Water Vapor Flux Convergence Research Articles

The Role of Free‐Tropospheric Moisture Convergence for Summertime Heavy Rainfall in Western Japan

AbstractThe role of vertically integrated water vapor flux convergence (IVFC) in heavy rainfall events in western Japan is investigated by dividing the atmosphere into a boundary layer and free troposphere using the Japan Meteorological Agency's mesoscale gridded analysis product and reanalysis product. Rainfall events are defined by peaks of area‐averaged precipitation. The results show an increase in the free‐tropospheric IVFC more than 15 h before rainfall events, contributing to atmosphere moistening. This preceding moistening is favorable for mesoscale convective systems (MCSs) with slantwise ascending deep inflow layers (layer lifting) that produce large precipitation amounts. Appearance frequency of the moist absolutely unstable layer (MAUL) increases around the precipitation peak times, which is especially notable for larger peaks. These results indicate that the free‐tropospheric IVFC contributes to heavy rainfall in western Japan by providing environments favorable for producing and maintaining MAUL, enhancing the organization of MCSs.

Urbanization Impacts on Pearl River Delta Extreme Rainfall Sensitivity to Land Cover Change Versus Anthropogenic Heat

AbstractImpacts of urban land cover and anthropogenic heat (AH) on extreme local rainfall over the coastal Pearl River Delta (PRD) megacity region during boreal summer are investigated by conducting numerical experiments using the Weather Research and Forecastingmodel coupled with a single‐layer urban canopy model. To examine the relative importance of land cover change versus the presence of AH, three numerical experiments corresponding to different levels of urbanization in the PRD area were designed: one with cropland covering the whole region, one with urban land cover but zero AH, and one with urban land cover and a strong diurnal maximum of 300 Wm−2 of AH in the model simulations. Results show that the increase of rainfall in the urban area is much more sensitive to the intensity of AH than the mere change of surface properties. Urbanization with intense AH can enhance both the intensity and frequency of extreme rainfall, which can be attributed to higher surface temperature (of about 3.5–4°C), higher convective available potential energy, and lower convective inhibition, thus creating an environment more conducive to strong convection over the urban areas. Moreover, enhanced rainfall is supported by moisture supply from the South China Sea and increased water vapor flux convergence over the PRD city area. The amount of moisture flux converging over the coastal megacity area was found to depend on the direction of prevailing background wind.

Forced Decadal Changes in Summer Precipitation Characteristics over China: The Roles of Greenhouse Gases and Anthropogenic Aerosols

We investigated the decadal changes in the different types of summer mean precipitation over China across the mid-1990s based on observational datasets. The spatial variations in the observed decadal changes were estimated by comparing the present day (PD) time period of 1994–2011 with an earlier period of 1964–1981. The summer total precipitation increased in southern China and decreased in northern China from the early period to the PD. The increases of precipitation in southern China were due to increases in the frequency of heavy and moderate rainfall, whereas the decreases over northern China were mainly due to decreases in the frequency of moderate and light rainfall. Based on a set of numerical experiments using an atmospheric general circulation model coupled with a multilevel mixed-layer ocean model, we found that the increase of precipitation frequency forced by greenhouse gases is the main reason of increasing precipitation over southern and northeastern China, while the decrease of frequency caused by anthropogenic aerosol (AA) induces the decreasing precipitation over northern China. The water vapor flux convergence and water vapor flux strengthen in southern China and northeastern China by anthropogenic greenhouse gases. This distribution is also conducive to precipitation in most of southern China and northeastern China. Under the control of weakened southwesterly winds and 850-hPa divergence, precipitation decreases over northern and southwestern China by AA.

Circulation characteristics of two cases of Sea-entering Tibetan Plateau Vortices causing obvious differences in China precipitation

By using the NCEP FNL, historical synoptic charts and the year books of Tibetan plateau vortex and shear Line, based on synoptic and diagnosis methods, the observation facts of the sea-entering Tibetan Plateau vortices (STPVs) from 1998 to 2018, (STPVs) from 1998 to 2018, the two southeast-path STPVs that made great differences in precipitation are comparatively analyzed. The results show that: (1) The would bring precipitation to the eastern coast of China, and further affecting Korean Peninsula, Japan and Russia. (2) The different circulation characteristics of large- and small-scale precipitation STPVs are as follows:there are strong north and south branch jets at 200hPa and the north branch jet extends to east-ward with the core moving to east, and the circulation is more stable at 500hPa to the north of 45°N in East Asia, and STPV induces low vortex in the lower atmosphere in large-scale precipiitation STPV process. The opposite situation is true for small-scale precipitation STPV process. As a result, there are rising motion areas with large range and strong strength in and near the large-scale precipitation STPV area in the middle and lower troposphere, where larger water vapor flux and strong water vapor flux convergence also exist.

Atmospheric Water Vapor Budget and Its Long‐Term Trend Over the Tibetan Plateau

AbstractThe rapid warming and consequent retreat of glaciers across the Tibetan Plateau (TP) have given rise to the debate on the ability of the atmospheric water supply to alleviate the depletion of surface water storage. We investigate long‐term changes in atmospheric water vapor balance across the TP using 40‐year fifth generation European Centre for Medium‐Range Weather Forecasts (ECMWF) (ERA5) reanalysis. Precipitation, water vapor convergence, and evaporation generally maintain an equilibrium but with different long‐term variation trends: 0.68, −0.18, and 0.69 mm/a, respectively. Results suggest the inability of the water vapor arriving from outside the TP to effectively replenish the surface water storage. Despite of huge changes in atmospheric water vapor balance during summer, the risk of water storage depletion is brought by other three seasons, especially the autumn. The climatology and long‐term trends of water vapor balance exhibit strong variation across the regions of TP. The surrounding areas of Yarlung Zangbo Grand Canyon experience sharp decrease in water vapor convergence, thus reducing precipitation. Moreover, increasing evaporation is expected to severely loss of surface water storage. For the Three Rivers Source Region with no significant changes in total precipitations, decrease in water transported from outside of TP overlaps increase in evaporation results in the possible depletion of surface water storage. Brahmaputra basin, inner TP, and Qilian Mountain exhibit significant wetting trends due to increases in both convergence of water vapor flux and evaporation. Above regional and seasonal characteristics of water vapor, balances across the TP are attributed by inhomogeneous variation of atmospheric heat source and complex changes of atmospheric circulations.

Intensification of the East Asian summer monsoon lifecycle based on observation and CMIP6

Long-term changes in the East Asian summer monsoon (EASM) lifecycle since 1979 are analyzed based on observational datasets and historical simulations of the Coupled Model Intercomparison Project Phase 6 (CMIP6). According to the observation, the active and break phases of EASM have intensified resulting in a shorter but stronger rainy season, followed by a longer dry spell. This intensification in the active-phase precipitation is accompanied by increased lower tropospheric southwesterly wind and subsequent convergence of water vapor flux. These changes are accompanied by the widely reported westward extension of the North Pacific Subtropical High, which has been associated with the warming climate. CMIP6 models generally underestimated the observed intensification of the EASM lifecycle and the monsoon precipitation. However, some of the models did simulate the intensified EASM lifecycle similar to that observed. The result highlights the reasonable performance on EASM shown in some CMIP6 models and those simulations lend support to a dynamically-driven intensification of the EASM lifecycle in the warmer climate.

Climate diagnostics of the extreme floods in Peru during early 2017

From January through March 2017, a series of extreme precipitation events occurred in coastal Peru, causing severe floods with hundreds of human casualties and billions of dollars in economic losses. The extreme precipitation was a result of unusually strong recurrent patterns of atmospheric and oceanic conditions, including extremely warm coastal sea surface temperatures (SST) and weakened trade winds. These climatic features and their causal relationship with the Peruvian precipitation were examined. Diagnostic analysis and model experiments suggest that an atmospheric forcing in early 2017, which was moderately linked to the Trans-Niño Index (TNI), initiated the local SST warming along coastal Peru that later expanded to the equator. In January 2017, soil moisture was increased by an unusual expansion of Amazonian rainfall. By March, localized and robust SST warming provided positive feedback to the weakening of the trade winds, leading to increased onshore wind and a subsequent enhancement in rainfall. The analysis points to a tendency towards more frequent and stronger variations in the water vapor flux convergence along the equator, which is associated with the increased precipitation in coastal Peru.

Spatiotemporal Variations of Precipitation in Bangladesh Revealed by Nationwide Rain Gauge Data

Bangladesh is under the strong influence of the South Asian monsoon. Extensive damages caused by frequent severe flood events in this country call for a study of nationwide precipitation climatology. Here, we examine spatiotemporal variations of precipitation in Bangladesh using rain gauge data at 35 stations for the period 2003–2016. The annual precipitation amount in Bangladesh is 2263 mm, and it shows large spatial variations. The annual precipitation amount is large in the southeastern coastal region of the country and the region close to the Meghalaya Plateau, and it is small in the west central region. 17% and 73% of the annual precipitation amount are observed in the pre-monsoon season (March to May) and monsoon season (June to September), respectively. The pattern of the diurnal variation of precipitation differs depending on regions of Bangladesh. In the northern region of the country, the precipitation maximum occurs in the late night to early morning in both the pre-monsoon and monsoon seasons. The late night to early morning maximum of precipitation is associated with the large horizontal convergence of low-level water vapor flux. The Himalaya Mountains and the Meghalaya Plateau together with more nighttime moisture transport due to the strengthened nighttime low-level wind seem to play roles in enhancing nighttime precipitation. In the southwestern region of the country, the precipitation maximum is observed in the early evening in the pre-monsoon season, which is associated with the large convective instability in the afternoon, and it is observed in the early afternoon in the monsoon season. In the southeastern region of the country, the diurnal variability of precipitation is smallest in the pre-monsoon season compared with other regions of the country in the pre-monsoon and monsoon seasons and the precipitation maximum occurs in the late night to early morning in the monsoon season.

Extreme Wet‐Bulb Temperatures in China: The Significant Role of Moisture

AbstractThis paper investigates the extreme wet‐bulb temperatures (TWs) in China, with a focus on understanding the relative contributions of temperature and moisture to the extremes. Analysis of station observations shows that daily extreme temperatures (T), specific humidity (q), and TWs generally co‐occur in Southeastern China, while extreme TW and T rarely overlap in the arid and semiarid North and Northwest China. Overall, q contributes more than T to extreme TWs, especially in North and Northwest China. Based on the relative contributions of q and T, regional extreme TW events are classified as q dominated and T dominated, respectively, to study their large‐scale environment. Cluster analysis of global reanalysis data shows that extreme TWs are generally accompanied by increased surface air temperature and humidity, concomitant with anomalous high pressure and notable water vapor flux convergence. However, important differences are also seen in the large‐scale environment during q‐dominated and T‐dominated extreme TWs. During q‐dominated extreme TWs, the large‐scale environment favors convection, as indicated by ascending motions, decreased downward solar radiation as well as increased precipitable water and near‐surface relative humidity. In contrast, during T‐dominated extreme TWs, convection is inhibited by the large‐scale environment that features descending motion and increased downward solar radiation, decreased precipitable water, and decreased relative humidity. Consistent with the contrasting environments, we demonstrate that T‐dominated extreme TWs tend to last longer than q‐dominated extremes. Given the significant role of moisture in extreme TWs, more research is needed to understand its impacts on heat stress now and in the future.

Ocean Salinity as a Precursor of Summer Rainfall over the East Asian Monsoon Region

AbstractThe sea surface salinity (SSS) varies largely as a result of the evaporation–precipitation difference, indicating the source or sink of regional/global water vapor. This study identifies a relationship between the spring SSS in the tropical northwest Pacific (TNWP) and the summer rainfall of the East Asian monsoon region (EAMR) during 1980–2017. Analysis suggests that the SSS–rainfall link involves the coupled ocean–atmosphere–land processes with a multifacet evolution. In spring, evaporation and water vapor flux divergence were enhanced in some years over the TNWP where an anomalous atmospheric anticyclone was established and a high SSS was well observed. As a result, the convergence of water vapor flux and soil moisture over the EAMR was strengthened. This ocean-to-land water vapor transport pattern was sustained from spring to summer and played a leading role in the EAMR rainfall. Moreover, the change in local spring soil moisture helped to amplify the summer rainfall by modifying surface thermal conditions and precipitation systems over the EAMR. As the multifacet evolution is closely related to the large-scale ocean-to-land water vapor transport, it can be well represented by the spring SSS in the TNWP. A random forest regression algorithm was used to further evaluate the relative importance of spring SSS in predicting summer rainfall compared to other climate indices. As the SSS is now monitored routinely by satellite and the global Argo float array, it can serve as a good metric for measuring the water cycle and as a precursor for predicting the EAMR rainfall.

Analysis of the convective characteristics during the mutual evolution of an inverted trough/low vortex and its induced rainstorm over the northeastern Sichuan basin, China

Based on a variety of ground-based and satellite-derived observational data, we studied a flood-rainstorm event that occurred over northeastern Sichuan, China, from the 8th to the 14th of September 2014. Four periods of mesoscale convective system (MCS) activity were found during a mutual evolution process of an 850-hPa basin inverted trough (BIT) and 850-hPa basin low vortex (BLV). Among them, the first three periods occurred in an alternating evolution of the BIT and BLV (called the first stage), and then, the fourth period was stimulated by continuous activity of the BLV (called the second stage). During the first stage, MCSs enhanced (weakened) under the situation of the BIT (BLV), and then during the second stage MCSs developed to their strongest levels. Further analysis of the reasons behind the enhancement and weakening of MCSs revealed an obvious characteristic of upper level (lower level) positive (negative) divergence in the BIT situation of the first stage and BLV situation of the second stage. By comparison, under the BLV situation of the first stage, the vertical helicity was larger in the upward airflow of the zonal circulation, and the direction of the wet Q-vector was toward the ascending airflow in the vertical direction. In the horizontal direction, the negative divergence of the wet Q-vector corresponded to the position of water vapor flux convergence. In addition, in the early development of convection, sounding data showed a humidity profile of dry upper and wet lower levels, as well as a larger value of convective available potential energy, which triggered convective activity under the favorable dynamic conditions of atmosphere. When the above characteristics weakened, the convective activity also weakened. Therefore, the formation of multiple convective systems was closely related to the adjustment in atmospheric conditions around the BIT and BLV.

Meso-scale transport characteristics and budget diagnoses of water vapor in binary typhoons

In this paper, we simulate a process of binary typhoon and the budget diagnoses of water vapor in this process to analyze the transportation characteristics of water vapor and their influences on the variation of typhoon intensity. The results show that the interactions between typhoon Fitow and surrounding systems, including subtropical high, mid-latitude trough, west of the continent high and Southeast trailing typhoon Danas, change the background wind fields of Fitow, and then adjust the transport channels of moisture. Those surrounding systems, especially the trailing typhoon Danas which can be called the collection-transfer station of water vapor, have important effects on the intensity maintenance and the northern strong precipitation in the offshore and landing period of Fitow. The distribution and evolution of water vapor flux convergence band are consistent with those of strong convection band, revealing that the water vapor transport has important influences on the structure and intensity of the inner-core convection band in typhoon. The budget results show that the time series of total water vapor flux and typhoon intensity change synchronously. And the eastern boundary is the main source of water vapor transport, and the southern and northern boundary are also important, while the western boundary makes a negative contribution. The inflow transport channel is mainly located at the bottom of the troposphere, while the outflow transport area of water vapor is located at middle- and low-level troposphere of western boundary. The vertical transportation of water vapor plays an important role in redistributing the internal moisture of typhoon. The duration of sever convection band in typhoon is accompanied by the strong vertical transport of water vapor, which indicates that the vertical transport of water vapor is important for developing the strong convection in U and V type typhoon.

Autumn snow cover variability over northern Eurasia and roles of atmospheric circulation

This study analyzes the variability of northern Eurasian snow cover (SC) in autumn and the impacts of atmospheric circulation changes. The region of large SC variability displays a southward shift from September to November, following the seasonal progression of the transition zones of surface air temperature (SAT). The dominant pattern of SC variability in September and October features a zonal distribution, and that in November displays an obvious west–east contrast. Surface air cooling and snowfall increase are two factors for larger SC. The relative contribution of SAT and snowfall changes to SC, however, varies with the region and depends upon the season. The downward longwave radiation and atmospheric heat advection play important roles in SAT changes. Anomalous convergence of water vapor flux contributes to enhanced snowfall. The changes in downward longwave radiation are associated with those in atmospheric water content and column thickness. Changes in snowfall and the transport of atmospheric moisture determine the atmospheric moisture content in September and October, and the snowfall appears to be a main factor for atmospheric moisture change in November. These results indicate that atmospheric circulation changes play an important role in snow variability over northern Eurasia in autumn. Overall, the coupling between autumn Eurasian snow and atmospheric circulation may not be driven by external forcing.

Improving numerical experiments on persistent severe rainfall events in southern China using spectral nudging and filtering schemes

Using the inner field spectral nudging (IFSN) and lateral boundary filtering (LBF) methods in the regional Weather Research and Forecasting model, version 3.4 (WRF3.4), the simulation of persistent severe rainfall (PSR) events over south China was investigated. The results showed: (i) simulation using IFSN improves the forecasting of precipitation, especially for a lead time of greater than 3 days. Meanwhile, simulation with a combination of the IFSN and LBF (IFSN + LBF) methods provides better forecasts at a lead time of 5–7 days. (ii) The improvement in precipitation forecasting derives mainly from the reasonable simulation of the large‐scale circulation fields and water vapour flux convergence patterns. (iii) In terms of large‐scale circulation, the anomaly correlation coefficient can be significantly improved for lead times of 1–5 days (7–11 days) by adopting the IFSN (IFSN + LBF) method.

Exploring the Tropically Excited Arctic Warming Mechanism with Station Data: Links between Tropical Convection and Arctic Downward Infrared Radiation

Abstract The Tropically Excited Arctic Warming (TEAM) mechanism ascribes warming of the Arctic surface to tropical convection, which excites poleward-propagating Rossby wave trains that transport water vapor and heat into the Arctic. A crucial component of the TEAM mechanism is the increase in downward infrared radiation (IR) that precedes the Arctic warming. Previous studies have examined the downward IR associated with the TEAM mechanism using reanalysis data. To corroborate previous findings, this study examines the linkage between tropical convection, Rossby wave trains, and downward IR with Baseline Surface Radiation Network (BSRN) downward IR station data. The physical processes that drive changes in the downward IR are also investigated by regressing 300-hPa geopotential height, outgoing longwave radiation, water vapor flux, ERA-Interim downward IR, and other key variables against the BSRN downward IR at Barrow, Alaska, and Ny-Ålesund, Spitsbergen. Both the Barrow and the Ny-Ålesund station downward IR anomalies are preceded by anomalous tropical convection and poleward-propagating Rossby wave trains. The wave train associated with Barrow resembles the Pacific–North America teleconnection pattern, and that for Ny-Ålesund corresponds to a northwestern Atlantic wave train. It is found that both wave trains promote warm and moist advection from the midlatitudes into the Arctic. The resulting water vapor flux convergence, multiplied by the latent heat of vaporization, closely resembles the regressed ERA-Interim downward IR. These results suggest that the combination of warm advection, latent heat release, and increased cloudiness all contribute toward an increase in downward IR.

Projected changes in atmospheric river events in Arizona as simulated by global and regional climate models

Inland-penetrating atmospheric rivers (ARs) affect the United States Southwest and significantly contribute to cool season precipitation. In this study, we examine the results from an ensemble of dynamically downscaled simulations from the North American Regional Climate Change Assessment Program (NARCCAP) and their driving general circulation models (GCMs) in order to determine statistically significant changes in the intensity of the cool season ARs impacting Arizona and the associated precipitation. Future greenhouse gas emissions follow the A2 emission scenario from the Intergovernmental Panel on Climate Change Fourth Assessment Report simulations. We find that there is a consistent and clear intensification of the AR-related water vapor transport in both the global and regional simulations which reflects the increase in water vapor content due to warmer atmospheric temperatures, according to the Clausius-Clapeyron relationship. However, the response of AR-related precipitation intensity to increased moisture flux and column-integrated water vapor is weak and no significant changes are projected either by the GCMs or the NARCCAP models. This lack of robust precipitation variations can be explained in part by the absence of meaningful changes in both the large-scale water vapor flux convergence and the maximum positive relative vorticity in the GCMs. Additionally, some global models show a robust decrease in relative humidity which may also be responsible for the projected precipitation patterns.

Delayed withdrawal of the autumn rainy season over central Vietnam in recent decades

ABSTRACTA significant delay in the autumn rainy season withdrawal (ARSW) along the central coast of Vietnam (CCV) is detected since 1993, and the associated dynamics are discussed. During 1979–1992, the mean ARSW date was in early December, which is three pentads earlier than that during 1993–2006. Since rainfall over the CCV is primarily produced by cold surge vortices formed by the interaction of easterly waves with the cold surge flow, the ARSW is characterized by a gradual equatorward propagation (retreat) of the northeasterly winter monsoon (tropical easterlies). Therefore, the relatively late ARSW in the recent epoch is determined by the intensification and delayed withdrawal of the tropical easterlies during December, which should cause an increase in the easterly wave activity over the Philippine Sea and South China Sea (SCS), in response to the significant warm sea surface temperature (SST) in the western Pacific and cold SST in the central‐eastern Pacific. Correspondingly, since 1993, remarkable increases of convection and water vapour flux convergence around the CCV have occurred in December. The decadal environmental circulation changes also favour an enhancement of the intraseasonal oscillation (ISO) activities on 30–60‐, 12–24‐, and 5‐day scales that maintained rainfall along the CCV. Another potential factor is a distinct increase in the number of tropical cyclones (TCs) passing through the southern SCS during 1993–2006 compared with those occurring during 1979–1992, which is related to a strengthening and more westward‐extended sub‐tropical high and a significant SST warming in the tropical western Pacific. This enhanced ISO and TC activity, and the markedly delayed ARSW, originated from the decadal circulation changes, may be attributed to a mean state change in the Pacific basin since the mid‐to‐late 1990s characterized by a grand La Niña‐like pattern, which also results in the simultaneous advance of the Asian summer monsoon onset.

A diagnostic study of the asymmetric distribution of rainfall during the landfall of typhoon Haitang (2005)

The precipitation during landfall of typhoon Haitang (2005) showed asymmetric structures (left side/right side of the track). Analysis of Weather Research and Forecasting model simulation data showed that rainfall on the right side was more than 15 times stronger than on the left side. The causes were analyzed by focusing on comparing the water vapor flux, stability and upward motion between the two sides. The major results were as follows: (1) Relative humidity on both sides was over 80%, whereas the convergence of water vapor flux in the lower troposphere was about 10 times larger on the right side than on the left side. (2) Both sides featured conditional symmetric instability [MPV (moist potential vorticity) <0], but the right side was more unstable than the left side. (3) Strong (weak) upward motion occurred throughout the troposphere on the right (left) side. The Q vector diagnosis suggested that large-scale and mesoscale forcing accounted for the difference in vertical velocity. Orographic lift and surface friction forced the development of the asymmetric precipitation pattern. On the right side, strong upward motion from the forcing of different scale weather systems and topography caused a substantial release of unstable energy and the transportation of water vapor from the lower to the upper troposphere, which produced torrential rainfall. However, the above conditions on the left side were all much weaker, which led to weaker rainfall. This may have been the cause of the asymmetric distribution of rainfall during the landfall of typhoon Haitang.

Study of Water Vapor Variations Associated with Meso-γ Scale Convection: Comparison between GNSS and Non-Hydrostatic Model Data

Water vapor variations associated with a meso-γ scale convection were investigated using GNSS (Global Navigation Satellite System) derived PWV (precipitable water vapor) and high resolution numerical model data with a 250 m horizontal grid interval. A rapid increase of GNSS-derived PWV that occurred prior to the initiation of surface rainfall was well simulated by the numerical model.In the model, PWV values began to increase 16 min before the rainfall occurred at the surface. A local maximum of PWV was formed because of the generation of shallow free convection and surface water vapor flux convergence due to a lifting of an air parcel at approximately 1 km elevation by a preceding surface wind convergence. Due to the existence of a stable inversion layer between 2.2 and 3.5 km elevation, the shallow free convection took 11 min to rise above the inversion layer to form a deep convection. These results suggest that observation of local distributions of GNSS-derived PWV is useful for monitoring the generation of deep moist convection.

Impacts of modified Richards equation on RegCM4 regional climate modeling over East Asia

AbstractTo remove the deficiency of the numerical solution of the mass conservation‐based Richards equation for soil moisture in a regional climate model (RegCM4 with its land surface component Community Land Model 3.5 (CLM3.5)), a revised numerical algorithm that is used in CLM4.5 is implemented into CLM3.5. Compared with in situ measurements, the modified numerical method improves the ground water table depth simulations in RegCM4. It also improves the temporal and spatial variability of soil moisture to some extent. Its impact on simulated summer precipitation is mixed, with improvements over three subregions in China but with increased errors in three other subregions. The impact on the simulated summer temperature is relatively small (with the mean biases changed by less than 10% over most subregions). The evapotranspiration differences between modified and control land‐atmosphere coupled simulations are enhanced over the northwest subregion and Tibetan Plateau compared to offline simulations due to land surface feedbacks to the atmosphere (in coupled simulations). Similarly the soil moisture differences in coupled simulations are geographically different from those in offline simulations over the eastern monsoon area. The summer precipitation differences between modified and control coupled simulations are found to be explained by the differences of both surface evapotranspiration and large‐scale water vapor flux convergence which have opposite signs over the northwest subregion and Tibetan Plateau but have the same signs over other subregions.