monitoring, being frequently used for the calibration, validation and downscaling of radar and remote sensing data, due to their major advantages–low cost, simplicity, and low energy consumption. Thus, many works have focused and continue to focus on their main disadvantage–measurement biases (mainly in wind and mechanical underestimations). However, despite arduous scientific effort, calibration methodologies are not frequently implemented by monitoring networks operators or data users, propagating bias in databases and in the different applications of such data, causing uncertainty in the modeling, management, and forecasting in hydrological research, mainly due to a lack of knowledge. Within this context, this work presents a review of the scientific advances in TBR measurement uncertainties, calibration, and error reduction strategies from a hydrological point of view, by describing different rainfall monitoring techniques in Section 2, summarizing TBR measurement uncertainties in Section 3, focusing on calibration, and error reduction strategies in Section 4, a discussion and perspectives in Section 5, and conclusions in Section 6, providing an overview of the of the state of the art and future perspectives of the technology.

Web-based distributed volunteer computing enables scientists to constitute platforms that can be used for computational tasks by using potentially millions of computers connected to the internet. It is a widely used approach for many scientific projects, including the analysis of radio signals for signs of extraterrestrial intelligence and determining the mechanisms of protein folding. User adoption and clients' dependence on the desktop software present challenges in volunteer computing projects. This study presents a web-based volunteer computing framework for hydrological applications that requires only a web browser to participate in distributed computing projects. The framework provides distribution and scaling capabilities for projects with user bases of thousands of volunteers. As a case study, we tested and evaluated the proposed framework with a large-scale hydrological flood forecasting model.

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Different means of hydrological data collection have developed and used. However, they are constraint in one way or other. This paper therefore revisited the rainfall simulator as potential tool for hydrological research. The research disclosed that there are three different types of rainfall simulators; drop former simulator, pressure nozzle simulator and hybrid simulator. It can further be classified as indoor model and outdoor. The research also showed that precipitation is the driving force in hydrological studies. Consequently, in the design of rainfall simulator, the following should be taken into consideration: nozzle spacing, pump size, nozzle size, nozzle type, nozzle spacing, plot size and pressure. Meanwhile, intensity, distribution uniformity, kinetic energy, rainfall drop size and rainfall terminal velocity should be noted in its evaluation. Factoring-in the aforementioned design considerations, data collection is made easy without necessarily waiting for the natural rainfall. Since the rainfall can be controlled, the erratic and unpredictable changeability of natural rainfall is eliminated. Emanating from the findings, pressurized rainfall simulator produces rainfall characteristics similar to natural rainfall, which is therefore recommended for laboratory use if natural rainfall-like characteristics is the main target.

The acceleration of climate change and its impact highlight the need for long-term reliable climate data at high spatiotemporal resolution to answer key science questions in cold regions hydrology. Prior to the digital age, climate records were archived on paper. For example, from the 1950s to the 1990s, solar radiation data from recording stations worldwide were published in booklets by the former Union of Soviet Socialist Republics (USSR) Hydrometeorological Service. As a result, the data are not easily accessible by most researchers. The overarching aim of this research is to develop techniques to convert paper-based climate records into a machine-readable format to support environmental research in cold regions. This study compares the performance of a proprietary optical character recognition (OCR) service with an open-source OCR tool for digitizing hydrometeorological data. We built a digitization pipeline combining different image preprocessing techniques, semantic segmentation, and an open-source OCR engine for extracting data and metadata recorded in the scanned documents. Each page contains blocks of text with station names and tables containing the climate data. The process begins with image preprocessing to reduce noise and to improve quality before the page content is segmented to detect tables and finally run through an OCR engine for text extraction. We outline the digitization process and report on initial results, including different segmentation approaches, preprocessing image algorithms, and OCR techniques to ensure accurate extraction and organization of relevant metadata from thousands of scanned climate records. We evaluated the performance of Tesseract OCR and ABBYY FineReader on text extraction. We find that although ABBY FineReader has better accuracy on the sample data, our custom extraction pipeline using Tesseract is efficient and scalable because it is flexible and allows for more customization.

Openly accessible global scale surface water chemistry datasets are urgently needed to detect widespread trends and problems, to help identify their possible solutions, and identify critical spatial data gaps where more monitoring is required. Existing datasets are limited in availability, sample size/sampling frequency, and geographic scope. These limitations inhibit the answering of emerging transboundary water chemistry questions, for example, the detection and understanding of delayed recovery from freshwater acidification. Here, we begin to address these limitations by compiling the global surface water chemistry (SWatCh) database, available on Zenodo (DOI: https://doi.org/10.5281/zenodo.4559696) We collect, clean, standardize, and aggregate open access data provided by six national and international agencies to compile a database consisting of three relational datasets: sites, methods, and samples, and one GIS shapefile of site locations. We remove poor quality data (for example, values flagged as suspect), standardize variable naming conventions and units, and perform other data cleaning steps required for statistical analysis. The database contains water chemistry data across seven continents, 17 variables, 38,598 sites, and over 9 million samples collected between 1960 and 2019. We identify critical spatial data gaps in the equatorial and arid climate regions, highlighting the need for more data collection and sharing initiatives in these areas, especially considering freshwater ecosystems in these environs are predicted to be among the most heavily impacted by climate change. We identify the main challenges associated with compiling global databases – limited data availability, dissimilar sample collection and analysis methodology, and reporting ambiguity – and provide recommendations to address them. By addressing these challenges and consolidating data from various sources into one standardized, openly available, high quality, and trans-boundary database, SWatCh allows users to conduct powerful and robust statistical analyses of global surface water chemistry.

Global Satellite Mapping of Precipitation (GSMaP), Climate Hazards Group InfraRed Preconception with Station data (CHIRPS), Tropical Rain Measurement Mission Multisatellite Precipitation Analysis (TRMM 3B42 V7) and Rainfall Estimation from Soil Moisture Observations (SM2RAIN) are satellite precipitation products with high applicability, but their applicability in hydrological research in arid mountainous areas is not clear. Based on precipitation and runoff data, this study evaluated the applicability of each product to hydrological research in a typical mountainous basin (the Qaraqash River basin) in an arid region by using two methods: a statistical index and a hydrological model (Soil and Water Assessment Tool, SWAT). Simulation results were evaluated by Nash efficiency coefficient (NS), relative error (PBIAS) and determination coefficient (R2). The results show that: (1) The spatial distributions of precipitation estimated by these four products in the Qaraqash River basin are significantly different, and the multi-year average annual precipitation of GSMaP is 97.11 mm, which is the closest to the weather station interpolation results. (2) On the annual and monthly scales, GSMaP has the highest correlation (R ≥ 0.82) with the observed precipitation and the smallest relative error (BIAS < 6%). On the seasonal scale, the inversion accuracy of GSMaP in spring, summer and autumn is significantly higher than other products. In winter, all four sets of products perform poorly in estimating the actual precipitation. (3) Monthly runoff simulations based on SM2RAIN and GSMaP show good fitting (R2 > 0.6). In daily runoff simulation, GSMaP has the greatest ability to reproduce runoff changes. The study provides a reference for the optimization of precipitation image data and hydrological simulation in data-scarce areas.

The present paper represents the complex monitoring results of the hydrological field condition and water dynamics in the Black Sea northern part within the economic region of Russia carried out in the scientific expeditions in 2016 (87th, 89th and 91st cruises of R/V Professor Vodyanitsky). It is shown that distributions of all the thermohaline characteristics obtained from the data of three surveys demonstrate a pronounced seasonal character of a signal. It is manifested in consistent decrease of the upper mixed layer mean temperature, growth of temperature in the cold intermediate layer core and in deepening of the lower boundary of the upper mixed layer, the cold intermediate layer core and the hydrogen sulphide zone upper boundary. In course of three surveys, the Rim Current deep stream was located above the continental slope. The maximum velocities are observed nearby the Crimea southwestern coast. In the western part of the region considered, a well pronounced Sevastopol anticyclone (most distinct in October, 2016) is observed. The Sevastopol anticyclone manifests itself also in distributions of the hydrological characteristics. Temperature increase, salinity decrease and deepening of the lower boundary of the upper mixed layer and the cold intermediate layer core are observed on the sea surface in the anticyclone area.

The National Institute of Hydrology (NIH) is a premier research Institute in India in the area of hydrology and water resources. The Institute was established in 1978 with the main objective of undertaking, aiding, promoting and coordinating systematic and scientific work in all aspects of hydrology. The Institute has its headquarters at Roorkee (Uttarakhand), four regional centres at Belagavi, Jammu, Kakinada and Bhopal and two centres for flood management studies at Guwahati and Patna. The Institute is well equipped to carry out computer, laboratory and field oriented studies. This article presents an overview of research activities being undertaken by the Institute.

Women play a central part in the provision, management and safeguarding of water. This pivotal role of women as providers and users of water and guardians of the living environment has seldom been reflected in institutional arrangements for the development and management of water resources. Acceptance and implementation of this principle requires positive policies to address women's specific needs and to equip and empower women to participate at all levels in water resources programmes, including decision-making and implementation. The objective of this paper is to highlight some of the recent contribution of women in the field of Hydrology.

The International Conference on Hydrological Research Basins and the Environment, was held at Wageningen from September 24th to 28th. The conference was organized by the Committee of the European Network of Experimental and Representative Basins and the National Committee of the Netherlands for the International Hydrological Programme of Unesco. Much of our basic knowledge on hydrological processes has come from studies in research basins. These well-instrumented basins have also produced much very suitable data for hydrological investigations an water resources management studies. In recent years the significance of the role of research basins in hydrology has considerably changed. It was found that research basins also constitute an irreplaceable tool for studying anthropogenic effects on water resources and the environment. Detailed observations and measurements have strongly increased the awareness of the effect of human activities on the quality of the environment and consequently the threat to life. Studying the changes caused by anthropogenic effects is most useful when carried out in well-equipped research basins, supported by basin experiments. Such studies are also a valuable starting point for sound future environmental management. The main objective of the conference was to bring together scientists involved in hydrological basin research, to stimulate the exchange of information and to encourage international cooperation in research projects. During the conference the Third General Meeting of the European Network of Experimental and Representative Basins was held. This network of basins, covering nine countries in Europe, organizes periodical meetings and tries to enhance harmonization of observations and methods of analysis, and to implement research projects of common interest.

The International Conference on Hydrological Research Basins and the Environment, was held at Wageningen from September 24th to 28th. The conference was organized by the Committee of the European Network of Experimental and Representative Basins and the National Committee of the Netherlands for the International Hydrological Programme of Unesco. Much of our basic knowledge on hydrological processes has come from studies in research basins. These well-instrumented basins have also produced much very suitable data for hydrological investigations an water resources management studies. In recent years the significance of the role of research basins in hydrology has considerably changed. It was found that research basins also constitute an irreplaceable tool for studying anthropogenic effects on water resources and the environment. Detailed observations and measurements have strongly increased the awareness of the effect of human activities on the quality of the environment and consequently the threat to life. Studying the changes caused by anthropogenic effects is most useful when carried out in well-equipped research basins, supported by basin experiments. Such studies are also a valuable starting point for sound future environmental management. The main objective of the conference was to bring together scientists involved in hydrological basin research, to stimulate the exchange of information and to encourage international cooperation in research projects. During the conference the Third General Meeting of the European Network of Experimental and Representative Basins was held. This network of basins, covering nine countries in Europe, organizes periodical meetings and tries to enhance harmonization of observations and methods of analysis, and to implement research projects of common interest.

The International Conference on Hydrological Research Basins and the Environment, was held at Wageningen from September 24th to 28th. The conference was organized by the Committee of the European Network of Experimental and Representative Basins and the National Committee of the Netherlands for the International Hydrological Programme of Unesco. Much of our basic knowledge on hydrological processes has come from studies in research basins. These well-instrumented basins have also produced much very suitable data for hydrological investigations an water resources management studies. In recent years the significance of the role of research basins in hydrology has considerably changed. It was found that research basins also constitute an irreplaceable tool for studying anthropogenic effects on water resources and the environment. Detailed observations and measurements have strongly increased the awareness of the effect of human activities on the quality of the environment and consequently the threat to life. Studying the changes caused by anthropogenic effects is most useful when carried out in well-equipped research basins, supported by basin experiments. Such studies are also a valuable starting point for sound future environmental management. The main objective of the conference was to bring together scientists involved in hydrological basin research, to stimulate the exchange of information and to encourage international cooperation in research projects. During the conference the Third General Meeting of the European Network of Experimental and Representative Basins was held. This network of basins, covering nine countries in Europe, organizes periodical meetings and tries to enhance harmonization of observations and methods of analysis, and to implement research projects of common interest.

The Niger Delta at the southernmost part of Nigeria, is a large and ecologically sensitive region. Natural and anthropogenic activities, such as subsidence, sea-level rise, upstream dams and reservoirs, dredging and overabstraction of groundwater, disturb this equilibrium, leading to adjustments in ecological conditions and boundaries. Ecological changes affecting large areas cannot be explained by local observation. Relating observed effects to causes of environmental behaviour therefore requires a regionalized data collection, that provides a broader perspective of the issues involved with resultant ease in the identification of common problems and formulation of effective solutions.

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In this study a 25-year (1976–2000) series of observed precipitation, temperature, runoff and further water-flows of a lysimeter balance within the pre-alpine research catchment Rietholzbach (Switzerland) is analyzed. The comparison of the precipitation volumes on this lysimeter to precipitation collected by a conventional rain gauge shows that conventional rain gauges provide strongly underestimated values for precipitation, especially in winter. The obtained monthly precipitation correction factors indicate that precipitation losses above 20% for rain and above 50% for snow are realistic. The observed hydrometeorological values allowed for improving the understanding of the model-based simulation of the hydrological processes with distributed hydrological models and for investigating both a conceptual and a physically based runoff-generation approach. The albedo, soil moisture and lysimeter water balance allowed for a simultaneous assessment of the performance of several model components, such as the soil moisture, runoff-generation and evapotranspiration modules and the module for the determination of snow cover accumulation and melt.

The role and relative importance of experimental and representative basins in pre-dieting anthropogenic effects on water resources and the environment was the goal of the International Conference on Hydrological Research Basins and the Environment, held in Wageningen, the Netherlands, September 24–28, 1990. About 70 persons, almost exclusively from Europe, attended the meeting, which was organized by the Committee of the European Network of Experimental and Representative Basins and the National Committee of the Netherlands for the International Hydrological Program of Unesco. During the conference, the 3rd General Meeting of the European Network of Experimental and Representative Basins was held. This network of basins, covering nine countries in Europe, organizes periodic meetings and tries to enhance the compatibility of observations and methods of analysis, and to implement research projects of common interest.

Intercepted rainfall may be evaporated during or after the rain event. Intercepted rain is generally determined as the difference between rainfall measurements outside and inside the forest. Such measurements are often used to discriminate between water storage and evaporation during rain as well. Two well-accepted methods underestimate water storage by a factor two as compared to direct observations. The underestimation of storage is compensated by an overestimation of evaporation during rain by a factor of three. The direct observations of water storage and evaporation appear to agree with previous direct observations. Thus, it is concluded that these observations are representative Also, our results based on methods using only rainfall measurements inside and outside the forest appear to agree with previous results, This would result in the conclusion that the common methods systematically underestimate water storage and overestimate evaporation during rain. Indeed, the systematic errors can be explained by the neglect of drainage before saturation. Water storage is better simulated assuming an exponential saturation of a larger storage capacity. A smaller evaporation can be simulated using an appropriate resistance to vapour transport. The observations in dense coniferous forest showed water storage to be the dominant process in rainfall interception, but this conclusion should not be generalized to other forests and climates. Direct observations of water storage and evaporation are recommended to build a realistic set of parameters for rainfall interception studies of the main vegetation types. (C) 1998 Elsevier Science B.V. All rights reserved.

This paper reports the effects of altering an aspen forest cover in Utah on evapotranspiration losses, overland flow, erosion, and mantle storage deficits during three successive growing seasons. These data, together with supplemental measures of winter precipitation and estimates of evaporation from snow, provided a basis for estimating amounts of water available for stream flow. Removal of aspen trees, leaving the herbaceous understory and litter undisturbed, reduced evapotranspiration losses and increased the amount of water available for stream flow by about four inches without seriously increasing overland flow or soil erosion during summer rains. Removal of the remaining herbaceous cover further reduced evapotranspiration losses and increased the amount of water available to streams by an additional four inches but resulted in an undesirable increase in summer rainfall runoff and soil loss.

Currently, the direction of hydrological research, highlighting certain aspects of the influenceof climatic factors on the average annual water discharge of river basins, is changing due to climate change,which is a function of annual atmospheric precipitation and average annual air temperature that characterizeevaporation, that is, hydrometeorological components of the geographical landscape reflecting that is theratio of heat and moisture, which is characteristic of the geographical area. One of the most importanttasks in the field of hydrological research is to study the genesis of long-term fluctuations in the averageannual water discharge and climatic indicators of the catchment area of river basins, and to identify theirregional patterns, modern geographic information systems and algorithms have been developed that makeit possible to quickly and efficiently solve this problem. On the basis of them, a research base was formedcovering the period 1934-2020, which is based on information and analytical materials of the reference andinformation portal «Weather and Climate», the RSE «Kazhydromet», the World Meteorological Organization(WMO) and the RSU «Tobol-Torgay Basin Inspection on the regulation of the use and protection of waterresources». The cyclical nature of the average annual water discharge, average annual air temperatures andannual atmospheric precipitation for the catchment area of the Tobol River basin manifests itself unequallyin separate periods at a particular phase of development, i.e. modeling linear trends and differential integralcurves. To assess the degree of synchronicity of average annual water discharge and average annual air temperatures and atmospheric precipitation, methodological support was developed, implemented in thecatchments of the Tobol River basin, which showed that in the steppe zone of Northern Kazakhstan, theirdegree of synchronicity is low, since the main source of runoff formation in the considered territory the snowcover of the previous year accumulated over the winter, that is, atmospheric precipitation at the end of theautumn and the beginning of the winter period, which are not taken into account when determining the degreeof synchronicity of a real year, which requires the need to clarify the structure of the calculated year, takinginto account the determining conditions for the formation of river flow.

Over time, the content, scope and objectives of hydrological research in the Romanian Black Sea coastal area varied according to the state of society development, technology development and financial resources. Along with the activities of capitalizing on natural resources, water use, river and sea navigation, there have been demands for knowledge of the water regime and the interaction between the resource potential and the characteristics of the hydrological regime. As a result, hydrographic and hydrological research was started and developed in the Black Sea coastal zone. These researches developed in the first half of the nineteenth century, and then continued throughout this century and later in the twentieth century, with interruptions caused by the two world wars. Among the important activities that have taken place over time, there have been hydro-technical works. The design and elaboration of the projects of these works were based on the knowledge of the hydrographic and hydrological characteristics of the Black Sea coastal zone. This knowledge has evolved over time so that there is currently an important pool of data and information related to the hydrological, morphological, hydrochemical, hydrobiological characteristics of the water bodies mentioned. The paper presents briefly the most important moments of the history of the monitoring activity carried out over time in the Black Sea coastal zone, the types of coastal and transitional waters in Romania, coastal rehabilitation projects of the Black Sea, hydrological features, the structure of the marine complex model pom / ersem III) BREG / BSHELF.

Snow depth mirrors regional climate change and is a vital parameter for medium- and long-term numerical climate prediction, numerical simulation of land-surface hydrological process, and water resource assessment. However, the quality of the available snow depth products retrieved from remote sensing is inevitably affected by cloud and mountain shadow, and the spatiotemporal resolution of the snow depth data cannot meet the need of hydrological research and decision-making assistance. Therefore, a method to enhance the accuracy of snow depth data is urgently required. In the present study, three kinds of snow depth data which included the D-InSAR data retrieved from the remote sensing images of Sentinel-1 synthetic aperture radar, the automatically measured data using ultrasonic snow depth detectors, and the manually measured data were assimilated based on ensemble Kalman filter. The assimilated snow depth data were spatiotemporally consecutive and integrated. Under the constraint of the measured data, the accuracy of the assimilated snow depth data was higher and met the need of subsequent research. The development of ultrasonic snow depth detector and the application of D-InSAR technology in snow depth inversion had greatly alleviated the insufficiency of snow depth data in types and quantity. At the same time, the assimilation of multi-source snow depth data by ensemble Kalman filter also provides high-precision data to support remote sensing hydrological research, water resource assessment, and snow disaster prevention and control program.

In this paper, we demonstrated a practical application of realistic river image generation using deep learning. Specifically, we explored a generative adversarial network (GAN) model capable of generating high-resolution and realistic river images that can be used to support modeling and analysis in surface water estimation, river meandering, wetland loss, and other hydrological research studies. First, we have created an extensive repository of overhead river images to be used in training. Second, we incorporated the Progressive Growing GAN (PGGAN), a network architecture that iteratively trains smaller-resolution GANs to gradually build up to a very high resolution to generate high quality (i.e., 1024x1024) synthetic river imagery. With simpler GAN architectures, difficulties arose in terms of exponential increase of training time and vanishing/exploding gradient issues, which the PGGAN implementation seemed to significantly reduce. The results presented in this study show great promise in generating high-quality images and capturing the details of river structure and flow to support hydrological research, which often requires extensive imagery for model performance.

Many small-scale water development initiatives are accompanied by hydrological research to study either the form of the intervention or its impacts. Humans influence both the development of intervention and research, and thus one needs to take human agency into account. This paper focuses on the effects of human actions in the development of the intervention and its associated hydrological research, as hydrological research is often designed without adequate consideration of how to account for human agency and that these effects have not yet been discussed explicitly in a systematic way. In this paper, we propose a systematic planning for hydrological research, based on evaluating three hydrological research efforts targeting small-scale water development initiatives in Vietnam, Kenya, and Indonesia. The main purpose of the three cases was to understand the functioning of interventions in their hydrological contexts. Aiming for better decision-making on hydrological research in small-scale water intervention initiatives, we propose two analysis steps, including (1) consideration of possible surprises and possible actions and (2) cost–benefit analysis. By performing the two analyses continuously throughout small-scale hydrological intervention-based initiatives, effective hydrological research can be achieved.

Spatiotemporally continuous soil moisture (SM) data are increasingly in demand for ecological and hydrological research. Satellite remote sensing has potential for mapping SM, but the continuity of satellite-derived SM is hampered by data gaps resulting from inadequate satellite coverage, snow cover, frozen soil, radio-frequency interference, and so on. Therefore, we propose a new gap-filling approach to reconstruct daily SM time series using the European Space Agency Climate Change Initiative (ESA CCI). The developed approach integrates satellite observations, model-driven knowledge, and a machine learning algorithm that leverages both spatial and temporal domains. Taking SM in China as an example, the reconstructed SM showed high accuracy when validated against multiple sets of in situ measurements, with a root mean square error (RMSE) and a mean absolute error (MAE) of 0.09–0.14 and 0.07–0.13 cm3 cm−3, respectively. Further evaluation with a 10-fold cross-validation revealed median values of the coefficient of determination (R2), RMSE, and MAE of 0.56, 0.025, and 0.019 cm3 cm−3, respectively. The reconstructive performance was noticeably reduced both when excluding one explanatory variable and keeping the other variables unchanged and when removing the spatiotemporal domain strategy or the residual calibration procedure. In comparison with gap-filled SM data based on a satellite-derived diurnal temperature range (DTR), the gap-filled SM data from bias-corrected model-derived DTRs exhibited relatively lower accuracy but higher spatial coverage. Application of our gap-filling approach to long-term SM datasets (2005–2015) produced a promising result (R2=0.72). A more accurate trend was achieved relative to that of the original CCI SM when assessed with in situ measurements (i.e., 0.49 versus 0.28, respectively, in terms of R2). Our findings indicate the feasibility of integrating satellite observations, model-driven knowledge, and spatiotemporal machine learning to fill gaps in short- and long-term SM time series, thereby providing a potential avenue for applications to similar studies.