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The increase in vegetation coverage resulting from the implementation of the Grain for Green Project (GFGP) on the Loess Plateau (LP) in China has sparked debates on how the GFGP affects the water cycle, due to the limited understanding of the interaction between land cover and the atmosphere. This study investigated spatiotemporal changes in atmospheric water vapor (WV) from 1979 to 2022 using ERA5 dataset and quantified the impacts of the GFGP on the WV budget on the LP through numerical simulations with the Community Earth System Model. The analysis of ERA5 data revealed an increase in WV content (WVC) after the implementation of the GFGP (2000–2022) compared to the pre-program period (1979–1999). This increase was primarily attributed to a greater reduction in WV outflow at the eastern boundary than the reduction in inflow at the western boundary, resulting in greater WV retention. Our sensitivity simulation experiments indicated that the GFGP had positive effects on WVC, with evident increases in the lower atmosphere (700–1000 hPa). The GFGP increased WV inflows at the southern and western boundaries by 3.84 × 104 kg·s-1·m-1, while WV outflows at the eastern and northern boundaries also increased by 1.40 × 104 kg·s-1·m-1, leading to a net WV input in the low atmospheric layer due to higher inflows than outflows. These findings suggested that although the GFGP positively impacted WV, the observed post-2000 WV increase cannot be solely attributed to the GFGP, indicating that changes in atmospheric circulation patterns under climate change also play an important role. [ABSTRACT FROM AUTHOR]

Tropical cyclone (TC) genesis prediction remains a major operational challenge. Using multiple satellite datasets and a state-of-the-art reanalysis dataset, this study identifies developing and non-developing tropical disturbances over the western North Pacific from June to November of 2000–2019 and conducts composite analyses of their water vapor budget components and relevant dynamic–thermodynamic parameters in the Lagrangian framework following three-day disturbance tracks. Both groups of disturbances have a similar initial 850 hPa synoptic-scale relative vorticity, while the water vapor budget of developing disturbances exhibits distinct stage-wise evolution characteristics from non-developing cases. Three days prior to TC genesis, developing cases are already associated with significantly higher total precipitable water (TPW), vertically integrated moisture flux convergence (VIMFC), and precipitation, of which TPW is the most important parameter to differentiate two groups of disturbances. One day later, all the water vapor budget components (i.e., TPW, VIMFC, precipitation, and evaporation) strengthened, linked with the enhancement of the mid-to lower-tropospheric vortices. A negative radial gradient of evaporation occurs, suggesting the beginning of the wind−evaporation feedback. On the day prior to TC genesis, the water vapor budget components, as well as the mid-to lower-tropospheric vortices, continue to intensify, eventually leading to TC genesis. By contrast, non-developing disturbances are associated with a drier environment and weaker VIMFC, precipitation, and evaporation during the three-day evolution. All these factors are not favorable for the intensification of the mid-to lower-tropospheric vortices; thus, the disturbances fail to upgrade to TCs. The results may shed light on TC genesis prediction. [ABSTRACT FROM AUTHOR]

Using meteorological analysis, composite analysis and water vapor trajectory analysis, the extreme value rainstorm process in northwest Hunan was analyzed. The results show that three types are summarized: the Southwest Vortex and Warm Shear Line Pattern (SVWSLP), the Subtropical High Edge Pattern (SHEP) and the Cold Trough and Shear Line Pattern (CTSLP). The main influence systems are upper trough, southwest vortex, shear line, low-level jet and subtropical high edge. For SVWSLP, the water vapor transport channels are only from the low-latitude ocean whether it is affected by long-distance typhoons. For SHEP, the main water vapor channel comes from the long-distance ocean and is finally transported to northwestern Hunan around 650 hPa in the form of warm and wet airflow, whether it is affected by long-distance typhoons. The CTSLP appears a significant water vapor confrontation between the north and the south and the baroclinicity of the atmosphere in the rainstorm area. The southern and western boundaries are the input boundary, while the eastern and northern boundaries are the outflow boundary. Therefore, one of the three types of weather systems appears in northwestern Hunan in May–August, with strong water vapor transport from the ocean surface, which is likely to cause extreme rainstorm. HIGHLIGHTS Climatic characteristics of extreme precipitation in northwest Hunan.; The terrain of northwest Hunan is complex, and the system extreme value is analyzed for the first time.; The influence of water vapor in northwest Hunan is analyzed by HYSPLT for the first time.; No one has ever studied the influence of long-distance typhoons in northwestern Hunan.; The results are of great significance to the prediction of extreme value rainstorms in northwest Hunan.;

The Three-River Headwaters (TRH) region in the Tibetan Plateau is vulnerable to climate change; changes in summer (June–August) precipitation have a significant impact on water security and sustainability in both local and downstream areas. However, the changes in summer precipitation of different intensities over the TRH region, along with their influencing factors, remain unclear. In this study, we used observational and ERA5 reanalysis data and employed a precipitation categorization and water vapor budget analysis to quantify the categorized precipitation variations and investigate their possible linkages with the water vapor budget. Our results showed an increasing trend in summer precipitation at a rate of 0.9 mm per year (p

Tropical cyclone (TC) genesis prediction remains a major operational challenge. Using multiple satellite datasets and a state-of-the-art reanalysis dataset, this study identifies developing and non-developing tropical disturbances over the western North Pacific from June to November of 2000–2019 and conducts composite analyses of their water vapor budget components and relevant dynamic–thermodynamic parameters in the Lagrangian framework following three-day disturbance tracks. Both groups of disturbances have a similar initial 850 hPa synoptic-scale relative vorticity, while the water vapor budget of developing disturbances exhibits distinct stage-wise evolution characteristics from non-developing cases. Three days prior to TC genesis, developing cases are already associated with significantly higher total precipitable water (TPW), vertically integrated moisture flux convergence (VIMFC), and precipitation, of which TPW is the most important parameter to differentiate two groups of disturbances. One day later, all the water vapor budget components (i.e., TPW, VIMFC, precipitation, and evaporation) strengthened, linked with the enhancement of the mid-to lower-tropospheric vortices. A negative radial gradient of evaporation occurs, suggesting the beginning of the wind−evaporation feedback. On the day prior to TC genesis, the water vapor budget components, as well as the mid-to lower-tropospheric vortices, continue to intensify, eventually leading to TC genesis. By contrast, non-developing disturbances are associated with a drier environment and weaker VIMFC, precipitation, and evaporation during the three-day evolution. All these factors are not favorable for the intensification of the mid-to lower-tropospheric vortices; thus, the disturbances fail to upgrade to TCs. The results may shed light on TC genesis prediction.

In this paper, synoptic-scale analyses of frontogenesis, moisture budget, and tropospheric diabatic heating are performed to reveal the development and maintenance mechanisms for the extreme heavy rainfall in Henan Province of central China from 19 to 21 July 2021, based on station observations and the ECMWF Reanalysis version 5 (ERA5) data. The results demonstrate that owing to the blocking effect of local topography, low-level wind convergence in Henan appeared underneath high-level divergence, conducive to development and maintenance of a midtropospheric low-pressure system saddled by the Asian continental high and the western Pacific subtropical high (WPSH), during the extreme heavy rainfall. In the lower troposphere, frontogenesis occurred in the θse intensive region, as a result of the divergence and horizontal deformation (which play equally important roles), generating frontal secondary circulation with strong vertical motion favorable to heavy rainfall. Moisture budget analysis reveals that 1) with the continuous strengthening of the easterly wind from the north side of Typhoon In-Fa (2106), strong wind shear and orographic uplift led to abnormally strong convergence of water vapor flux in the boundary layer in Henan; 2) there occurred extremely strong net inflow of moisture in the boundary layer from the east. Horizontally, both the apparent heat source 1> and the moisture sink 2> coincided with the area of heavy rainfall; vertically, however, Q1 exhibited a single peak with the heating center in the middle and upper troposphere, while large Q2 values evenly resided over 850–400 hPa; and Q1 (Q2) was dominated by vertical (horizontal) transport of potential temperature (moisture). These indicate that the latent heat release from condensation of initial heavy rainfall provided a positive feedback, leading to increasingly heavy precipitation. All these synoptic settings sustained the extreme rainfall process. [ABSTRACT FROM AUTHOR]

In this study, we investigate the variation of characteristics of summer precipitation with different magnitudes and the water vapor budget in different key areas of the Sichuan-Tibet Railway by using the daily precipitation data from meteorological stations and the monthly mean ERA-Interim reanalysis data from 1979 to 2018. The results show that the summer heavy precipitation anomaly in the Brahmaputra valley and mountain (BVM) area is generated by the multi-scale interactions between the unique topography and different water vapor transports at low latitudes. When an intense anticyclonic circulation occurs over the western Pacific and the South China Sea, there is also an anomalous anticyclonic circulation extending from the northern Indian Peninsula to the Bay of Bengal. This circulation pattern is conductive to the increase of the water vapor inflow from the southern boundary and the net water vapor budget in the BVM area. The strong southwesterly wind and water vapor convergence over this area thus leading to heavy precipitation in the summer. The summer heavy precipitation amount, frequency and intensity in the western parts of the steep terrain (ST) area on the east slope of the plateau are positively correlated with the water vapor inflow from its western boundary. However, the correlations of the water vapor budget to the summer heavy precipitation amount and frequency are opposite in the eastern parts of the ST area. The unique terrain and circulation patterns lead to the localization and diversity of heavy precipitation in the ST area. [ABSTRACT FROM AUTHOR]

On 20 July 2021, the city of Zhengzhou in Henan Province, China experienced a record-breaking rainfall event ("21·7") with a maximum hourly precipitation of 201.9 mm, which caused a significant loss of life and property. Knowledge of the moisture sources and atmospheric circulations associated with this rainstorm can help understand the mechanisms of such extreme rainfall events for more accurate forecasts in the future. To this end, we investigate the moisture sources and pathways related to the "21·7" extreme rainfall with the water vapor budget analysis and the Hybrid Single-Particle Lagrangian Integrated Trajectory model. In addition, the role of the circulation pattern is analyzed systematically based on ERA5 reanalysis. Results indicate that the Western Pacific Ocean and East China contribute 68.8% and 29.5% of the moisture to the extreme rainfall over Zhengzhou, respectively. Under the impact of tropical cyclone In-fa and Cempaka, and Western Pacific Subtropical High, the stable and abundant moisture transports toward Zhengzhou. Strong convergence and dynamic uplift trigger the convection due to the low vortex and the topography of mountains. Our findings can provide implications for short-term, extreme rainfall and flood forecasts under a changing environment. [ABSTRACT FROM AUTHOR]

Using the ERA5 reanalysis dataset during the period 1979–2019, the diurnal variation in summer water vapor budget (Bt) over the Tibetan Plateau (TP) is investigated in this study. It is found that the TP Bt shows a distinct diurnal cycle. It tends to increase in the morning, reaches a peak in the afternoon, and falls to a minimum in the early morning. The diurnal variations in four boundary water vapor budgets of the TP contribute to the growth in the TP Bt from the early morning to the afternoon, of which the western and eastern boundaries are more important. To understand the reasons for the diurnal variations in boundary water vapor budgets, the temporal evolutions of water vapor transports and relevant circulations at the four boundaries are examined. The results show that the temporal evolutions of water vapor transports and budgets at the four boundaries are essentially regulated by the changes in the orographic thermodynamic effect. Specifically, rapid and strong warming (cooling) on the TP slopes generates anomalous water vapor inputs (outputs) by anomalous upslope (downslope) flows during the daytime (nighttime). At the southern and western boundaries, apart from the terrain effects, the diurnal variation in the Indian southerly monsoon also has an effect on the changes in water vapor budgets by modulating the water vapor input towards the TP below 700 hPa. At the northern and eastern boundaries, under the orographic thermodynamic effects, low-level water vapor transports towards the TP accompanying by plateau-scale vertical circulations, exist significant diurnal variations and thereby adjust the boundary water vapor budgets. In this study, it is also found that the deviated water vapor flux vectors over the TP present a daily clockwise rotation, which mainly results from the diurnal variation in wind below 450 hPa. In addition, the largest amount of precipitation over the TP occurs 2–3 h after the Bt peak. [ABSTRACT FROM AUTHOR]

The mid-Holocene (MH; 6 ka) is one of the benchmark periods for the Paleoclimate Modeling Intercomparison Project (PMIP) and provides a unique opportunity to study monsoon dynamics and orbital forcing (i.e., mostly precession) that differ significantly from the present day. We conducted a data–model comparison along with a dynamic analysis to investigate monsoonal (i.e., East Asian summer monsoon; EASM) precipitation changes over East Asia during the MH. We used the three phases of the PMIP simulations for the MH, and quantitatively compare model results with pollen-based climate records. The data–model comparison shows an overall increase in the summer monsoon precipitation, except a local decrease during the MH. Decomposition of the moisture budget into thermodynamic and dynamic components allows us to assess their relative role in controlling EASM precipitation during the MH, and to investigate the precipitation changes obtained from pollen records in terms of physical processes. We show that the dynamic effect, rather than the thermodynamic effect, is the dominant control in increased EASM precipitation during the MH in both the proxy records and models. The dynamic increase in precipitation results mainly from the enhancement of horizontal monsoonal moisture transport that is caused by intensified stationary eddy horizontal circulation over East Asia. In addition, a cloud-related cooling effect reduced the thermodynamic contribution to the increase in EASM precipitation during the MH. [ABSTRACT FROM AUTHOR]

Water resources are essential for the economic development and social security in East Asia, especially under global warming. Based on newly released CMIP6 149-year simulation data from a pre-industrial control experiment (piControl) and a forced experiment on the abrupt quadrupling of CO2 concentration (abrupt-4xCO2), changes of water vapor budget over East Asia due to 4xCO2 concentration forcing and their possible mechanisms are investigated. Change of precipitation (P) demonstrates a spatial pattern of "Southern Flood and Northern Drought" (SFND) in eastern China, which can also be seen in the change of evaporation (E), though at a much smaller amplitude. The change of water vapor budget represented by E–P is dominated by P, which is primarily induced by changes of water vapor divergence associated with both moisture-related thermodynamic contribution and atmospheric circulation-related dynamic contribution. Specifically, under global warming, tropical El Nino-like SST warming causes weakened Walker circulation through decreased zonal temperature gradient, while amplified Arctic warming induces a negative Arctic Oscillation pattern via reduced meridional temperature gradient. The combined signals from tropical and mid-high latitudes result in significant long-term changes of water vapor convergence as well as much more precipitation in the Yangtze River Valley, forming the SFND. Furthermore, the intensity of the SFND change pattern could also have notable interdecadal variation, which is mainly attributed to the modulation of interdecadal signals of the Indian Ocean basin mode (IOBM) and Pacific Decadal Oscillation (PDO). Results of this study could provide an important scientific basis for the future planning and management of water resources over East Asia, specifically in eastern China. [ABSTRACT FROM AUTHOR]

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The spatiotemporal variations of water vapor budget (Bt) and their relationships with local precipitation over the Tibetan Plateau (TP) are critical for understanding the characteristics of spatial distributions and evolutions of water resources over the TP. Based on a boundary of the TP, this paper explored the spatiotemporal characteristics of Bt over the TP using the European Centre for Medium-Range Weather Forecasts interim (ERA-Interim) reanalysis datasets. On the climatological mean, the TP is a water vapor sink throughout four seasons and the seasonal variation of Bt is closely associated with the water vapor budget at the southern boundary of the TP. The transient water vapor transport is quasimeridional in the mid- and high-latitude areas and plays a leading role in winter Bt but contributes little in other seasons. At the interannual timescale, the variation of Bt is mainly determined by anomalous water vapor transports at the western and southern boundaries. The Bay of Bengal, the North Arabian Sea, and mid-latitude West Asia are the main sources of excessive water vapor for a wetter TP. At the southern and western boundaries, the transient water vapor budget regulates one-third to four-fifths of Bt anomalies. Moreover, the variability of the TP Bt is closely associated with precipitation over the central-southern and southeastern parts of the TP in summer and winter, which is attributed to the combined effect of the stationary and transient water vapor budgets. Given the role of the transient water vapor transport, the linkage between the TP Bt and local precipitation is tighter. [ABSTRACT FROM AUTHOR]

In this study, we investigate the variation of characteristics of summer precipitation with different magnitudes and the water vapor budget in different key areas of the Sichuan-Tibet Railway by using the daily precipitation data from meteorological stations and the monthly mean ERA-Interim reanalysis data from 1979 to 2018. The results show that the summer heavy precipitation anomaly in the Brahmaputra valley and mountain (BVM) area is generated by the multi-scale interactions between the unique topography and different water vapor transports at low latitudes. When an intense anticyclonic circulation occurs over the western Pacific and the South China Sea, there is also an anomalous anticyclonic circulation extending from the northern Indian Peninsula to the Bay of Bengal. This circulation pattern is conductive to the increase of the water vapor inflow from the southern boundary and the net water vapor budget in the BVM area. The strong southwesterly wind and water vapor convergence over this area thus leading to heavy precipitation in the summer. The summer heavy precipitation amount, frequency and intensity in the western parts of the steep terrain (ST) area on the east slope of the plateau are positively correlated with the water vapor inflow from its western boundary. However, the correlations of the water vapor budget to the summer heavy precipitation amount and frequency are opposite in the eastern parts of the ST area. The unique terrain and circulation patterns lead to the localization and diversity of heavy precipitation in the ST area.

Using the ERA5 reanalysis dataset during the period 1979–2019, the diurnal variation in summer water vapor budget (Bt) over the Tibetan Plateau (TP) is investigated in this study. It is found that the TP Bt shows a distinct diurnal cycle. It tends to increase in the morning, reaches a peak in the afternoon, and falls to a minimum in the early morning. The diurnal variations in four boundary water vapor budgets of the TP contribute to the growth in the TP Bt from the early morning to the afternoon, of which the western and eastern boundaries are more important. To understand the reasons for the diurnal variations in boundary water vapor budgets, the temporal evolutions of water vapor transports and relevant circulations at the four boundaries are examined. The results show that the temporal evolutions of water vapor transports and budgets at the four boundaries are essentially regulated by the changes in the orographic thermodynamic effect. Specifically, rapid and strong warming (cooling) on the TP slopes generates anomalous water vapor inputs (outputs) by anomalous upslope (downslope) flows during the daytime (nighttime). At the southern and western boundaries, apart from the terrain effects, the diurnal variation in the Indian southerly monsoon also has an effect on the changes in water vapor budgets by modulating the water vapor input towards the TP below 700 hPa. At the northern and eastern boundaries, under the orographic thermodynamic effects, low-level water vapor transports towards the TP accompanying by plateau-scale vertical circulations, exist significant diurnal variations and thereby adjust the boundary water vapor budgets. In this study, it is also found that the deviated water vapor flux vectors over the TP present a daily clockwise rotation, which mainly results from the diurnal variation in wind below 450 hPa. In addition, the largest amount of precipitation over the TP occurs 2–3 h after the Bt peak.

Based on the NCEP reanalysis, conventional observation and Global Data Assimilation System (GDAS) data, the characteristics of water vapor transport were analyzed in a historically extreme event of persistent heavy rainstorm affected by a monsoon low pressure in Guangdong province from August 27 to September 1, 2018. Using the Hysplit backward trajectory model, the water vapor source was diagnosed. The results show that:(1) During the continuous heavy rainstorm, the southeast coast of China was the water vapor convergence area in northern hemisphere, and water vapor mainly came from the Indian Ocean, which then flowed northward from the Indian peninsula to the south of the Qinghai-Tibet Plateau, and then turned east into the south of China. Other portion of the water vapor came from the northwestern Pacific Ocean and the South China Sea. The three water vapor sources gathered in the South China and established a stable and continuous water vapor transport channel, which made the torrential rain process wide and lasted for a long time. (2) The water vapor convergence center in the early stage of precipitation occurred on the eastern coast of South China. On August 29th, its center gradually moved westward and the potential function averaged over Guangdong area reached the peak of the whole precipitation event at the night of 29th when the water vapor convergence was the most obvious. At the 31st night, the water vapor convergence center moved further westward and tended to weaken. The change of the high value of the water vapor flux potential function corresponded to the daily variation of precipitation peak during the torrential rain. (3) The daily water vapor convergence showed obvious daily variation. During the daytime, the water vapor convergence was weakened and obviously strengthened at the nighttime, showing the characteristics for monsoon precipitation. (4) The southern boundary of South China was the main water vapor input boundary and mainly concentrated in the lower layer, especially the water vapor input of the southeastern border of South China has been maintained at a high level. The water vapor input from the southern boundary of South China has been significantly increased from the night of 29th, and the whole layer's water vapor flux reached its maximum on the 30th, which was consistent with the area and time of the heavy rain.

Drought in eastern Northwest China (ENC) is severely affected by water vapor conditions. An in-depth study of the primary sources of water vapor and its characteristics, at intraseasonal and interannual timescales, was conducted. This information is crucial for further study of the causes and mechanisms of extreme droughts and floods in the ENC. This study evaluated the spatial distribution and transport characteristics of water vapor over ENC during the 1981–2019 period based on the fifth generation of the European Center for Medium-Range Weather Forecasts atmospheric reanalyzes data of the global climate (ERA5). We studied the water vapor transport routes, water vapor convergence, water vapor budgets as well as the changes in water vapor fluxes and budgets over time in four areas surrounding ENC. The Mediterranean Sea, Black Sea, Caspian Sea, Indian Ocean, Bay of Bengal, and the South China Sea were the main sources of water vapor in ENC, supplemented by mid to high-latitude continental sources. The monthly change in water vapor flux in ENC exhibited the peak on July. The transport of water vapor in ENC was mainly toward the east and north. For most cross-seasonal drought events, the water vapor output is the main way in the south boundary and the west boundary. However, for the longest duration of cross-seasonal strong drought events, it is characterized by that the water vapor output is the main way in the south boundary, while the water vapor input in the north boundary is obviously weak. Water vapor paths in cross-seasonal strong drought events are analyzed, by which the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT). The intensity of the subtropical high in the western Pacific is weak and the position is south, which corresponds to the occurrence of cross-seasonal strong drought in the ENC.

The Last Glacial Maximum (LGM; 21 ka BP) was the most recent glacial period when the global ice sheet volume was at a maximum. Therefore, the LGM can be used to investigate atmospheric dynamics under a climate that differed significantly from the present. This study quantitatively compares pollen records of boreal summer (June–July–August) precipitation with the PMIP3 LGM simulations. The data-model comparison shows an overall agreement on a drier than pre-industrial East Asian summer monsoon (EASM) climate. Nevertheless, 17 out of 55 records show a regional precipitation increase that is also simulated over the additional land mass area due to sea level drop. The thermodynamic and dynamic responses are analyzed to explain a drier LGM EASM as a combination of these two antagonistic mechanisms. Relatively low atmospheric moisture content was the main thermodynamic control on the lower LGM (relative to pre-industrial levels) EASM precipitation amounts in both the reconstructions and the models. In contrast, two dynamic processes in relation to stationary eddy activity act to increase EASM precipitation regionally in records and simulations, respectively. Precipitation increase in records is explained by dynamic enhancement of the horizontal moisture transport, while dynamic enhancement of the vertical moisture transport leads to simulated precipitation increase over the specific region where landmass was exposed during LGM along continental coastlines of China due to significant drop in sea level (relative to pre-industrial levels). Overall, the opposing effects of thermodynamic and dynamic processes on precipitation during the LGM provide a means to reconcile the spatial heterogeneity of recorded precipitation changes in sign, although data-model comparison suggests that the simulated dynamic wetting mechanism is too weak relative to the thermodynamic drying mechanism over data-model disagreement regions. [ABSTRACT FROM AUTHOR]

During 19–21 July 2021, Henan located in central-eastern China experienced torrential rainfall that caused devastating floods and claimed more than 300 casualties. It remains unclear whether and to what extent this extreme precipitation event is contributed by Typhoon In-Fa (TIF). Here we quantify the contribution of TIF to this record-breaking ‘21/7’ rainfall using an air–sea coupled model with ensemble simulations. The modeling results show that the northwestward moisture transport along the confluence front of TIF and the western Pacific subtropical high (WPSH) contribute mostly to the precipitation extremes across Henan. A sensitivity experiment that removes the TIF effect confirms TIF’s role in shaping extreme rainfall. Specifically, without TIF, WPSH shifts the moisture transport northeastward and causes a heavy rainband over the Korean Peninsula, with much less precipitation over Henan. The water vapor budget over Henan suggests that the TIF-induced moisture advection is nine times greater than the local moisture supply and is effectively converted into clouds therein to reinforce precipitation extremes. The contribution of TIF to the ‘21/7’ Henan torrential rainfall on average could be as large as 42% by comparing the differences between simulated results with and without TIF’s effects.

Atmospheric rivers (ARs) are narrow regions of strong horizontal water vapor transport that play important roles in the global water cycle, weather, and hydrology. Motivated by challenges in simulating ARs with state-of-the-art global models, this paper diagnoses model errors with a focus on relative contributions of moisture convergence, evaporation, and precipitation to AR column-integrated water vapor (IWV) budget. Using 20-year simulations by 24 global weather/climate models, budget terms are calculated for four AR sectors: postfrontal, frontal, prefrontal, and pre-AR, with biases assessed against two reanalysis products. The results indicate that each sector is unique in terms of the dominant water vapor balance, and that the terms exhibiting the largest intermodel spread are the same terms dominating thewater vapor balance in each sector. Overall, simulated bulk AR characteristics (e.g., geometry, frequency, and intensity) aremore sensitive to biases in IVT convergence andIWVtendency than to biases in evaporation and precipitation, although evaporation/precipitation biases do affect key AR bulk characteristics in selected sectors. The large intermodel spread (particularly for precipitation) and, in certain cases, discrepancies between the reanalysis references themselves (particularly for precipitation types) highlight the need for observational efforts that target better constraining AR processes in weather/climate models and reanalyses. [ABSTRACT FROM AUTHOR]

Abstract In this study, long-term (1961–2011) variations in the moisture budget and drought/flood events in six subregions of China are analyzed. Water vapor is mainly transported zonally during winter, while meridional transport is much stronger during summer. During winter, both the input moisture from the western boundary and the output moisture from the eastern boundary are slightly weakened; thus, the total amount of regional moisture in these subregions does not change much in eastern China. During summer, the decline in input moisture from the south is slightly weaker than the decrease in output moisture via the northern boundary; therefore, the net moisture budget is slightly increased in eastern China, resulting in more flood events during recent decades in this region. Generally, China tends to suffer much less drought risk and higher flood risk in the mature winter and decaying summer of El Niño; the opposite impact appears during a La Niña event, but with lower intensity.

Based on the daily precipitation data from the meteorological stations in Sichuan and the monthly average ERA-Interim reanalysis data from 1979 to 2016, the variation characteristics of summer water vapor budget in the Sichuan Basin and its relationship with precipitation are discussed in this study. The results show that, in summer, the water vapor in the Sichuan Basin and its four sub-basins flows in from the southern and western boundaries and flows out through the eastern and northern boundaries, and the basin is obviously a water vapor sink. From 1979 to 2016, the water vapor inflow from the southern and western boundaries significantly decreased, as well as the water vapor outflow through the eastern boundary. The summer precipitation in the Sichuan Basin is significantly positively correlated with the water vapor inflow at the southern boundary and net water vapor budget of the basin in the same period, and it is negatively correlated with the water vapor outflow at the northern boundary. The southern and northern boundaries are the two most important boundaries for the summer precipitation in the Sichuan Basin. Additionally, this study reveals that, under the multi-scale topography on the east side of the Tibet Plateau, the spatio-temporal distribution of precipitation in the Sichuan Basin results from the interactions between the unique topography of the Sichuan Basin and the different modes of water-vapor transport from low latitudes. The atmospheric circulation over the key area of air–sea interaction in the tropical region and its accompanying systems, as well as the anomalies of regional circulations and water vapor transport over the eastern China and Sichuan Basin, are the main reasons for the variation in summer precipitation in the Sichuan Basin.

Surface evaporation is an important factor in the hydrological cycle. It is unknown however how much the recycling of surface precipitation contributes to rainfall in a landfalling tropical cyclone. In this study, ensemble simulations were performed using the Weather Research and Forecasting model to quantify the contribution of re‐evaporation of surface precipitation to rainfall in Typhoon Utor (2013) during and after its landfall over South China. Two sets of ensemble simulations were conducted, one with all default model settings (CTRL) and the other with the surface precipitation rate in the land surface model being set to zero within a radius of 500 km from the storm center so that the re‐evaporation of surface precipitation was removed. Results show that the re‐evaporation of surface precipitation contributed about 15–20% to the total rainfall in the inner core within a 100‐km radius from the storm center after landfall. It is found that the removal of surface precipitation in the land surface model reduced soil moisture and thus surface latent heat flux, which led to a slightly weaker storm, thus the weaker boundary layer inflow and reduced inward moisture transport into the inner‐core region of the storm. The results demonstrate that the reduced surface evaporation and inward moisture transport contributed about 30–40 and 60–70%, respectively, to the decrease in precipitation in the inner‐core region in the experiment with the re‐evaporation of surface precipitation removed. Key Points: The recycling of surface precipitation is important for landfalling tropical cyclone rainfallThe re‐evaporation of surface precipitation contributed about 15–20% to the total rainfall in the inner core within a landfall TCThe removal of surface precipitation reduced soil moisture and surface latent heat flux, and also reduced inward moisture transport into TC [ABSTRACT FROM AUTHOR]

The impact of mid- and upper-level dry air, represented by low relative humidity (RH) values, on the genesis of tropical cyclone (TC) Durian (2001) in the South China Sea was investigated by a series of numerical experiments using the Weather Research and Forecasting model. The mid-level RH was lowered in different regions relative to TC Durian (2001)’s genesis location. Results suggest that the location of dry air was important to Durian (2001)’s genesis and intensification. The rapid development of the TC was accompanied by sustained near-saturated mid- and upper-level air, whereas low humidity decelerated its development. Water vapor budget analysis showed that moisture at mid and upper levels was mainly supplied by the vertical convergence of moisture flux and the divergence terms, and consumed by the condensation process. The horizontal convergence of moisture flux term supplied moisture in the air moistening process but consumed moisture in the air drying process. With a dryer mid- and upper-level environment, convective and stratiform precipitation were both inhibited. The upward mass fluxes and the diabatic heating rates associated with these two precipitation types were also suppressed. Generally, convection played the dominant role, since the impact of the stratiform process on vertical mass transportation and diabatic heating was much weaker. The vorticity budget showed that the negative vorticity convergence term, which was closely related to the inhibited convection, caused the vorticity to decrease above the lower troposphere in a dryer environment. The negative vorticity tendency is suggested to slow down the vertical coherence and the development rate of TCs. [ABSTRACT FROM AUTHOR]

Using the ERA-5 monthly reanalysis data and precipitation observations, this paper analyses the interdacal dry-wet transition and its mechanism in the Tarim Basin(TB) during summer. From the long-term perspective(1961–2021), TB is in a trend of "wet in the west and dry in the east". By taking a nine-year moving average of the precipitation(PRE), the research period is divided into three subperiods: P1(1961–1987), P2(1988–2009) and P3(2010−2021). From P1 to P3, the regional averaged Standardized Precipitation Evapotranspiration Index(SPEI) demonstrates an interdecadal turning of "wetting to drying". During P2(1988–2009), the dynamic component of water vapor increases the zonal moisture transport, causing a slight increase in PRE. The potential evapotranspiration(PET) is weakened by the increase in PRE and relative humidity(RH), the decrease in 2-m temperature(T2m) and 10-m wind speed(10UV), resulting in the humidification of the TB. In the P3(2010–2021), the non-linear component of water vapor increases moisture convergence in the western TB, causing a significant increase in PRE. However, the decrease in RH, accompanied by increases in T2m and UV10, results in a rapid increase in PET. The TB gets dry. The South Asian high(SAH) develops southeastward, guiding more water vapor transport from the upstream westerly and the tropical Indian Ocean. The Western Pacific subtropical high(WPSH) extends northwestward, increasing water vapor convergence in the western TB. The main reason for the increased precipitation changes from increased water vapor advection to enhanced water vapor convergence. The differences in PRE formation and T2m amplitude cause the interdecadal change in RH, deriving an interdecadal transition of wet and dry in the TB. Our findings may deepen the understanding of climate change, and provide a scientific support for ecological development, and global climate governance in arid/semi-arid regions. • TB has been presented an interdacal dry-wet transition in summer. • The summer SPEI in the TB is consistent with the interdacadal variations of PET. • The SAH and the WPSH modulate the moisture transport pathways and precipitation formation, influence the dry-wet transition in the TB. [ABSTRACT FROM AUTHOR]

The water vapor budget (WVB) over the Tibetan Plateau (TP) is closely related to the large-scale atmospheric moisture transportation of the surrounding mainland and oceans, especially for the Indo-Pacific warm pool (IPWP). However, the procession linkage between the WVBs over the TP and its inner basins and IPWP has not been sufficiently elucidated. In this study, the relationship between the summer WVB over the TP and the IPWP was quantitatively investigated using reanalysis datasets and satellite-observed sea surface temperature (SST). The results show that: (1) the mean total summer vapor budget (WVBt) over the TP in the period of 1979–2018 was 72.5 × 106 kg s−1. Additionally, for the 13 basins within the TP, the summer WVB has decreased from southeast to northwest; the Yarlung Zangbo River Basin had the highest WVB (33.7%), followed by the Upper Yangtze River Basin, Ganges River Basin and Qiangtang Plateau. (2) For the past several decades, the WVBt over the TP has experienced an increasing trend (3.81 × 106 kg s−1 decade−1), although the southern boundary budget (WVBs) contributed the most and is most closely related with the WVBt, while the eastern boundary budget (WVBe) experienced a decreasing trend (4.21 × 106 kg s−1 decade−1) which was almost equal to the interdecadal variations of the WVBt. (3) For the IPWP, we defined a new warm pool index of surface latent heat flux (WPI-slhf), and found that an increasing WPI-slhf would cause an anticyclone anomaly in the equatorial western Indian Ocean (near 70° E), resulting in the increased advent of water vapor to the TP. (4) On the interdecadal scale, the correlation coefficients of the variation of the summer WVBt over the TP with the WPI-slhf and Indian Ocean Dipole (IOD) signal were 0.86 and 0.85, respectively (significant at the 0.05% level). Therefore, the warming and the increasing slhf of the IPWP would significantly contribute to the increasing WVB of the TP in recent decades.

Abstract: In order to better understand the water vapor (WV) intrusion into the tropical stratosphere, a mesoscale simulation of the tropical tropopause layer using the BRAMS (Brazilian version of Regional Atmospheric Modeling System (RAMS)) model is evaluated for a wet season. This simulation with a horizontal grid point resolution of 20 km × 20 km cannot resolve the stratospheric overshooting convection (SOC). Its ability to reproduce other key parameters playing a role in the stratospheric WV abundance is investigated using the balloon‐borne TRO‐Pico campaign measurements, the upper‐air soundings over Brazil, and the satellite observations by Aura Microwave Limb Sounder, Microwave Humidity Sounder, and Geostationary Operational Environmental Satellite 12. The BRAMS exhibits a good ability in simulating temperature, cold‐point, WV variability around the tropopause. However, the simulation is typically observed to be warmer by ∼2.0°C and wetter by ∼0.4 ppmv at the hygropause, which can be partly affiliated with the grid boundary nudging of the model by European Centre for Medium‐Range Weather Forecasts operational analyses. The modeled cloud tops show a good correlation (maximum cross‐correlation of ∼0.7) with Geostationary Operational Environmental Satellite 12. Furthermore, the overshooting cells detected by Microwave Humidity Sounder are observed at the locations, where 75% of the modeled cloud tops are higher than 11 km. Finally, the modeled inertia‐gravity wave periodicity and wavelength are comparable with those deduced from the radio sounding measurements during TRO‐Pico campaign. The good behavior of BRAMS confirms the SOC contribution in the WV abundance, and variability is of lesser importance than the large‐scale processes. This simulation can be used as a reference run for upscaling the impact of SOC at a continental scale for future studies. [ABSTRACT FROM AUTHOR]

In this study, long-term (1961-2011) variations in the moisture budget and drought/flood events in six subregions of China are analyzed. Water vapor is mainly transported zonally during winter, while meridional transport is much stronger during summer. During winter, both the input moisture from the western boundary and the output moisture from the eastern boundary are slightly weakened; thus, the total amount of regional moisture in these subregions does not change much in eastern China. During summer, the decline in input moisture from the south is slightly weaker than the decrease in output moisture via the northern boundary; therefore, the net moisture budget is slightly increased in eastern China, resulting in more flood events during recent decades in this region. Generally, China tends to suffer much less drought risk and higher flood risk in the mature winter and decaying summer of El Niño; the opposite impact appears during a La Niña event, but with lower intensity. [ABSTRACT FROM AUTHOR]

Sea-effect snowfall is a special form of snow in the coastal areas of the Bohai Sea in China. However, a quantitative understanding of its water vapor and cloud microphysical mechanisms is still lacking. In this study, the Weather Research and Forecasting model version 4.0 with three microphysics schemes was employed to investigate a sea-effect snowstorm that occurred in the north of Shandong Peninsula on 9–10 January 2018. The simulated snowfall amount, temperature and humidity profiles, and radar reflectivity were in general agreement with the observations. The moisture budget revealed that the water vapor came completely from evaporation of the surface of Bohai Sea. The largest water vapor sink term was the moisture advection, followed by the deposition and condensation (accounting for only 15% of the sea surface evaporation). This phenomenon is analogous to heating water in a kettle and then the water vapor drifting away with the wind. In the main snowfall area, the total water vapor transport was positive (i.e., inflow) below the height of 1.5 km, and was almost zero above 3.0 km. The period of maximum moisture inflow in the low layer was about 30 min ahead of the maximum surface snowfall. In addition, the hydrometeor distributions in this sea-effect snowstorm were relatively simple compared to those in non-sea-effect snowstorm; the snow content was the most (0.09 g kg−1), followed by the supercooled cloud water (0.01 g kg−1), owing to the weak convection in it. Snow growth was dominated by the vapor deposition, and the process of rimming accounted for only 1/4 of the vapor deposition. The evidently weaker vapor condensation than vapor deposition is quite different from that in summertime heavy rainfall. • Water vapor came completely from evaporation of the Bohai Sea, like heating water in a kettle then drifting away with wind. • Hydrometeor distributions were simple due to the weak convection, and snow growth was mainly dominated by vapor deposition. • Vapor condensation was evidently weaker than vapor deposition, which was quite different from that in summer heavy rainfall. [ABSTRACT FROM AUTHOR]

The consistency of global atmospheric mass and water budget performance in 20 state-of-the-art ocean-atmosphere Coupled Model Intercomparison Project Phase 5 (CMIP5) coupled models has been assessed in a historical experiment. All the models realistically reproduce a climatological annual mean of global air mass (AM) close to the ERA-Interim AM during 1989-2005. Surprisingly, the global AM in half of the models shows nearly no seasonal variation, which does not agree with the seasonal processes of global precipitable water or water vapor, given the mass conservation constraint. To better understand the inconsistencies, we evaluated the seasonal cycles of global AM tendency and water vapor source (evaporation minus precipitation). The results suggest that the inconsistencies result from the poor balance between global AM tendency and water vapor source based on the global AM budget equation. Moreover, the cross-equatorial dry air mass flux, or hemispheric dry mass divergence, is not well represented in any of the 20 CMIP5 models, which show a poorly matched seasonal cycle and notably larger amplitude, compared with the hemispheric tendencies of dry AM in both the Northern Hemisphere and Southern Hemisphere. Pronounced erroneous estimations of tropical precipitation also occur in these models. We speculate that the large inaccuracy of precipitation and possibly evaporation in the tropics is one of the key factors for the inconsistent cross-equatorial mass flux. A reasonable cross-equatorial mass flux in well-balanced hemispheric air mass and moisture budgets remains a challenge for both reanalysis assimilation systems and climate modeling. [ABSTRACT FROM AUTHOR]

The climatological characteristics of precipitation and the water vapor budget in the Haihe River basin (HRB) are analyzed using daily observations at 740 stations in China in 1951-2007 and the 4-time daily ERA40 reanalysis data in 1958-2001. The results show that precipitation and surface air temperature present significant interannual and interdecadal variability, with cold and wet conditions before the 1970s but warm and dry conditions after the 1980s. Precipitation has reduced substantially since the 1990s, with a continued increase of surface air temperature. The total column water vapor has also reduced remarkably since the late 1970s. The multi-model ensemble from the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) has capably simulated the 20th century climate features and successfully reproduced the spatial patterns of precipitation and temperature. Unfortunately, the models do not reproduce the interdecadal changes. Based on these results, future projections of the climate in the HRB are discussed under the IPCC Special Report on Emissions Scenarios (SRES) B1, A1B, and A2. The results show that precipitation is expected to increase in the 21st century, with substantial interannual fluctuations relative to the models' baseline climatology. A weak increasing trend in precipitation is projected before the 2040s, followed by an abrupt increase after the 2040s, especially in winter. Precipitation is projected to increase by 10%-18% by the end of the 21st century. Due to the persistent warming of surface air temperature, water vapor content in the lower troposphere is projected to increase. Relative humidity will decrease in the mid-lower troposphere but increase in the upper troposphere. On the other hand, precipitation minus evaporation remains positive throughout the 21st century. Based on these projection results, the HRB region is expected to get wetter in the 21st century due to global warming. [ABSTRACT FROM AUTHOR]

Abstract: Eclipse provides a rare occasion to study the interactions between radiation, land and atmosphere under a solar forcing distinctly different from normal conditions. An opportunity came during the annular solar eclipse of 15 January 2010, the longest annular eclipse of the millennium where parts of India experienced up to 92% obscurity in early afternoon hours. Detailed measurements were carried out in the surface layer during 8–18 January at a land station located close to the central line of the eclipse. The focus of this study is on the effect of the annular eclipse on water vapor concentration, an aspect neglected in the past studies. During the entire 11-day study period, the lowest value in relative humidity occurred towards the end of the eclipse. Specific humidity decreased by 2gkg−1 during the eclipse and continued to decrease for few more hours. It recovered to the pre-eclipse values in the following afternoon. Humidity decrease is attributed to increased subsidence of drier air during and after the eclipse. [Copyright &y& Elsevier]

The water vapor budget and the cloud microphysical processes associated with a heavy rainfall system in the Dabie Mountain area in June 2008 were analyzed using mesoscale reanalysis data (grid resolution 0.03° × 0.03°, 22 vertical layers, 1-h intervals), generated by amalgamating the local analysis and prediction system (LAPS). The contribution of each term in the water vapor budget formula to precipitation was evaluated. The characteristics of water vapor budget and water substances in various phase states were evaluated and their differences in heavy and weak rainfall areas were compared. The precipitation calculated from the total water vapor budget accounted for 77% of actual precipitation; surface evaporation is another important source of water vapor. Water vapor within the domain of interest mainly came from the lower level along the southern boundary and the lower-middle level along the western boundary. This altitude difference for water vapor flux was caused by different weather systems. The decrease of local water vapor in the middle-lower layer in the troposphere during the system development stage also contributed to precipitation. The strength and the layer thickness of water vapor convergence and the content of various water substances in the heavy rainfall areas were obviously larger than in the weak rainfall areas. The peak values of lower-level water vapor convergence, local water vapor income, and the concentration of cloud ice all preceded the heaviest surface rainfall by a few hours. [ABSTRACT FROM AUTHOR]

Based on the daily precipitation data from the meteorological stations in Sichuan and the monthly average ERA-Interim reanalysis data from 1979 to 2016, the variation characteristics of summer water vapor budget in the Sichuan Basin and its relationship with precipitation are discussed in this study. The results show that, in summer, the water vapor in the Sichuan Basin and its four sub-basins flows in from the southern and western boundaries and flows out through the eastern and northern boundaries, and the basin is obviously a water vapor sink. From 1979 to 2016, the water vapor inflow from the southern and western boundaries significantly decreased, as well as the water vapor outflow through the eastern boundary. The summer precipitation in the Sichuan Basin is significantly positively correlated with the water vapor inflow at the southern boundary and net water vapor budget of the basin in the same period, and it is negatively correlated with the water vapor outflow at the northern boundary. The southern and northern boundaries are the two most important boundaries for the summer precipitation in the Sichuan Basin. Additionally, this study reveals that, under the multi-scale topography on the east side of the Tibet Plateau, the spatio-temporal distribution of precipitation in the Sichuan Basin results from the interactions between the unique topography of the Sichuan Basin and the different modes of water-vapor transport from low latitudes. The atmospheric circulation over the key area of air–sea interaction in the tropical region and its accompanying systems, as well as the anomalies of regional circulations and water vapor transport over the eastern China and Sichuan Basin, are the main reasons for the variation in summer precipitation in the Sichuan Basin. [ABSTRACT FROM AUTHOR]

The water vapor budget (WVB) over the Tibetan Plateau (TP) is closely related to the large-scale atmospheric moisture transportation of the surrounding mainland and oceans, especially for the Indo-Pacific warm pool (IPWP). However, the procession linkage between the WVBs over the TP and its inner basins and IPWP has not been sufficiently elucidated. In this study, the relationship between the summer WVB over the TP and the IPWP was quantitatively investigated using reanalysis datasets and satellite-observed sea surface temperature (SST). The results show that: (1) the mean total summer vapor budget (WVBt) over the TP in the period of 1979–2018 was 72.5 × 106 kg s−1. Additionally, for the 13 basins within the TP, the summer WVB has decreased from southeast to northwest; the Yarlung Zangbo River Basin had the highest WVB (33.7%), followed by the Upper Yangtze River Basin, Ganges River Basin and Qiangtang Plateau. (2) For the past several decades, the WVBt over the TP has experienced an increasing trend (3.81 × 106 kg s−1 decade−1), although the southern boundary budget (WVBs) contributed the most and is most closely related with the WVBt, while the eastern boundary budget (WVBe) experienced a decreasing trend (4.21 × 106 kg s−1 decade−1) which was almost equal to the interdecadal variations of the WVBt. (3) For the IPWP, we defined a new warm pool index of surface latent heat flux (WPI-slhf), and found that an increasing WPI-slhf would cause an anticyclone anomaly in the equatorial western Indian Ocean (near 70° E), resulting in the increased advent of water vapor to the TP. (4) On the interdecadal scale, the correlation coefficients of the variation of the summer WVBt over the TP with the WPI-slhf and Indian Ocean Dipole (IOD) signal were 0.86 and 0.85, respectively (significant at the 0.05% level). Therefore, the warming and the increasing slhf of the IPWP would significantly contribute to the increasing WVB of the TP in recent decades. [ABSTRACT FROM AUTHOR]