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This study uses precipitation oxygen isotopes (δ18Op) to examine key dynamics that deliver moisture to the southern slope of central Himalayas over different seasons. Results show that the majority of pre‐monsoon δ18Op values are relatively high and controlled by the westerlies and local moisture. However, some abnormally low δ18Op values coincide with higher precipitation amounts during the pre‐monsoon season due to moisture driven northwards from the Bay of Bengal and Arabian Sea to central Himalayas by anomalous circulations (quasi‐anticyclone, anticyclone, or/and westerlies trough). The size and location of the quasi‐anticyclone also influences the magnitude of the δ18Op decrease. In comparison, the monsoon δ18Op values are lower due to the combined effects of the Indian summer monsoon and convection. Our findings indicate that researchers need to consider the signals of abnormally low δ18Op values during the pre‐monsoon season when attempting to interpret ice core and tree‐ring records from central Himalayas. Plain Language Summary: How moisture is transported to the southern slope of central Himalayas remains unclear, especially for the frequent heavy precipitation events that occur during the pre‐monsoon season. Here, we address this issue using δ18Op measurements from the Asang station on the southern slope of central Himalayas during 2018–2019. We find that some abnormally low δ18Op values coincide with heavy precipitation during the pre‐monsoon season. These abnormally low δ18Op values are caused by the development of anomalous circulations that drives the Indian Ocean moisture to the Asang station. During the monsoon season, the δ18Op values are much lower than other seasons. Such low values are the product of the combined effects of the Indian summer monsoon and convection. We propose that the abnormally low δ18Op values during the pre‐monsoon season need to be considered in paleoclimate reconstructions using ice core and tree‐ring records in the region. The abnormally low δ18Op values during the pre‐monsoon season are closely correlated to anomalous circulations. This finding implies that δ18Op records from ice core and tree ring archives may have potential to reconstruct the frequency and intensity of such anomalous circulations during the pre‐monsoon season. Key Points: Abnormally low δ18Op values during the pre‐monsoon season coincide with heavy precipitation eventsOccurrences of anomalous circulations lead to the abnormally low δ18Op values during the pre‐monsoon seasonCombined effects of the Indian summer monsoon and convection cause lower δ18Op values during the monsoon season [ABSTRACT FROM AUTHOR]

An extreme haze‐fog event occurred during October 20–22, 2013, in Harbin, Northeast China, which lasted for nearly 60 h with local visibility as low as 20 m. However, causes of the extreme haze‐fog formation remain unclear. Through the analysis of in situ data and objective weather circulation classification, it is revealed that high pollutant emissions from biomass burning played a very important role in the extreme event. Stable weather conditions under the circulation type 8 (CT8), marked by weak high‐pressure control, strong inversion (6.55°C), shallow boundary layer depth (<300 m), and high relative humidity (>90%), aided in the accumulation of pollutants and hygroscopic aerosol growth. All of these factors collectively contributed to the extreme haze‐fog formation. The insights derived from this study can improve the predictability of extreme haze‐fog events, and indicate that pollution emissions should be tightly controlled in the adverse meteorological circulation type in Northeast China. [ABSTRACT FROM AUTHOR]

Tibetan Plateau (TP) has experienced a slowdown of the vegetation greening since the late 1990s. This structural change (i.e., greening) along with canopy physiology (i.e., potential photosynthetic productivity) regulates vegetation gross primary productivity (GPP). However, it remains unclear how the joint regulation influences the trend of alpine GPP under climate change. Here, we validate a universal productivity model against flux‐based and satellite‐derived observations at TP and diagnose the long‐term climatic impacts on GPP via canopy physiology and structure. We found an increasing but weakening trend of GPP after 1998. About 3/4 of this slowdown was attributed to the slowing greening after 1998, which was caused by the fact that the stress of atmospheric aridity and reduced benefits of warming overwhelmed the positive effects of CO2 fertilization and radiation enhancement. This study highlights the coupling between canopy structure and productivity for the long‐term period. Plain Language Summary: Plants absorb CO2 from the atmosphere through their leaves via process of photosynthesis. The green surface area of leaves and portions exposed to sunlight harvest the energy from the sun, while the plant's physiology determines how much and how well light radiation is used. The Tibetan Plateau is one of the most sensitive regions to climate change and has experienced a slowdown since 1998 of its hitherto increasing total vegetation greenness. An important point that remains unclear is whether, and to what proportion this slowdown in the capacity to absorb CO2 is attributed to the green canopy vegetation and/or its physiology. To gain insight into this question, we input data from 1982 to 2015 into a simulation model to separate the contributions of different environmental factors that brought about variation in CO2 capture. In this way we can understand what factors related to the canopy structure and/or plant physiology. We found that increased atmospheric aridity and reduced warming together led to a marked slowdown of canopy greening after 1998, leading to a continuous decline in efficiency to capture atmospheric CO2. Our research continues to highlight the important role of canopy structure on carbon capture trends for the alpine ecosystem and provides insights for the vegetation‐climate response. Key Points: The increasing trend of gross primary productivity on the Tibetan Plateau has slowed down from +3.15 ± 0.41 to +0.77 ± 0.03 g C m−2 yr−2 around 1990sCanopy greenness change contributed much more (about 3/4) to slow the gross primary productivity (GPP) increasing trend than canopy physiology effects after 1998Increasing atmospheric aridity and slowing warming rate diminished the persistent greening and led to the slowdown of increasing GPP [ABSTRACT FROM AUTHOR]

Snowfall on the Tibetan Plateau (TP) is crucially important to the hydrological cycle and glacier acceleration over the TP and surroundings. Climate and weather models are challenged by biases and uncertainties in representing microphysical characteristics of snowfall over TP. In order to bridge the gaps in our understanding of microphysical characteristics of snowfall on the southeastern TP (SETP), an integrated and systematic measurement is conducted at the South‐East Tibetan Plateau Station during the two winters of 2022–2023. It is the first time to conduct a long‐term measurement of microphysical characteristics of snowfall on the SETP. The major objective of this campaign was to collect cloud microphysical properties including, fall velocity, aspect ratio, and particle size distribution (PSD). The results show that the particle number concentration is less than 103 mm−1·m−3, which is one to two orders of magnitude smaller than that reported in low‐altitudes in eastern China. The shape parameter μ is mainly in the range 0–4, and the slope parameter λ is mainly in the range 3–7 mm−1, exceeding the values for eastern China. In heavy snowfall processes (snowfall rate (SR) exceeding 2 mm/hr), the collision‐coalescence process between snowfall particles is enhanced, and the number concentration of small particles decreases with SR, whereas that of large particles increases. A negative correlation was observed between the aspect ratio and the diameter of snowfall particles. The microphysical characteristics of snowfall will be used to improve the microphysical scheme and evaluate the representation of precipitation in the climate model. Plain Language Summary: Snowfall on the southeastern Tibetan Plateau (SETP) affects the mass change of glaciers, the energy balance, and precipitation patterns on the TP and their surrounding areas. However, a large part of the forecast bias for snowfall in climate and weather models comes from the representation of the microphysical characteristics of snowfall. In order to close the knowledge gap, we conducted a long‐term observation experiment of the microphysical characteristics of snowfall on the SETP for the first time. The research purpose of this experiment is to investigate the microphysical characteristics of snowfall on the southeastern TP, such as fall velocity, aspect ratio, particle size distribution, and its vertical variation. The results show that the particle size distribution of snowfall particles on the southeastern TP is lower than that in the low‐altitudes. With the increase of snowfall rate, the collision‐coalescence process between snowfall particles is enhanced, the number of small particles decreases, and the number of large particles increases. Observations of the microphysical characteristics of snowfall will help improve snowfall estimates in climate weather models. Key Points: The first time to conduct a long‐term measurement of microphysical characteristics of snowfall on the southeastern Tibetan Plateau (SETP)Comparing the particle number concentration of snowfall on the SETP with that in low‐altitudes areasThe microphysical processes that dominate snowfall under different snowfall rates are different [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) impacts local and remote atmospheric circulations, wherein it mechanically and thermally affects air masses or airflows. Moreover, the TP provides a key channel for substance transport between the troposphere and the stratosphere. This study reviews recent advances in research regarding land–atmosphere coupling processes over the TP. The TP experiences climate warming and wetting. Climate warming has caused glacier retreat, permafrost degradation, and a general increase in vegetation density, while climate wetting has led to a significant increase in the number of major lakes, primarily through increased precipitation. Local and regional climates are affected by interactions between the land and the atmosphere. Namely, the TP drives surface pollutants to the upper troposphere in an Asian summer monsoon (ASM) anticyclone circulation, before spreading to the lower stratosphere. Further, the thermal forcing of the TP plays an essential role in the ASM. TP forcing can modulate hemispheric‐scale atmospheric circulations across all seasons. The TP interacts with remote oceans through a forced atmospheric response and is substantially affected by the evolution of the Earth's climate via promoting Atlantic meridional overturning circulation and eliminating Pacific meridional overturning circulation. The extensive influence of the TP is facilitated by its coupling with the ASM in the summer; whereas its winter influence on climate mainly occurs through Rossby waves. The observed increasing trends of temperature and precipitation over the TP are projected to continue throughout the 21st century. Plain Language Summary: The impact of the Tibetan Plateau on atmospheric circulation and the climate has been of great interest to the scientific community. Here, we review the literature on the mechanisms of its climate effects, to provide an overview of recent progress in the field and directives for future research. Key Points: We summarize recent advances in climate change research and observations of the land–atmosphere coupling processes over the Tibetan Plateau (TP)We highlight the impact of the TP on the global climate, including atmospheric species transport, circulation, and air‐sea interactionsWe conclude projected future climate changes over the TP and discuss future research directives for assessing the TP's global climate impact [ABSTRACT FROM AUTHOR]

The atmospheric boundary layer (ABL) over the Tibetan Plateau (TP) is important to the study of the interactions between the underlying surface and the atmosphere. Radiosondes were released during three intensive ABL experimental periods (monsoon‐onset, monsoon, and post‐monsoon) in 2014 and 2019. Using these observational data, this study explored the features of the ABL height (ABLH) in the northern, central, and southern parts of the TP during the three periods and their possible association with the westerlies. Measurements showed that the ABLH over the northern part of the TP in the monsoon season was the highest (average 3 km above ground level [AGL]) among the three intensive observation periods. Meanwhile, the southern part of the TP had the highest ABLH (almost 3.5 km AGL) in post‐monsoon. Using ERA5, we discovered that the ABLH over the TP was not only affected by the surface sensible heat flux but also was influenced by the seasonal north‐south movement of the westerlies. The westerlies correspond to an upper‐level high potential vorticity (PV) center that is associated with the weak atmospheric stability below the westerlies and is conducive to the development of the ABL. When the westerlies are located above the southern TP in winter, they provide conditions that favor ABL increase. Westerlies are above the north TP in summer, and this provides favorable conditions for ABL increase in the northern TP. The role of westerlies in the ABLH explains why the northern and southern parts of the TP have different seasonal variation patterns. Plain Language Summary: The atmospheric boundary layer (ABL) is the bottom layer of the atmosphere and is directly affected by the Earth's surface. The Tibetan Plateau (TP), the highest plateau in the world, has unique features of the ABL structure. As one of the key variables describing the structure of the ABL, the ABL height (ABLH) over the TP is of great significance for climate change research, weather forecasting, numerical simulation verification, and diagnosis of air pollutant transmission. In this study, we present a detailed analysis of the diurnal and seasonal variation characteristics of ABLH in the northern, central, and southern parts of the TP during three monsoon seasons. The ABLH over the TP was affected not only by the surface heat flux but also by the seasonal north‐south movement of the westerlies that prevail over the TP throughout the year. The westerlies correspond to an upper‐level high potential vorticity center that is conducive to ABL growth. The results can provide important reference for further investigation of the structure of the ABL over the TP. Key Points: Atmospheric boundary layer height (ABLH) exhibits seasonal variation and regional differences over the Tibetan PlateauThe ABLH was not only affected by the sensible heat flux but also was influenced by the seasonal north‐south movement of the westerliesThe westerlies correspond to a high potential vorticity center that is conducive to the ABL increase by weakening atmospheric stability [ABSTRACT FROM AUTHOR]

The local land–atmosphere coupling (LoCo) over the Tibetan Plateau (TP) in the rainy season and the possible influence of the South Asian monsoon (SAM) on LoCo characteristics are investigated by applying two LoCo diagnostic metrics to 12‐year observational data at six stations over the TP and the ERA5 from June to September (JJAS) from 1980 to 2018. The validation of ERA5 in estimating monthly mean diurnal evolutions of T2m, q2m, and surface fluxes (Hsfc and LEsfc) at the six stations reveals that these variables in the ERA5 are relatively reliable for the LoCo analysis. The mixing diagram analysis based on the observational data and ERA5 suggests that the monthly variations in the planetary boundary layer (PBL) energy budget are strong and vary from station to station, revealing the complexity of the influence of the SAM on the PBL energy budget over TP. The relationship between Hsfc and PBL height (PBLH) and lifted condensation level (LCL) deficit at the six stations based on the ERA5 reveal a strong influence of soil moisture on PBL growth and convective cloud formation, although the topography may also exert its influence. Analyses of the correlations of the PBL energy budget, PBLH, and LCL deficit over the TP with the SAM in JJAS indicate that the LoCo characteristics over the TP show large spatial variability between the southeastern and central‐western parts of the TP. Such spatial variability can be attributed to the spatial differences in monthly mean soil moisture and rainfall closely related to the evolution of SAM's influence and the complex topography of the TP. The topography of the TP can also affect the LoCo characteristics in JJAS, but the mechanisms in the areas dominated by SAM and by the westerly winds are different. [ABSTRACT FROM AUTHOR]

The Yarlung Tsangbo Grand Canyon (YGC), one of the world's deepest canyons, is located within the East Himalayas, which are remote and poorly instrumented. In this study, a rain gauge network was established around the YGC region. Data collected from the network for more than three years disclose that the rainfall spatial pattern in the south of the YGC region is relatively homogeneous. Diurnal cycles showed some variations among sites, but a clear floor was visible in the afternoon and peak values were exhibited in the early morning. The monthly precipitation in the YGC region shows two peaks, in April and July. There are two regions (500 m and 2,500 m AMSL) with high precipitation in the YGC. For rainfall extremes, vertical convection and vapor transport are important in this region. The diurnal cycle from our observations provides a key test of the physical parameterizations for use in the fifth‐generation ECMWF (European Centre for Medium‐Range Weather Forecasts) reanalysis product (ERA5). Our observations indicate that ERA5 cannot reproduce the diurnal patterns of precipitation in the YGC region. ERA5 showed a wet bias when estimating light cumulus rainfall and a dry bias when estimating heavier (convective) precipitation. The erroneous diurnal variation of ERA5 precipitation (false afternoon rainfall) was due to the CAPE (Convectively Available Potential Energy)‐based convective precipitation scheme. The higher ERA5 precipitation than observed was due to the large‐scale rainfall scheme in the Integrated Forecasting System (IFS) of ERA5. These findings indicate that there still is room for improvement of the ERA5 reanalysis data in the eastern Himalaya region. [ABSTRACT FROM AUTHOR]

Stable hydrogen isotopes in monsoonal precipitation (δDp) at three sites (Port Blair, Barisal and Darjeeling) reveal the factors governing δDp variations over a south‐north gradient across the Bay of Bengal. We found that the δDp at each site continuously decreases from May to September and these trends become more pronounced from south to north. The decreasing trends of downstream δDp closely follow the decreasing trends of upstream stable hydrogen isotopes in water vapor (δDv), which indicates that upstream δDv properties shape initial spatiotemporal patterns of the downstream δDp ("shaping effect"). Additionally, our results demonstrate that, during moisture transport, upstream vertical air motions (convection and downward motion) and topographic relief magnify the amplitude of the decreasing trends of downstream δDp ("magnifying effect"). Our findings imply that upstream δDv properties and relevant atmospheric and topographical conditions along the moisture transport pathway need to be considered collectively to better interpret paleoclimate records. Plain Language Summary: The stable isotope records from paleoclimate archives in South Asia have been widely used to indicate the Indian Summer Monsoon (ISM) intensity. However, precipitation stable isotopes across most areas of South Asia show a continuous decrease throughout the monsoon season, which does not track the ISM intensity. Clearly, factors other than the ISM influence the variability of the monsoonal precipitation stable isotopes. Here, we reveal the factors governing the variations of precipitation stable hydrogen isotopes (δDp) over a south‐north gradient across the Bay of Bengal using the δDp at three sites (Port Blair, Barisal and Darjeeling). Our results show that a gradual decreasing trend of δDp from May to September appears at each site. We find that changes in stable hydrogen isotopes in upstream water vapor (δDv) largely control the decreasing trends of downstream δDp from May to September. In addition, we also find that the decreasing trends of δDp gradually strengthen from south to north. These patterns are attributed to the continuous enhancing influences of upstream vertical air motions, including upstream accumulative convection and downward motion, and topographic relief from south to north. These findings help to explain the inconsistency between the lowest δDp and the strongest ISM. Key Points: δDp at each site continuously decreases in May‒September and amplitude of decreasing trends gradually strengthens from south to northUpstream water vapor isotope properties shape the continuous decreasing trends of downstream δDpUpstream vertical air motions and topographic relief magnify the amplitude of the decreasing trends of the downstream δDp [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) features unique and highly heterogeneous soils, terrains, vegetation, and climate. Accurately modeling complex freeze‐thaw processes and their hydrothermal impacts remains a great challenge. This study focused on deciphering the spatiotemporal variability of diverse parameterization schemes in the soil hydrothermal simulations using the Noah‐MP land surface model. We first discussed the spin‐up time required by the model to reach the equilibrium state, and then performed a sensitivity analysis of these schemes. The Moderate Resolution Imaging Spectroradiometer land surface temperature and Soil Moisture Active Passive remote sensing products were used as benchmarks to evaluate the schemes' performance. Results show that longer spin‐up times are required in permafrost regions owing to water phase changes. Ground temperature and soil temperature are mainly sensitive to energy‐related schemes. Vegetation‐related schemes play an important role after the growing season begins on the southeastern TP. Soil water content shows strong sensitivity to schemes related to both water and energy transport. However, the sensitivity of these energy‐related schemes is weakened when simulating total soil moisture, including the total amount of water and ice, indicating that these schemes have marked impacts on soil freeze‐thaw processes. These results reveal the different spatial (both regional and depth‐related) and temporal effects of parameterization schemes; we also provided a preliminary selection of these schemes at a regional scale that could facilitate the further improvement of the soil hydrothermal simulations on the TP. Plain Language Summary: Soil variables related to energy and water transfer play key roles in the control of land surface simulations. Some parameterization schemes perform them well in specific regions or over specific periods but have limited effect on the overall performance of soil hydrothermal simulations over the entire Tibetan Plateau throughout the year. Our study was based on a unified model, whereby we discovered the sources of simulation differences when using different schemes; we then selected appropriate schemes for soil hydrothermal simulations through comparisons with remote sensing data. We highlighted the spatiotemporal characteristics of scheme performance and provided a more suitable scheme combination for soil hydrothermal simulations. Key Points: The spin‐up time of the land surface model is affected by the soil freeze‐thaw processesThe total soil moisture simulations show strong sensitivity to the scheme of frozen soil permeability in permafrost regions throughout the yearMore suitable parameterization schemes for the entire Tibetan Plateau were obtained, which have specific spatiotemporal patterns [ABSTRACT FROM AUTHOR]

The dependence of the feedback signal on atmospheric conditions is still poorly understood and may lead to an underestimation of feedback strength due to opposite responses of precipitation to soil moisture. Based on data from observation stations on the Tibetan Plateau and from satellites, this study evaluated the response of convective clouds to the change of evaporation fraction (EF) and analyzed how surface conditions affect the initiation and development of convection in different coupling regimes. After considering coupling regimes classified by the tropospheric state, the afternoon convective cloud showed a strong response to EF, which is negative feedback in the dry coupling regime and positive feedback in the wet coupling regime. Organized deep convection defined by both the cloud properties and the afternoon precipitation displayed this phenomenon. This shows that the lack of a strong response of convection to EF is due to the dependence of this response on the coupling regime, rather than on the method of defining convection. We also found that the difference in surface heat flux between the two regimes is more significant in the afternoon, while the difference of meteorological elements is most significant before noon. These results provide support for the use of ground‐based meteorological data to determine coupling regimes. We also used a regression tree to decompose the effects of coupling regimes and EF into basic near‐surface meteorological elements, the results of which provide support for some of our conclusions. Key Points: Considering coupling regimes classified by the tropospheric condition, the convection showed a strong response to evaporation fraction (EF)Two convection definitions, depending on cloud properties and afternoon rainfall, showed regime‐dependent responses to EFIt is possible to determine the regime without profiles, surface meteorological elements are significantly different in the morning [ABSTRACT FROM AUTHOR]

In this paper, three parameterization schemes, one considering gravel influence (test1), one considering organic carbon influence (test2), and one comprehensively considering gravel and organic carbon influence (test3), were set up to modify different typical underlying surfaces of the Tibetan Plateau (TP). In addition, their soil thermal properties and hydraulic property variations were discussed. Additionally, discussing the key thermal and hydraulic parameters affected the performance of different schemes from the perspective of observation data in the TP to improve the simulation ability of soil temperature and soil moisture in the plateau areas. Compared the original Community Land Model (CLM) scheme, test1 resulted in higher soil temperature and lower soil moisture, while test2 had lower soil temperature and higher soil moisture. The key thermal and hydraulic parameters are the changes in the saturated thermal conductivity and the thermal conductivity of dry soil and the variations of the porosity and exponent B, respectively. The test3 scheme was the same as test2 for the modified changes of thermal properties, except that the proportion of change was slightly different. In terms of soil thermal properties, test2 and test3 were better at 0–20 cm depth, while test1 and test3 were better for the deeper (40 cm) simulation. Regarding hydraulic properties, the test1 and test3 schemes performed better on the Gobi and alpine meadows at 20–40 cm depth, while the original CLM scheme and test2 performed better on the underlying grassland surface. Test3 was better at balancing the relationship between the thermal and hydraulic parameters and could be used for the further research on the entire plateau area. Key Points: According to the observation data, the CLM5.0 thermal and hydrological parameterization schemes are modified in this paperThe new scheme is better at balancing the relationship between the thermal and hydraulic parametersThe modified CLM5.0 improves the ability to simulate soil temperature and moisture on the plateau [ABSTRACT FROM AUTHOR]

Land‐atmosphere interactions are an essential component of the climate system. However, no detailed description of the underlying effects of the surface forcing of the atmosphere has been established. In this study, GLEAM, MODIS, and ERA5 were the input set of multiple analysis algorithms, "segmentation" was the core idea of the analysis method. The study area is segmented into six surface response functional groups, and the multidimensional evaporation regime function was segmented into piecewise functions controlled by segment authoritative variables. Inspired by the surface heat balance equation and moisture‐limited, energy‐limited evaporation regimes, we chose soil moisture content and the net radiation flux to represent the moisture and energy status, respectively, and chose the leaf area index (LAI) to characterize the vegetation cover to investigate the primary effects of surface parameters on the energy partitioning of the land surface and evaporative regime. The results show that though a coupling strength 1.8 times greater was obtained when the LAI was used as the response variable instead of soil moisture, soil moisture was still the highest response variable in the regression tree analysis. This is consistent with the essence of the evaporative fraction and indicates that water should be the most fundamental response variable. The evaporative regime was subdivided from two phases into five phases according to the effects such as water extraction by vegetation, photosynthesis, soil shading, and roughness changes, each with an authoritative response variable. Key Points: Remote‐sensing data and reanalysis data are the input set of neural network and regression tree, the integrated results of multiple actions are dividedThe study area is segmented into six surface response functional groups, and the evaporation regime is segmented into five piecewise functionsThe coupling strength of leaf area index and evaporative fraction (EF) is 1.8 times greater than that of soil moisture and EF, but soil moisture is still the most preferred variable in the evaporation regime [ABSTRACT FROM AUTHOR]

Over the past decades, human‐induced climate change has led to a widespread wetting and warming of the Tibetan Plateau (TP), affecting both ecosystems and the carbon cycling therein. Whether the previously observed climate changes stimulate carbon uptake via enhanced photosynthesis or carbon loss via enhanced soil respiration remains unclear. Here we present 14 years of observations of carbon fluxes, meteorological variables and remotely sensed plant cover estimations from a central Tibetan alpine steppe ecosystem at Nam Co, the third largest lake on the TP. Using modified Mann‐Kendall trend tests, we found a significant increasing daily net carbon uptake of 0.5 g C m−2 decade−1, which can be explained by a widespread greening at the southern shore of lake Nam Co. The Plateau‐wide changes in temperature and precipitation are locally expressed as an increasing diurnal temperature range during winter, higher water availability during spring, higher cloud cover during early summer and less water availability during late summer. While these changes differ over the course of the year, they tend to stimulate plant growth more than microbial respiration, leading to an increased carbon uptake during all seasons. This study indicates that during the 14 years study period, a higher amplitude in winter temperatures and an earlier summer monsoon promote carbon uptake in a central Tibetan alpine steppe ecosystem. Plain Language Summary: Similar to the northern and southern high latitudes, global warming is especially pronounced on the Tibetan Plateau (TP). It remains uncertain, in which way the alpine short grass steppe responds to the observed warming and wetting of the TP. By analyzing nearly 14 years of data describing the carbon dioxide (CO2) exchange between the steppe and the atmosphere, we found that the ecosystem acts as a small carbon sink during recent years. Furthermore, we found that the steppe is becoming greener and stores more CO2 during our study period. The trend in carbon uptake can be attributed to different mechanisms for different seasons. During winter, higher daytime temperatures promote plant growth which leads to higher uptake of CO2 through photosynthesis. An earlier summer monsoon provides more cloud cover during early summer, which relieves drought stress from the plants, thus increasing photosynthetic uptake of CO2. We observed increasing drought conditions during late summer, which hampers soil respiration stronger than plant growth. Together, these changes lead to stronger and earlier greening of the central Tibetan alpine steppe ecosystem and to more carbon storage than release. Key Points: A widespread greening of the alpine steppe at Nam Co was observed, increasing the daily ecosystem carbon uptake by 0.5 g C m−2 decade‐1Larger diurnal temperature range during winter promotes plant growth more than soil respirationEarlier summer monsoon cloud cover and greater aridity in autumn both lead to increased net carbon uptake during these times [ABSTRACT FROM AUTHOR]

Currently available evapotranspiration (ET) products have not provided us with an accurate estimation for global irrigated land area. Thermal energy balance (EB) model has the potential to solve this problem. The accurate estimation of aerodynamic resistances is a major complication in most remote sensing ET models. An EB model using a column canopy‐air turbulent heat diffusion method was developed to more realistically depict dynamic changes in aerodynamic resistance. In order to estimate global ET and land surface fluxes for all weather conditions, Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra land surface temperature fields were combined and a nearest‐evaporative‐fraction gap‐filling method was merged into the EB model. A global ET product covering the period 2003–2017 was produced using the EB model. By combining thermal and optional information from MODIS satellites and surface meteorological forcing data from ERA‐Interim reanalysis data, the EB model provides a 5 × 5 km resolution estimate of daily ET without spatio‐temporal gaps at the global scale. Assessment of the daily EB ET at 238 flux sites showed a mean bias of 0.05 mm/day and an RMSE of 1.56 mm/day. Analysis of global precipitation minus ET demonstrated that EB ET has a relatively higher potential for agriculture water resource management than currently available global ET products, such as Landflux, GLEAM, MOD16, GLDAS, and ERA‐Interim ET. In addition, the EB model developed in this study can be applied to both polar and geostationary satellite thermal sensors. Plain Language Summary: A new global evapotranspiration (ET) product was derived from satellite data using an energy balance (EB) model. The product has a daily scale and at a high spatial resolution (5 km for a global scale) for 2003–2017, which is particularly useful for agricultural studies. The model makes use of satellite remotely sensed land surface temperature (LST) and roughness length to calculate instantaneous sensible and latent heat fluxes. These instantaneous fluxes were further used to estimate daily ET. To provide a spatially and temporally continuous map of daily ET globally, two gap‐filling methods were employed to correct for the gaps in LST and evaporative fraction products under cloudy sky conditions. The daily ET product has been successfully evaluated with ground based flux tower data. The global ET dataset has a relatively higher potential for agriculture water resource management than currently available global ET products. In addition, the EB model developed in this study can be applied to other polar and geostationary satellites. Key Points: An energy balance (EB) model was developed to take into account more accurate dynamic changes of aerodynamic resistance than other evapotranspiration (ET) modelsThe thermal EB model can estimate daily ET for all weather conditionsThe EB ET data has a higher potential for application in agriculture water resource management than most of the global ET products [ABSTRACT FROM AUTHOR]

The contrasting responses of ice core δ18O records (δ18Oice) from the northern and southern Tibetan Plateau (TP) to the El Niño Southern Oscillation (ENSO) complicate δ18Oice‐based temperature reconstructions. These contrasting responses were explored using stable hydrogen isotopes in water vapor (δDv). We found that the interannual variation in δDv from the northern TP is influenced by midtropospheric moisture sources from the Indo‐Pacific Warm Pool, with enriched (depleted) δDv values in La Niña (El Niño) years due to enhanced (weakened) deep convection. In comparison, the interannual δDv variation in the southern TP is mainly influenced by low‐tropospheric moisture from the central Indian Continent, whose δDv is depleted (enriched) in La Niña (El Niño) years. These results demonstrate that moisture transported from different altitudes can lead to opposite isotopic signals of water vapor over the northern and southern TP and can be used to reconcile the contrasting responses of δ18Oice to ENSO. Plain Language Summary: The seasonal and interannual variations in stable hydrogen isotopes in water vapor (δDv) over the northern Tibetan Plateau (TP) are analyzed using satellite retrievals and model simulations. While seasonal variations in δDv from the northern TP are highly correlated with local temperature, the interannual variation in δDv is weakly related to local temperature but is significantly and positively correlated with the Southern Oscillation Index (SOI). Moreover, the positive correlation between the δDv and the SOI is in direct contrast with results from the southern TP. Our results indicate that reconstructed temperatures based on ice core δ18O records are biased higher (lower) in the northern (southern) TP when the tropical Pacific is in a La Niña phase, and vice versa when the tropical Pacific is in an El Niño phase. Hence, we suggest that the ENSO‐related isotopic signals should be removed to constrain the uncertainty of temperature reconstruction in the TP. Key Points: Changes of δDv in the northern Tibetan Plateau link to remote deep convection which is modulated by El Niño Southern Oscillation (ENSO)Moisture transported from different altitudes can lead to opposite isotopic signalsThe contrasting responses of ice core δ18O records from the northern and southern TP to ENSO are reconciled [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) is characterized by complex topography and heterogeneous surface cover, which makes it difficult to obtain accurate precipitation data at a regional scale. Therefore, it is important to use dense ground observations to evaluate satellite‐derived precipitation products. In this study, the top‐down‐based Global Precipitation Measurement Integrated MultisatellitE Retrievals (GPM IMERG) and bottom‐up‐based Soil Moisture TO RAIN‐Advanced SCATterometer (SM2RAIN‐ASCAT; SM2RASC) precipitation products were evaluated against 1,584 unevenly distributed rain gauges over the TP from May to October 2015. Results show: (1) The overall performances of IMERG and SM2RASC are comparable at the daily scale, with a higher correlation coefficient (CC) for IMERG and lower root‐mean‐square error (RMSE) for SM2RASC. Regarding the precipitation detectability, IMERG outperforms SM2RASC; (2) Spatially, SM2RASC shows better performance than IMERG in grasslands, but IMERG outperforms SM2RASC in forest areas, due to the low quality of the soil moisture retrieved by satellite in the areas; (3) The accuracy of both SM2RASC and IMERG is closely correlated with altitude and rainfall intensity. The SM2RASC product estimates light to moderate rainfall (5–25 mm/day) more accurately than the IMERG, but the IMERG product shows better performance for drizzle and heavy rainfall (>25 mm/day). Due to relatively frequent fluctuations of the ASCAT soil moisture product, SM2RASC frequently reports false rainfall in dry conditions. This study demonstrates the good performance of the SM2RASC product over the TP and suggests that the impact of vegetation density and topography should be considered for improving the SM2RAIN algorithm. Key Points: Soil Moisture TO RAIN‐Advanced SCATterometer (SM2RAIN‐ASCAT) estimates daily rainfall better in grassland areas, and the Global Precipitation Measurement‐Integrated MultisatellitE Retrievals for GPM (GPM IMERG) product outperforms in forestsSM2RAIN‐ASCAT estimates light to moderate rainfall more accurately than GPM IMERG, but it cannot detect heavy rainfall eventsDue to relatively frequent fluctuations of ASCAT soil moisture product, SM2RAIN‐ASCAT frequently reports false rainfall in dry conditions [ABSTRACT FROM AUTHOR]

Evapotranspiration (ET) is composed of soil evaporation (ETs), canopy transpiration (ETc), and canopy intercepted water evaporation (ETw), and it plays an indispensable role in the water and energy cycles of land surface processes. More accurate estimations of variations in ET are essential for natural hazard monitoring and water resource management. An improved algorithm for ETs with soil moisture and texture (SMT) and an optimized ETc based on the MOD16 model (MOD16‐STM) are proposed for the cold, arid, and semiarid regions of the Tibetan Plateau (TP). The nonlinear relationships between the soil surface resistance (rss) and soil surface hydration state in different soil textures were redefined by using five flux tower measurements over the TP. The value of the mean potential stomatal conductance per unit leaf area (CL) used for ETc calculation in grasslands was optimized at 0.0038 (m s−1). The MOD16‐STM was compared with the MOD16 and a soil water index‐based Priestley‐Taylor algorithm (SWI‐PT) at five independent sites. The results showed that the half‐hourly, daily, and monthly estimations from the MOD16‐STM were closer to observations than those from the other two models. The results indicated that the MOD16‐STM increased R2 by 0.2/0.05 and the index of agreement by 0.37/0.23 and deceased RMSE by 43.89/42.77 W m−2 and the absolute mean bias (|MB|) by 46.23/45.89 W m−2, when compared to the results of the MOD16 at daily/monthly scales. The results suggested that the MOD16‐STM will produce more accurate ET estimates over the flux sites and has great potential for ET estimation and land surface model improvement for the TP region. Key Points: The topsoil water content is the dominant factor in evapotranspiration over the Tibetan PlateauDifferences in the surface soil content and soil texture were used to optimize the soil resistance of bare soilThe model accurately simulates the latent heat flux by considering the impacts of soil properties on the evaporation from bare soil [ABSTRACT FROM AUTHOR]

Precipitation is a key hydrometeorological variable for understanding surface energy partitioning and water budget over the Tibetan Plateau (TP). A substantial proportion of summer precipitation falls as rain. The effects of different land surface models (LSMs) on the TP's precipitation and their inner mechanisms remain unclear. Therefore, the assessments of different LSMs coupled with the Weather Research and Forecasting model in precipitation simulation were investigated over the TP during June 28–29 of 2008. The simulated results were evaluated with the merged Climate Prediction Center (CPC) MORPHing technique (CMORPH) precipitation data set developed by the China Meteorological Administration. The assessment demonstrated that precipitation simulated by the Community Land Model Version 4 (CLM4), Noah‐Multiparameterization (Noah‐MP), and Pleim‐Xiu LSM schemes was wider and stronger compared with the merged CMORPH over the central and western TP but was underestimated over the eastern and southern regions. Generally, both CLM4 and Noah‐MP schemes exhibited higher forecasting quality and accuracy in simulating precipitation over the TP. The optimal precipitation simulation was achieved by applying the Noah‐MP scheme, with a lowest root mean square error of 9.53 mm/day, mainly attributed to its corrections of overforecasting for precipitation that did not occur. Further mechanism analysis indicated that soil moisture‐energy flux‐precipitation feedback play an important role in different LSM schemes. Key Points: The Weather Research and Forecasting model with different land surface parameterization schemes was used to simulate a precipitation event over the Tibetan PlateauBoth the Community Land Model Version 4 and Noah‐Multiparameterization (Noah‐MP) schemes showed higher forecasting quality and accuracy, whereas the best performance was achieved by Noah‐MPA soil moisture‐energy flux‐precipitation feedback mechanism was identified to explain the discrepancies among different model performances [ABSTRACT FROM AUTHOR]

This study focused on planetary boundary layer (PBL) growth in winter under the influence of the westerlies over the Rongbuk Valley on the north side of the central Himalayas. Two sunny November days in 2014 with different synoptic conditions in terms of large‐scale wind direction and speed were selected to investigate the ways in which large‐scale synoptic forcing affected the vertical structure of the PBL, atmospheric stability, surface wind field, and land surface energy fluxes. This was done by using radiosonde and in‐situ measurements, the European Centre for Medium‐Range Weather Forecasts ERA5 reanalysis data set, and a one‐dimensional model. The results revealed that the valley winds and PBL growth were strongly influenced by the variations of the westerlies, which prevail in this region during the winter. When the synoptic wind direction at the height of the mountain ridges was parallel to the axis of the valley and strong, the downward transmission of the westerlies to the valley floor (DTWTV) was strong, causing high near‐surface wind speeds and sensible heat flux values. These conditions, together with a deep residual layer, unstable atmosphere, and thermally driven local wind, produced an extremely deep PBL (9 km above sea level) in the early afternoon of November 23. When the synoptic wind direction at the ridge height intersected the axis of the valley and was weak, the DTWTV was weak, and the PBL became relatively low on November 28. These results demonstrate that the interaction between the topography and synoptic circulation plays a critical role in PBL growth. Key Points: Planetary boundary layer (PBL) growth in the central Himalayas can be strongly influenced by variations in the westerlies which prevail during winterThe downward transmission of the westerlies to the valley floor can cause a high sensible heat flux and an unusually strong thermally driven local windThrough its impact on atmospheric stability, the westerlies can create a deep residual layer, promoting formation of an extremely deep PBL in the early afternoon [ABSTRACT FROM AUTHOR]

In this study, a decade long measurement of aerosol optical properties at two AERONET stations (Nam Co during 2006–2016 and QOMS during 2009–2017) in the Tibetan Plateau (TP), a region sensitive to climate change and human perturbation, is presented. The baseline value of aerosol optical depth (AOD) was 0.029 and 0.027 at Nam Co and QOMS, respectively, which are comparable to or even lower than those at some Arctic and remote ocean locations. The seasonality of AOD values were the order of spring > summer > winter > autumn. Based on AOD and Ångström exponent (α), major aerosol types over the TP were further identified as continental background, biomass burning, and dust. Although continental background aerosol was the main feature in remote areas of TP, biomass burning plumes frequently occurred, especially during spring (March–April). In one of such biomass burning event in April 2014, MODIS observations demonstrated that intensive open fires occurred in South Asia, covering the foothills of Himalayas and Indo‐Gangetic Plain. The air mass back trajectories and CALIOP observations further revealed that biomass burning plume could be uplifted to higher altitudes and reach the Himalayas. Moreover, an occasional dust event detected in April 2008 over the TP demonstrated that the dust from Taklamakan Desert may impact the main body of TP episodically, although the local dust from the inside of TP cannot be excluded and warrants further study. Key Points: The baseline value of AOD in Tibetan Plateau is comparable to or even lower than that at Arctic and remote ocean locationsMajor aerosol types over the Tibetan Plateau were identified as continental background, biomass burning, and dustBiomass burning emissions in South Asia and dust from Taklamakan Desert could impact Tibetan Plateau episodically [ABSTRACT FROM AUTHOR]

Downwelling shortwave radiation (DSWR) and downwelling longwave radiation (DLWR) are two important components of the Earth's surface radiation balance. In this study, the Heliosat method and the parameterization of Crawford and Duchon (1999, https://doi.org/10.1175/1520‐0450(1999)038<0474:AIPFEE>2.0.CO;2, hereafter CD99) were calibrated to make them suitable for estimation of DSWR and DLWR over the Tibetan Plateau (TP). Based on meteorological data, forcing data, and observations from polar‐orbiting satellites, the cloud albedo was calculated, and the clear‐sky index estimation scheme of the Heliosat method was improved. These improvements were then applied to derive 10‐day DSWR under all‐sky conditions over the TP by combining the clear‐sky shortwave radiation scheme with a clear‐sky index. The coefficient of the CD99 parameterization scheme clear‐sky DLWR was also calibrated, and 10‐day all‐sky DLWR was then determined and validated using ground‐based measurements. The spatiotemporal distributions of DSWR and DLWR were analyzed in detail. The results showed that the modified methods are efficient and applicable for downward radiation retrieval under all‐sky conditions over the TP with a reasonable accuracy. The mean percentage errors for DSWR and DLWR were −4.75% and 0.11%, respectively. The variation in the monthly DSWR (DLWR) showed a convex shape, with a maximum appearing in May (July). The spatial distributions of DLWR showed a southeast‐high and northwest‐low pattern. As the subsolar point moves northward, DSWR increases gradually and is clearly influenced by the Asian summer monsoon. Key Points: The Heliosat method was improved to derive all‐sky downwelling shortwave radiation (DSWR) for the Tibetan Plateau (TP) areaAll‐sky downwelling longwave radiation (DLWR) in the TP was estimated by combining the clear‐sky radiation scheme with a clear‐sky indexAll‐sky DSWR and DLWR estimations show good agreement with in situ measurements [ABSTRACT FROM AUTHOR]

Snow cover in mountainous terrain plays an important role in regional and global water and energy balances, climate change, and ecosystems. Blowing snow is a frequent and important weather phenomenon over the Tibetan Plateau (TP); however, this process is neglected in most current land surface models, despite the consequential role it plays in the land surface and atmospheric water and energy budgets. In this paper, we present a blowing snow model PIEKTUK coupled with the Community Land Model (CLM4.5) to provide a better estimate of the snow dynamics for the consideration of snow redistribution induced by wind. Two simulations with a 0.065° spatial resolution were performed in 2010 over the TP, namely, a sensitivity experiment with the inclusion of blowing snow effects (CLM_BS) and a control run with the original model (CLM). A specific objective of this study was to evaluate the improvements in the simulations of snow dynamics and other key variables in surface energy partitioning provided by the coupled model, such as the surface albedo and land surface temperature (LST). Compared with a variety of remote‐sensing observations, the results show that the surface snow cover, snow depth, and surface albedo can be better reproduced in most of the TP region by CLM_BS than by the original CLM, particularly in the Kunlun Mountains, Hoh Xil area, and the southwestern TP. In areas with reduced bias, variations in the monthly mean snow cover fraction can be reflected particularly well by CLM_BS. For LST, however, a significant decrease in the nighttime LST bias was detected in CLM_BS, while the bias in the daytime LST increases. The results show considerable potential for the inclusion of the blowing snow process to promote the modeling of snow dynamics and land‐atmosphere interactions on the TP. Key Points: The PIEKTUK blowing snow model was coupled to the Community Land Model to better estimate the snow dynamics over the Tibetan PlateauSnow cover, snow depth, and surface albedo can be better represented by the coupled model with the inclusion of blowing snow effectsA remarkable decrease of bias in the nighttime land surface temperature is detected in the coupled model simulation [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) is an ecologically fragile region that is sensitive to climate change. In the context of global climate change, the climate change trends of the TP and the vegetation dynamic response need to be investigated. Based on in situ meteorological data, Satellite Pour l'Observation de la Terre vegetation data, and Moderate Resolution Imaging Spectroradiometer land cover data, a comprehensive analysis was conducted to determine the trends of climate parameters in the TP region at different time scales (long term: 1960–2014; midterm: 1980–2014; short term 1999–2014). A consistent warming trend was observed for different temporal scales, while a warming slowdown was identified during 1999 and 2014. The warming rate was also shown to be much higher in the high‐altitude regions (>4,000 m), especially at midterm and short‐term time scales. 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. The major significant greening trend of the TP was mainly caused by climate factors. The reforestation projects may have played a minor role in the vegetation greening in specific regions of the TP. In addition, various vegetation types showed markedly different responses to climate changes. The grassland in semiarid regions, which accounted for 41.9% of the territory of the TP, was identified to be very sensitive to variations in both temperature and precipitation. Key Points: The warming trend was observed at different temporal scales in the TP, while a warming slowdown was identified during 1999 and 2014A new cloud‐free time series of vegetation index data sets was reconstructed, and the vegetation density showed a general increasing trendThe grassland in semiarid regions was found to be very sensitive to changes in both temperature and precipitation [ABSTRACT FROM AUTHOR]

In recent days there have been discussions regarding the impact of climate change and its vagaries of the weather, particularly concerning extreme events. Nepal, being a mountainous country, is more susceptible to precipitation extreme events and related hazards, which hinder the socioeconomic development of the nation. In this regard, this study aimed to address this phenomenon for one of the most naturally and socioeconomically important regions of Nepal, namely, Eastern Nepal. The data were collected for the period of 1997 to 2016. The interdecadal comparison for two periods (1997–2006 and 2007–2016) was maintained for the calculation of extreme precipitation indices as per recommended by Expert Team on Climate Change Detection and Indices. Linear trends were calculated by using Mann‐Kendall and Sen's Slope estimator. The average annual precipitation was found to be decreasing at an alarming rate of −20 mm/year in the last two decades' tenure. In case of extreme precipitation events, consecutive dry days, one of the frequency indices, showed a solo increase in its trend (mostly significant). Meanwhile, all the intensity indices of extreme precipitation showed decreasing trends (mostly insignificant). Thus, it can be concluded that Eastern Nepal has witnessed some significant drier days in the last two decades, as the events of heavy, very heavy, extremely heavy precipitation events, and annual wet day precipitation (PRCPTOT) were found to be decreasing. The same phenomena were also seen in the Tropical Rainfall Measuring Mission 3B42 V7 satellite precipitation product for whole Nepal. Key Points: Extreme precipitation indices were subjected to their spatial and temporal analysis for the period of 1997 to 2016Average annual precipitation was found to be decreasing at an alarming rate of −20 mm/yearDecreasing precipitation in the Eastern Nepal can also be seen in the satellite precipitation product (TRMM 3B42 V7) [ABSTRACT FROM AUTHOR]

Snowfall and the subsequent evolution of the snowpack play important roles in the cryospheric and hydrospheric processes that occur on the Tibetan Plateau (TP). Current literature provides scarce evidence covering the sensitivity of solid precipitation to land surface physics schemes and initial and boundary conditions on the TP. Six numerical experiments using the Weather Research and Forecasting (WRF) model were conducted to simulate a snow event over the TP in March 2017. Different land surface physics schemes, that is, Community Land Model (CLM), Noah, and Noah‐MP, and initial and boundary conditions provided by atmospheric reanalysis data sets, that is, the National Centers for Environmental Prediction‐FNL and ERA‐Interim data sets, were applied in sensitivity analyses. The observed near‐surface air temperature, snow depth, and snow water equivalent (SWE) values were used to evaluate each model's performance. The results demonstrate that (1) the sensitivity of the near‐surface air temperature to land surface physics schemes is greater than it is to both the initial and boundary conditions; (2) the best performance is achieved when applying WRF + CLM with a root‐mean‐square error of 8.4 °C, a mean absolute deviation of 7.3 °C, a correlation coefficient of 0.75, and a spatial correlation coefficient of ~0.5 to air temperature estimates. A potentially important factor appears to be the advanced parametrization of albedo in the CLM scheme; (3) the advanced land surface schemes in the WRF model describes the physics of cryospheric and hydrospheric processes in detail, and the land surface response is determined by multiple variables and parameters in such schemes. The spatial patterns in such variables and parameters determined the detailed spatial variabilities observed in snow cover and amount and its temporal evolution. The WRF model overestimates, however, the intensity and extent of snow depth and SWE; (4) simulations of solid precipitation are more accurate when applying CLM or Noah‐MP + ERA‐Interim in WRF; and (5) WRF performance with regard to SWE estimates clearly depends upon the discrimination of lighter from heavier snowfall. Key Points: Land surface schemes (CLM, Noah, and Noah‐MP) and atmospheric forcing (NCEP‐FNL and ERA‐Interim) were applied in WRF to analyze a snow eventWe found that sensitivity of air temperature to land surface schemes is larger than to the forcing with best performance WRF + CLMWe found that simulations of solid precipitation are more accurate when applying CLM or Noah‐MP + ERA‐Interim in WRF [ABSTRACT FROM AUTHOR]

Abstract: Evapotranspiration (ET) is one of the major uncertain components of the energy and water cycle and was derived for the Nagqu River Basin based on remote sensing data and atmospheric surface layer observations under cloudless conditions. Two process‐based models were used to determine the ET: a Priestley‐Taylor (PT)‐based model and a topographical enhanced surface energy balance system (TESEBS) model. Improved broadband albedo, downward shortwave radiation flux, and reconstructed normalized difference vegetation index (NDVI) were coupled into the TESEBS model and PT‐based model to estimate the actual ET. The atmospheric surface layer meteorological data, SPOT Vegetation (VGT) data, and Moderate Resolution Imaging Spectroradiometer data were used as inputs for 10‐day ET calculations. The model‐estimated results were compared with ground truths calculated via the combinatory method. The results indicated that the ET determined by both models well fit the actual ET, with correlation coefficients (R) of 0.88 and 0.82, respectively. However, the TESEBS model showed a better performance than the PT model, with a lower mean bias error (−0.02 mm/hr) and lower root–mean‐square error (0.08 mm/hr). Although the PT model is computationally simple and requires few parameters, the strong weighting of the NDVI may lead to some overestimations, especially during the growing season. [ABSTRACT FROM AUTHOR]

Abstract: The snow‐albedo feedback is a crucial component in high‐altitude cryospheric change but is poorly quantified over the Third Pole, encompassing the Karakoram and Tibetan Plateau. Here we present an analysis of present‐day and future spring snow‐albedo feedback over the Third Pole, using a 28 year satellite‐based albedo and the latest climate model simulations. We show that present‐day spring snow‐albedo feedback strength is primarily determined by the decrease in albedo due to snow metamorphosis, rather than that due to reduced snow cover in the Karakoram, but not found in Southeastern Tibet. We further demonstrate an emergent relationship between snow‐albedo feedback from the seasonal cycle and that from climate change across models. Combined with contemporary satellite‐based snow‐albedo feedback from seasonal cycle, this relationship enables us to estimate that the feedback strength for the Karakoram with a relatively high glaciated area is −2.42 ± 0.48% K−1 under an unmitigated scenario, which is much stronger than that for Southeastern Tibet (−1.64 ± 0.48% K−1) and for the Third Pole (−0.89 ± 0.44% K−1), respectively. Moreover, it is noteworthy that the magnitude of the constrained strength is only half of the unconstrained model estimate for the Third Pole, suggesting that current climate models generally overestimate the feedback of spring snow change to temperature change based on the unmitigated scenario. [ABSTRACT FROM AUTHOR]

The uncertainties of China's gross primary productivity ( GPP) estimates by global data-oriented products and ecosystem models justify a development of high-resolution data-oriented GPP dataset over China. We applied a machine learning algorithm developing a new GPP dataset for China with 0.1° spatial resolution and monthly temporal frequency based on eddy flux measurements from 40 sites in China and surrounding countries, most of which have not been explored in previous global GPP datasets. According to our estimates, mean annual GPP over China is 6.62 ± 0.23 PgC/year during 1982-2015 with a clear gradient from southeast to northwest. The trend of GPP estimated by this study (0.020 ± 0.002 PgC/year2 from 1982 to 2015) is almost two times of that estimated by the previous global dataset. The GPP increment is widely spread with 60% area showing significant increasing trend ( p < .05), except for Inner Mongolia. Most ecosystem models overestimated the GPP magnitudes but underestimated the temporal trend of GPP. The monsoon affected eastern China, in particular the area surrounding Qinling Mountain, seems having larger contribution to interannual variability ( IAV) of China's GPP than the semiarid northwestern China and Tibetan Plateau. At country scale, temperature is the dominant climatic driver for IAV of GPP. The area where IAV of GPP dominated by temperature is about 42%, while precipitation and solar radiation dominate 31% and 27% respectively over semiarid area and cold-wet area. Such spatial pattern was generally consistent with global GPP dataset, except over the Tibetan Plateau and northeastern forests, but not captured by most ecosystem models, highlighting future research needs to improve the modeling of ecosystem response to climate variations. [ABSTRACT FROM AUTHOR]

ABSTRACT A parameterization approach of effective roughness length was introduced into the Surface Energy Balance System ( SEBS) model to account for subgrid-scale topographical influences. Regional distribution of land surface heat flux values (including net radiation flux, ground heat flux, sensible heat flux, and latent heat flux) was estimated on the Tibetan Plateau ( TP) based on the SEBS model, and utilizing remote sensing products and reanalysis datasets. We then investigated annual trends in these fluxes for the period 2001-2012. It was found that land surface net radiation flux increased slightly, especially in high, mountainous regions and the central TP, and was influenced by glacial retreat and topsoil wetting, respectively. Sensible heat flux decreased overall, especially in the central and northern TP. In the Yarlung Zangbo River ( YZR) Basin, the sensible heat flux increased because of a rise in the ground-air temperature difference. The latent heat flux increased over the majority TP, except for areas in the YZR Basin. This can be attributed to increases in precipitation and vegetation greening. [ABSTRACT FROM AUTHOR]

Accurate simulation of energy, water, and carbon fluxes exchanging between the land surface and the atmosphere is beneficial for improving terrestrial ecohydrological and climate predictions. We systematically assessed the Noah land surface model (LSM) with mutiparameterization options (Noah-MP) in simulating these fluxes and associated variations in terrestrial water storage (TWS) and snow cover fraction (SCF) against various reference products over 18 United States Geological Survey two-digital hydrological unit code regions of the continental United States (CONUS). In general, Noah-MP captures better the observed seasonal and interregional variability of net radiation, SCF, and runoff than other variables. With a dynamic vegetation model, it overestimates gross primary productivity by 40% and evapotranspiration (ET) by 22% over the whole CONUS domain; however, with a prescribed climatology of leaf area index, it greatly improves ET simulation with relative bias dropping to 4%. It accurately simulates regional TWS dynamics in most regions except those with large lakes or severely affected by irrigation and/or impoundments. Incorporating the lake water storage variations into the modeled TWS variations largely reduces the TWS simulation bias more obviously over the Great Lakes with model efficiency increasing from 0.18 to 0.76. Noah-MP simulates runoff well in most regions except an obvious overestimation (underestimation) in the Rio Grande and Lower Colorado (New England). Compared with North American Land Data Assimilation System Phase 2 (NLDAS-2) LSMs, Noah-MP shows a better ability to simulate runoff and a comparable skill in simulating R n but a worse skill in simulating ET over most regions. This study suggests that future model developments should focus on improving the representations of vegetation dynamics, lake water storage dynamics, and human activities including irrigation and impoundments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Wind profile data were measured by a wind profiler at QOMS (The Qomolangma Station for Atmospheric Environmental Observation and Research, Chinese Academy of Sciences) and, in separate experiments, GPS radiosondes were used at Shiquanhe Station and Litang Station on the Tibetan Plateau (TP). All three stations are located in the most rugged areas of the TP. QOMS is surrounded by the Himalaya, Shiquanhe Station by the Transhimalaya and Litang station is near the Hengduan Mountains. Using observational wind profile data, effective aerodynamic roughness length [ABSTRACT FROM AUTHOR]

ABSTRACT δ18O variability in daily precipitation at two stations (Lanzhou and Zhangye) north of the Qinling Mountains at the eastern margin of the Tibetan Plateau, China, and monthly precipitation δ18O at four stations to the south of the Qinling Mountains were examined. The data show that the δ18O composition of precipitation south of the Qinling Mountains is influenced strongly by the prevailing westerlies during winter and by the summer Asian monsoon during its most active periods. To the north, the westerlies prevail in winter, and δ18O trends coincide strongly with temperature. In summer, the Qinling Mountains block or weaken the Asian monsoon, which crosses them only during the most active periods. In these periods, the stations to the north experience relatively depleted δ18O values (<−7‰). During weak monsoon periods, however, most of the δ18O values in summer precipitation at Lanzhou and Zhangye are relatively enriched (>−5‰, and even as high as +9.2‰). A positive northward weighted average δ18O gradient of summer precipitation with increasing distance from the coast suggests the influence of the prevailing westerlies and of continental recycling of moisture. Both the frequency of these heavily depleted δ18O values and their duration decrease from south to north, reaching minimums at Zhangye, which may have been in the monsoonal tail region during the sampling period. The data reveal that the Qinling Mountains act as an important climatic divide along the eastern margin of the Tibetan Plateau. The effects of the Asian summer monsoon and of different moisture sources should be considered for paleoclimatic studies. [ABSTRACT FROM AUTHOR]

Two versions of the band-pass covariance technique were applied to the turbulence data collected during daytime with a simple and portable measurement system over the sparse grasslands of the Tibetan Plateau. The coherency spectra between the temperature and the specific humidity, which is a spectral counterpart of the correlation coefficient, were used as a dynamic indicator of the energy-containing ranges as well as that of the sensor attenuation at higher frequencies. The comparison with independent measurements by the eddy covariance method showed that the original version of the band-pass covariance technique occasionally fails. This indicates breakdowns of the similarity between the temperature and the water vapor, especially in the lowest-frequency regions. On the other hand, the latent heat flux computed with the advanced version exhibited adequate agreement with the eddy covariance method. This paper demonstrates that the current implementation of the advanced version with the embedded self-calibration procedure provides a robust method of frequency extrapolation in scalar flux measurements under unstable conditions. [ABSTRACT FROM AUTHOR]

Explores the potential for documenting regional fields of surface energy fluxes over the Tibetan plateau using published algorithms and previously calibrated empirical formulae with data from NOAA-14 AVHRR and atmospheric data collected during the GAME-Tibet field experiment. Comparison with observations at three field sites suggests errors in the resulting estimates are less than 10% in the clear sky conditions necessary for application of this approach. Because of the need for clear skies, it was only possible to calculate the desired regional fields for one satellite scene during the 5 month study period. Maps of surface energy fluxes, and frequency analyses of these maps, are presented for this scene. The need for an alternative, more consistently applicable, satellite-based method to map surface energy fields is highlighted.