Onset of summer monsoon in Northeast India is preceded by enhanced transpiration.
ABSTRACT: Variations in isotopic composition of water vapor in the atmosphere is an important indicator of the processes within the hydrological cycle. Isotopic signature of water vapor and precipitation can be helpful in partitioning evaporation and transpiration fluxes. It is well known that transpiration from forested regions supplies a significant amount of vapor to the atmosphere in monsoon and post-monsoon seasons. Here, we utilize observations from Tropospheric Emission Spectrometer (TES), Atmospheric Infra-Red Sounder (AIRS) and simulation models to ascertain that transpiration is dominant in the forests of Northeast India (NE) during pre-monsoon season. Our results show an increase in ?D of 78.0?±?7.1‰ and in specific humidity of 3.1?±?0.2?g?kg-1 during the pre-monsoon months of April-May compared to January-February. In the monsoon months of July-August, ?D reduces by 53.0?±?6.5‰ albeit the specific humidity increases by 3.4?±?0.2?g?kg-1. Using joint observations of specific humidity and isotope ratio in lower troposphere, we discern the moisture sources over NE India in pre-monsoon and monsoon seasons and posit the role of transpiration in continental recycling during pre-monsoon season.
Project description:The isotopic characteristics of plant transpired water are strongly controlled by soil evaporation process, primarily by relative humidity. The monsoon system is characterised by large variability of several atmospheric parameters; the primary one being the rainfall, which in turn, modulates the relative humidity. Due to the strong dependency of transpiration on relative humidity, it is expected that this process would vary in accordance with the active and break periods of the monsoon season, which are known to produce cycles of humid and relatively dry phases during a monsoon season. To study the transpiration process, an experiment was conducted wherein rainwater and transpired water were collected from a few plants and analyzed for their isotopic ratios during the summer monsoon seasons of 2016 and 2017. The difference between the isotopic characteristics of the transpired water and rain water is expected to be nominally positive, however, a large variability was observed. This difference is found to be high (low) during the reduced (enhanced) humidity conditions and varies in tandem with the break and active phases of the monsoon season. This characteristic feature may thus be used to delineate the dry and wet phases of monsoon on local to regional scale.
Project description:This study integrated isotopic composition in precipitation at 50 stations on and around the Tibetan Plateau (TP) and demonstrated the distinct seasonality of isotopic composition in precipitation across the study period. The potential effect of water vapor isotopes on precipitation isotopes is studied by comparing the station precipitation data with extensive isotopic patterns in atmospheric water vapor, revealing the close linkage between the two. The analysis of contemporary water vapor transport and potential helps confirm the different mechanisms behind precipitation isotopic compositions in different areas, as the southern TP is more closely related to large-scale atmospheric circulation such as local Hadley and summer monsoon circulations during other seasons than winter, while the northern TP is subject to the westerly prevalence and advective moisture supply and precipitation processes. The new data presented in this manuscript also enrich the current dataset for the study of precipitation isotopes in this region and together provide a valuable database for verification of the isotope-integrated general circulation model and explanation of related physical processes.
Project description:The Asian summer monsoon has great socioeconomic impacts. Understanding how the huge Tibetan and Iranian Plateaus affect the Asian summer monsoon is of great scientific value and has far-reaching significance for sustainable global development. One hypothesis considers the plateaus to be a shield for monsoon development in India by blocking cold-dry northerly intrusion into the tropics. Based on astronomical radiation analysis and numerical modeling, here we show that in winter the plateaus cannot block such a northerly intrusion; while in summer the daily solar radiation at the top of the atmosphere and at the surface, and the surface potential temperature to the north of the Tibetan Plateau, are higher than their counterparts to its south, and such plateau shielding is not needed. By virtue of hydrological analysis, we show that the high energy near the surface required for continental monsoon development is maintained mainly by high water vapor content. Results based on potential vorticity-potential temperature diagnosis further demonstrate that it is the pumping of water vapor from sea to land due to the thermal effects of the plateaus that breeds the Asian continental monsoon.
Project description:Popular perception claims that rain following a hot day brings relief, indicating a bio-meteorological perspective of 'rainy' forecasts. However, the hypothesis has rarely been examined on India which experiences distinct pre- and post-monsoon seasons with continuous dry days, occasionally interrupted by thunderstorms or cyclones. The current study analyzes 54 years of observed daily meteorological records across India to assess the impact of shower effect, defined as the amount of change in the temperature on the first day of a wet spell that succeeds a dry spell. Nine combinations of low to high probability rainfall events on the first day of a wet spell and short to prolonged dry spell categories are evaluated. Results indicate that the north, the northeastern, and the eastern states of India witness a decrease in the maximum and minimum temperatures, up to 5?°C during the pre-monsoon season while mostly exhibiting a statistically insignificant long-term temporal trend. During the post-monsoon season, a rainfall event decreases the maximum temperature, providing significant relief by reducing the heat index (HI) warning from 'Caution' to 'Normal', but is unable to lower the HI warning from 'danger' during the pre-monsoon season.
Project description:Plant transpiration, a process of water movement through a plant and its evaporation from aerial parts especially leaves, consumes a large component of the total continental precipitation (?48%) and significantly influences global water distribution and climate. To date, various chemical and/or biological explorations have been made to tune the transpiration but with uncertain environmental risks. In recent years, interfacial solar steam/vapor generation is attracting a lot of attention for achieving high energy transfer efficiency. Various optical and thermal designs at the solar absorber-water interface for potential applications in water purification, seawater desalination, and power generation appear. In this work, the concept of interfacial solar vapor generation is extended to tunable plant transpiration by showing for the first time that the transpiration efficiency can also be enhanced or suppressed through engineering the solar absorber-leaf interface. By tuning the solar absorption of membrane in direct touch with green leaf, surface temperature of green leaf will change accordingly because of photothermal effect, thus the transpiration efficiency as well as temperature and relative humidity in the surrounding environment will be tuned. This tunable transpiration by interfacial absorber-leaf engineering can open an alternative avenue to regulate local atmospheric temperature, humidity, and eventually hydrologic cycle.
Project description:This work investigated the relationship of host size, seasons, and water quality parameters with the prevalence and intensity of Cornudiscoides agarwali on Mystus bleekeri collected from the Dikrong River in Arunachal Pradesh, India from February 2016 to January 2017. A total of 2760 specimens of C. agarwali were recovered from 114 individuals of M. bleekeri. The levels of mean intensity, but not the prevalence, of infection of C. agarwali were positively correlated with fish host size, peaking in the largest size class (45.20 ± 5.69 parasites/fi sh). The prevalence values had a statistically significant seasonal trend, reaching highest (100 %) during the pre-monsoon season, followed by 91.8% during the post-monsoon period and 87.5 % during the monsoon season. The levels of mean intensity of infection were also dependent on the seasons, reaching significantly higher levels during the pre-monsoon season (42.75 ± 4.18 parasites/fi sh). All water quality parameters measured were within the safety value recommended for freshwater aquaculture. Cornudiscoides agarwali maintained its prevalence above 87.5 % throughout the annual cycle, which means it was able to reproduce year-round in a non-polluted river. This could be an indication of monogenoidean community and population dynamics thriving best under optimum water quality parameters. Also, this article draws the attention of parasitologists and ichthyologists to a taxonomic problem of the misidentification of Mystus spp., and therefore, possibly of their parasitic monogenoids.
Project description:BACKGROUND:The expansion of dengue vectors from lowland plains to the upland hilly regions of Nepal suggests the likelihood of increased risk of dengue. Our objective was to assess the effects of meteorological variables on vector indices and populations of dengue vectors in two different ecological regions of Nepal. An entomological survey was conducted in Kathmandu and Lalitpur (upland) and Chitwan (lowland) of Nepal in three different seasons from July 2015 to May 2016. The effect of meteorological variables on vector indices (house index, container index and Breteau index) and Aedes spp. population abundance was analyzed. A gamma regression was used to fit the models for vector indices and a negative binomial regression was used to model Aedes spp. population abundance. RESULTS:Monsoon season showed higher values for vector indices and vector populations compared to post-monsoon and pre-monsoon. Overall, the factor temperature-rainfall effect had a more significant influence on vector indices compared to relative humidity. The regression models showed that relative humidity has a greater impact in Chitwan than in Kathmandu. Variation was observed in the effect of predictor variables on Aedes aegypti and Ae. albopictus abundance. CONCLUSIONS:Temperature and rainfall contribute to the vector indices in the upland hilly region while relative humidity contributes in the lowland plains. Since vector prevalence is not only linked to meteorological factors, other factors such as water storage practices, waste disposal, sanitary conditions and vector control strategy should also be considered. We recommend strengthening and scaling up dengue vector surveillance and control programmes for monsoon season in both upland and lowland regions in Nepal.
Project description:Isotopic analysis of precipitation over the Andaman Island, Bay of Bengal was carried out for the year 2012 and 2013 in order to study the atmospheric controls on rainwater isotopic variations. The oxygen and hydrogen isotopic compositions are typical of the tropical marine sites but show significant variations depending on the ocean-atmosphere conditions; maximum depletion was observed during the tropical cyclones. The isotopic composition of rainwater seems to be controlled by the dynamical nature of the moisture rather than the individual rain events. Precipitation isotopes undergo systematic depletions in response to the organized convection occurring over a large area and are modulated by the integrated effect of convective activities. Precipitation isotopes appear to be linked with the monsoon intraseasonal variability in addition to synoptic scale fluctuations. During the early to mid monsoon the amount effect arose primarily due to rain re-evaporation but in the later phase it was driven by moisture convergence rather than evaporation. Amount effect had distinct characteristics in these two years, which appeared to be modulated by the intraseasonal variability of monsoon. It is shown that the variable nature of amount effect limits our ability to reconstruct the past-monsoon rainfall variability on annual to sub-annual time scale.
Project description:Anthropogenic modification of the water cycle involves a diversity of processes, many of which have been studied intensively using models and observations. Effective tools for measuring the contribution and fate of combustion-derived water vapor in the atmosphere are lacking, however, and this flux has received relatively little attention. We provide theoretical estimates and a first set of measurements demonstrating that water of combustion is characterized by a distinctive combination of H and O isotope ratios. We show that during periods of relatively low humidity and/or atmospheric stagnation, this isotopic signature can be used to quantify the concentration of water of combustion in the atmospheric boundary layer over Salt Lake City. Combustion-derived vapor concentrations vary between periods of atmospheric stratification and mixing, both on multiday and diurnal timescales, and respond over periods of hours to variations in surface emissions. Our estimates suggest that up to 13% of the boundary layer vapor during the period of study was derived from combustion sources, and both the temporal pattern and magnitude of this contribution were closely reproduced by an independent atmospheric model forced with a fossil fuel emissions data product. Our findings suggest potential for water vapor isotope ratio measurements to be used in conjunction with other tracers to refine the apportionment of urban emissions, and imply that water vapor emissions associated with combustion may be a significant component of the water budget of the urban boundary layer, with potential implications for urban climate, ecohydrology, and photochemistry.
Project description:Oxygen isotope signatures of transpiration (? E ) are powerful tracers of water movement from plant to global scale. However, a mechanistic understanding of how leaf morphological/physiological traits effect ? E is missing. A laser spectrometer was coupled to a leaf-level gas-exchange system to measure fluxes and isotopic signatures of plant transpiration under controlled conditions in seven distinct species (Fagus sylvatica, Pinus sylvestris, Acacia longifolia, Quercus suber, Coffea arabica, Plantago lanceolata, Oxalis triangularis). We analyzed the role of stomatal conductance (gs ) and leaf water content (W) on the temporal dynamics of ? E following changes in relative humidity (rH). Changes in rH were applied from 60 to 30% and from 30 to 60%, which is probably more than covering the maximum step changes occurring under natural conditions. Further, the impact of gs and W on isotopic non-steady state isofluxes was analyzed. Following changes in rH, temporal development of ? E was well described by a one-pool modeling approach for most species. Isofluxes of ? E were dominantly driven by stomatal control on E, particularly for the initial period of 30 min following a step change. Hence, the deviation of isofluxes from isotopic steady state can be large, even though plants transpire near to isotopic steady state. Notably, not only transpiration rate and stomatal conductance, but also the leaf traits stomatal density (as a measure of gmax) and leaf water content are significantly related to the time constant (?) and non-steady-state isofluxes. This might provide an easy-to-access means of a priori assumptions for the impact of isotopic non-steady-state transpiration in various ecosystems. We discuss the implications of our results from leaf to ecosystem scale.