Tropical Monsoon Areas Research Articles

Analysis of Paddy Field Changes (1989–2021) Using Landsat Images and Flooding-Assisted MLC in an Urbanizing Tropical Watershed, Vientiane, Lao PDR

Paddy fields are essential for food security and sustaining global dietary needs, yet urban expansion often encroaches on agricultural lands. Analyzing paddy fields and land use/land cover changes over time using satellite images provides critical insights for sustainable food production and balanced urban growth. However, mapping the paddy fields in tropical monsoon areas presents challenges due to persistent weather interference, monsoon-submerged fields, and a lack of training data. To address these challenges, this study proposed a flooding-assisted maximum likelihood classification (F-MLC) method. This approach utilizes accurate training datasets from intersecting flooded paddy field maps from the rainy and dry seasons, combined with the Automated Water Extraction Index (AWEI) to distinguish natural water bodies. The F-MLC method offers a robust solution for accurately mapping paddy fields and land use changes in challenging tropical monsoon climates. The classified images for 1989, 2000, 2013, and 2021 were produced and categorized into the following five major classes: urban areas, vegetation, paddy fields, water bodies, and other lands. The paddy field class derived for each year was validated using samples from various sources, contributing to the overall accuracies ranging from 83.6% to 90.4%, with a Kappa coefficient of between 0.80 and 0.88. The study highlights a significant decrease in paddy fields, while urban areas rapidly increased, replacing 23% of paddy fields between 1989 and 2021 in the watershed. This study demonstrates the potential of the F-MLC method for analyzing paddy fields and other land use changes over time in the tropical watershed. These findings underscore the urgent need for robust policy measures to protect paddy fields by clearly defining urban expansion boundaries, prioritizing paddy field preservation, and integrating these green spaces into urban development plans. Such measures are vital for ensuring a sustainable local food supply, promoting balanced urban growth, and maintaining ecological balance within the watershed.

Meteorological Factors Affecting Infectious Diarrhea in Different Climate Zones of China.

Meteorological factors and the increase in extreme weather events are closely related to the incidence rate of infectious diarrhea. However, few studies have explored whether the impact of the same meteorological factors on the incidence rate of infectious diarrhea in different climate regions has changed and quantified these changes. In this study, the time series fixed-effect Poisson regression model guided by climate was used to quantify the relationships between the incidence rate of various types of infectious diarrhea and meteorological factors in different climate regions of China from 2004 to 2018, with a lag of 0–2 months. In addition, six social factors, including per capita Gross Domestic Product (GDP), population density, number of doctors per 1000 people, proportion of urbanized population, proportion of children aged 0–14 years old, and proportion of elderly over 65 years old, were included in the model for confounding control. Additionally, the intercept of each province in each model was analyzed by a meta-analysis. Four climate regions were considered in this study: tropical monsoon areas, subtropical monsoon areas, temperate areas and alpine plateau areas. The results indicate that the influence of meteorological factors and extreme weather in different climate regions on diverse infectious diarrhea types is distinct. In general, temperature was positively correlated with all infectious diarrhea cases (0.2 ≤ r ≤ 0.6, p < 0.05). After extreme rainfall, the incidence rate of dysentery in alpine plateau area in one month would be reduced by 18.7% (95% confidence interval (CI): −27.8–−9.6%). Two months after the period of extreme sunshine duration happened, the incidence of dysentery in the alpine plateau area would increase by 21.9% (95% CI: 15.4–28.4%) in that month, and the incidence rate of typhoid and paratyphoid in the temperate region would increase by 17.2% (95% CI: 15.5–18.9%) in that month. The meta-analysis showed that there is no consistency between different provinces in the same climate region. Our study indicated that meteorological factors and extreme weather in different climate areas had different effects on various types of infectious diarrhea, particularly extreme rainfall and extreme sunshine duration, which will help the government develop disease-specific and location-specific interventions, especially after the occurrence of extreme weather.

COVID-19 incidence and local average rainfall: An analysis from a tropical monsoon area.

Sir, COVID-19 pandemic is an important global problem that has affected more than 30,000,000 people worldwide. The disease is a viral respiratory infection. The effect of climate on the incidence of COVID-19 is interesting. There are a few reports on the climate–geographical pathology of COVID-19. It is mentioned that there might be an association between COVID-19 incidence and environmental background.[1] Here, the authors analyze the data to assess the relationship between COVID-19 incidence and local average rainfall in a tropical monsoon area in Indochina where the second area of the world affected by COVID-19 after China is. The official data from the local Public Health Ministry on the incidence of COVID-19 and the data from the local Metrological Department are collected as primary data for further analysis. The focus area is on 20 provinces in the northeastern region of the country, which is not an international tourist destination and is not affected by the importation of disease by foreign tourists. The incidence is the case with local transmission and the imported case from aboard are excluded. The period of the analysis is from March to September 2020. The relationship between COVID-19 incidence and local average rainfall is shown in Figure 1. There was no statistically significant correlation (r = −0.227, P = 0.336) between COVID-19 incidence and local average rainfall in the studied tropical area. This is in contrast to other local endemic diseases such as malaria and dengue that have a significant correlation between disease incidence and local average rainfall in the study setting.[23] Because this study was on a limited area in the tropical zone, a further comparative study between tropical and non-tropical countries should be done for further conclusion on the interrelationship between COVID-19 epidemiology and background rainfall.Figure 1: Figure showing the relationship between COVID-19 incidence and local average rainfallFinancial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Leaf phenology and trunk growth of Avicennia alba (Blume) under a seasonally fluctuating saline environment in the tropical monsoon area of eastern Thailand

AbstractMangrove forests are said to be highly productive ecosystems but it is unclear how they maintain high productivity under the fluctuation of saline environment in the tropical monsoon region. A study of phenological aspects linked with the growth of mangrove trees may be a supportive evidence for this. Here, we studied the seasonal variation in leaf phenology and trunk growth of Avicennia alba trees in a tropical monsoon mangrove forest which has clear rainy and dry seasons at Trat Province, eastern Thailand. For the leaf phenology, the number of new and lost leaves was counted by using demographic techniques, and the monthly rates of leaf emergence and loss were calculated from 45 sample shoots from June 2019 to May 2020. In this period, trunk basal‐area increments were also recorded monthly by using dendrometer bands. The rate of leaf emergence showed a remarkable seasonal pattern that was high during the rainy season and low during the dry season. The monthly rate of leaf emergence and trunk growth showed a positive relationship, indicating that both the leaf and trunk growth of A. alba responded to the changing water salinity in the soil. However, the leaf loss rate fluctuated throughout the study period. It was considered that the cambial activity of trunk growth associated with new leaf formation stimulates tree growth under the low saline environment during the rainy season in the tropics. We discussed a growth strategy that will benefit mangrove trees growing in the intertidal areas under fluctuated saline environment.

Millennial-scale interaction between the East Asian winter monsoon and El Niño-related tropical Pacific precipitation in the Holocene

Both the East Asian winter monsoon (EAWM) and El Niño (EN) activities are vital climate modes that regulate the Pacific hydrologic cycle. However, the Holocene interactions among the EAWM, EN activities, and tropical Pacific precipitation remain unclear due to the lack of appropriate EAWM proxies. Here, we present high-resolution grain size records from the East China Sea shelf along with a transient climate model simulation to study the Holocene EAWM evolution and compare the findings with paleo-EN precipitation-related proxies records. The millennial-scale oscillations of grain size records, which are indicative of the intensity of the EAWM-driven coastal current, reveal an anti-phase coupling between the EAWM and EN-related tropical Pacific precipitation on a millennial timescale since 5.8 ka. These results, which are consistent with simulation results, indicate that the intensified EAWM could not only reduce equatorial western Pacific precipitation by reducing the sea surface temperature but also likely change boundary conditions in the tropical Pacific (i.e., the east-west Pacific temperature gradient and westerly anomaly) to favor the formation of subsequent intensive EN activities. The enhanced EN activities, inferred by the positive tropical eastern Pacific precipitation anomalies, could subsequently suppress the EAWM through anomalous low-level anticyclones and associated southerly anomalies, thereby generating intensified tropical western Pacific (mainly tropical monsoon areas) precipitation. Our study highlights these intrinsic interactions during the mid- to late Holocene and has useful implications for understanding this millennial-scale climate oscillation, which may represent periodic atmospheric exchange between high- and low-latitude climate systems by mediating the EAWM.

Modelling rice yield with temperature optima of rice productivity derived from satellite NIRv in tropical monsoon area

Tropical rice production is at risk from rising temperature. Understanding regional and seasonal heterogeneity of optimum temperatures for rice production is important for model simulation to predict rice yield change under climate change. However, studies or tools for widely observation of crop responses to temperature over broad spatial scales with long time spans are limited. In this study, we detected optimum temperature range for rice gross primary production (ToptGPP) in the lower Gangetic plains and delta region using the near-infrared reflectance of vegetation (NIRV), which is a new photosynthetic proxy, to improve ORYZA model performance in high-temperature season and assessed how tropical rice would respond to temperature increase in the study area. According to satellite observations of NIRV from 2001 to 2015, current ambient air temperature has exceeded the mean ToptGPP of Boro rice (24.8 ± 1.8 °C) and Aman rice (26.7 ± 1.2 °C) in the lower Gangetic plains and delta region, suggesting a downtrend of rice production under future warming. The detection results show that rice has lower ToptGPP in the regions with more drought stress and lower background temperature under water-limited conditions. Furthermore, the model modified by NIRv-ToptGPP shows better performance in potential yields, especially in high-temperature seasons on the region scale. Without CO2 fertilization effect, each degree-Celsius increase is expected to reduce rice potential yields by 4.9 ± 1.6% based on the default ToptGPP range in ORYZA model and by 7.0 ± 1.2% based on the detected NIRv-ToptGPP range in the study area. This study implies that global grid-based model simulation may underestimate sensitivity of tropical rice yield to temperature rise due to the neglect of regional and seasonal heterogeneity of ToptGPP. NIRV makes it possible to determine local optimal temperatures for crop production, and to improve grid-based modelling across various agricultural systems in different growing seasons at the regional scale.

Badland Erosion and Its Morphometric Features in the Tropical Monsoon Area

Climatically driven processes are important controls on the Earth’s surface and on interactions between the hydrological cycle and erosion in drainage basins. As a result, landscape forms such as hillslope topography can be used as an archive to reconstruct historical climatic conditions. Recent progress in the Structure-from-Motion (SfM) photogrammetric technique allows for the construction of high-resolution, low-cost topography data using remote-controlled unmanned aerial vehicle (UAV) surveys. Here, we present the climatic effects on the hillslope erosion rate that can be obtained from the drainage frequency of hillslopes. We quantify the centimeter-scale accuracy of surveys across 72 badland hillslopes in SE Taiwan, which is a tropical monsoon area with an annual precipitation of over 2 m. Our observations indicate that climatic erosion results in a higher drainage frequency and the number of furrows, instead of drainage density. Additionally, the morphometric slope index (MSI) has a strong positive correlation with erosion and its rate but shows a negative correlation with drainage length and a positive correlation with inclination. This suggests that the erosion pattern is due to gravitational mass wasting instead of hydrological erosion. MSI should always be calculated relying on the normalized slope length and is less applicable to landslide-dominated erosion. We, therefore, suggest that UAV-driven digital elevation models (DEMs) are integrated into erosion mapping to aid in identifying erosion patterns. We highlight the unique opportunity for cross-climate zone comparative studies offered by badland landscapes and differential rainfall patterns, with remote sensing techniques and the morphometric slope index.

Predicting local-scale impact of climate change on rice yield and soil organic carbon sequestration: A case study in Roi Et Province, Northeast Thailand

Climate change poses a serious threat to rice production and soil quality in tropical monsoon areas where it is the lifeline of regional food security. In this study, the Environmental Policy Integrated Climate (EPIC) model was evaluated for the reliability of model calibration and validation procedures using local-scale data. The model was then employed to evaluate the possible impact of climate change on rice yield and soil organic carbon (SOC) sequestration in Roi Et Province, Northeast Thailand. The dominant factors that influence the changes in rice yield and SOC sequestration were identified. Four Representative Concentration Pathway (RCP) scenarios (RCPs 2.6, 4.5, 6.0, and 8.5) and Sixteen General Circulation Models under four future time periods; near future (2020–2039), mid future (2040–2059), far future (2060–2079), and very far future (2080–2099) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) were used as future climate projections. The findings revealed that climate change will impact rice yields positively, which will benefit farmers, especially in rain-fed areas, by +2.6% (RCP8.5: 2080–2099) to +22.7% (RCP6.0: 2080–2099). Rice yields in all case tend to increase significantly by +0.7% (RCP8.5: 2060–2079) to +18.8% (RCP6.0: 2080–2099), with the exception of 2080–2099 under RCP8.5, which results in a decline of rice yield by −8.4%. The precipitation is the most important factor for rice yield in this area. Although rising temperatures will bring a slight rice yield reduction, its impact will be negated by large amounts of increased CO2 concentration and precipitation. Conversely, SOC decreased significantly in all time periods. The highest decreased SOC was a -32.0% decline under RCP8.5 in the very far future. This is because rises in temperature and precipitation, with precipitation being the most important driver, negated the enrichment of CO2 fertilization, resulting in accelerated SOC decomposition rates, which may increase nitrogen availability to the soil and increase yield.

Modeling of tropospheric NO2 column over different climatic zones and land use/land cover types in South Asia

We have applied regression analyses for the modeling of tropospheric NO2 (tropo-NO2) as the function of anthropogenic nitrogen oxides (NOx) emissions, aerosol optical depth (AOD), and some important meteorological parameters such as temperature (Temp), precipitation (Preci), relative humidity (RH), wind speed (WS), cloud fraction (CLF) and outgoing long-wave radiation (OLR) over different climatic zones and land use/land cover types in South Asia during October 2004–December 2015. Simple linear regression shows that, over South Asia, tropo-NO2 variability is significantly linked to AOD, WS, NOx, Preci and CLF. Also zone-5, consisting of tropical monsoon areas of eastern India and Myanmar, is the only study zone over which all the selected parameters show their influence on tropo-NO2 at statistical significance levels. In stepwise multiple linear modeling, tropo-NO2 column over landmass of South Asia, is significantly predicted by the combination of RH (standardized regression coefficient, β = − 49), AOD (β = 0.42) and NOx (β = 0.25). The leading predictors of tropo-NO2 columns over zones 1–5 are OLR, AOD, Temp, OLR, and RH respectively. Overall, as revealed by the higher correlation coefficients (r), the multiple regressions provide reasonable models for tropo-NO2 over South Asia (r = 0.82), zone-4 (r = 0.90) and zone-5 (r = 0.93). The lowest r (of 0.66) has been found for hot semi-arid region in northwestern Indus-Ganges Basin (zone-2). The highest value of β for urban area AOD (of 0.42) is observed for megacity Lahore, located in warm semi-arid zone-2 with large scale crop-residue burning, indicating strong influence of aerosols on the modeled tropo-NO2 column. A statistical significant correlation (r = 0.22) at the 0.05 level is found between tropo-NO2 and AOD over Lahore. Also NOx emissions appear as the highest contributor (β = 0.59) for modeled tropo-NO2 column over megacity Dhaka.

Yield and resource use efficiency of Plukenetia volubilis plants at two distinct growth stages as affected by irrigation and fertilization

This study is to test how seedlings (vegetative) and large plants (reproductive) of an oilseed crop (Plukenetia volubilis) responded to regulated deficit irrigation techniques (conventional deficit irrigation, DI; alternative partial root-zone irrigation, APRI) in a tropical humid monsoon area. Seedlings were more sensitive to water deficit than large plants. Although APRI did better than DI in saving water for both seedlings and large plants at the same amount of irrigation, full irrigation (FI) is optimal for faster seedling growth at the expense of water-use efficiency (WUE). The seed number per unit area was responsible for the total seed oil yield, largely depending on the active process of carbon and nitrogen storages at the whole-plant level. The magnitude of the increase in total seed and seed oil yield by fertilization was similar under different irrigation regimes. Compared with FI, DI can save water, but reduced the total seed yield and had lower agronomic nutrient-use efficiency (NUEagr); whereas APRI had similar total seed yield and NUEagr, but reduced water use greatly. Although the dual goal of increasing the yield and saving water was not compatible, maintaining a high yield and NUEagr at the cost of WUE is recommended for P. volubilis plantation in t he water-rich areas.

Photosynthetic gas exchange responses of Swietenia macrophylla King and Melia azedarach L. plantations under drought conditions

BackgroundThe environmental stresses caused by climate change have become more severe in recent decades, affecting tree growth and physiology. Tropical forests have great potential for global carbon sequestration. However, they suffer from heavy rainfall and prolonged dry periods due to climate change. Swietenia macrophylla King and Melia azedarach L. are economically valuable trees that are widely planted in southern Taiwan. Plantations are exposed to either prolonged dry periods or heavy rainfall within the seasons of tropical monsoon areas. Photo-physiological comparisons may provide information that can improve management of S. macrophylla and M. azedarach plantations in tropical regions.ResultsBoth species exhibited a midday depression in leaf photosynthesis regardless of the season. The net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) in the dry season all significantly decreased in both tree species. In addition, M. azedarach used water more efficiently than did S. macrophylla during the dry season, but S. macrophylla had higher PN compared with that in M. azedarach during the wet season. Temperature and vapor pressure deficit influenced PN variation in S. macrophylla and M. azedarach, respectively. Our data suggested that the PN and gs of M. azedarach, but not of S. macrophylla, were linearly correlated during the dry season. The reduction of the leaf area was more sever in M. azedarach than in S. macrophylla, thus preventing water loss more efficiently.ConclusionsM. azedarach adapted to drought by reducing total leaf area and maintaining higher PN, gs, E, and WUE compared with those measured in S. macrophylla during the dry season. M. azedarach is more drought adaptation and more suitable for both humid and semi-humid areas than S. macrophylla, whereas the latter should be limited to more humid areas.

Dry-season deficit irrigation increases agricultural water use efficiency at the expense of yield and agronomic nutrient use efficiency of Sacha Inchi plants in a tropical humid monsoon area

Application of deficit irrigation (DI) will be problematic in tropical humid monsoon areas, since high relative air humidity during growth there leads to stomata malfunctioning. A field split-plot experiment was used to evaluate the physiological features, growth and seed and oil yield of Sacha Inchi (Plukenetia volubilis Linneo) plants, a tropical promising woody oilseed crop, responded to DI and fertilization in southwest China. The field experiment consisted of a factorial combination of five irrigation levels applied in the dry season [rainfed; DI20, DI50, DI100 (i.e., with irrigation amount of 20, 50 and 100% crop evapotranspiration, respectively); and full irrigation (irrigation of water saturated soil)] combined with two levels of compound fertilizer (0 and 200kgha−1) over two growing seasons, in a randomized complete block design with three replicates.Results showed the growth and root to stem mass ratio had lower sensitivity responded to DI, probably owing to their extremely low root mass fraction and seasonal short-term effect of DI on leaf photosynthetic traits. Irrigation affected the seasonal variations in seed size, seed oil concentration and seed yield, depending on the harvest date; whereas, with constant mean seed size and mean seed oil concentration across irrigation and fertilization treatments, the total seed and seed oil yield over the growing seasons were largely determined by the seed numbers per unit area. The soluble sugar and nitrogen storages as the active process, are related to effective flower formation, fruit (seed) development and enhance productivity of Sacha Inchi plants, which was indicated by the positive relationships between total seed yield and total nitrogen pool in the vegetative tissues or sugar pool in stems across all treatments. Fertilization increased total seed and seed oil yield, but no interaction between irrigation and fertilization was found. Compared with DI100, DI50 and DI20 had significant lower total seed yield, especially under the fertilized condition, although having higher agronomic water use efficiency (WUEagr, yield divided by irrigated water applied) but lower agronomic nutrient use efficiency (NUEagr, increased yield divided by fertilization rate). As a water-demanding crop species, Sacha Inchi plants under DI100 with the similar values to full irrigation had the highest total seed yield and NUEagr, but at the expense of water use efficiency. The maximum seed yield and maximum WUEagr, or maximum WUEagr and maximum NUEagr of Sacha Inchi plants are not compatible because the negative relationships existed between each of them. The polynomial regression relationships between total seed or seed oil yield and relative evapotranspiration could help to develop appropriate water-saving techniques for Sacha Inchi plantation in the tropical humid monsoon region.

A global water resources ensemble of hydrological models: the eartH2Observe Tier-1 dataset

Abstract. The dataset presented here consists of an ensemble of 10 global hydrological and land surface models for the period 1979–2012 using a reanalysis-based meteorological forcing dataset (0.5° resolution). The current dataset serves as a state of the art in current global hydrological modelling and as a benchmark for further improvements in the coming years. A signal-to-noise ratio analysis revealed low inter-model agreement over (i) snow-dominated regions and (ii) tropical rainforest and monsoon areas. The large uncertainty of precipitation in the tropics is not reflected in the ensemble runoff. Verification of the results against benchmark datasets for evapotranspiration, snow cover, snow water equivalent, soil moisture anomaly and total water storage anomaly using the tools from The International Land Model Benchmarking Project (ILAMB) showed overall useful model performance, while the ensemble mean generally outperformed the single model estimates. The results also show that there is currently no single best model for all variables and that model performance is spatially variable. In our unconstrained model runs the ensemble mean of total runoff into the ocean was 46 268 km3 yr−1 (334 kg m−2 yr−1), while the ensemble mean of total evaporation was 537 kg m−2 yr−1. All data are made available openly through a Water Cycle Integrator portal (WCI, wci.earth2observe.eu), and via a direct http and ftp download. The portal follows the protocols of the open geospatial consortium such as OPeNDAP, WCS and WMS. The DOI for the data is https://doi.org/10.1016/10.5281/zenodo.167070.

Multisource Remote Sensing Imagery Fusion Scheme Based on Bidimensional Empirical Mode Decomposition (BEMD) and Its Application to the Extraction of Bamboo Forest

Most bamboo forests grow in humid climates in low-latitude tropical or subtropical monsoon areas, and they are generally located in hilly areas. Bamboo trunks are very straight and smooth, which means that bamboo forests have low structural diversity. These features are beneficial to synthetic aperture radar (SAR) microwave penetration and they provide special information in SAR imagery. However, some factors (e.g., foreshortening) can compromise the interpretation of SAR imagery. The fusion of SAR and optical imagery is considered an effective method with which to obtain information on ground objects. However, most relevant research has been based on two types of remote sensing image. This paper proposes a new fusion scheme, which combines three types of image simultaneously, based on two fusion methods: bidimensional empirical mode decomposition (BEMD) and the Gram-Schmidt transform. The fusion of panchromatic and multispectral images based on the Gram-Schmidt transform can enhance spatial resolution while retaining multispectral information. BEMD is an adaptive decomposition method that has been applied widely in the analysis of nonlinear signals and to the nonstable signal of SAR. The fusion of SAR imagery with fused panchromatic and multispectral imagery using BEMD is based on the frequency information of the images. It was established that the proposed fusion scheme is an effective remote sensing image interpretation method, and that the value of entropy and the spatial frequency of the fused images were improved in comparison with other techniques such as the discrete wavelet, à-trous, and non-subsampled contourlet transform methods. Compared with the original image, information entropy of the fusion image based on BEMD improves about 0.13–0.38. Compared with the other three methods it improves about 0.06–0.12. The average gradient of BEMD is 4%–6% greater than for other methods. BEMD maintains spatial frequency 3.2–4.0 higher than other methods. The experimental results showed the proposed fusion scheme could improve the accuracy of bamboo forest classification. Accuracy increased by 12.1%, and inaccuracy was reduced by 11.0%.

Is precipitation a predictor of mortality in Bangladesh? A multi-stratified analysis in a South Asian monsoon climate

While numerous studies have assessed the association between temperature and mortality in various locations, few have addressed the relationship between precipitation and mortality. Given the high amounts of rainfall in many tropical monsoon areas and the often seasonally pronounced differences, there might be a potentially strong impact on health outcomes and death. In this study, we investigated the association between precipitation and daily death counts in Bangladesh from 2003 to 2007 using regression models with a quasipoisson distribution adjusting for long-term time and seasonal trends, day of the month, age and perceived temperature. Effects were assessed for all ages, the elderly and by gender. During the dry season a sharp increase in death risk was found at very high precipitation amounts which are most likely to be cyclone-related. This cyclone effect was most pronounced for females at the immediate day with an increase of 18.7% (3.8–35.6%) in non-external cause mortality per mm precipitation above 5mm. At longer lags we found a negative association between precipitation and mortality indicating some kind of dry effect which was more pronounced for the elderly with a mortality increase of 4.4% (2.6–6.2%) per mm decrease in precipitation. During the rainy season, we observed a protective effect of rainfall which was strongest during periods of seasonally high equivalent temperatures with a decrease in mortality of 4.0% (2.3–5.6%) per mm increase in precipitation on the immediate day. The observed associations between precipitation and mortality differed by season, age and gender. Generally, a strong short-term increase in mortality was associated with cyclonic activity during the dry season, while ongoing low rainfall seemed to have an adverse impact at higher lags. During the rainy season, precipitation seemed to mitigate heat effects.

Riverine hydrochemistry and CO2 consumption in the tropic monsoon region: a case study in a granite-hosted basin, Hainan Island, China

To evaluate the carbon sink capacity caused by rock chemical weathering processes and its controlling factors in the tropical monsoon region, the hydrochemistry of the granite-hosted Changhuajiang River (CHJR) basin in Hainan Island, China, were systematically investigated by collecting water samples from the river mouth to headwater in the dry season and the wet season, respectively. The results show that Na+, Ca2+ and HCO3 − are dominant in the chemical runoff of the CHJR. The spatial and temporal variations of major ions imply the influence of the multi-sources. The concentrations of Ca2+, Mg2+, HCO3 − and DSi, mainly sourcing from rock (silicates and carbonates) weathering, are lower in the wet season than those in the dry season. However, the concentrations of K+, Cl−, SO4 2−and NO3 −, mainly sourcing from the atmospheric precipitation and human activities, are significantly controlled by the monsoon rainfall and hydrological stage in the CHJR basin. The contributions of the silicates chemical weathering, human activities, atmospheric input, evaporites dissolution and carbonates chemical weathering to the chemical runoff are 82.62, 9.05, 5.24, 2.05 and 1.05 % in the CHJR, respectively. The chemical weathering rates of silicates, carbonates and evaporites are 16.25, 0.40 and 0.62 t km−2 year−1, respectively. Chemical weathering rates in global granite-hosted basins significantly correlate with temperatures (P 10 °C). On a regional scale, we find that the chemical weathering rates in the southern China appear a weak positive correlation with normalized differential vegetation indexes (NDVI), which need to be confirmed by enough data. The flux of atmospheric CO2 consumption from rock weathering in the CHJR basin is 2.71 × 105 mol km−2 year−1 by the discharge water of 2014, with being close to that (2.9 × 105 mol km−2 year−1) in the other tropical basins and far from that (5.06 × 105 mol km−2 year−1) calculated by the averaged discharge water of over years in the CHJR. The silicates weathering intensity lies at the moderate phase, implying that the weathering processes are still developing in global tropical granite basins. Hence, how the atmospheric CO2 consumption from rock weathering will change with increasing the atmospheric CO2 level and dam construction altering water cycle in the tropical monsoon area is expected to be deserved.

High rates of erosion and rapid weathering in a Plio-Pleistocene mudstone badland, Taiwan

The badlands of southwest Taiwan are characterized by sharp ridges, and are located in a tropical monsoon area that experiences contrasting rainy and dry seasons. Surface erosion predominates and subsurface erosion by piping is rather limited to accumulation of mud in valley bottoms. Erosion rates on Plio-Pleistocene mudstone slopes, measured using erosion pins over a period of 4 years, averaged up to 9 cm/y, which is considerably faster than the rates of a few cm/y typical in arid or semi-arid areas. Mudstone sample cores recovered from the slopes in the dry season (April), and in the early rainy season (July), prior to the extensive erosion that occurs later in the rainy season, suggested the following mechanism for weathering and erosion. Near-surface layers (< 10 cm deep) on these slopes develop lower bulk densities, larger void ratios, and higher salt contents during the early rainy season, and this degraded near-surface layer is rapidly removed by slaking and erosion during the intense precipitation of the main rainy season. This slaking may be caused by the electric repulsion and dispersion of grains. Following the period of erosion, the newly exposed rock dries during the subsequent dry season, and the near-surface layer then follows the same cycle of development and rapid removal during the next dry and early rainy seasons.

Influence of the Madden–Julian Oscillation and Intraseasonal Waves on Surface Wind and Convection of the Tropical Atlantic Ocean

Abstract Atmospheric intraseasonal variability in the tropical Atlantic is analyzed using satellite winds, outgoing longwave radiation (OLR), and reanalysis products during 2000–08. The analyses focus on assessing the effects of dominant intraseasonal atmospheric convective processes, the Madden–Julian oscillation (MJO), and Rossby waves on surface wind and convection of the tropical Atlantic Ocean and African monsoon area. The results show that contribution from each process varies in different regions. In general, the MJO events dominate the westward-propagating Rossby waves in affecting strong convection in the African monsoon region. The Rossby waves, however, have larger contributions to convection in the western Atlantic Ocean. Both the westward- and eastward-propagating signals contribute approximately equally in the central Atlantic basin. The effects of intraseasonal signals have evident seasonality. Both convection amplitude and the number of strong convective events associated with the MJO are larger during November–April than during May–October in all regions. Convection associated with Rossby wave events is stronger during November–April for all regions, and the numbers of Rossby wave events are higher during November–April than during May–October in the African monsoon region, and are comparable for the two seasons in the western and central Atlantic basins. Of particular interest is that the MJOs originating from the Indo-Pacific Ocean can be enhanced over the tropical Atlantic Ocean while they propagate eastward, amplifying their impacts on the African monsoon. On the other hand, Rossby waves can originate either in the eastern equatorial Atlantic or West African monsoon region, and some can strengthen while they propagate westward, affecting surface winds and convection in the western Atlantic and Central American regions.

Expression of type II iodothyronine deiodinase gene in the brain of a tropical spinefoot, Siganus guttatus

Type II iodothyronine deiodinase (D2) converts 3,5,3′,5′-tetraiodothyronine to 3,5,3′-triiodothyronine and is involved in regulating thyroid hormone-dependent processes in various tissues. D2 mRNA expression in the mediobasal hypothalamus is affected by photoperiod, which influences reproductive processes in temperate birds and mammals. We examined whether D2 mRNA is expressed in the hypothalamus (located in the forebrain within the diencephalon area) and whether its abundance is affected by day length, temperature, or food availability in the tropical spinefoot, Siganus guttatus, which is endemic to tropical monsoon areas. The reverse transcription-polymerase chain reaction (RT-PCR) revealed that D2 mRNA is expressed in various brain regions. The abundance of hypothalamic D2 mRNA was higher at 12.00h than at 06.00h or 24.00h. Rearing fish under constant dark conditions resulted in a decrease in D2 mRNA abundance during the subjective night. A single injection of melatonin lowered D2 mRNA abundance within 3h. Collectively, it appears that hypothalamic D2 mRNA abundance is regulated by the circadian system and/or melatonin. No differences in D2 mRNA abundance were observed, when fish were reared at 20, 25, and 30°C. However, food deprivation stimulated D2 mRNA expression during the daytime. These results suggest that photoperiodic and nutritive conditions affect hypothalamic D2 mRNA expression in S. guttatus.

Patchy stomatal behavior in broad-leaved trees grown in different habitats

Effects of heterogeneity in stomatal behavior on gas-exchange characteristics of leaves from four tree species growing in different climates, including temperate, tropical monsoon and tropical rain forest, were investigated by combining gas-exchange measurements and the pressure-infiltration method. Field observations indicated linear relationships between whole-leaf conductance and the ratio of infiltrated to non-infiltrated leaf area (open stomata area) in Dipterocarpus sublamellatus Foxw. and Neobalanocarpus heimii (King) Ashton in a tropical rain forest in Peninsular Malaysia, whereas the ratio of infiltrated to non-infiltrated area rapidly increased up to the whole-leaf conductance at which the entire leaf was infiltrated in Cinnamomum camphora Sieb. in a temperate evergreen forest in Japan and in Azadirachta indica Juss. in a tropical monsoon area in Thailand. These results strongly suggest small ranges in bell-shaped stomatal conductance distributions in C. camphora and A. indica and bimodal stomatal conductance distributions in D. sublamellatus and N. heimii. The values of normalized maximum carboxylation rate at 25 degrees C (V(cmax25)) derived from gas-exchange measurements were not constant, but decreased with decreasing whole-leaf conductance in D. sublamellatus and N. heimii. A gas-exchange model analysis revealed a linear relationship between whole-leaf conductance and the ratio of infiltrated to non-infiltrated leaf area for bimodal stomatal conductance distributions, whereas for bell-shaped distributions, the relationships were nonlinear. Midday depression of apparent V(cmax25) in these species was mainly caused by bimodal stomatal closure. The bimodal stomatal distribution model could also explain diurnal changes in photosynthetic assimilation and transpiration rates in these species.