Onset Of Rains Research Articles

Synoptic stability and anomalies in NE China inferred from dust provenance of Sihailongwan maar sediments during the past ∼80 kyr

The paleo-synoptic conditions that prevailed during the past ∼80 kyr in northeastern China are inferred from the elemental and Sr–Nd isotopic compositions of Lake Sihailongwan Maar sediments. The detrital fraction in the lake sediments is dominated by aeolian input of felsic-rock origin, with little contribution of local volcanic material. Based on the isotopic Sr–Nd composition of the lake core-sediments, we postulate that the deserts of northern China are the main source of allochthonous particles to the lake throughout the past ∼80 kyr. Northwesterly winds associated with the East Asian winter monsoon and high latitude westerlies are the main carriers of dust from these deserts to the lake. The deserts of central China are an additional minor dust source. The episodic dust input from these deserts results from anomalous dry southwesterly winds. These could be related to either El Niño conditions, or to delays in the onset of the East Asian summer monsoon rains.

Rooting depth as a key woody functional trait in savannas.

Dimensions of tree root systems in savannas are poorly understood, despite being essential in resource acquisition and post-disturbance recovery. We studied tree rooting patterns in Southern African savannas to ask: how tree rooting strategies affected species responses to severe drought; and how potential rooting depths varied across gradients in soil texture and rainfall. First, detailed excavations of eight species in Kruger National Park suggest that the ratio of deep to shallow taproot diameters provides a reasonable proxy for potential rooting depth, facilitating extensive interspecific comparison. Detailed excavations also suggest that allocation to deep roots traded off with shallow lateral root investment, and that drought-sensitive species rooted more shallowly than drought-resistant ones. More broadly across 57 species in Southern Africa, potential rooting depths were phylogenetically constrained, with investment to deep roots evident among miombo Detarioids, consistent with results suggesting they green up before onset of seasonal rains. Soil substrate explained variation, with deeper roots on sandy, nutrient-poor soils relative to clayey, nutrient-rich ones. Although potential rooting depth decreased with increasing wet season length, mean annual rainfall had no systematic effect on rooting depth. Overall, our results suggest that rooting depth systematically structures the ecology of savanna trees. Further work examining other anatomical and physiological root traits should be a priority for understanding savanna responses to changing climate and disturbances.

A statistical comparison of spatio‐temporal surface moisture patterns beneath a semi‐natural grassland and permanent pasture: From drought to saturation

AbstractSome 60% of the agricultural land in the UK is grassland. This is mostly located in the wetter uplands of the west and north, with the majority intensively managed as permanent pasture. Despite its extent, there is a lack of knowledge regarding how agricultural practices have altered the hydrological behaviour of the underlying soils relative to the adjacent moorland covered by semi‐natural grassland. Near‐surface soil moisture content is an expression of the changes that have taken place and is critical in the generation of flood‐producing overland flows. This study aims to develop a pioneering paired‐plot approach, producing 1,536 moisture measurements at each of the monitoring dates throughout the studied year, that were subsequently analysed by a comparison of frequency distributions, visual cum geostatistical investigation of spatial patterns and mixed‐effects regression modelling. The analysis demonstrated that the practices taking place in the pasture (ploughing, re‐seeding and drainage) reduced the natural diversity in moisture patterns. Compared to adjacent moorland, the topsoil dried much faster in spring with the effects requiring offset with moisture from slurry applications in summer. With the onset of autumn rains, these applications then made the topsoil wetter than the moorland, heightening the likelihood of flood‐producing overland flow. During the sampling within one such storm event, the adjacent moorland was almost as wet as the pasture with both visibly generating overland flow. These contrasts in soil moisture were statistically significant throughout. Further, they highlight the need to scale‐up the monitoring with numerous plot pairs to see if the observed highly dynamic, contrasting behaviour is present at the landscape scale. Such research is fundamental to designing appropriate agricultural interventions to deliver sustainable sward production for livestock or methods of mitigating overland‐flow incidence that would otherwise heighten flood risk or threaten water quality in rivers.

Predicting Seasonal Rainfall Patterns and Trends in Juba County, South Sudan Using Artificial Neural Networks

A simple Feed Forward Neural Network (FFNN) model with a learning back-propagation algorithm was applied to forecast rainfall data from 1997-2016 of Juba County, South Sudan. Annual rainfall data were aggregated into three seasons MAMJ, JAS and OND and later trained for best predictions for the period 2017-2034 using the Alyuda Forecaster XL software. Best training was attained once the minimum error or cost function of the weight was attained during gradient descent and expressed as Mean Square Error (MSE) and AE of the input variable. The results showed that for MAMJ and JAS months, the number good forecasts were over 97% whereas this was between 60-80% for OND months. The Seasonal Kendal (SK) test on future rainfall forecasts as well as the Theil-Sen slope showed a declining monotonic trend in the mean amounts in all three seasons with MAMJ, JAS at OND at 100, 150 and 80 mm respectively towards the end of 2034. Declining onset of MAMJ rains is expected to significantly affect the timing for land preparation and crop planting. The forecast accuracy of the FFNN can be used as a vital tool for decision makers in projecting future rainfall events.

SMALLHOLDER FARMER’S LIVELIHOOD DIVERSIFICATION AS A RESPONSE TO CHANGED CLIMATIC PATTERNS IN CHONGWE DISTRICT, ZAMBIA.

Purpose: Climate change affects local and global rainfall patterns and hence has a counter effect on smallholder agriculture. Impacts of climate change on agriculture are largely due to rainfall variability resulting in reduced yields due to crop-water stress and emergency of pathogens and diseases. In Zambia, climate change has been manifested through increased intensity of droughts and floods. These rainfall anomalies adversely affect agriculture and food systems. In order to survive the impacts of climate change and variability, smallholder farmers in Chongwe have adopted their livelihoods and farming systems to the new climatic patterns.Methodology: This study assessed how smallholder farmers in Chongwe District have adopted their livelihoods as a response to changed climatic conditions. It also investigated the perceptions of smallholder farmers as regards changes in aspects of their climatic conditions. Data collection involved a critical review of literature related to climate change and agriculture, observations, semi- structured interviews with 60 smallholder farmers and eight key informants. The data were analysed using multiple analysis techniques which included the descriptive statistics, One-way analysis of Variance (ANOVA), and the post-hoc Least Square Difference for pairwise comparisons of incomes from different livelihoods engaged in by smallholder farmers .The gendered comparisons of livelihood engagement was done using the chi-square test of association.Findings: The results showed that all farmers perceived occurrence of changes in climatic conditions in the light of changed rainfall patterns in that there has been uncertainty in onset of rains, short rainy season, more intermittent rainfall and increased frequency of intra-seasonal droughts. These changes have led to farmers to adopt such farming techniques as potholing in preference to oxen and tractor ploughing when farming is done on smaller pieces of land. There was a significant difference in the mean annual incomes generated from on-farm livelihoods (ZMW 3677.59; n=58) and off-farm livelihoods (ZMW 6840.91; n = 58) (p= 0.001). Farmers generated the highest income returns by engaging in casual work (ZMW 10307.69; n = 13) compared to every other livelihoods common in the area such as gardening (p=0.002), petty trade (p=0.002) and on-farm livelihoods (p=0.001).Contribution to policy, theory and practice: It was therefore concluded that diversification of income through diversified livelihoods would help smallholder farmers enhance their resilience in the face of changed climatic conditions. On-farm livelihoods should not always be the main income source for farmers as results indicated that farmers engaged in casual work generated higher incomes than those who depended on farming. It was recommended that policy direction should be towards introduction of a gender responsive credit facility that can help improve women’s engagement in off-farm income generating livelihoods, as well as encourage climate change resilience.

Springtime Onset of Isolated Convection Precipitation across the Southeastern United States: Framework and Regional Evolution

Abstract This study examines the geographic and temporal characteristics of the springtime transition to the summer precipitation regime of isolated convection in the southeastern (SE) United States during 2009–12, using a high-resolution surface radar-based precipitation dataset. Isolated convection refers herein to isolated elements or small clusters of precipitation in radar imagery less than 100 km in horizontal dimension. Though the SE United States does not have a monsoon climate, it is useful to apply the established framework of monsoon onset to study the timing and regional variation of the onset of the summer isolated convection regime. Overall, isolated convection rain onset in the SE U.S. domain occurs in late May. Onset begins in south Florida in mid-April, continuing nearly simultaneously across the southeastern coastal plain in early to mid-May. In the northern domain, from Virginia to the Ohio Valley, onset generally occurs much later (mid-June to early July) with more variable onset timing. The sharpness of onset timing is most evident in the coastal plain and Florida. Results suggest the hypothesis, to be examined in a forthcoming study, that the timing of isolated convection onset in the spring may be triggered by specific synoptic-scale events within gradual seasonal changes in atmospheric conditions including extratropical cyclone tracks, convective instability, and the westward migration of the North Atlantic subtropical high. This approach may offer a useful framework for evaluating long-term changes in precipitation for subtropical regimes in an observational and modeling context.

Indigenous Knowledge Systems and Indicators of Rain: Evidence from Rwenzori Region, Western Uganda

AbstractThis study investigated the abiotic and biotic environmental indicators used among pastoralists and arable farmers to predict the onset and cessation of rain as well as to make short-term and seasonal forecasts in the Rwenzori region of Western Uganda. We used a mixed-methods approach that included surveys of 907 households, focus group discussions, and key informant interviews. The results indicate that resident birds such as white-browed coucals and turacos and migrant birds such as eagles and swallows were important indicators of the onset of rains. Butterflies were an important indicator for the cessation of rains, and red ants were an indicator for the onset of rains. Among the abiotic indicators, winds, clouds, earthquakes, and cloud formation on Mount Rwenzori were important indicators. Behavior of cattle at the onset of rains was important among the pastoralists, and flowering of coffee plants was important among the arable farmers. The behavior of the biotic indicators was driven by the availability of food, water, or other necessities. An attempt to explain the phenology underlying the behavior of biotic indicators and the meteorological science underlying some of the abiotic indicators is made. Although biotic environmental indicators are rudimentary and their accuracy is influenced by external factors such as climate change, they provide climate information within the locality of the farmers. Our results suggest that the indicators used in indigenous forecasting could be incorporated in national meteorological systems in a bid to improve the accuracy of rainfall forecasts and their use among farmers and pastoralists in rural Africa.

The function of food storing in shrikes: the importance of larders for the condition of females and during inclement weather

Food storing is a well-known phenomenon among birds, described in shrikes Laniidae. The preferred explanation suggests that its function is to signify male quality to females and to mark territorial borders during the mating period. The importance of food storing must vary among different species, however, because in the Red-backed Shrike Lanius collurio, this behaviour takes place during the nestling care period. The aim of this study was to evaluate the significance of food storing by male Red-backed Shrikes. We did not find any differences in the breeding parameters between pairs in which the males did or did not store food. There was, however, a significant tendency for the number of stored prey items to increase when the atmospheric pressure was falling prior to the onset of rain. The mates of males that did store food had a larger body mass than those females whose partners did not do so. This study showed that food storage have a variety of functions, including different ones compared with those described for the best-known shrike species. Differences in food storing phenology in various shrike species are probably due to the period when they start nesting: Red-backed Shrikes start their breeding season in late spring, when food is plentiful. Our study demonstrates that the abundance of food in territories and one’s own condition, as expressed by the number of prey items stored when food is readily available, is not really so relevant. The food store of a Red-backed Shrike thus functions as a larder, which the female makes use of when her energy requirements are the highest, i.e. when caring for her young. Larders are thus essential if females are to remain in good bodily condition: this could be significant if a clutch is lost and a replacement one has to be laid.

Climate Change-Resilient Rice Production Technology: A High Yielding, Water Efficient and Remunerative Option for South Asian Farmers

Rice (Oryza sativa L.) production in South Asia is increasingly threatened by the erratic nature of onset of monsoon rain and climate change. Wide variance in rainfall pattern affects the timing of nursery raising and transplanting later in the main field. Existing rice cultivation practices such as direct seeded rice using drum seeder (DSR), system of rice intensification (SRI) and conventional transplanting (CT) are not able to address the production problems adequately. Therefore, we developed a package of practices - Climate Change-Resilient Rice Production Technology (CRRPT) - which allows keeping rice seedlings in the seedbed for an extended period to synchronize with the onset of monsoon rain. On-station trials during 2015-2016 comparing CRRPT with DSR, SRI and CT demonstrated that in CRRPT the seedlings can be maintained successfully in the seedbed for up to 55 days while achieving the equivalent yield of CT (30 days seedling) because of improved plant vigour. The CRRPT seedlings of 25 d and 35 d gave 22% and 11% more yield compared to CT (30 d seedling). Total water requirement in CRRPT was reduced by 20%, 14% and 13% in case of 55d, 45d and 35 d seedling, respectively, compared to that for CT (30 d seedling). In an on-farm study with 120 farmers’ fields in West Bengal during 2017-2018, average yield increased by 32% and net profit increased by 96%. Thus, CRRPT is remunerative, water efficient, climate change-resilient and can be easily adopted in the farmers’ fields. Results demonstrate that there is wide scope for its adoption for sustainable rice production in West Bengal and South Asia.

Pythium ultimum Causing Black Stem Rot of Brassica oleracea var. alboglabra in China

Brassica oleracea var. alboglabra, locally known as gailan, is an important leafy vegetable crop of China, widely cultivated in southern provinces. During 2016 to 2018, stem rot disease was seen in some agricultural fields around Guangzhou city of Guangdong province, China. Plants were affected by the disease at all growth stages. Black necrotic lesions developed and extended upward from the base of the stem on diseased plants. Symptoms first appeared as black lesions covering the stem surface. Under severe infestation, the infected stems got cracked and the whole plant collapsed. Mycelial masses were seen on the infected stem surface of some of the infected plants. Onset of rain increased disease incidence each year, and it reached up to 30% in severely infested fields. A large number of oospores were seen in infected plant tissues microscopically. Infected tissues were taken from the margins of the diseased stem and cut into small pieces (5 × 5 mm). This plant material was surface sterilized by 2% sodium hypochlorite solution, rinsed in sterile water several times, and placed on to V8 medium plates. Fungi were purified by successive subculturing on fresh media plates using the hyphal tipping technique. The fungi were rapidly growing with coenocytic mycelia. Light microscopy showed terminal and intercalary sporangia, thick-walled aplerotic oospores, and globose intercalary and terminal hyphal swellings. The diameters of 20 sporangia and oospores were 19.7 to 27.3 μm (mean 22.18 μm; SD 2.4) and 16.5 to 23.9 μm (mean 19.02 μm; SD 1.8), respectively. Morphological characters were consistent with Pythium ultimum Trow (Van der Plaats-Niterink 1981; Watanabe 2002). Genomic DNA was extracted from mycelial masses using a Dzup fungal DNA extraction kit (Sangon Biotechnology, Shanghai, China). Molecular identifications were performed by amplifying the internal transcribed spacer region (ITS) using primers ITS1/ITS4 (White et al. 1990) of five pathogen isolates. BLAST analysis showed that all the isolates shared 99% nucleotide identity with the previously submitted P. ultimum sequences (GenBank accessions KU210389, KU210177, and AY243070). The nucleotide sequence has been assigned GenBank accession number MK615615. Pathogenicity tests were performed on plants of B. oleracea of variety Dasun using five different pathogen isolates (VRI-1 to VRI-5). Pathogen isolates were considered as the treatments, and each treatment consisted of 12 individual plants. Uninoculated potato dextrose agar (PDA) was included as the control. The experiment was performed as a randomized complete block design and repeated twice. Plants were raised in plastic pots filled with sterilized commercial potting mix. Two weeks after emergence, plants were inoculated with quarter-strength PDA medium pieces (5 × 5 mm) colonized with different isolates of P. ultimum separately. The inoculum was placed 5 to 10 mm away from the plants. Plants were incubated in a growth room at 25 ± 2°C and 16-h/8-h photoperiod. Symptoms developed within 10 days after inoculation. Infected plants showed reduced growth and dark brown lesions on stem that coalesced and turned into a rotted mass. All five pathogen isolates caused disease, and none of the pathogen isolates showed disease incidence less than 80%. Stems of diseased plants showed numerous oospores when observed under a microscope. Control plants remained healthy and uninfected. The same pathogen was consistently reisolated from infected tissues of plants. Pathogen identity was reconfirmed by both molecular and morphological methods. To our knowledge, this is the first report of Pythium stem rot of B. oleracea var. alboglabra caused by P. ultimum in China. This disease can be of great economic loss because the whole aboveground portion of this plant is of economic importance and is consumed as a salad or cooked as a vegetable. Timely measures must be taken to manage this disease. This disease may increase in incidence in rainy seasons.

Phenology, flowering and fruit-set patterns of baobabs, Adansonia digitata, in southern Africa

Baobabs (Adansonia digitata) are iconic and highly valued trees that characterise many semi-arid environments across Africa. The aim of this study was to describe leaf, flowering and fruit phenology, flower production and fruit-set patterns of southern African baobabs. This was done on a sample of 106 trees across five land-use types at monthly intervals over two-years. Rainfall in the first year (2006/7, Year 1) was only 275 mm, but doubled in the second year (516 mm; 2007/8, Year 2), being below and above the long term mean of 461 mm, respectively. Leaf flush preceded the onset of rains (October) in 88% of trees in Year 1, but after the onset of rains (August) in all trees in Year 2. Leaves flushed in November and were retained until April and in October and retained until March, respectively. Leaf fall occurred one month later in Year 1 (May) than in Year 2 (April). Flowering followed a steady-state pattern, lasting for 1–5 months with peak flowering in November in both years. For adult trees, flower number/tree (Year 1: 711 ± 72 (S.E.) and Year 2: 287 ± 33), but not fruit-set (mean of 20 ± 4%) varied significantly between years. Flower number showed a logarithmic relationship with tree size (stem diameter) (R2 = 0.3830, P < 0.0001), while fruit-set was unrelated to tree size (R2 = 0.0045, P = 0.5081). Flower number and fruit-set did not vary between five land-use types, but length of flowering did, with village trees flowering for the longest period. Baobabs are hermaphrodite plants with both male and female reproductive structures in the same flower. Yet, across Africa many people refer to individual trees as being ‘male’ (fruiting is absent or minimal) or ‘female’ (substantial fruiting). Producer ‘female’ and poor-producer ‘male’ trees, did not differ in flowering phenology (number, timing and length of flowering), but fruit-set over two sequential years differed greatly between producer (33.5 ± 5.2%) and poor producer (0.2 ± 0.1%) trees. Leaf flush was responsive to early rains and hence baobabs appear to be facultative early greeners. However flowering and fruit-set patterns were not significantly different between these two years, despite the large rainfall difference. Although flower production was not different between producer and poor-producer trees in either year, fruit set was three orders of magnitude higher in producer than poor-producer trees. These quantitative results suggest that baobabs may be functionally dioecious and thus a complete characterization of the reproductive biology is required. Mechanisms underlying this pattern are discussed in terms of tree age, environment, pollination, genetics and evolutionary biology.

Leaf Spot Disease Caused by Alternaria arborescens, A. tenuissima, and A. infectoria on Brassica rapa subsp. parachinensis in China

Leaf Spot Disease Caused by <i>Alternaria arborescens</i>, <i>A. tenuissima</i>, and <i>A. infectoria</i> on <i>Brassica rapa</i> subsp. <i>parachinensis</i> in China

Crop Performance and Water Productivity of Transplanted Rice as Affected by Seedling Age and Seedling Density under Alternate Wetting and Drying Conditions in Lao PDR

Drought is common under rainfed lowlands in Lao People’s Democratic Republic, and with the uncertain onset of rains during the wet season, delay in transplanting results in yield reduction. This study aims to explore ways to ameliorate the negative influence of delayed transplanting on rice crop. A field experiment was conducted for two wet seasons to investigate the effect of seedling age and seedling density on crop performance in terms of grain yield and water productivity. The experiment was laid out in a split–split plot design in four replicates, with seedling age as the main plot, seedling density as the subplot, and varieties as the sub-sub plot. In both years, there were significant seedling age and variety interactions on grain yield. Higher grain yields were observed with older seedlings having stronger tillering propensity. Seedling density did not affect grain yields in both years, but on grain yield components. Shorter duration variety received less supplemental irrigation than longer duration varieties. Late transplanting improved total water productivity but decreased irrigation water productivity due to harvesting delay. The total crop growth duration (from sowing to maturity) was prolonged with transplanting delay. However, the total stay of plants in the main field (from transplanting to maturity) was reduced by 3–5 d for every 10 d delay in transplanting. The results indicated that a good selection of varieties and increasing seedling density improve crop performance and water productivity with delayed transplanting.

HVDC Corona Current Characteristics and Audible Noise During Wet Weather Transitions

For the connection of remote energy sources, HVDC offers higher efficiency and flexibility compared to conventional HVAC. As the acceptance for overhead lines in Europe is often low, the detailed understanding of its environmental effects, such as audible noise is of crucial importance. Still, only few experimental studies have investigated HVDC corona. Recent publications have demonstrated, that existing prediction models for DC audible noise show strong deviations when extrapolated for higher surface gradients. While audible noise is considered negligible in rain, research has shown that the discharge amplitudes increase significantly during transitions from dry to wet weather and vice-versa. In this study, the corona current and audible noise are investigated for a large range of surface gradients and rain rates. A special focus is set on the behavior during rain onset and dry-off. While the corona current increased during rain, the measured audible noise was significantly higher during the transitions before and after the steady state. The duration of these transition periods varied with rain rate and surface gradient. The observed effects are explained using corona pulse patterns and UV data. Compared to these measurements, existing audible noise prediction models were found to overestimate the sensitivity regarding the electric field.

Do indigenous forecasts and scientific forecasts influence arable farmers’ and agro-pastoralists’ estimation of onset and cessation of rains? Empirical evidence from Rwenzori region, Western Uganda

This study investigated the influence of indigenous forecasts (IF) and scientific forecasts (SF) on arable farmers’ and pastoralists’ estimation of onset and cessation of rains in the Rwenzori region of Western Uganda. Daily rainfall data (1970–2010) from 3 weather stations in different agro-ecological zones was used to determine mean onset and cessation dates using the Sivakaumar method. After obtaining the household survey of number of farmers and pastoralists whose estimation of onset and cessation dates were in agreement with the stations’ dates, the relationship between forecast type used and estimation of the dates was investigated using the Pearson correlation coefficient. The results indicate that onset dates for the 1st season were on 11th, 17th, 19th March while cessation was 8th, 11th, 21st June for lowlands, mountainous and forested areas, respectively. For the 2nd season, forested and mountainous areas had their onsets on 3rd and 20th August, respectively but the lowland area their onset on 3rd September. The cessation date for 2nd season for forested areas was on 8th December, while dates for lowland and mountainous areas were 17th and 24th November, respectively. The results suggest that there is positive relationship between using both IF and SF and estimation of onset and cessation dates but negative relationship with IF had for arable farmers. There was strong negative relationship between using both IF and SF and estimation of onset dates for the 2nd season for arable farmers in forested areas, but strong positive relationship with those using IF only season. The coefficients of variation for the rain onsets were high implying climate variability. The adopted Sivakaumar method is easy to operationalize by farmers and pastoralists with primary level of education, and access to daily rainfall data from established institutions like schools, local clinics and facilities provided by agricultural extension workers.

The Effect of Seasonal Humidity on Survival and Duration of Dormancy on Diverging Mexican Rhagoletis pomonella (Diptera: Tephritidae) Populations Inhabiting Different Environments.

Phytophagous insects synchronize emergence with plant phenology by engaging in dormancy during periods of host scarcity and environmental stress. Regulation of dormancy is achieved through response to seasonal cues. While temperature and photoperiod are important cues in temperate latitudes, seasonal humidity, such as the onset of rains, can be a reliable cue to for synchronization of emergence and affects survival of overwintering insects. We compared response of Mexican Rhagoletis pomonella (Walsh) (Diptera: Tephritidae) populations inhabiting subtropical environments differing in humidity patterns, to seasonal humidity regimes. Both populations emerged as adults in high proportions and suffered lower mortality under humidity regimes ending with a humid summer, but the effect was more pronounced for the Eje Volcanico Trans Mexicano (EVTM) population, which inhabits a dryer environment and undergoes longer dormancy. While there were no differences among pupae from the Sierra Madre Oriental (SMO) in percent of non-emerged pupae surviving and engaging in prolonged dormancy after a year, EVTM pupae exposed to an initial humid period engaged in prolonged dormancy in higher proportions than those exposed to other regimes. Seasonal humidity had little effect on the duration of dormancy, but EVTM pupae exposed to consecutive dry periods took longer to emerge than those exposed to other regimes. Our results suggest that rather than being used as a token stimulus, humidity affected survival of overwintering R. pomonella, especially at the end of dormancy when energy reserves are depleted and there is an increase in metabolic rate that renders EVTM pupae more susceptible to desiccation.

Analysis of Length of Growing Season in Some Agro-ecological Zones Using Non-parametric Trend Test

The ever increasing population and consequently increase in demand for food and the increasing exploitation of the land justifies the need for adequate studies on rainfall as an important factor affecting agricultural production. The date of the onset of rains is an important factor in planning agricultural operations such as land preparation and sowing. The study conducted agro-statistical analysis of rainfall characteristics over three different zones of Nigeria. Daily rainfall data were collected for the period between 1971 and 2005 for 6 stations and were subjected to standard analysis to determine trends and variations in the onset dates, cessation dates, length of rainy season, number of wet days, drought episodes. The results showed that the inter-annual variability of the onset dates is higher than that of cessation dates with a progressive shift in both onset and cessation dates. The length of rainy season varied from 77-291 days in Guinea zone, 77-243 days for Savannah and 73-155 days for the Sahel. Changes in the length of growing season ranged between -9 and -10 for Guinea zone, -21 and 11 days for Savannah zone and -28 and 20 days for the Sahel. Similarly, the numbers of wet days have declined over Nigeria. The information presented in this study are to serve as input for proper land and water resources management for productive agricultural enterprise across the three major agro-ecological zones of Nigeria.

Non-Monotonic Aerosol Effect on Precipitation in Convective Clouds over Tropical Oceans

Aerosol effects on convective clouds and associated precipitation constitute an important open-ended question in climate research. Previous studies have linked an increase in aerosol concentration to a delay in the onset of rain, invigorated clouds and stronger rain rates. Here, using observational data, we show that the aerosol effect on convective clouds shifts from invigoration to suppression with increasing aerosol optical depth. We explain this shift in trend (using a cloud model) as the result of a competition between two types of microphysical processes: cloud-core-based invigorating processes vs. peripheral suppressive processes. We show that the aerosol optical depth value that marks the shift between invigoration and suppression depends on the environmental thermodynamic conditions. These findings can aid in better parameterizing aerosol effects in climate models for the prediction of climate trends.

Cloud droplet growth in shallow cumulus clouds considering 1-D and 3-D thermal radiative effects

Abstract. The effect of 1-D and 3-D thermal radiation on cloud droplet growth in shallow cumulus clouds is investigated using large eddy simulations with size-resolved cloud microphysics. A two-step approach is used for separating microphysical effects from dynamical feedbacks. In step one, an offline parcel model is used to describe the onset of rain. The growth of cloud droplets to raindrops is simulated with bin-resolved microphysics along previously recorded Lagrangian trajectories. It is shown that thermal heating and cooling rates can enhance droplet growth and raindrop production. Droplets grow to larger size bins in the 10–30 µm radius range. The main effect in terms of raindrop production arises from recirculating parcels, where a small number of droplets are exposed to strong thermal cooling at cloud edge. These recirculating parcels, comprising about 6 %–7 % of all parcels investigated, make up 45 % of the rain for the no-radiation simulation and up to 60 % when 3-D radiative effects are considered. The effect of 3-D thermal radiation on rain production is stronger than that of 1-D thermal radiation. Three-dimensional thermal radiation can enhance the rain amount up to 40 % compared to standard droplet growth without radiative effects in this idealized framework. In the second stage, fully coupled large eddy simulations show that dynamical effects are stronger than microphysical effects, as far as the production of rain is concerned. Three-dimensional thermal radiative effects again exceed one-dimensional thermal radiative effects. Small amounts of rain are produced in more clouds (over a larger area of the domain) when thermal radiation is applied to microphysics. The dynamical feedback is shown to be an enhanced cloud circulation with stronger subsiding shells at the cloud edges due to thermal cooling and stronger updraft velocities in the cloud center. It is shown that an evaporation–circulation feedback reduces the amount of rain produced in simulations where 3-D thermal radiation is applied to microphysics and dynamics, in comparison to where 3-D thermal radiation is only applied to dynamics.

Spatiotemporal Change of Plum Rains in the Yangtze River Delta and Its Relation with EASM, ENSO, and PDO During the Period of 1960–2012

The Plum Rains process is a complex process, and its spatiotemporal variations and influencing factors on different time scales still need further study. Based on a dataset on the Plum Rains in the Yangtze River Delta, from 33 meteorological stations during the period of 1960 to 2012, we investigated the spatiotemporal variations of Plum Rains and their relation with the East Asian Summer Monsoon (EASM), the El Niño-Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO) using an integrated approach that combines ensemble empirical mode decomposition (EEMD), empirical orthogonal function (EOF), and correlation analysis. The main conclusions were as follows: (1) the plum rainfall (i.e., the rainfall during the period of Plum Rains) showed a trend of increasing first and then decreasing, and it had a three-year and six-year cycle on the inter-annual scale and a 13-year and 33-year cycle on the inter-decadal scale. The effect of the onset and termination of Plum Rains and the daily intensity of plum rainfall on plum rainfall on the inter-annual scale was greater than the inter-decadal scale, (2) the EOF analysis of plum rainfall revealed a dominant basin-wide in-phase pattern (EOF1) and a north-south out-of-phase pattern (EOF2), and (3) ENSO and EASM were the main influencing factors in the three-year and six-year periods, respectively.