Lei Wang | Chinese Academy of Sciences (original) (raw)
Papers by Lei Wang
Water
Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at dow... more Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at downstream regions during the monsoon season (June to September). This paper presents comprehensive hazard mapping and risk assessments in the downstream region of the Karnali River basin for different return-period floods, with the aid of the HEC-RAS (Hydrologic Engineering Center’s River Analysis System). The assessment was conducted on a ~38 km segment of the Karnali River from Chisapani to the Nepal–India border. To perform hydrodynamic simulations, a long-term time series of instantaneous peak discharge records from the Chisapani gauging station was collected. Flooding conditions representing 2-, 5-, 10-, 50-, 100-, 200-, and 1000-year return periods (YRPs) were determined using Gumbel’s distribution. With an estimated peak discharge of up to 29,910 m3/s and the flood depths up to 23 m in the 1000-YRP, the area vulnerable to flooding in the study domain extends into regions on both the...
Monitoring changes in river runoff at the Third Pole (TP) is important because rivers in this reg... more Monitoring changes in river runoff at the Third Pole (TP) is important because rivers in this region support millions of inhabitants in Asia and are very sensitive to climate change. Under the influence of climate change and intensified cryospheric melt, river runoff has changed markedly at the TP, with significant effects on the spatial and temporal water resource distribution that threaten water supply and food security for people living downstream. Despite some in situ observations and discharge estimates from state-of-the-art remote sensing technology, the total river runoff (TRR) for the TP has never been reliably quantified, and its response to climate change remains unclear. As part of the Chinese Academy of Sciences' "Pan-Third Pole Environment Study for a Green Silk Road," the TP-River project aims to construct a comprehensive runoff observation network at mountain outlets (where rivers leave the mountains and enter the plains) for 13 major rivers in the TP region, thereby enabling TRR to be accurately quantified. The project also integrates discharge estimates from remote sensing and cryosphere-hydrology modeling to investigate long-term changes in TRR and the relationship between the TRR variations and westerly/monsoon. Based on recent efforts, the project provides the first estimate (656 ± 23 billion m 3) of annual TRR for the 13 TP rivers in 2018. The annual river runoff at the mountain outlets varies widely between the different TP rivers, ranging from 2 to 176 billion m 3 , with higher values mainly corresponding to rivers in the Indian monsoon domain, rather than in the westerly domain.
Science Bulletin
A new pollen record of the last 2.8 Ma from the Co Ngoin,central Tibetan Plateau Science in China... more A new pollen record of the last 2.8 Ma from the Co Ngoin,central Tibetan Plateau Science in China Series DEarth Sciences 44, 292 (2001); New evidence from stable isotope for the uplift of mountains in northern edge of the Qinghai-Tibetan Plateau Science in China Series B-Chemistry 45, 1 (2002); New proofs of the recent climate warming over the Tibetan Plateau as a result of the increasing greenhouse gases emissions
The Tibetan Plateau (TP) is the highest plateau in the world, playing an essential role in Asian ... more The Tibetan Plateau (TP) is the highest plateau in the world, playing an essential role in Asian monsoon development and concurrent water and energy cycles. In this study, the Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) was calibrated and used to simulate water and energy cycles in a central TP watershed during the summer season. The model was first calibrated at a point scale (BJ site). The simulation results show that the model can successfully reproduce energy fluxes and soil surface temperature with acceptable accuracies. The model was further calibrated at basin scale, using observed discharges in summer 1998 and the entire year of 1999. The model successfully reproduced discharges near the basin outlet (Nash-Sutcliffe efficiency coefficients 0.60 and 0.62 in 1998 and 1999, respectively). Finally, the model was validated using MODIS land surface temperature (LST) data and measured soil water content (SWC) at 15 points within the watershed in 2010. The simulation results show that the model successfully reproduced the spatial pattern and LST means in both nighttime and daytime. Furthermore, the model can generally reproduce 15-site averaged SWC in four soil layers, with small bias error and root mean square error. Despite the absence of long-term discharge
data for model verification, we validated it using MODIS LST and measured SWC data. This showed that the WEB-DHM has the potential for use in poorly gauged or ungauged
areas such as the TP. This could improve understanding of water and energy cycles in these areas.
Land surface hydrological modeling is sensitive to near-surface air temperature, which is especia... more Land surface hydrological modeling is sensitive to near-surface air temperature, which is especially true for the cryosphere. The lapse rate of near-surface air temperature is a critical parameter when interpolating air temperature from station data to gridded cells. To obtain spatially distributed, fine-resolution near-surface (2 m) air temperature in the mainland China, monthly air temperature from 553 Chinese national meteorological stations (with continuous data from 1962 to 2011) are divided into 24 regional groups to analyze spatiotemporal variations of lapse rate in relation to surface air temperature and
relative humidity. The results are as follows: (1) Evaluation of estimated lapse rate shows that the estimates are reasonable and useful for temperature-related analyses and modeling studies. (2) Lapse rates generally have a banded spatial distribution from southeast to northwest, with relatively large values on the Tibetan Plateau and in northeast China. The greatest spatial variability is in winter with a range of 0.3°C–0.9°C · 100m1, accompanied
by an inversion phenomenon in the northern Xinjiang Province. In addition, the lapse rates show a clear seasonal cycle. (3) The lapse rates maintain a consistently positive correlation
with temperature in all seasons, and these correlations are more prevalent in the north and
east. The lapse rates exhibit a negative relationship with relative humidity in all seasons,
especially in the east. (4) Substantial regional differences in temporal lapse rate trends over the study period are identified. Increasing lapse rates are more pronounced in northern China, and decreasing trends are found in southwest China, which are more notable in
winter. An overall increase of air temperature and regional variation of relative humidity together influenced the change of lapse rate.
For the purpose of real-time dam operation in large river basins, an integrated simulation and op... more For the purpose of real-time dam operation in large river basins, an integrated simulation and optimization system (ISOS) has been constructed by combining distributed hydrological inflow predictions with rolling horizon decision making. First, with operational quantitative
precipitation forecasts (QPFs) over a forecast horizon (FH), the ISOS is applied to obtain an optimal rule for dam releases; second, with the corrected satellite precipitation, the prescribed rule is employed for the reservoir operation over a decision horizon (DH). The ISOS is applied to the Red River Basin (169,000 km2), to test its performance for optimizing multidam releases in the large river basin. Results show that by using the ISOS, two things were simultaneously achieved, reducing the water level at Hanoi to avoid flooding while raising water storage in Hoa Binh reservoir at the end of flood season for better hydropower generation. Through comparing reservoir performances with different FHs, the effective forecast horizon (EFH) was derived for the 3-reservoir system in the Red River.
Adequate estimation of the spatial distribution of snowfall is critical in hydrologic modelling. ... more Adequate estimation of the spatial distribution
of snowfall is critical in hydrologic modelling. However,
this is a well-known problem in estimating basinscale
snowfall, especially in mountainous basins with data
scarcity. This study focuses on correction and estimation
of this spatial distribution, which considers topographic effects
within the basin. A method is proposed that optimises
an altitude-based snowfall correction factor (Cfsnow).
This is done through multi-objective calibration of a spatially
distributed, multilayer energy and water balance-based
snowmelt model (WEB-DHM-S) with observed discharge
and remotely sensed snow cover data from the Moderate Resolution
Imaging Spectroradiometer (MODIS). The Shuffled
Complex Evolution–University of Arizona (SCE–UA) automatic
search algorithm is used to obtain the optimal value of
Cfsnow for minimum cumulative error in discharge and snow
cover simulations. Discharge error is quantified by Nash–
Sutcliffe efficiency and relative volume deviation, and snow
cover error was estimated by pixel-by-pixel analysis. The
study region is the heavily snow-fed Yagisawa Basin of the
Upper Tone River in northeast Japan. First, the system was
applied to one snow season (2002–2003), obtaining an optimised
Cfsnow of 0.0007m−1. For validation purposes, the optimised
Cfsnow was implemented to correct snowfall in 2004,
2002 and 2001. Overall, the system was effective, implying
improvements in correlation of simulated versus observed
discharge and snow cover. The 4 yr mean of basin-average
snowfall for the corrected spatial snowfall distribution was
1160mm (780mm before correction). Execution of sensitivity
runs against other model input and parameters indicated
that Cfsnow could be affected by uncertainty in shortwave radiation
and setting of the threshold air temperature parameter.
Our approach is suitable to correct snowfall and estimate
its distribution in poorly gauged basins, where elevation
dependence of snowfall amount is strong.
Evapotranspiration (E) at regional or basin scale is difficult to estimate. This study estimates ... more Evapotranspiration (E) at regional or basin scale is difficult to estimate. This study estimates E with a
water balance method for the upper Yellow River and Yangtze River basins on the Tibetan Plateau, where
in situ data accessibility is especially insufficient. Results indicate that annual terrestrial water storage
change in the two basins is negligible, and basin-scale E can be reliably estimated by the difference
between precipitation and runoff. Thus, four E products from Zhang—(Zhang_E), MODIS (MODIS_E), Japanese
25-year reanalysis product (JRA_E), and the newly published Global Land Data Assimilation System
with Noah Land Surface Model-2 (GLDAS_E)—are evaluated against E estimated by the water balance
method. GLDAS_E and Zhang_E had the best performance for the upper Yellow River basin and Yangtze
River basin, respectively, with relatively small underestimation. Further analysis showed that the underestimation
of GLDAS_E was mainly caused by its negative bias for precipitation, whereas the overestimation
of JRA_E was due to overestimation of downward shortwave radiation. MODIS_E greatly
overestimated E in both basins, which was also caused by high downward shortwave radiation flux
inputs from the Global Modeling and Assimilation Office. Thus, more accurate forcing data for these products
should be a future focus, since they can improve E estimates, at least for the Tibetan Plateau.
Water
Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at dow... more Originating from the southern slope of Himalaya, the Karnali River poses a high flood risk at downstream regions during the monsoon season (June to September). This paper presents comprehensive hazard mapping and risk assessments in the downstream region of the Karnali River basin for different return-period floods, with the aid of the HEC-RAS (Hydrologic Engineering Center’s River Analysis System). The assessment was conducted on a ~38 km segment of the Karnali River from Chisapani to the Nepal–India border. To perform hydrodynamic simulations, a long-term time series of instantaneous peak discharge records from the Chisapani gauging station was collected. Flooding conditions representing 2-, 5-, 10-, 50-, 100-, 200-, and 1000-year return periods (YRPs) were determined using Gumbel’s distribution. With an estimated peak discharge of up to 29,910 m3/s and the flood depths up to 23 m in the 1000-YRP, the area vulnerable to flooding in the study domain extends into regions on both the...
Monitoring changes in river runoff at the Third Pole (TP) is important because rivers in this reg... more Monitoring changes in river runoff at the Third Pole (TP) is important because rivers in this region support millions of inhabitants in Asia and are very sensitive to climate change. Under the influence of climate change and intensified cryospheric melt, river runoff has changed markedly at the TP, with significant effects on the spatial and temporal water resource distribution that threaten water supply and food security for people living downstream. Despite some in situ observations and discharge estimates from state-of-the-art remote sensing technology, the total river runoff (TRR) for the TP has never been reliably quantified, and its response to climate change remains unclear. As part of the Chinese Academy of Sciences' "Pan-Third Pole Environment Study for a Green Silk Road," the TP-River project aims to construct a comprehensive runoff observation network at mountain outlets (where rivers leave the mountains and enter the plains) for 13 major rivers in the TP region, thereby enabling TRR to be accurately quantified. The project also integrates discharge estimates from remote sensing and cryosphere-hydrology modeling to investigate long-term changes in TRR and the relationship between the TRR variations and westerly/monsoon. Based on recent efforts, the project provides the first estimate (656 ± 23 billion m 3) of annual TRR for the 13 TP rivers in 2018. The annual river runoff at the mountain outlets varies widely between the different TP rivers, ranging from 2 to 176 billion m 3 , with higher values mainly corresponding to rivers in the Indian monsoon domain, rather than in the westerly domain.
Science Bulletin
A new pollen record of the last 2.8 Ma from the Co Ngoin,central Tibetan Plateau Science in China... more A new pollen record of the last 2.8 Ma from the Co Ngoin,central Tibetan Plateau Science in China Series DEarth Sciences 44, 292 (2001); New evidence from stable isotope for the uplift of mountains in northern edge of the Qinghai-Tibetan Plateau Science in China Series B-Chemistry 45, 1 (2002); New proofs of the recent climate warming over the Tibetan Plateau as a result of the increasing greenhouse gases emissions
The Tibetan Plateau (TP) is the highest plateau in the world, playing an essential role in Asian ... more The Tibetan Plateau (TP) is the highest plateau in the world, playing an essential role in Asian monsoon development and concurrent water and energy cycles. In this study, the Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) was calibrated and used to simulate water and energy cycles in a central TP watershed during the summer season. The model was first calibrated at a point scale (BJ site). The simulation results show that the model can successfully reproduce energy fluxes and soil surface temperature with acceptable accuracies. The model was further calibrated at basin scale, using observed discharges in summer 1998 and the entire year of 1999. The model successfully reproduced discharges near the basin outlet (Nash-Sutcliffe efficiency coefficients 0.60 and 0.62 in 1998 and 1999, respectively). Finally, the model was validated using MODIS land surface temperature (LST) data and measured soil water content (SWC) at 15 points within the watershed in 2010. The simulation results show that the model successfully reproduced the spatial pattern and LST means in both nighttime and daytime. Furthermore, the model can generally reproduce 15-site averaged SWC in four soil layers, with small bias error and root mean square error. Despite the absence of long-term discharge
data for model verification, we validated it using MODIS LST and measured SWC data. This showed that the WEB-DHM has the potential for use in poorly gauged or ungauged
areas such as the TP. This could improve understanding of water and energy cycles in these areas.
Land surface hydrological modeling is sensitive to near-surface air temperature, which is especia... more Land surface hydrological modeling is sensitive to near-surface air temperature, which is especially true for the cryosphere. The lapse rate of near-surface air temperature is a critical parameter when interpolating air temperature from station data to gridded cells. To obtain spatially distributed, fine-resolution near-surface (2 m) air temperature in the mainland China, monthly air temperature from 553 Chinese national meteorological stations (with continuous data from 1962 to 2011) are divided into 24 regional groups to analyze spatiotemporal variations of lapse rate in relation to surface air temperature and
relative humidity. The results are as follows: (1) Evaluation of estimated lapse rate shows that the estimates are reasonable and useful for temperature-related analyses and modeling studies. (2) Lapse rates generally have a banded spatial distribution from southeast to northwest, with relatively large values on the Tibetan Plateau and in northeast China. The greatest spatial variability is in winter with a range of 0.3°C–0.9°C · 100m1, accompanied
by an inversion phenomenon in the northern Xinjiang Province. In addition, the lapse rates show a clear seasonal cycle. (3) The lapse rates maintain a consistently positive correlation
with temperature in all seasons, and these correlations are more prevalent in the north and
east. The lapse rates exhibit a negative relationship with relative humidity in all seasons,
especially in the east. (4) Substantial regional differences in temporal lapse rate trends over the study period are identified. Increasing lapse rates are more pronounced in northern China, and decreasing trends are found in southwest China, which are more notable in
winter. An overall increase of air temperature and regional variation of relative humidity together influenced the change of lapse rate.
For the purpose of real-time dam operation in large river basins, an integrated simulation and op... more For the purpose of real-time dam operation in large river basins, an integrated simulation and optimization system (ISOS) has been constructed by combining distributed hydrological inflow predictions with rolling horizon decision making. First, with operational quantitative
precipitation forecasts (QPFs) over a forecast horizon (FH), the ISOS is applied to obtain an optimal rule for dam releases; second, with the corrected satellite precipitation, the prescribed rule is employed for the reservoir operation over a decision horizon (DH). The ISOS is applied to the Red River Basin (169,000 km2), to test its performance for optimizing multidam releases in the large river basin. Results show that by using the ISOS, two things were simultaneously achieved, reducing the water level at Hanoi to avoid flooding while raising water storage in Hoa Binh reservoir at the end of flood season for better hydropower generation. Through comparing reservoir performances with different FHs, the effective forecast horizon (EFH) was derived for the 3-reservoir system in the Red River.
Adequate estimation of the spatial distribution of snowfall is critical in hydrologic modelling. ... more Adequate estimation of the spatial distribution
of snowfall is critical in hydrologic modelling. However,
this is a well-known problem in estimating basinscale
snowfall, especially in mountainous basins with data
scarcity. This study focuses on correction and estimation
of this spatial distribution, which considers topographic effects
within the basin. A method is proposed that optimises
an altitude-based snowfall correction factor (Cfsnow).
This is done through multi-objective calibration of a spatially
distributed, multilayer energy and water balance-based
snowmelt model (WEB-DHM-S) with observed discharge
and remotely sensed snow cover data from the Moderate Resolution
Imaging Spectroradiometer (MODIS). The Shuffled
Complex Evolution–University of Arizona (SCE–UA) automatic
search algorithm is used to obtain the optimal value of
Cfsnow for minimum cumulative error in discharge and snow
cover simulations. Discharge error is quantified by Nash–
Sutcliffe efficiency and relative volume deviation, and snow
cover error was estimated by pixel-by-pixel analysis. The
study region is the heavily snow-fed Yagisawa Basin of the
Upper Tone River in northeast Japan. First, the system was
applied to one snow season (2002–2003), obtaining an optimised
Cfsnow of 0.0007m−1. For validation purposes, the optimised
Cfsnow was implemented to correct snowfall in 2004,
2002 and 2001. Overall, the system was effective, implying
improvements in correlation of simulated versus observed
discharge and snow cover. The 4 yr mean of basin-average
snowfall for the corrected spatial snowfall distribution was
1160mm (780mm before correction). Execution of sensitivity
runs against other model input and parameters indicated
that Cfsnow could be affected by uncertainty in shortwave radiation
and setting of the threshold air temperature parameter.
Our approach is suitable to correct snowfall and estimate
its distribution in poorly gauged basins, where elevation
dependence of snowfall amount is strong.
Evapotranspiration (E) at regional or basin scale is difficult to estimate. This study estimates ... more Evapotranspiration (E) at regional or basin scale is difficult to estimate. This study estimates E with a
water balance method for the upper Yellow River and Yangtze River basins on the Tibetan Plateau, where
in situ data accessibility is especially insufficient. Results indicate that annual terrestrial water storage
change in the two basins is negligible, and basin-scale E can be reliably estimated by the difference
between precipitation and runoff. Thus, four E products from Zhang—(Zhang_E), MODIS (MODIS_E), Japanese
25-year reanalysis product (JRA_E), and the newly published Global Land Data Assimilation System
with Noah Land Surface Model-2 (GLDAS_E)—are evaluated against E estimated by the water balance
method. GLDAS_E and Zhang_E had the best performance for the upper Yellow River basin and Yangtze
River basin, respectively, with relatively small underestimation. Further analysis showed that the underestimation
of GLDAS_E was mainly caused by its negative bias for precipitation, whereas the overestimation
of JRA_E was due to overestimation of downward shortwave radiation. MODIS_E greatly
overestimated E in both basins, which was also caused by high downward shortwave radiation flux
inputs from the Global Modeling and Assimilation Office. Thus, more accurate forcing data for these products
should be a future focus, since they can improve E estimates, at least for the Tibetan Plateau.