The sensitivity of precipitation over land to surface evapotranspiration (ET) is among the most uncertain issues in land‐atmosphere interactions. Past studies have mostly investigated this issue ...locally, and it remains a challenge to assess the nonlocal impacts. Here, we use a moisture tracking method and statistical analyses to quantify the sensitivity of precipitation to both local and nonlocal ET. It is found that, in a point‐to‐point sense, boreal summer precipitation is more sensitive to local ET than nonlocal ET for about 2/3 of land areas, while for about 1/5 land areas, precipitation is sensitive to ET of more than 1,000 km away. Remote sensitivities are generally an order of magnitude smaller than local sensitivities, but their combined effect could be large and useful, especially for regions without significant local sensitivities. Future studies of land‐atmosphere interactions should be careful when making local assumptions.
Plain Language Summary
The water vapor for rainfall comes from the local and nonlocal surface evaporation, and evaporation is an important factor that may affect rainfall, in addition to wind and other factors. There have been many studies on the local impact of evaporation on rainfall, but it remains a challenge to assess the nonlocal impacts. Here, we use a moisture tracking method and statistical analyses to quantify the sensitivity of rainfall over land to both local and nonlocal evaporation. It is found that although rainfall is more sensitive to local evaporation than nonlocal evaporation over most land areas, there are still about 20% land areas where precipitation is overall sensitive to evaporation variations of more than 1,000 km away. Remote sensitivities are generally an order of magnitude smaller than local sensitivities, but their combined effect could be strong. For regions without significant local sensitivities, the remote sensitivities may provide useful information for precipitation prediction. Future studies of land‐atmosphere interactions should be careful when making local assumptions.
Key Points
For about 2/3 land areas, JJA precipitation is more sensitive to local ET than nonlocal ET in a point‐to‐point sense
For about 1/5 land areas, JJA precipitation is on average sensitive to ET of more than 1,000 km away
Remote sensitivities are much smaller than local sensitivities but could be large when combined and may be useful for some regions
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The evapotranspiration (ET) regime is an illustration of the water‐energy interactions at the land surface and is important for regional climate. In this study, we propose a revised framework for ...land aridity classification based on the ET regime and the conditional mutual information method. The proposed framework effectively captures the influences of short‐term water and energy supply on ET and highlights their potential roles in extreme events. This framework can be a supplement to the traditional classification schemes that rely on long‐term mean climate. Furthermore, we examine the sensitivity of this land aridity framework to different model physics parameterization schemes. The cumulus schemes are found to have the most important impact, followed by the radiation and microphysics schemes, while the planetary boundary layer schemes have the weakest impact. These findings provide valuable insights for the identification of land aridity and its relationship with land–atmosphere interactions.
Plain Language Summary
Land aridity, important for many uses, is typically measured using long‐term mean climate data (e.g., Aridity Index) and provides a static picture of how water and energy interact. In this study, we propose a new framework to classify land aridity, focusing on evapotranspiration (ET)—the process of water evaporating from the land and being released by plants. Our method looks at the changing relationship between water and energy over short periods, giving us a better understanding of how fluctuations in surface water and energy affect ET. This offers a more detailed view than indexes like the Aridity Index, and is especially helpful for studying extreme events. We also explore how different ways of modeling physical processes, such as cloud formation, sunlight and heat transfer, and air movements near the ground, impact our simulations of land aridity. Understanding these elements is key to getting a clearer picture of land aridity and how the land and atmosphere interact, which is crucial for accurate predictions and assessments in various environmental scenarios.
Key Points
A revised framework for land aridity classification based on the ET regime and conditional mutual information method is proposed
The proposed framework effectively captures the influence of short‐term water and energy supply on ET
The choice of cumulus scheme is important for model simulated land aridity while the choice of boundary layer scheme has minor impact
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The responses of atmospheric variability to Tibetan Plateau (TP) snow cover (TPSC) at seasonal, interannual and decadal time scales have been extensively investigated. However, the atmospheric ...response to faster subseasonal variability of TPSC has been largely ignored. Here, we show that the subseasonal variability of TPSC, as revealed by daily data, is closely related to the subsequent East Asian atmospheric circulation at medium-range time scales (approximately 3-8 days later) during wintertime. TPSC acts as an elevated cooling source in the middle troposphere during wintertime and rapidly modulates the land surface thermal conditions over the TP. When TPSC is high, the upper-level geopotential height is lower, and the East Asia upper-level westerly jet stream is stronger. This finding improves our understanding of the influence of TPSC at multiple time scales. Furthermore, our work highlights the need to understand how atmospheric variability is rapidly modulated by fast snow cover changes.
North China, characterized by its strong land–atmosphere coupling, also has a high concentration of atmospheric aerosols from anthropogenic emissions. However, the impact of aerosols on ...land–atmosphere coupling in this region remains partially unclear. Here, we use Weather Research and Forecasting model coupled with Chemistry (WRF‐Chem) experiments to show that the aerosol radiative effect weakens land–atmosphere coupling in North China. This weakening occurs across all five indexes used to measure different aspects of land–atmosphere coupling. Notably, the weakening is more pronounced for indexes that describe surface coupling compared to the index that characterizes the coupling between the planetary boundary layer (PBL) and clouds. The mechanisms underlying the aerosol influence can be primarily attributed to the reduction of land surface fluxes and their sensitivities to soil moisture, while the weakened entrainment of moisture at the upper boundary of the PBL may also contribute to the effects.
Plain Language Summary
The connection between land surface processes and atmospheric elements (land‐atmosphere coupling) is robust in North China due to its semi‐arid to semi‐humid climates. Additionally, the region experiences a high concentration of atmospheric pollution particles (aerosols) from human emissions. However, the impact of these aerosols on the land‐atmosphere coupling remains incompletely understood. To address this, we conducted experiments using a computer model. Our findings reveal that pollution weakens the land‐atmosphere coupling in North China. This effect is evident in various measures used to assess the coupling. Notably, the impact is more pronounced on the surface coupling compared to the coupling higher up in the atmosphere. The reasons behind this weakening effect are twofold. First, pollution reduces the exchange of heat and moisture between the land and the atmosphere. Second, it reduces the exchange of moisture in the upper atmosphere. Our research advances the understanding of land‐atmosphere interactions and their relationship with air pollution, potentially guiding future weather and climate predictions.
Key Points
Aerosol radiative effect weakens land–atmosphere coupling in North China, as found across five indexes of land–atmosphere coupling
The weakening is more pronounced for surface coupling than the coupling between the planetary boundary layer and clouds
The reduction of land surface fluxes and their sensitivities to soil moisture, along with the weakened entrainment are the primary mechanism
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
This study used a global hydrological model (GHM), PCR-GLOBWB, which simulates surface water storage changes, natural and human induced groundwater storage changes, and the interactions between ...surface water and subsurface water, to generate scaling factors by mimicking low-pass filtering of GRACE signals. Signal losses in GRACE data were subsequently restored by the scaling factors from PCR-GLOBWB. Results indicate greater spatial heterogeneity in scaling factor from PCR-GLOBWB and CLM4.0 than that from GLDAS-1 Noah due to comprehensive simulation of surface and subsurface water storage changes for PCR-GLOBWB and CLM4.0. Filtered GRACE total water storage (TWS) changes applied with PCR-GLOBWB scaling factors show closer agreement with water budget estimates of TWS changes than those with scaling factors from other land surface models (LSMs) in China's Yangtze River basin. Results of this study develop a further understanding of the behavior of scaling factors from different LSMs or GHMs over hydrologically complex basins, and could be valuable in providing more accurate TWS changes for hydrological applications (e.g., monitoring drought and groundwater storage depletion) over regions where human-induced interactions between surface water and subsurface water are intensive.
•PCR-GLOBWB is used to generate scaling factors to restore GRACE signals.•PCR-GLOBWB scaling factors show reasonable spatial variability for the study basin.•GRACE total water storage changes (TWSC) are evaluated using water balance.•GRACE TWSC applied with PCR-GLOBWB scaling factors are improved.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The ability of soil moisture to affect precipitation (SM‐P) can be dissected into the ability of soil moisture to affect evapotranspiration (ET; SM‐ET) and the ability of ET to affect precipitation ...(ET‐P). SM‐ET is a local process that is relatively easy to quantify, but ET‐P includes nonlocal atmospheric processes and is more complex. Here, ET‐P is quantified both locally and remotely with a back‐trajectory method for water vapor transport, using corrected reanalysis data. It is found that, for SM‐P and ET‐P, local impact is greater than that from remote for most land areas with significant local impacts. By examining the responses of the three metrics (SM‐ET, ET‐P, and SM‐P) to climate variations over different climate regimes, we show that SM‐ET is the principal factor that determines the spatial pattern and variation of SM‐P. For climatologically wet regions, SM‐ET and SM‐P are higher during dry periods, and vice versa for climatologically dry regions. All three metrics show highest values over the transitional zones.
Key Points
The impact of soil moisture on precipitation is dissected into two segments
Land segment dominants over atmospheric segment in the impact
Local impact dominants over nonlocal impacts over a majority of impact areas
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In this study, we investigated the synchronous responses of vegetation to extreme temperatures and/or precipitation at middle-to-high latitudes in Asia using semi-monthly observations of the GIMMS ...and GLASS leaf area index (LAI) from 1982 to 2016. The extreme vegetation and climate states were specified using standard anomalies of the annual cycle with removed variables. The results show that the area with the maximum or minimum LAI increased or decreased in correspondence with global warming. Both the GIMMS and GLASS LAI mostly reached their maximum in spring and autumn. The GIMMS LAI mostly reached its minimum in summer, while the GLASS LAI mostly reached its minimum in late spring or late summer. The GIMMS and GLASS datasets were generally consistent regarding the vegetation responses to extreme temperatures and precipitation, especially in the areas covered by trees. Extreme cold and/or wet conditions inhibited forest growth in the area south of 60 °N, particularly from October to November. Extreme hot and/or dry conditions promoted forest growth, particularly in the central and northern parts of Siberia from August to September. However, in some arid areas of Central Asia and the Mongolian Highlands, which are mostly covered by sparse vegetation and grasses, low temperature extremes and/or strong precipitation promoted vegetation growth, while high temperature extremes and/or low precipitation had adverse effects on vegetation growth. This was more apparent in the GIMMS LAI than it was in the GLASS LAI, since the GIMMS dataset supplied more values representing extreme states of vegetation. The compound extreme of hot-and-dry and cold-and-wet climates were more frequent than the combination of cold and dry climates and hot-and-wet climates were. The overall positive response of the vegetation was superior to the negative response. The results of this study suggest that a continuous increase in vegetation density and coverage will occur over the boreal region in the future if the warming trend persists. The consequent climate feedback in this area on the regional and global scales should be afforded more attention.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Soil moisture is a key variable of the land surface and its variations are an important issue in climate studies. In this study, we employed the Community Earth System Model (CESM) for 20 ensemble ...member simulations of the 50-year period from 1965 to 2014 and used canonical correlation analysis (CCA) and multiple regression to analyze the spatiotemporal characteristics of soil moisture predictability. The effects of soil moisture persistence and sea surface temperature (SST) as an external forcing on its predictability were analyzed. Results show that the soil moisture predictability due to its persistence is 1–2 months and considering SST as an external forcing can significantly increase its predictability. Regions that exhibit a significant increase in predictability are mainly tropical regions, North America and Western Asia during winter and spring. In tropical regions, SST increases the predictability of soil moisture by influencing the local surface temperature and precipitation. In other regions, the effects of SST on wind speed, cloud cover, and surface evaporation also contribute significantly to the increase in soil moisture predictability. The results were validated through the analysis based on soil moisture data from land data assimilation system and observed precipitation.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Mid- to high-latitude Asia (MHA) is one of the regions with the strongest warming trend and it is also a region where ecosystems are most sensitive to climate variability. However, how the vegetation ...in the region will change in the future remains uncertain. Using observation-based Leaf Area Index (LAI) and meteorological data and the multiple regression method, this study analyzes the response of vegetation in the MHA to climate elements during 1982–2020. Then, machine learning prediction models based on the Random Forest (RF) and Extreme Random Tree (ERT) algorithms are built and validated. Based on the calibrated meteorological fields from 17 Coupled Model Intercomparison Project Phase 6 (CMIP6) models under intermediate (SSP2-4.5) and high (SSP5-8.5) emission scenarios and the machine learning models, the LAI over the MHA in 2021–2100 is projected. The historical long-term increasing trends of LAI in the MHA since 1982 are found to be mainly caused by the increasing near-surface air temperature, while the interannual variations of LAI are also greatly affected by precipitation and surface downward solar radiation, especially in summer. The LAI over most of the MHA shows a significant increasing trend in the future, except over some dry areas, and the increasing trends are stronger under the SSP5-8.5 scenario than under the SSP2-4.5 scenario.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
This study investigated the relationship between the pre-summer soil moisture (SM) over the Indo-China Peninsula (ICP) and the summer precipitation in the middle and lower reaches of the Yangtze ...River basin (MLR-YRB) under different SST backgrounds. When spring soil over the ICP was dry (wet), summer precipitation in most parts of the MLR-YRB was significantly higher (lower) under normal SST backgrounds (in the inner-quartile years). However, the SM anomalies produced a limited influence on summer precipitation under strong SST conditions (in the outer-quartile years). Further analysis indicates that in the inner-quartile years, the thermal heating anomalies induced by abnormal SM evidently increased (decreased) the geopotential heights above the western tropical Pacific, and enhanced (weakened) the low-level anticyclonic circulation, thereby increasing (decreasing) the warm and moist southerly flow from the ICP and western Pacific regions to the MLR-YRB, which was conducive to more (less) precipitation in the MLR-YRB. In the outer-quartile years, thermal anomalies of the ICP had very weak effects on both the wind fields above the western Pacific and the water vapor flux to the MLR-YRB, thereby leading to a limited increase (decrease) in summer precipitation. The different responses of the local and surrounding atmospheric circulations to pre-summer SM anomalies over the ICP against different SST backgrounds produced distinct impacts on the distribution of summer precipitation in the MLR-YRB. The dry (wet) anomalies of spring SM in the ICP could also increase (decrease) the zonal thermal contrast between the ICP and the South China Sea (SCS) and impact the SCS summer monsoon differently in the inner-quartile and outer-quartile years. Based on numerical experiments with the Community Earth System Model (CESM), this work further confirmed the observational results and explored the physical mechanism by which the ICP spring soil moisture affects the MLR-YRB summer precipitation under various SST backgrounds. The simulation results show that a dry (wet) ICP spring soil significantly increased (decreased) the MLR-YRB rainfall in the following summer. This negative correlation was stronger in the inner-quartile years. The atmospheric response to changes in the surface thermal conditions was more significant in the inner-quartile years. This surface heating anomaly over the ICP led to anomalous southwest wind over the SCS, which could enhance the Asian summer monsoon and increase summer precipitation in the MLR-YRB.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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