Evaluation of SWAT Model performance on glaciated and non-glaciated subbasins of Nam Co Lake, Southern Tibetan Plateau, China

This paper presents an assessment of the Soil and Water Assessment Tool(SWAT) on a glaciated(Qugaqie) and a non-glaciated(Niyaqu) subbasin of the Nam Co Lake. The Nam Co Lake is located in the southern Tibetan Plateau, two subbasins having catchment areas of 59 km^2 and 388 km^2, respectively. The scores of examined evaluation indices(i.e., R^2, NSE, and PBIAS) established that the performance of the SWAT model was better on the monthly scale compared to the daily scale. The respective monthly values of R^2, NSE, and PBIAS were 0.94, 0.97, and 0.50 for the calibration period while 0.92, 0.88, and -8.80 for the validation period. Glacier melt contribution in the study domain was simulated by using the SWAT model in conjunction with the Degree Day Melt(DDM) approach. The conjunction of DDM with the SWAT Model ensued improved results during both calibration(R^2=0.96, NSE=0.95, and PBIAS=-13.49) and validation (R^2=0.97, NSE=0.96, and PBIAS=-2.87) periods on the monthly time scale. Average contribution(in percentage) of water balance components to the total streamflow of Niyaqu and Qugaqie subbasins was evaluated. We found that the major portion(99.45%) of the streamflow in the Niyaqu subbasin was generated by snowmelt or rainfall surface runoff(SURF_Q), followed by groundwater(GW_Q, 0.47%), and lateral(LAT_Q, 0.06%) flows. Conversely, in the Qugaqie subbasin, major contributor to the streamflow(79.63%) was glacier melt(GLC_Q), followed by SURF_Q(20.14%), GW_Q(0.13%), and LAT_Q(0.089%). The contribution of GLC_Q was the highest(86.79%) in July and lowest(69.95%) in September. This study concludes that the performance of the SWAT model in glaciated catchment is weak without considering glacier component in modeling; however, it performs reasonably well in non-glaciated catchment. Furthermore, the temperature index approach with elevation bands is viable in those catchments where streamflows are driven by snowmelt. Therefore, it is recommended to use the SWAT Model in conjunction with DDM or energy base model to simulate the glacier melt contribution to the total streamflow. This study might be helpful in quantification and better management of water resources in data scarce glaciated regions.

Lake water storage change estimation and its linkage with terrestrial water storage change in the northeastern Tibetan Plateau

Tibetan Plateau(TP) lakes are important water resources,which are experiencing quick expansion in recent decades.Previous researches mainly focus on analyzing the relationship between terrestrial water storage(TWS) change and lake water storage(LWS) change in the total inner TP,it is still lack of researches about the spatial difference and the characteristic of sub-region in the inner TP.In this study,we estimated the area change of 34 lakes by using Landsat images in the northeastern TP during 1976–2013,and LWS change by using the Shuttle Radar Topography Mission(SRTM).The results suggested that LWS had shrunk from 1976 to 1994,and then expanded quickly until 2013.LWS had a serious decrease by 13.6 Gt during 1976–1994,and then it increased quickly by 35.4 Gt during 1994–2013.We estimated TWS change,soil moisture change,and permafrost degradation based on the satellite data and related models during 2003–2013.The results indicated that their changing rates were 1.86 Gt/y,0.22 Gt/y,and –0.19 Gt/y,respectively.We also calculated the change of groundwater based on the mass balance with a decreasing trend of –0.054 Gt/y.The results suggested that the cause of TWS change was the increase of LWS.We analyzed the cause of lake change according to water balance,and found that the primary cause of lake expansion was the increasing precipitation(80.7%),followed by glacier meltwater(10.3%) and permafrost degradation(9%).The spatial difference between LWS change and TWS change should be studied further,which is important to understand the driving mechanism of water resources change.

The evapotranspiration and environmental controls of typical underlying surfaces on the Qinghai-Tibetan Plateau

To reveal the characteristics of evapotranspiration and environmental control factors of typical underlying surfaces(alpine wetland and alpine meadow)on the Qinghai-Tibetan Plateau,a comprehensive study was performed via in situ observations and remote sensing data in the growing season and non-growing season.Evapotranspiration was positively correlated with precipitation,the decoupling coefficient,and the enhanced vegetation index,but was energy-limited and mainly controlled by the vapor pressure deficit and solar radiation at an annual scale and growing season scale,respectively.Compared with the non-growing season,monthly evapotranspiration,equilibrium evaporation,and decoupling coefficient were greater in the growing season due to lower vegetation resistance and considerable precipitation.However,these factors were restricted in the alpine meadow.The decoupling factor was more sensitive to changes of conductance in the alpine wetland.This study is of great significance for understanding hydro-meteorological processes on the Qinghai-Tibetan Plateau.

Cryospheric functions and services

The cryosphere is the sphere around the Earth that has a certain thickness, existing at a temperature below 0 ℃, and it comprises components mainly including glaciers, ice sheets, snow cover, permafrost, lake and river ice, sea ice, and ice shelves. It is regarded as one of spheres in the climate system, and well known for its sensitivity to climate change. Cryospheric science is an interdisciplinary subject related to all cryospheric components and is also linked to other earth sciences, including studies of the atmosphere, hydrosphere, biosphere, lithosphere, and anthroposphere (Qin et al., 2017).

Variation of sea ice and perspectives of the Northwest Passage in the Arctic Ocean

The continued warming of the Arctic atmosphere and ocean has led to a record retreat of sea ice in the last decades.This retreat has increased the probability of the opening of the Arctic Passages in the near future.The Northwest Passage(NWP)is the most direct shipping route between the Atlantic and Pacific Oceans,producing notable economic benefits.Decadal variations of sea ice and its influencing factors from a high-resolution unstructured-grid finite-volume community ocean model were investigated along the NWP in 1988-2016,and the accessibility of the NWP was assessed under shared socioeconomic pathways(SSP245 and 585)and two vessel classes with the Arctic transportation acces-sibility model in 2021-2050.Sea ice thickness has decreased with increasing seawater temperature and salinity,especially within the Canadian Arctic Archipelago(CAA)in 1988-2016,which has facilitated the opening of the NWP.Complete ship navigation is projected to be possible for polar class 6 ships in August-December in 2021-2025,after when it may extends to July under SSP585 in 2026-2030,while open water ships will not be able to pass through the NWP until September in mid-21st century.The navigability of the NWP is mainly affected by the ice within the CAA.For the accessibility of the Parry Channel,the west part is worse than that of the eastern part,especially in the Viscount-Melville Sound.

Temperature variability in northern Iran during the past 700 years

Warming is significantly affecting ecosystems in dry-warm areas,such as the Middle East[1],but long-term climatic records are often scarce in these regions.One important proxy source of climate data is tree rings,which have contributed to understanding climate changes over the past millennium[1].Under the PAGES2K framework[2],a tree-ring network of the Eurasian continent

Timing of the initial collision between the Indian and Asian continents

There exist three mainstream opinions regarding the timing of the initial collision between the Indian and Eurasian continents,namely,65±5,45±5,and 30±5 Ma.Five criteria are proposed for determining which tectonic event was related to the initial collision between India and Asia:the rapid decrease in the rate of plate motion,the cessation of magmatic activity originating from the subduction of oceanic crust,the end of sedimentation of oceanic facies,the occurrence of intracontinental deformation,and the exchange of sediments sourced from two continents.These criteria are used to constrain the nature of these tectonic events.It is proposed that the 65±5 Ma tectonic event is consistent with some of the criteria,but the upshot of this model is that the magmatic activity originating from the Tethyan subduction since the Mesozoic restarted along the southern margin of the Asian continent in this time after a brief calm,implying that the subduction of the Neotethys slab was still taking place.The magmatic activity that occurred along the southern margin of the Asian continent had a 7-Myr break during 72-65 Ma,which in this study is interpreted as having resulted from tectonic transformation from subduction to transform faulting,indicating that the convergence between the Indian and Asian continents was once dominated by strike-slip motion.The 30±5 Ma tectonic event resulted in the uplift of the Tibetan Plateau,which was related to the late stage of the convergence between these two continents,namely,a hard collision.The 45±5 Ma tectonic event is in accordance with most of the criteria,corresponding to the initial collision between these two continents.

Progress and prospects of applied research on physical geography and the living environment in China over the past 70 years (1949-2019)

Physical geography is a basic research subject of natural sciences. Its research object is the natural environment which is closely related to human living and development, and China’s natural environment is complex and diverse. According to national needs and regional development, physical geographers have achieved remarkable achievements in applied basis and applied research, which also has substantially contributed to the planning of national economic growth and social development, the protection of macro ecosystems and resources, and sustainable regional development. This study summarized the practice and application of physical geography in China over the past 70 years in the following fields: regional differences in natural environments and physical regionalization;land use and land cover changes;natural hazards and risk reduction;process and prevention of desertification;upgrading of medium-and low-yield fields in the Huang-Huai-Hai region;engineering construction in permafrost areas;geochemical element anomalies and the prevention and control of endemic diseases;positioning and observation of physical geographical elements;and identification of geospatial differentiation and geographical detectors. Furthermore, we have proposed the future direction of applied research in the field of physical geography.