Rainfall Anomalies Research Articles

Assessing Spatial Variability and Trends of Droughts in Eastern Algeria Using SPI, RDI, PDSI, and MedPDSI—A Novel Drought Index Using the FAO56 Evapotranspiration Method

Drought is one of the most severe natural disasters worldwide, but with a particular emphasis in sub-humid and semi-arid climates. Several indices have been created to appropriately identify drought’s characteristics and variability. The main objectives of this study consisted of analyzing the behavior of different indices applied in northeast Algeria and comparing them across a long-term data set (1961–2014). The SPI and RDI at 9-month time scales were compared to the PDSI and MedPDSI based on 123 rainfall stations and gridded PET data interpolated to all the locations. A principal component analysis (PCA) in S-mode with varimax rotation (RPC) was applied to the monthly values of all indices to analyze the spatiotemporal patterns of droughts. Two principal components were retained, which identified two sub-regions with coherent differences related to their distance from the Mediterranean Sea and the UNEP aridity index. Trends in the RPC scores were assessed using the modified Mann–Kendall (MMK) test and Sen’s slope estimator, which showed a fundamental difference between the two sub-regions. The RPC of all drought indices showed trends of decreases in the frequency and severity of droughts in the northern sub-region, and trends of increases in the frequency and severity of droughts in the southern region, where the climate is mostly semi-arid and arid. Only a few cases were statistically significant, mostly when using the PDSI and MedPDSI for the southern sub-region. The spatial patterns of moderate, severe, and extreme drought occurrences were similar for the SPI and RDI pair of indices based on the probability of rainfall anomalies, and for the Sc-PDSI and MedPDSI pair based on water balance anomalies. The interpretation of the spatial variability of droughts, mainly of the extreme ones, was supported by an analysis of semi-variograms. The novel index MedPDSI compared well with the other indices and showed advantages of performing the soil water balance following the FAO56 dual Kc method with the actual olive evapotranspiration instead of PET, and of better explaining the spatial variability of extreme droughts; in addition, the trends detected were significant for both the northern and southern sub-regions.

Extreme Heavy Rainfall Events at Mid-Latitudes as the Outcome of a Slow Quasi-Resonant Ocean—Atmosphere Interaction: 10 Case Studies

Based on case studies, the development of low-pressure systems leading to extreme precipitation events reveals common characteristics. They highlight the co-evolution of sea surface temperature (SST) anomalies and the clustering of mesoscale convective systems in characteristic period ranges according to harmonic modes of the annual declination of the sun. This suggests a quasi-resonance of the heat exchanges of the ocean and the atmosphere during cyclogenesis. The formation of coherent extensive positive SST anomalies in characteristic period ranges, which reflects various interactions from baroclinic waves at mid-latitudes, i.e., Rossby waves especially present where the western boundary currents move away from the continents, may be a precursor of an extreme heavy rainfall event. Fed by warm and humid air coming from coherent SST anomalies, the convective cyclonic system strengthens concomitantly with the formation of cut-off lows, favoring blocks. However, the concentration in space and time of large-amplitude rainfall anomalies requires a relative stability of the atmospheric blocking circulation during the slow maturation processes. Intensification of extratropical cyclones is presumably the consequence of natural and anthropogenic warming, which strengthens the mechanisms leading to the clustering of mesoscale convective systems. The present study should help to refine the prediction of these extreme events while contributing to enrich our understanding of their presumed link with global warming.

Interannual Variability of the Australian Summer Monsoon Sustained through Internal Processes: Wind–Evaporation Feedback, Dynamical Air–Sea Interaction, and Soil Moisture Memory

Abstract In northern Australia (NAUS), mean rainfall during the Australian summer monsoon (AUSM) season exhibits distinct interannual variability despite weak influence from tropical sea surface temperature (SST) variability. The present study investigates mechanisms for the strong and persistent rainfall anomalies throughout the AUSM season. When the AUSM is stronger than normal, the low-level monsoonal circulation intensifies in response to the stronger convective activity over NAUS. The intensified surface westerlies over the tropical southeastern Indian Ocean (SEIO) enhance oceanic evaporation locally and downstream moisture transport into NAUS. This wind–evaporation feedback is verified through a moist static energy budget analysis. For this feedback to work effectively, SST cooling due to the stronger AUSM should be weak enough not to suppress the oceanic evaporation in the tropical SEIO. Our mixed layer heat budget analysis based on an ocean model hindcast experiment reveals that anomalous downwelling in the subsurface SEIO, which is induced dynamically by the intensified monsoon westerlies, partially offsets the SST cooling. The land surface evaporation over the continental inland area is also enhanced significantly in the middle and later portions of the monsoon season associated with increased soil moisture, suggesting its memory effect for the persistence of rainfall anomalies. The AUSM variability can therefore be regarded as a self-sustaining internal variability in the atmosphere–ocean–land surface coupled system, rather than just an atmospheric internal variability. Significance Statement We aim to understand why summer monsoon rainfall in northern Australia varies markedly from one year to another even under the weak influence of large-scale sea surface temperature fluctuations, such as El Niño/La Niña. Our analyses based mainly on observational datasets reveal that wind-induced changes in oceanic evaporation south of Java significantly modulates the water vapor transport into northern Australia. We also find that ocean dynamics helps this wind–evaporation feedback process and continental soil moisture may act to prolong anomalous rainfall by its memory effect. This study shows the self-sustaining nature of the Australian summer monsoon variability under the atmosphere–ocean–land surface interactions, which deepens our understandings of the monsoon system.

El Nino/La Nina and IOD impact on Kharif season crops over western agro-climatic zones of India

Climate modes like ENSO (El Nino Southern Oscillation) and IOD (Indian Ocean Dipole) produce an impact on the monsoon rainfall over India. Monsoon rainfall is extremely important for the agriculture of our country. The impact of these climate modes on monsoon rainfall thus in turn affects the rain-fed crops (kharif). In this study, four kharif season crops namely rice (Oryza sativa), maize (Zea mays), pulses and sugarcane (Saccharum officinarum) are chosen over four arid/semi-arid agro-climatic zones of western India to study the effect of the climate modes on selected crops. The detailed analysis has been carried out to show the impact of rainfall in the El Nino/La Nina (phases of ENSO) and IOD years on the crop productions over the mentioned zones viz. (Central plateau and hills region; Western plateau and hills region; Gujarat hills and plains region; Western dry region) from 1966–2011. The results show that rice productions which require hot and humid conditions have been largely affected during drought years associated with El Nino which results in poor rainfall over all the zones. The production of pulses which does not require excess humid conditions shows marginal improvement during the neutral years or non-El Nino/non-La Nina years. Maize production seems to be better in La Nina years and worst in the El Nino years as La Nina years are responsible for good rainfall in all zones. El Nino years provide a minor impact on sugarcane productions in different zones. La Nina years are well suited for sugarcane production in all zones of our study as sugarcane requires a good amount of moisture. Positive IOD years are associated with poor crop productions as compared to negative IOD years mostly in all zones as most of the positive IOD years happen to be El Nino years. El Nino-rainfall relation being dominant than positive IOD-rainfall relation is, therefore, responsible for negative rainfall anomalies over the selected zones.

Spatiotemporal variability of soil moisture over Ethiopia and its teleconnections with remote and local drivers

Soil moisture is one of the essential climate variables with a potential impact on local climate variability. Despite the importance of soil moisture, studies on soil moisture characteristics in Ethiopia are less documented. In this study, the spatiotemporal variability of Ethiopian soil moisture (SM) has been characterized, and its local and remote influential driving factors are investigated. An empirical orthogonal function (EOF) and KMeans clustering algorithm have been employed to classify the large domain into homogeneous zones. Complex maximum covariance analysis (CMCA) is applied to evaluate the covariability between SM and selected local and remote variables such as rainfall (RF), evapotranspiration (ET), and sea surface temperature (SST). Inter-comparison among SM datasets highlight that the FLDAS dataset better depicts the country’s SM spatial and temporal distribution (i.e., a correlation coefficient r=0.95\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r=0.95$$\\end{document}, rmsd=0.04m3m-3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$rmsd=0.04{\\mathrm{m}}^{3}{\\mathrm{m}}^{-3}$$\\end{document} with observations). Results also indicate that regions located in northeastern Ethiopia are drier irrespective of the season (JJAS, MAM, and OND) considered. In contrast, the western part of the country consistently depicted a wetter condition in all seasons. During summer (JJAS), the soil moisture variability is characterized by a strong east–west spatial contrast. The highest and lowest soil moisture values were observed across the country’s central western and eastern parts, respectively. Furthermore, analyses indicate that interannual variability of SM is dictated substantially by RF, though the impact on some regions is weaker. It is also found that ET likely drives the SM in the eastern part of Ethiopia due to a higher atmospheric moisture demand that ultimately invokes changes in surface humidity and rainfall. A composite analysis based on the extreme five wettest and driest SM years revealed a similar spatial distribution of wet SM with positive anomalies of RF across the country and ET over the southern regions. Remote SSTs are also found to have a significant influence on SM distribution. In particular, equatorial central Pacific and western Indian oceans SST anomalies are predominant factors for spatiotemporal SM variations over the country. Major global oceanic indices: Oceanic Nino Index (ONI), Indian Ocean Dipole (IOD), Pacific warm pool (PACWARMPOOL), and Pacific Decadal Oscillations (PDO) are found to be closely associated with the SM anomalies in various parts of the country. The associationship between these remote SST anomalies and local soil moisture is via large-scale atmospheric circulations that are linked to regional factors such as precipitation and temperature anomalies.

Meridional circulation dominates the record-breaking “Dragon Boat Water” rainfall over south China in 2022

During the “Dragon Boat Water” season in 2022, record-breaking anomalous rainfall occurred over South China (SC). In this study, the causes of anomalous rainfall are investigated by using the novel moisture budget equation of three-pattern circulations. The results show that the anomalous rainfall over SC caused by the horizontal, meridional, and zonal circulations was −10 mm, 168 mm, and 45.3 mm, which contribute −5%, 86%, and 23% of the actual rainfall anomaly (195.1 mm), respectively, suggesting that the meridional circulation contributes most to anomalous rainfall, followed by zonal circulation, and horizontal circulation contributes negatively. Further analysis based on the three-pattern decomposition of the global atmospheric circulation shows that the spatial configuration of the anomalous horizontal circulation and vertical vorticity provides the background for generating the anomalous divergence and convergence of meridional and zonal circulations and further anomalous vertical velocity of the meridional and zonal circulations, ultimately resulting in anomalous rainfall.

Large‐scale forcing over the homogeneous regions of summer rainfall anomalies in southern Africa

AbstractFor the study region (southern Africa), regional and remote large‐scale climate forcing play vital roles in the seasonal rainfall variability. Thus, uncovering the nature of the relationship between large‐scale circulations and homogeneous regions of rainfall anomalies will enhance the predictability of seasonal rainfall at specific domains in southern Africa. Considering both land and adjacent oceans in southern Africa, six austral summer homogeneous regions of rainfall anomalies were classified using the rotated principal component analysis. The analysis of the physical processes associated with the modulation of the distinct rainfall variability patterns reveals that generally, regional variations in cyclonic/anticyclonic circulations and convergence/divergence in the adjacent oceans (and landmasses) modulate the regional convergence of moisture fluxes in southern Africa. Some classified rainfall variability patterns feature homogeneous landmasses that are contiguous with the adjacent ocean, revealing land and adjacent oceans that respond coherently to the large‐scale circulation anomalies associated with the time development of the rainfall variability pattern. Further, remote climate drivers were found to be distinctively related to the regionalized rainfall anomalies, implying that the respective homogeneous rainfall regions respond differently to the large‐scale forcing induced by the (remote) climate drivers over southern Africa. Specifically, among the climate drivers that influence the hydroclimate of southern Africa, variations in the Southern Annular Mode (SAM) and the El Niño Southern Oscillation are relatively more associated with regionalized summer rainfall anomalies in southern Africa. Above‐average Nino 3.4 index (i.e., El Niño) negatively correlates with regionalized summer rainfall anomalies over large parts of southern Africa. The positive phase of the SAM positively correlates with rainfall anomaly in the homogeneous summer rainfall region comprising the subtropical parts of southern Africa and the homogeneous summer rainfall region comprising the western equatorial parts of the study region.

Symmetric and asymmetric response of Indian Summer Monsoon rainfall to different ENSO decay phases in observations and CMIP6 models

The present study assesses the ability of the World Climate Research Programme's Coupled Model Intercomparison Project-6 (CMIP6) models in simulating the Indian Summer Monsoon (ISM) rainfall variability and its symmetric or asymmetric relationship with the El Niño–Southern Oscillation (ENSO) decay phase. The El Niño decays are classified into three categories based on their transition characteristics (rapid/slow) with respect to the subsequent boreal summer season, namely El Niño early-decay, El Niño mid-decay, and El Niño no-decay. Similarly, La Niña decays are also classified into the La Niña early-decay, La Niña mid-decay, and La Niña no-decay. In the case of El Niño and La Niña early-decay events, the observed summer rainfall anomalies over India are similar in spatial distribution and amplitude but opposite in sign, suggesting the symmetric rainfall response. This symmetric response is mainly due to the influence of the westward extension of western north Pacific (WNP) anomalous anticyclone/cyclone accompanied by tropical Indian Ocean (TIO) warming/cooling. In contrast to this, summers of El Niño and La Niña mid-decay events exhibited asymmetric rainfall anomaly pattern over India. This asymmetry in rainfall pattern between these two summers is attributed to differences mainly in the moisture divergence and low-level circulation over the Indo-Western Pacific region. Similar to El Niño and La Niña mid-decay cases, the summers of observed El Niño and La Niña no-decay events displayed ISM rainfall asymmetry. Differences in spatial distribution and magnitude of Sea surface temperature anomalies and related atmospheric circulation between these events mainly responsible for ISM rainfall asymmetry. Analysis of CMIP6 revealed that only ∼ 14% of selected CMIP6 models have simulated the rainfall anomalies somewhat correctly compared to observations during summers of different decay phases of ENSO. Further, symmetric/asymmetric response of summer rainfall anomalies over India between decay phases of El Niño and La Niña are not well captured by CMIP6 models. It is also noted that the CMIP6 models have displayed a tendency to simulate positive (negative) Indian Ocean Dipole conditions during the summers of El Niño no-decay (La Niña no-decay) events unlike in the observations.

The spatial distribution of debris flows in relation to observed rainfall anomalies: Insights from the Dolan Fire, California

A range of hydrologic responses can be observed in steep, recently burned terrain, which makes predicting the spatial distribution of large debris flows challenging. Studies from rainfall-induced landslides in unburned areas show evidence of hydroclimatic tuning of landslide triggering, such that the spatial distribution of events is best predicted by the observed rainfall anomaly relative to climatic norms rather than by absolute rainfall. In this paper, we test whether the spatial distribution of debris flows in response to rainfall can be similarly predicted by rainfall anomaly. The 520 km2 Dolan Fire burn scar in Monterey County, California, USA, spans a sharp hydroclimatic gradient and experienced a widespread storm in January 2021 that triggered floods and debris flows, providing a natural experiment in which to test this hypothesis. In this study, we use remote and field methods to map debris-flow response and examine its spatial heterogeneity. Together with rainfall data, our mapping reveals that the observed anomalies in peak 15-min rainfall intensity (I15) relative to the intensity of the 1-yr return interval storm predict debris-flow occurrence better than the absolute peak I15. Our findings indicate that debris-flow processes and threshold rainfall required for debris-flow initiation may be tuned to local hydroclimate.

Atmospheric impacts of local sea surface temperatures versus remote drivers during strong South China Sea winter cold tongue events

AbstractSea surface temperatures (SSTs) in the western part of the South China Sea (SCS) are cooler than in the eastern part in boreal winter, owing to a winter climatological cold tongue (CT). In this study, using a regional atmospheric model configured for the Maritime Continent, we assess the atmospheric impacts of local (or SCS) SSTs versus those from remote drivers (e.g., western tropical Pacific SSTs) during strong CT events with anomalously cool SSTs. In the local run, more rainfall is observed over the eastern SCS, but no significant atmospheric impacts are found over the CT region when SSTs associated with strong CT events are imposed within the SCS while climatological conditions are imposed elsewhere. SCS SST anomalies during strong CT events do not significantly modify the regional wind circulation. The lack of atmospheric response to SSTs over the CT region may be explained by the wintertime mean SSTs (i.e., <27–28°C) over the CT region that are inadequate to trigger deep atmospheric convection, while eastern SCS SSTs are high enough. The increase of anomalous positive moist static energy (MSE) near the sea level over the eastern SCS indicates underlying warm eastern SCS SST anomalies could be influencing positive rainfall anomalies. In the remote run, imposing climatological SCS SSTs but remote SSTs and lateral boundary conditions linked to strong CT events results in cyclonic wind and positive rainfall anomalies over the eastern SCS and Philippines, which are a Matsuno–Gill response to the diabatic heating anomalies over the warm western tropical Pacific SST anomalies. Positive rainfall and cloud cover anomalies associated with the cyclonic wind anomalies are due to the anomalous positive MSE import into the eastern SCS by horizontal advection.

The financial value of seasonal forecast-based cultivar choice: Assessing the evidence in the Central Rift Valley of Ethiopia

Among many other options, seasonal weather forecasts and the use of cultivars that are better adapted to local climate and climate variability have been discussed as two potential supporting measures to assist farmer adaptation to climatic variability and change. In this article, we evaluate the potential benefit of combining these two measures, i.e., choosing specific crop varieties based on seasonal forecasts – focusing on the Central Rift Valley in Ethiopia. We base our value of information analysis on the available records of field trial data for publicly released crop varieties. We find that experimental evidence must be extended and improved in order to provide reliable evidence of yield performance differences between crop varieties, which is an essential prerequisite for exploiting forecast information. Classification of cumulative seasonal rainfall based on the modified Rainfall Anomaly Index provides a sharper distinction than using the standard tercile-based approach employed in the Ethiopian seasonal forecast communication. Even with a fairly optimistic interpretation of the evidence with respect to exploitable yield differences, we find only modest benefits of seasonal forecasts at realistic forecast accuracy for the region. Given the empirical limitations when assembling long-run yield data, the presented results have to be understood as a first approximation. Apart from sufficiently accurate forecasts, success of forecast-based cultivar choice will depend on (i) more reliable evidence on performance differences between crop varieties under different weather conditions, and (ii) changes in the current seed breeding and distribution system in developing countries, because the full potential of high-accuracy seasonal forecast information could only be tapped, if forecast-matching cultivars are being made available to farmers in time.

Impacts of climate change in the meteorological conditions during the period 2022 in Albania

The impacts of climate change on the meteorological conditions in our country, analysing the main climate indicators (temperatures, rainfall for the last year) will be addressed in this paper. In the last years, in our country, rising temperatures and seasonal rainfall anomalies were the two most encountered phenomena. The assessment of the meteorological conditions of each month during the last year and the comparison with the norm has enabled some conclusions to be drawn regarding different indicators of climate and its changes. Some of the results show an increase in the average annual air temperature by about +2.0°C, where in particular the summer season differ by +3.4°C, while precipitation marks a decrease around -13.1%, which is most pronounced in the season of winter by -30.4%. According to data analyses, the number of rainy days decreased by 18.8%. In recent years, due to the reduction in the number of rainy days and a lower cloud, there has been an increase of sunshine by about +5% in the area of Albania. The impact of these climate change indicators has had positive and negative impacts on various branches of the economy, such as energy, agriculture, transport, etc., but the most negative effects of the decrease of the precipitation and the increase of temperatures is related to droughts.

The Regional Diagnosis of Onset and Demise of the Rainy Season over Tropical and Subtropical Australia

Abstract In this paper, we introduce a novel strategy to robustly diagnose the onset and demise of the rainy season using daily observed rainfall over seven specific regions across Australia, as demarcated by the Natural Resource Management (NRM) agency of Australia. The methodology lies in developing an ensemble spread of the diagnosed onset and demise from randomly perturbing the observed daily time series of rainfall at synoptic scales to obtain a measure of the uncertainty of the diagnosis. Our results indicate that the spread of the ensemble in the diagnosis of the onset and demise dates of the rainy season is higher in the subtropical region than the tropical region. Secular change of earlier onset, later demise, longer length, and wetter season are also identified in many of these regions. The influence of the PDO at decadal scale, ENSO and Indian Ocean dipole at interannual scale, and MJO at intraseasonal scale also reveals significant influence on the evolution of the rainy season over these regions in Australia. Most important, the covariability of the onset date with the length of the season and seasonal rainfall anomaly of the season is highlighted as a valuable relationship that can be exploited for real-time monitoring and providing an outlook of the forthcoming rainy season, which could serve some of the NRM regions. Significance Statement We document the rainfall variability during the rainy season over tropical, subtropical, and semiarid regions of Australia and relate them to modes of climate variability spanning from intraseasonal to secular time scales. The study highlights the varied influence of the modes of climate variability on various aspects of the evolution of the rainy season, such as its onset and demise dates and the seasonal rainfall anomaly over these Australian regions. The study uses 114 years of data and shows that the variations in the length of the rainy season and its seasonal rainfall anomaly are strongly dictated by variations of rainy-season onset date. This provides a quick seasonal outlook of the forthcoming rainy season by just monitoring the onset-date evolution in these regions.

Research on Rainfall Characteristics in Zhengzhou Based on Pearson Correlation Analysis and Moving Average Method

The occurrence of flood disasters is related to persistent heavy rainfall anomalies. Under the influence of climate anomalies, the rainfall, rainfall intensity and frequency in Zhengzhou have been rising in recent decades. In order to further describe the rainfall characteristics in Zhengzhou area, Pearson correlation analysis and moving average method are used to analyze the characteristics of precipitation in Zhengzhou from 1973 to 2020 from the Total amount, intensity and duration of precision. The results show that during this period, the average annual precision in Zhengzhou was 660 mm, and the top three years were 2003, 2016 and 1983. The annual average precipitation intensity in Zhengzhou is 3.12 mm/d, And the linear tendentiousness trends of heavy rain and torrential rain are -0.0008 d/a and -0.005 d/a respectfully. The above research in this paper can provide reference for the urban response plan and long-term construction planning under extreme precipitation conditions.

Fluvial connectivity in the Brazilian semi-arid, Araripe sedimentary plateau

This article aims at identifying and describing short-term connectivity scenarios in a semi-arid watershed in northeastern Brazil. The emergence of different decadal connectivity patterns is discussed, addressing the role of recent climatic inputs in triggering cut-and-fill erosive-depositional patterns within a valley bottom. A confluence stretch between a tributary and the stem channel was selected in order to analyze changes in connectivity and dysconnectivity patterns in response to climatic inputs from 2004 to 2014. The climatic behavior was assessed using the Rainfall Anomaly Index, which established dry and wet years, hence highlighting the relationship between connected and unconnected channel phases and a decennial precipitation dynamic. The years of 2004, 2008 and 2011 stand out as the rainiest and with the highest RAI values, in contrast to 2012, with a total rainfall of less than 600 mm and a RAI value below -2. The discrepancy between the 2012 rainfall total and the 2013/2014 biennium points to the relevance of this period for the reworking of alluvial deposits and connectivity resumption in the watershed. In the ephemeral drainages, connectivity is dramatically interrupted every dry season, creating fluvial disconnection. Dysconnectivity is characteristic of tropical semi-arid fluvial environments, but at landscape scale it may attest to the longevity of dry conditions, hence shall be addressed at time intervals ranging from a few days to thousands and tens of thousands of years.

Assessing the Impact of Long-Term ENSO, SST, and IOD Dynamics on Extreme Hydrological Events (EHEs) in the Kelani River Basin (KRB), Sri Lanka

Hydrological extremes are common throughout the world and can be considered a globally significant phenomenon with severe environmental and social consequences. In recent decades, especially in the second half of the 20th century, Extreme Hydrological Events (EHEs) have attracted extensive attention. Physiological and anthropogenic factors have increased the frequency and severity of hydrological extremes worldwide in the last few decades. Recently, it has become a significant environmental issue in Sri Lanka. Both floods and droughts are widespread throughout the country, and the influence of floods is becoming more common every year. Currently, the frequency and severity of EHEs in the Kelani River Basin (KRB), Sri Lanka, are very common and have increased due to climate variations. Therefore, this study focused mainly on evaluating the EHEs and the impact of long-term El Niño Southern Oscillation (ENSO), Sea Surface Temperature (SST), and Indian Ocean Dipole (IOD) dynamics on extreme events. Rainfall Anomaly Index (RAI) and Extreme Precipitation Indices (EPIs) were calculated to examine the EHEs and their spatial variability. In addition, the relationships between EHEs and ENSO were investigated using several climate indices based on SST anomalies. Both observed and satellite-derived daily precipitation from 1951 to 2019 were used to assess the EHEs in the KRB. The trend of EHEs and the change points were evaluated using the Pettitt test, and teleconnection with global indices was examined using the correlation coefficient in the R application. The result of the study revealed that the pattern of EHEs varied spatially from 1951 to 2019. The strong La Niña years showed a high degree of teleconnection with EHEs in April (r = 0.622 at 0.05 significance level) and August (r = −0.732 at 0.05 significance level). NINO3.4 and the Southern Oscillation Index (SOI) have shown a significant positive impact on EHEs in the Northeast Monsoon (NEM) period. This research on KRB will be a popular scientific measure that can provide scientific results and solutions for the comprehensive decision-making process in the future. Investigating the global physical changes that influence EHEs is critical to taking the necessary steps to reduce the severity of hydrological extremes in Sri Lanka.

Fire Dynamics in an Emerging Deforestation Frontier in Southwestern Amazonia, Brazil

Land management and deforestation in tropical regions cause wildfires and forest degradation, leading to a loss of ecosystem services and global climate regulation. The objective of the study was to provide a comprehensive assessment of the spatial extent and patterns of burned areas in a new deforestation frontier in the Amazonas state. The methodology applied cross-referenced burned area data from 2003 to 2019 with climate, land cover, private properties and Protected Areas information and performed a series of statistical tests. The influence of the Multivariate ENSO Index (MEI) contributed to a decreasing rainfall anomalies trend and increasing temperature anomalies trend. This process intensified the dry season and increased the extent of annual natural vegetation affected by fires, reaching a peak of 681 km2 in 2019. The results showed that the increased deforestation trend occurred mostly in public lands, mainly after the new forest code, leading to an increase in fires from 66 to 84% in 2019. The methods developed here could identify fire extent, trends, and relationship with land cover change and climate, thus pointing to priority areas for preservation. The conclusion presented that policy decisions affecting the Amazon Forest must include estimates of fire risk and impact under current and projected future climates.

INDICES DE SEVERIDADE DA SECA NO SEMIÁRIDO, PARAÍBA

The occurrence of annual and multiannual droughts in the Brazilian semiarid is a recurrent phenomenon that triggers a series of consequences, impacting the environment and the quality of life of the population inhabiting this region. Due to its location in the drought polygon, the Immediate Geographical Region of Monteiro – PB (REGIM does not diverge from this reality. Given the above, this research aims to correlate the DM, PNI, and RAI Severity Indices of Drought Events in the REGIM, through the historical rainfall series data, to classify the quantitative data on a monthly and annual scale and identify these cycles' Severity of Events (SDE) and consequently evaluate the variation of precipitation over time, identifying the dry and rainy periods. The research sourced monthly rainfall data from the Northeast Development Superintendence (SUDENE), National Institute of Meteorology (INMET), and Executive Agency of Water Management of Paraíba (AESA) to compose the spatial and temporal precipitation variability, which was calculated through the Normal Percentage Index – NPI (CUNHA, 2008), Decision Method – DM (GIBBS; MAHER, 1967) and Rainfall Anomaly Index – RAI (ROOY, 1965). Keywords: Rainfall Standardization Indices – Ipp; Severity of Events – SDE; Water Resources.

An assessment methodology for drought severity and vulnerability using precipitation-based indices for the arid, semi-arid and humid districts of Tamil Nadu, India

Abstract As the short- and long-term impacts of climate change are becoming more visible at smaller regional scales, frequent occurrence (absence) of erratic precipitation as well as water scarcity issues can be identified as reliable indicators for predicting meteorological droughts. A supervised declaration of meteorological drought based on available precipitation data requires an understanding of reliability and consistency of drought indices for appropriate severity classification. An attempt has been made in this study to critically evaluate the performance of six popular drought indices namely, Standardized Precipitation Index (SPI), China Z Index (CZI), Modified China Z Index (MCZI), Deciles Index (DI), Rainfall Anomaly Index (RAI), and Z-Score Index (ZSI) for four districts in Tamil Nadu falling under arid (Karur), semi-arid (Cuddalore), dry sub-humid (Kanyakumari) and moist sub-humid (Coimbatore) conditions based on 120 years of precipitation records. Results showed that the SPI and CZI provided similar quantification of drought events (about 18% of the total months) irrespective of their climatic considerations while ZSI and RAI resulted in overestimation of drought severity (about 30–47%). Based on the classification strategy adopted for the selected indices, a framework for drought vulnerability assessment is proposed in conjunction with the estimated drought severity classifications.

Impacts of atmospheric CO2 increase and Amazon deforestation on the regional climate: A water budget modelling study

AbstractGlobal air temperature increase has caused changes in the global climate such as droughts, floods and severe events. Land cover shifts and the increase in greenhouse gas emissions can intensify these impacts. Therefore, the application of Specific Warming Level 2 (SWL2) technique has been considered to evaluate the global warming issue in various climate scales, which may induce different responses in the climate system. The objective of this study is to evaluate the impacts of a doubling of current atmospheric CO2 concentrations as well as the influence of deforestation of the Amazon Forest on the climate of South America. In this study, the CPTEC‐BAM1.2 global model was used to simulate these processes. The first scenario of simulations considered doubled atmospheric CO2 concentration (2XCO2 = 776 ppm) and the second scenario is the total conversion of the Amazon Forest to pasture (DEF). In the third scenario both CO2 and deforestation are considered simultaneously (2XCO2 + DEF). A control simulation considers the natural Amazon Forest shape and a steady CO2 concentration of 388 ppm. Results suggest that the temperature increased in all scenarios, the highest increment in the 2XCO2 + DEF experiment (5.4°C in 2XCO2 + DEF, 5.1°C in DEF and 3.2°C in 2XCO2). The model simulated drastic negative rainfall anomalies in each of three scenarios (2XCO2 + DEF: −2.1 mm day−1, 2XCO2: −1.3 mm day−1 and DEF: −0.9 mm day−1). Besides less precipitation and evapotranspiration, shifts in moisture transport were identified in each of the three scenarios. The effect of doubled atmospheric CO2 produces results similar to deforestation for hydrological water budget changes, and total pasture conversion may intensify such changes.