Rain Season Research Articles

Assessment of Runoff and Soil Loss Under Natural Vegetation Cover and Rainfall in a Semi-Arid Catchment, West Pokot County, Kenya

Soil erosion has become a major cause of land degradation with regrettable economic losses. It has affected livelihoods of many agro-pastoral communities in Arid and Semi-arid Lands (ASALs). There is need for continuous assessment of soil erosion in these areas in order to provide sufficient data on soil loss for soil resource management, conservation, and land use planning. The purpose of this study was to determine the rate of soil loss by water for soil conservation planning in West Pokot County, Kenya. Two adjacent fields with variable vegetation cover density were identified in a semi-arid catchment for runoff plot research. Vegetation cover on the fields was measured using the transect line-intercept survey method. Field 1 had 25–50% vegetation cover while field 2 had 50–75% vegetation cover. On each field, three identical erosion plots with dimensions 20 m along the slope and 10 m wide were constructed. Runoff and sediment from the plots were measured for fifteen rainfall-runoff events during the long rains season. Data was analysed using correlation analysis and linear regression methods. The results show that runoff production varied from 1.03% to 1.44% of total rain water. Soil loss from the plots was 120.3–155.5 g/ . Runoff-rainfall correlation analysis showed a significant positive relationship (r =0.9609, P<0.05%) with 92.33% variance in runoff production. Soil loss had significant positive relationship with runoff (r =0.9840, P<0.05%) with 96.83% variance in soil loss. The study found that runoff production and soil loss was slow in the field with dense vegetation cover. Studies project an increase in human and livestock populations in semi-arid areas. This points at possible decrease in vegetation cover and increase in the rate of soil loss by water. The study recommends development of a soil conservation and management strategy in the study area.

Assessment of the impacts of landscape patterns on water quality in Trondheim rivers and Fjord, Norway

Abstract Due to the impacts of hydrological and ecological processes on water quality, discharges from upstream catchments have induced significant pollution to the recipients. This study aims to investigate the possible pollution sources from catchments with different types of land use and landscape patterns and develop the relationships between water quality and the catchment hydro-geological and environmental variables. Data from 10 monitoring sites in Trondheim formulated the basis of the case study. Thermotolerant coliform bacteria (TCB) and total phosphorus (TP) were applied as main indicators to represent the water quality in the recipient rivers, streams and in Trondheim Fjord. Based on the GIS-oriented spatial analysis, 15 hydro-geographical and landscape parameters were selected as explanatory variables. Multiple linear regression (MLR) models were developed at catchment and river reach scales to study correlations between the explanatory variables and the response variables, TCB and TP, in rain and snow seasons. The study showed that the spatial landscape patterns resulted in differences in the concentrations of TCB and TP in the recipients. The agricultural land was shown to be the main pollution source, leading to a higher concentration of TP in streams. Buildings, roads, and other impervious areas have induced an increase in both TCB and TP. In contrast, the forest areas, lakes, river density and steep river slopes were shown to have capacity to filter incoming P-rich runoff, thus prevent pollutant conveyance and accumulation in recipients.

Hydrophobic Effect of Soil Stabilization for a Sustainable Subgrade Soil Improvement.

The chemical process of using additives to stabilize soils is to improve soil that lacks strong engineering properties. In particular, the moisture susceptibility of subgrade soil through seasonal rains is still questionable. The presence of water in the construction is the cause of deterioration and premature distress of pavements and their supporting geotechnical structures. In this work, the chemical use of hydrophobic caltite (HC) in various amounts (ranging from 3%, 5%, to 7%) and 5% of cement to enhance laterite soils is investigated. The investigation includes the evaluation of soil properties, such as, unconfined compressive strength (UCS) by curing in air and under water, flexural strength (FS), and California Bearing Ratio (CBR) soaked and unsoaked. The addition of caltite with cement increases the strength characteristics with the UCS values of 2078–2853 kPa during the early curing stages (7th day), and 4688–4876 kPa after 90 days of curing. The added caltite in the cement soil samples shows a reduction index of strength loss underwater with the UCS values of 3196, 3334, and 3751 kPa for caltite cemented soil when compared with cement soil alone. FS results suggest that the inclusion of caltite in cement means that post-peak behavior can be enhanced, reducing the brittleness and increasing the ductility. The successful reaction with soil additives occurred in the curing period of 7 days. In terms of the microstructural analysis, results show that HC with cement reduces the porosity, voids, and cracking of laterite soils. Furthermore, new polymer globules, products from the reaction, appeared on the clay particle surfaces, thereby reducing the water absorption. The addition of hydrophobic-caltite to the soil–cement mixture results in increased strength and reduced water absorption in a soil–cement mix, thus achieving a given strength value.

Simulated degradation of low-density polyethylene and polypropylene due to ultraviolet radiation and water velocity in the aquatic environment

Low-density polyethylene (LDPE) and polypropylene (PP) are the two main polymers with extensive applications. It might lead to plastic pollution and degradation in the aquatic environment. Former laboratory simulation studies of plastic degradation have been presented. However, most of the studies were only applied a single degradation agent without specific environmental conditions, which indicated a research gap. This research aimed to investigate LDPE and PP degradation under the influence of UV radiation and water velocity with specific environmental conditions. Five reactors of simulated aquatic environments were adjusted to desire calculated UV B dose of 158.98–438.91 W.S/cm2 and water velocity variations of the Surabaya River, one of Indonesia’s urban rivers that has been polluted by microplastics. The water velocity was set in high (0.3–0.6 m/s) and low ones (0.1–0.3 m/s) to represent the fluctuated river discharge at rain and dry seasons. Total simulation time of 480 h (8 h/day for 60 days simulation) has initiated LDPE and PP degradation. LDPE experienced more weight loss (3.07%) under the combined exposure of UV and high water velocity, than PP (2.37%) under high water velocity. Synergetic effects of photodegradation, physical-mechanical, and hydrolysis degradation mechanisms could affect more severe crack tip formation of LDPE and PP rather than in single agent simulation. Major surface morphology deterioration of LDPE and PP, changes in transmittance intensities, carbonyl index in this study have revealed the importance of combined exposure of UV radiation and water velocity to plastic degradation in the aquatic environment.

Atmospheric and oceanic conditions associated with early and late onset for Eastern Africa short rains

AbstractTiming of the rainy season is essential for a number of climate sensitive sectors over Eastern Africa. This is particularly true for the agricultural sector, where most activities depend on both the spatial and temporal distribution of rainfall throughout the season. Using a combination of observational and reanalysis datasets, the present study investigates the atmospheric and oceanic conditions associated with early and late onset for Eastern Africa short rains season (October–December). Our results indicate enhanced rainfall in October and November during years with early onset and rainfall deficit in years with late onset for the same months. Early onset years are found to be associated with warmer sea surface temperatures (SSTs) in the western Indian Ocean, and an enhanced moisture flux and anomalous low‐level flow into Eastern Africa from as early as the first dekad of September. The late onset years are characterized by cooler SSTs in the western Indian Ocean, anomalous westerly moisture flux and zonal flow limiting moisture supply to the region. The variability in onset date is separated into the interannual and decadal components, and the links with SSTs and low‐level circulation over the Indian Ocean basin are examined separately for both timescales. Significant correlations are found between the interannual variability of the onset and the Indian Ocean dipole mode index. On decadal timescales the onset is shown to be partly driven by the variability of the SSTs over the Indian Ocean. Understanding the influence of these potentially predictable SST and moisture patterns on onset variability has huge potential to improve forecasts of the East African short rains. Improved prediction of the variability of the rainy season onset has huge implications for improving key strategic decisions and preparedness action in many sectors, including agriculture.

Potential of the Coupled WRF/WRF-Hydro Modeling System for Flood Forecasting in the Ouémé River (West Africa)

Since the beginning of the 2000s, most of the West-African countries, particularly Benin, have experienced an increased frequency of extreme flood events. In this study, we focus on the case of the Ouémé river basin in Benin. To investigate flood events in this basin for early warning, the coupled atmosphere–hydrology model system WRF-Hydro is used, and analyzed for the period 2008–2010. Such a coupled model allows exploration of the contribution of atmospheric components into the flood event, and its ability to simulate and predict accurate streamflow. The potential of WRF-Hydro to correctly simulate streamflow in the Ouémé river basin is assessed by forcing the model with operational analysis datasets from the European Centre for Medium-Range Weather Forecasts (ECMWF). Atmospheric and land surface processes are resolved at a spatial resolution of 5 km. The additional surface and subsurface water flow routing are computed at a resolution of 500 m. Key parameters of the hydrological module of WRF-Hydro are calibrated offline and tested online with the coupled WRF-Hydro. The uncertainty of atmospheric modeling on coupled results is assessed with the stochastic kinetic energy backscatter scheme (SKEBS). WRF-Hydro is able to simulate the discharge in the Ouémé river in offline and fully coupled modes with a Kling–Gupta efficiency (KGE) around 0.70 and 0.76, respectively. In the fully coupled mode, the model captures the flood event that occurred in 2010. A stochastic perturbation ensemble of ten members for three rain seasons shows that the coupled model performance in terms of KGE ranges from 0.14 to 0.79. Additionally, an assessment of the soil moisture has been developed. This ability to realistically reproduce observed discharge in the Ouémé river basin demonstrates the potential of the coupled WRF-Hydro modeling system for future flood forecasting applications.

Carbon isotope composition for agronomic diagnostic: Predicting yield and yield response to nitrogen in wheat

Rainfed crops rely on two sources of water: stored soil water at sowing and seasonal rain. In strongly seasonal winter-rainfall environments, stored soil water at sowing is minor, and uncertain seasonal rainfall is a source of risk. In south-eastern Australia, under-fertilisation is a common outcome of nitrogen risk management with implications for wheat yield and mining of soil organic matter. Here we explore the use of carbon isotope composition (δ 13 C) to capture the effects of crop water status on grain yield in a context of nitrogen top dressing. In the sampled environments, crops receive at least 50% of seasonal rainfall by stem elongation, and at least 70% of seasonal rainfall by flowering. In a sample of 1518 plots, yield varied from 0.07 to 9.96 t ha -1 and correlated with δ 13 C measured with isotope ratio mass spectrometer (IRMS) at flowering (r = −0.76, p < 0.0001); this is consistent with the rainfall pattern and the physiology of the crop featuring a critical period for yield from 300 °Cd before to 100 °Cd after anthesis. In a sample of 135 plots, yield varied from 1.2 to 8.4 t ha -1 and correlated with δ 13 C measured with IRMS at stem elongation (r = −0.56, p < 0.0001). Yield response to nitrogen, defined as the difference between yield in fertilised crops (50–200 kg N ha -1 ) and unfertilised controls, correlated with δ 13 C measured with IRMS at stem elongation, except for late-sown crops. Mid-infrared spectroscopy (MIR) returned estimates of δ 13 C that agreed with δ 13 C measured with IRMS (calibration: R 2 = 0.82, RMSE = 0.53‰, n = 833; validation: R 2 = 0.70, RMSE = 0.75‰, n = 364). We conclude that a MIR based, high-throughput, affordable measurement of δ 13 C could be scaled to guide nitrogen management of wheat in winter-rainfall environments. • In a sample of 1518 plots, yield varied from 0.07 to 9.96 tha -1 and correlated with δ 13 C at flowering. • Yield response to nitrogen correlated with δ 13 C at stem elongation, except for late-sown crops. • Mid-infrared spectroscopy is a cost-effective, high-throughput approach to estimate δ 13 C for agronomic applications.

Landslide and Moving Ground Disasters in Sumurup Village, Trenggalek District, East Java, Indonesia: A Case Study

The research aims to analyze the impact of disasters that occurred in the Trenggalek Regency, East Java, Indonesia. Method: Descriptive impact analysis is used as a research method to analyze disaster events in examining disaster risk factors and as a basis for early stage designs to reduce the impact of disasters. Result: The natural disasters in Trenggalek Regency are caused by high rainfall, and for its own territory. Trenggalek Regency is surrounded by mountains and steep slopes. When rain season happened, water seeps into the ground but is difficult to drain, as a result of which the cliffs are prone to landslides. The cliffs have a very high or extreme level of security, so that the level of vulnerability and vulnerability to landslides and landslides is very likely. Conclusion: The visible soil conditions indicate that the condition is prone to landslides, coupled with its geological location in the fault zone, as well as its rock structure consisting of volcanic rock. The high intensity of landslides was also caused by the high intensity of rain. The management disaster resilience applied to prepare people around village of Sumurup.

The 2020 Maize Production Failure in Ghana: A Case Study of Ejura-Sekyedumase Municipality

This paper examines the causes of widespread maize production failure in Ghana during the 2020 minor growing season. A mixed-methods approach was used to study smallholder maize farmers in the Ejura-Sekyedumase Municipality to provide a holistic understanding of the factors behind the maize production failure and to inform policy interventions. The results show that the decline in maize grain yield was caused by the failure of the minor season rains and, more importantly, the destruction of maize plants by fall armyworms. Other factors including poor soils and inadequate farm inputs contributed minimally to the observed maize failures. The agronomic practices adopted by the farmers to mitigate crop failures were undermined by their inability to master the onset and cessation of rainfall, the ineffectiveness of pesticides to control the fall armyworms and financial challenges. It is recommended that the government promotes and supports rainwater harvesting to address the impacts of drought and pests on food crop production. Furthermore, to ensure sustainable food production, a combination of indigenous knowledge and scientific farm practices are crucial to accurately forecast the weather and to control the fall armyworms.

Evidence for widespread gene flow and migration in the Globe Skimmer dragonfly Pantala flavescens

The global population structure and dispersal patterns of Pantala flavescens (Fabricius, 1798) are evaluated using a geographically extensive mitochondrial DNA dataset, a more limited samples of nuclear markers, wing isotopic (δ²H) data and a literature review. No spatial or temporal haplotype structure was recovered between the samples. Isotope data suggest that most samples were immigrants at the collection locations. A literature review of migration events for the species confirms regular inter-and intra-continental migrations occur (the majority reported from Asia, Africa and Australasia), with individuals and swarms dispersing thousands of kilometers over land and oceans. Migrations coincide with prevailing winds and seasonal rains, which points to a mechanism we name the “pantropical Pantala conveyor belt”, suggesting widespread gene flow is possible for an aquatic insect with excellent flying ability linked to rapid larval development.

Seasonal dynamics of agro-meteorological drought in Mberengwa and Zvishavane districts between 2017 and 2020, Zimbabwe

Drought severity is increasing in Southern Africa which is affecting rain-fed agriculture, the main source of livelihood in most countries in this region. The study assessed the seasonal spatio-temporal dynamics of agro-meteorological drought between 2017 and 2020 in Mberengwa and Zvishavane districts. An empirical research design supported by quantitative geographical information system techniques for data analysis was adopted in this study. Remote sensing data and precipitation records from the Meteorological Services Department were main data sources in this study. Microsoft excel 2013, SPI generator and ArcMap 10.5 software were used for data analysis in this study. Results showed that both Mberengwa and Zvishavane districts experienced an increasing trend in spatial coverage of drought from 2017 to 2019 before a slight decline in 2020. From 2017, drought severity increased in terms of spatial coverage with this spatial distribution increasing to almost over ¾ of the wards in both Mberengwa and Zvishavane districts between 2018 and 2020. Since 2017, on a ward level basis, both districts have been experiencing late onset and early cessation of the rain season as shown by increasingly dry October, November and March, months which determine the length of crop growing season in these two districts. Results indicated that the month of March was drier in Mberengwa whilst the month of December was drier in Zvishavane, an indication of more mid-season dry spells in Zvishavane and earlier rainfall cessation in Mberengwa. Drought is worsening in both Mberengwa and Zvishavane districts; hence, long-term drought resilience interventions are required to improve drought resilience of communities in these areas. The study recommends the Government of Zimbabwe and other stakeholders of drought resilience building like CARE International, World Vision among others to prioritise launching of resilience building initiatives in most vulnerable areas whilst guided by fine empirical information on spatial distribution of drought.

A rapid sedimentary response to the Paleocene-Eocene Thermal Maximum hydrological change: New data from alluvial units of the Tremp-Graus Basin (Spanish Pyrenees)

A massive emission of light carbon about 56 Ma, recorded in marine and terrestrial sediments by a negative carbon isotope excursion (CIE), caused a short-lived (~170 kyr) global warming event known as the Paleocene–Eocene Thermal Maximum (PETM). The onset and core of this event is represented in the south Pyrenean Tremp-Graus Basin by two successive alluvial units, the Claret Conglomerate (CC) and the Yellowish Soils, which represent laterally juxtaposed depositional environments. It is generally agreed that these units record a dramatic increase in seasonal rain and an increased intra-annual humidity gradient during the PETM, but the timing of the sedimentary response to this hydrological change is a matter of debate. Some authors maintain that the CC was developed during the early, most intense phase of the carbon emission, others that its formation lagged by 16.5 ± 7.5 kyr behind the onset of the PETM. The latter claim was mainly based on the assumption that in two sections of this basin, Claret and Tendrui, the onset of the CIE occurs 3 and 8 m below the base of the CC, respectively. Here we show that in some zones between these two sections the CC was not deposited and the Yellowish Soil unit rests directly and conformably on the underlying Esplugafreda Formation. New δ 13 C org data from this intervening zone provide evidence that the onset of the CIE is situated just ~1 m below the Yellowish Soils. In adjacent sections the CC erosional base cuts down deeper than 5 m, thus removing or obscuring the chemostratigraphically-defined base of the PETM. A tentative estimate based on averaged sedimentation rates indicates that ~3.8 kyr, or less, may have elapsed from the onset of the CIE to the arrival of PETM alluvium into the Claret-Tendrui study area, less than half of the lowest estimate of previous authors. Since the study area was situated about 15 km from the source area, our new estimate supports a rapid response of the sedimentary system to the hydrological change at the onset of the PETM. • The PETM hydrological change is recorded in the Pyrenees by two alluvial units. • Between the PETM onset and the alluvial accumulation a lag of ~3.8 kyr is estimated. • The new data entail a rapid sedimentary response to the PETM hydrological change.

Crisis-induced intermittency in Mexican dam flows

Historical data from 4 different dams from Mexico have been analyzed in order to investigate on the nonlinear behavior. The dams are into 4 distinct hydrological basins, which are located at the north of Mexico where dry climate displays seasonal rain. The phase plane suggests the expanding and suddenly contractions of its orbits shows intermittency. The correlation dimension is derived by careful computing of two parameters: time delay and embedding dimensions. In addition, the scaling exponent is computed as well, which reinforces the appearance of intermittency. The computation of phase plane, correlation dimension, and scaling exponent allows us to find an underlying route to chaos from each of the dam time series. The Lyapunov exponents were employed in order to strengthen the conclusion about chaotic behavior. The results suggest that the intermittency (attributable to reliefs and reservoirs and their sudden effects) is the possible mechanisms to chaos at the nonlinear behavior of dam flows; however, stochastic nature deserves additional investigation.

Performance evaluation of metric measures for converting 30-min GPM rain data to 1-min for microwave applications in Tropical region of Nigeria: A multivariate approach

The quest for a one-minute rain rate is high because it is an important input for generating high accuracy of rain-induced attenuation and will in turn earn good use by radio engineers in designing good and high-quality terrestrial and satellite links. This study utilizes eleven (11) years (2008–2018) rain rate data obtained from a satellite-based program, the Global Precipitation Measurement (GPM) over five different locations in the South West, Nigeria, and 2 years (2017 and 2018) gauge measured rain rate data in one of the locations Akure, Nigeria for validation. The GPM platform was an improved satellite-based program over the Tropical Rainfall Measuring Mission (TRMM) for measuring tropical rainfall with spatial and temporal resolution. Hence, a good application of measured GPM rain rate data can be a good tool for estimating rain-induced attenuation if an adequate conversion is made for a one-minute integration regime as recommended by the \\International Telecommunication Union (ITU). The 30 min GPM rain rate data was converted to one-minute integration time based on a multivariate approach. The coefficient of determination of GPM rain rate data closely matches with the gauge and was found to be 0.9194. Analyses were also performed on seasonal bases for rain rate and rain-induced attenuation ranging from frequencies 10 GHz, to 30 GHz, to assess the seasonal trend between the two sources of data. The seasonal analyses were scaled as pre-monsoon, intensive, cessation, and dry months. A seasonal comparison shows that the GPM data presented the highest rain rate and rain attenuation during the intense rainy regime. Attenuations are considerably high at 0.01, 0.005, and 0.001 percentages of time. Overall, a deduction was made that the GPM rain rate measurements offered reliability in the estimation of rain-induced attenuation analyses in the tropical region of Nigeria due to the spatial–temporal coverage when compared with the rain gauge coverage which is sparse and costly to implement. This research has presented a reliable 30 min to one-minute integration time conversion model suitable for tropical locations, as well as information on seasonal rain attenuation statistics which would be utilized for effective satellite communication systems by the radio engineers.

Metagenomics indicate that public health risk may be higher from flooding following dry versus rainy periods.

Urban floodwater could lead to significant risk for public and environmental health from mobilization of microbial pathogens and overflow of wastewater treatment systems. Here, we attempted to assess this risk by obtaining metagenomic profiles of antibiotic resistance genes (ARGs), virulence factors (VFs) and pathogens present in floodwater samples collected in urban Atlanta, GA that were categorized in two distinct groups: floods that occurred after periods of drought and those after regular (seasonal) rain events. Even though no major (known) pathogens were present at the limit of detection of our sequencing effort (~3 Gbp/sample), we observed that floodwaters after drought showed a 2.5-fold higher abundance of both ARGs and VFs compared to floodwater after rainy days. These differences were mainly derived by several novel species of the Pseudomonas genus, which were more dominant in the former versus the latter samples and carried several genes to cope with osmotic stress in addition to ARGs and VFs. These results revealed that there are previously undescribed species that become mobilized after flooding events in the Southeast US urban settings and could represent an increased public health risk, especially after periods of drought, which warrants further attention.

Nutritive value of forages and diets in some small-scale dairy farms in Kiambu County, Kenya in the short rains season

Sixteen selected small-scale dairy farms were investigated in Kiambu County (Kenya) during the short rains seasonto develop a snapshot of the types of rations fed, milk yields obtained and sources of fodder. On average farmers had1 ha of land and 2.2 lactating cows yielding 8.93 kg milk/cow/d with feed intake of 10.5 kg DM/d. Only 35% of feedconsumed was produced on farm. Boma Rhodes grass hay and green Napier grass were the main forage components(37.9 and 28.3% of total DM). Protein forages used were the herbaceous legumes lucerne and desmodium (19.9 and15.9% CP, respectively) and leguminous shrubs (Leucaena, Calliandra and Sesbania with 21.1% CP and 43.4%aNDFom, on average). Grasses had higher aNDFom digestibility (47.1%) than legumes (39.7%). Napier grass, BomaRhodes grass, lucerne and desmodium had fiber digestibility of 51.9, 48.6, 46.8 and 32.6%, respectively. The energyand protein balances (actual vs. requirements) of the cows were on average -19.3 and -16.4%, respectively, indicatingthat cows utilized body tissues to produce the levels of milk obtained. Mutiple correspondence analysis showed that amilk yield higher than 9.1 kg/d was associated with a level of Boma Rhodes grass &lt;5 kg DM/d, concentration of nonfibrous carbohydrates in the diet &gt;22.0% (DM basis), concentrate level &gt;2.63 kg/cow/d and CP% in the ration &gt;9.1%. To improve milk yields during this season farmers should harvest grass forage at a younger age, include leguminous forage in the diets and increase the level of concentrates fed. These strategies should be demonstrated on farms to show possible benefits.

Land – sea contrast of diurnal cycle characteristics and rain event propagations over Sumatra according to different rain duration and seasons

This study investigated fundamental issues on diurnal cycle variations over Sumatra, especially concerning land - sea contrasts and rain event propagations according to changing rain duration and seasons. Based on the Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement (IMERG) final-run product version 6 covering 2015–2019 and observed precipitation data from 97 rain gauge stations, precipitation amount (PA), frequency (PF) and intensity (PI) were computed and analyzed. The land-sea contrasts in PA, PF and PI were apparent but the contributions to diurnal cycle of precipitation came mainly from PA and PF. Early morning peaks of PA and PF were observed in the coastal sea in contrast to afternoon and evening peaks in the land regions. Furthermore, the variations of peak times of PA and PF were also dependent on rain duration, particularly over land regions. The peak time of short-duration rain events (〈3h) over land regions manifested much earlier than long-duration rains (> 6 h). The precipitation system's peak time dependence on rain duration tended to affect westward and eastward propagations. Long-duration rain can migrate hundreds of kilometers from the coastline toward inland and offshore regions, whereas short-duration rain travels only tens of kilometers. For rain events over mainland, the initiation point of rain propagation often coincided with the highest point of the topography, indicating the prominent role of the island's mountainous areas in the development and propagation of the precipitation system. The propagation of rain events was also dependent on the width of Sumatra island where it was more prominent in equatorial and southern regions compared to the northern region where the width is narrower. Hence, the peak time of PA and PF showed little variation across northern Sumatra. In addition, the spatial patterns of PA, PF, and the number of rain events for different durations also showed seasonal variations due to the influence of the Inter-tropical Convergence Zone (ITCZ). However, the propagation features of rain events including peak time showed little evidence of variations with season.

A Study on Sensitivities of Tropical Forest GPP Responding to the Characteristics of Drought—A Case Study in Xishuangbanna, China

Droughts that occur in tropical forests (TF) are expected to significantly impact the gross primary production (GPP) and the capacity of carbon sinks. Therefore, it is crucial to evaluate and analyze the sensitivities of TF-GPP to the characteristics of drought events for understanding global climate change. In this study, the standardized precipitation index (SPI) was used to define the drought intensity. Then, the spatially explicit individual-based dynamic global vegetation model (SEIB-DGVM) was utilized to simulate the dynamic process of GPP corresponding to multi-gradient drought scenarios—rain and dry seasons × 12 level durations × 4 level intensities. The results showed that drought events in the dry season have a significantly greater impact on TF-GPP than drought events in the rainy season, especially short-duration drought events. Furthermore, the impact of drought events in the rainy season is mainly manifested in long-duration droughts. Due to abundant rainfall in the rainy season, only extreme drought events caused a significant reduction in GPP, while the lack of water in the dry season caused significant impacts due to light drought. Effective precipitation and soil moisture stock in the rainy season are the most important support for the tropical forest dry season to resist extreme drought events in the study area. Further water deficit may render the tropical forest ecosystem more sensitive to drought events.

Push-pull technology improves carbon stocks in rainfed smallholder agriculture in Western Kenya

Push-pull technology improves agricultural productivity. However, its long-term effect on biomass carbon and soil organic carbon (SOC) is not yet known. The aims of this study were: to assess the effect of push-pull technology on (1) biomass carbon and (2) SOC, considering climatic conditions and the length of time that push-pull had been practiced on a farm; and (3) to establish the relationship between biomass carbon and SOC on farms. Aboveground biomass carbon and SOC were measured on 36 farms in western Kenya, encompassing three contrasting sites (Bondo, Siaya and Vihiga) and six cropping systems (push-pull and five non-push-pull systems). Farms in western Kenya stock between 3.0 ± 0.3 and 4.0 ± 0.4 t C ha−1 in crop biomass and between 24.4 ± 2.1 and 37.0 ± 2.6 t C ha−1 in the soil for those practicing push-pull, and between 1.1 ± 0.3 and 2.1 ± 0.2 t C ha−1 biomass carbon and between 19.2 ± 2.1 and 31.1 ± 1.7 t C ha−1 soil carbon for those without push-pull. There was no correlation between biomass carbon and SOC. Adoption of push-pull offers opportunities to mitigate climate change through carbon sequestration in plants and soils in low-, medium- and high-rainfall environments in both long and short rain seasons.

Using real-time mobile phone data to characterize the relationships between small-scale farmers’ planting dates and socio-environmental factors

Accurate and operational indicators of the start of growing season (SOS) are critical for crop modeling, famine early warning, and agricultural management in the developing world. Erroneous SOS estimates–late, or early, relative to actual planting dates–can lead to inaccurate crop production and food-availability forecasts. Adapting rainfed agriculture to climate change requires improved harmonization of planting with the onset of rains, and the rising ubiquity of mobile phones in east Africa enables real-time monitoring of this important agricultural decision. We investigate whether antecedent agro-meteorological variables and household-level attributes can be used to predict planting dates of small-scale maize producers in central Kenya. Using random forest models, we compare remote estimates of SOS with field-level survey data of actual planting dates. We compare three years of planting dates (2016–2018) for two rainy seasons (the October-to-December short rains, and the March-to-May long rains) gathered from weekly Short Message Service (SMS) mobile phone surveys. In situ data are compared to SOS from the Water Requirement Satisfaction Index (SOSWRSI) and other agro-meteorological variables from Earth observation (EO) datasets (rainfall, NDVI, and evaporative demand). The majority of farmers planted within 20 days of the SOSWRSI from 2016 to 2018. In the 2016 long rains season, many farmers reported planting late, which corresponds to drought conditions. We find that models relying solely on EO variables perform as well as models using both socio-economic and EO variables. The predictive accuracy of EO variables appears to be insensitive to differences in reference periods that were tested for deriving EO anomalies (1, 3, 5, or 10 years). As such, it would appear that farmers are either responding to short-term weather conditions (e.g., intra-seasonal variability), or longer trends than were included in this study (e.g., 25–30 years), when planting. The methodologies used in this study, weekly SMS surveys, provide an operational means for estimating farmer behaviors–information which is traditionally difficult and costly to collect.