Short Dry Spells Research Articles

Climate change over South America simulated by the Brazilian Earth system model under RCP4.5 and RCP8.5 scenarios

Climate projections simulated by the Brazilian Earth System Model (BESM2.5) under RCP4.5 and RCP8.5 climate scenarios are analyzed based on future changes of surface air temperature (SAT) and precipitation with respect to the historical reference period 1971–2000. Since BESM2.5 is the only climate model developed in a South American country, this study gives a particular emphasis to South American future climate projections. Regarding the surface air temperature, BESM2.5 projects a steady warming throughout the 21st century, with the highest warming over eastern Amazonia, northern Chile and central South America for both scenarios. The SAT changes range between 2 °C and 3–4 °C for RCP4.5 and RCP8.5, respectively. On the other hand, projected precipitation varies over different regions of South America, with decreasing and increasing trends over the Amazon and southern South America, respectively. Interestingly, this study shows contrasting results with respect to extreme precipitation indicators, projecting enhanced extreme events with higher numbers of both consecutive dry days and days in which the precipitation exceeds 20 mm over the southeastern region. The model projects a meridional dipole pattern in the precipitation, with decreasing precipitation and longer dry spells over Northeast Brazil and the East Amazon region and increasing precipitation and shorter dry spells over Northwest South America and West Amazon, that is driven by future changes in the SLP that imposes a meridional gradient over these regions, causing the increase of westerlies that are likely to increase the moisture transport from the Pacific Ocean into western South America and the weakening of the easterlies that transport moisture over eastern South America and East Amazon.

Observed and projected changes in wet and dry spells for the major river basins in East Asia

AbstractSpatiotemporal changes in wet and dry spells had significantly contributed to climate‐related natural hazards in East Asia, especially in river basins undergoing warming. However, few studies have systematically analysed these changes for river basins at different latitudes. Herein, we investigated the observed and projected variations in wet and dry spells for East Asian river basins at different latitudes. We found that river basins at low latitudes (Yangtze and Pearl rivers) had obvious wet characteristics, whereas those at high latitudes (Amur and Yellow rivers) had obvious dry characteristics. In general, the river basins presented a ‘wet south but dry north’ spatial pattern. Long‐duration wet spells have been shown to be the primary contributor to total wet spells in low‐latitude river basins, while long‐duration dry spells have been found to be the primary contributor to total dry spells in high‐latitude river basins. Importantly, climate is changing from prolonged wet spells to short, intense wet spells in low‐latitude river basins, whereas the climate is changing from single, short dry spells to moderate, prolonged dry spells at high latitudes. These changes indicate a high probability of flash floods in river basins at low latitudes and a high probability of droughts at high latitudes. In the future, more temporally clustered heavy precipitation events and prolonged dry spells may lead to increasingly uneven precipitation in high‐latitude river basins and the Pearl River basin, especially under the higher shared socioeconomic pathway scenarios. In contrast, more frequent consecutive heavy precipitation events may aggravate the risk of flooding in the Yangtze River basin. These findings are expected to serve as a guide for flood and drought risk mitigation in East Asia under a warming climate.

Evaluation and future projection of the extreme precipitation over India and its homogeneous regions: A regional earth system model perspective

AbstractA regional earth system model (ROM) was used to examine the projected change in the precipitation extremes (PEs) and associated dynamical and thermodynamical processes over India during the Indian summer monsoon (ISM). In this regard, PEs are computed for India, its six homogeneous regions and subregions the Western Ghats (WG) and central India (CI). The changes are computed for mid‐future (2040–2069: MDF) and far‐future (2070–2099: FRF) with respect to the historical period (1969–2000). ROM showed better resemblance with observation in simulating PEs over other regional climate models (RCMs) that participated in the CORDEX‐CORE simulation. The intense rainfall (95th percentile: R95) is expected to be enhanced over most of the region during MDF that further intensifies in FRF except CNE (central northeast) and NEI (northeast India), where the increase in R95 was restricted only up to MDF. Interestingly, very intense rainfall (99.9th percentile: R99) showed robust increases in both MDF and FRF for all regions. Additionally, long wet (dry) events were shortened (lengthen). Moreover, the short wet and dry spell frequency has increased, while the duration of the wet (dry) spell has decreased (increased) in both time slices over India with noticeable regional variation. This is attributed to the strong cyclonic circulation, reduced vertical wind shear and enhanced moisture transport during the ISM in both time slices. It is very important to highlight the substantial changes in the precipitation extremes to have better planning and strategies that will be helpful to minimize the incurred losses.

Effects of Meteorological Conditions and Irrigation Levels during Different Growth Stages on Maize Yield in the Jing-Jin-Ji Region

Maize is a major crop that is particularly sensitive to climate change. In addition, the extreme shortage of water resources threatens crop production. Thus, improving the effective utilization rate of water is an important problem to discuss. In this regard, we quantified the combined effects of meteorological conditions and irrigation levels during different growth stages on city-level maize yields in the Jing-Jin-Ji region from 1993 to 2019. The results show that the sowing period was affected by the minimum temperature, while the other growth stages were affected by the maximum temperature. At the ear stage of summer maize, when the effective irrigation rate reached the average level (52%), the inflection point of the total precipitation was 401.42 mm in the Jing-Jin-Ji region. When the total precipitation was higher than 401.42 mm, the summer maize yield decreased with the increasing total precipitation. Furthermore, the summer maize growth was significantly affected by drought at the seedling stage. At high effective irrigation rates and over long dry spells, as the mean daily temperature during dry spells increased, the maize yield easily increased. The increase in the effective irrigation rate can reverse the decrease in the summer maize yield. Moreover, the effective irrigation rate increased the maize yield with the increase rise in the temperature during longer dry spells, but the maize yield decreased with warmer temperatures during shorter dry spells. As such, our evaluation results will be useful for assessing food security and moving gradually toward achieving a water–energy–food nexus.

Effects of dry spells on soil moisture and yield anomalies at a montane managed grassland site: A lysimeter climate experiment

AbstractThe frequency and severity of droughts in the Alps are expected to increase due to rising air temperatures and changes in precipitation regimes. Although biomass production in humid mountain areas tends to be energy limited rather than water limited, an increase in droughts may have negative impacts on the water availability and thus agricultural yields. This study aimed to analyse the impacts of dry spells on soil moisture and yield anomalies at a montane permanent grassland site in Austria. Dry spells in the time period from 2018 to 2020 were identified using the Standardized Precipitation Index, Palmer Drought Severity Index and the Soil Moisture Anomaly Index. Data from a lysimeter climate experiment were used to evaluate drought impacts on soil water storage and grassland yield under ambient and manipulated conditions. The results indicated the occurrence of three extreme droughts between 2018 and 2020. Although the studied grassland is generally considered a nonwater‐limited ecosystem, the most extreme drought in summer 2019 caused severe and extreme yield anomalies under ambient and heated conditions. Only mild yield anomalies were observed on plots with elevated atmospheric carbon dioxide concentration. This drought‐mitigating effect was attributed to the water savings enabled by partial stomatal closure under elevated CO2. The shorter dry spells in spring and late summer 2018 led to more diverse effects; mildly to moderately negative yield anomalies were found on the heated plots, whereas the anomalies tended to be less negative or even positive on plots under ambient temperature. In contrast, some time periods without water stress showed positive effects of heating on yield. These findings suggest that drought impacts on a humid montane grassland depend on both water availability and air temperature. Higher air temperature can have positive effects on yield if the ecosystem is energy limited. However, global warming suggests a tendency from energy to water limitation, in which the increased evaporative demand of the atmosphere aggravates soil moisture droughts and thus has potentially negative effects on yield.

Drought Risk Assessment of Sugarcane-Based Electricity Generation in the Rio dos Patos Basin, Brazil

Brazil has a large share of hydropower in its electricity matrix. Since hydropower depends on water availability, it is particularly vulnerable to drought events, making the Brazilian electricity matrix vulnerable to climate change. Starting in 2005, Brazil opened the matrix to new renewable sources, including sugarcane-based electricity. Sugarcane is known for its resilience to short dry spells. Over the last decades, its production area moved from the coastal plains of the Atlantic Forest biome to the savannahs of the Cerrado biome, which is characterised by a five- to six month-long dry season. The sugarcane-based electricity system is highly dynamic and complex due to the interlinkages, dependencies, and cascading impacts between its agricultural and industrial subsystems. This paper applies the risk framework proposed by the IPCC to assess climate-change-driven drought risks to sugarcane electricity generation systems to identify their strengths and weaknesses, considering the system dynamics and linkages. Our methodology aims to understand and characterize drought in the agriculture as well as industrial subsystems and offers a specific understanding of the system by using indicators tailored to sugarcane-based electricity generation. Our results underline the relevance of actions at different levels of management. Initiatives, such as regional weather forecasts specifically for agriculture, and measures to increase industrial water-use efficiency were identified to be essential to reduce the drought risk. Actions from farmers and mill owners, supported and guided by the government at different levels, have the potential to increase the resilience of the system. For example, the implementation of small dams was identified by local actors as a promising intervention to adapt to the long dry seasons; however, they need to be implemented based on a proper technical assessment in order to locate these dams in suitable places. Moreover, the results show that creating and maintaining small water reservoirs to enable the adoption of deficit-controlled irrigation technology contribute to reducing the overall drought risk of the sugarcane-based electricity generation system.

Biophysical Properties of Inner Bark and Sapwood in Tree Species From Forests With Contrasting Precipitation in Subtropical South America

Stem capacitance and water storage are known to play an important role in the water economy of trees by acting as an intermediate water source for transpiring leaves. The bark, in addition to be involved in protection and mechanical support of the trees, can also serve as a water reservoir. We examined the relationship between inner bark and sapwood biophysical properties in tree species occurring in forests at the opposite ends of a moisture gradient in subtropical South America. We also assessed the relationships between wood density, growth rate and the magnitude of the water reservoir. The inner bark thickness varied between 1.89 and 0.50 cm across species and sites and there were not significant differences between forests. Inner bark capacitance of species from the dry forest was higher than sapwood capacitance, and the opposite was found in the moist forest. Sapwood capacitance (262 ± 80.8 Kg m−3 MPa−1) was significantly higher in the moist forest compared to the dry forest (41.9 ± 4.5 Kg m−3 MPa−1), while the opposite was found for inner bark (50.7 ± 8.4 and 83.1 ± 11.4 Kg m−3 MPa−1, respectively). Inner bark capacitance and density were linear and positively correlated across species, while for sapwood the relationship was well-described by a negative exponential function. In species with higher percentage of inner bark, the time lags in the daily contractions of bark and sapwood tissues were lower. Relative growth rate was negatively correlated with inner bark and sapwood density and positively with daily stored water used and percentage of inner bark across species and sites. Our results suggest that sapwood is a relevant water storage tissue in the trees of the moist forest while inner bark is important for tree functioning in the dry forest. High stem capacitance and water storage are needed to cope with short dry spells or seasonal periods of water deficit, and for maintaining growth rates. These stem properties will be more relevant under climatic scenarios with more frequent extreme drought events or seasonal reduction in precipitation in these forest ecosystems.

Soil fertility status of soils of Sudano-Sahelian and Humid Forest Zones of West Africa and some soil management strategies for smallholder farms

Knowledge of soil properties and fertility status of farmers’ fields are basic information needed by Agricultural Extension Agents to guide farmers on wise and sustainable management of soil. The properties of some cultivated fields in the Sudano-Sahelian of Ghana and Humid Forest zones of Nigeria were studied. The aim was to quantify the soil properties and fertility status with a view to prescribing low input ecological technologies that would improve and sustain soil productivity. Core samples were taken from the depth of 0 – 40 cm in eleven and eight farmers’ fields in the Upper East Ghana and South East Nigeria, respectively. Soil properties determined using standard methods were; pH, TN, SOC, SOM, P, Exchangeable bases, EA, base saturation, PSD, WP, FC, bulk density, P and SHC. Both soils were sand in texture (> 700 g kg-1). The WP and FC were either below or within the lower border of critical levels. This shows crops in all the fields are prone to incipient wilting under any short dry spell. The chemical properties of the Sahelian-Sahelian zone showed that pH averaged 6.54 (moderate acidic), SOC 16 g kg-1 (low), TN 13 g kg-1 (very high), P, 18 mg kg-1 (moderate), K 0.23 C mol kg-1) (moderate), ECEC 8.18 C mol kg-1(medium fertility class). In the Humid Forest zones, pH was 4.38 (extremely acidic), SOC 7.41 g kg-1 (very low), N 1.78 g kg-1 (low), P 15.94 mg kg-1 (moderate), K 1.94 C mol kg-1 (very high) and ECEC 8.8 C mol kg-1 (medium fertility class). The fertility class indicates that the soils will response to external inputs and wise land management practices. A mix of Arbuscular mycorrhizal fungus (AMF), multipurpose tree species, contour cultivation, organic mulch, multiple crop mixture, under vetiver grass buffer strip is recommended.

English

This work aims at characterizing the conditional probability of single or consecutive dry and wet days in West Africa using the first-order Markov chain approach during the monsoon season (June to October). The results show that the probabilities of having a wet day (PW), a wet day preceded by another wet day (PWW) and a wet day preceded by a dry day (PDW) are stronger in regions where the rainfall is maximum (mountain regions). In contrast, the probabilities of having a dry day (PD), a dry day preceded by a wet day (PWD) and a dry day preceded by another dry day (PDD) are lower in the regions with higher precipitation. The seasonal cycle of PWW (PDD) is consistent with that of PW (PD), respectively in Western Sahel and Central Sahel regions. At the interannual timescale, MK test results show that PW and PDW (PD and PDD) exhibit statistically significant increasing (decreasing) trends the Western Sahel and the Central Sahel. Besides, the shorter dry spells (3 days) show statistically significant decreasing trends only in the Western Sahel. The longer dry spells (5, 7 and 10 days) show statistically significant downward trends over the Western and Central Sahel. Wet spells probabilities show non-significant decreasing trends in all sub-domains, except in the Western Sahel for the 10 days spells. Knowledge of theses probabilities will contribute to develop efficient strategies for water resources management and agricultural decision making in West African countries. Key words: Markov chain, rainfall, occurrence, wet spell, dry spell, West Africa.

Beneficial microbial species and metabolites alleviate soybean oxidative damage and increase grain yield during short dry spells

Short dry spells are an important grain yield constraint in tropical regions. Plant growth-promoting bacteria (PGPB) and their metabolites can mitigate the impact of drought stress by promoting changes in plant metabolism, physiology, and biochemistry. However, the effects of PGPB on soybean [Glycine max (L.) Merril] under drought stress in tropical regions have not been established. The experiments were carried out under tropical field conditions with short dry spells. Therefore, in this study we used a three-factorial trial to evaluate the effects of bacterial consortium consisting of N2-fixing Bradyrhizobium japonicum (strain SEMIA 5079) and Bradyrhizobium diazoefficiens (strain SEMIA 5080), the biocontrol agent Bacillus subtilis (strain QST 713), and the plant growth-promoting Azospirillum brasilense (strains Ab-V5 and Ab-V6) with or without application of microbial secondary metabolites (MSM, rhizobial metabolites enriched in lipo-chitooligosaccharides (LCOs)) during two growing seasons. Photosynthetic pigments, gas exchange parameters, antioxidant enzyme activity and proline concentrations in leaves, nodulation, plant growth development and grain yield were evaluated. The bacterial consortium comprising Bradyrhizobium spp., A. brasilense strains and MSM application increased the contents of chlorophyll a (14.5 %), chlorophyll b (30.8 %), total chlorophyll (17.2 %), and total carotenoids (27.3 %) compared with Bradyrhizobium spp. treatment alone. This consortium also increased the net photosynthetic rate (17.7 %), stomatal conductance (56.5 %), internal CO2 concentration in the substomatal chamber (8.3 %), and transpiration (44 %) compared with plants that received the standard inoculation (Bradyrhizobium spp. only), while reducing the leaf contents of hydrogen peroxide (−18.8 %) and proline (−29.4 %), lipid peroxidation (−15.9 %), and the activities of superoxide dismutase (−18.2 %), catalase (−21.2 %), and ascorbate peroxidase (−19.1 %). Taken together, the results indicate that a beneficial bacterial consortium comprising Bradyrhizobium spp. and A. brasilense strains combined with MSM application can alleviate oxidative damage during dry spells. Furthermore, this consortium improved soybean nodulation, plant growth development, and grain yield by up to 12.2 %.

Characterisation of wet and dry spells and associated atmospheric dynamics at the Pra River catchment of Ghana, West Africa

Study regionThe Pra river catchment in Ghana, West Africa. Study focusKnowledge of the spatio-temporal distribution of wet and dry spells are crucial for rain-fed agriculture at the Pra River catchment. This study characterised spells and their associated atmospheric dynamics at the Pra river catchment. Specifically, the variability of historical and future wet and dry spells and atmospheric dynamics on the rainfall and spell patterns at the catchment were studied. New hydrological insightsShort duration spells have a higher occurrence at the catchment as compared to long duration spells. Seasonally, short duration dry spells are most common in December–February, whereas wet spells are expected in March–May. Future scenarios show an increase in both wet and dry spells. Composites of the atmospheric dynamics for 2–3 day dry spells show moisture convergence over the entire catchment, with lower total column water levels. However, there is a dipole of moisture convergence and divergence for wet spell composites, with higher than normal total column water. An anticyclonic circulation, inducing a ridge at 500 hPa, coupled with low-level southerlies at 850 hPa act to support wet spell occurrences in JJA. The findings contribute to sub-seasonal and seasonal forecasting, and hence will improve agricultural practices in the catchment in support of food security.

Evolution of Dry and Wet Spells Under Climate Change Over North‐Eastern North America

AbstractRisks associated to extreme hydrological conditions, such as floods and droughts, are expected to increase in future climate because of projected changes in precipitation and temperature. Assessing how wet and dry persisting conditions (or spells) will evolve in future climate is a crucial step in the study of extreme hydrological events. Projected changes over the north‐eastern part of North America in the annual number of wet days, wet, and dry spells characteristics (number, duration), and wet spells intensities are analyzed. Two regional climate model ensembles are considered: the multimember ensemble from the Canadian RCM v5 (CRCM5‐LE), and 16 simulations from the NA‐CORDEX multimodel ensemble both using the Representative Concentration Pathway 8.5 (RCP8.5) scenario. Comparison of observed and simulated wet and dry spells characteristics is first performed in present climate (1971–2000). Regional Climate Model (RCM)s tend to generate too many wet days and wet or dry spells resulting in shorter dry spells and slightly longer wet spells. Modeling uncertainties are accounted for a bigger contribution to the bias than internal variability since the multimodel ensemble dispersion is the largest. Throughout the 21st century, both ensembles project significant trends in winter at higher latitudes resulting in increasing wet day frequency, increasing number of wet spell, longer wet spells and shorter dry spells. For other seasons, internal variability of the CRCM5‐LE and differences among the various NA‐CORDEX simulations seems to overwhelm the climate change signal. Wet spell intensities increases are projected for all seasons over almost the entire domain. Globally, wetter climate with potential significant hydrological impacts are expected in many regions.

Spatial and temporal analysis of mean and frequency variations of dry spells in Iran

For probabilistic modeling of variations in averages and frequencies of length of dry spells in Iran and obtaining a set of suitable patterns in this relation, the data on daily precipitation from 41 synoptic meteorological stations for a 30-year period (1989-2018) were obtained from the Iran Meteorological Organization. A dry spell is defined as a sequence of consecutive dry days with precipitation equal to or less than 0.1 mm per day. In order to evaluate the probabilistic distribution of the mean length and frequency of short (1-10 days), medium (11-20 days), and long dry spells (21-30 days), a first-order Markov chain model, a second-order Markov chain model, an exponential distribution model, and a negative binomial distribution were used. The results showed that there were longer dry spells at more southern latitudes and shorter dry spells at more northern latitudes in Iran. At an annual scale, the longest dry spell in southeastern Iran was 351 days and the longest in northern Iran was 37 days. Simulation of seasonal variations in mean and frequency of different lengths of dry spells using the four probabilistic models showed that the exponential and the negative binomial distributions gave the closest approximations to the empirical mean of the length of dry spells at the studied stations. However, these estimates were relatively simulated well only for mean length of dry spells that lasted less than 10 days and were not simulated well at all for dry spells with lengths of more than 10 days. Moreover, considering that the average frequencies of medium dry spells (11-20 days) and long dry spells (21-30 days) indicated the length and severity of dry spells in different parts of Iran, it was observed that the exponential and negative binomial distributions provided closer approximations to the empirical averages compared to the other two models. In general, we can conclude that the selected models performed poorly in simulating the average length of dry spells but performed better in simulating the average number of short, medium, and long dry spells.

Analysis and Predictability of Dry Spell Lengths Observed in Synoptic Stations of Benin Republic (West Africa)

The complex behavior and predictability of the Dry Spell Lengths (DSL) series obtained in Benin synoptic stations, from 1951 to 2010 are analyzed in this paper using a fractal approach. The synoptic stations are located in Cotonou, Bohicon, Save (subequatorial climate), and Parakou, Natitingou, Kandi (Sudanian climate). The DSLs are computed by considering four thresholds level, R0 = {1.0, 1.5, 2.0 and 5.0} mm/day. The fractal trace is estimated for dry spell density by the mean of the “Dry Spell Spell” (DSS) n-index. The rescaled range method is used to determine the predictability of DSL. By analyzing the DSS, results show that low DSS n-index values (n-index 0.4) occur preferentially in the southern part. Therefore, during 1951-2010, the Sudanian region presents frequent wet spells, alternated with short dry spells than in the subequatorial one. However, a high degree of long dry spell persistence, followed by short dry events is observed in the subequatorial region than in the Sudanian one. The longest DSL is observed in the subequatorial region, especially in Cotonou. Except for the Kandi station, the DSLs series obtained at synoptic stations are characterized by persistence. Therefore, autoregressive processes could be applied to the DSL series. Generally, the physical process governing dry spells observed at Save, Natitingou, and Bohicon are consistently predictable than the process governing the stations of the Cotonou and Parakou. However, at Kandi station, the DSL process approximates the usual Brownian motion, and it is, therefore, unpredictable or difficult to predict.

Cowpea yield variation in three dominant soil types in the Sudan Savanna of West Africa

Cowpea (Vigna unguiculata) is a legume crop widely cultivated across the Sudan Savanna. Despite its importance for farmers’ food security in this region, the grain yields are highly variable among years and locations. To identify environmental and plant factors underlying this yield variation and select cowpeas with a stable yield, the grain yield variation of 16 cowpea genotypes in three dominant soils in the Sudan Savanna, namely, Ferric Lixisols (LXfr), Petric Plinthosols (PTpt), and Pisoplinthic Petric Plinthosols (PTpt.px), were analyzed in two consecutive years with different precipitation. In this study, the three soils were located near each other at the experimental site and thus the meteorological conditions were assumed to be identical for the soil types. Results of analysis of variance showed that the factor of year, representing the effect of precipitation, was the largest cause of annual yield variation although there was a significant interaction between year and soil type. Based on this result, environment was defined as each combination of year and soil type in a subsequent additive main effect and multiplicative interaction (AMMI) model analysis to detect the effects of the environment, genotype, and genotype-environmental interaction (GEI) on grain yield variation. Then, additive Bayesian network (ABN) analysis was performed to investigate the relationships between environmental and plant factors. The AMMI model revealed that the effect of GEI on grain yield was the complete opposite between the years even for the same soil type, indicating no single genotype achieved both stable and high yields across these soil types. The ABN analysis suggested that the primary cause of yield variation among the different soil types under same precipitation was the difference in soil total nitrogen and available phosphorus content rather than that in available soil water. The larger GEI in LXfr and PTpt was caused partly by their high water holding capacity, which led to excess water stress under high precipitation for LXfr and PTpt, and partly by deep soils, which led to drought stress under low precipitation for LXfr because of infiltration into the subsurface layer. However, the higher fertility of these two soils compensated for excess water/drought stress, and thus, the average yields were higher than that in PTpt.p × . PTpt.px showed the lowest mean yield and the smallest GEI because of poor soil fertility, although the soil with low water holding capacity was prone to drought stress even during short dry spells. The AMMI model uncovered two cowpea genotypes with stable yield across all the environments; however, the grain yields of these genotypes were not the highest in each environment. Selection of a genotype with a medium but stable yield would be favorable to improve long-term average yield in the Sudan Savanna, where multiple soils with a large GEI are distributed in mosaic patterns.

Using the CHIRPS Dataset to Investigate Historical Changes in Precipitation Extremes in West Africa

This study aims to provide improved knowledge and evidence on current (1986–2015) climate variation based on six rainfall indices over five West African countries (Senegal, Niger, Burkina Faso, Ivory Coast, and Benin) using the Climate Hazards Group InfraRed Precipitation with Station (CHIRPS) dataset. On average, precipitation has increased over the central Sahel and the western Sahel. This increase is associated with increase in the number of rainy days, longer wet spells and shorter dry spells. Over the Guinea Coast, the slight increase in precipitation is associated with an increase in the intensity of rainfall with a shorter duration of wet spells. However, these mean changes in precipitation are not all statistically significant and uniform within a country. While previous studies are focused on regional and sub-regional scales, this study contributes to deliver a climate information at a country level that is more relevant for decision making and for policy makers, and to document climate-related risks within a country to feed impact studies in key sectors of the development, such as agriculture and water resources.

Characteristics of southwest summer monsoon rainfall events over East India

The variability in Indian summer monsoon rainfall (ISMR) has an immense socioeconomic impact on India, especially over the monsoon core region. In this study, a thorough analysis of the ISMR (June to September—JJAS) has been performed for East India (EI), a part of the monsoon core zone, and for its four subdivisions (Odisha, Chhattisgarh, Jharkhand, and Bihar). The long-term climatology, variability, and trends of various categorical rainfall events as defined by India Meteorological Department (IMD) have been analyzed by using IMD high-resolution (0.25° × 0.25°) gridded dataset for 116 years (1901–2016). Also, the percentage contribution of various rainfall events to the total seasonal rainfall and wet days is estimated. To get the changes in the frequency of various dry spells, rainfall events, and associated seasonal rainfall, study period is divided into two halves, earlier period (P1: 1901–1958) and recent period (P2: 1959–2016). The results suggest that the percentage contribution of medium-intensity rainfall events (7.6–64.4 mm/day) to the total ISMR is higher (~ 72%) followed by high-intensity rainfall events (~ 15%) and low-intensity rainfall events (12%), while most percentage contribution to the total number of wet days is from low-intensity rainfall events (~ 54%) followed by medium-intensity rainfall events (~ 43%) and high-intensity rainfall events (~ 3%). In the recent period (P2), the ISMR significantly decreased over the central part of EI because of the significant decrease in the frequency of low and medium-intensity rainfall events and wet days. The remarkable decrease of wet days leads to an increase in the short (1 week) and long-duration (> 2 week) dry spells in P2. And at the same time, high-intensity rainfall events significantly increased over EI in the recent period (P2) and led to an increase in the flood situation over this region. The profound relation of deficit rainfall of EI with ENSO is getting weak in the P2. This study is certainly useful in determining the effects on various sectors because of the variability and changes in various categorical extreme rainfall events, short and long-duration dry spells during summer monsoon time over EI. Also, this study may assist the risk management sectors in acclimating advanced technologies for a sustainable future in the changing climate of the present global warming era.

Spatial-Temporal Characterization of Atmospheric Aerosols via Airborne Spectral Imaging and Growing Hierarchical Self-Organizing Maps

Neural network analysis based on Growing Hierarchical Self-Organizing Map (GHSOM) is used to examine Spatial-Temporal characteristics in Aerosol Optical Depth (AOD), Ångström Exponent (ÅE) and Precipitation Rate (PR) over selected East African sites from 2000 to 2014. The selected sites of study are Nairobi (1°S, 36°E), Mbita (0°S, 34°E), Mau Forest (0.0° - 0.6°S; 35.1°E - 35.7°E), Malindi (2°S, 40°E), Mount Kilimanjaro (3°S, 37°E) and Kampala (0°N, 32.1°E). GHSOM analysis reveals a marked spatial variability in AOD and ÅE that is associated to changing PR, urban heat islands, diffusion, direct emission, hygroscopic growth and their scavenging from the atmosphere specific to each site. Furthermore, spatial variability in AOD, ÅE and PR is distinct since each variable corresponds to a unique level of classification. On the other hand, GHSOM algorithm efficiently discriminated by means of clustering between AOD, ÅE and PR during Long and Short rain spells and dry spell over each variable emphasizing their temporal evolution. The utilization of GHSOM therefore confirms the fact that regional aerosol characteristics are highly variable be it spatially or temporally and as well modulated by PR received over each variable.

Phenology of a dipterocarp forest with seasonal drought: Insights into the origin of general flowering

Abstract Our understanding of the factors that shape reproductive phenology in Southeast Asian tropical forests comes almost exclusively from studies of everwet, general flowering (GF) forests. Therefore, we examined the phenology of an evergreen dipterocarp forest in a climate exhibiting seasonal drought in Southeast Asia, with the aim of evaluating what evidence it brings to bear on the hypothesis that reproductive phenology in contemporary dipterocarp forests is the product of evolutionarily conserved responses to seasonal drought. We hypothesized that (1) dipterocarp forests that experience seasonal drought would exhibit annual reproduction and seasonality similar to that of forests with similar climates in other parts of the world, (2) within species, flowering frequency would be climate‐dependent, not a fixed trait, and (3) climatic events that cue flowering in everwet forests would also cue flowering in seasonally dry forests. From 2001 to 2009, we monitored flowering and fruiting monthly for 1,344 trees (>300 spp.) in a forest in Khao Chong (KC), Thailand that experiences an annual 2–4 month dry season, assessing frequency, duration, seasonality and synchrony of reproduction. We also examined phenological records for trees in three dipterocarp‐dominated forests in everwet climates. Reproductive phenology of the KC forest was more similar to tropical forests with similar rainfall seasonality in other parts of the world than it was to dipterocarp‐dominated forests in everwet regions of Southeast Asia. The forest exhibited annual reproduction, with peak flowering occurring at the end of the dry season and peak fruiting occurring early in the wet season. Approximately half of all species and individuals reproduced annually, including several species that are known to exhibit “general flowering” in everwet climates. Short dry spells appeared to cue flowering for early flowering species, while later flowering species may have responded to either low precipitation or temperature, consistent with data from everwet forests. GF behaviour also showed significant phylogenetic signal. Synthesis. Our results support the hypothesis that the phenological behaviour of both seasonal and everwet dipterocarp forests may have initially evolved in response to seasonal drought and that the general flowering phenomenon is a product of evolutionary conservatism.

Development of heat and drought related extreme weather events and their effect on winter wheat yields in Germany

Climate change constitutes a major challenge for high productivity in wheat, the most widely grown crop in Germany. Extreme weather events including dry spells and heat waves, which negatively affect wheat yields, are expected to aggravate in the future. It is crucial to improve the understanding of the spatiotemporal development of such extreme weather events and the respective crop-climate relationships in Germany. Thus, the present study is a first attempt to evaluate the historic development of relevant drought and heat-related extreme weather events from 1901 to 2010 on county level (NUTS-3) in Germany. Three simple drought indices and two simple heat stress indices were used in the analysis. A continuous increase in dry spells over time was observed over the investigated periods from 1901–1930, 1931–1960, 1961–1990 to 2001–2010. Short and medium dry spells, i.e., precipitation-free periods longer than 5 and 8 days, respectively, increased more strongly compared to longer dry spells (longer than 11 days). The heat-related stress indices with maximum temperatures above 25 and 28 °C during critical wheat growth phases showed no significant increase over the first three periods but an especially sharp increase in the final 1991–2010 period with the increases being particularly pronounced in parts of Southwestern Germany. Trend analysis over the entire 110-year period using Mann-Kendall test revealed a significant positive trend for all investigated indices except for heat stress above 25 °C during flowering period. The analysis of county-level yield data from 1981 to 2010 revealed declining spatial yield variability and rather constant temporal yield variability over the three investigated (1981–1990, 1991–2000, and 2001–2010) decades. A clear spatial gradient manifested over time with variability in the West being much smaller than in the east of Germany. Correlating yield variability with the previously analyzed extreme weather indices revealed strong spatiotemporal fluctuations in explanatory power of the different indices over all German counties and the three time periods. Over the 30 years, yield deviations were increasingly well correlated with heat and drought-related indices, with the number of days with maximum temperature above 25 °C during anthesis showing a sharp increase in explanatory power over entire Germany in the final 2001–2010 period.