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Over‐estimation of summer precipitation over the Tibetan Plateau (TP) is a well‐known and persistent problem in most climate models. This study demonstrates the impact of a Gaussian Probability Density Function cloud fraction scheme on rainfall simulations using the Weather Research and Forecasting model. It is found that this scheme in both 0.1° and 0.05° resolutions significantly reduces the wet bias through both local feedbacks and large‐scale dynamic process. Specifically, increased cloud water/ice content with this scheme reduces surface shortwave radiation, and consequently surface heat fluxes and evapotranspiration. This, in turn, dampens the large‐scale thermal effect of the TP and weakens the exaggerated monsoon circulation and low‐level moisture convergence. It is this large‐scale dynamic process that contributes the most (∼70%) to the wet bias reduction. Although this paper presents a modeling study, it highlights the cloud radiative feedback to the large‐scale dynamics and precipitation over the TP. Plain Language Summary: Despite numerous attempts to correct the overestimation of summer precipitation over the Tibetan Plateau (TP) in current global and regional climate models, the issue persists. This study applies the Gaussian Probability Density Function (GPDF) cloud fraction scheme in the Weather Research and Forecasting model at two different resolutions (0.1° and 0.05°) during a summer over the TP. The results show that the GPDF scheme significantly mitigates the precipitation overestimation, particularly in the high‐resolution modeling. We explored the physical processes, both local and remote, that contribute to this improvement. Specifically, an increase in cloudiness reduces the amount of radiation reaching the land surface. This decrease in surface radiative heating not only reduces local evaporation but also weakens the thermal effect of the TP. The latter is a major driver of the South Asian monsoon that conveys moisture to the TP, and its weakening reduces moisture convergence over the TP. Both the decreases in local evaporation and remote moisture convergence contribute to the alleviation of the precipitation overestimation, and the latter plays a dominant role. These findings provide a unique perspective for reducing the wet bias over the TP, focusing on the surface available energy and associated remote moisture processes. Key Points: The use of the Gaussian Probability Density Function cloud fraction scheme in high resolution greatly reduces wet bias over the Tibetan Plateau (TP) during summerMore cloud water/ice with the scheme lessens TP's thermal effect, causing a weaker South Asian monsoon and moisture convergenceWet bias reduction is mainly governed by the decrease in remote moisture rather than local evapotranspiration [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]

Simple Summary: Two-spotted spider mites (Tetranychus urticae Koch, TSSMs) greatly harm vegetables and other crops in Tibet, but predatory mites are potential effective biological agents against them. Herein, we measure the fitness and predatory abilities of four predatory mite species in the Tibetan Plateau and confirm that the predatory mite Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) had the highest fecundity, the highest pre-adult survival rate, and the highest predation capacity toward adult TSSMs at 15 d post-release. The results imply that A. swirskii is more effective for the control of TSSMs in laboratory conditions and can be viewed as an effective biological control agent candidate against TSSMs in Tibet. Predatory mites are biological control agents used in many countries against various vegetable pests, particularly spider mites. Despite the significant presence of predatory mites in the Tibetan plateau, there is limited research on their potential against spider mites in the area. This study investigated the fitness parameters and performance against TSSM of four predatory, including Amblyseius swirskii (Athias-Henriot) and three species from the genus Neoseiulus (Neoseiulus californicus (McGregor), Neoseiulus barkeri (Hughes), and Neoseiulus cucumeris (Oudemans)), originally collected from fields in the Tibetan Plateau. Compared to the other three predatory species, A. swirskii exhibited the highest fecundity (11.60 ± 0.34) and the highest pre-adult survival rate (83.33 ± 3.33%). Since their juvenile survival rate (SR) was extremely low (13.33% ± 5.77%), most N. barkeri nymphs died before emergence. Compared to the other three predatory mites, A. swirskii showed the highest predation capacity against adult TSSMs at 15 d post-release (14.28 ± 2.24). Based on the results, A. swirskii was the most effective, and N. barkeri was the least effective in controlling two-spotted mites in the Tibetan Plateau among the four species tested in this study. Collectively, these findings imply notable advantages in employing A. swirskii for controlling two-spotted mites in the Tibetan Plateau. This study informs the development of a feasible biological control method based on suitable predatory mite species to manage TSSMs in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Reliable precipitation simulation over the Tibetan Plateau (TP) remains a challenge, manifested by a prominent systematic wet bias in the warm season. Previous studies have generally neglected the potential linkage between surface radiation energy budget and precipitation bias. Prevalent scattered cumulus and thunderstorms over the TP in summer strongly influence surface radiation. A cloud fraction scheme considering subgrid temperature and humidity fluctuations is implemented in the WRF model and tested for a month‐long simulation. It is found that the scheme better reproduces the surface solar radiation compared to a default cloud fraction scheme in the WRF model. Using abundant surface observations, we find that overestimation of the downward surface shortwave radiation (DSSR) would lead to wet bias. DSSR overestimation contributes to higher surface temperature and larger evaporation and enhanced atmospheric instability, which favor more simulated convective precipitation. The study suggests that a better simulation of clouds and surface radiation would benefit precipitation simulation over the plateau. Plain Language Summary: Summer precipitation over the Tibetan Plateau (TP) is generally overestimated in general circulation models as well as regional weather forecasts and climate models. The prevailing "popcorn‐like" clouds over the TP in summer would strongly impact surface radiation. Considering the potential linkage between surface radiation energy budget and precipitation bias, a statistical cloud fraction and subgrid condensation scheme (GS‐PDF scheme) is implemented in the WRF model and tested for a month‐long simulation. The GS‐PDF scheme better captures clouds over the TP with more mid‐low cloud water (ice) than the default Xu‐Randall scheme. Increased mid‐low cloud water in the GS‐PDF scheme reduced simulated downward surface shortwave radiation, reduced simulated surface temperatures, atmospheric instabilities and convective precipitation, leading to alleviated wet bias over the TP. This study suggests that better simulations of cloud and surface radiation would be beneficial for simulations of hydrological cycles over the TP. Key Points: A new cloud macrophysics scheme considering subgrid temperature and humidity fluctuations is implemented in the WRF modelThe new macrophysics scheme reduced simulated downward surface shortwave radiation, surface temperatures and atmospheric instabilitiesA better simulation of clouds and surface radiation would benefit precipitation simulation over the Tibetan Plateau [ABSTRACT FROM AUTHOR]

Most climate models show systematic cold biases during snow‐covered period over the Tibetan Plateau (TP), which is associated with snow and surface albedo overestimations. In this work, a snow cover fraction (SCF) scheme and a recently developed albedo scheme for shallow snow are implemented in the Noah‐MP land surface model coupled with the Weather Research and Forecasting (WRF) model. The SCF scheme introduces subgrid orographic variability to reduce the SCF, and the shallow‐snow albedo scheme parameterizes the fresh‐snow albedo as a function of the snow depth (SD). Evaluations by remote sensing data show that both schemes can effectively alleviate the overestimation of the simulated surface albedo, SCF, snow water equivalent, and SD over the TP. The reductions in the modeled SCF and snow albedo directly lead to lower surface albedo values and thus more surface solar radiation absorption, which accelerates snow melting and causes surface warming effects. Further comparisons with Moderate Resolution Imaging Spectroradiometer data and station observations show that both schemes can significantly reduce the cold biases in the surface skin temperature (from −4.39°C to 0.19°C for the TP mean) and 2‐m air temperature (from −4.48°C to −1.05°C for the station mean) during the cold season (October to May of next year) in the study region. This work provides guidance for advancing the snow‐related physics in climate models and the improved WRF model could facilitate weather forecasting and climate prediction for the plateau region. Plain Language Summary: The cold bias of the Weather Research and Forecasting model over the Tibetan Plateau is significantly reduced by implementing a snow coverage‐topography relationship and a fresh snow albedo scheme. With the introduction of the subgrid orographic variability in parameterizing the snow cover fraction and a shallow‐snow albedo scheme in parameterizing the fresh‐snow albedo, less snow and a lower surface albedo are simulated. Thus, more solar radiation is absorbed by the land surface, leading to a surface warming effect. As a result, the cold biases in the surface skin temperature and 2‐m air temperature are significantly reduced when evaluated by Moderate Resolution Imaging Spectroradiometer data and station observations. Key Points: A snow coverage‐topography relationship and a fresh snow albedo scheme are implemented in Weather Research and Forecasting and applied to the Tibetan Plateau (TP)The overestimation in the simulated snow cover, snow depth (SD) and albedo over the TP is significantly alleviatedThe modeled cold biases over the TP are significantly reduced due to the enhanced surface net solar radiation induced by albedo reduction [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]

Understanding cloud distribution over lakes is crucial to determine input radiation and precipitation for lake thermal and water balance processes. Based on Himawari‐8 satellite observation and Weather Research and Forecasting model results, this study examines the influences of lakes on daytime cloud cover during warm seasons over the Tibetan Plateau (TP), which is home to thousands of lakes. Observation shows the existence of cloud holes and narrow cloud rings around the lakes, that is, fewer clouds over the lakes and more clouds along the shoreline, which has rarely been reported and is considered typical to TP by comparison with lakes outside of TP. The threshold size of lakes that can produce the shoreline cloud ring is identified to be about 300 km2, as a conservative estimate. We further highlight the importance of atmosphere advection/background wind in the formation of lake‐associated clouds. Lake breeze forms under weak background winds and the downdraft branch inhibits cloud formation over the lakes; while the updraft branch causes convection to form clouds over lakeshores. However, strong background winds do not favor lake breeze formation, changing cloud distribution over the lakes. Fewer clouds are also found in the downwind regions, and this influence is at a distance comparable to the lake scale. Due to fewer clouds over lakes, shortwave radiation is significantly larger (∼100 W/m2) and longwave radiation is smaller (∼a few W/m2) than that of the further land region. Therefore, the above observational facts provide a new perspective to advance the understanding of lake‐air interactions. Plain Language Summary: There are lots of lakes over the Tibetan Plateau (TP), but the influence of these lakes on cloud during warm seasons remain unclear. Satellite data shows the existence of cloud holes and narrow cloud rings around the lakes, that is, fewer clouds over the lakes and more clouds along the shoreline, which has rarely been reported before. Simulation results demonstrate that the lake breeze accounts for this phenomenon: air descends over the lake, which inhibits cloud formation, while ascending branch over the shoreline favors cloud formation. Lakes over 300 km2 can yield these cloud influences, so this area is thought as the threshold area that lakes can have influence on atmosphere. Clouds in the downwind regions are also fewer under the influence of background wind, and this influencing distance is almost equal to the lake scale itself. Due to less block by clouds, solar radiation is much higher over the lake than surrounding land, but downward longwave radiation is a little lower because of less emission from the cloud bottom, resulting an increase of net radiation in total at the lake surface. The conclusions of this study can help understand energy and hydrology processes of lakes better over the TP. Key Points: Evident "cloud holes" and "cloud rings" are found for lakes over the Tibetan Plateau, which are mainly induced by lake breezeClouds in the downwind regions are also fewer due to atmosphere advection; this distance is almost equal to the size of the lake itselfFewer clouds over the lake increase the net radiation mainly due to much higher downward shortwave radiation [ABSTRACT FROM AUTHOR]

SM2RAIN is a well-established methodology for estimating precipitation from satellite or observed soil moisture and it has been applied as a complementary approach to conventional precipitation monitoring methods. However, satellite soil moisture retrievals are usually subject to various biases and limited number of retrievals (and therefore large intervals) in remote areas, such as the Tibetan Plateau (TP), and little is known about their potential impacts on precipitation estimation. This study seeks to quantify the uncertainties in Soil Moisture Active and Passive (SMAP) soil moisture estimated precipitation through the commonly used SM2RAIN by referring to in situ soil moisture observations from the central Tibetan Plateau soil moisture network. The estimated precipitation is evaluated against rain gauge observations. Additional attention is paid to different orbits of the SMAP retrievals. Results show that the original SM2RAIN algorithm tends to underestimate the precipitation amount in the central TP when using SMAP soil moisture retrievals as input. The retrieval accuracy and sampling interval of SMAP soil moisture from ascending (descending) orbits each count for 1.04 mm/5 d (−0.18 mm/5 d) and 1.67 mm/5 d (0.72 mm/5 d) of estimated precipitation uncertainties as represented by root mean square error. Besides, the descending product of SMAP with a relatively less sampling interval and higher retrieval accuracy outperforms the ascending one in estimating precipitation, and the combination of both two orbits does add value to the overall SM2RAIN estimation. This study is expected to provide guidance for future applications of SM2RAIN-derived precipitation. Meanwhile, more reliable SM2RAIN precipitation estimations are desired when using higher quality satellite soil moisture products with better retrieval accuracy and smaller intervals. [ABSTRACT FROM AUTHOR]

The ecosystems of the Tibetan Plateau (TP) provide multiple important ecosystem services that benefit both local populations and those beyond, such as through climate regulation services on precipitation for East Asia and China. However, the precipitation regulation service of the TP ecosystems for supplying moisture and maintaining precipitation is yet to be evaluated. In this study, we used the moisture recycling framework and a moisture tracking model to quantify the precipitation regulation services of TP ecosystems for their contribution to precipitation. We found TP ecosystems contributed substantially to local and downwind precipitation, with a contribution of 221 mm/year for the TP and neighboring areas through evapotranspiration (ET) (104 mm/year through transpiration), declined to <10 mm/year for eastern China and other surrounding countries. Among ecosystem types, grassland contributed most to precipitation, followed by barren and snow lands, forests, and shrublands. In terms of seasonality, precipitation contribution from TP ecosystems was greater in summer months than in non‐summer months for western China, while the opposite was true for eastern China—although the magnitude was much smaller. Over the past two decades, the significant ET increases in TP translated to a widespread increase in precipitation contribution for TP and downwind beneficiary regions from 2000 to 2020. Our study provides a quantitative way to understand the precipitation regulation services of TP ecosystems through moisture recycling, substantiating their key role to maintain precipitation and the water cycle for downwind regions—effectively acting as an ecological safeguard that could be perceived by the public. [ABSTRACT FROM AUTHOR]

An observation‐based parameterization of thermal roughness length (TRP) for bare ground has been implemented in the Weather Research and Forecasting model. This scheme introduces a temperature scale to account for the impact of atmospheric stability. The effect of the TRP scheme is evaluated by comparing simulations with the default and with the implemented one for the Tibetan Plateau (TP) region. We find that the newly implemented scheme generally shows remarkable improvement in simulating the nighttime near‐surface 2m air temperature (T2) and daytime surface skin temperature (TSK), with a reduction in cold biases. The newly implemented scheme directly leads to weakened sensible heat release to the atmosphere in the daytime, thereby increasing energy storage in the land. These changes enhance snow melting in spring and reduce snow accumulation in autumn. Due to reduced snow cover and decreased albedo in the two transitional seasons, more solar radiation is absorbed by the land surface, leading to higher TSK and T2. In summer, the snow albedo feedback plays a minor role when there is minimal snow cover. In winter, the solar radiation is weak, and the atmosphere is relatively stable. Consequently, the warming effect due to the newly implemented scheme is more remarkable in the transitional seasons than in summer and winter. This work demonstrates the importance of the TRP in simulating T2 and TSK in the coupled atmosphere‐land model, and reveals that the influence of this scheme on T2 and TSK over the TP region is mainly associated with snow‐albedo‐shortwave radiation processes. Key Points: The parameterization of thermal roughness length (TRP) is important for simulating the 2m air temperature (T2) and skin temperature (TSK)The influence of the TRP on T2 and TSK is more significant during transitional seasons than in summer and winterAt seasonal scale, the TRP influences T2 and TSK mainly through snow‐albedo‐shortwave radiation processes [ABSTRACT FROM AUTHOR]

Lake surface water temperature (LSWT) is a key parameter in understanding the variability of lake thermal conditions and evaporation. The MODIS-derived LSWT is widely used as a reference for lake model validations and process studies in data-scarce regions. In this study, the accuracy of the MODIS LSWT was examined on the Tibetan Plateau (TP). In-situ subsurface temperatures were collected at five large lakes. Although the observation period covers from summer to winter, only the observations during the lake turnover period (from October to freeze-up), when the lakes are well mixed, can be used as ground truth. The MODIS LSWT agrees well with the selected in-situ data for the five large lakes, with root mean square error (RMSE) < 1 °C at nighttime and <2 °C in the daytime, indicating a high accuracy of the MODIS LSWT data. Before the turnover period, the water is thermally stratified and the surface water is warmer than the subsurface water, and thus the in-situ subsurface water temperature data and the MODIS LSWT have different representativeness. In this case, if the observations are used as a validation basis, the MODIS errors could be much magnified. This in turn indicates the importance of period selection for the validation. [ABSTRACT FROM AUTHOR]

Temperature extremes have widespread implications for maintenance of the solid water reservoir on the Tibetan Plateau (TP), but their changing spatiotemporal patterns and elevation dependence have not been well understood. Using observations at 124 stations, this study shows that the TP as a whole has experienced increasing intensities/frequencies of warm extremes (0.37°C decade−1/2.4% decade−1) and decreasing intensities/frequencies of cold extremes (0.59°C decade−1/2.4% decade−1) during 1973–2018, and that these changes strengthen as regional mean warming intensifies. Unlike extreme high temperature, trends in extreme low temperature depend strongly on elevation, and the temporal evolution of such elevation‐dependency is dominated by rapid snow decline in high altitudes caused by regional mean warming. The stronger regional mean warming, the more significant elevation dependency of trends in extreme low temperatures. These results indicate that TP extreme temperature changes, especially at higher elevations, will become more significant in a warmer future, which has important implications for the ecosystems dependent on high‐elevation water resources. Plain Language Summary: Presently, the Tibetan Plateau (TP), known as the Earth's Third Pole, is home to large areas of snow and ice which act as a water resource for billions of people. In the context of climate warming, extreme temperature events are becoming more frequent and this will impact the maintenance of these water resources. However, changes in extreme temperature events on the TP and their elevation dependency are not as yet well understood. Using observations at 124 stations, we highlight spatiotemporal patterns of changes in temperature extreme showing increasing (decreasing) intensities/frequencies of warm extremes (cold extremes) and that these changes strengthen as regional mean warming intensifies. We also reveal that the amplitude of regional mean warming determines the existence of elevation dependency of extreme low temperature trends, and that changing elevation gradients in snow depth over time have been responsible. Key Points: Changes in temperature extremes strengthen as regional mean warming intensifies over the Tibetan Plateau (TP)Regional mean warming determines the existence of elevation dependency in TP cold extreme trendsSnow depth change acts as a bridge in the connection between regional mean warming and elevation dependency of TP cold extreme trends [ABSTRACT FROM AUTHOR]

As a 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) breaks. Few studies have investigated the impact of SAM breaks 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 SAM breaks 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 SAM break‐impacted region, which is distributed in the central‐eastern part of TP, photosynthesis become more active during SAM breaks. 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 SAM breaks on the central‐eastern TP. Our analysis indicates that more carbon assimilated by photosynthesis 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. Key Points: South Asia monsoon (SAM) breaks occur almost every year impacting a wide area on the central‐eastern Tibetan Plateau (roughly east of 92°E)The carbon assimilation becomes more active during SAM breaksThe increase in solar radiation absorbed boosts grass productivity during SAM break on the central‐eastern Tibetan Plateau [ABSTRACT FROM AUTHOR]

Solid water resources such as glaciers and snow cover are widely distributed in the western Tibetan plateau (WTP), and precipitation is the key supply of them. However, the characteristics of precipitation over the WTP remain unclear due to sparse observations. Using observation‐based gridded data (APHRODITE, GPCC), satellite products (TRMM, GPM), reanalysis data (ERA5, ERA‐Interim, JRA‐55) and weather research and forecasting model (WRF)‐simulation data (HAR10, HAR30), this study investigated the precipitation characteristics in high mountain areas (altitude >2,500 m a.s.l.) of the WTP (26–44°N, 70–85°E) from 2001 to 2013. Results show that annual GPM precipitation (336 mm) is much lower than that of other data sets (570–800 mm) for the WTP and appears to be an outlier; meanwhile, the other data sets show increasing precipitation as grid resolution decreases (becomes coarser). In contrast, high spatial resolution WRF simulations (HAR10, HAR30) yielded considerably higher precipitation in four strongly glacierized alpine areas (Western Himalaya, Karakorum, Tajikistan, and west Kunlun) than the other data sets. When compared to precipitation estimated using the water balance in nine glacierized catchments of the Upper Indus River Basin, the HAR data sets more reasonably represent the amount of precipitation in high mountain areas than the other data sets. The surface albedo, snow cover extent, and snow cover duration observed by satellites further indicate that the HAR data sets yield reasonable spatial variability of precipitation. This implies that the commonly used data sets (such as observation data and satellite products) underestimate the precipitation in high mountain areas. According to the HAR10 data, the four major glacierized areas on the WTP have similar precipitation amounts in summer and autumn, and the winter–spring contribution to annual precipitation is at least 70% in three of these areas (Western Himalaya, Karakorum, and Tajikistan). This pattern indicates that precipitation over the high‐altitude areas in WTP is mainly controlled by the mid‐latitude westerlies. The annual precipitation in these areas is over 1,000 mm, which is comparable to that of the southeast TP but much larger than that on the central plateau. Therefore, the spatial precipitation pattern across the TP is 'wet east and west, dry middle'. [ABSTRACT FROM AUTHOR]

Given the threats that climate change poses to solid water reservoirs on the Tibetan plateau (TP), there is significant interest in understanding spatial patterns of climate change and their causes. Weather station observations have been extensively examined, but are scarce, resulting in an incomplete understanding of climate change across the TP, particularly in the west. Using recent (2001–2015) satellite‐based data sets (2 m air temperature, land surface temperature, albedo and snow cover), this study reveals that mean annual 2 m air temperature in the southwestern TP has decreased by 0.15°C/decade in contrast to overall warming (+0.18°C/decade) on the rest of the TP. Up to 45% (74%) of the variance in the annual (spring) 2 m air temperature can be explained by simultaneous change in snow‐induced albedo in the southwestern TP. The free atmosphere column over this region and Northwest India is cooling, providing a favourable environment for the decrease in 2 m air temperature observed. Moreover, the anomalous water vapour transport into the southwestern TP is advantageous for increased snowfall and the associated decrease in 2 m air temperature. The implications of this anomalous cooling under global warming have yet to be fully considered, in particular for the futures of glaciers and snowpack over the Himalayan Mountains in the southwestern TP. [ABSTRACT FROM AUTHOR]

Correct understanding of the land-surface processes and cloud-precipitation processes in the Tibetan Plateau (TP) is an important prerequisite for the study and forecast of the downstream activities of weather systems and one of the key points for understanding the global atmospheric movement. In order to show the achievements that have been made, this paper reviews the progress on the observations for the atmospheric boundary layer, land-surface heat fluxes, cloud-precipitation distributions and vertical structures by using ground- and space-based multiplatform, multisensor instruments and the effect of the cloud system in the TP on the downstream weather. The results show that the form drag related to the topography, land–atmosphere momentum and scalar fluxes is an important part of the parameterization process. The sensible heat flux decreased especially in the central and northern TP caused by the decrease in wind speeds and the differences in the ground-air temperatures. Observations show that the cloud and precipitation over the TP have a strong diurnal variation. Studies also show the compressed-air column in the troposphere by the higher-altitude terrain of the TP makes particles inside clouds vary at a shorter distance in the vertical direction than those in the non-plateau area so that precipitation intensity over the TP is usually small with short duration, and the vertical structure of the convective precipitation over the TP is obviously different from that in other regions. In addition, the influence of the TP on severe weather downstream is preliminarily understood from the mechanism. It is necessary to use model simulations and observation techniques to reveal the difference between cloud precipitation in the TP and non-plateau areas in order to understand the cloud microphysical parameters over the TP and the processes of the land boundary layer affecting cloud, precipitation and weather in the downstream regions. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau is regarded as the Earth's Third Pole, which is the source region of several major rivers that impact more 20% the world population. This high‐altitude region is reported to have been undergoing much greater rate of weather changes under global warming, but the existing reanalysis products are inadequate for depicting the state of the atmosphere, particularly with regard to the amount of precipitation and its diurnal cycle. An ensemble Kalman filter (EnKF) data assimilation system based on the limited‐area Weather Research and Forecasting (WRF) model was evaluated for use in developing a regional reanalysis over the Tibetan Plateau and the surrounding regions. A 3‐month prototype reanalysis over the summer months (June−August) of 2015 using WRF‐EnKF at a 30‐km grid spacing to assimilate nonradiance observations from the Global Telecommunications System was developed and evaluated against independent sounding and satellite observations in comparison to the ERA‐Interim and fifth European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5) global reanalysis. Results showed that both the posterior analysis and the subsequent 6‐ to 12‐hr WRF forecasts of the prototype regional reanalysis compared favorably with independent sounding observations, satellite‐based precipitation versus those from ERA‐Interim and ERA5 during the same period. In particular, the prototype regional reanalysis had clear advantages over the global reanalyses of ERA‐Interim and ERA5 in the analysis accuracy of atmospheric humidity, as well as in the subsequent downscale‐simulated precipitation intensity, spatial distribution, diurnal evolution, and extreme occurrence. Key Points: A pilot reanalysis over the Tibetan Plateau using the PSU WRF‐EnKF system was developed and evaluated against independent soundings and satellite observations as well as ERA‐Interim and ERA5The pilot reanalysis had clear advantage in atmospheric humidity than existing global reanalysisThe subsequent downscaled precipitation forecasts from the pilot reanalysis compared favorably against those from the global reanalyses of ERA‐Interim and ERA5 [ABSTRACT FROM AUTHOR]

Satellite data, characterized by extensive regional coverage and relatively high spatial resolution, have a distinct advantage for examining elevation‐dependent warming (EDW) across rugged topography in mountain regions where there are sparse in situ observations. Based on recent (2001–2015) comprehensive satellite‐based data sets (2 m air temperature, land surface temperature, snow cover, and daytime and nighttime cloud), this study finds that annual mean 2 m  air temperature warming rates show rapid decrease above 4,500 m despite increasing from 2,000 to 4,500 m. This indicates a reversal in EDW at the highest elevations on the Tibetan Plateau, which is somehow different from the EDW derived from short‐term land surface temperature presented in earlier research. The decrease of warming rate above 4,500 m coincides with the elevation at which most of the current solid water resources reside. Thus, their decline may be less rapid than previously thought. Trends in nighttime cloud and snow cover are both correlated with patterns of EDW on the Tibetan Plateau, but the leading factor varies on an annual and seasonal basis. These results provide important evidence for understanding EDW and its controlling mechanisms in an extreme high‐elevation context. Key Points: The warming rate of satellite‐based 2 m air temperatures rapidly decreases above 4,500 m despite an increase from 2,000 to 4,500 m over the Tibetan PlateauThe decrease of warming rate above 4,500 m is conducive to less rapid decline of 83% of the current plateau solid water resourcesChanges in nighttime cloud cover and snow cover have a strong control on EDW patterns on the plateau [ABSTRACT FROM AUTHOR]

Although the impact of El Niño–Southern Oscillation on the Tibetan Plateau (TP) is reflected through stable isotopes of precipitation and ice cores, the hydroclimate response of TP lakes to El Niño–Southern Oscillation is seldom investigated. Here we show that significant lake water deficit occurred on the central TP (CTP) due to a dramatic decrease in precipitation 2016 El Ni/2016 El Niño event, followed by extreme lake water surplus in 2016 and 2017 over most of the TP (except the eastern CTP). Similar but weaker lake shrinkage and afterward expansion can also be found during historical El Niño events. Further exploration reveals that the CTP dry anomaly during El Niño events tends to bridge the dry anomalies over India and northern China, thereby forming a dry zone along the northwestern edge of the Asian monsoon domain. This study may shed light on the prediction of lake level changes on the TP. Plain Language Summary: The 2015/2016 El Niño was one of the three strongest on record and had tremendous impact on global climate, but its impact on the hydroclimate of the Tibetan Plateau is seldom investigated. Between 2013 and 2017, we carried out extensive fieldwork to monitor lake level changes on the central Tibetan Plateau and were fortunate to capture the whole process of lake level changes during this event. We found that lakes on the central Tibetan Plateau experienced significant shrinkage due to a dramatic decrease in precipitation in 2015. In the following 2016 and 2017, most lakes over the Tibetan Plateau expanded at unusually high speed. Similar but weaker lake shrinkage and afterward lake expansion also occurred during historical El Niño events. We further investigate how El Niño–Southern Oscillation can influence the climate of the Tibetan Plateau on a large scale and find that the central Tibetan Plateau dry anomaly tends to bridge the dry anomalies over India and northern China, thereby forming a dry zone along the northwestern edge of the Asian monsoon domain during an El Niño developing summer. This study may shed light on the prediction of lake level changes on the Tibetan Plateau. Key Points: Dramatic lake shrinkage occurred on the TP during the 2015/2016 El Niño event, followed by rapid lake expansion in 2016 and 2017Considerable drought and lake shrinkage on the CTP also occurred during historical El Niño eventsENSO may have dramatic impact on the hydroclimate of the TP, especially the CTP [ABSTRACT FROM AUTHOR]

The ability of FLake, WRF‐Lake, and CoLM‐Lake models in simulating the thermal features of Lake Nam Co in Central Tibetan Plateau has been evaluated in this study. All the three models with default settings exhibited distinct errors in the simulated vertical temperature profile. Then model calibration was conducted by adjusting three (four) key parameters within FLake and CoLM‐Lake (WRF‐Lake) in a series of sensitive experiments. Results showed that each model's performance is sensitive to the key parameters and becomes much better when adjusting all the key parameters relative to tuning single parameter. Overall, setting the temperature of maximum water density to 1.1 °C instead of 4 °C in the three models consistently leads to improved vertical thermal structure simulation during cold seasons; reducing the light extinction coefficient in FLake results in much deeper mixed layer and warmer thermocline during warm seasons in better agreement with the observation. The vertical thermal structure can be clearly improved by decreasing the light extinction coefficient and increasing the turbulent mixing in WRF‐Lake and CoLM‐Lake during warm seasons. Meanwhile, the modeled water temperature profile in warm seasons can be significantly improved by further replacing the constant surface roughness lengths by a parameterized scheme in WRF‐Lake. Further intercomparison indicates that among the three calibrated models, FLake (WRF‐Lake) performs the best to simulate the temporal evolution and intensity of temperature in the layers shallower (deeper) than 10 m, while WRF‐Lake is the best at simulating the amplitude and pattern of the temperature variability at all depths. Key Points: The performance of three one‐dimensional lake models in simulating the thermal structure of Nam Co Lake is evaluated and improvedKey processes related to the simulated thermal regime of alpine lakes on the Tibetan Plateau are indicated and revealed [ABSTRACT FROM AUTHOR]

Parameterizations of fractional vegetation cover (FVC) in land surface models have important effects on simulations of surface energy budget, especially in arid and semiarid regions. This study uses a FVC scheme in which FVC is derived from leaf area index and a remotely sensed clumping index. The performance of the new scheme (SMFVC) is evaluated against Moderate Resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) and in situ soil temperature observations, together with two other FVC schemes, a general FVC scheme (CTL) based on land cover map and a climatology‐based FVC scheme (RSFVC) that uses long‐term remotely sensed Normalized Difference Vegetation Index of MODIS. The three FVC schemes were implemented in the Common Land Model (CoLM) and applied in the Tibetan Plateau using the same forcing data and default parameters. Our results demonstrate that FVC schemes have significant influence on the CoLM performance: (1) the RSFVC and SMFVC schemes significantly reduce the LST biases found in CTL, particularly in grassland and during summer; (2) soil temperature evaluation by in situ observations from three networks on the Tibetan Plateau corroborates the LST results; and (3) the improvements are mainly related to representing temporal (seasonal) variability and subgrid heterogeneity of FVC, which improves surface albedo and surface energy balance. In other words, by including more vegetation characteristics, such as using a clumping index, land surface models may better simulate surface vegetation condition and further better represent the land surface energy budget over the Tibetan Plateau. Key Points: A fractional vegetation cover scheme based on leaf area index and a remotely sensed clumping index is adopted in CoLMThe new scheme significantly reduces the land surface temperature biases in grassland over the Tibetan Plateau during summerAccounting for seasonal variability and subgrid heterogeneity of vegetation cover improves surface albedo and surface energy balance [ABSTRACT FROM AUTHOR]

High‐resolution modeling became popular in recent years due to the availability of multisource observations, advances in understanding fine‐scale processes, and improvements in computing facilities. However, modeling of hydrological changes over mountainous regions is still a great challenge due to the sensitivity of highland water cycle to global warming, tightly coupled hydrothermal processes, and limited observations. Here we show a successful high‐resolution (3 km) land surface modeling over the Sanjiangyuan region located in the eastern Tibetan plateau, which is the headwater of three major Asian rivers. By developing a new version of a Conjunctive Surface‐Subsurface Process model named as CSSPv2, we increased Nash‐Sutcliffe efficiency by 62–130% for streamflow simulations due to the introduction of a storage‐based runoff generation scheme, reduced errors by up to 31% for soil moisture modeling after considering the effect of soil organic matter on porosity and hydraulic conductivity. Compared with ERA‐Interim and Global Land Data Assimilation System version 1.0 reanalysis products, CSSPv2 reduced errors by up to 30%, 69%, 92%, and 40% for soil moisture, soil temperature, evapotranspiration, and terrestrial water storage change, respectively, as evaluated against in situ and satellite observations. Moreover, CSSPv2 well captured the elevation‐dependent ground temperature warming trends and the decreased frozen dates during 1979–2014, and significant increasing trends (p < 0.05) in evapotranspiration and terrestrial water storage during 1982–2011 and 2003–2014 respectively, while ERA‐Interim and Global Land Data Assimilation System version 1.0 showed no trends or even negative trends. This study implies the necessity of developing high‐resolution land surface models in realistically representing hydrological changes over highland areas that are sentinels to climate change. Key Points: CSSPv2 land model was developed over headwaters with conjunctive surface‐subsurface flows, storage‐based runoff, and soil organic matterCSSPv2 outperformed global reanalysis for simulations of hydrological cycle as validated with multisource observationsCSSPv2 captured elevation‐dependent warming, increasing ET and TWS in the satellite era, while global reanalysis failed over headwaters [ABSTRACT FROM AUTHOR]

ABSTRACT The trends and variations in precipitable water (PW) over the Tibetan Plateau (TP) from 2000 to 2010 are analysed using the monthly mean PW datasets from Moderate Resolution Imaging Spectroradiometer (MODIS) and ERA-Interim reanalysis of European Centre for Medium-Range Weather Forecasts (ECMWF). Three different methods (including linear fit, non-parametric and non-linear) are used to estimate PW trends and their significance. The trend patterns derived from MODIS and ECMWF are very similar except for the magnitude. Increasing trends are found in the eastern and western TP; with decreasing trends in the middle. Atmospheric water vapour is more changeable compared to the surrounding areas and large PW anomalies occur frequently in July and August over the TP. Regression analysis between monthly mean anomalies of ECMWF PW and ECMWF surface air temperature (SAT) indicates reanalyses data show larger regression slope (7.36 ± 0.75 % K-1) over the TP than the MODIS observations (4.81 ± 0.72 % K-1) mainly in the non-monsoon season. The comparison of the vertically integrated moisture flux and its divergence between the wettest and driest monsoon seasons indicates that the PW spatial variability in monsoon seasons over the TP is affected by the large-scale atmospheric circulation. Although the TP region is under the influence of one large-scale circulation pattern (the monsoon) and the consistent warming background, the PW trends and the relation of PW and temperature are spatially heterogeneous, which is particularly important for predicting hydrological changes in this region. [ABSTRACT FROM AUTHOR]

Abstract: Soil moisture plays an essential role in the terrestrial water cycle. It is very important to obtain soil moisture for many applications. Soil moisture acquired by remote sensing, land surface modeling, and data assimilation must be evaluated against in-situ measurements before being used, but a procedure should be performed to upscale the point-scale measurements to the grid-scale or footprint-scale. In this study, a new upscaling algorithm is developed by introducing MODIS-derived apparent thermal inertia (ATI). First, a functional relationship between the station-averaged soil moisture and the pixel-averaged ATI is constructed. Second, this relationship is used to calculate the representative soil moisture time series at a certain spatial scale. Last, the Bayesian linear regression is applied to obtain the upscaled area-averaged soil moisture by using in-situ measurements as independent variables. The algorithm is evaluated using a network of in-situ moisture sensors in the central Tibetan Plateau. The results indicate that it can effectively obtain the area-averaged soil moisture, reducing the root mean square error (RMSE) from 0.023m3/m3 before upscaling to 0.013m3/m3 after upscaling. Finally, the algorithm is implemented to the 100km×100km grid box where the network is installed, and the temporal pattern of the upscaled soil moisture agrees with the hydro-meteorological knowledge of this region. [Copyright &y& Elsevier]

Summary: A mesoscale Tibetan Plateau Soil Moisture/Temperature Monitoring Network (SMTMN) has been established to study large-scale soil–vegetation–atmosphere interactions and to validate satellite soil moisture products. Soil moisture at four layers (0–5cm, 10cm, 20cm, and 40cm) of 30 sites was monitored since July, 2010. This paper firstly introduces the network and then presents preliminary spatiotemporal analyses based on the in situ soil moisture measurements in SMTMN. Three temporal scales (half-hourly, daily, and 10-days) and three time periods corresponding to typical soil wetness conditions, including frozen soil in winter times, are discussed. Primary findings are: (a) generally 13 randomly distributed sites in the study domain are required (i.e. number of required sites) to estimate areal mean soil moisture with correlation coefficient ⩾0.99 and root mean square difference ⩽0.02m3 m−3. This provides guidance for future soil moisture network establishment in similar regions; (b) both number of required sites and the most representative site are insensitive to temporal scales while conversely sensitive to soil wetness conditions; (c) the combination of a few optimally-selected sites can give more robust estimate of areal mean soil moisture than a single site does because the former contains more information on spatial heterogeneity. These findings can provide not only a practical compromise between maintenance cost and risk on reliability for an existing soil moisture network, but also insights for soil moisture upscaling studies and satellite soil moisture products validations. [ABSTRACT FROM AUTHOR]

Abstract: The land surface soil moisture is a crucial variable in weather and climate models. This study presents a land data assimilation system (LDAS) that aims to improve the simulation of the land surface soil moisture and energy fluxes by merging the microwave remote sensing data and the general circulation model (GCM) output into a land surface model (LSM). This system was applied over the Tibetan Plateau, using the National Centers for Environmental Prediction (NCEP) reanalysis data as forcing data and the Advanced Microwave Scanning Radiometers for EOS (AMSR-E) brightness temperatures as an observation. The performance of our four data sources, which were NCEP, AMSR-E, LDAS and simulations of Simple Biosphere Model 2 (SiB2), was assessed against 5 months of in situ measurements that were performed at two stations: Gaize and Naqu. For the surface soil moisture, the LDAS simulations were superior to both NCEP and SiB2, and there was more than a one-third reduction in the root mean squared errors (RMSE) for both of the stations. Compared with the AMSR-E soil moisture retrievals, the LDAS simulations were comparable at the Gaize station, and they were superior at the Naqu station. For the whole domain inter-comparison, the results showed that the LDAS simulation of the soil moisture field was more realistic than the NCEP and SiB2 simulations and that the LDAS could estimate land surface states properly even in the regions where AMSR-E failed to cover and/or during the periods that the satellite did not overpass. For the surface energy fluxes, the LDAS estimated the latent heat flux with an acceptable accuracy (RMSE less than 35W/m2), with a one-third reduction in the RMSE from the SiB2. For the 5-month whole plateau simulation, the LDAS produced a much more reasonable Bowen Ratio than the NCEP, and it also generated a clear contrast of the land surface status over the plateau, which was wet in the southeast and dry in the northwest, during the monsoon and post-monsoon seasons. Because the LDAS only uses globally available data sets, this study reveals the potential of the LDAS to improving the land surface energy and water flux simulations in ungauged and/or poorly gauged regions. [Copyright &y& Elsevier]

Abstract: The downward solar or shortwave radiation (SWD) and atmospheric longwave radiation (LWD) play essential roles in controlling alpine environment and ecosystem. Meanwhile, utilization of solar energy has a growing demand by local residents, due to high energy cost in high altitude regions. However, it is always costly for acquiring the radiation data and there are few studies on the radiation modeling in these regions. This paper presented the major characteristics of SWD and LWD over the Tibetan Plateau (TP), which were measured at 11 stations built in the region. The results showed that LWD received by TP is much lower than that of its surrounding areas and their monthly-mean differences can be up to 100Wm−2. On the contrary, SWD over TP is significantly higher than that over its surrounding areas, due to low extinction rate of airmass, water vapor, and aerosol occurred in TP. The recorded maximum value (∼0.9) of daily-mean transmittances much exceeds the upper bound (∼0.75) implied in most of the Angström–Prescott models; therefore, these models may under-estimate SWD over TP. One set of surface data-based estimate by a non-Angström–Prescott model and two sets of satellite estimates were also evaluated against the measurements. It is found that the surface data-based estimate, though not calibrated locally, shows a good agreement with the measurements and has an advantage of producing less root-mean-square errors and higher correlation coefficients than the satellite estimates. Under this condition, it is suggested to combine both the surface data-based estimate together with the satellite estimates in order to improve the accuracy of the SWD and LWD data. [Copyright &y& Elsevier]

Evaluation of the gridded products in the detection accuracy and spatio-temporal variabilities of precipitation over the Tibetan Plateau (TP) is crucial to the research of climate change and extreme events. Previous evaluation works mainly focus on the amount of precipitation and the capability in event detection. This study presents a multi-scale evaluation of four gridded precipitation datasets with relatively high resolutions against stations data in the variabilities of precipitation over the TP from 2004 to 2017. The four gridded products are the fifth-generation ECMWF atmospheric reanalysis of the global climate (ERA5), the Global Land Data Assimilation Systems (GLDAS), the High Asian Refined Analysis version 2 (HAR v2), and the Tropical Rainfall Measuring Mission (TRMM). Results show that TRMM and GLDAS have good performances in the occurrence frequency of daily precipitation over the TP but cannot precisely detect the daily precipitation events. In contrast, ERA5 can well detect the daily precipitation events although it overestimates the frequency of daily precipitation. Regarding the longer time scales, ERA5 outperforms the other three gridded products. It succeeds in reproducing the interannual and decadal variabilities of precipitation and reflecting the spatio-temporal patterns of precipitation over the whole TP. Thus, this study highlights that there are different optimal choices of precipitation products for different study purposes, and demonstrates the potential capability of ERA5 for being used in the studies of climate and hydrological change over the TP. • An evaluation of four gridded datasets is performed in the features of precipitation at different time scales over the Tibetan Plateau. • TRMM fails to detect the precipitation events correctly and capture the decadal variability and spatio-temporal patterns of precipitation over the Tibetan Plateau. • ERA5 overestimates the precipitation amount but performs the best in most temporal variabilities and spatio-temporal patterns of precipitation over the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

• Permafrost has a stronger influence on runoff process than seasonally frozen ground. • Soil warming trends show a turning point around 4800 m in the permafrost region. • A longer freezing zero-curtain period often leads to discontinuous runoff recession. The Tibetan Plateau (TP) is a region rich in extensive frozen ground and the source of many major Asian rivers. However, how soil freeze/thaw (F/T) dynamics influence runoff production at the catchment scale in the TP is poorly understood. This study employs a process-based permafrost hydrology model with a new soil parameterization to investigate soil F/T dynamics and their impact on runoff in a TP permafrost watershed, i.e., the source region of Yangtze River (SRYR). The revised model separates soil evaporation and plant transpiration, and accounts for the influence of soil gravel and organic carbon content, as well as variation in saturated hydraulic conductivity along the soil profile. Validation results demonstrate that the revised model accurately simulates daily soil temperature (mean RMSE of 1.3 °C), soil moisture (mean ubRMSE of 0.05 cm3 cm−3), and runoff discharge (NSE = 0.82). The results reveal different altitudinal patterns of warming trend between permafrost and seasonally frozen ground (SFG). Warming rates in SFG area increase monotonously with elevation, while a turning point is observed in permafrost region around 4800 m. With active layer deepening, deep-soil water content increases but primarily replenishes soil water storage rather than directly contributing to runoff recharge, while rootzone and the middle part of the active layer become drier. Soil F/T cycles in the permafrost region exert stronger influences on runoff process compared to SFG. Delayed soil thaw onset generally results in higher spring runoff coefficient, while delayed soil freeze onset is related to slower runoff recession. The freezing zero-curtain period is likely to impact the continuity of runoff recession processes by affecting the connectivity of groundwater flow channels. These findings uncover the regulatory mechanisms of soil F/T dynamics on runoff production and river discharge characteristics, providing a fundamental basis for predicting permafrost hydrology responses to future climate change in the TP. [ABSTRACT FROM AUTHOR]

Climate change is having disproportionate impacts on the Tibetan plateau. Elevation-dependent- warming (EDW), faster warming in high mountains, poses an enhanced threat to life-supporting snow/ice reserves above 5000 m. Past studies debate how EDW is caused, and cannot predict how it will change in future. This study, for the first time, shows that the amplitude of regional warming determines the pattern of EDW, and that changing elevation gradients in snow depth over time have been responsible. Snow loss at increasingly higher elevations moves the zone of enhanced impact uphill, probably continuing in future. Our results explain the divergence in previous studies about causes of EDW, and also have critical implications for longer-term sustainability of water resources on the Tibetan Plateau. [Display omitted] Elevation-dependent warming (EDW), whereby warming rates are stratified by elevation, may increase the threat to the life-supporting solid water reservoir on the Tibetan Plateau. Previous studies have debated whether EDW exists and how it is driven. Using temperatures at 133 weather stations on the Tibetan Plateau during 17 different periods generated using a 30-year sliding window over 1973–2018, this study finds that the existence of EDW varies as the period moves forward, and critically it has become more severe over time. During the early part of the record with weaker regional warming, there were limited changes in snow depth and no EDW, but as time advances and regional warming intensifies, snow depth declines significantly at higher elevations, causing development of EDW. We conclude that enhanced regional warming has caused decreases in snow depth, largely controlling the pattern of EDW on the Tibetan Plateau. This may explain contrasting conclusions on EDW from previous studies which have used data for different periods, and our findings support enhanced EDW and more severe depletion of the Tibetan Plateau solid water reserves in a warmer future. [ABSTRACT FROM AUTHOR]

Climate warming has induced significant changes in permafrost and seasonally frozen ground (SFG) in the Tibetan Plateau, which have complex influences on local environments. A better understanding of the impacts of soil freeze/thaw (F/T) dynamics on soil water transfer and vegetation growth is important to explore related eco-hydrological influences. We investigated soil F/T dynamics and their impacts with in-situ and satellite-based observations. Our results showed the contrasting F/T dynamics between SFG and permafrost areas. In permafrost areas, soil froze downward from the ground surface and upward from the active layer bottom with a distinct freezing zero-curtain, and minimum soil moisture occurred in the intermediate layer, but the thawing process was unidirectional. However, the vertical F/T directions were contrary in SFG areas, where soil moisture generally increased with depth and the thawing zero-curtain was distinct. The spring onset showed a positive correlation with thaw onset in permafrost areas, but such a correlation was variable in SFG areas likely depending on soil-moisture level. Our results implied that the different soil-moisture patterns and the varying vegetation response might be related to the spatially contrasting F/T dynamics, which may have different impacts on soil water transfer, and further affect the zero-curtain and vegetation phenology. [ABSTRACT FROM AUTHOR]

Soil freeze-thaw is typically not fully considered in quantifying the hydrology of seasonally frozen catchments located, for instance, on the Third Pole. We investigate the role of soil water content and freeze-thaw state on the runoff dynamics of the headwaters of the Yellow and Yangtze rivers, both situated on the eastern Tibetan Plateau. A version of augmented Noah land surface model (LSM) allowing reliable simulation of key hydrometeorological processes over the Tibetan Plateau is employed and further validated using measured monthly discharge records. From measurements supported by the Noah LSM simulations for more than thirty years (1979–2010), we deduce an annual hysteresis loop, viz. a time lag between measured/simulated runoff and precipitation for both catchments. Our simulation results with the augmented Noah LSM further demonstrate that annual anticlockwise (or clockwise) hysteresis loops are also observed for the liquid soil water (or soil ice). We infer from the LSM simulations that the amount of water stored in the soil is the factor driving the hysteresis between runoff and precipitation, whereby the state of the stored water plays a crucial role in the seasonality of the runoff regime. Further analyses illustrate that inclusion of soil freeze-thaw model physics effectively increases the thermal inertia of the soil column that dampens large variations of soil temperature and turbulent heat fluxes. These findings highlight the importance of soil freeze-thaw for the hydrology and runoff regime across the High Asia’s rivers as well as the need for a thorough understanding of this process to generate reliable projections. [ABSTRACT FROM AUTHOR]

• Unprecedented lake expansion occurred in 2017–2018 on the inner Tibetan Plateau. • The rapid lake expansion exerted a significant impact on regional ecosystems and human living environments. • The rapid lake expansion was mainly attributed to anomalously high precipitation. Extreme events on the Tibetan Plateau (TP) have become increasingly frequent and severe in recent decades in tandem with rapid climate warming and moistening. Thus, it is highly important to investigate their processes, causes and environmental impacts. Using in-situ observations of lake level changes in combination with satellite altimetry data, we showed that lakes on the central TP (CTP) expanded unprecedentedly in 2017–2018, with lake level increases of 1.4–2.8 m at the five observed lakes. This extreme lake expansion occurred over almost the entire inner TP, which was mainly attributed to anomalously high precipitation (approximately 43–97% higher in 2017–2018 than in normal years on the CTP). The rapid lake expansion posed a substantial threat to regional ecosystems, infrastructure, and even residential habitats. Therefore, it is necessary to identify the potential sites threatened by lake expansion on the TP using high-resolution satellite images and perform near real-time observations of lake level changes through satellite and in-situ observations. [ABSTRACT FROM AUTHOR]