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Xu, Chong-Yu
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Publications (10 of 66) Show all publications
Reynolds, J. E., Halldin, S., Seibert, J. & Xu, C.-Y. (2018). Definitions of climatological and discharge days: do they matter in hydrological modelling?. Hydrological Sciences Journal, 63(5), 836-844
Open this publication in new window or tab >>Definitions of climatological and discharge days: do they matter in hydrological modelling?
2018 (English)In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 63, no 5, p. 836-844Article in journal (Refereed) Published
Abstract [en]

The performance of hydrological models is affected by uncertainty related to observed climatological and discharge data. Although the latter has been widely investigated, the effects on hydrological models from different starting times of the day have received little interest. In this study, observational data from one tropical basin were used to investigate the effects on a typical bucket-type hydrological model, the HBV, when the definitions of the climatological and discharge days are changed. An optimization procedure based on a genetic algorithm was used to assess the effects on model performance. Nash-Sutcliffe efficiencies varied considerably between day definitions, with the largest dependence on the climatological-day definition. The variation was likely caused by how storm water was assigned to one or two daily rainfall values depending on the definition of the climatological day. Hydrological models are unlikely to predict high flows accurately if rainfall intensities are reduced because of the day definition.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
Keywords
climatological day, discharge day, rainfall-runoff model, daily resolution, regionalization, floods
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-353191 (URN)10.1080/02626667.2018.1451646 (DOI)000430212100010 ()
Available from: 2018-06-12 Created: 2018-06-12 Last updated: 2018-12-05Bibliographically approved
Reynolds, E., Halldin, S., Seibert, J., Xu, C.-Y. & Grabs, T. J. (2018). Robustness of Flood-Model Calibration using Single and Multiple Events. Hydrological Sciences Journal
Open this publication in new window or tab >>Robustness of Flood-Model Calibration using Single and Multiple Events
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2018 (English)In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435Article in journal (Refereed) Submitted
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-368457 (URN)
Funder
Sida - Swedish International Development Cooperation Agency
Available from: 2018-12-04 Created: 2018-12-04 Last updated: 2018-12-05
Fuentes-Andino, D., Beven, K., Kauffeldt, A., Xu, C.-Y., Halldin, S. & Di Baldassarre, G. (2017). Event and model dependent rainfall adjustments to improve discharge predictions. Hydrological Sciences Journal, 62(2), 232-245
Open this publication in new window or tab >>Event and model dependent rainfall adjustments to improve discharge predictions
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2017 (English)In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 62, no 2, p. 232-245Article in journal (Refereed) Published
Abstract [en]

Most conceptual rainfall–runoff models use as input spatially averaged rainfall fields which are typically associated with significant errors that affect the model outcome. In this study, it was hypothesised that a simple spatially and temporally averaged event-dependent rainfall multiplier can account for errors in the rainfall input. The potentials and limitations of this lumped multiplier approach were explored by evaluating the effects of multipliers on the accuracy and precision of the predictive distributions. Parameter sets found to be behavioural across a range of different flood events were assumed to be a good representation of the catchment dynamics and were used to identify rainfall multipliers for each of the individual events. An effect of the parameter sets on identified multipliers was found; however, it was small compared to the differences between events. Accounting for event-dependent multipliers improved the reliability of the predictions. At the cost of a small decrease in precision, the distribution of identified multipliers for past events can be used to account for possible rainfall errors when predicting future events. By using behavioural parameter sets to identify rainfall multipliers, the method offers a simple and computationally efficient way to address rainfall errors in hydrological modelling.

Keywords
rainfall multiplier, rainfall input error, reliability of the predictions, precision of predictions, Topmodel, floods
National Category
Earth and Related Environmental Sciences
Research subject
Earth Science with specialization in Environmental Analysis
Identifiers
urn:nbn:se:uu:diva-291537 (URN)10.1080/02626667.2016.1183775 (DOI)000392602000006 ()
Funder
Sida - Swedish International Development Cooperation Agency, 54100006Swedish National Infrastructure for Computing (SNIC), p2011010
Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2018-09-03Bibliographically approved
Fuentes–Andino, D., Beven, K., Halldin, S., Xu, C.-Y., Reynolds, E. & Di Baldassarre, G. (2017). Reproducing an extreme flood with uncertain post-event information. Hydrology and Earth System Sciences Discussions, 21(7), 3597-3618
Open this publication in new window or tab >>Reproducing an extreme flood with uncertain post-event information
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2017 (English)In: Hydrology and Earth System Sciences Discussions, ISSN 1812-2108, E-ISSN 1812-2116, Vol. 21, no 7, p. 3597-3618Article in journal (Refereed) Published
Abstract [en]

Studies for the prevention and mitigation of floods require information on discharge and extent of inundation, commonly unavailable or uncertain, especially during extreme events. This study was initiated by the devastating flood in Tegucigalpa, the capital of Honduras, when Hurricane Mitch struck the city. In this study we hypothesized that it is possible to estimate, in a trustworthy way considering large data uncertainties, this extreme 1998 flood discharge and the extent of the inundations that followed from a combination of models and post-event measured data. Postevent data collected in 2000 and 2001 were used to estimate discharge peaks, times of peak, and high-water marks. These data were used in combination with rain data from two gauges to drive and constrain a combination of well-known modelling tools: TOPMODEL, Muskingum-Cunge-Todini routing, and the LISFLOOD-FP hydraulic model. Simulations were performed within the generalized likelihood uncertainty estimation (GLUE) uncertainty-analysis framework. The model combination predicted peak discharge, times of peaks, and more than 90% of the observed highwater marks within the uncertainty bounds of the evaluation data. This allowed an inundation likelihood map to be produced. Observed high-water marks could not be reproduced at a few locations on the floodplain. Identifications of these locations are useful to improve model set-up, model structure, or post-event data-estimation methods. Rainfall data were of central importance in simulating the times of peak and results would be improved by a better spatial assessment of rainfall, e. g. from radar data or a denser rain-gauge net-work. Our study demonstrated that it was possible, considering the uncertainty in the post-event data, to reasonably reproduce the extreme Mitch flood in Tegucigalpa in spite of no hydrometric gauging during the event. The method proposed here can be part of a Bayesian framework in which more events can be added into the analysis as they become available.

National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-317261 (URN)10.5194/hess-21-3597-2017 (DOI)000405652200001 ()
Funder
Sida - Swedish International Development Cooperation Agency, 54100006Swedish National Infrastructure for Computing (SNIC), p2011010
Available from: 2017-03-12 Created: 2017-03-12 Last updated: 2018-01-13Bibliographically approved
Reynolds, E., Halldin, S., Xu, C.-Y., Seibert, J. & Kauffeldt, A. (2017). Sub-daily runoff predictions using parameters calibrated on the basis of data with a daily temporal resolution. Journal of Hydrology, 550, 399-411
Open this publication in new window or tab >>Sub-daily runoff predictions using parameters calibrated on the basis of data with a daily temporal resolution
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2017 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 550, p. 399-411Article in journal (Refereed) Published
Abstract [en]

Concentration times in small and medium-sized basins (similar to 10-1000 km(2)) are commonly less than 24 h. Flood-forecasting models are thus required to provide simulations at high temporal resolutions (1 h-6 h), although time-series of input and runoff data with sufficient lengths are often only available at the daily temporal resolution, especially in developing countries. This has led to study the relationships of estimated parameter values at the temporal resolutions where they are needed from the temporal resolutions where they are available. This study presents a methodology to treat empirically model parameter dependencies on the temporal resolution of data in two small basins using a bucket-type hydrological model, HBV-light, and the generalised likelihood uncertainty estimation approach for selecting its parameters. To avoid artefacts due to the numerical resolution or numerical method of the differential equations within the model, the model was consistently run using modelling time steps of one-hour regardless of the temporal resolution of the rainfall-runoff data. The distribution of the parameters calibrated at several temporal resolutions in the two basins did not show model parameter dependencies on the temporal resolution of data and the direct transferability of calibrated parameter sets (e.g., daily) for runoff simulations at other temporal resolutions for which they were not calibrated (e.g., 3 h or 6 h) resulted in a moderate (if any) decrease in model performance, in terms of Nash-Sutcliffe and volume-error efficiencies. The results of this study indicate that if sub-daily forcing data can be secured, flood forecasting in basins with sub-daily concentration times may be possible with model-parameter values calibrated from long time series of daily data. Further studies using more models and basins are required to test the generality of these results.

Keywords
Rainfall-runoff modelling, Parameter transferability, Temporal resolution, Modelling time-step, Flood forecasting
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-330029 (URN)10.1016/j.jhydrol.2017.05.012 (DOI)000404816000032 ()
Funder
Sida - Swedish International Development Cooperation Agency
Available from: 2017-09-29 Created: 2017-09-29 Last updated: 2018-12-05
Ye, X., Li, X., Xu, C.-Y. & Zhang, Q. (2016). Similarity, difference and correlation of meteorological and hydrological drought indices in a humid climate region - the Poyang Lake catchment in China. HYDROLOGY RESEARCH, 47(6), 1211-1223
Open this publication in new window or tab >>Similarity, difference and correlation of meteorological and hydrological drought indices in a humid climate region - the Poyang Lake catchment in China
2016 (English)In: HYDROLOGY RESEARCH, ISSN 1998-9563, Vol. 47, no 6, p. 1211-1223Article in journal (Refereed) Published
Abstract [en]

Based on the estimation of standardized precipitation-evapotranspiration index (SPEI) and standardized runoff index (SRI), this study investigated the variability and correlation of hydrological drought and meteorological drought in a humid climate region - the Poyang Lake catchment in China. Results indicate that the occurrences of hydrological droughts in the catchment are different from those of meteorological drought on both a seasonal and annual basis. However, annual variability of both indices showed the same periodic variation characteristics during the study period. With comparison of the performance of SPEI and SRI time series at different timescales, our observation reveals that the two drought indices show a higher degree of similarity and correlation as timescales increased. In addition, SRI is found to be less variable than SPEI at shorter timescales and it shows an obvious hydrologic delay of about 1-2 months in response to SPEI at timescales > 12 months. Due to hydrologic detention of subsurface soil moisture, shallow groundwater and perhaps reservoir storage, a 2-month timescale of SPEI is found to be more appropriate for river discharge monitoring, especially for those rivers with similar drainage area, climate and geographical conditions as in this study region.

Keywords
drought variability, hydrological drought, meteorological drought, Poyang Lake catchment
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-313548 (URN)10.2166/nh.2016.214 (DOI)000390691700009 ()
Available from: 2017-01-23 Created: 2017-01-20 Last updated: 2018-01-13Bibliographically approved
Zhang, Z., Chen, X., Xu, C.-Y., Hong, Y., Hardy, J. & Sun, Z. (2015). Examining the influence of river-lake interaction on the drought and water resources in the Poyang Lake basin. Journal of Hydrology, 522, 510-521
Open this publication in new window or tab >>Examining the influence of river-lake interaction on the drought and water resources in the Poyang Lake basin
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2015 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 522, p. 510-521Article in journal (Refereed) Published
Abstract [en]

In recent years, the Poyang Lake basin is in a prolonged drought which has placed immense pressure on the water resources utilization. In this paper, we explore the spatial and temporal distributions of extreme droughts in the Poyang Lake basin by using the methods of SPI (Standardized Precipitation Index) and EOF (Empirical Orthogonal Function) for the period of 1956-2009, which are influenced by regional precipitation anomalies and river-lake interaction due to water impounding of the Three Gorges Dam (TGD). The results show that: (I) the Poyang Lake basin experienced six extreme droughts during the past 60 years, which lead to decreases in streamflow from five tributary rivers down to the Poyang Lake. The droughts in the 1960s and the 2000s were the most serious ones. However, there was an increasing trend of streamflow in the upper and middle Yangtze in the 1960s, and a decreasing trend appeared in the 2000s. The decline of streamflow in the upper Yangtze reaches has lowered the water level of lower Yangtze River which has-caused more outflow from the Poyang Lake to the Yangtze River; (2) the operation of the Three Gorges Dam (TGD) has altered the seasonal pattern of flow regimes in the Poyang Lake and significantly reduced the water level in the lower Yangtze River during the TGD impounding period from late September to early November; and (3) the conjunction of extreme droughts in the Poyang lake and the upper Yangtze reaches coincided with the impounding of the TGD is the main cause of the low water level in the Poyang Lake. Although the impact of the recent droughts in the Poyang Lake and upper Yangtze reaches has played a crucial role in the low water level of Poyang lake, more attention should be paid to its sensitivity to the influence of the large dam-induced changes in the interaction between river and lake, particularly during impounding periods.

Keywords
Extreme droughts, Poyang Lake, Yangtze River, The Three Gorges Dam, River-lake interaction
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-251502 (URN)10.1016/j.jhydrol.2015.01.008 (DOI)000350920200042 ()
Available from: 2015-04-23 Created: 2015-04-20 Last updated: 2018-01-11Bibliographically approved
Li, L., Diallo, I., Xu, C.-Y. & Stordal, F. (2015). Hydrological projections under climate change in the near future by RegCM4 in Southern Africa using a large-scale hydrological model. Journal of Hydrology, 528, 1-16
Open this publication in new window or tab >>Hydrological projections under climate change in the near future by RegCM4 in Southern Africa using a large-scale hydrological model
2015 (English)In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 528, p. 1-16Article in journal (Refereed) Published
Abstract [en]

This study aims to provide model estimates of changes in hydrological elements, such as EvapoTranspiration (ET) and runoff, in Southern Africa in the near future until 2029. The climate change scenarios are projected by a high-resolution Regional Climate Model (RCM), RegCM4, which is the latest version of this model developed by the Abdus Salam International Centre for Theoretical Physics (ICTP). The hydrological projections are performed by using a large-scale hydrological model (WASMOD-D), which has been tested and customized on this region prior to this study. The results reveal that (1) the projected temperature shows an increasing tendency over Southern Africa in the near future, especially eastward of 25 degrees E, while the precipitation changes are varying between different months and sub-regions; (2) an increase in runoff (and ET) was found in eastern part of Southern Africa, i.e. Southern Mozambique and Malawi, while a decrease was estimated across the driest region in a wide area encompassing Kalahari Desert, Namibia, southwest of South Africa and Angola; (3) the strongest climate change signals are found over humid tropical areas, i.e. north of Angola and Malawi and south of Dem Rep of Congo; and (4) large spatial and temporal variability of climate change signals is found in the near future over Southern Africa. This study presents the main results of work-package 2 (WP2) of the 'Socioeconomic Consequences of Climate Change in Sub-equatorial Africa (SoCoCA)' project, which is funded by the Research Council of Norway.

Keywords
Large-scale hydrological model, Climate change, RegCM4, Southern Africa, Near future
National Category
Oceanography, Hydrology and Water Resources Climate Research
Identifiers
urn:nbn:se:uu:diva-261225 (URN)10.1016/j.jhydrol.2015.05.028 (DOI)000358968200001 ()
Available from: 2015-09-08 Created: 2015-08-31 Last updated: 2018-01-11Bibliographically approved
Kauffeldt, A., Halldin, S., Pappenberger, F., Wetterhall, F., Xu, C.-Y. & Cloke, H. L. (2015). Imbalanced land surface water budgets in a numerical weather prediction system. Geophysical Research Letters, 42(11), 4411-4417
Open this publication in new window or tab >>Imbalanced land surface water budgets in a numerical weather prediction system
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2015 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 11, p. 4411-4417Article in journal (Refereed) Published
Abstract [en]

There has been a significant increase in the skill and resolution of numerical weather prediction models (NWPs) in recent decades, extending the time scales of useful weather predictions. The land surface models (LSMs) of NWPs are often employed in hydrological applications, which raises the question of how hydrologically representative LSMs really are. In this paper, precipitation (P), evaporation (E), and runoff (R) from the European Centre for Medium-Range Weather Forecasts global models were evaluated against observational products. The forecasts differ substantially from observed data for key hydrological variables. In addition, imbalanced surface water budgets, mostly caused by data assimilation, were found on both global (P-E) and basin scales (P-E-R), with the latter being more important. Modeled surface fluxes should be used with care in hydrological applications, and further improvement in LSMs in terms of process descriptions, resolution, and estimation of uncertainties is needed to accurately describe the land surface water budgets.

Keywords
water budget, data assimilation, runoff, reanalysis, precipitation
National Category
Geophysics Geology
Identifiers
urn:nbn:se:uu:diva-260141 (URN)10.1002/2015GL064230 (DOI)000357511200021 ()
Available from: 2015-08-18 Created: 2015-08-17 Last updated: 2017-12-04Bibliographically approved
Li, B.-d., Zhang, X.-h., Xu, C.-Y., Zhang, H. & Song, J.-x. (2015). Water balance between surface water and groundwater in the withdrawal process: a case study of the Osceola watershed. Hydrological Research, 46(6), 943-953
Open this publication in new window or tab >>Water balance between surface water and groundwater in the withdrawal process: a case study of the Osceola watershed
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2015 (English)In: Hydrological Research, ISSN 1998-9563, Vol. 46, no 6, p. 943-953Article in journal (Refereed) Published
Abstract [en]

A generalized hierarchical approach with a water balance function is introduced to simulate stream-flow depletion in a complex groundwater system in Osceola County. The groundwater flow system at the site, because of the complex interaction between ambient streams, exhibits a unique multi-scale pattern that proves to be difficult to simulate using standard modelling tools. The hierarchical modelling system was first calibrated to water level measurements collected from monitoring wells. Afterwards, systematic hierarchical simulations and integrated water budget analyses were performed to evaluate the adverse resource impact of the ongoing water withdrawal. The multi-scale process-based results from this generic hierarchical modelling system provided critical storage and flux information that can be used to comprehensively assess the pros and cons of water resource development and management, such as artificial water withdrawal.

Keywords
hierarchical approach; stream-flow depletion; three-dimensional model; water balance
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-271094 (URN)10.2166/nh.2015.137 (DOI)000368317600008 ()
Available from: 2016-01-05 Created: 2016-01-05 Last updated: 2018-01-10Bibliographically approved
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