Early Monsoon Season Research Articles

Seasonal variation in river water chemistry of the middle reaches of the Yellow River and its controlling factors

In order to reveal the seasonal variations of river water chemistry and its controlling factors in the middle reaches of the Yellow River, river water samples were collected weekly from the Longmen hydrological station over the whole year of 2013. Major cation and anion compositions were measured. The major ionic compositions of the dissolved load exhibited distinct seasonal variability over the one year period, reflecting seasonal differences in relative inputs from various sources and weathering reactions within the catchment. A forward model was used to calculate the apportionments of rain, anthropogenic, silicate, evaporite, and carbonate origins on a seasonal basis. The contributions of both rain and anthropogenic sources to the middle Yellow River were less than ~12% in average, with little seasonal variations in 2013. The calculations showed that silicate sources had a relatively large impact on water chemistry during the pre- and early-monsoon seasons, though both silicate and carbonate weathering increased greatly during the monsoon season. The high silicate input during the pre- and early-monsoon seasons was attributed to the waters potentially derived from plateau headstream, glacial melting, and soil pore. Meanwhile, the dominated contributions of evaporites and carbonates in the late- and post-monsoon seasons were resulted from their rapid dissolution from the loess plateau through physical erosion acceleration along with high water discharge, because widespread loess is characterized by easy denudation and high carbonates and evaporites. Our densely time-series data also highlighted a significant impact of extreme hydrological events on water chemistry in semi-arid area. During the ice melting interval in the springtime, more silicate-origin ions entered the river from melting water, whereas during the stormy event interval in the peak monsoon, more carbonates and evaporites reached the Yellow River from the loess plateau via accelerated physical erosion. Our data shed further light on processes responsible for seasonal variation of river chemistry of the Yellow River and modern loess weathering.

Robust features of future climate change impacts on sorghum yields in West Africa

West Africa is highly vulnerable to climate hazards and better quantification and understanding of the impact of climate change on crop yields are urgently needed. Here we provide an assessment of near-term climate change impacts on sorghum yields in West Africa and account for uncertainties both in future climate scenarios and in crop models. Towards this goal, we use simulations of nine bias-corrected CMIP5 climate models and two crop models (SARRA-H and APSIM) to evaluate the robustness of projected crop yield impacts in this area. In broad agreement with the full CMIP5 ensemble, our subset of bias-corrected climate models projects a mean warming of +2.8 °C in the decades of 2031–2060 compared to a baseline of 1961–1990 and a robust change in rainfall in West Africa with less rain in the Western part of the Sahel (Senegal, South-West Mali) and more rain in Central Sahel (Burkina Faso, South-West Niger). Projected rainfall deficits are concentrated in early monsoon season in the Western part of the Sahel while positive rainfall changes are found in late monsoon season all over the Sahel, suggesting a shift in the seasonality of the monsoon. In response to such climate change, but without accounting for direct crop responses to CO2, mean crop yield decreases by about 16–20% and year-to-year variability increases in the Western part of the Sahel, while the eastern domain sees much milder impacts. Such differences in climate and impacts projections between the Western and Eastern parts of the Sahel are highly consistent across the climate and crop models used in this study. We investigate the robustness of impacts for different choices of cultivars, nutrient treatments, and crop responses to CO2. Adverse impacts on mean yield and yield variability are lowest for modern cultivars, as their short and nearly fixed growth cycle appears to be more resilient to the seasonality shift of the monsoon, thus suggesting shorter season varieties could be considered a potential adaptation to ongoing climate changes. Easing nitrogen stress via increasing fertilizer inputs would increase absolute yields, but also make the crops more responsive to climate stresses, thus enhancing the negative impacts of climate change in a relative sense. Finally, CO2 fertilization would significantly offset the negative climate impacts on sorghum yields by about 10%, with drier regions experiencing the largest benefits, though the net impacts of climate change remain negative even after accounting for CO2.

West Nile encephalitis outbreak in Kerala, India, 2011

BackgroundAn outbreak of acute encephalitis syndrome (AES) was reported in Kerala in India in May 2011. The outbreak features were unusual in terms of seasonality, geographical distribution, age group, and clinical manifestations in comparison to the epidemiological features of Japanese Encephalitis. ObjectiveTo detect the etiology of the acute encephalitis syndrome outbreak. Study designInvestigation of outbreak was undertaken by collection of brief clinical history and epidemiological details along with the specimens for viral diagnosis. The serum/CSF samples (patients=208) received from the sentinel hospitals were subjected to IgM capture ELISA and RT-PCR specific for Japanese encephalitis (JE) virus and West Nile virus (WNV). The JE/WN IgM positive samples were further tested by serum neutralization assay for the presence of JE and WNV specific neutralizing antibody. ResultMost of the affected patients were aged above 15 years. No spatial clustering of the disease was noticed. Cases were observed in premonsoon and early monsoon season and in JE non-endemic area of Kerala. A total of 47 patient samples were positive for in-house JE IgM capture ELISA and WNV IgM capture ELISA. Serum neutralization assay result revealed that 32 of 42 (76.19%) sera were positive for WNV neutralization antibodies. WNV was isolated from a clinical specimen. Phylogenetic analysis of WNV envelope gene revealed 99% homology with Russian Lineage 1 WNV. ConclusionWest Nile virus (WNV) etiology was confirmed by virus isolation and detection of virus specific antibody from clinical specimen. Phylogenetic analysis grouped the current strain in lineage I West Nile virus.

Density of Indian Grey Hornbills (Ocyceros birostris) in and Around Haveri

Indian Grey Hornbill (Ocyceros birostris) prefers dry deciduous forests, but these habitats are subjected to maximum anthropogenic disturbances. Habitat destruction is the major cause of disturbance for the hornbills population. Indian Grey Hornbill is a fairly common, mostly arboreal found throughout India. But it is not common to be sighted in towns. The regular observations for Indian Grey Hornbill was made during summer and early monsoon season in and around Haveri for two decades (March 1994 to July 2013). As hornbills depend on tree cavities for nesting, search for nest cavities was carried out. Prior to road widening works, density of these birds was high on the trees of highways. This study evaluated that, with the removal of trees in the name of development, the number of these birds increased in the recent months in Haveri town and this is due to suitable environment available for their survival.

The response of the North American Monsoon to increased greenhouse gas forcing

We analyze the response of the North American Monsoon (NAM) to increased greenhouse gas (GHG) forcing (emissions scenario RCP 8.5) using new simulations available through the Coupled Model Intercomparison Project version 5 (CMIP5). Changes in total monsoon season rainfall with GHG warming are small and insignificant. The models do, however, show significant declines in early monsoon season precipitation (June‐July) and increases in late monsoon season (September‐October) precipitation, indicating a shift in seasonality toward delayed onset and withdrawal of the monsoon. Early in the monsoon season, tropospheric warming increases vertical stability, reinforced by reductions in available surface moisture, inhibiting precipitation and delaying the onset of the monsoon. By the end of the monsoon season, moisture convergence is sufficient to overcome the warming induced stability increases, and precipitation is enhanced. Even with no change in total NAM rainfall, shifts in the seasonal distribution of precipitation within the NAM region are still likely to have significant societal and ecological consequences, reinforcing the need to not only understand the magnitude, but also the timing, of future precipitation changes.

Seasonal variation in diatoms in response to physico-chemical characteristics of coastal waters of Uttara Kannada district, West Coast of India

The present study was undertaken to know the diatom distribution in different seasons in response to physico-chemical properties of Arabian Sea water in the Uttara Kannada District, Karnataka over a period of one year from November 2009-0ctober 2010. The study revealed the presence of 55 species of diatoms, highest number was recorded in post-monsoon and the least in monsoon season. The major genera belong to Amphora, Chaetoceros, Coscinodiscus, Navicula, Pleurosigma, Achnanthes, Cymbella, Mastogloia, Nitzschia, Biddulphia, Diploneis and Licmophora. Bloom of Asterionella japonica was observed during early monsoon season. The physico-chemical parameters studied showed noticeable seasonal variations, which may be attributed to the local climatic conditions and water exchange mechanisms. The physicochemical parameters like temperature, salinity, conductivity and nutrients were found to influence the occurrence of diatoms.

Changes in Precipitation Seasonality in West Africa Predicted by RegCM3 and the Impact of Dynamic Vegetation Feedback

Using a regional climate model asynchronously coupled to a dynamic vegetation model, this study examines future climate predictions for the West Africa region and how dynamic vegetation feedback may influence such predictions. Without accounting for the impact of vegetation dynamics, the model predicts a future decrease of annual rainfall over Sahel. Dynamic vegetation feedback reverses this trend, leading to a substantial increase of annual rainfall. Regardless of how vegetation is treated, the predicted future trend of precipitation in the Sahel region follows a specific seasonal pattern, with a decrease during the pre- and early-monsoon season (May-June and early July) due to the warming-induced enhancement of spring convective barrier and an increase after the monsoon is fully established (typically in July-August-September) due to enhanced moisture import from a warmer ocean. Dynamic vegetation feedback reduces the magnitude of the predicted rainfall reduction in the early season and increases the magnitude of the predicted rainfall increase later in the rainy season. The future decrease of early-season rainfall has significant agronomic implications.

Assessment of area favourable for crop sowing using AMSR-E derived Soil Moisture Index (AMSR-E SMI)

Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) soil moisture product was used to assess the progression of Area Favourable for Crop Sowing (AFCS) over Andhra Pradesh State of India during summer monsoon. The AMSR-E soil moisture data were normalized with respect to soil texture to calculate AMSR-E Soil Moisture Index (AMSR-E SMI). The index had significant correlation (r value 0.7–0.8) with the amount of rainfall during early monsoon period. Progression of soil wetness condition was mapped week-wise by thresholding the AMSR-E SMI. Logical criteria were developed based on the surface soil moisture content, its persistence and the type of crop to classify AFCS. The estimated AFCS was found to have significant correlation (r=0.92 and root mean square error=0.66) with the reported official sown area by Directorate of Economics & Statistics, Govt. of Andhra Pradesh. The study demonstrated the potential use of AMSR-E SMI for assessment of agricultural drought during early monsoon season at regional level.

Seasonal contributions of catchment weathering and eolian dust to river water chemistry, northeastern Tibetan Plateau: Chemical and Sr isotopic constraints

relative to winter. It is noticeable that both the lowest and the highest 87 Sr/ 86 Sr values of the Buha River waters occurred in the monsoon season, indicating a sensitive response of carbonate versus silicate weathering sources to hydrological forcing on a seasonal basis. A significant decrease in Na/cation, together with lower Sr isotope ratios, is consistent with a greater proportion of carbonate weathering relative to silicate weathering in the early monsoon season. High temperature and increased rainfall during the peak of the monsoon facilitate an increased proportion of ions derived from silicates, partly from groundwaters, to river water. In other seasons, elemental and 87 Sr/ 86 Sr ratios vary much less, indicating a constant ratio of silicate to carbonate weathering, consistent with limited variation in discharge. Our results highlight that in a semiarid region where climatic conditions vary seasonally, in addition to silicate and carbonate contributions, supply from eolian dust may also play a significant role in controlling seasonal variations in chemistry of river waters.

Pacific Ocean sea-surface temperature variability and predictability of rainfall in the early and late parts of the Indian summer monsoon season

For central India and its west coast, rainfall in the early (15 May–20 June) and late (15 September–20 October) monsoon season correlates with Pacific Ocean sea-surface temperature (SST) anomalies in the preceding month (April and August, respectively) sufficiently well, that those SST anomalies can be used to predict such rainfall. The patterns of SST anomalies that correlate best include the equatorial region near the dateline, and for the early monsoon season (especially since ~1980), a band of opposite correlation stretching from near the equator at 120°E to ~25°N at the dateline. Such correlations for both early and late monsoon rainfall and for both regions approach, if not exceed, 0.5. Although correlations between All India Summer Monsoon Rainfall and typical indices for the El Nino-Southern Oscillation (ENSO) commonly are stronger for the period before than since 1980, these correlations with early and late monsoon seasons suggest that ENSO continues to affect the monsoon in these seasons. We exploit these patterns to assess predictability, and we find that SSTs averages in specified regions of the Pacific Ocean in April (August) offer predictors that can forecast rainfall amounts in the early (late) monsoon season period with a ~25% improvement in skill relative to climatology. The same predictors offer somewhat less skill (~20% better than climatology) for predicting the number of days in these periods with rainfall greater than 2.5 mm. These results demonstrate that although the correlation of ENSO indices with All India Rainfall has decreased during the past few decades, the connections with ENSO in the early and late parts have not declined; that for the early monsoon season, in fact, has grown stronger in recent decades.

Effect of the summer monsoon on aerosols at two measurement stations in Northern India – Part 2: Physical and optical properties

Abstract. Aerosol physical and optical properties were measured at two locations in northern India. The first measurement station was a background site in Mukteshwar, about 350 km northeast of New Delhi, in the foothills of the Indian Himalayas, with data from 2006 to 2009. The second measurement site was located in Gual Pahari, about 25 km south of New Delhi, with data from 2008 to 2009. At both stations, the average aerosol concentrations during the monsoon were decreased by 40–75 % compared to the pre-monsoon average concentrations. The decrease varied with the total local rainfall. In Mukteshwar, the monsoon season removed particles from all size classes, due to a combination of rain scavenging and activation to cloud and mountain fog droplets. The scavenging by rain is least effective for the size range of the accumulation mode particles. In Gual Pahari, this was the only major wet removal mechanism and, as a result, the accumulation mode particles were less effectively removed. Aerosol concentrations during the early monsoon were found to be affected by mineral dust which in Gual Pahari was observed as an increased particle volume at a diameter around 3–4 μm. The single scattering albedo varied from 0.73 to 0.93 during the monsoon season, being slightly lower in Gual Pahari than in Mukteshwar. This is due to the fact that Gual Pahari resided closer to high anthropogenic black carbon emissions. As the absorbing particles are typically in the accumulation mode, they were not effectively removed by rain scavenging. The aerosol columnar properties, which were measured in Gual Pahari, showed a somewhat different seasonal behaviour compared to the surface measurements, with the aerosol optical depth increasing to an annual maximum in the early monsoon season.

Did aboriginal vegetation burning impact on the Australian summer monsoon?

[1] Aboriginal vegetation burning practices and their role in the Australian environment remains a central theme of Australian environmental history. Previous studies have identified a decline in the Australian summer monsoon during the late Quaternary and attributed it to land surface-atmosphere feedbacks, related to Aboriginal burning practices. Here we undertake a comprehensive, ensemble model evaluation of the effects of a decrease in vegetation cover over the summer monsoon region of northern Australia. Our results show that the climate response, while relatively muted during the full monsoon, was significant for the pre-monsoon season (austral spring), with decreases in precipitation, higher surface and ground temperatures, and enhanced atmospheric stability. These early monsoon season changes can invoke far-reaching ecological impacts and set-up land surface-atmosphere feedbacks that further accentuate atmospheric stability.

Effects of intraseasonal variation of summer monsoon rainfall on stable isotope and growth rate of a stalagmite from northwestern Thailand

An annually laminated stalagmite from Namjang cave (19°40′30″N, 98°12′12″E), northwestern Thailand, has been analyzed to investigate the annual resolution climate signal persevered within its oxygen isotopic composition (δ18O) and growth rate parameters. The cave site is under the influence of Asian monsoon, and local rainfall shows noticeable variations through the monsoon season. Both δ18O and growth rate records, covering the last 105 years, exhibit persistent decadal‐scale variability and can be compared with local instrumental data. Low δ18O values coincide with high growth rates in the specimen and correspond to higher relative amounts of rainfall in later monsoon season (August–October; hereinafter referred to as ASO rainfall) versus rainfall in early monsoon season (May–July; hereinafter referred to as MJJ rainfall). The strong correlation between the δ18O value and the 5 year averaged ratio of ASO to MJJ rainfall (r = −0.50, p < 0.001) indicates a significant imprint of intraseasonal variation of monsoonal rainfall on stalagmite δ18O. The close resemblance between the speleothem δ18O record and Western Pacific Warm Pool (WPWP) sea surface temperature (SST) implies that the WPWP may play an important role on the decadal variability of later monsoon rainfall in this region. Unique in its annual chronology, high‐resolution δ18O, and direct comparison with instrumental data, our record shows for the first time that the climate in northwestern Thailand has undergone decadal‐scale variability and speleothem δ18O is a robust proxy for regional monsoon intensity.

Common tree growth anomalies over the northeastern Tibetan Plateau during the last six centuries: implications for regional moisture change

AbstractThe world's hydrological cycle is believed to intensify with global warming, yet current climate models have only a limited ability to assess moisture responses at regional scales. Tree‐ring records are a valuable source of information for understanding long‐term, regional‐scale moisture changes, particularly for large regions such as the Tibetan Plateau (TP), where the observational data are short and sparse. Here, we present a new ring‐width chronology developed from Qilian Juniper (Sabina przewalskii) wood at two sites on the northeastern TP. This chronology, combined with others from the same region, demonstrates that tree growth anomalies are linked to regional late spring to early summer moisture availability. Although late monsoon season precipitation in the study area decreased during recent decades, tree growth continued to increase due to persistent moisture availability in the early monsoon season. Comparison with global sea surface temperatures (SSTs) indicates that early (late) monsoon season precipitation is closely related to tropical Pacific (Indian Ocean) SSTs, suggesting a possible seasonal shift in the dominant moisture source area for monsoonal precipitation over the northeastern TP. It is further shown that there is a very high degree of coherency regarding low‐frequency tree growth anomalies over the northeastern TP during the last six centuries. The most prominent drought epoch occurred during ca. 1450–1500, which may have been caused by a significant decrease in the thermal gradient between the Eurasian continent and the tropical oceans. A persistent tree growth increase since the 1880s is coincident with global warming, suggesting an intensified early monsoon season moisture regime in the study area.

Hydrogen and oxygen isotopes in precipitation in the northern part of the North China Plain: climatology and inter‐storm variability

AbstractTo clarify the processes of atmospheric water vapour transport to the northern part of the North China Plain (NCP), isotopic variations in precipitation are investigated. Pattern of seasonal variation in the isotopic composition of precipitation over China can be classified into three types: winter depression, summer depression and intermediate. The northern NCP is located at the northern margin of the region where isotopic composition decreases in summertime, associated closely with the Asian summer monsoon. Inter‐storm variability of isotopic composition over the northern NCP during the monsoon season has an inverse relationship with atmospheric moisture content, although it cannot be accounted for by the amount effect. Thus, the isotopic composition is inferred to be primarily controlled by large‐scale monsoon activity, which supplies water vapour into the northern NCP, rather than by local precipitation processes. From an analysis based on a relationship between the deuterium excess and humidity conditions at possible oceanic source areas, it is revealed that precipitating water in the early monsoon season originates in the South China Sea, and its source area tends to shift to the East China Sea and/or Yellow Sea in the later period of the season. Copyright © 2004 John Wiley & Sons, Ltd.

Seasonal variations in aerosol concentrations and compositions in the Nepal Himalaya

This paper summarizes a 15-month long study (September 1996–November 1997) on water soluble components (Na +, NH 4 +, K +, Mg 2+, Ca 2+, Cl −, NO 3 −, and SO 4 2−) in atmospheric aerosols conducted at a remote Himalayan site and a rural Middle-Mountain site in Nepal. Most of the species sampled behave similarly in terms of seasonal and short-term variations. The aerosol concentrations were low during the second half of the monsoon and post-monsoon seasons and gradually increased during the winter season. Aerosol concentrations in some samples were up to 20 times higher during the pre-monsoon and early-monsoon seasons than they were in post-monsoon. The seasonal variations are clearly related to variations in atmospheric circulation. The high concentrations during the pre-monsoon season are attributed to regional scale valley wind systems and the maximum concentrations at both sites coincide with maxima in the local wind speed record. Occasional shifts in the large-scale circulation resulted in dramatic fluctuations in aerosol concentrations during the pre-monsoon and early monsoon seasons. In the middle of May the large-scale circulation changed from westerly to south-easterly monsoon in the Himalaya. The summer monsoon circulation brought considerable amounts of pollution to the sites from southeast. Precipitation played an important role in short-term (few samples, e.g., during the late winter at the Himalayan site) to longer-term (several samples, e.g., after mid-June at both sites) reduction in the aerosol concentrations, while the lack of precipitation in the pre-monsoon and early monsoon supported a gradual build-up of pollutants in the atmosphere. During the pre-monsoon and early monsoon, when concentrations were elevated at both sites, they were often higher at the remote Himalayan site than at the middle mountain site. A pollution layer in the monsoon circulation due to dry convective rise of pollutants at distant sources and horizontal upper air transport by monsoon flow could have caused these elevated concentrations.

Management of runoff stored in small tanks for transplanted rice production in the mid-hills of Northwest Himalaya

Scarcity of water in upland areas limits the growing of transplanted rice and the yield of rice grown under rainfed conditions is very low. As the first priority for the use of runoff recycling based water resources is in the dry season followed by the monsoon season, a strategy has been developed to use the surplus water (occurring during the early monsoon season) to grow transplanted rice without compromising the dry season irrigation. Field experiments revealed that under the mid-hill conditions, transplanted rice can be grown as transplanted in 5 cm standing water and thereafter tainted, requiring only 3.0–3.5 cm of water with a yield reduction of about 25% as compared to generally recommended intermittent submergence (2 days after the disappearance of water) requiring 100–130 cm of water. However, the reduction in yield was not significant if 1 week of initial ponding just after transplanting was created. Based on rainfall-runoff analysis, graphs were developed for runoff and volume of water available in water tanks in different durations of early monsoon periods, command-catchment area ratio and the volume of water available after irrigation which is to be used in dry season, as a function of runoff curve numbers. These graphs can be consulted directly to plan irrigation systems for transplanted rice in upland areas.

Inter-individual and seasonal weight variation in rural Nepali women

Changes in body weight were examined for non-pregnant women in rural Nepal, using 183 anthropometric measures between the early winter and monsoon seasons in 1982, 1982-83, 1990-91 and 1993. The women gained weight when work loads decreased after the monsoon, but despite substantial changes in total energy expenditure, which were out of phase with changes in food intake, seasonal changes were small, averaging only up to 2.6% of initial body weight. There were notable differences between individual women, changes in body weight ranging from -5.6 kg to 4.8 kg. Weight change was examined with respect to lactation status, age, body mass index, mid upper arm circumference and skinfolds as well as total energy expenditure and intake. Nonlactating women, very thin women and women aged under 25 years gained more weight than their counterparts, both before and after the monsoon. Data for a sub-sample in 1982-83 indicated that women who maintained high physical activity levels throughout the year were less prone to weight loss than women whose activity fluctuated between seasons. Initial energy reserves, age-related maturation factors, levels of physical activity and energy intake combine to produce the notable inter-individual variation in body weight changes observed in this population.

Field Evaluation of Insecticides for Asian Corn Borer on Vegetable Corn, Pangasinan, Philippines, 1980

Abstract Five trials on farmers’ fields evaluated 33 insecticides on vegetable corn for Asian corn borer in early monsoon season in Pao village, Manaoag municipality, Pangasinan province, Philippines. The 75-day corn variety precedes puddled rice. Corn (2-4 seeds/hill; 50-cm between hills) was planted by hand in furrows 1-m wide and received 60 kg N|/ha. The trial fields were planted 1-2 months later than the surrounding farmers’ fields in order to obtain high corn borer populations. Ridomil applied as a seed treatment (2 g ai/kg seed) ensured protection against downy mildew Sclerosporaphilippinensis Weston which normally infects late plantings. Sprays were applied 4 times in 650 l/ha spray volume by a manually operated 19-1 knapsack sprayer with a fan jet nozzle. Azodrin served as a check in each trial. Granulars were applied once by hand in the whorls. Plot size was 100 m2 in a randomized complete block design replicated 4 times. Rainfall was 522 mm, RH averaged 85%, and the mean daily maximum and minimum temperatures were 32° and 24°C, respectively, from 20 days after crop emergence to harvest. At harvest 50 plants/plot were examined and cut open to record the number of corn borer tunnels and larvae + pupae (inside and outside the stems). Yield was based on 25 m2 . Ears were sorted by length to select those which were marketable (> 10 cm). Insect damaged ears are marketable to local consumers.