| 1. |
- Wang, L., et al.
(författare)
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Development of a land surface model with coupled snow and frozen soil physics
- 2017
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Ingår i: Water Resources Research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 53:6, s. 5085-5103
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Tidskriftsartikel (refereegranskat)abstract
- Snow and frozen soil are important factors that influence terrestrial water and energy balances through snowpack accumulation and melt and soil freeze-thaw. In this study, a new land surface model (LSM) with coupled snow and frozen soil physics was developed based on a hydrologically improved LSM (HydroSiB2). First, an energy-balance-based three-layer snow model was incorporated into HydroSiB2 (hereafter HydroSiB2-S) to provide an improved description of the internal processes of the snow pack. Second, a universal and simplified soil model was coupled with HydroSiB2-S to depict soil water freezing and thawing (hereafter HydroSiB2-SF). In order to avoid the instability caused by the uncertainty in estimating water phase changes, enthalpy was adopted as a prognostic variable instead of snow/soil temperature in the energy balance equation of the snow/frozen soil module. The newly developed models were then carefully evaluated at two typical sites of the Tibetan Plateau (TP) (one snow covered and the other snow free, both with underlying frozen soil). At the snow-covered site in northeastern TP (DY), HydroSiB2-SF demonstrated significant improvements over HydroSiB2-F (same as HydroSiB2-SF but using the original single-layer snow module of HydroSiB2), showing the importance of snow internal processes in three-layer snow parameterization. At the snow-free site in southwestern TP (Ngari), HydroSiB2-SF reasonably simulated soil water phase changes while HydroSiB2-S did not, indicating the crucial role of frozen soil parameterization in depicting the soil thermal and water dynamics. Finally, HydroSiB2-SF proved to be capable of simulating upward moisture fluxes toward the freezing front from the underlying soil layers in winter.
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| 2. |
- Aryal, D., et al.
(författare)
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A Model-Based Flood Hazard Mapping on the Southern Slope of Himalaya
- 2020
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 12:2
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Tidskriftsartikel (refereegranskat)abstract
- 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 m(3)/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 east and west banks of the Karnali River. Such flooding in agricultural land poses a high risk to food security, which directly impacts on residents' livelihoods. Furthermore, the simulated flood in 2014 (equivalent to a 100-YRP) showed a high level of impact on physical infrastructure, affecting 51 schools, 14 health facilities, 2 bus-stops, and an airport. A total of 132 km of rural urban roads and 22 km of highways were inundated during the flood. In summary, this study can support in future planning and decision-making for improved water resources management and development of flood control plans on the southern slope of Himalaya.
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| 3. |
- Bibi, S., et al.
(författare)
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Climatic and associated cryospheric, biospheric, and hydrological changes on the Tibetan Plateau: a review
- 2018
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Ingår i: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38
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Forskningsöversikt (refereegranskat)abstract
- We review recent climate changes over the Tibetan Plateau (TP) and associated responses of cryospheric, biospheric, and hydrological variables. We focused on surface air temperature, precipitation, seasonal snow cover, mountain glaciers, permafrost, freshwater ice cover, lakes, streamflow, and biological system changes. TP is getting warmer and wetter, and air temperature has increased significantly, particularly since the 1980s. Most significant warming trends have occurred in the northern TP. Slight increases in precipitation have occurred over the entire TP with clear spatial variability. Intensification of surface air temperature is associated with variation in precipitation and decreases in snow cover depth, spatial extent, and persistence. Rising surface temperatures have caused recession of glaciers, permafrost thawing, and thickening of the active layers over the permafrost. Changing temperatures, precipitation, and other climate system components have also affected the TP biological system. In addition, elevation-dependent changes in air temperature, wind speed, and summer precipitation have occurred in the TP and its surroundings in the past three decades. Before projecting multifaceted interactions and process responses to future climate change, further quantitative analysis and understanding of the change mechanisms is required.
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| 4. |
- Bibi, S., et al.
(författare)
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Response of Groundwater Storage and Recharge in the Qaidam Basin (Tibetan Plateau) to Climate Variations From 2002 to 2016
- 2019
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Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 124:17-17, s. 9918-9934
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater (GW) and recharge as the main drivers of the water budget are challenging to quantify due to the complexity of hydrological processes and limited observations. Understanding these processes in relation to climate is crucial for evaluating future water availability of Tibetan Plateau. By computing storage changes in Gravity Recovery and Climate Experiment terrestrial water storage and Global Land Surface Data Assimilation System land surface state variables and water balance approach, we calculated GW storage changes and recharges. In the Qaidam Basin (northern Tibetan Plateau), terrestrial water storage from the Gravity Recovery and Climate Experiment revealed a significant increasing trend of 25.5 mm/year during 2002-2012. However, an obviously turning point was found around 2012 and terrestrial water storage revealed a significant decreasing rate of 37.9 mm/year during 2013-2016. Similarly, GW (recharge) had a significant increasing trend of 21.2 (4.5) mm/year before 2012 and a decreasing rate of 32.1 (10.9) mm/year after 2012. Domain-averaged difference (P-ET) between precipitation (P) and evapotranspiration (ET) also exhibited an increasing trend of 4.4 mm/year during 2002-2012 and a decreasing rate of 9.0 mm/year during 2013-2016. Precipitation followed dissimilar pattern with an increasing rate of 5.3 mm/year during 2002-2012 while no significant trend during 2013-2016. However, ET had a consistent increasing trend over the basin during the past 15 years (0.9 mm/year before 2012 and 9.0 mm/year thereafter). This study concluded that GW amount and distribution is mainly controlled by precipitation and ET. Decrease in precipitation at high elevations and increase in ET may impact future groundwater availability in this region.
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| 5. |
- Fan, X. F., et al.
(författare)
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Increased discharge across the Yellow River Basin in the 21st century was dominated by precipitation in the headwater region
- 2022
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Ingår i: Journal of Hydrology-Regional Studies. - : Elsevier BV. - 2214-5818. ; 44
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Tidskriftsartikel (refereegranskat)abstract
- Study region: The Yellow River Basin in China. Study focus: The discharge in the lowlands of a watershed is susceptible to the variations in its high-altitude headwaters in terms of climate, land cover/use and anthropogenic interference. This study not only focuses on the key role of the high-altitude headwaters of the Yellow River Basin (YRB) on the water supply in its droughty downstream lowlands, but also analyzes the contri-butions of the headwaters' changes to affect the variations of discharge in the entire basin especially in the early 21st century compared to the last half of the 20th century. New hydrological insights for the region: The results indicated that more than 1/3 of the actual flow out of the headwaters of the YRB supported the excessive water demand (mainly for irrigation) downstream. The observed discharge (QObs) increased by 44.07% in the YRB as a whole before and after the mutation year 2002 during 1986-2019, and 76.45% of the discharge increment derived from the headwaters. The increasing precipitation in the headwaters dominated the discharge recovery of the YRB, and resulted in a relative increase of 36.28% in the QObs of the entire YRB; whereas the variations of the headwaters in terms of potential evapotranspiration, land cover and water use for human activities have decreased the QObs of the entire YRB by 4.68%, 2.07% and 5.10%, respectively.
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| 6. |
- Li, X. P., et al.
(författare)
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Contribution of vanishing mountain glaciers to global and regional terrestrial water storage changes
- 2023
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Ingår i: Frontiers in Earth Science. - : Frontiers Media SA. - 2296-6463. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Mountain is called the water towers of the world. Due to high sensitivity and vulnerability to climate change, more attention is paid to the change of water resources in mountain regions, where provide water for environmental and human demands downstream. Mountains glacier, as one of the most important components of terrestrial water storage (TWS), effectively regulates and stabilizes surface water resources. TWS appears to be trending below previous ranges in recent years, and glacier retreating is becoming the primary cause of TWS depletion in mountain regions. However, how much mountain glacier changes contribute to TWS changes around mountain regions is unknown. Here, we combine multi-source datasets to quantify the contribution rate over high-elevation mountain regions. On a global scale, the glacial melting is equivalent to about 49% of the total TWS decline during 2006-2015. TWS and glacier show decreasing trends in most of mountain regions and watersheds of the Third Pole and surroundings (TPs), but the contribution ranges from -23% to 728% in mountain regions and -21% to 99% in watersheds of TPs. There are larger contributions in regions with more glaciers, while smaller in less glaciercovered regions. Glacier together with other storage components play diverse roles across different mountain regions and watersheds, but factors with great influence are glacier, groundwater, soil water, reservoirs and lakes.
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| 7. |
- Li, X. P., et al.
(författare)
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Large-scale circulation dominated precipitation variation and its effect on potential water availability across the Tibetan Plateau
- 2023
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Ingår i: Environmental Research Letters. - 1748-9326. ; 18:7
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Tidskriftsartikel (refereegranskat)abstract
- The large-scale circulation, Indian summer monsoon (ISM), has a strong influence on the Tibetan Plateau (TP) since its onset and intensity have profound impacts on regional precipitation, which then can supply water for glaciers, lakes, rivers and social demands. Weakening monsoon intensity and longer monsoon duration seem contradictory, as a weaker monsoon tends to produce less precipitation, while a longer duration increases the probability of precipitation. Past research has focused on how ISM's intensity affects precipitation, with little consideration of the impacts of ISM duration. Here, we investigate the long-term (1979-2100) variability in the ISM's duration and intensity. We find a prolonged ISM from 1979 to 2018, accompanied by monsoon weakening. Different combinations of duration and intensity have resulted in different spatial patterns of precipitation across the southeastern TP. Weakening and prolonged ISM is helpful to produce more precipitation around the southeastern TP, with intensity acting as a dominant control. Afterwards, an obvious impact can be found on potential water availability. Climate projections suggest that the ISM will weaken and lengthen until 2100, thereby increasing precipitation and potential water availability across the southeastern TP. This long-term trend should receive more attentions as increased regional extreme precipitation will increase the probability of flood risks until the end of this century.
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| 8. |
- Li, X. P., et al.
(författare)
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Near-surface air temperature lapse rates in the mainland China during 1962-2011
- 2013
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Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X. ; 118:14, s. 7505-7515
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Tidskriftsartikel (refereegranskat)abstract
- 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 (2m) 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 degrees C-0.9 degrees C100m(-1), 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.
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| 9. |
- Li, X. P., et al.
(författare)
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Seasonal evapotranspiration changes (1983-2006) of four large basins on the Tibetan Plateau
- 2014
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Ingår i: Journal of Geophysical Research-Atmospheres. - : American Geophysical Union (AGU). - 2169-897X. ; 119:23, s. 13079-13095
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Tidskriftsartikel (refereegranskat)abstract
- Lack of reliable historical basin-scale evapotranspiration (ET) estimates is a bottleneck for water balance analyses and model evaluation on the Tibetan Plateau (TP). This study looks at four large basins on the TP to develop a general approach suitable for large river basins to estimate historical monthly ET. Five existing global ET products are evaluated against monthly ET estimated by the water balance method as a residual from precipitation (P), terrestrial water storage change (Delta S), and discharge (R). The five ET products exhibit similar seasonal variability, despite of the different amounts among them. A bias correction method, based on the probability distribution mapping between the reference ET and the five products during 2003-2012, effectively removes nearly all biases and significantly increases the reliability of the products. Then, the surface water balance changes for the four basins are analyzed based on the corrected ET products as well as observed P and R during 1983-2006. A trend analysis shows an upward trend for ET in the four basins for all seasons during the past three decades, along with the regional warming, as well as a dominating increasing trend in P and negative trend in R.
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| 10. |
- Sichangi, A. W., et al.
(författare)
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Estimating continental river basin discharges using multiple remote sensing data sets
- 2016
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Ingår i: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 179, s. 36-53
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Tidskriftsartikel (refereegranskat)abstract
- Rivers act as a source of fresh water for terrestrial life, yet the discharges are poorly documented since the existing direct observations are inadequate and some observation stations have been interrupted or discontinued. Discharge estimates using remote sensing thus have a great potential to supplement ground observations. There are remote sensing methods established to estimate discharge based on single parameter derived relationships; however, they are limited to specific sections due to their empirical nature. In this study, we propose an innovative method to estimate daily discharges for continental rivers (with river channel widths >800 m (Birkett and Beckley, 2010)) using two satellite derived parameters. Multiple satellite altimetry data and Moderate Resolution Imaging Spectroradiometer (MODIS) data are used to provide a time series of river stages and effective river width. The derived MODIS and altimetry data are then used to optimize unknown parameters in a modified Manning's equation. In situ measurements are used to derive rating curves and to provide assessments of the estimated results. The Nash-Sutcliffe efficiency values for the estimates are between 0.60 and 0.97, indicating the power of the method and accuracy of the estimations. A comparison with a previously developed empirical multivariate equation for estimating river discharge shows that our method produces superior results, especially for large rivers. Furthermore, we found that discharge estimates using both effective river width and stage information consistently outperform those that only use stage data. (C) 2016 The Authors. Published by Elsevier Inc.
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