Seasonal Rainfall Distribution Research Articles

Spatio-Temporal Trend Analysis of Annual and Seasonal Rainfall in Ho Chi Minh City

Spatio-temporal variations and trends in climatic variables play an essential role in the adaptation and mitigation of climate change policy. This study analyzed spatial and temporal variability of annual and seasonal rainfall in Ho Chi Minh City based on non-parametric statistical trend tests and spatial interpolation techniques. In particular, Sen’s Slope Estimator and Inverse Distance Weighting (IDW) methods were applied to construct the spatial distribution of annual and seasonal rainfall over the city. The outcomes show that annual and seasonal rainfall experienced significant increasing trends. Generally, these findings draw out an overall picture of rainfall variability in terms of space and time, which makes it possible for local decision-makers to promote more promising action plans in order to respond to natural disasters in the context of climate change.

Temporal Dynamics and Trend Analysis of Areal Rainfall in Muger Subwatershed, Upper Blue Nile, Ethiopia

This study was employed to investigate the temporal variability and trend analysis of areal rainfall in the Muger subwatershed, Upper Blue Nile, Ethiopia. The study was run over the following procedures to handle the main objective: (1) determining the areal rainfall from gauged point rainfall using the Thiessen polygon method, (2) grouping the months in the season according to the study area, (3) evaluating the temporal dynamics of annual and seasonal areal rainfall using the coefficient of variation (CV), standard anomaly index (SAI), and precipitation concentration index (PCI), and (4) analyzing the trend of annual and seasonal areal rainfall using modified Mann–Kendall’s (modifiedmk) test in RStudio. Based on the temporal variability analysis, CV results depict that annual and summer areal rainfall had low variability with values of 13.43% and 13.7%, respectively. Winter and spring areal rainfall shows high variation with a CV value of 50.5% and 36%, respectively. According to the SAI output, around 70% of the considered year was in the normal condition of wetness. On the other hand, the seasonal (winter, spring, and summer) rainfall distribution of the study area shows strong irregularity distribution throughout the considered years as a result of PCI with a value of 57.5%. The trend of the areal rainfall was shown to be both increasing and decreasing. However, the trend was insignificant with a 10% confidence level.

The implication of spatiotemporal rainfall distribution on the estimation of areal rainfall characteristics in Upper Erer Sub-basin, Ethiopia

Abstract The distribution of rainfall is not uniform in various regions of the world. Rainfall study is used to recognize the characteristics, duration, and variability of temporal and spatial rainfall distributions. In Ethiopia, the annual and seasonal rainfall distributions are variable in space and time. This study is focused on the implication of spatiotemporal rainfall distribution on the areal rainfall characteristics evaluation under the Upper Erer Sub-basin, located in Eastern Ethiopia. In the study area, average annual rainfall amount for Dire Dawa, Harar and Haramaya, Girawa, and Gursum stations are found to be 647, 816, 801, 958, and 840 mm with coefficients of variation of 23, 20, 20, 19, and 31%, respectively. However, the rain gauges here are sparsely distributed. The rainfall occurrence and distribution at various gauging stations have been found to vary significantly both temporally and spatially. The rainfall occurrence and distribution at various gauging stations had been found to vary significantly both temporally and spatially. The spatiotemporal rainfall distribution found in the stations was assessed using a joint probability of rain days approach. The result indicated joint probability of rain days estimation approach under monthly time step has better performance than daily, decadal, and seasonal data. The joint probability approach is used along with rainfall amount under monthly rainfall for areal rainfall estimation assessment in rainfall–runoff modeling.

Potentiality of Sustainable Maize Production under Rainfed Conditions in the Tropics by Triggering Agro-Physio-Biochemical Traits Ascertained from a Greenhouse.

A major portion of maize is produced under rainfed conditions in the tropics with relatively poor yield because of the unpredictable and irregular distribution of seasonal rainfall, as well as a decline in pre-rainy season rainfall due to climate change, so identification of sustainable production options is utmost needed. Thus, the present studies were conducted in a greenhouse (GH) to ascertain the water stress-tolerant traits of maize and at the field level in the tropical environment of Thailand to see the stimulating possibility of the ascertained traits in a locally popular cultivar using ethephon. Depending on tolerance level, three maize genotypes (Suwan 2301 > Suwan 4452 > S 7328) were tested under different water conditions-well-watered, short-term, and long-term water stress-in the GH. At the field level, the locally popular maize cultivar Suwan 5819 was examined with six ethephon levels (doses in g a.i. ha-1 of ethephon, i.e., T1, 281 at V6 stage; T2, 281 at V6 + 281 at V10 stage; T3, 281 at V10 stage; T4, 562 at V6 stage; T5, 562 at V6 + 562 at V10 stage; T6, 562 at V10 stage) against no ethephon application (T0) under rainfed conditions. Maize suffered from the scarcity of sufficient rainfall during 26-39 days after planting (DAP) and 43-63 DAP in the field. The yield index (YI) was identified from biplot analysis as one of the suitable standards for drought tolerance checks for maize at GH as well as at field level in the tropics. The YI value of observed agro-physio-biochemical traits of maize in GH showed that relative water content (RWC, 1.23), stem base diameter (SBD, 1.21), total soluble sugar (TSS, 1.15), proline (Pr, 1.13), aboveground plant biomass (APB, 1.13), root weight (RW, 1.13), relative growth rate (RGR, 1.15), specific leaf weight (SLW, 1.12), and net assimilation rate (NAR, 1.08) were the most desirable. Efforts were made to stimulate these traits under water stress at the field level. Ethephon application as T1 helped to gain higher kernel yield (KY) (5.26 t ha-1) with the support of higher RWC (90.38%), proline (24.79 µmol g-1 FW), TSS (1629 mg g-1 FW), SBD (24.49 mm), APB (271.34 g plant-1), SLW (51.71 g m-2), RGR (25.26 mg plant-1 day-1), and NAR (0.91 mg cm-2 day-1) compared to others, especially no ethephon application. Furthermore, the attributes SLW, SBD, Pr, heat utilization efficiency (HUE), 100-kernel weight, TSS, electrolyte leakage, and lodging percentage showed a substantial direct effect and significant correlation with KY. Aside from higher KY, ethephon application as T1 tactics resulted in higher values of energy efficiency (1.66), HUE (2.99 kg ha-1 °C days-1), gross margin (682.02 USD ha-1), MBCR (3.32), and C absorption (6.19 t C ha-1), indicating that this practice may be a good option for maize sustainable production under rainfed conditions.

Assessing seasonal variation and trends in rainfall patterns of Madhya Pradesh, Central India

Abstract Climate change is a worldwide problem caused by various anthropogenic activities, leading to changes in hydroclimatic variables like temperature, rainfall, riverine flow, and extreme hydrometeorological events. In India, significant changes are noted in its natural resources and agriculture sectors. In this study, we analysed the long-term spatio-temporal change in rainfall patterns of Madhya Pradesh, Central India, using Indian Meteorological Department high-resolution gridded data from 439 grid points. The coefficient of variance analysis showed low variability in annual and monsoon rainfall but significant variability in pre-monsoon, post-monsoon, and winter seasons, indicating considerable seasonal variation. Pre-monsoon rainfall exhibited an increasing trend (0.018 mm annually), while annual, monsoon, post-monsoon, and winter rainfall showed decreasing trends. Change point analysis identified shifts in rainfall patterns in 1998 (monsoon, annual), 1955 (pre-monsoon), 1987 (post-monsoon), and 1986 (winter). Spatio-temporal distribution maps depicted irregular rainfall, with some areas experiencing drastic declines in precipitation after 1998. The maximum average annual rainfall reduced from 1,769 to 1,401 mm after 1998 affecting water availability. The study's findings highlight a significant shift in Madhya Pradesh's seasonal rainfall distribution after 1998, urging researchers and policymakers to address water-intensive cropping practices and foster climate resilience for a sustainable future in the region.

Examining the past 120 years’ climate dynamics of Ethiopia

Climate change is one of the environmental threats around the globe. However, this change is not uniform throughout the world, both spatially and temporally. This study, therefore, examined the spatiotemporal (annual and seasonal) variability and trends of rainfall and temperature over Ethiopia from 1901 to 2020. Monthly rainfall and temperature (maximum, minimum, and mean) data were extracted from the latest version of the Climatic Research Unit (CRU 4.05) dataset. Using long-term seasonal rainfall patterns and pixel-based correlation techniques, five homogeneous rainfall zones were identified. The rainfall and temperature from CRU were validated using observed data from 235 and 145 meteorological stations, respectively. The results revealed that inter-seasonal rainfall and temperature variabilities are more pronounced than interannual variabilities in all rainfall zones. Only 19% (215,700 km2) and 3% (33, 900 km2) of the country’s total area experienced statistically significant (α = 0.05) decreasing and increasing trends of rainfall, respectively from 1901 to 2020. A statistically significant decreasing trend in rainfall with time was observed during the summer in only one zone that received rainfall in all months. A precipitation concentration index analysis revealed that the country exhibited a moderate to strongly irregular annual and seasonal rainfall distribution, except during the summer when the rainfall distribution was uniform. There was hence a high degree of rainfall seasonality throughout the study period. In addition to the devastating 1984 nationwide drought, Ethiopia also experienced local droughts for a number of 10 to 20 years. Unlike rainfall, there was a significant (α = 0.05) spatiotemporal increasing trend of temperature over the country. The spatial and temporal increasing trend of mean temperature over 120 years ranged from 0.24oC to 1.92oC and 0.72oC to 1.08oC, respectively. This increasing trend was higher in two zones located in the western and northwest parts of Ethiopia and the inflection points occurred after the 1970s in all zones. It is noteworthy that the maximum temperature increased at a lower rate than the minimum temperature. The warming trends and changes in rainfall patterns are likely to increase the frequency of climate extreme events and impact ecosystem services. This study suggests that climate change-sensitive zones require more attention and further study to enhance awareness of climate change in Ethiopia and facilitate adaptation to climate change and inform actions to mitigate adverse effects.

Phenology of Terminalia chebula tree in the Dry Deciduous Forest of Cauvery Wildlife Sanctuary, Karnataka, Southern India

The study was conducted at Cauvery wildlife sanctuary, Karnataka, India from 2015 to 2019. This study intended to understand the periodic events in biological life cycles concerning changes in the timings of seasonal events. It includes leafing, flowering, and fruiting patterns among the selected tree species of Terminalia chebula Retz., which is an important non-timber forest product (NTFPs) species in the Cauvery wildlife sanctuary. A total of 32 adult individual trees, from two transects at different places were selected and were observed at thirty days intervals. It was observed that there was a species-specific phenological relationship between the deciduous period and the initiation of seasonal rainfall and warm periods. Leaf maturity peak was in August. Leaf fall activity was in January before the arrival of an intense dry period. The reproductive phenology like flowering, fruiting, and fruit obsession was significantly varied across the different seasons among the observed tree species. The majority of tree species (56%) revealed synchronous flowering with Leaf flush activity. The results indicate that Leafing (58%) and flowering phenology (75%) occur during the dry period before the onset of first rains and fruiting, fruit fall timing was in consequence to utilize the growing season. Thus, species specificity was recorded concerning flowering and fruiting and was found to be with the seasonal rainfall distribution and in turn soil moisture availability in the study area. The results of the study would help in better management of fruiting tree species in natural forests.

Impact of dust aerosols on the Indian Summer Monsoon Rainfall on intra-seasonal time-scale

The Indian subcontinent is a major hotspot of aerosol loading and several studies have demonstrated the importance of interaction between Asian dust aerosols and the Indian Summer Monsoon Rainfall (ISMR). However, a few studies have suggested a declining trend in the pre-monsoon dust loading over the Indian region. The present study investigates how the decrease in dust emissions influences the intensity of the monsoon rainfall over the Indian region using a fully coupled Weather Research and Forecasting model coupled with chemistry (WRF-Chem). We have conducted two sets of simulation experiments for the June-July-August-September (JJAS) season of 2017: (1) a control experiment with the default dust aerosol emissions, and (2) a sensitivity experiment by reducing dust emissions by 60%. Our analyses show that the reduction in dust emissions significantly alters the spatial distribution of seasonal mean monsoon rainfall with enhanced rainfall over the Bay of Bengal (BoB) and eastern coastal regions, and decreased rainfall over the lower Indo-Gangetic Plain (IGP), and parts of Central India (CI). It is found that the low aerosol loading conditions alter the large-scale circulation patterns along the tropical/sub-tropical region centred between 15°N and 35°N and 40°E −130°E, and through dynamical feedback, strengthens the convective rainfall over the BoB region. As a result, the 10–20 days sub-seasonal mode of the ISMR strengthens, facilitating enhanced westward propagation of rain-bearing systems formed over northern BoB which provides substantial rainfall over vast regions of the Indian subcontinent.

Assessing Urban Flood Hazard Vulnerability Using Multi-Criteria Decision Making and Geospatial Techniques in Nabadwip Municipality, West Bengal in India

The flood hazard risks and vulnerability in the urban areas alongside major rivers of India have been gradually increasing due to extreme climatic events. The present study is intended to assess flood hazard vulnerability and potential risk areas and aims to ascertain the management strategies in Nabadwip Municipality, a statutory urban area of West Bengal. The multi-criteria decision making (MCDM) of selected criteria and geospatial techniques have been employed to determine the urban flood vulnerability in the study area. The study has been conducted using secondary datasets including relevant remotely sensed data and participant observation. The potential flood-affected zones have been determined using the normalized difference flood index (NDFI) and flood vulnerability index (FVI). The analysis of the standardized precipitation index (SPI) of 20 years of monthly precipitation shows the variability of seasonal rainfall distribution in the study area. Furthermore, the spatial distribution of the composite Ibrahim index of socio-economic development accents that the urban development of the study area was uneven. The municipal wards situated in the central and northeastern portions of Nabadwip Municipality were extremely vulnerable, whereas the western and southwestern wards were less vulnerable. It is also revealed from the strengths–weaknesses–opportunities–challenges (SWOC) of the principal management strategies of the flood situation analysis that the unplanned sewerage system is one of the most effective weaknesses in the area. All-embracing and integrative flood management strategies need to be implemented in the study area considering the intra-regional vulnerability and development for the resilient and sustainable development of the study area.

Changes in Rainfall and Temperature and Its Impact on Crop Production in Moyamba District, Southern Sierra Leone

Rainfall and temperature are the important variables that are often used to trace climate variability and change. A Perception study and analysis of climatic data were conducted to assess the changes in rainfall and temperature and their impact on crop production in Moyamba district, Sierra Leone. For the perception study, 400 farmers were randomly selected from Farmer-Based Organizations (FBOs) in 4 chiefdoms and 30 Agricultural Extension Workers (AWEs) in the Moyamba district were purposely selected as respondents. Descriptive statistics and Kendall’s test of concordance was used to analyze the data collected from the farmers and AEWs. Data for the analysis of variability and trends of rainfall and temperature from 1991 to 2020 were obtained from the Sierra Leone Meteorological Agency and Njala University and grouped into monthly, seasonal and annual time series. Regression analyses were used to determine the statistical values and trend lines for the seasonal and annual time series data. The Mann-Kendall test and Sen’s Slope Estimator were used to analyze the significance and magnitude of the trends respectively. The results of both studies show evidence of climate change in the Moyamba district. A substantial number of farmers and AEWs perceived a decrease in the annual rainfall amount, length of the rainy season, a late start and end of the rainy season, an increase in the temperature during the day and night, and a shortened harmattan period over the last 30 years. Analysis of the meteorological data shows evidence of variability in the seasonal and annual distribution of rainfall and temperature, a decreasing and non-significant trend in the rainy season and annual rainfall and an increasing and significant trend in seasonal and annual temperature from 1991 to 2020. However, the observed changes in rainfall and temperature by the farmers and AEWs partially agree with the results of the analyzed meteorological data. The majority of the farmers perceived that; adverse weather conditions have negatively affected crop production in the district. Droughts, high temperatures, and irregular rainfall are the three major adverse weather events that farmers perceived to have contributed to a substantial loss in the yields of the major crops cultivated in the district. In response to the negative effects of adverse weather events, a substantial number of farmers take no action due to their lack of knowledge, technical or financial capacity to implement climate-sensitive agricultural (CSA) practices. Even though few farmers are practicing some CSA practices on their farms, there is an urgent need to build the capacity of farmers and AEWs to adapt to and mitigate the negative impacts of climate change. The most priority support needed by farmers is the provision of climate-resilient crop varieties whilst the AEWs need training on CSA practices.

Evaluation of CORDEX‐CORE regional climate models in simulating rainfall variability in Rwanda

AbstractIn this study, three regional climate models (RCMs), CCLM5‐0‐15, RegCM4‐7 and REMO2015, from CORDEX‐CORE (AFR‐22) are evaluated in their ability to reproduce rainfall variability in Rwanda for the period 1981–2005. They are driven by three different global climate models (GCMs), namely MPI‐M‐MPI‐ESM‐LR, NCC‐NorESM1‐M and MOHC‐HadGEM2‐ES, and the European Centre for Medium‐Range Weather Forecasts Reanalysis (ECMWF‐ERAINT). Simulated rainfall is evaluated against observations from Rwanda Meteorology Agency to assess models' performance. A set of metrics are used to quantify discrepancies of models' simulations from observations. A possible association of El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) to rainfall over Rwanda is investigated. It is found that in general, all RCMs, their ensemble and multimodel ensemble means reproduce satisfactorily the spatial distribution of the mean seasonal rainfall (MSR), the mean rainfall annual cycle, and the interannual variability of the MSR for both March–April–May (MAM) and October–November–December (OND). However, significant biases in individual RCMs are observed with varying magnitude of bias in space. Observed MSR indicates a positive trend of 0.045 and 0.058 mm·day·year−1, respectively, for MAM and OND at 0.05 significance level, but almost all models indicate no significant trend (at 0.05 significance level). The seasonal correlations between observed rainfall anomalies and sea surface temperature (SST) anomalies indices across the tropical Pacific (Niño1+2 and Niño3.4) and Indian Oceans associated, respectively, with ENSO and IOD, although relatively weak, are reproduced by the three RCMs driven by ECMWF‐ERAINT and the multimodel ensemble means of ECMWF‐ERAINT and MPI‐M‐MPI‐ESM‐LR. Analysis of the Taylor diagram indicates that CCLM5‐0‐15_MPI‐M‐MPI‐ESM‐LR and the multimodel ensemble mean of MPI‐M‐MPI‐ESM‐LR outperform individual models. Overall, the evaluation finds reasonable model skill in representing seasonal rainfall climatology and variability, suggesting the potential use of CORDEX‐CORE (AFR‐22) RCMs for the assessment of future climate projections in Rwanda.

Assessment of climate characteristics and long-term trends of rainfall and drought in the Congo River Basin

AbstractThis study aims to assess patterns, variability, and trends of rainfall and meteorological drought and identify the different climatic zones using 42-year monthly TerraClimate gridded precipitation data at 23 sites distributed to cover the entire Congo River Basin. The spatial distribution of seasonal rainfall and the Köppen climate classifications indicated that the Congo River Basin has three main climatic zones. Where the highest rainfall is received in zone A (north of 2.5°N) during June–August (JJA), in zone B (3.5°S–2.5°N) during March–May (MAM) and September–November (SON), and in zone C (south of 3.5°S) during December–February (DJF). The Mann–Kendall (M–K) trend analysis of seasonal and annual patterns of rainfall and standardized precipitation drought index (SPI) revealed that there were significant negative trends in most of the three climatic Congo zones except for slight positive trends in small parts within zone C, especially during JJA, which are found sometimes in zone B. Finally, the three Congo climatic zones are characterized by negative trends for seasonal and annual data of both rainfall and the SPI, indicating increased drought risks in the Congo Basin except for small parts in zone C which have positive (wet) trends, especially during JJA followed by DJF.

A multi-decadal analysis of river discharge and suspended sediment load in three Texas coastal rivers in relation to hurricanes, seasonal rainfall, and ENSO

Coastal river discharge and sediment load exert major influence on the sustainability of coastal systems. Controlled by various hydroclimatic/hydrometeorological agents, they exhibit distinct trend/variability at different time scales. Coastal Texas, while being a major target for tropical cyclones over the past 6 decades, has been experiencing drought and flood cycles associated with ENSO in the long term. However, it is still unclear the temporal variability of river discharge and the associated sediment delivery over this area at different time scales, and the controlling factors behind it. In this study, a 58-years (1960–2017) dataset is compiled to analyze the influence of ENSO, seasonal rainfall distribution and hurricanes event on the river discharge and suspended sediment load of three Texas coastal rivers-the San Bernard River, the Brazos River, and the Trinity River, at annual, seasonal and event scales, respectively. In the short-term, all three rivers attained the highest average daily discharge and sediment load during Hurricane Harvey. On a seasonal scale, the precipitation regime exerts more influence on the Texas watersheds than tropical storms and hurricanes. Over a multi-decadal scale, amplified rainstorms during the El Niño phases likely play an important role in the overall discharge and sediment transport in large rivers along the northern Gulf coast. Overall, it is reasonable to conclude that the magnitude of hurricane impacts on the overall discharge and suspended sediment load is regulated by the duration and intensity of the rainfall, as well as the coupled drought-flood cycle in relation to the intensity of ENSO.

Development of an analytical probabilistic model to estimate runoff event volumes in South Korea

• A lognormal distribution best represents the rainfall characteristics of South Korea. • An analytical probabilistic model (APM) for lognormal distribution is developed. • The return period of APM is overestimated due to the seasonal rainfall distribution. • The APM adjustment magnitudes and the seasonal rainfall distributions are correlated. This study showed that the complex rainfall characteristics of South Korea, where rainfall is concentrated during a specific period, are poorly represented with a simple single parameter distribution. Thus, a two-parameter lognormal distribution that best represents the rainfall characteristics of South Korea was proposed by comparing four different distributions. Using this distribution, this study developed a suitable analytical probabilistic model (APM) to simulate runoff event volumes in South Korea and suggested an APM parameter-adjustment method based on rainfall characteristics. Thirty-year rainfall data recorded at ten stations were grouped based on the interevent time definition (IETD) of each station. With the grouped rainfall events, the probability density function (PDF) of the lognormal distribution was confirmed to best fit the rainfall event characteristic histograms in South Korea, including those of the rainfall event volume, duration, and interevent time. The APM was developed by deriving the PDF of the runoff event volume with a lognormal distribution, and a frequency analysis was performed based on the runoff event volume obtained by the APM and the Storm Water Management Model (SWMM) to verify the suitability of the derived model. The runoff event volumes output by the APM were compared with the runoff event volumes simulated by the SWMM. The exceedance probabilities and return periods output by the developed APM with a lognormal distribution were very close to the SWMM results. However, the return periods output by the APM were overestimated, and adjustment parameters were needed to match the outputs to the SWMM results. This study found a strong correlation between the adjustment parameters and the coefficients of variation in the average monthly rainfall. This result suggested that model parameter adjustments are necessary before applying an APM to rainfall datasets with large coefficients of variation in average monthly rainfall data.

Rainfall dynamics observed over India during last century (1901–2020) using innovative trend methodology

Abstract This study investigates the spatio-temporal distribution and trends of seasonal rainfall for different meteorological sub-divisions (MSDs) of India using statistical analysis and the innovative trend analysis (ITA) method. The gridded dataset of daily rainfall for 120 years from 1901 to 2020 was obtained from the India Meteorological Department (IMD) and analysed using statistical results of mean rainfall, standard deviation, coefficient of variation, skewness, kurtosis, maximum seasonal rainfall, percent deviation of rainfall, number of rainy days, rainfall intensity, rainfall categorization, trend detection, and cross-correlation coefficients. The period was divided into three quad-decadal times (QDT) of 40 years each (i.e., 1901–1940: QDT1, 1941–1980: QDT2, and 1981–2020: QDT3). A general decrease in the number of rainfall events was observed in all the seasons except for a few MSDs of northwest India showing a rise throughout the pre-monsoon season in recent times (QDT3). Significant trends were detected using the ITA method in seasonal rainfall in nearly all the MSDs of India. Our findings are highlighting the qualitative and quantitative characteristics of seasonal rainfall dynamics at the MSDs level which will be useful for comprehending the rainfall dynamics as impacted by climate change and climate variability in India, and may further lead the policymakers and stakeholders for making the best use of available water resources.

Dynamics of Pedogenic Carbonate Growth in the Tropical Domain of Myanmar

AbstractPedogenic carbonate is widespread at mid latitudes where warm and dry conditions favor soil carbonate growth from spring to fall. The mechanisms and timing of pedogenic carbonate formation are more ambiguous in the tropical domain, where long periods of soil water saturation and high soil respiration enhance calcite dissolution. This paper provides stable carbon, oxygen and clumped isotope values from Quaternary and Miocene pedogenic carbonates in the tropical domain of Myanmar, in areas characterized by warm (>18°C) winters and annual rainfall up to 1,700 mm. We show that carbonate growth in Myanmar is delayed to the driest and coldest months of the year by sustained monsoonal rainfall from mid spring to late fall. The range of isotopic variability in Quaternary pedogenic carbonates can be solely explained by temporal changes of carbonate growth within the dry season, from winter to early spring. We propose that high soil moisture year‐round in the tropical domain narrows carbonate growth to the driest months and makes it particularly sensitive to the seasonal distribution of rainfall. This sensitivity is also enabled by high winter temperatures, allowing carbonate growth to occur outside the warmest months of the year. This high sensitivity is expected to be more prominent in the geological record during times with higher temperatures and greater expansion of the tropical realm. Clumped isotope temperatures, δ13C and δ18O values of tropical pedogenic carbonates are impacted by changes of both rainfall seasonality and surface temperatures; this sensitivity can potentially be used to track past tropical rainfall distribution.

Seasonal rainfall distribution drives nitrogen use efficiency and losses in dryland summer sorghum

Nitrogen (N) fertiliser inputs represent one of the largest variable costs in dryland cropping systems, and a key determinant of water-limited yield. Despite extensive research into microbial N losses via intermediate denitrification products such as N2O, limited research exists on total N losses, and the effect of increasing soil N surplus has on fertiliser use-efficiency is not clear. In this study, the fate of banded urea fertiliser N across crop uptake, soil residual N and N losses was determined using the 15N recovery technique over nine trials with four N rates (0, plus low, medium and high industry rates) across N responsive and non-N responsive sites over 3 years in dryland sorghum (Sorghum bicolor). On average, crop uptake efficiency ranged from 50% at the low and medium N rate (80 kg N ha−1) to < 38% at the highest N rate, and was as low as 5%. Nitrogen losses averaged 26.5% across all rates and trials. At the medium N rate, losses exceeded 18% in all trials, despite relatively dry seasons, and in some trials exceeded 34%. Losses of N were driven by large cumulative rain events and high early-season rainfall. In dryland systems, the inability of crops to acquire banded N fertiliser can potentially leave fertiliser stranded in the topsoil, leaving it vulnerable to losses.Download : Download high-res image (141KB)Download : Download full-size image

Meteorological Observation in the Central Kathmandu Valley using the First Automated Meteorological Observatory of Tri-Chandra Multiple Campus

The main meteorological features of the central Kathmandu valley, Nepal were investigated by means of the dataset recorded by the automated meteorological observatory of Tri-Chandra Multiple Campus (1295m a.s.l. and 27.708217oN, and 85.315369oE) from May 2018 to April 2021. Initially, this observatory was installed for laboratory work with promoting clean energy resources by phasing out mercury instruments, since the onset of the coronavirus pandemic the growing importance of having resilience in the meteorological observation system has been more clearly demonstrated. Now, this automated real-time meteorological observatory becomes a backbone of our academic system, whereby students and teachers can have direct access to the data source and can self-analyze the prevailing atmospheric condition. As the detailed picture of the seasonal and diurnal cycle of meteorological parameters over the central Kathmandu valley, Ranipokhari premises, has been unavailable, this study tries to outline the prevailing surface air condition more precisely. The analysis was made on the basis of seasonal and diurnal variations of the weekly and monthly mean of meteorological parameters. The results confirmed that the surface heating by solar radiation mainly drives the variation in surface meteorological parameters. It was observed that the daily minimum temperature is recorded just before dawn and a maximum by mid-day with lagging to the daily solar maxima. In the time, the relative humidity was derived in a reverse cyclic pattern. During the summer monsoon and winter monsoon season, when the diurnal range of solar intensity became lower, also the temperature, relative humidity, and wind strength possessed a smaller diurnal range. The seasonal rainfall distribution in central Kathmandu valley also agreed with the climatic normal, about 80% of the total annual rainfall is solely contributed by the summer monsoon season. Summer monsoon possesses some incoherent phase pattern of the diurnal cycle of mean rainfall with two comparable peaks, one as mid-night/nocturnal maxima and the other as of late afternoon maxima. While, the early morning rainfall intensity tends to decrease and attains its minima around late morning, whereby, the frequency of drizzle type of rainfall was most dominant.

Spatio-Temporal Analysis of Rainfall Dynamics of 120 Years (1901–2020) Using Innovative Trend Methodology: A Case Study of Haryana, India

As we know, climate change and climate variability significantly influence the most important component of global hydrological cycle, i.e., rainfall. The study pertaining to change in the spatio-temporal patterns of rainfall dynamics is crucial to take appropriate actions for managing the water resources at regional level and to prepare for extreme events such as floods and droughts. Therefore, our study has investigated the spatio-temporal distribution and performance of seasonal rainfall for all districts of Haryana, India. The gridded rainfall datasets of 120 years (1901 to 2020) from the India Meteorological Department (IMD) were categorically analysed and examined with statistical results using mean rainfall, rainfall deviation, moving-average, rainfall categorization, rainfall trend, correlation analysis, probability distribution function, and climatology of heavy rainfall events. During each season, the eastern districts of Haryana have received more rainfall than those in its western equivalent. Rainfall deviation has been positive during the pre-monsoon season, while it has been negative for all remaining seasons during the third quad-decadal time (QDT3, covering the period of 1981–2020); rainfall has been declining in most of Haryana’s districts during the winter, summer monsoon, and post-monsoon seasons in recent years. The Innovative Trend Analysis (ITA) shows a declining trend in rainfall during the winter, post-monsoon, and summer monsoon seasons while an increasing trend occurs during the pre-monsoon season. Heavy rainfall events (HREs) were identified for each season from the last QDT3 (1981–2020) based on the available data and their analysis was done using European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis Interim (ERA-Interim), which helped in understanding the dynamics of atmospheric parameters during HREs. Our findings are highlighting the qualitative and quantitative aspects of seasonal rainfall dynamics at the districts level in Haryana state. This study is beneficial in understanding the impact of climate change and climate variability on rainfall dynamics in Haryana, which may further guide the policymakers and beneficiaries for optimizing the use of hydrological resources.

More intense daily precipitation in CORDEX‐SEA regional climate models than their forcing global climate models over Southeast Asia

AbstractThe ability of regional climate models (RCMs) to accurately simulate the current climate is increasingly important for impact assessments over Southeast Asia (SEA), identified as one of the world's most vulnerable regions to climate change. In this study, we evaluate the performance of a set of regional high‐resolution simulations from the Coordinated Regional Climate Downscaling Experiment‐SEA (CORDEX‐SEA) in simulating rainfall over the region. Simulations of the 1982–2005 seasonal mean climatology of daily precipitation and precipitation distribution over land are compared to observations from different sources (i.e., in situ‐based and satellite‐based). We also evaluate to what extent the precipitation distribution in RCMs is closer to observations than their associated forcing global climate models (GCMs). Observational estimates of precipitation over SEA have large uncertainties, making the model evaluations complicated. Despite these difficulties, our results highlight that RCMs can reproduce some complexities in the spatial distribution of seasonal rainfall but generally have a larger wet bias than GCMs. This is particularly true for the extremes in which RCMs show a large overestimation of rainfall intensity. There are some precipitation quantiles and grid points in which RCMs show limited reductions in biases compared to observations, but there is no consistency across all simulations and RCMs are generally further away from observations than their forcing GCMs. We find that greater intensity in RCMs over CORDEX‐SEA compared to their associated forcing GCMs is firstly associated with the increased supply of moisture from both local and large‐scale sources. Second, a widespread increase in convective precipitation is found across the region in RCMs. Our findings suggest that a model's ability to simulate precipitation over the region relies more on the RCM setup itself (e.g., parameterization scheme), rather than its forcing GCM. This should be considered when assessing the reliability of RCM precipitation simulations for future projections.