Rainfall Episodes Research Articles

Assessing the impact of climate change on Combined Sewer Overflows based on small time step future rainfall timeseries and long-term continuous sewer network modelling

The evolution of the climate in the future will probably lead to an increase in extreme rainfall events, particularly in the Mediterranean regions. This change in rainfall patterns will have impacts on combined sewer systems operation with a possible increase of spilled flows, leading to an increase of untreated water volumes released to the receiving water. Due to the impact of overflows on the water cycle, local authorities managing combined sewer systems are wondering about the extent of these changes and the possibility of taking it into account in stormwater management structure design. To do this, rainfall data with a fine time step are required to better master the shape of the hyetographs that are crucial to get a relevant rainfall/runoff relationship in an urban environment. However, there are currently no simulations of future rainfall series available at a time step compatible with the needs in urban drainage field. In this work, future rainfall time series with a fine time step are elaborated with the aim to be used in urban hydrology. The proposed approach is based on simulations results from five regional climate models in the framework of the Euro-Cordex program. It consists in a spatial downscaling step followed by a temporal disaggregation. The rainfall time series obtained are then used as input for a calibrated and validated hydrological model to investigate the evolution of annual CSO volumes and frequencies by 2100. The results show an increase of annual spilled volumes between 13% and 52% according to the considered climate model. This increase will most likely be a problem regarding compliance of sewer networks in line with the water framework directive, particularly the current French regulations. No clear trends were observed on the CSO frequencies. If there is a consensus for all the carried-out simulations to conclude that the CSO volumes will increase, we must remember that actual regional climate models suffer from limited spatial and temporal resolution and don't explicitly solve convection processes. Due to this point uncertainty concerning the evolution rate remains important particularly for intense rainfall episodes. New generations of climate models are needed to accurately predict intense episodes.

Marine Heatwaves, Upwelling, and Atmospheric Conditions during the Monsoon Period at the Northern Coast of the Gulf of Guinea

Ocean conditions influence the economies and climate of West Africa. Based on the 30-year daily Optimum Interpolation Sea Surface Temperature (OISST) dataset during May–October, upwelling surface variability and marine heatwaves (MHWs) at the northern coast of the Gulf of Guinea are investigated. The cooling surface decreases more rapidly around Cape Palmas than around Cape Three Points and extends eastward. MHWs variability exhibits a frequent occurrence of such events since 2015 that is consistent with the observed oceanic warming and the decrease in upwelling surface. The empirical orthogonal functions performed on the annual cumulated intensity of MHWs show four variability modes that include the whole northern coast, an east–west dipole between the two capes, a contrast between the northern coast at the two capes and the meridional section east of 5° E, and a north–south opposition. These patterns show 3-year, 6-year, and 8-year trends, and are related to coastal upwelling at the northern coast of the Gulf of Guinea. Similarly, surface ocean and atmospheric conditions are modified according to MHW periods. These changes take place before, during, and after MHW events. These results could be used to understand how this change influences the marine ecosystem, the local fisheries resources, and the extreme rainfall episodes in West Africa.

Risks of seasonal extreme rainfall events in Bangladesh under 1.5 and 2.0 °C warmer worlds – how anthropogenic aerosols change the story

Abstract. Anthropogenic climate change is likely to increase the risk (probability of occurrence of a hazard) of extreme weather events in the future. Previous studies have robustly shown how and where climate change has already changed the risks of weather extremes. However, developing countries have been somewhat underrepresented in these studies, despite high vulnerability and limited capacities to adapt. How additional global warming would affect the future risks of extreme rainfall events in Bangladesh needs to be addressed to limit adverse impacts. Our study focuses on understanding and quantifying the relative risks of extreme rainfall events in Bangladesh under the Paris Agreement temperature goals of 1.5 and 2.0 ∘C warming above pre-industrial levels. In particular, we investigate the influence of anthropogenic aerosols on these risks given their likely future reduction and resulting amplification of global warming. Using large ensemble regional climate model simulations from weather@home under different forcing scenarios, we compare the risks of rainfall events under pre-industrial (natural; NAT), current (actual; ACT), 1.5 and 2.0 ∘C warmer, and greenhouse gas (GHG)-only (with pre-industrial levels of anthropogenic aerosols) conditions. Both GHGs and anthropogenic aerosols have an impact on seasonal mean rainfall over this region. In general, higher global mean temperature levels lead to higher rainfall and higher aerosol concentrations to lower rainfall, however the relative importance of the two factors varies between the regions. For extreme rainfall events, we find that the risk of a 1 in 100 year rainfall episode has already increased significantly compared with pre- industrial levels across parts of Bangladesh, with additional increases likely for 1.5 and 2.0 ∘C warming. Climate change impacts on the probabilities of extreme rainfall episodes are found during both pre-monsoon and monsoon seasons. Results show that reduction in anthropogenic aerosols will exacerbate the effects of GHG-induced warming and thereby increasing the rainfall intensity, which has otherwise attenuated the impacts. We highlight that the net aerosol effect varies from region to region within Bangladesh, which leads to different outcomes of aerosol reduction on extreme rainfall statistics and must therefore be considered in future risk assessments. While there is a substantial reduction in risk at 1.5 ∘C warming when compared to 2 ∘C warming, the difference is spatially and temporally variable too, specifically with respect to seasonal extreme rainfall events.

The Impact of Depopulation on Reduction of the Peaks of Torrential Floods in Selected Watersheds of the Southeastern Serbia

The processes of emigration, depopulation and deagrarization in hilly-mountainous border areas in Serbia have intensified in last several decades. These processes have resulted in land use changes which means that anthropogenic impact on environment has diminished so the agriculture areas have decreased and have made room to the other land use types. These changes should entail lower soil erosion, slower generation of surface runoff during rainfall episode as well as reduction of the peak discharges and destructiveness of a torrential flood event. In this paper, we quantified the influence of land use changes on surface runoff indicators for 15 watersheds in the Southeastern Serbia. The greatest reduction of the curve number (CNR) happened in the Toplodolska watershed (2.34), then the Korbevačka (1.98) and the Dojkinačka (1.60) watersheds. The decrease of maximal discharge of 100-year return period is presented on example of a small watershed of the Ravna reka and it equals to 11%. It is expected that noticed land use changes will have the same trend, meaning that CN numbers will continue decreasing. Alongside these spontaneous positive anthropogenic impact on lowering the peaks of torrential floods, there should be a set of other preventive measures implemented.

THE IMPACT OF DEPOPULATION ON REDUCTION OF THE PEAKS OF TORRENTIAL FLOODS IN SELECTED WATERSHEDS OF THE SOUTHEASTERN SERBIA

The processes of emigration, depopulation and deagrarization in hilly-mountainous border areas in Serbia have intensified in last several decades. These processes have resulted in land use changes which means that anthropogenic impact on environment has diminished so the agriculture areas have decreased and have made room to the other land use types. These changes should entail lower soil erosion, slower generation of surface runoff during rainfall episode as well as reduction of the peak discharges and destructiveness of a torrential flood event. In this paper, we quantified the influence of land use changes on surface runoff indicators for several watersheds in the Southeastern Serbia. The greatest reduction of the curve number (CNR) happened in the Toplodolska watershed (2.34), then the Korbevačka (1.98) and the Dojkinačka (1.60) watersheds. The decrease of maximal discharge of 100-year return period is presented on example of a small watershed of the Ravna reka and it equals to 11%. Alongside these spontaneous positive anthropogenic impact on lowering the peaks of torrential floods, there should be a set of other preventive measures implemented.

Contrasting Mesoscale Convective System Features of Two Successive Warm-Sector Rainfall Episodes in Southeastern China: A Satellite Perspective

Based on Himawari-8 satellite observations, the mesoscale convective system (MCS) behaviors of two successive but distinct warm-sector rainfall episodes (EP1 and EP2) on 6–7 May 2018 over southeastern China were compared, with the latter episode being a record-breaking rainfall event. Results showed that MCSs played a dominant role in EP2, but not in EP1, by contributing over 80% of the extreme rainfall total and all the 10-min rainfalls over 20 mm. MCS occurrences were more frequent in EP2 than EP1, especially in the coastal rainfall hotspots, along with more frequent merging processes. Overall, the MCS samples in EP2 were larger in size, more intense, and moved slower and more in parallel to their orientation, which facilitated local rainfall accumulation. Two new indices are proposed—the overlap index (OLI) and merging potential index (MPI)—to evaluate two MCS processes vital for rainfall production: the repeated passage of an individual MCS over given areas and the merging between MCSs, respectively. Both OLI and MPI in EP2 were significantly larger than in EP1, which tended to produce larger maximum rainfall amount and stronger 10-min rain rates in the following hour. These results demonstrate the potential value of satellite-based MCS information for heavy rainfall nowcasting, which is particularly significant for warm-sector rainfall with its limited predictability.

Analysis of the Influence of Deforestation on the Microphysical Parameters of Clouds in the Amazon

Studies have shown that deforestation can cause changes in energy, moisture, and precipitation flows, with implications for local and regional climate. These studies generally focus on understanding how the hydrological cycle is impacted by deforestation, but few studies have investigated these impacts on cloud microphysics in tropical forest regions. The objective of this study was to quantitatively evaluate the impacts of deforestation on the microphysical parameters of clouds, based on data extracted from active and passive orbital sensors from the TRMM satellite. The study area comprised the state of Rondônia, Brazil. The analyses of the microphysical parameters extracted from the Microwave Imager (TMI) and Precipitation Radar (PR) sensors of the 2A-CLIM and 2A25 products were performed considering a period of 14 years. The parameters analyzed were Rain Water Path (RWP), Ice Water Path (IWP), Surface Precipitation (SP), Freezing Level Height (FH), and Rainfall Type (RT). Land cover type data were extracted from the Project to Monitor Deforestation in the Legal Amazon (PMDA). Our results showed that local deforestation significantly altered the microphysical parameters of the study region. In general, the values of the microphysical parameters of the clouds in the transition areas (locations where forest pixels are neighbors to deforested pixels) were about 5–25% higher compared to forested and deforested areas associated with a higher frequency of episodes of convective rainfall possibly driven by mesoscale circulations. Correspondingly, forested areas had higher rainfall rates compared to deforested areas. Meanwhile, deforested areas had higher amounts for IWP, of around 1–16%, and FH, of around 2–8%, in relation to forested areas. Conversely, the RWP showed a decrease of around 2–20%. These results suggest that the microphysical structure of clouds has different characteristics when related to forested and deforested areas in the Amazon. This is useful for evaluation of simulations of cloud microphysical parameters in numerical models of weather and climate.

Comparative analysis of Sub division wise rainfall INSAT-3D vs Ground based observations

Rainfall monitoring during south west monsoon season both are very important ad crucial activity. It is important mainly because it is a boon for agriculture, a mirror for future for both social and economic activities and crucial for its measurements (ground as well as remote). In this current works authors made an attempt to know the performance of recently Space Application Centre (SAC), ISRO developed INSAT-3D improved rainfall algorithms (Hydro Estimator and corrected IMSARA) with actual ground based rainfall data by calculating the bias (Actual –Satellite) for each sub-division. The analysis is done for the southwest monsoon season -2021 in by calculating weekly, monthly and seasonal bias for each subdivisions of Indian domain. It is seen that both the algorithms behave similar fashion (both show increase or decrease, simultaneously) with actual data and mostly satellite overestimate with actual data ranges from ~ 20-40 mm. In some subdivisions bias reached within the range 40 -70 mm (except Konkan & Goa ). Almost 40 % of the subdivisions have bias within 0 to 20 mm range, however the variation on weekly, monthly or seasonal differs subdivision and magnitude-wise. Overall, both the algorithms captures and performance well the trends in weekly, monthly and seasonal accumulated rainfall values. Corrected IMSRA (IMC) algorithm perform slightly better (15-20 %) except heavy rainfall episodes during the monsoon season -2021. In both the heavy and very heavy rainfall cases Hydro Estimators pick up well and performs better (~ 10 -12 %) than IMC algorithm especially over orographic areas. In extremely heavy rainfall cases both the algorithms behave in the same manner and captures the events although it is differing magnitude wise. Seasonal analysis of monsoon 2021 rainfall shows that 8 subdivisions have negative biases in the range of 50-60 mm) and 24 subdivisions have negative biases in the range of 0-20 mm, except Konkan Goa, Coastal Karnataka & A & N Islands have positive biases. Therefore, there is need to strengthen the actual observation rainfall measuring network and re-examine the performance of algorithms with larger data sets so that current algorithms retuned as per changing scenario.

Breeding phenology of amphibians in a Mediterranean ephemeral stream (Ardèche, France)

We present the results of the monitoring of breeding phenology of an assemblage of eight species of amphibians in a Mediterranean ephemeral stream, located in the Ardèche department, France. For most species, during 11 consecutive years, phenology was rather constant from year to year, which is rather unusual in Mediterranean temporary ponds. The occurrence of summer breeding was not rare for three species: Pelobates cultripes (Cuvier, 1829), Pelodytes punctatus (Daudin, 1803) and Hyla meridionalis Böttger, 1874. Breeding occurrence is linked to rewetting events caused by active karst resurgences, fuelled by periods of intense rainfall episodes called “cévenol” episodes. We document for the first time a triannual breeding occurrence (spring, summer, and autumn), and an in situ record of a short tadpole development period, concerning particularly P. cultripes. The ecological factors which can explain this species richness and these unusual observations are outlined. In conclusion, we encourage the conservation and monitoring of amphibian communities in ephemeral streams, as the natural and scientific interests for this type of habitat are often underestimated.

Are Atmospheric Situations Now More Favourable for Heavy Rainfall in the Spanish Mediterranean? Analysis of Episodes in the Alicante Province (1981–2020)

Intense rainfall (≥100 mm/24 h) constitutes the most frequent atmospheric hazard on Spain’s Mediterranean coast; this phenomenon causes serious damage to property and kills or injures inhabitants. The Intergovernmental Panel on Climate Change, in its latest report in 2022, indicates that in the current climate change scenario, these episodes will become more frequent, hence the importance of analysing and characterising them. The present paper analysed intense rainfall episodes in the central sector of the Spanish Mediterranean coast (province of Alicante) in the 1981–2020 period. A total of 129 episodes were identified which have affected different areas of this province. The rainfall events were analysed by means of three synoptic classification methods subjective/manual and objective/automatic in order to assess the strengths and weaknesses of the two modalities. The main objective was to identify the most favourable atmospheric situations triggering intense rainfall in the study area. The period with the highest propensity for these episodes to develop was identified, as well as the geographical areas most affected in the study period. Autumn concentrates the biggest amount of intense rainfall episodes throughout the year. Herein, we attempt to demonstrate the relationship between atmospheric situation, accumulated rainfall volume, geographical area affected, and the most favourable period of the year for the development of these events. The main results of the synoptic analysis of extreme events show the coincidence, in the three classification methods used, that the existence of instability in the middle and upper layers of the atmosphere (DANA and troughs) and humid and warm E and NE surface flows are decisive. In addition, the warming recorded in the waters of the western Mediterranean in recent decades is related to extreme events.

Stuck in the Wild—The Hydrology of the Teklanika River (Alaska) in the Summer of 1992

In late spring of 1992, Christopher McCandless crossed the Teklanika River, west of Healy, Alaska (United States). His summer has been well documented both in the book and the movie ‘Into the Wild.’ In early summer of 1992, he attempted to cross back over the river, but was stopped by high waters and he died later that summer. This paper investigates the hydrologic conditions of the Teklanika River watershed. We consider both climatological conditions and also conditions during the summer of 1992. We run process-based snowpack and runoff models in order to estimate the river hydrograph at the point of Mr. McCandless’ attempted crossing. Our results demonstrate that the Teklanika river is very flashy during the summer, responding rapidly to strong episodic rainfall events. The main snowmelt signal occurred in mid-to-late May, after Mr. McCandless’ first crossing and before his second attempt. The specific day of his attempted re-crossing corresponded to a large runoff event, driven by rainfall. We conclude that Mr. McCandless had unfortunate timing and that, had he tried to cross a day or two earlier or later, the outcome may have been different. This paper is also an opportunity to explore the hydrologic compromises that must be made when trying to study ungauged, or poorly gauged, areas. There is a spectrum of choices regarding input datasets and methodological simplifications and the correct location on that spectrum will depend on the particular watershed the objectives and expectations of the study.

The extreme precipitation events of August 2018 and 2019 over southern Western Ghats, India: A microphysical analysis using in-situ measurements

The extreme rainfall events observed at the High-Altitude Cloud Physics Observatory (HACPO) in Rajamallay, Munnar (10° 9′19.94″N, 77° 1′6.65″E; 1820 m above MSL) over the southern Western Ghats (India) during the floods in 2018 and 2019 monsoon periods are investigated. The observations from Micro Rain Radar (MRR) and Ceilometer are used to analyze precipitation microphysics and the vertical distribution of clouds during the intense rainfall episodes on 14 - 16th August 2018 and on 8th August 2019. The drop size distribution (DSD) spectra during the 2018 event is characterized by a large number of small to medium-sized drops resulting in maximum reflectivity of 48dBZ with mass-weighted mean diameter (Dm) value of 1.2 mm. At the same time, the 2019 event is characterized by larger drops and resulted in high reflectivity of 53dBZ and Dm value shifted to 1.4 mm. The consistent increment of Dm and σm with slight variation in Nt during the intensive rain hours on 8th August 2019 shows a mixed-phase microphysical process that can invigorate the production of convective rainfall from deep cloud bands (217 K of cloud top temperature) with enhanced rain water content (22 gm−3). The parameters of scaled raindrop size distributions corresponding to higher rain rates (>50 mmhr−1) suggest that the microphysical process that control the variations in DSD is strongly number controlled during these extreme rainfall events. The DSDs are evolved from a consistent, widespread rainfall supported by anomalous moisture advection from the Arabian Sea in 2018 monsoon period. The moisture convergence occurred on the elevated terrains leads to an intense spell of rainfall in two consecutive hours and satisfies the occurrence of a mini-cloud burst (MCB) event on 8th August 2019 causing flash flood in the region.

Synoptic Features of August Heavy Rainfall Episodes Accompanied By a Quasi-Stationary Front Over the Korean Peninsula and Its Relationship With the Western Pacific Subtropical High

In this study, we investigated the synoptic features of the August 26–27, 2018 heavy rainfall episode, which was accompanied by a quasi-stationary front over the Korean peninsula, as well as its relationship with the climatological characteristics of the Western Pacific Subtropical High (WPSH), using reanalysis and observational data. Through a case study, we analyzed the synoptic environment and frontal structure of the heavy rainfall event by comparing it with a heavy rainfall event associated with a quasi-stationary front that occurred on June 26–27, 2018 (during the Changma period). The case study indicates that the environment and structure of the quasi-stationary fronts in both events exhibited common characteristic features: an extended WPSH and strong low-level winds along the western or northwestern edge of the WPSH and a northward tilted frontal structure. Although differences in the moisture transport path were observed (southwesterly for the Changma event and southerly for the August event), their contributions to maintaining the quasi-stationary fronts were comparable around the Korean peninsula. We further investigated the climatological characteristics of these two heavy rainfall episodes for a 30 year period (1990–2019). We identified heavy rainfall days similar to those of the case study using pattern correlations of the 850 hPa geopotential height anomaly. The occurrence frequencies for each period indicate that the environmental features of the Changma event can be regarded as the typical heavy rainfall environment during the Changma period, whereas the environmental features of the August event were not typical for heavy rainfall during August. The main difference between similar and different cases to the August event is the expansion of the WPSH. Analysis of the relationship between annual variations in the WPSH indices and the occurrence frequency of heavy rainfall days during each August period also indicates that heavy rainfall with a quasi-stationary front similar to the August event is closely related to WPSH expansion.

Effects of the Irrigation of Chelva Grapevines on the Aroma Composition of Wine

Climate change scenarios are predicting an increase in temperature as well as more scarce and torrential rainfall episodes. Due to this, an imbalance between grape technological and phenolic maturity is being observed, which detrimentally affects the grapes’ composition. In semi-arid areas, irrigation management is a main field practice used to influence grape ripening. The goal of the present study was to investigate the influence of vine irrigation on the aroma composition and sensory characteristics of La Mancha Chelva wines. Volatile compounds were studied by gas chromatography–mass spectrometry (GC/MS). A total of 75 aroma compounds were identified and quantified in Chelva wines elaborated with grapes of irrigated and non-irrigated vines. The results show that the application of irrigation during vine cultivation produced small changes in the concentration of wine volatile compounds. Nevertheless, it increased, in general, the intensity of the attributes of the main aroma sensory profile of the wines. According to the results, the vine irrigation of Chelva cultivated in the La Mancha region can be used as a method to increase the aroma of wines.

The sensitivity of the WRF-4DVar data assimilation system to the control variables: A study on heavy rainfall events over India

The impact of different formulations of background error covariances (BECs) is examined for three heavy rainfall episodes over north India with a regional 4-dimensional variational (4DVar) data assimilation (DA) system. Three BEC formulations are analyzed, in which two of them employ stream function and velocity potential (ψ and χ) and the third one uses zonal and meridional velocity components (v and v) as momentum control variables. The uv-based formulation is completely univariate whereas, the correlations among the control variables are taken into account in the ψχ-based formulations through linear regression relations. Among the two ψχ-based BECs, one uses univariate relation and the other one uses multivariate relations for the moisture field. The multivariate relationship allows for impacting the moisture analysis through the assimilation of temperature or wind observations. Three experiments are carried out for each case with cyclic 4DVar assimilation. The conventional surface and upper-air observations are assimilated in combination with atmospheric motion vectors (AMVs) and ocean surface winds. Free forecast for 48 h is performed from respective final analysis fields for all the experiments. The results indicate that the uv-based analysis fields are closer to the observations. A comparative analysis of the 4DVar experiments with the 3DVar DA system provided a critical insight on the role of the 4DVar DA system on implicitly accounting for the multivariate correlations. The precipitation forecasts confirm the improved performance of the ψχ-based experiment, when multivariate nature of the humidity is incorporated. The time evolution of the intense rainfall episodes over the location of maximum rainfall are relatively well reproduced in the uv-based experiment. The results indicate that the inclusion of multivariate humidity variable in the BEC formulation does have a significant impact on suppressing the excessive overestimation in rainfall intensity.

Observations of heavy short-term rainfall hotspots associated with warm-sector episodes over coastal South China

Coastal South China is frequently exposed to substantial rainfall within fronts-free environments during the presummer rainy season, which recurrently leads to severe disasters due particularly to the heavy short-term rainfall (HSR). The present study is motivated to identify the HSR hotspots over coastal South China through 10 notorious episodes of warm-sector heavy rainfall, with emphasis on the mesoscale features linking with the HSR hotspots. These episodes suggest complex rainfall features in the occurrence frequency and intensity. HSR mainly occurs rather over the coastal areas than the windward piedmont farther inland, and contributes over 80% to the rainfall accumulation in the regions of Yangjiang and Shanwei. Mesoscale topographies in both regions play an important role in the presence of HSR hotspots, but in different ways. Convergence perturbation line related to the inland mountains migrates southward, and enhances the preexisting convection along the coast resulted from the differential surface friction between land and ocean as well as small hills, which is the primary cause for the high frequency of HSR in coastal Yangjiang. While concave terrain drives cyclone-like perturbation, modulating the convection activity prior to the presence of HSR over Shanwei region. A cold dome induced by the previous convection dominates the mesovalley, furthering the subsequently convective enhancement at coastal zone. Collectively, both inland mountains and ocean-to-land friction regulate the mesoscale surface processes by governing the convergent wind perturbations and upscale convective growth, responsible for the HSR hotspots over the low-altitude coastal areas.

Mid-latitude alluvial and hydroclimatic changes during the Paleocene–Eocene Thermal Maximum as recorded in the Tremp-Graus Basin, Spain

A short episode (~170 kyr) of extremely high global temperatures that occurred ~56 Ma, known as the Paleocene–Eocene Thermal Maximum, is widely considered an ancient analogue of the ongoing anthropogenic warming. This ancient hyperthermal event consisted of three phases, onset, core and recovery, which are respectively represented in the mid-latitude south Pyrenean Tremp-Graus Basin by three successive terrestrial units, the Claret Conglomerate, the Yellowish Soils and the Gypsum-rich Unit, each of them recording a different sedimentary response to evolving climatic and hydrological regimes. The Claret Conglomerate is mainly made up of calcareous conglomerates and is acknowledged to record an abrupt hydrological change during the onset phase. This unit most likely formed in an alluvial megafan, an interpretation here reinforced with new architectural information and by comparison with naturally occurring small-scale fan-like accumulations. Assuming the similarity between the onset of the Paleocene–Eocene Thermal Maximum and the anthropogenic warming, recent hydrological and meteorological data from mid-latitude Spain were compiled for comparison purposes. This comparison concurs with published modelling results about hydroclimate changes in the Pyrenees during the hyperthermal event, postulating an enhancement of seasonal contrast with augmented frequency and intensity of floods but no significant change in total rain. Furthermore, the comparison suggests that the Claret Conglomerate accumulated during extreme rainfall episodes that mainly occurred in autumn. The Yellowish Soils are mostly composed of silty marls with ubiquitous small-sized carbonate nodules and intercalated calcarenites. The marls were deposited in floodplains and the calcarenites in point bars and crevasse splays of meandering rivers. The scarcity of conglomerates entails a near absence of strong currents, and the carbonate nodules perennial or seasonal arid conditions. These nodules occur within cumulate palaeosols, the development of which required regular sedimentary increments during inundations on the floodplains. Sedimentation rates of siliciclastic material on the floodplains increased significantly during the core of the hyperthermal event, as well as at river outlets in coastal settings, which shows that erosion was accelerated and rules out the occurrence of protective, dense vegetation. Combined, these characteristics suggest persistent very dry summers, but a smooth wet season without intense precipitation events. Lastly, the profusion of gypsum in the youngest unit is clear proof of an arid climate during the recovery of the hyperthermal event. In essence, the studied deposits provide a unique window into the sequence of hydroclimatic change during the rise, peak and decline of an ancient global warming event in a mid-latitude terrestrial setting, against which ongoing climate-change data and future projections can be compared.

Rainfall Variability during El Nino, La Nina and Neutral Years Over Karnataka

The El Niño-Southern Oscillation (ENSO) is a recurring climate pattern involving changes in the temperature of waters in the central and eastern tropical Pacific Ocean. The three phases of the El Niño–Southern Oscillation (ENSO) namely the neutral phase, El Niño and La Niña oscillations. El Niño refers to the above-average sea-surface temperatures that periodically develop across the east-central equatorial Pacific. It represents the warm phase of the ENSO cycle. La Niña refers to the periodic cooling of sea-surface temperatures across the east-central equatorial Pacific. The state of Karnataka is located on a table land in the angle where the Western and Eastern Ghat ranges converge into the Nilgiri hill complex. 41 year (1980-2020) average annual rainfall of Karnataka collected from the rain gauge station located under the farm universities of Karnataka and, SST and SOI data collected from NOAA were used to study the rainfall variability while ENSO events. The El Niño events will deviate the rainy winds towards eastern pacific region causing lesser rainfall on Indian sub-continent or draughts in some years, but when it comes to Karnataka El Niño events have given above average rainfall. There were 8 episodes of excess rainfall and 6 episodes of deficient rainfall during the 14 El Niño episodes, and 3 episodes of excess rainfall and 8 episodes of deficient rainfall during the 11 La Niña episodes. The remaining 16 episodes were neutral years, with 10 episodes having excessive rainfall and the remaining 6 having deficient rainfall. Hence the El Niño episodes is good when compared to La Niña episodes over Karnataka.

Changes in the Indian Summer Monsoon during the past 600 years: A high-resolution record from the Anshupa Lake, Upper Mahanadi Delta, Core Monsoon Zone of India

• Indian summer monsoon experienced alternate episodes of high and low rainfall. • The little ice age (LIA) was dominated by arid conditions. • Dominance of bacterial magnetism during LIA suggest low sedimentation rate . • Periodicities in χ lf reaffirm solar influence on Indian summer monsoon. The core monsoon zone (CMZ) is an ideal region for reconstructing the Indian summer monsoon rainfall (ISMR). Mineral magnetic and organic geochemical parameters have been measured for an AMS 14 C-dated sediment core from the Anshupa Lake, situated in the eastern part of the CMZ, to reconstruct changes in the paleo-monsoonal precipitation on a sub-decadal scale during the past 600 years. Based on the data obtained, two phases may be recognised in the sedimentation history of the lake over the past six centuries: Phase-I (1397 to 1850 CE) comprising sediments deposited during the Little Ice Age (LIA), and Phase-II (1850 CE to the Present) comprising sediments deposited after the LIA. The measured proxies show decadal to sub-decadal scale variations. The relatively low values of mineral magnetic parameters ( χ lf , χ hf , χ fd , SIRM, χ ARM / χ lf , χ ARM / S I R M , χ ARM / χ lf , and χ ARM / S I R M ) and more positive δ 13 C values during Phase-I suggest a weak ISMR compared to Phase-II. The variations in mineral magnetic parameters suggest that the ISMR was the lowest during the Spörer, Maunder and Dalton Minima, but strong during the intervening periods. This inference resonates with the δ 13 C and C/N profiles of the core. Bacterial magnetite is documented during the mid-16th to mid-17th century, suggesting warm and humid conditions in the intervening phase between the Spörer and Maunder Minima. The magnetic susceptibility ( χ lf ) data exhibit a number of periodicities similar to those shown by cosmogenic nuclide-derived Total Solar Irradiance (TSI) data, reaffirming a solar influence on the Indian summer monsoon in the core monsoon zone of India.

MJO Phase Swings Modulate the Recurring Latitudinal Shifts of the 2020 Extreme Summer‐Monsoon Rainfall Around Yangtse

AbstractConsidering the unprecedented extremity of the Meiyu episodes in early summer of 2020, here the authors perform a comprehensive study of the intraseasonal evolution characteristics of the observed rainfall round Yangtse as well as the potential modulating effect of Madden‐Julian Oscillation (MJO). Results suggest that the Meiyu rainfall manifests as recurring latitudinal shifts around Yangtse during June–July of 2020, corresponding well to the continued swings of MJO circulation and convection between Phase 1 and Phase 2. The MJO affects the meridional migration of the 2020 Meiyu rainfall mainly through regulating the westward extended ridge line and southwesterly of the anomalous anticyclone over the western North Pacific (WNP). Specifically, the northeastward propagation of boreal summer MJO from Phase 1 to 2 shifts the ridge line of the anomalous WNP anticyclone northeastward. Consequently, the associated southwesterly anomaly over the southeastern China penetrates to the north of Yangtse and enhances the lower‐tropospheric moisture flux convergence, supporting heavy precipitation there. However, when the MJO swings back to Phase 1, the anomalous southwesterly and moisture flux convergence retreat southward, so does the Meiyu rain band. The present results advanced our understanding of the interactions between the latitudinal shifts of extreme Meiyu rainfall episodes and MJO Phase swings.