Simulating the ice phenology of deep alpine lakes is important and challenging in coupled atmosphere-lake models. In this study, the Weather Research and Forecasting (WRF) model, coupled with two lake models, the freshwater lake (WRF-FLake) model and the default lake (WRF-CLake) model, was applied to Nam Co, a typical deep alpine lake located in the centre of the Tibetan Plateau, to simulate its lake ice phenology. Due to the large errors in simulating lake ice phenology, related key parameters and parameterizations were improved in the coupled model based on observations and physics-based schemes. By improving the momentum, hydraulic, and thermal roughness length parameterizations, both the WRF-FLake model and the WRF-CLake model reasonably simulated the lake freeze-up date. By improving the key parameters associated with shortwave radiation transfer processes when lake ice exists, both models generally simulated the lake break-up date well. Compared with WRF-CLake without improvements, the coupled model with both revised lake models significantly improved the simulation of lake ice phenology. However, there were still considerable errors in simulating the spatial patterns of freeze-up and break-up dates, implying that significant challenges in simulating the lake ice phenology still exist in representing some important model physics, including lake physics such as grid-scale water circulation and atmospheric processes such as snowfall and surface snow dynamics. Therefore, this work can provide valuable new implications for advancing lake ice phenology simulations in coupled models, and the improved model also has practical application prospects in weather and climate forecasts.

In this study, a process-based lake model is used to investigate the influence of climate change on the thermodynamics of 30 large lakes over Tibetan Plateau (TP). The lake model was driven by the atmospheric forcing derived from the bias-corrected projections of three global climate models in the twenty-first century under three Shared Socioeconomic Pathways (SSPs). The hindcasts during 2000-2014 can reasonably capture the seasonality and magnitude of satellite retrieved lake surface temperature (LST). Future projections during 2015-2100 suggest a widespread increased LST, declined ice cover, and prolonged stratification, with the severity of changes in line with the climate driver shifts under different SSPs. Under the scenario with the highest level of anthropogenic radiative forcing (SSP5-8.5), the end-of-century (2086-2100) changes of LST, ice thickness, and stratification duration averaged across all studied lakes reach 4.90 degrees C, -0.43 m, and 65.46 days, respectively. Note that the positive ice-albedo feedback can cause excess lake warming by accelerating ice break-up (30.07 days earlier) and stratification onset (46.83 days earlier). By the end of this century, more frequent, multi-seasonal thermal extremes are anticipated to push nearly half of the studied lakes into a permanent heatwave state. Together with the remarkable LST increase and winter ice loss, the lakes will mix less frequently and may shift from a dimictic to warm monomict mixing regime. Hopefully, the irreversible thermal changes can be avoided if the anthropogenic radiative forcing is controlled within the envelope outlined by the stringent climate mitigation scenario SSP1-2.6. Lake thermodynamics play a fundamental role in controlling a wide range of physical and biogeochemical processes within lakes, for example, evaporation, nutrients and dissolved gases cycling, zooplankton and phytoplankton proliferation. This study uses lake numerical modeling to understand how climate change will affect the thermodynamics of 30 large lakes over TP, examining simulations throughout the twenty-first century under three SSPs. From 2000 to 2014 to 2086-2100, LST increase, ice loss, and stratification prolongation are anticipated across all studied lakes. These changes are more severe under the scenario with higher levels of climate driver shifts. Under the worst scenario SSP5-8.5, the above end-of-century changes reach 4.90 degrees C, -0.43 m, and 65.46 days, respectively. Additionally, by 2100, nearly half of the studied lakes will be in a constant state of "heatwave", meaning the water will be unusually warm all the time. The substantial lake warming and ice loss further cause the lakes to mix less frequently and risk shifts from a dimictic to warm monomict mixing regime. On a hopeful note, the thermal changes can possibly be controlled within the natural envelope if we adhere to the stringent climate mitigation scenario SSP1-2.6. Lake numerical modeling gains insights on the large-lake thermal response to a changing climate over TP during the twenty-first century Results from the worst scenario project substantial end-of-century changes of LST, thermal extreme, ice, stratification, and mixing regime Out-of-control thermal response can be avoided by adhering to the stringent climate mitigation scenario

Skin cooling, wherein the surface temperature of a water body Tskin is lower than the temperature below the surface, is a widespread phenomenon. Previous studies have almost ignored this effect on the Tibetan Plateau (TP), despite the presence of thousands of lakes on the TP and the fact that extraordinary solar heating leads to very strong energy exchanges on the lake surfaces. This study utilizes in situ observations and MODIS-derived Tskin data at Lake Nam Co, one of the largest lakes on the TP, to quantify the skin cooling effect. The observed nighttime skin cooling is approximately 0.52 degrees C on average, with the maximum of about 1 degrees C, during the lake water turnover period (from October to mid-November), which obviously surpasses reported values for oceans (less than 0.4 degrees C). To understand the impact of the skin cooling on the lake thermal processes, a skin cooling parameterization is validated and incorporated into the WRF-lake model. Simulations with the updated model show that accounting for the skin cooling process systematically lowers sensible and latent heat fluxes by a few watts per square meter, which yields an increase in water temperature by 0.45 degrees C at the end of December and may delay the onset of lake freeze. Finally, we show that the inclusion of the skin cooling process in a lake model needs simultaneous adjustment of the parameterization of heat/water vapor transfer.

Abstract 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.

AbstractThe Tibetan Plateau (TP) is covered by numerous lakes, and lake surface water temperature (LSWT) is an essential indicator of climate change, while few observations hinder our understanding of LSWT variation and its causes over TP. This study aims to simulate the summer LSWT long‐term trends of 81 TP lakes during 1980–2018 and quantify the impacts and contributions of atmospheric variables. Results show that TP lakes warmed with 0.32°C decade−1 on average. Northern TP lakes warmed faster than the southern ones (0.44 vs. 0.16°C decade−1) due to stronger trends of atmospheric variables and higher sensitive of colder lakes to atmospheric changes. 55 (67.9%) lakes of the total lakes studied in current work warmed slower than air due to weakened shortwave radiation (SW↓). Attribution analysis suggests that the air warming and wetting over TP dominate lakes' warming. Regarding synthesis contributions, air warming contributed 79.3%, with increased surface air temperature (SAT) and downward longwave radiation (LW↓) accounting for 41.6% and 37.7%, respectively, and air wetting indicated by increased surface specific humidity (SSH) contributed 39.0%, followed by a positive contribution (16.8%) from declined wind speed (WS). The negative contribution (−35.1%) from weakened SW↓ nearly counterbalances the positive effects of increased LW↓. 55.1% of the total synthesis contribution arises from the cross contribution through interactions among atmospheric variables and is mainly reflected in SAT and SSH, accounting for 26.8% and 24.8%, respectively. The findings enhance understanding of climate change impacts on lake systems and offer insights for lake resource management.

Study region: Lake Nam-Co, a typical deep alpine lake in the central of Tibetan Plateau. Study focus: This study investigates the role of surface turbulent fluxes in simulating lake freeze-up and the role of solar radiation transfer (when lake ice exists) in simulating the lake ice break-up. New hydrological insights: In the coupled model, the realistic representation of surface turbulent heat fluxes is crucial to simulate the lake freeze-up. This is because turbulent heat fluxes, especially the latent heat, directly controlling the lake water temperature through energy exchange between water and atmosphere. Additionally, the partitioning of solar radiation transfers when lake ice exist is crucial in simulating lake ice break-up. The proportion absorbed by the ice surface will be released associated with upward longwave radiation and turbulent heat fluxes, and only a fraction is used for surface ice-water phase change. The proportion absorbed by the subsurface layer ice is directly used for ice-water phase changes. The proportion absorbed by the water, through ice penetration, is temporarily stored and used for ice melting through heat exchange between the ice and water. The offline FLake model is much less sensitive to the above two processes, implying the importance and necessity in improving the model physics in coupled model.

Lake stratification and mixing processes can influence gas and energy transport in the water column and water–atmosphere interactions, thus impacting limnology and local climate. Featuring the largest high-elevation inland lake zone in the world, comprehensive and comparative studies on the evolution of lake stratification and mixing and their driving forces are still quite limited. Here, using valuable temperature chain measurements in four large lakes (Nam Co, Dagze Co, Bangong Co, and Paiku Co) and a “small lake” adjacent to Nam Co, our objectives are to investigate the seasonal and diurnal variations of epilimnion depth (Ep, the most important layer in stratification and mixing process) and to analyze the driving force differences between “small lake” and Nam Co. Results indicate that Ep estimated by the methods of the absolute density difference (<0.1 kg m−3) from the surface and the Lake-Analyzer were quite similar, with the former being more reliable and widely applicable. The stratification and mixing in the four large lakes showed a dimictic pattern, with obvious spring and autumn turnovers. Additionally, the stratification form during heat storage periods, with Ep quickly locating at depths of approximately 10–15 m, and, after that, increasing gradually to the lake bottom. Additionally, the diurnal variation in Ep can be evidenced both in the large and small lakes when temperature measurements above 3 m depth are included. For Nam Co, the dominant influencing factors for the seasonal variation of Ep were the heat budget components (turbulent heat fluxes and radiation components), while wind speed only had a relatively weak positive correlation (r = 0.23). In the “small lake”, radiation components and wind speed show high negative (r = −0.43 to −0.59) and positive (r = 0.46) correlation, with rare correlations for turbulent heat flux. These reported characteristics have significance for lake process modeling and evaluation in these high-elevation lakes.

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 km 2 , 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/m 2 ) and longwave radiation is smaller (∼a few W/m 2 ) than that of the further land region. Therefore, the above observational facts provide a new perspective to advance the understanding of lake‐air interactions.

Satellite precipitation products can provide alternative data in remote areas with sparse surface observations, but the performance of these products must be evaluated before hydrometeorological applications. The western Tibetan Plateau (WTP) covers an area of nearly 1,500,000 km2, where China Meteorological Administration stations are very sparse due to the harsh natural environment. Therefore, previous evaluations of satellite precipitation products have resulted in a gap on the WTP. In this study, hourly data collected from 29 newly established rain gauges on the WTP were applied to evaluate the performance of four Global Precipitation Measurement (GPM)-Era precipitation products without calibration (IMERG-UC and GSMaP-MVK) and with calibration (IMERG-C and GSMaP-Gauge). The evaluation results for the WTP were compared with those for the eastern Tibetan Plateau (ETP). (1) The effect of the calibration of satellite products highly depends on the temporal resolution of precipitation data used for calibration. The GSMaP-Gauge, which are calibrated with daily data, outperforms the IMERG-C, which are calibrated with monthly data, on both monthly scale and daily scale. (2) The calibration effect of the satellite products is not positive in reproducing the precipitation amount on the WTP due to few observations available for calibration but was notable on the ETP. (3) None of the four satellite precipitation products can reproduce the hourly precipitation frequency-intensity structure well. Both IMERG and GSMaP produce too much light precipitation events on the WTP. In addition, the four products produce too early timing of diurnal precipitation peak on the WTP. The calibration does not improve the timing phase of precipitation amount but affects the intensity of diurnal precipitation peaks on the WTP. These new findings provide important information on the accuracy of the four widely used satellite precipitation products on the WTP and thus can be a solid reference for hydrometeorological applications on the WTP.

The central and western Tibetan Plateau (CWTP) is characterized by harsh environment and strong interactions among the spheres of earth as well as significant changes in climate and water cycles over the past four decades. The lack of precipitation observations is a bottleneck for the study of land surface processes in this region. Over the past six years, we have designed and established two observation transects across the south-north and the west-east in this region to obtain hourly rainfall data during the warm season (May-September). The south-north transect extends from Yadong Valley on the southern slope of the Himalayas to Shuanghu County in the hinterland of the plateau, with a total of 31 stations; the west-east transect extends from Shiquanhe in the west to Naqu in the central TP, with a total of 22 stations. The observation dataset has been applied to clarify the spatiotemporal characteristics of precipitation in the CWTP, to evaluate the quality of typical gridded precipitation products, to support the development of regional climate models, and to reveal the processes of summertime lake-air interactions. The observation dataset has been released in the National Tibetan Plateau Data Center.

Thousands of lakes and complex topography on Tibetan Plateau (TP) have important impacts on the local weather and climate, especially extreme weather events. In this study, the Weather Research and Forecasting model was adopted to quantify the impacts of Lake Nam Co (LNC) and surrounding topography on the extreme snowfall event over Nam Co basin on 24 October 2006 based on numerical experiments. The accumulated precipitation of 12 hr in this event is characterized by a maximum precipitation center with an intensity exceeding 20 mm over eastern LNC and downwind regions. Results show that the precipitation regionally averaged over eastern LNC and downstream regions can be reduced by 53%, 26%, and 68% when LNC, surrounding terrain, and both of them are absent, respectively, suggesting that LNC plays a dominant role in the formation of this event while the surrounding mountains further amplify the lake effect precipitation/snow over the downwind of LNC. Mechanism analysis indicates that the low‐level convective instability and water vapor convergence induced by LNC are essential for the formation of this extreme snowfall event, while the wind deflection and topographic lifting further strengthen the precipitation over the downwind of LNC and shift the snow belt distribution. This study is not only important to deepen the understanding of the complex interactions between the lake and orography and their combined influences on regional extreme precipitation, but also helpful for further improving the refined forecasting of the extreme precipitation induced by the lake and surrounding terrain in other regions over TP.

The lake surface water temperature (LSWT) on Tibetan Plateau (TP) is sensitive to climate change. Based on a 1‐D lake model, we have investigated the interdecadal variation and long‐term trend of LSWT in Lake Nam Co (LNC) on TP during 1980–2018 and quantified the relative contributions of atmospheric factors to the LSWT trend. Results show LNC was warmed with a rate of 0.29°C decade −1 , which is smaller than the warming of ambient air (0.45°C decade −1 ). The weakened wind speed, rising air temperature, increased downward longwave radiation, and decreased shortwave radiation contributed about 35%, 30%, 20%, and −15% of the estimated long‐term LSWT trend during 1980–2018, respectively. The contribution rate of 32.5% was from the interactions among all forcing variables. The primary warming was completed before 1997 (0.30°C decade −1 ) and was followed by a hiatus that the LSWT jumped to a warm level with a slightly negative trend (−0.08°C decade −1 ) after 1997. During this hiatus, the wind speed recovered from decrease and the deceleratingly increased downward longwave radiation slowed down the LNC warming. Particularly, the specific humidity shifted from increasing to decreasing trend played a key role in the hiatus of LNC warming after 1997, despite its slight contribution (−2.5%) to the LSWT trend during 1980–2018. The results showed the particularity of warming for a TP lake compared to the other ice‐covered lakes worldwide and provided a quantitative perspective for understanding the relative contributions of atmospheric factors to the long‐term trend of LSWT.

The alpine lakes widely distributed over the Tibetan Plateau (TP) are not only highly sensitive to climate but also regulate the regional climate. However, the lack of TP alpine lake observations limits the understanding of the lake‐atmosphere interactions. Here, we show the relative importance of parameterizing lake surface and internal thermal processes in describing the lake energy budget and lake‐atmosphere interactions. Based on the in situ observations at Lake Nam Co, a large and deep lake in the TP, we employed the coupled Weather Research and Forecasting with lake (WRF‐Lake) model to clarify their relative roles. Results show that the original model produces cold biases and too early timing of lake freeze onset. The adjustments of parameterizations of lake internal (temperature of maximum water density, extinction coefficient) and lake surface (roughness length) processes significantly improve the ability of the WRF‐Lake in simulating the lake thermal features and the freeze onset timing. The different parameterizations of lake internal thermal processes affect the onset timing of lake freeze mainly by altering the release of turbulent heat fluxes in summer, but the adjustments of lake surface roughness lengths change the turbulent heat fluxes during the unfrozen season from summer through early winter. Accordingly, the simulated lake freeze onset is much more sensitive to the surface roughness length schemes than to the internal thermal processes schemes. As the lake‐atmosphere interactions are very sensitive to the lake freeze onset, our results are critical for understanding and simulating the impact of TP lakes on the regional climate.

The thermal regimes of lakes are important for understanding the functions and services of lake ecosystems. However, continuous lake temperature monitoring across the Tibetan Plateau is sparse, which inhibits verification of modeling results and also in-depth understanding of the lake thermal and mixing dynamics in this region. Here, we present the results of continuous temperature monitoring of a dimictic lake, Bangong Co, during 2012-2014, and a meromictic lake, Dagze Co, during 2012-2015, to gain insight into the differences in their thermal dynamics and to understand the factors influencing these differences. No evident changes in the thermal and mixing regimes were observed at the two lakes during the observational period. However, the thermal structure changed in different hydrological years. The air temperature changes and associated glacier melt possibly contribute to changes in the water temperature for Bangong Co, while heat transfer related to wind speed is vital for Dagze Co. Developing in-depth knowledge necessitates long-term monitoring data to confirm the influence of various individual climatic parameters.

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

A three-dimensional (3-D) hydrodynamic model based on the Princeton Ocean Model (POM) was applied to simulate the thermal structure and circulation of Lake Nam Co (LNC), the third largest lake over the Tibetan Plateau (TP), during May-December 2013. Compared with a spatially distributed set of one-dimensional thermal diffusion lake models, POM better reproduced the observed seasonal evolution of the horizontal distribution of lake surface temperature and the vertical thermal structure. A heat budget analysis confirmed that the lateral heat exchange made significant contributions to the horizontal variability of lake temperature. The model results showed that LNC was thermally stratified in summer, had a weak inverse stratification since mid-December, and was fully turned over during late spring and autumn. During both overturning phases, the modeled "thermal bar" was developed as a result of the density-driven convection in response to the radiative heating (surface cooling) during spring (autumn). The 3-D model results showed that the monthly mean circulation featured a predominant mid-lake cyclonic gyre throughout the ice-free period; upwelling along the western coast and strong coastal currents occurred in all months except in July-August. Model sensitivity experiments confirmed that the lake circulation was primarily driven by the barotropic dynamics of the prevailing southwesterly wind, while the baroclinic process made a secondary contribution. The results pointed out the necessity to resolve lateral processes when modeling large TP lakes. Plain Language Summary The Tibetan Plateau has the highest alpine lake concentration in the world and Lake Nam Co is the third largest lake in the region. This study showed that a three-dimensional (3-D) hydrodynamic model performed better than a spatially distributed set of one-dimensional thermal diffusion lake models in reproducing the observed spatial and temporal variations of the lake temperature, and depicted the existence of lake gyre circulation, coastal currents, and upwelling. Model sensitivity experiments revealed that the lake circulation during the ice-free season was primarily driven by the prevailing southwesterly wind, while the thermal structure made a secondary contribution. The improved simulation of the thermal structure and circulation with 3-D models is important to understand the variations of the ecosystem in large lakes and the impacts of lakes on the regional weather and climate.

To improve the performance of the second generation of Beijing Climate Center Atmosphere-Vegetation Interaction Model (BCC_AVIM2.0) with a fine resolution (45 km) over lake-rich areas, the default lake scheme in BCC_AVIM2.0 is replaced by the Common Land Surface Model (CoLM)-Lake scheme with much more realistic treatments of the energy exchanges in the snow-ice-water-sediment system relative to the default lake scheme. Results show that the lake surface temperature (LST) biases produced by BCC_AVIM2.0 with the default lake scheme can be largely reduced by adopting the CoLM-Lake scheme in winter due to much more realistically simulated vertical water temperature profiles over the Great Lakes region. The spatial distributions and seasonal variations of the LST simulations can also be significantly improved by the CoLM-Lake scheme within BCC_AVIM2.0. The performances of BCC_AVIM2.0 in simulating the lake ice in winter can be largely improved by replacing the default lake scheme with the CoLM-Lake scheme. The improvements in the LST simulated by BCC_AVIM2.0 with the CoLM-Lake scheme further lead to reduced biases in the simulated ground surface temperature. The simulations of air temperature and precipitation in the coupled model are also improved by adopting the CoLM-Lake scheme over the Great Lakes region, which indicates the improvements in simulating the energy and water exchange between the atmosphere and lakes. This study highlights the importance of a more realistic lake scheme in simulating the ground surface temperature and the energy exchanges between the atmosphere and lakes.

Current climate models often have significant wet biases in the Tibetan Plateau and encounter particular difficulties in representing the climatic effect of the Central Himalaya Mountain (CHM), where the gradient of elevation is extremely steep and the terrain is complex. Yet, there were few studies dealing with the issue in the high altitudes of this region. In order to improve climate modeling in this region, a network consisting of 14 rain gauges was set up at elevations > 2800 m above sea level along a CHM valley. Numerical experiments with Weather Research and Forecasting model were conducted to investigate the effects of meso- and micro-scale terrain on water vapor transport and precipitation. The control case uses a high horizontal resolution (0.03°) and a Turbulent Orographic Form Drag (TOFD) scheme to resolve the mesoscale terrain and to represent sub-grid microscale terrain effect. The effects of the horizontal resolution and the TOFD scheme were then analyzed through comparisons with sensitivity cases that either use a low horizontal resolution (0.09°) or switch off the TOFD scheme. The results show that the simulations with high horizontal resolution, even without the TOFD scheme, can not only increase the spatial consistency (correlation coefficient 0.84–0.92) between the observed and simulated precipitation, but also considerably reduce the wet bias by more than 250%. Adding the TOFD scheme further reduces the precipitation bias by 50% or so at almost all stations in the CHM. The TOFD scheme reduces precipitation intensity, especially heavy precipitation (> 10 mm h−1) over high altitudes of the CHM. Both high horizontal resolution and TOFD enhance the orographic drag to slow down wind; as a result, less water vapor is transported from lowland to the high altitudes of CHM, causing more precipitation at lowland area of the CHM and less at high altitudes of CHM. Therefore, in this highly terrain-complex region, it is crucial to use a high horizontal resolution to depict mesoscale complex terrain and a TOFD scheme to parameterize the drag caused by microscale complex terrain.

Lake surface temperature is a key parameter in understanding the variability of lake thermal condition and evaporation. MODIS-derived LST is widely used as a reference for lake-model validations and process studies in data-scarce regions. In this study, the accuracy and limitation of MODIS LST were examined on the Tibetan Plateau, where there are thousands of lakes. It is found that agreement between MODIS LST and in-situ subsurface (~1 m depth) temperature collected at six large lakes depends on the thermal phases. During lake turnover period (nighttime or from October to freeze-up date), the sink of surface water causes mixed with subsurface water. The MODIS LST was consistent with the in-situ data, indicating its high accuracy. During stratification period (from May to September), the lakes were thermally stratified due to intense solar heating and high salinity in some lakes; the daytime MODIS LST is systematically higher than the in-situ subsurface temperature, indicating it is credible. However, the MODIS LST has two limitations in this region. First, nighttime retrievals during monsoon season have considerable cold biases in monsoon-controlled region. This can be associated with shallow clouds or fog near the lake surface that occur frequently at night but are not well detected by MODIS. Second, the retrievals for narrow and small lakes have warm (cold) biases in the daytime (at night), perhaps due to proximity effect of mountains and land. The two situations are common across the Tibetan Plateau and thus severely restrict the applications of MODIS LST in lake studies.

While the Himalayas act as a natural barrier to water vapor transport to the Tibetan Plateau, many north-south-oriented valleys channel moisture onto the Plateau. However, owing to the lack of in situ data, the spatiotemporal characteristics of precipitation remain unclear along these valleys. In this study, a high-altitude (2,800-4,500 m above mean sea level) rain-gauge network was established in the Yadong Valley, one of the main valleys in the central Himalayan Region (CHR). New observations from this network are used to evaluate the Integrated Multi-satellitE Retrieval for Global Precipitation Measurement (IMERG) precipitation product, with results demonstrating that the IMERG data can reproduce the seasonal and diurnal patterns of precipitation seen in the observational data. This combination of in situ and IMERG precipitation data reveals two unique characteristics in the CHR. First, precipitation during the premonsoon season (March-May) contributes 20-40% of the annual total, from the high altitudes of the CHR to Southeast Tibetan Plateau, due to water vapor flux conveyed by southwesterlies from the Bay of Bengal, whereas this percentage is much lower in the northern Himalaya and South Asia. Second, diurnal variations in precipitation during the monsoon season (June-September) vary between the low and high altitudes of the north-south-oriented valleys in the CHR: Precipitation at high altitudes has two peaks (one in the afternoon and the other at night), which is different from the single nighttime peak in low altitudes that is usually reported. These two notable spatiotemporal characteristics are indicative of the unique climate that exists at the high altitudes of the CHR.