Cycle Of Water Vapor Research Articles

Machine Learning-Based Soil Moisture Retrieval Using CYGNSS and Interpolated SMAP Data

Abstract. Soil moisture is a crucial component of the global terrestrial ecosystem water vapor cycle, and higher spatial-temporal soil moisture product has significant impacts on research in agriculture, hydrology, and ecology. Spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) is a new remote sensing technology which can be used to retrieve soil moisture. Cyclone Global Navigation Satellite System (CYGNSS), launched by NASA in 2016 to observe ocean surface hurricanes, has also collected a substantial amount of data of GNSS signals reflected over the land. This paper focuses on soil moisture retrieval using CYGNSS and SMAP dataset. In this study, three machine learning methods (GSVM, BP and RF) are used for spatial interpolation of SMAP soil moisture data. Result shows RF interpolation is the best with the RMSE of 0.044 cm3/cm3 and the CC of 0.959 compared with SMAP truly SM. Then soil moisture data after RF interpolation and conventional linear interpolation are respectively used as response variables to train the retrieval model by ELM, BP and RF machine learning methods respectively. Results show that, among the six regression models, the RF-RF regression model performs the best with the RMSE of 0.012 cm3/cm3 and the CC of 0.986. Using this model, we get a global soil moisture product and have higher temporal and spatial resolution.

Using the NAMA as a Natural Integrator to Quantify the Convective Contribution to Lower Stratospheric Water Vapor Over North America

AbstractThe dynamical environment of the stratosphere, during the summer over North America, provides a natural integrator of the impact of convection in the lower stratosphere, as air can be confined for periods of a few days to more than a week. In situ data obtained during the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign show increasing water vapor mixing ratios in background air as a function of time the air parcel spent within the North American Monsoon Anticyclone region. We find that water vapor added to the stratosphere by convection decreases with altitude and tends to drop below detectable limits by the 415 K isentrope in 2021 and the 430 K isentrope in 2022. Integrating between potential temperatures of 380 and 460 K we find that convection added between 20 and 32 Tg per summer to the stratosphere in 2021 and 2022. While the total amount is only 1%–4% of the amount ascending in the tropics across the tropical tropopause, small changes in the annual flux of water can have a significant effect on the radiation budget of the atmosphere. Locally, over North America we find that convection increased the water vapor mixing ratio at 380 K by as much as 40%. Tropopause‐penetrating convection is part of the yearly cycle of stratospheric water vapor and we suggest that it must be included in extratropical models to accurately predict future trends in stratospheric water vapor.

Trends in atmospheric water vapour over the Thar Desert during Indian Summer Monsoon period of 2003-2020.

The Thar is the most densely populated desert in the world, which supports diverse ecosystems and human endeavours such as agriculture and socioeconomic activities. Water demand and supply in the Thar play an essential role in regulating the socioeconomic activities of the region. Inland water and precipitation aid the movement of water in the Thar Desert. Precipitation in the Thar is governed by the Indian Summer Monsoon (ISM), during which the winds distribute water vapour to regulate precipitation across the region. Therefore, we analyse the water vapour, its sources and its relation with precipitation using satellite measurements and reanalysis data in the Thar during ISM. Like other regions, a clear seasonal cycle of water vapour is observed in the Thar, with very high values (> 45 kg/m2) during ISM and low in winter (< 15 kg/m2). Evapotranspiration and moisture transport have significant effects on the amount of water vapour during ISM. There is a significant increase in water vapour in the troposphere, with high trends at the surface (0.032 g/kg/year) and small at the tropopause (0.00002 g/kg/year). A significant increase in column water vapour is also estimated in the Thar during ISM, with high trends in the eastern and southern areas, at about 0.15-0.35 kg/m2/year. The rise in water vapour in the Thar can be attributed to the increase in evapotranspiration (0.03-0.07 mm/day/year) and water vapour transport (> 0.5 kg/m/s/year) from the Arabian Sea and Indian Ocean. The rise in water vapour can lead to an increase in precipitation in the Thar, as it shows significant positive trends (0.05-0.1 mm/day/year) in the eastern areas during ISM. The increase in precipitation and water vapour in the arid Thar Desert can have significant implications for the regional environment and agriculture.

Two decades of riparian woodland water vapor and carbon dioxide flux responses to environmental variability

Riparian woodlands occupy a small area of global drylands but are hotspots for carbon and water cycling because groundwater supplements a small moisture supply from precipitation (P). Despite their regional importance, it is unclear if and how climate variability alters water vapor and carbon dioxide (CO2) fluxes in these ecosystems, and how ecosystem drivers vary across annual and seasonal scales. Here we use 21 years of eddy covariance measurements to understand land-atmosphere controls on water vapor and CO2 fluxes of a semiarid riparian mesquite (Prosopis velutina) woodland with year-round access to deep groundwater and highly variable summer and winter rainfall. Access to groundwater supplemented evapotranspiration (ET) that exceeded precipitation (ET:P range 1.9–5.4), making this riparian forest a substantial CO2 sink (367 ± 83 g C m-2yr-1). Contrary to general expectations of regional climatic drying, there was a shift to more favorable water conditions as P and soil moisture increased over time. Annual gross ecosystem production (GEP) and respiration (Reco) increased at the same rate (∼9 g C m-2yr-2) due to GEP and Reco increases during the wettest periods of the year. Growth year separation based on GEP phenology and regression models show that water availability and antecedent phenophase fluxes control seasonal ET and GEP, with CO2 fertilization detected only during winter dormancy, the least-active phenophase. The major Reco driver during the spring and summer was GEP, and this coupling intensified following the onset of summer rainfall. Groundwater subsidies support ET during the dry growing season and decouple water vapor and CO2 fluxes. These results highlight the dynamic nature of water vapor and CO2 cycling in semiarid riparian woodlands, the value of groundwater subsidies to buffering ecosystem responses from the interannual effects of climate variability, and the importance of two water sources in driving seasonal ecosystem responses.

Quasi-biennial oscillation modulation of stratospheric water vapour in the Asian monsoon

Abstract. The Asian monsoon (AM) plays a key role in the transport of water vapour to the lower stratosphere and contributes significantly to the wet phase of the annual global stratospheric water vapour cycle. Although it is known that the quasi-biennial oscillation (QBO) is one of the main drivers of the interannual variability in the AM water vapour, the physical mechanisms responsible for this variability remain unclear. Here we have used daily microwave limb sounder data for the period 2005–2020 to characterize the QBO signature on the lower stratosphere AM water vapour during the boreal summer. We show that the QBO has the strongest impact during August, when QBO westerly minus QBO easterly differences may reach 1 ppmv at 100 hPa, although a significant signature is also observed during July. We find that the region whose temperature controls the QBO signal on water vapour over the AM differs between July and August. In July, when the key region is over the tropical Indian Ocean, the QBO modulation of the AM water vapour occurs in phase with the signal over the Equator, whereas in August, when the key region is at the subtropics, over the southern edge of the monsoon, the signal over the AM is opposite to that over the Equator. Our results reveal that the QBO signal on the temperature on the south side of the AM anticyclone, which ultimately has an impact on AM water vapour, is, in turn, modulated by the QBO impact on tropical clouds. Thus, we find that the QBO signature on clouds over the eastern Indian Ocean gives rise to Rossby wave trains that produce variations in the circulation over the southern side of the AM anticyclone such that weaker anticyclone over this region generates an increase in water vapour, and vice versa.

The Arabian Sea and Bay of Bengal play a key role in extreme precipitation during the snow season over the Tibetan Plateau

AbstractWater vapour is a critical component of the hydrological cycle and plays a key role in climate systems and water resources on the Tibetan Plateau (TP). However, the effect of water vapour on extreme precipitation during the snow season over the TP, where snow cover is widespread, has not been determined. In this study, we investigated the water vapour contributions from extreme precipitation events during the snow season from 1980 to 2017 in four subregions of the TP using the flexible particle dispersion method. We divided the TP into four regions: the northeastern TP (NETP), northwestern TP (NWTP), southeastern TP (SETP) and southwestern TP (SWTP). The water vapour contributions from extreme precipitation among the four subregions were clearly different. The most important water vapour area that contributed the most water vapour to extreme precipitation over the NETP was from local contributions; nevertheless, Central Asia contributed the most water vapour to the NWTP. Water vapour from the Arabian Sea and Bay of Bengal (ASBB) dominantly controlled extreme precipitation in the SETP at a ratio of 45% and in the SWTP at a ratio of 72.9%. The water vapour contribution from the ASBB was significantly correlated with the extreme precipitation occurring in the TP subregions during the snow season in comparison to that of non‐extreme precipitation. These results could improve the understanding of water vapour cycle differences across the interior TP; additionally, our study provides a theoretical reference for the relationship between the snow distribution and water vapour sources in the TP.

Stable isotope tracing internal recycling and evaporation losses in saline lakes on the Qinghai-Tibet Plateau

Direct measuring of internal lake recycling and evaporation losses remains challenging for lakes on the Qinghai-Tibet Plateau (QTP). Stable isotope techniques provide an effective approach for estimating water vapor cycling ratios and evaporation losses of lakes on the QTP. In this study, the stable isotope values of saline lakes on the QTP were modeled using the stable isotope values of the sampled lake water and their influencing factors. The water vapor recycling ratio and evaporation loss (E/I) of 135 saline lakes on the QTP were evaluated and their influencing factors were revealed. The results showed that stable isotopes in saline lakes on the QTP showed significant spatial variability. Their stable isotopes were affected by the source of water vapor, recharge patterns, and local evaporation conditions. It's worth noting that the average water vapor recycling ratio of saline lakes on the QTP was 20.16 %, one-fifth of the saline lakes had a water vapor recycling ratio beyond 30 %. Saline lakes lose 26 % of their water through evaporation. 26 % of the saline lakes experienced high evaporation losses of >40 % of the total inflow. We found that the main factors controlling the water vapor recycling ratio and evaporation loss in saline lakes on the QTP were precipitation and altitude, respectively. Interestingly, the control factors of water vapor recycling ratio and evaporation loss in saline lakes with elevation above 4500 m showed significant differences compared to saline lakes with elevation below 4500 m. Therefore, the strengthening of lake system monitoring can provide reliable data support for security assessment and effective management of water resources on the QTP.

In situ analysis of surface composition and meteorology at the Zhurong landing site on Mars.

The Zhurong rover of the Tianwen-1 mission landed in southern Utopia Planitia, providing a unique window into the evolutionary history of the Martian lowlands. During its first 110 sols, Zhurong investigated and categorized surface targets into igneous rocks, lithified duricrusts, cemented duricrusts, soils and sands. The lithified duricrusts, analysed by using laser-induced breakdown spectroscopy onboard Zhurong, show elevated water contents and distinct compositions from those of igneous rocks. The cemented duricrusts are likely formed via water vapor-frost cycling at the atmosphere-soil interface, as supported by the local meteorological conditions. Soils and sands contain elevated magnesium and water, attributed to both hydrated magnesium salts and adsorbed water. The compositional and meteorological evidence indicates potential Amazonian brine activities and present-day water vapor cycling at the soil-atmosphere interface. Searching for further clues to water-related activities and determining the water source by Zhurong are critical to constrain the volatile evolution history at the landing site.

Effects of microclimatic factors on stomatal conductance of plants in vertical greenery systems in humid subtropical areas

• Reduced irrigation in winter does not significantly affect VGS. • The transpiration in winter is about 1/3 of that in other seasons. • The E of southwest-oriented VGS is 41% higher in the afternoon than morning. • A stomatal model in VGS in humid subtropical areas is proposed. Plant transpiration through stomata is crucial in land surface physical processes and the hydrosphere-atmosphere-biosphere water vapor cycle. Applying stomatal models to vertical greenery systems (VGSs) is challenging because of the unique plant habitat. However, VGSs are widely used in subtropical areas; thus, plant transpiration in these systems should be investigated. Field measurements are used to determine the relationship between stomatal conductance ( g s ) and different microclimatic factors: solar radiation ( I ), air temperature ( T a ), relative humidity (RH), and soil volumetric water content ( θ ). A stomatal model based on multiple nonlinear regression is proposed, and its accuracy for different VGS plant species is verified with field measurements. The model's root mean square error (RMSE) is 57% lower than that of existing models. The latent heat flux from transpiration ( E ) of VGS in different seasons and orientations are calculated, and design strategies are proposed to utilize the cooling potential of VGS better. The prediction accuracy of the water vapor transfer, thermal comfort, and building energy consumption can be improved by incorporating the proposed model into an urban canopy model (UCM) and building energy model (BEM). It will provide guidelines for sustainable urban planning and VGS design regarding heat island mitigation and building energy savings.

Study of the Relationship between High Mountain Asia Snow Cover and Drought and Flood in the Yangtze River Basin during 1980–2019

High Mountain Asia (HMA), with its high altitude, widely distributed snow and frozen soil, influences the climate of the northern hemisphere and even the world through thermal balance and the water vapor cycle and is also an indicator of global climate change. The influence of HMA snow cover on its surrounding areas has always been a research hotspot. Taking the Yangtze River Basin (YRB) of China as an example, this paper analyzes the relationship between winter snow depth in HMA and drought and flood in spring and summer in the YRB in the recent 40 years by using Singular Value Decomposition (SVD). The results show that the influence of snow cover on drought and flood in spring is inversely different between eastern and western parts of HMA, while the effect in summer is consistent. When the snow depth is larger (smaller) in the east and smaller (larger) in the west in winter, the YRB is drier (wetter) in spring. When the overall snow depth in HMA is larger (smaller) in winter, the northern part of the middle and lower reaches of the YRB is drier (wetter) in summer. The results provide support for understanding the impact of HMA snow cover on the surrounding climate and some important indicators for drought and flood prediction in the YRB.

Improved combined system and application to precipitation forecasting model

Reliable precipitation forecasting is essential for effective water management and timely warning of natural disasters such as floods and droughts. However, precipitation is a nonlinear water vapor cycle with certain spatial and temporal dependence, and stable prediction accuracy cannot be obtained by using a single model. Therefore, this paper proposes a novelty prediction model based on original feature extraction and an improved multi-objective swarm intelligence optimization algorithm, and it carries out multi-step prediction tests for two sites in the arid/semi-arid region (Qilian Mountain-Hexi Corridor). Finally, through the 19 comparison models, 5 evaluation indexes and 3 model performance tests, it is confirmed that the precipitation combined forecasting model constructed in this study is a reliable prediction system with optimal parameters. And it can provide favorable technical support for weather forecasting.

The annual cycle of water vapor above gale crater as retrieved by CRISM and compared to ChemCam passive sky spectroscopy

Using spectra returned from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter (MRO), we report atmospheric water vapor column abundances at a spatial resolution of ~ 1 km from observations taken over Gale crater, the landing site of the Mars Science Laboratory (MSL). The observations span a little more than 3 Mars years (MY) from MY 28 at Ls = 116° (October 04, 2006) to MY 31 at Ls = 101° (April 24, 2012). The retrievals were performed using an improved algorithm to correct for the changes in wavelength in the cross-track direction of CRISM images, also known as the “spectral smile”, allowing for a larger fraction of area from each observation to be covered. The water vapor column abundances are retrieved using the strong absorption band of H2O centered at 2600 nm. The seasonal cycle of water vapor above Gale is compared against that from reprocessed and new MSL Curiosity rover ChemCam passive sky observations using updated gas absorption parameters and covering the period between MY 31 at Ls = 291° (March 30, 2013) and MY 35 at Ls = 42° (June 20, 2019). The retrieved annual variation of water vapor from CRISM and ChemCam both display a similar trend with respect to the timing of the maximum and minimum in water abundance, with only minor differences caused by the interannual differences in water vapor and the different retrieval approaches between both instruments, addressing a previously existing discrepancy between ChemCam and CRISM water vapor column abundances.

Using Machine Learning Algorithm to Detect Blowing Snow and Fog in Antarctica Based on Ceilometer and Surface Meteorology Systems

Blowing snow is a common weather phenomenon in Antarctica and plays an important role in the water vapor cycle and ice sheet mass balance. Although it has a significant impact on the climate of Antarctica, people do not know much about this process. Fog events are difficult to distinguish from blowing snow events using existing detection algorithms by a ceilometer. In this study, based on ceilometer, the meteorological parameters observed by surface meteorology systems are further combined to detect blowing snow and fog using the AdaBoost algorithm. The weather phenomena recorded by human observers are ‘true’. The dataset is collected from 1 January 2016 to 31 December 2016 at the AWARE site. Among them, three-quarters of the data are used as the training set and the rest of the data as the testing set. The classification accuracy of the proposed algorithm for the testing set is about 94%. Compared with the Loeb method, the proposed algorithm can detect 89.12% of blowing snow events and 76.10% of fog events, while the Loeb method can only identify 64.29% of blowing snow events and 31.87% of fog events.

First Observations of Mesospheric OH Emission Profiles from OMPS/LP

Abstract The hydroxyl radical (OH) is one of the most reactive trace species and plays several important roles in the photochemical equilibrium and energy balance in the mesosphere. Global observations of OH from satellite instruments have a role to play in the study of OH and water vapor variations. This study describes an advanced algorithm to detect mesospheric OH emission profiles from the Suomi NPP satellite Ozone Mapping and Profiler Suite Limb Profiler (OMPS/LP). A triplet technique has been adapted to the OMPS/LP radiance measurements for determining OH emission signatures and OH index (OHI) from the OH A2Σ+-X2Π 0-0 band near the 308.8-nm wavelength. The derived mesospheric profiles provide an overall picture of the vertical distribution of OHI between 55 and 84 km and seasonal and latitudinal variability of the strength and height of the OHI. The observed annual cycle is correlated with the water vapor cycle and anticorrelated with the mesospheric temperature cycle. The data show that the relationships persist during the period of April 2012–December 2020. The seasonal behavior of OHI may be associated with variations in solar illumination or mesospheric water vapor abundance. The influence of solar illumination is dominant in the midlatitudes, while the OHI pattern is dominated by water vapor photolysis and other influences in the tropics.

Martian atmospheric water vapor abundances in MY26-30 from Mars Express PFS/LW observations

I report on retrievals of water vapor abundances in the Martian atmosphere using observations by Planetary Fourier Spectrometer Long Wavelength channel (PFS/LW) aboard the Mars Express (MEx) spacecraft. PFS/LW observations used in this work cover almost 4 Martian Years from Ls ~ 331° in MY26 (January 2004) to Ls ~ 209° in MY30 (December 2010). Vapor abundances were retrieved from nadir spectra collected over a range of latitudes, seasons and local hours. Most of the retrieved abundances correspond to daytime observations at local hours from 8 to 17 h. The spatial and temporal coverage of retrieved abundances varies significantly between years of observations, with the best coverage in MY27 and MY29. The average annual water vapor cycle observed by PFS/LW is qualitatively similar to the cycle observed by the Thermal Emission Spectrometer (TES) onboard Mars Global Surveyor (MGS), however the PFS/LW abundances are systematically lower. The likely reason for this difference is the difference in the respective water vapor absorption models. Comparison between PFS/LW abundances for time periods with low atmospheric dust opacity between different years of observations does not show significant interannual variability. PFS/LW abundances are significantly lower than the abundances retrieved from observations by Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on Mars Reconnaissance Orbiter (MRO) in MY29. The difference is likely due to the differences in retrieval models for different spectral regions used by CRISM and PFS/LW to retrieve water vapor abundances and due to different environmental parameters used in the retrievals. PFS/LW abundances are generally similar to abundances retrieved by the SPICAM IR instrument, except in the polar regions during summer. The difference likely arises because of non-uniform vertical distribution of water vapor in the summer polar atmospheres and different sensitivities of the two instruments to vertical distribution of vapor. The PFS/LW observed systematic longitudinal dependence of scaled vapor abundances in the northern tropics with two maxima at longitudes ~30–60°E and ~ 240–270°E. This longitudinal dependence resembles a standing wave forced in the local atmospheric flow by topography and surface thermo-physical properties. The longitudinal non-uniformity of water vapor possibly shows a seasonal dependence increasing around solstices and decreasing around equinoxes. During northern spring in the Northern Polar Region (NPR) PFS/LW observed an increase of vapor near the edge of the seasonal cap interpreted as a buildup of vapor by repeated cycles of water ice freezing and sublimation at the cap edge. Similar, but weaker and longitudinally non-uniform increase in vapor near the edge of the seasonal cap is observed in the Southern Polar Region (SPR) during spring. Tentative signs of water vapor diurnal variability were observed in the PFS/LW data over northern mid-latitudes during late spring and early summer, potentially reflecting vapor exchange between the regolith and the atmosphere.

Amazonian Moisture Recycling Revisited Using WRF With Water Vapor Tracers

AbstractPrevious studies have estimated that 25%–35% of Amazonian precipitation comes from evapotranspiration (ET) within the basin. However, due to simplifying assumptions of traditional models, these studies primarily focus on large spatial and temporal scales. This study is the first to analyze the moisture of Amazonian origin at the annual to daily timescale in four different subregions of the Amazon. We analyze the sources, sinks and stores of moisture that originates as Amazonian ET. To do this, we use the Weather Research and Forecast (WRF) regional meteorological model with the added capability of water vapor tracers to track this moisture. Moisture of Amazonian origin shows strong annual and semi‐annual signals, with contrasting behavior between the northern and southern parts of the basin. The tracers reveal a strong diurnal cycle of Amazonian water vapor which had not been previously reported. This signal is related to the diurnal cycle of ET, convective precipitation and advected moisture. ET's contribution to atmospheric moisture increases from early morning into the afternoon. Some of this moisture is rained out through convective storms in the early evening. Later in the night and following morning, strong winds associated with the South American Low Level Jet advect moisture downwind. The beating pattern becomes apparent when visualizing the Amazonian water vapor as an animation.

Diurnal Cycle of Heating and Water Vapor in the Metropolitan Area of Porto in Portugal

In this work, it is investigated the Urban Heat Island (UHI) using conservative thermodynamic variables observed by surface weather stations on the Metropolitan Area of Porto (Oporto) in Portugal, under adiabatic conditions at the surface. These conditions are usually present and associated with the development of a mixture layer into the diurnal Convective Boundary Layer (CBL), which residual layer in the late afternoon defines the initial state for the development of the nocturnal UHI. Both the spatial structure and temporal variation of potential temperature and specific humidity were considered, along the hours and days of the year, from a statistical point of view, resulting in hourly climatology. Details of the hourly evolution of the meteorological variables on the Oporto surface are presented and discussed. Results show a seasonal variation of the potential temperature up to 17°C throughout the year, which is associated with horizontal thermal gradients that can control and trigger mesoscale circulations such as sea-land, urban and valley-mountain breezes.

Experimental and theoretical study of urban tree instantaneous and hourly transpiration rates and their cooling effect in hot and humid area

The transpiration of trees is an important factor in the surface energy balance and the hydrosphere-atmosphere-biosphere water vapor cycle. It is also the main cause of a tree’s ecological effects, such as cooling and humidification. A major challenge is to establish a model that can accurately predict the transpiration rate of urban trees at different time scales. To address this challenge, field measurements are used to obtain the instantaneous and hourly transpiration rates of four common subtropical trees (Bauhinia blakeana, Mangifera indica, Ficus microcarpa and Michelia alba), and their cooling effects are analyzed. The transpiration rate for the four trees ranges from 18 to 54 mg m−2 s−1, and the estimated energy loss due to transpiration ranges from 178 to 274 W/m2, with an average of 229 W/m2. On average, 33.2 % of incoming solar radiation is converted into latent heat. The Shuttleworth-Wallace model, including canopy resistance and soil resistance parameters, is adapted to urban tree characteristics in built-up environments. The resulting model is a theoretical model that provides a new methodology and reasonable results for predicting an urban tree’s transpiration rate under urban conditions. Its accuracy at different time scales is verified with field measurements. The predictability of water vapor cycle, thermal comfort and surface energy budgets in urban environments will be enhanced by incorporating the transpiration model into urban canopy model. Future applications and development of this model will help provide guidelines for sustainable urban planning and urban landscape management in terms of water vapor cycle and heat island mitigation.

Densification of the Ground-Based GNSS Observation Network in the Southwest Indian Ocean: Current Status, Perspectives, and Examples of Applications in Meteorology and Geodesy

In the frame of the research project IOGA4MET, a new ground-based GNSS network is being deployed in the Southwest Indian Ocean (SWIO) since November 2017. This new network opens up for new research opportunities in geodesics and atmospheric sciences in this area regularly exposed to natural hazards, and significantly expands the International GNSS System (IGS) network, which only includes eight stations so far in the SWIO. After a description of the current status of IOGA4MET, examples of regional applications in meteorology (climatology and numerical modelling) and geodesy (monitoring of ground deformations) are presented using data collected in northern Madagascar and small neighboring islands in 2018-2020. The observed water vapor cycle is shown to exhibit different characteristics and important variability at all locations. At the seasonal scale, maximum IWV values are similar everywhere, minimum values decrease away from the equator and a sharp IWV gradient can be noticed during the wet-dry transition period. At this time scale, the seasonal IWV cycle analyzed with the high-resolution NWP system AROME-IO matches observations with little discrepancies . At the diurnal scale, IWV characteristics show different behavior on each side of Madagascar, which emphasizes the important role of this island in driving the regional circulation. Finally, examination of ground displacements measured by GNSS stations in relationship with the ongoing Mayotte seismic-volcanic crisis indicates that ground deformation associated with the current off-shore volcanic activity east of Mayotte does not extend up to 250 km, or is currently too low to be detected in very far field.

半干旱区城市环境下油松林分蒸腾特征及其影响因子

PDF HTML阅读 XML下载 导出引用 引用提醒 半干旱区城市环境下油松林分蒸腾特征及其影响因子 DOI: 10.5846/stxb201811262571 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家科技支撑计划项目（2015BAD07B06-4） The stand transpiration characteristics of Pinus tabulaeformis and its influential factors in a semi-arid urban environment Author: Affiliation: Fund Project: The research and demonstration on the cultivation and management technology system of water-saving urban landscape forests in Inner Mongolia and Beijing 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在城市环境下，由于不透水地面面积的增加，土壤-植物-大气之间水汽循环减弱，水汽调节能力差，因而研究城市树木蒸腾对环境因子的响应对于城市进行合理的水汽调节具有重要意义。于2017年生长季，在内蒙古呼和浩特市区树木园内选择58年生油松（Pinus tabulaeformis Carr.）作为研究树种，采用热扩散法测定其树干液流，并同步监测气象因子和土壤含水量变化，利用彭曼公式计算冠层气孔导度。结果表明：（1）生长季内，油松林分蒸腾存在明显日、月变化，晴天天气下林分蒸腾日变化呈单峰曲线，月林分蒸腾量5月最大，其次是7月、8月、6月和9月，分别为20.96、19.89、18.09、17.25 mm和7.49 mm。（2）油松林分蒸腾与饱和水汽压差、太阳总辐射、土壤含水量和风速均存在极显著相关关系（P<0.01），太阳总辐射、饱和水汽压差和土壤含水量是影响林分蒸腾的主要环境因子（R2=0.47、R2=0.31和R2=0.16），风速对林分蒸腾的影响程度最小（R2=0.12）；不同降雨量对林分蒸腾的影响作用不同，10 mm以上的日降雨量对油松林分蒸腾作用明显。（3）除环境因子外，油松叶片气孔通过响应环境变化控制蒸腾作用，当饱和水汽压差<1.5 kPa时，叶片气孔对饱和水汽压差的响应更敏感；当太阳总辐射<250 W/m2时，叶片气孔对蒸腾起促进作用，超过该阈值，叶片气孔关闭从而抑制树木蒸腾。 Abstract:The water vapor cycle between soil-plant-atmosphere is weakened and its ability for regulation is poor due to the increase in impervious surface areas in urban environments. Therefore, it is of great significance to study the transpiration response of urban trees to environmental factors amidst reasonable water vapor regulation in urban areas. In the growing season of 2017, 58-year-old Pinus tabulaeformis Carr. was selected as a research tree species for sap flow measurement, by thermal diffusion, at the Hohhot arboretum, Inner Mongolia. We measured meteorological factors and soil water content simultaneously and estimated canopy stomatal conductance using the Penman Formula. The results showed that (1) stand transpiration of P. tabulaeformis had obvious daily and monthly changes in the growing season. The diurnal stand transpiration variation graph showed a single peak curve on sunny days. Monthly stand transpiration reached the maximum in May, followed by July, August, June and September, which was 20.96, 19.89, 18.09, 17.25 mm and 7.49 mm, respectively. (2) There were extreme significant correlations between stand transpiration and vapor pressure deficits, global radiation, soil water content, and wind speed (P<0.01). Global radiation, vapor pressure deficit, and soil water content were the main environmental factors affecting forest transpiration (R2=0.47, R2=0.31 and R2=0.16), and wind speed had the smallest impact on forest transpiration (R2=0.12). Different rainfall events had varied effects on stand transpiration, but a significant effect when daily rainfall exceeded 10 mm. (3) In addition to environmental factors, leaf stomata of P. tabulaeformis controlled transpiration in response to environmental factors. Leaf stomata were more sensitive to vapor pressure deficits when it was < 1.5 kPa, whereas, global radiation, when < 250 W/m2, promoted transpiration. When the threshold was exceeded, leaf stomata would close to suppress tree transpiration. 参考文献 相似文献 引证文献