| 1. |
- Koster, R. D., et al.
(författare)
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The Second Phase of the Global Land–Atmosphere Coupling Experiment: Soil Moisture Contributions to Subseasonal Forecast Skill
- 2011
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Ingår i: Journal of Hydrometeorology. - : American Meteorological Society. - 1525-755X .- 1525-7541. ; 12:5, s. 805-822
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Tidskriftsartikel (refereegranskat)abstract
- The second phase of the Global Land–Atmosphere Coupling Experiment (GLACE-2) is a multi-institutional numerical modeling experiment focused on quantifying, for boreal summer, the subseasonal (out to two months) forecast skill for precipitation and air temperature that can be derived from the realistic initialization of land surface states, notably soil moisture. An overview of the experiment and model behavior at the global scale is described here, along with a determination and characterization of multimodel “consensus” skill. The models show modest but significant skill in predicting air temperatures, especially where the rain gauge network is dense. Given that precipitation is the chief driver of soil moisture, and thereby assuming that rain gauge density is a reasonable proxy for the adequacy of the observational network contributing to soil moisture initialization, this result indeed highlights the potential contribution of enhanced observations to prediction. Land-derived precipitation forecast skill is much weaker than that for air temperature. The skill for predicting air temperature, and to some extent precipitation, increases with the magnitude of the initial soil moisture anomaly. GLACE-2 results are examined further to provide insight into the asymmetric impacts of wet and dry soil moisture initialization on skill.
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| 2. |
- Seibert, Jan
(författare)
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Hydrological Modeling to Evaluate Climate Model Simulations and Their Bias Correction
- 2018
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Ingår i: Journal of Hydrometeorology. - 1525-755X .- 1525-7541. ; 19, s. 1321-1337
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Tidskriftsartikel (refereegranskat)abstract
- Variables simulated by climate models are usually evaluated independently. Yet, climate change impacts often stem from the combined effect of these variables, making the evaluation of intervariable relationships essential. These relationships can be evaluated in a statistical framework (e.g., using correlation coefficients), but this does not test whether complex processes driven by nonlinear relationships are correctly represented. To overcome this limitation, we propose to evaluate climate model simulations in a more process-oriented framework using hydrological modeling. Our modeling chain consists of 12 regional climate models (RCMs) from the Coordinated Downscaling Experiment-European Domain (EURO-CORDEX) forced by five general circulation models (GCMs), eight Swiss catchments, 10 optimized parameter sets for the hydrological model Hydrologiska Byrans Vattenbalansavdelning (HBV), and one bias correction method [quantile mapping (QM)]. We used seven discharge metrics to explore the representation of different hydrological processes under current climate. Specific combinations of biases in GCM-RCM simulations can lead to significant biases in simulated discharge (e.g., excessive precipitation in the winter months combined with a cold temperature bias). Other biases, such as exaggerated snow accumulation, do not necessarily impact temperature over the historical period to the point where discharge is affected. Our results confirm the importance of bias correction; when all catchments, GCM-RCMs, and discharge metrics were considered, QM improved discharge simulations in the vast majority of all cases. Additionally, we present a ranking of climate models according to their hydrological performance. Ranking GCM-RCMs is most meaningful prior to bias correction since QM reduces differences between GCM-RCM-driven hydrological simulations. Overall, this work introduces a multivariate assessment method of GCM-RCMs, which enables a more process-oriented evaluation of their simulations.
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| 3. |
- Springer, Anne, et al.
(författare)
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New Estimates of Variations in Water Flux and Storage over Europe Based on Regional (Re)Analyses and Multisensor Observations
- 2014
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Ingår i: Journal of Hydrometeorology. - 1525-755X .- 1525-7541. ; 15:6, s. 2397-2417
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation minus evapotranspiration, the net flux of water between the atmosphere and Earth's surface, links atmospheric and terrestrial water budgets and thus represents an important boundary condition for both climate modeling and hydrological studies. However, the atmospheric-terrestrial flux is poorly constrained by direct observations because of a lack of unbiased measurements. Thus, it is usually reconstructed from atmospheric reanalyses. Via the terrestrial water budget equation, water storage estimates from the Gravity Recovery and Climate Experiment (GRACE) combined with measured river discharge can be used to assess the realism of the atmospheric-terrestrial flux in models. In this contribution, the closure of the terrestrial water budget is assessed over a number of European river basins using the recently reprocessed GRACE release 05 data, together with precipitation and evapotranspiration from the operational analyses of high-resolution, limited-area NWP models [Consortium for Small-Scale Modelling, German version (COSMO-DE) and European version (COSMO-EU)] and the new COSMO 6-km reanalysis (COSMO-REA6) for the European Coordinated Regional Climate Downscaling Experiment (CORDEX) domain. These closures are compared to those obtained with global reanalyses, land surface models, and observation-based datasets. The spatial resolution achieved with the recent GRACE data allows for better evaluation of the water budget in smaller river basins than before and for the identification of biases up to 25 mm month(-1) in the different products. Variations of deseasoned and detrended atmospheric-terrestrial flux are found to agree notably well with flux derived from GRACE and discharge data with correlations up to 0.75. Finally, bias-corrected fluxes are derived from various data combinations, and from this, a 20-yr time series of catchment-integrated water storage variations is reconstructed.
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| 4. |
- Sun, H., et al.
(författare)
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Corrected ERA5 Precipitation by Machine Learning Significantly Improved Flow Simulations for the Third Pole Basins
- 2022
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Ingår i: Journal of Hydrometeorology. - : American Meteorological Society. - 1525-755X .- 1525-7541. ; 23:10, s. 1663-1679
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation is one of the most important atmospheric inputs to hydrological models. However, existing precipitation datasets for the Third Pole (TP) basins show large discrepancies in precipitation magnitudes and spatiotemporal patterns, which poses a great challenge to hydrological simulations in the TP basins. In this study, a gridded (10 km x 10 km) daily precipitation dataset is constructed through a random-forest-based machine learning algorithm (RF algorithm) correction of the ERA5 precipitation estimates based on 940 gauges in 11 upper basins of TP for 1951-2020. The dataset is evaluated by gauge observations at point scale and is inversely evaluated by the Variable Infiltration Capacity (VIC) hydrological model linked with a glacier melt algorithm (VIC-Glacier). The corrected ERA5 (ERA5_cor) agrees well with gauge observations after eliminating the severe overestimation in the original ERA5 precipitation. The corrections greatly reduce the original ERA5 precipitation estimates by 10%-50% in 11 basins of the TP and present more details on precipitation spatial variability. The inverse hydrological model evaluation demonstrates the accuracy and rationality, and we provide an updated estimate of runoff components contribution to total runoff in seven upper basins in the TP based on the VIC-Glacier model simulations with the ERA5_cor precipitation. This study provides good precipitation estimates with high spatiotemporal resolution for 11 upper basins in the TP, which are expected to facilitate the hydrological modeling and prediction studies in this high mountainous region. Significance StatementThe Third Pole (TP) is the source of water to the people living in the areas downstream. Precipitation is the key driver of the terrestrial hydrological cycle and the most important atmospheric input to land surface hydrological models. However, none of the current precipitation data are equally good for all the TP basins because of high variabilities in their magnitudes and spatiotemporal patterns, posing a great challenge to the hydrological simulation. Therefore, in this study, a gridded daily precipitation dataset (10 km x 10 km) is reconstructed through a random-forest-based machine learning algorithm correction of ERA5 precipitation estimates based on 940 gauges in 11 TP basins for 1951-2020. The data eliminate the severe overestimation of original ERA5 precipitation estimates and present more reasonable spatial variability, and also exhibit a high potential for hydrological application in the TP basins. This study provides long-term precipitation data for climate and hydrological studies and a reference for deriving precipitation in high mountainous regions with complex terrain and limited observations.
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| 5. |
- Titley, H. A., et al.
(författare)
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Key Factors Influencing the Severity of Fluvial Flood Hazard from Tropical Cyclones
- 2021
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Ingår i: Journal of Hydrometeorology. - : American Meteorological Society. - 1525-755X .- 1525-7541. ; 22:7, s. 1801-1817
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the key drivers of the severity of river flooding from tropical cyclones (TCs) is vital for emergency preparedness and disaster risk reduction activities. This global study examines landfalling TCs in the decade from 2010 to 2019 to identify those characteristics that influence whether a storm has an increased flood hazard. The highest positive correlations are found between flood severity and the total precipitation associated with the TC. Significant negative correlations are found between flood severity and the translation speed of the TC, indicating that slower-moving storms that rain over an area for longer tend to have higher flood severity. Larger and more intense TCs increase the likelihood of having a larger area affected by severe flooding but not its duration or magnitude, and it is found that the fluvial flood hazard can be severe in all intensity categories of TC, including those of tropical storm strength. Catchment characteristics such as antecedent soil moisture and slope also play a role in modulating flood severity, and severe flooding is more likely in cases in which multiple drivers are present. The improved knowledge of the key drivers of fluvial flooding in TCs can help to inform research priorities to help with flood early warning, such as increasing the focus on translation speed in model evaluation and impact-based forecasting. Significance Statement Knowing ahead of landfall which TCs are likely to lead to significant river flooding will help those responsible for emergency planning make appropriate decisions to minimize loss of life and property. We compare 280 TCs and find that the cases with slow-moving, large, and intense cyclones, affecting areas with wet antecedent conditions, have the highest likelihood of experiencing widespread flooding. Slower-moving storms also have an increased risk of longer and more extreme floods. Our results show the importance of considering aspects such as the speed of forward movement along the whole flood early warning chain, from model evaluation and development, through to warning design and communication, to better inform forecast-based action prior to TC landfall.
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| 6. |
- Zhang, Aoqi, et al.
(författare)
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Structure of Cyclonic Precipitation in the Northern Pacific Storm Track Measured by GPM DPR
- 2020
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Ingår i: Journal of Hydrometeorology. - 1525-755X .- 1525-7541. ; 21:2, s. 227-240
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Tidskriftsartikel (refereegranskat)abstract
- Despite the long existence of theoretical studies, few statistical studies of precipitation characteristics on the northern Pacific storm track have been reported due to lack of observation. Using data from GPM DPR and ERA-Interim, we examined the precipitation features of extratropical cyclones in the northern Pacific storm-track region. Extratropical cyclones were classified into four categories including developing, mature, dissipating, and short-term based on their life stages. Our results show that extratropical cyclones of all categories had a comma rainband and precipitation mostly occurred to the east of the cyclonic center. The extratropical cyclones promote precipitation to the east of their centers, but suppress precipitation to the west. Precipitation to the east of the extratropical cyclones had larger and more condensed droplets, a stronger intensity, and a higher rain top than the local seasonal average, while the opposite characteristics were seen to the west. Our results suggest that the different types of vertical air motion and moisture content in these two regions induced by the frontal structure of extratropical cyclones play important roles in the different impact of extratropical cyclones. Furthermore, the different life stages of extratropical cyclones had different degrees of impact on precipitation: the highest impact in the developing stage, followed by the mature stage, and the weakest impact in the dissipating stage.
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| 7. |
- Zhang, Chi, et al.
(författare)
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Moisture source changes contributed to different precipitation changes over the northern and southern Tibetan Plateau
- 2019
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Ingår i: Journal of Hydrometeorology. - 1525-755X .- 1525-7541. ; 20:2, s. 217-229
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Tidskriftsartikel (refereegranskat)abstract
- © 2019 American Meteorological Society. Precipitation on the Tibetan Plateau (TP) showed different spatial changes during 1979-2016, with an increasing trend over the northern Tibetan Plateau (NTP) and a slightly negative trend over the southern Tibetan Plateau (STP). The changes in precipitation moisture sources over the NTP and STP are investigated using the improved Water Accounting Model with an atmospheric reanalysis as well as observational precipitation and evaporation data. The results show the region in the northwest (region NW), ranging from the TP to Europe dominated by the westerlies, provides 38.9% of precipitation moisture for the NTP, and the region in the southeast (region SE), ranging from the TP to the Indian Ocean and Indochina dominated by the Asian monsoons, provides 51.4% of precipitation moisture for the STP. For the precipitation increase over the NTP, the SE and TP are the main contributors, contributing around 35.8% and 51.7% of the increase, respectively. The contributions from the SE and TP to the STP are, however, minor and insignificant. Meanwhile, the NW shows a negative trend of -4.2 ± 2.9mmyr -1 decade -1 (significant at the 0.01 level), which contributes to the negative precipitation trend over the STP. Results during the wet season indicate that moisture sources from the areas dominated by the Asian monsoons have contributed more precipitated moisture for the NTP, but not for the STP. Further analysis reveals that precipitated moisture originating from the Indian subcontinent has increased for the NTP while it has decreased for the STP during 1979-2016.
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| 8. |
- Zsoter, Ervin, et al.
(författare)
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How Well Do Operational Numerical Weather Prediction Configurations Represent Hydrology?
- 2019
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Ingår i: Journal of Hydrometeorology. - : AMER METEOROLOGICAL SOC. - 1525-755X .- 1525-7541. ; 20:8, s. 1533-1552
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Tidskriftsartikel (refereegranskat)abstract
- Land surface models (LSMs) have traditionally been designed to focus on providing lower-boundary conditions to the atmosphere with less focus on hydrological processes. State-of-the-art application of LSMs includes a land data assimilation system (LDAS), which incorporates available land surface observations to provide an improved realism of surface conditions. While improved representations of the surface variables (such as soil moisture and snow depth) make LDAS an essential component of any numerical weather prediction (NWP) system, the related increments remove or add water, potentially having a negative impact on the simulated hydrological cycle by opening the water budget. This paper focuses on evaluating how well global NWP configurations are able to support hydrological applications, in addition to the traditional weather forecasting. River discharge simulations from two climatological reanalyses are compared: one "online" set, which includes land-atmosphere coupling and LDAS with an open water budget, and an "offline" set with a closed water budget and no LDAS. It was found that while the online version of the model largely improves temperature and snow depth conditions, it causes poorer representation of peak river flow, particularly in snowmelt-dominated areas in the high latitudes. Without addressing such issues there will never be confidence in using LSMs for hydrological forecasting applications across the globe. This type of analysis should be used to diagnose where improvements need to be made; considering the whole Earth system in the data assimilation and coupling developments is critical for moving toward the goal of holistic Earth system approaches.
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| 9. |
- Ali Maher, Osama, et al.
(författare)
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Comparison between two extreme NAO winters and consequences on the thermal regime of Lake Vendyurskoe, Karelia
- 2005
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Ingår i: Journal of Hydrometeorology. - 1525-755X. ; 6:5, s. 775-783
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Tidskriftsartikel (refereegranskat)abstract
- For 10 consecutive winters, measurements were carried out in Lake Vendyurskoe, Karelia, Russia. The aim of these measurements was to investigate some of the physical processes in this small shallow lake during its ice-covered period. Detailed measurements of ice thickness and condition, snow thickness, water temperature, salt content, and currents were developed into a database. Within this database are the winters 1994/95 and 1995/96, which are characterized by a very sharp change between positive and negative phases of the North Atlantic Oscillation (NAO). This note investigates and compares the effects of these two NAO phases on the regional climate and their relation to the thermal regime of Lake Vendyurskoe. It became clear that the ice-covered period length did not vary much from one winter to the other; however, a large difference was observed in the maximum average ice cover thickness and in the average water temperature at ice formation ( e. g., larger thickness and colder water temperature during the 1995/ 96 winter).
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| 10. |
- Chen, Cheng, et al.
(författare)
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Performance of multiple satellite precipitation estimates over a typical arid mountainous area of China : Spatiotemporal patterns and extremes
- 2020
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Ingår i: Journal of Hydrometeorology. - 1525-755X. ; 21:3, s. 533-550
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation in arid mountainous areas is characterized by low rainfall intensity and large spatial heterogeneity, which challenges satellite-based monitoring by the spaceborne sensors. This study aims to comparatively evaluate the detection ability of spatiotemporal patterns and extremes of rainfall by a range of mainstream satellite precipitation products [TMPA, Climate Hazards Group Infrared Precipitation with Station Data (CHIRPS), and PERSIANN-Climate Data Record (PERSIANN-CDR)] over a typical arid mountainous basin of China, benchmarking against rain gauge data from 2000 to 2015. Results showed that satellite precipitation estimates had relatively low accuracy at the daily scale, while a significant improvement of correlation coefficient (CC;>0.6) and a significant reduction of relative root-mean-square error (RRMSE;, 1.0) were found as time scale increases beyond the monthly scale. CHIRPS tended to overestimate the gauge precipitation with positive relative bias (RB), while the negative RBvalues for TMPAand PERSIANN-CDR indicated there was an underestimation. CHIRPS had the most similar spatial pattern and slope trends of the seasonal precipitation and interannual variations of annual precipitation with gauge observations. With the increase in rainfall rates, the probability of detection (POD) and critical success index (CSI) were reduced and the false alarm ratio (FAR) was increased significantly, demonstrating the limited capability for all the three satellite products for detecting heavy rainfall events. CHIRPS showed the best performance in detecting rainfall extremes compared to TMPA and PERSIANN-CDR, evidenced by the largerCSI values and similar extreme rainfall indices obtained from gauge records. This study provides valuable guidance for choosing satellite precipitation products instead of gauge observations for rainfall monitoring (especially rainfall extremes) and agricultural production management over arid mountainous area.
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