HS6.10

EDI
The Third Pole Environment (TPE) under global changes

The Tibetan Plateau and surrounding mountain regions, known as the Third Pole, cover an area of > 5 million km2 and are considered to be the water tower of Asia. The Pan Third Pole expands on both the north-south and the east-west directions, going across the Tibetan Plateau, Pamir, Hindu Kush, Iran Plateau, Caucasian and Carpathian, and covering an area of about 20 million km2. Like the Arctic and Antarctica, the Pan Third Pole’s environment is extremely sensitive to global climate change. In recent years, scientists from around the globe have increased observational, remote sensing and numerical modeling research related to the Pan Third Pole in an effort to quantify and predict past, current and future scenarios. Co-sponsored by TPE (www.tpe.ac.cn), this session is dedicated to studies of Pan Third Pole atmosphere, cryosphere, hydrosphere, and biosphere and their interactions with global change. Related contributions are welcomed.

Convener: Yaoming Ma | Co-conveners: Franco Salerno, Bob Su, Fan Zhang
vPICO presentations
| Tue, 27 Apr, 09:00–12:30 (CEST)

vPICO presentations: Tue, 27 Apr

Chairpersons: Yaoming Ma, Lei Zhong
09:00–09:10
|
EGU21-8365
|
ECS
|
solicited
Mickaël Lalande, Martin Ménégoz, and Gerhard Krinner

The High Mountains of Asia (HMA) region and the Tibetan Plateau (TP), with an average altitude of 4000 m, are hosting the third largest reservoir of glaciers and snow after the two polar ice caps, and are at the origin of strong orographic precipitation. Climate studies over HMA are related to serious challenges concerning the exposure of human infrastructures to natural hazards and the water resources for agriculture, drinking water, and hydroelectricity to whom several hundred million inhabitants of the Indian subcontinent are depending. However, climate variables such as temperature, precipitation, and snow cover are poorly described by global climate models because their coarse resolution is not adapted to the rugged topography of this region. Since the first CMIP exercises, a cold model bias has been identified in this region, however, its attribution is not obvious and may be different from one model to another. Our study focuses on a multi-model comparison of the CMIP6 simulations used to investigate the climate variability in this area to answer the next questions: (1) are the biases in HMA reduced in the new generation of climate models? (2) Do the model biases impact the simulated climate trends? (3) What are the links between the model biases in temperature, precipitation, and snow cover extent? (4) Which climate trajectories can be projected in this area until 2100? An analysis of 27 models over 1979-2014 still show a cold bias in near-surface air temperature over the HMA and TP reaching an annual value of -2.0 °C (± 3.2 °C), associated with an over-extended relative snow cover extent of 53 % (± 62 %), and a relative excess of precipitation of 139 % (± 38 %), knowing that the precipitation biases are uncertain because of the undercatch of solid precipitation in observations. Model biases and trends do not show any clear links, suggesting that biased models should not be excluded in trend and projections analysis, although non-linear effects related to lagged snow cover feedbacks could be expected. On average over 2081-2100 with respect to 1995-2014, for the scenarios SSP126, SSP245, SSP370, and SSP585, the 9 available models shows respectively an increase in annual temperature of 1.9 °C (± 0.5 °C), 3.4 °C (± 0.7 °C), 5.2 °C (± 1.2 °C), and 6.6 °C (± 1.5 °C); a relative decrease in the snow cover extent of 10 % (± 4.1 %), 19 % (± 5 %), 29 % (± 8 %), and 35 % (± 9 %); and an increase in total precipitation of 9 % (± 5 %), 13 % (± 7 %), 19 % (± 11 %), and 27 % (± 13 %). Further analyses will be considered to investigate potential links between the biases at the surface and those at higher tropospheric levels as well as with the topography. The models based on high resolution do not perform better than the coarse-gridded ones, suggesting that the race to high resolution should be considered as a second priority after the developments of more realistic physical parameterizations.

How to cite: Lalande, M., Ménégoz, M., and Krinner, G.: Climate change in the High Mountain Asia simulated with CMIP6 models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8365, https://doi.org/10.5194/egusphere-egu21-8365, 2021.

09:10–09:20
|
EGU21-6877
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ECS
|
solicited
Shixue Li, Tomonori Sato, and Tetsu Nakamura

This study investigates the controlling factors of the interannual variability of Tibetan Plateau snow cover (TPSC) in winter. Since snow observation in Tibetan Plateau is limited in space and time, high-resolution multi-satellite data for TPSC were analyzed during 1982-2016. In addition, a large ensemble AGCM experiment from d4PDF (hereafter, HIST), driven by observed SST and anthropogenic forcings were analyzed during 1951-2010 to compare the contributions arising from internal variability and external forcings including the change in greenhouse gases (GHGs) concentration on TPSC variation. In this study TPSC fraction (hereafter, TPSCF) is defined as the percentage of the snow-covered area over the Tibetan Plateau. For both observation and HIST, high and low TPSCF years determined by the standardized January-March TPSCF were analyzed. The range of interannual TPSCF variation (i.e., TPSCF difference between high and low TPSCF years) is about 11% in both observation and the model, suggesting the AGCM well reproduced the TPSCF variability in the interannual timescale. 

We found that high TPSCF is linked to a positive-AO-like pattern. The interannual variation of the observed AO index and TPSCF are significantly correlated. In d4PDF high TPSCF more likely appears with a higher (positive) AO index and vice versa. In high TPSCF years, the subtropical jet is strengthened, which significantly enhances zonal water vapor flux reaching the plateau supporting more precipitation. Another interesting result is a disagreement for ENSO’s contribution to TPSC appears between observation and HIST. However, several members in HIST show a feature close to the observation, in which TPSCF anomalies are not sensitive to the El Niño/La Niña events. Thus, this weak linkage between ENSO and TPSCF is more likely due to the limited cases of observations rather than the model bias. Finally, by comparing HIST and non-warming experiments (NAT), we found historical global warming has decreased the snow-to-rain ratio over TP. Nonetheless, increased precipitation compensates for it. As a result, the impact of historical global warming on TPSCF could be considered negligibly weak.

How to cite: Li, S., Sato, T., and Nakamura, T.: Historical change of winter Tibetan Plateau snow cover and its controlling factors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6877, https://doi.org/10.5194/egusphere-egu21-6877, 2021.

09:20–09:25
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EGU21-9150
|
solicited
Rongxiang Tian and Jiayu Xu

Vertical motion is an important feature of the atmosphere, being closely linked to clouds and precipitation. We present a comparison of the vertical velocity of air over Tibetan Plateau during the period 1981–2010 using three reanalysis datasets: ERA-Interim, JRA-55 and NCEP/NCAR. Statistical analysis methods were used to examine consistency between the datasets and their suitability in research and application in Tibetan Plateau. The results show that the vertical velocity fields from ERA-Interim and JRA-55 are more consistent than they are with those from NCEP/NCAR. The atmospheric vertical velocity fields from NCEP/NCAR lack details compared with those obtained from ERA-Interim and JRA-55. Use of ERA-Interim or JRA-55 may be preferable over NCEP/NCAR. The intensity of atmospheric vertical motion in the lower troposphere in JRA-55 is significantly higher than in ERA-Interim and NCEP/NCAR. In summer, the JRA-55 data are closest to the observed wind fields and the data stability best for the Tibetan Plateau region. Our results provide guidance for better application of reanalysis data and more accurate climate prediction for this region.

How to cite: Tian, R. and Xu, J.: Comparison of atmospheric vertical motion of three reanalysis datasets over Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9150, https://doi.org/10.5194/egusphere-egu21-9150, 2021.

09:25–09:30
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EGU21-2318
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solicited
Maoshan Li, Lingzhi Wang, Wei Fu, Ming Gong, and Na Chang

 Different underlying surfaces have differing diversities, complex compositions and uneven distributions and contribute to diverse and complex land surfaces. As the main input factor for atmospheric energy, the surface greatly affects the various interactions between the ground and the atmosphere and even plays a key role in local areas on the Tibetan Plateau. The characteristics of the atmospheric boundary layer structure of the plateau and the land-atmosphere interaction under the control of different wind fields in the south branch of the westerly wind and the plateau monsoon are discussed. Results show that the height of the atmospheric boundary layer at each station under the westerly south branch wind field is higher than that under the summer monsoon wind field. The height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River in the southwest wind field are 3250 m, 2250 m, 2760 m and 3500 m. while the height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River under the plateau monsoon field are 2000 m, 2100 m, 1650 m and 2000 m. The specific humidity of the surface layer at all site is larger on July than it on other months. The specific humidity of the surface layer in Linzhi area is larger than that of the other three regions, and it reaches 12.88 g·kg-1 at the maximum. The wind direction on Mount Everest over 1200 m is dominated by westerly winds in May and October. The wind direction on Nyingchi above 1500 m is dominated by westerly winds in May and October, and in July, winds above 1200 m is dominated by southerly winds. The wind direction of Shiquan River in May and October is dominated by west-southwest wind, and the wind direction of Shiquan River in July is dominated by west-northwest wind. Secondly, variation characteristics of surface fluxes were analyzed by using the eddy covariance observations from four stations of Pailong(entrance of Canyon), Danka (middle of Canyon), Kabu (end of Canyon) , and Motuo (end of Canyon) in the southeastern gorge area of Tibet. The changing trend of monthly averaged daily sensible heat flux at Kabu station is fluctuating. Sensible heat flux and latent heat flux at Motuo station have the same variation characteristics. Latent heat fluxes increase first and then decrease at all four stations. Seasonal variations of soil heat flux are obvious, characterizing positive values in spring and summer and negative values in autumn and winter. The diurnal variation intensity of net radiation flux is summer>spring>autumn>winter.   Energy closure rates of Danka, Pailong, Motuo, and Kabu stations are 70.86%, 68.91%, 69.29%, and 67.23%, respectively. Latent heat fluxes and soil heat fluxes increase, and sensible heat fluxes decrease as increasing precipitation at the four stations. The sensible heat flux and soil heat flux respond synchronously to precipitation changes, and the changes in latent heat have a significant lag in response to precipitation changes.

How to cite: Li, M., Wang, L., Fu, W., Gong, M., and Chang, N.: Study on the Land-Atmosphere Interaction in the Coordination Effect of Westerly Wind and Monsoon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2318, https://doi.org/10.5194/egusphere-egu21-2318, 2021.

09:30–09:32
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EGU21-16426
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solicited
Zhuoxuan Xia, Lingcao Huang, and Lin Liu

Permafrost in the Tibetan plateau is undergoing warming and degradation due to thermal and anthropogenic disturbance. As visible indicators of permafrost degradation, retrogressive thaw slumps (RTSs) are slope failures resulting from thawing of ice-rich permafrost, which can retreat and expand in thawing seasons, and may destroy infrastructure, change ecosystems and release carbon preserved in permafrost. However, the distribution of RTSs over Tibet is seldom investigated and poorly understood.

In this study, we used optical images collected by the Planet CubeSat constellation in 2019 to identify RTSs over a vast area of ~45000 km2 along the Qinghai-Tibet Engineering Corridor, where the main highways and railways across the plateau are running through and a new highway is under planning. We planned to use the deep learning model DeepLabv3+, which can classify every pixel in the entire study area. However, with limited training data (300 RTSs) centered in a relatively small subregion (Beiluhe Region), it is infeasible to delineate all RTSs accurately in such a large and diverse area by using deep learning alone. Therefore, we proposed an iteratively semi-automatic method. In each iteration, we used DeepLabv3+ to automatically identify and delineate all possible RTSs, then manually checked them and selected newly-found RTSs based on their geomorphic features and temporal changes. To minimize the chance that DeepLabv3+ may miss some RTSs in each iteration, we added newly-found RTSs into the positive training dataset for the next iteration. We stopped iteratively mapping until no new RTSs could be identified.

Eventually, our method identified and delineated 877 RTSs which affect a total area of 17 km2. They tend to spread out across the region, while Beiluhe is characterized as a cluster. Among these, 57 RTSs are within 500 m from major roads and the railway and potentially threaten their safety. This study demonstrates the applicability of using our deep-learning-aided method to obtain a comprehensive inventory of RTSs in large areas such as the engineering corridor, give us an overall understanding of RTS distribution, and provide an important benchmark dataset and knowledge for further quantifying temporal changes of RTSs.

How to cite: Xia, Z., Huang, L., and Liu, L.: Inventorying Retrogressive Thaw Slumps along the Qinghai-Tibet Engineering Corridor using a deep-learning-aided semi-automatic method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16426, https://doi.org/10.5194/egusphere-egu21-16426, 2021.

09:32–09:34
|
EGU21-5201
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ECS
|
solicited
Yigang Liu, Shihua Lyu, Cuili Ma, Yue Xu, and Jiangxin Luo

In this paper, the impact of gravel is taken into account in regional simulations on the Tibetan Plateau (TP). The differences of ground surface and soil hydrological processes in the TP are compared when the gravel parameterization schemes and the original soil hydrothermal parameterization schemes are respectively adopted in the regional climate model version 4.7 (RegCM4.7), which is driven by the EIN15. Moreover, the performances in simulating the liquid soil moisture (LSM) by using the two schemes are also assessed. When the impact of gravel is considered, the changes of ground hydrological processes are consistent with those of liquid precipitation and snow meltwater except the infiltration, indicating the dominance of liquid precipitation and snow meltwater in ground hydrological processes. The lower gravel content will facilitate the downward transportation of LSM. However, in the case of high gravel content, the roles of gravel content are completely opposite in the western and central TP. The most obvious change is that the simulated LSM by the gravel schemes is lower at most soil depths compared with that by the original schemes, which is beneficial in most cases. For instance, the mean absolute errors of the reference data with the simulations by the gravel schemes and original schemes at the soil depth of 0.1 m in the southeastern TP are 0.026 and 0.101, respectively. Besides the southeastern TP, the performance in simulating the temporal variation of the LSM below the middle soil layers still needs to be improved.

How to cite: Liu, Y., Lyu, S., Ma, C., Xu, Y., and Luo, J.: The Gravel Parameterization Schemes on Tibetan Plateau and Its Assessment Using RegCM4, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5201, https://doi.org/10.5194/egusphere-egu21-5201, 2021.

09:34–09:36
|
EGU21-7072
|
ECS
Lingxin Huang, Wei Huang, Song Feng, Kun Yang, and Fahu Chen

Based on the Köppen–Trewartha climate classification schemes, we examined the shifts in terrestrial climate regimes in the Tibetan Plateau (TP) by analyzing the WorldClim high-resolution (~25 km) downscaled climate dataset for the mid-Holocene (MH, 6,000 cal yr BP), the present day (PD, 1970-2000), and in the future (2041-2060, represented by 2050). The climate types of the PD are compared to those of the MH and the future. Our aim was to place ongoing anthropogenic climatic and environmental changes in the TP within the context of changes due to natural forcing in the three selected warm period, and to determine the differences in the spatial expression of ecosystem among these selected periods. The results indicate that the climate of the TP will continue to warm in the future. The intensity of the South Asian monsoon may increase in the future which will affect precipitation in the southern TP. There will be a significant decrease in the areas covered by polar climate, while the spatial coverage of the other climate types will increase. A tropical climate which did not exist in the MH and PD will develop in some areas and the shrinking polar climate indicates that the cryosphere of the TP will change significantly, which in turn may cause the climate system to pass a tipping point and cause irreversible consequences. The large changes in the climate regimes of the TP suggest that there will be a widespread redistribution of the surface vegetation and significant changes in plant species distributions by 2050. Compared to changes in precipitation, increasing temperature is the dominant factor that driving the change of climate types in the TP. The warming alone may cause the climate types to change in more than 20% areas by 2050.

How to cite: Huang, L., Huang, W., Feng, S., Yang, K., and Chen, F.: Changes of Köppen–Trewartha climate types in the Tibetan Plateau during the mid-Holocene, present day, and the future based on high-resolution datasets, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7072, https://doi.org/10.5194/egusphere-egu21-7072, 2021.

09:36–09:38
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EGU21-7076
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ECS
Jingyu Dan and Yanhong Gao

As the highest plateau in the world, the Tibetan Plateau (TP) exerts great impacts on regional and global climate and water cycle through interactions between land and free atmosphere. Terrestrial evapotranspiration is a critical component of the Earth's water cycle. To better understand the heterogeneity of the evapotranspiration over the Tibetan Plateau and its influences, we conducted a whole year dynamical downscale modelling (DDM) with the horizontal resolution at 28km and a convection permitting modelling (CPM) at 4km for 2014. DDM and CPM simulation results are compared with an satellite retrieving dataset, which is referred as OBS in the following, the global land surface data assimilation system (GLDAS) and two commonly used reanalyses ERA-Interim and ERA5, as well. The annual and seasonal means and seasonal variabilities are inter-compared. The evapotranspiration over ten dominant land use types are investigated based on six datasets. Differences with the satellite dataset are illustrated and relationships with soil moisture and temperature, precipitation and radiation are explored. The followings are obtained. GLDAS generally reproduces magnitude and pattern of the OBS; reanalyses overestimate, DDM and CPM underestimate compared to the OBS and GLDAS.

The overestimations in reanalyses occur in the monsoon season and the underestimations in DDM and CPM occur in the non-monsoon season. Large evapotranspiration biases exist over the vegetated ground which exert large impacts on the TP-average biases for growing season.

How to cite: Dan, J. and Gao, Y.: Detecting evapotranspiration biases in reanalyses and regional climate modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7076, https://doi.org/10.5194/egusphere-egu21-7076, 2021.

09:38–09:40
|
EGU21-7742
Zhiqiang Lin, Weidong Guo, Xiuping Yao, Jun Du, and Jun Ge

The Tibetan Plateau vortices (TPVs) are mesoscale weather systems active at the near-surface of the Tibetan Plateau (TP), which are one of the major precipitation-producing systems over the TP and its surrounding areas. TPVs mainly occur in the warm season from May to September. In this paper, we investigate the inter-decadal change of TPVs in the warm seasons of 1979–2017 by analyzing five widely used reanalysis datasets. A significant change of the TPVs’ frequency appears around the mid-1990s, associated with less TPVs during 1979–1996 and more TPVs during 1997–2017. The abrupt change is caused by a transition of the Atlantic Multi-decadal Oscillation (AMO) from a cold phase to a warm phase in the mid-1990s. The shift of AMO leads to a silk-road pattern wave train and a spatially asymmetric change of tropospheric temperature. It modifies the intensity of the subtropical westerly jet and the TP heating, leading to the inter-decadal change of TPV activities.

How to cite: Lin, Z., Guo, W., Yao, X., Du, J., and Ge, J.: Inter-decadal Change of Tibetan Plateau Vortices during the past four Decades and its Possible Mechanism, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7742, https://doi.org/10.5194/egusphere-egu21-7742, 2021.

09:40–09:42
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EGU21-1568
Weiqiang Ma, Yaoming Ma, Yizhe Han, Wei Hu, Lei Zhong, Zhipeng Xie, Zeyong Hu, Rongmingzhu Su, and Fanglin Sun

Firstly, based on the difference of model and in-situ observations, a serious of sensitive experiments were done by using WRF. In order to use remote sensing products, a land-atmosphere model was initialized by ingesting land surface parameters, such as AMSR-E RS products, and the results were compared with the default model configuration and with in-situ long-term CAMP/Tibet observations.

Secondly, a land-atmosphere model was initialized by ingesting AMSR-E products, and the results were compared with the default model configuration and with in-situ long-term CAMP/Tibet observations. The differences between the AMSR-E initialized model runs with the default model configuration and in situ data showed an apparent inconsistency in the model-simulated land surface heat fluxes. The results showed that the soil moisture was sensitive to the specific model configuration. To evaluate and verify the model stability, a long-term modeling study with AMSR-E soil moisture data ingestion was performed. Based on test simulations, AMSR-E data were assimilated into an atmospheric model for July and August 2007. The results showed that the land surface fluxes agreed well with both the in-situ data and the results of the default model configuration. Therefore, the simulation can be used to retrieve land surface heat fluxes from an atmospheric model over the Tibetan Plateau.

All of the different methods will clarify the land surface heating field in complex plateau, it also can affect atmospheric cycle over the Tibetan Plateau even all of the global atmospheric cycle pattern.

How to cite: Ma, W., Ma, Y., Han, Y., Hu, W., Zhong, L., Xie, Z., Hu, Z., Su, R., and Sun, F.: The evaluation of land surface parameters for model to derive land surface fluxes in the Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1568, https://doi.org/10.5194/egusphere-egu21-1568, 2021.

09:42–09:44
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EGU21-7059
Ge Wang and Lin Han

This study analyses the diurnal seasonal mean and the seasonal and annual variation in the radiation budget at the Ali Meteorological Bureau observation station in the northern Tibetan Plateau for 2019. The results indicate that the daily average variation in incidental shortwave and reflected radiation across all seasons in the Ali area had typical unimodal symmetry. The average daily variation in incidental shortwave radiation was in phase with reflected radiation, but the amplitude of the incidental shortwave radiation was greater than that of reflected radiation. The daily amplitude, daily average, and monthly average upwelling longwave radiation were greater than those for downwelling radiation, and the diurnal cycle of downwelling atmospheric radiation lagged behind that of upwelling longwave radiation. The daily amplitude of surface net radiation in winter in the Ali area was less than in other seasons, as expected, and the seasonal transformation had a great impact on the net radiation for this region. The net radiative energy at the surface was highest in late spring and early summer, which played a decisive role in the formation of terrestrial and atmospheric heating.

How to cite: Wang, G. and Han, L.: Surface Radiation Characteristics of the Ali Area, Northern Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7059, https://doi.org/10.5194/egusphere-egu21-7059, 2021.

09:44–09:46
|
EGU21-1956
Lian Liu, Massimo Menenti, Yaoming Ma, and Weiqiang Ma

Snowfall and the subsequent evolution of the snowpack have a large effect on surface energy balance and water cycle, among which albedo is a major driver. However, the current widely used Noah land surface model does not describe snow albedo correctly, although it keeps snow-related variables i.e. snow cover and age into account. In our study, the impact of an improved albedo parameterization scheme in WRF coupled with Noah was investigated. In the improved albedo scheme, albedo was parameterized as functions of snow depth and age which was developed using remote sensing retrievals of albedo.

Numerical experiments were conducted to model a severe snow event in March 2017. The performance of WRF coupled with Noah applying the improved albedo scheme was compared with that of applying the default albedo scheme and with that of WRF coupled with CLM applying CLM’s complex albedo scheme. First, the improved albedo scheme largely reduces the WRF coupled with Noah default albedo overestimation in the southeastern Tibetan Plateau, remarkably reducing the large cold bias estimates by 0.7 ℃ air temperature RMSE. Second, the improved albedo scheme gives the highest correlationship between the satellite-derived and the model estimated albedo, contributing to achieve the SWE spatial pattern, heavy snow belt and maximum SWE estimates in eastern Tibetan Plateau. Third, the fine resolution simulation, such as 5 km (1 km), significantly reduces the eastern SWE overestimation by 29% (49%).

In order to investigate the applicability of the improved albedo scheme in snow events simulation in the Tibetan Plateau, 16 numerical experiments were conducted to simulate 8 snow events by using WRF coupling with Noah default and improved albedo schemes. The assessment demonstrates that the improved albedo scheme significantly reduces the air temperature underestimation, and reduces the air temperature RMSE by 0.5 - 1 ℃ for both 5 km and 1 km resolution simulations. It is expected that the improved albedo parameterization scheme will have a good prospect in high resolution simulation of snow events in the Tibetan Plateau.

How to cite: Liu, L., Menenti, M., Ma, Y., and Ma, W.: Improved parameterization of albedo in WRF + Noah in snow events simulation in the Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1956, https://doi.org/10.5194/egusphere-egu21-1956, 2021.

09:46–09:48
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EGU21-14593
Nan Yao, Lian Liu, and Yaoming Ma

Snowfall is a key component of the hydrological system of the Tibetan Plateau (TP), and it is also a very sensitive factor to climate change. To understand the mechanism of extreme snowfall in different regions of the TP, we used the 50-year snow depth data from the China Meteorological Administration (CMA) ground observations and the ERA5 reanalysis datasets of European Centre for Medium-Range Weather Forecasts (ECMWF). Results show the threshold of extreme snow in the southern TP is four times greater than that in the eastern region. Sixteen numerical experiments using the weather research and forecasting (WRF) model were conducted to quantify the contribution of water vapor and dynamic conditions to snowfall events. Here are the preliminary results: (1) For the snowfall event caused by local circulation in the eastern TP, the contribution of dynamic conditions is greater than that of moisture conditions. An increase of 10% in the wind field (water vapor) will enhance the snow water equivalent (SWE) by more than 25% (10%). (2) For large-scale circulation, q has a greater effect. But the overall increase in snowfall is smaller than the local circulation. (3) The severe snowfall frequently takes place in the southern TP, where water vapor channel and topographic uplift are significant factors to snowfall. we think the southern simulation will produce interesting results. Our results will provide scientific reference in improving the snowstorm forecasting and disaster prevention and mitigation.

How to cite: Yao, N., Liu, L., and Ma, Y.: The different mechanisms of extreme snowfall in the eastern and southern Tibetan Plateau., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14593, https://doi.org/10.5194/egusphere-egu21-14593, 2021.

09:48–09:50
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EGU21-1660
Fan Zhang, Xiong Xiao, and Guanxing Wang

Permafrost degradation under global warming may change the hydrological regime of the headwater catchments in alpine area such as the Tibetan Plateau (TP). In this study, he runoff generation processes in permafrost-influenced area of the Heihe River Headwater were investigated with the following results: 1) The observed stable isotope values of various water types on average was roughly in the order of snowfall and snowmelt < bulk soil water (BSW) < rainfall , stream water, mobile soil water (MSW) , and lateral subsurface flow. The depleted spring snowmelt and enriched summer rainfall formed tightly bound soil water and MSW, respectively. The dynamic mixing between tightly bound soil water and MSW resuted in BSW with more depleted and variable stable isotopic feature than MSW. 2) Along with the thawing of the frozen soil, surface runoff and shallowsubsurface flow (SSF) at 30−60 cm was the major flow pathway in the permafrost influenced alpine meadow hillslope during spring snowmelt and summer rainfall period, reapectively, with the frozen soil maintaining supra-permafrost water level. 3) Comparison between two neighouring catchments under similar precipitation conditions indicated that streamflow of the lower catchment with less permafrost proportion and earlier thawing time has larger SSF and higher based flow component, indicating the potential changes of hydrological regims subject to future warming.

How to cite: Zhang, F., Xiao, X., and Wang, G.: Runoff generation processes in permafrost-influenced area of the Heihe River Headwater, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1660, https://doi.org/10.5194/egusphere-egu21-1660, 2021.

09:50–09:52
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EGU21-16555
Xiaonan Shi, Fan Zhang, and Li Wang

Serious soil erosion is observed during the spring because soil thawing coincides with the period of snowmelt and low meadow coverage at this time. Studies relating to soil erosion caused by spring meltwater are limited and controversial. In this study, a field experimental study was conducted in an alpine meadow slope in the Binggou watershed on the northern edge of the Tibetan Plateau to assess the impact of multiple factors on spring meltwater erosion. The multiple factors included three flow rates, four slope gradients, and three underlying surface conditions (meadow, disturbed meadow, and alluvial soil). An equal volume of concentrated meltwater flow was used in all experiments. The results showed that rapid melting at a high flow rate could accelerate soil erosion. The influence of the slope gradient on the amount of runoff was positively linear and the influence was relatively low. However, the slope gradient had a strong impact on soil erosion. The meadow could effectively reduce soil erosion, although when the meadow was disturbed, the total runoff increased by 60% and the sediment yield by a factor of 1.5. The total runoff from the alluvial soil doubled in comparison to the meadow, while the sediment yield increased nearly 7-fold. The findings of this study could be helpful to understand the characteristics and impact of multiple controlling factors of spring meltwater erosion. It also aims to provide a scientific basis for an improved management of alpine meadows as well as water and soil conservation activities in high-altitude cold regions.

 

How to cite: Shi, X., Zhang, F., and Wang, L.: The effects of multiple factors on spring meltwater erosion on an alpine meadow slope, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16555, https://doi.org/10.5194/egusphere-egu21-16555, 2021.

09:52–10:30
Break
Chairpersons: Fan Zhang, Weiqiang Ma
11:00–11:10
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EGU21-3669
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ECS
|
solicited
Yanxin Zhu, Yan-Fang Sang, Deliang Chen, Bellie Sivakumar, and Donghuan Li

The South Asian summer monsoon (SASM) system is one of the most energetic regional monsoon systems. Its onset and demise timings determine the propagation, duration, and magnitude of precipitation through thermodynamic and dynamic processes in the SASM-prevailing areas. Particularly, anomalous onsets and demises of the SASM could generate a large anomaly in precipitation and serious water-related disasters over the SASM-prevailing areas.

The South-Central Tibetan Plateau (SCTP), known as the “Asian water tower”, is the origin of several major Asian rivers, including the Yellow River, Yangtze River, Brahmaputra River, Mekong River, and the Indus River, providing a huge amount of freshwater for ecosystems and billions of people in Asia. It is widely known that the SCTP is controlled by the SASM system in summer, accounting for approximately 60% of annual precipitation, but with significant spatiotemporal heterogeneity due to the complex topographic and geographic conditions. Presently, most studies have focused on the effects and physical causes of the linear trend of SASM onset over the SCTP. However, little attention has been paid to the question as to how both anomalous onset and anomalous demise of the SASM influence the interannual precipitation variation in this region. In particular, the spatial manifestation of thermodynamic and dynamic mechanisms for the interannual precipitation variation is largely unknown. Adequate knowledge about these mechanisms is critical for sustainable freshwater management and water disasters control in this region and surrounding areas.

These call a detailed study to investigate the influences of the early and late onset (demise) of the SASM system on the interannual variations in precipitation and their underlying mechanisms over the SCTP. In this study, we mainly clarify the following key questions: (1) How do the onset and demise of the SASM control the interannual variations in precipitation over the SCTP? (2) Is there an asymmetric effect of the SASM on SCTP precipitation between its onset and demise, and between its early and late onset (demise)? and (3) What are the underlying mechanisms that are responsible for the variations in interannual precipitation? The results would help improve our understanding of the SASM-precipitation relationship over the SCTP and alleviation of water-related disasters in the region.

How to cite: Zhu, Y., Sang, Y.-F., Chen, D., Sivakumar, B., and Li, D.: How does the South Asian summer monsoon anomaly influence the interannual variations in precipitation over the South-Central Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3669, https://doi.org/10.5194/egusphere-egu21-3669, 2021.

11:10–11:20
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EGU21-1565
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ECS
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solicited
Paula Galindo, Peter Frenzel, Sten Anslan, Sonja Rigterink, Julieta Massaferro, Wengang Kang, Bernd Wuennemann, Liseth Pérez, Philipp Hoelzmann, Nicole Börner, Anja Schwarz, Ping Peng, Liping Zhu, and Antje Schwalb

High altitudinal aquatic ecosystems are subject to environmental change due to global warming and increasing solar radiation. The Nam Co catchment is part of the highest and largest alpine plateau on Earth, where the effects of climate change are expressed stronger than the global average. Thus, this area has experienced rapid changes in biodiversity. Fluctuations between wetter and drier periods during the last 2,000 calibrated (cal.) years were detected. These changes may alter the dynamics in ecosystems and therefore their resilience to climate change.

A ~65 cm sediment record from Nam Co spanning the late Holocene, was analyzed to evaluate the assemblage composition of three of the most abundant and diverse benthic taxa (Arcellinidae, Ostracoda and Chironomidae) and the diverse family of small bivalves (Sphaeriidae). In general, the presence of the bivalve Pisidium stewarti, together with a high abundance of black-coated ostracod shells, and high Ca/Ti and Zr/Rb ratios correspond to the driest period (~ 1,000 - 1,860 cal. years BP) detected in our sediment record. For the last 256 cal. years, higher lake levels were inferred from aquatic fauna composition and geochemical analysis (XRF and XRD) suggesting a more humid environment. This period was characterized by higher temperatures and a higher input of organic matter. Species not previously reported for Lake Nam Co such as Arcellinida species, the ostracod Ilyocypris angulata, several chironomid species, and the bivalve P. stewarti, were observed. These new records, as well as the detection of varieties in morphological structures (e.g. spines, aggregate material, valve ornamentations, etc.) highlight the probable existence of cryptic species in the ecosystem, which is an important factor to take into account for biodiversity evaluation and paleoenvironmental inferences, due to potential misleading ecological interpretation.

Therefore, emphasis should be placed on combining ecology, morphology and DNA analysis to corroborate the taxonomy of species already described, and determine the accurate richness and distribution of the species in an environment where endemism is expected. This is essential in order to evaluate possible losses or gains in terms of diversity that climate change may exert on aquatic ecosystems in the future.

How to cite: Galindo, P., Frenzel, P., Anslan, S., Rigterink, S., Massaferro, J., Kang, W., Wuennemann, B., Pérez, L., Hoelzmann, P., Börner, N., Schwarz, A., Peng, P., Zhu, L., and Schwalb, A.: Ecological impacts caused by the alternance of wet/dry episodes occurred in the last 2,000 years in southern Tibetan Plateau: A paleoecological record from Lake Nam Co, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1565, https://doi.org/10.5194/egusphere-egu21-1565, 2021.

11:20–11:25
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EGU21-8602
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ECS
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solicited
Xiaohang Wen, Wenqi Pan, Xiaoguang Sun, Maoshan Li, and Siqiong Luo
To study the variation trend of potential evapotranspiration (PET) in the Three-River Headwaters (TRH) region of the Qinghai-Tibet Plateau in China, we use 2-m temperature and surface pressure observation data from 14 meteorological weather stations in the TRH region, and the surface PET is calculated by the Penman-Monteith formula. The global land surface data assimilation system from 2000 to 2018 were used to compare and verify the accuracy and applicability of the calculated PET in the THR region. The results show that in the past 20 years, the PET of 14 weather stations in the TRH region has shown an increasing trend, with annual averaged growth rate of 1.4 ± 1.2 mm·a−1 , and the spatial distribution of the annual variation rate of PET has obvious difference. PET is higher in the eastern area of TRH region, and lower in the western area. The drought in this area increased from southeast to northwest, which was consistent with the spatial distribution of precipitation. The aridity index K has flfluctuated and increased before 2015, but there was a sudden change in 2018, and the aridity index K in the TRH began to decline after 2018, and the climate changed from dry to wet.

How to cite: Wen, X., Pan, W., Sun, X., Li, M., and Luo, S.: Study on the Variation Trend of Potential Evapotranspiration in the Three-River Headwaters Region in China Over the Past 20 years, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8602, https://doi.org/10.5194/egusphere-egu21-8602, 2021.

11:25–11:30
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EGU21-6825
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ECS
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solicited
Shuoqiu Wu and Xiaoyan Ma

The melting of glaciers and snow on the Qinghai-Tibet Plateau, known as the Earth’s “Third Pole” and “World Water Tower”, is source of fresh water for hundreds of millions of people in South Asia, Southeast Asia, and East Asia, but it is now suffering from an unprecedented crisis. The black carbon deposited on the surface of the glacier will reduce the snow albedo and absorb more solar radiation, leading to accelerated melting of ice and snow.Previous studies have shown that black carbon from South Asia is one of the main sources of the Qinghai-Tibet Plateau, and the transportation of black carbon to the Qinghai-Tibet Plateau presents obviously seasonal differences.However, the transport of black carbon from South Asia to the Qinghai-Tibet Plateau in different seasons shows a completely opposite trend to wind field conditions.This study uses the WRF-Chem model to study the transmission mechanism of South Asian black carbon to the Tibetan Plateau in April (pre-monsoon), July (summer monsoon) and December (winter monsoon).MIX emission inventory and Peking University's global black carbon emission inventory (PKU-BC) were involved to analyze the seasonal distribution of black carbon concentration, dry and wet deposition in the Qinghai-Tibet Plateau and South Asia, and the distribution of BC concentration and wind field at different altitudes.Combined with the vertical distribution of BC concentration across the Himalayas, the transport mechanism of black carbon in South Asia to Qinghai-Tibet Plateau in different seasons is studied.In the selected three months, December had the highest surface black carbon concentration in South Asia and the Qinghai-Tibet Plateau, while July had the lowest black carbon concentration; Mainly because of the large amount of wet deposition of black carbon brought about by the heavy precipitation in South Asia in July;According to the vertical distribution of black carbon,black carbon can climb up the hillside and eventually reach the southern slope of the Qinghai-Tibet Plateau in April. In July, black carbon is mainly distributed below 3km. In December, black carbon can be uplifted to 4-5km, and finally transported into Qinghai-Tibet Plateau.

How to cite: Wu, S. and Ma, X.: Comparing Seasonal Diffences of Black Carbon in Tibetan Plateau transported from South Asia using WRF-Chem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6825, https://doi.org/10.5194/egusphere-egu21-6825, 2021.

11:30–11:32
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EGU21-3653
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ECS
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solicited
Chao Zhang, Meilian Chen, Shichang Kang, Fangping Yan, and Chaoliu Li

Carbonaceous particles play an important role in climate change, and the increase in their emission and deposition causes glacier melting in the Himalayas and the Tibetan Plateau (HTP). This implies that studying their basic characteristics is crucial for a better understanding of the climate forcing observed in this area. Thus, we investigated characteristics of carbonaceous particles at Yaze village, a typical remote site of southeastern HTP.  The results showed that the organic carbon and elemental carbon concentrations at this study site were 1.86 ± 0.84 and 0.18 ± 0.09 μg m-3, respectively, which were much lower than those reported for other frequently monitored stations in the same region. Thus, these values reflect the background characteristics of the study site. Additionally, the absorption coefficient per mass (α/ρ) of water-soluble organic carbon (WSOC) at 365 nm was 0.60 ± 0.19 m2 g-1, which was lower than those reported for other remote stations in the HTP. This value could be attributed to a lower and higher contribution of mineral dust and secondary organic carbon, respectively. Multi-dimensional fluorescence analysis showed that the WSOC consisted of approximately 37% and 63% protein and humic-like components, respectively, and the latter was identified as the determining component of light absorption ability of the WSOC. Combined the significant relationships between WSOC and sulfate ion, potassium ion, and nitrate ion with the air masses at the study site originated primarily from South Asia, it is suggested that the levels of carbonaceous particles in Yaze village were predominantly influenced by emissions from South Asia.

How to cite: Zhang, C., Chen, M., Kang, S., Yan, F., and Li, C.: Light absorption and fluorescence characteristics of water-soluble organic compounds in carbonaceous particles at a typical remote site in the southeastern Himalayas and Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3653, https://doi.org/10.5194/egusphere-egu21-3653, 2021.

11:32–11:34
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EGU21-1559
Yaoming Ma, Zeyong Hu, Binbin Wang, Lei Zhong, Weiqiang Ma, Cunbo Han, Xuelong Chen, Lian Liu, Sunil Subba, Zhipeng Xie, and Yuyang Wang

The exchange of heat and water vapor between land surface and atmosphere over the Third Pole region (Tibetan Plateau and nearby surrounding region) plays an important role in Asian monsoon, westerlies and the northern hemisphere weather and climate systems. Supported by various agencies in the People’s Republic of China, a Third Pole Environment (TPE) observation and research Platform (TPEORP) is now implementing over the Third Pole region. The background of the establishment of the TPEORP, the establishing and monitoring plan of long-term scale (5-10 years) of it will be shown firstly. Then the preliminary observational analysis results, such as the characteristics of land surface energy fluxes partitioning and the turbulent characteristics will also been shown in this study. Then, the parameterization methodology based on satellite data and the atmospheric boundary layer (ABL) observations has been proposed and tested for deriving regional distribution of net radiation flux, soil heat flux, sensible heat flux and latent heat flux (evapotranspiration (ET)) and their variation trends over the heterogeneous landscape of the Tibetan Plateau (TP) area. To validate the proposed methodology, the ground measured net radiation flux, soil heat flux, sensible heat flux and latent heat flux of the TPEORP are compared to the derived values. The results showed that the derived land surface heat fluxes over the study areas are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface feature. And the estimated land surface heat fluxes are in good agreement with ground measurements, and all the absolute percent difference in less than 10% in the validation sites. The sensible heat flux has increased slightly and the latent heat flux has decreased from 2001 to 2018 over the TP. It is therefore conclude that the proposed methodology is successful for the retrieval of land surface heat fluxes and ET over heterogeneous landscape of the TP area. Further improvement of the methodology and its applying field over the whole Third Pole region and Pan-Third Pole region were also discussed.

How to cite: Ma, Y., Hu, Z., Wang, B., Zhong, L., Ma, W., Han, C., Chen, X., Liu, L., Subba, S., Xie, Z., and Wang, Y.: The observation and modeling of air-land interaction over heterogeneous landscapes of the Third Pole, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1559, https://doi.org/10.5194/egusphere-egu21-1559, 2021.

11:34–11:36
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EGU21-5776
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ECS
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solicited
Yanghang Ren, Kun Yang, and Han Wang

As region that is highly sensitive to global climate change, the Tibetan Plateau (TP) experiences an intra-seasonal soil water deficient due to the reduced precipitation during the South Asia monsoon (SAM) break. Few studies have investigated the impact of the SAM break on TP ecological processes, although a number of studies have explored the effects of inter-annual and decadal climate variability. In this study, the response of vegetation activity to the SAM break was investigated. The data used are: (1) soil moisture from in situ, satellite remote sensing and data assimilation; and (2) the Normalized Difference Vegetation Index (NDVI) and Solar-Induced chlorophyll Fluorescence (SIF). We found that in the region impacted by SAM break, which is distributed in the central-eastern part of TP, photosynthesis become more active during the SAM break. And temporal variability in the photosynthesis of this region is controlled mainly by solar radiation variability and has little sensitivity to soil moisture. We adopted a diagnostic process-based modeling approach to examine the causes of enhanced plant activity during the SAM break on the central-eastern TP. Our analysis indicates that active photosynthetic behavior in the reduced precipitation is stimulated by increases in solar radiation absorbed and temperature. This study highlights the importance of sub-seasonal climate variability for characterizing the relationship between vegetation and climate.

How to cite: Ren, Y., Yang, K., and Wang, H.: The South Asia Monsoon Break Promotes Grass Growth on the Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5776, https://doi.org/10.5194/egusphere-egu21-5776, 2021.

11:36–11:38
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EGU21-6903
Zeyong Hu and Xiaoqiang Yan

Based on multi-level AWS data during 2001 to 2015 and eddy covariance data during 2011 to 2014 at Nagqu Station of Plateau Climate and Environment, the turbulent fluxes were calculated by a surface energy balance combination (CM) and eddy covariance ( EC) method. A long-term heat fluxes and surface heat source were obtained with comparison and correction of EC and CM fluxes. The surface energy closure ratio is close to 1 in spring, summer and autumn. But it reaches to 1.34 in winter due to low net radiation observation value on snow surface. The sensible heat flux shows a ascend trend while latent heat flux shows a descend trend during 2002 to 2015. The surface heat source shows a descend trend. The analysis of the surface heat source indicates that it has a significant relationship with net radiation flux, surface temperature, soil moisture and wind speed. Particularly, the surface heat source has a significant response to net radiation flux throughout the year. There are obvious influences of surface temperature and soil moisture on the surface heat source in spring, autumn and winter. And the influence of wind speeds on surface heat source is strong only in spring. The annual variation of sensible heat flux and latent heat flux are obvious. Sensible heat flux reaches the maximum value of the year in April and the minimum value in July. however, latent heat flux shows the maximum value in July and the minimum value in January. 

How to cite: Hu, Z. and Yan, X.: Characteristics of Long-term Surface Heat Source and Its Climate Influence Factors in Central Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6903, https://doi.org/10.5194/egusphere-egu21-6903, 2021.

11:38–11:40
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EGU21-2676
Lei Zhong, Yaoming Ma, Zhongbo Su, Weiqiang Ma, Zeyong Hu, and Cunbo Han

Estimation of land surface characteristic parameters and turbulent heat fluxes is important for energy and water cycle studies, especially on the Tibetan Plateau (TP), where the topography is unique and the land-atmosphere interactions are strong. The land surface heating conditions also directly influence the movement of atmospheric circulation. However, high temporal resolution information on the plateau-scale land surface parameters has lacked for a long time, which significantly limits the understanding of diurnal variations in land-atmosphere interactions. On the other hand, how to remove cloud effects for optical satellite images is another important research issue. Based on Chinese FY geostationary satellite data and other polar orbiting satellite data, the hourly land surface characteristic parameters and turbulent heat fluxes were estimated. A new cloud‐free time series of vegetation index data sets was reconstructed, and the vegetation density showed a general increasing trend along with a warming trend in the TP. The regions showing significant increases accounted for 7.63% of the total Tibetan territory. Downwelling shortwave and longwave radiation parameterization schemes were improved to derive all-sky radiation over the TP. The diurnal and seasonal cycles of the land surface parameters were clearly identified, and their spatial distribution was found to be consistent with the heterogeneous land surface conditions and the general hydrometeorological conditions of the TP.

How to cite: Zhong, L., Ma, Y., Su, Z., Ma, W., Hu, Z., and Han, C.: Estimation of land surface key parameters for the study of energy and water cycle over the Tibetan Plateau based on geostationary and polar orbiting satellites, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2676, https://doi.org/10.5194/egusphere-egu21-2676, 2021.

11:40–11:42
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EGU21-16556
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ECS
Yizhe Han, Yaoming Ma, Zhongyan Wang, and Weiqiang Ma

The northern slopes of Himalaya (NSH) have the highest average elevation in the world. It is difficult to assess how climate change has affected this region because only a few observations are available from the high terrain and harsh environment. This study investigates the long-term characteristics of temperature and precipitation in the NSH. Further, the association of these variations with atmospheric circulation patterns is also investigated. Our results indicated that the warming trend in this region is almost 1.5 times that of the TP region, 2 times that of China, and 3.5 times that of the world. Additionally, the warming rate of the NSH is more obvious than other regions in the Himalayas, which shows that different regions of the Himalayas have different sensitivity to climate change. Although the warming trend in the NSH region does not show obvious seasonal differences like the TP, the temperature increase rate in autumn and winter is still higher than that in spring and summer. The abrupt change point for the temperature increase in summer was about 5 years later than that in other seasons, indicating that the NSH region is more sensitive to climate warming in cooler seasons, which is similar to the western and northwestern Himalaya. Furthermore, the Southern Oscillation Index (SOI) displays significant relationships with the temperature in the NSH, meanwhile, the North Atlantic Oscillation index (NAO) and Western Pacific Subtropical High Intensity Index (WPI) also exist some correlations with seasonal temperature change. This indicating that the atmospheric circulation would also have affected the temperature increase in this region, especially in summer and winter. The changes in precipitation are only affected by the SOI during the monsoon season (June to September), indicating that ENSO influences precipitation changes through water vapor transmission. In contrast, the precipitation in the TP is correlated with NAO, SOI and WPI, which indicating the precipitation of the TP might be affected by multiple circulation systems.

 

 

How to cite: Han, Y., Ma, Y., Wang, Z., and Ma, W.: Variation characteristics of temperature and precipitation on the northern slopes of the Himalaya region from 1979 to 2018, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16556, https://doi.org/10.5194/egusphere-egu21-16556, 2021.

11:42–11:44
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EGU21-16557
Chen Zeng and Fan Zhang

Precipitation usually is the main source of river discharge in the high mountain headwater areas and therefore as a key parameter in hydrological modelling. However, spatiotemporal distribution of precipitation in the remote high mountain headwater areas on the Tibetan Plateau (TP) has been poorly described due to the scarce meteorological stations located in high elevations. A series of rain gauges were set-up in three catchments of the southern TP to study their precipitation (liquid) gradient (PG) characteristics under different precipitation intensity grades (PIG) during the monsoon season (July to September) from 2013 to 2016. Results showed that the average PG varied during 0.71 to 0.82 mm·100 m-1 in the three study catchments for the total (non-intensity-graded) precipitation during the monsoon, and varied up to 2.4 times under different PIGs. Besides, PGs were all strongly correlated to precipitation amounts in the three study catchments, these patterns were relatively persistent among different years but varied among different catchments. Generally, the correlations between PG and precipitation amount showed a steep positive slope under fine precipitation grade but became flat or even negative with stronger PIG. We concluded that the precipitation in southern Tibet was influenced more by valley-scale convection than by large-scale vapor circulation during the monsoon season.

How to cite: Zeng, C. and Zhang, F.: Study on the precipitation gradient characteristics in the high mountains of southern Tibet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16557, https://doi.org/10.5194/egusphere-egu21-16557, 2021.

11:44–11:46
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EGU21-7886
Guanxing Wang and Fan Zhang

Being an important water resource of the local and downstream living hoods, precipitation amount is experiencing drastic changes in the Babao River basin in the northeast of the Tibetan Plateau. Precipitation types also have great impacts on the runoff. However, in usual cases, weather stations only record precipitation amount without discriminating its type. Here, we compared results from three methods at improving precipitation type (solid and liquid) estimation with discontinuous 24 years precipitation type records of the Qilian gauging station. The results (bias rank of the three methods is 2.5% < 17.3% < 20.1%) showed that the estimation of different thresholds for wet season (4 °C) and dry season (5.5 °C) is the closest to the actual records. Based on the precipitation type distinction, the precipitation type and its amount changing trend in recent 50 years of the Babao River basin was examined. On average, snowfall accounts for 10.7% in whole year, and mainly happens in March, April, May and October (8.9% in whole year). In the context of climate warming, the annual precipitation and rainfall increasing significantly while the annual snowfall decreased slightly. Furthermore, on the perspective of monthly changes, rainfall amounts of May and August enhanced significantly while snowfall amount decreased significantly in June and September. The above conclusions indicated the warming climate also changed the precipitation pattern in the Babao River basin which would likely cause drought in the spring season and bring challenge to the local agriculture.

How to cite: Wang, G. and Zhang, F.: Types and amounts of the precipitation changes in recent 50 years of the Babao River basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7886, https://doi.org/10.5194/egusphere-egu21-7886, 2021.

11:46–11:48
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EGU21-9331
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ECS
Zhaoyang Liu and Yanhong Gao

The Tibetan Plateau (TP), known as the "Third Pole" and "Water Tower of Asia", plays an essential role in the regional water cycle and global climate change through its unique topography and abundant water resources. Precipitation is an important part of the hydrological process, but realistically simulating precipitation over the TP is still a major challenge for most models, which hinders our understanding of the strength of the land-atmosphere interaction and its influences on regional, or even global climate and water cycle. In order to better depict precipitation spatial and temporal distributions over the TP, a 4-km convection permitting modelling (CPM) and a 28-km dynamical downscale modelling (DDM) using the weather Research and Forecasting model (WRF) were conducted for a summer (from June to August 2014). WRF simulations are evaluated against CMA in-situ observations, the Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of water resources (APHRODITE), the Global Precipitation Measurement (GPM), as well as two reanalysis datasets ERA-Interim and ERA5. We focus on the added values of the CPM in summer precipitation simulations, in terms of the spatial seasonal mean precipitation amounts, spatial distributions, and diurnal cycles. We found the six datasets (CPM, DDM, APHRODITE, GPM, ERA-Interim and ERA5) showed great differences in summer precipitation over the TP. The great advantages of CPM and DDM over reanalyses are observed. Slight improvements are found in CPM over DDM as well. Mechanisms for these differences will be explored.

How to cite: Liu, Z. and Gao, Y.: Convection permitting simulation of summer precipitation over the Tibetan Plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9331, https://doi.org/10.5194/egusphere-egu21-9331, 2021.

11:48–11:50
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EGU21-5391
Genhou Sun, Zeyong Hu, yaoming Ma, Zhipeng Xie, Wei Wei, and Song Yang

This study investigates the long-term variations of local land atmosphere coupling (LoCo) over Tibetan Plateau (TP) by applying a mixing diagram to the observational data at six stations over TP and ERA5 and the possible influence of Southern Asian monsoon. The result indicates that the monthly-mean daily variation in T2m, q2m, Hsfc, and LEsfc at Nyingchi, Nagqu, Nam Co, Qomolangma, Ngari, and Muztagata in ERA5 are close to those in observational data. Comparison of mixing diagram analysis using the monthly-mean variables of ERA5 and the observational data indicates ERA5 could provide reliable information of LoCo at six stations. The relationships between Hsfc and daytime PBLH, and the variations of LCL deficit at six stations are different due to the differences in the soil states. The long-term variations in the PBL energy budgets, mean daytime PBLH, and LCL deficits at 31N and 90E show clear annual variations and have a close relationship between Southern Asian monsoon. The possible influence of the Southern Asian monsoon is also discussed in terms of the relationship between the Webster-Yang index and the PBL energy budgets, mean PBLH and mean LCL over TP.

How to cite: Sun, G., Hu, Z., Ma, Y., Xie, Z., Wei, W., and Yang, S.: Long-term variation of characteristics of local land atmosphere coupling over TP and the possible influence of Southern Asian Monsoon, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5391, https://doi.org/10.5194/egusphere-egu21-5391, 2021.

11:50–11:52
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EGU21-6869
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ECS
Chao Xu, Yaoming Ma, Jiehua Ma, Chao You, and Huijun Wang

Dust is a major component of atmospheric aerosol worldwide, greatly affecting regional and global climate. A dust belt can be clearly found at altitudes higher than 6 km over the downwind direction of the TP at latitudes of around 30°–40°N, crossing the Pacific Ocean and extending to North America during spring. Dust is uplifted to the midtroposphere over the source regions; then, frequent, deep, dry convection prevailing over the TP during spring can cause convective overshooting that uplifts the dust aerosols to the upper troposphere. The TP thus acts as a channel for transporting dust from the lower atmosphere to the upper troposphere, enabling the long-range zonal transport of dust around the Northern Hemisphere. Estimated spring dust mass flux (DMF) showed a significant declining trend over the TP during 2007-2019. The total spring DMF across the TP was mainly affected by DMFs over the Tarim Basin, while the spring DMF across the TP in the mid-troposphere was also connected with DMFs over the northwest Indian Peninsula and Central Asia. Inter-annual variability of spring DMF across the TP was strongly correlated with the North Atlantic winter sea surface temperature (SST) tripole. The North Atlantic winter SST tripole anomalies persist into the subsequent spring, and induce a corresponding atmosphere response. A strong positive North Atlantic winter SST tripole anomaly strengthens the upper-level westerly jets, enhancing air flow towards the TP mid-troposphere; together, these circulation patterns cause anomalous cyclonic conditions in the lower troposphere, especially over the Tarim Basin, via the eastwards propagation of a Rossby wave train. These atmospheric circulation conditions are likely to increase the frequency of dust occurrence and promote the transport of dust onto the TP.

How to cite: Xu, C., Ma, Y., Ma, J., You, C., and Wang, H.: Spring Dust over the Tibetan Plateau and Connections with North Atlantic SST Variability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6869, https://doi.org/10.5194/egusphere-egu21-6869, 2021.

11:52–12:30