Intraseasonal Scales Research Articles

Intra-seasonal variations of dust activity over East Asia in spring 2023 and their mechanisms

Dust activity in East Asia has shown multi-scale temporal variations in the past. Many studies have been devoted to the interannual variations of dust activity, but little attention is paid to its variations at the intra-seasonal scale and our knowledge on this is still limited. Several dust storms have occurred over East Asia in spring 2023, which is taken as a good example for us to explore the intra-seasonal variations of dust activity. Based on station observations of dust events, meteorology reanalysis, and satellite observations of surface vegetation cover, here we find that there is much difference in dust storm activity between March and April of 2023 in terms of both the location and intensity. Dust storms mainly occurred in the central and eastern parts of Inner Mongolia and in the central and northern parts of Tarim Basin in March. In contrast, they mainly occurred in the western part of Inner Mongolia, eastern part of Northwest China, and a large region of Tarim Basin. For the regional mean number of dust storm days (NDS), it is significantly higher than the climatological mean value of 2003–2022 in April but lower for March of 2023. Further analysis reveals that the frequency of strong wind is below (above) the climatological mean for March (April) in the Tarim Basin and Gobi Deserts, indicating that wind speed may play a key role in the intra-seasonal variations of dust storm activity, although its effect is offset or enhanced by that of soil moisture and vegetation cover to a lesser extent. The shift of wind field is closely related to the evolution of geopotential height from positive anomaly in March to negative anomaly in April in Mongolia Plateau and southern Central Siberia at 500 hPa. Overall these results highlight the intra-seasonal variation of dust activity in spring 2023 in East Asia and the essential role of associated atmospheric circulation in driving this.

Resin acid δ13C and δ18O as indicators of intra-seasonal physiological and environmental variability.

Understanding the dynamics of δ13C and δ18O in modern resin is crucial for interpreting (sub)fossilized resin records and resin production dynamics. We measured the δ13C and δ18O offsets between resin acids and their precursor molecules in the top-canopy twigs and breast-height stems of mature Pinus sylvestris trees. We also investigated the physiological and environmental signals imprinted in resin δ13C and δ18O at an intra-seasonal scale. Resin δ13C was c. 2‰ lower than sucrose δ13C, in both twigs and stems, likely due to the loss of 13C-enriched C-1 atoms of pyruvate during isoprene formation and kinetic isotope effects during diterpene synthesis. Resin δ18O was c. 20‰ higher than xylem water δ18O and c. 20‰ lower than δ18O of water-soluble carbohydrates, possibly caused by discrimination against 18O during O2-based diterpene oxidation and 35%-50% oxygen atom exchange with water. Resin δ13C and δ18O recorded a strong signal of soil water potential; however, their overall capacity to infer intraseasonal environmental changes was limited by their temporal, within-tree and among-tree variations. Future studies should validate the potential isotope fractionation mechanisms associated with resin synthesis and explore the use of resin δ13C and δ18O as a long-term proxy for physiological and environmental changes.

Ensemble hydrological predictions at an intraseasonal scale through a statistical–dynamical downscaling approach over southwestern Amazonia

ABSTRACT We developed and analyzed the performance of an ensemble forecasting system for the Madeira River basin, the largest sub-basin of the Amazon, with forecasts up to 30 days under different hydrometeorological conditions. We used outputs from the regional Eta model of precipitation and global climatological data as inputs to a large-scale hydrological model. Bias correction of precipitation through quantile mapping significantly improved the results, achieving a hit rate >70%. The system demonstrated the ability to discriminate between high, medium, and low flow conditions. Forecast performance is better for larger catchment areas. This system is expected to increase decision-making efficiency for flood and drought situations in the largest Amazon tributary.

Intraseasonal response of marine planktonic ecosystem to summertime Madden-Julian Oscillation in the South China Sea: A model study

In summer, the Madden-Julian Oscillation (MJO) greatly influences the intraseasonal variability of the South China Sea (SCS). Previous studies have revealed MJO effects on surface chlorophyll (Chl) concentration, but the impact of the MJO on the ecosystem's structure and functionality remains unexplored. Here, we investigated the marine ecosystem response to the MJO by analyzing phytoplankton pigment data collected in cruises from 2010 to 2014. The results indicated the strong influence of the MJO on the structure of phytoplankton size classes (PSCs) in the upper 50 m of the SCS basin. To further explore the ecosystem's response to MJO, we utilized a well-calibrated physical-biogeochemical model (ROMS-CoSiNE) of the SCS to conduct numerical experiments with and without MJO forcings. Our model demonstrated that MJO-induced deep mixing and upwelling increased nutrients in the upper layer, increasing the Chl concentration with a higher proportion of nanophytoplankton (15 %) and a lower proportion of picophytoplankton (−20 %). Moreover, The MJO-forced model experiment exhibited a substantial enhancement in primary production (56 %) and export production (23 %), resulting in a notable decrease in the e-ratio. This reduction in the e-ratio cannot be attributed to changes in PSCs but can be explained by the time lag between primary and export production. This lag was prolonged by the physical processes of upwelling and mixing, which slows down the particle sinking. Our results emphasize the important role of MJO in regulating the ecosystem at intraseasonal scale, thus improving our comprehension of the nonsteady dynamics of ecosystems in the SCS.

Modulations of Madden–Julian Oscillation and Quasi-Biweekly Oscillation on Early Summer Tropical Cyclone Genesis over the Bay of Bengal and South China Sea

Abstract The Madden–Julian oscillation (MJO) and the quasi-biweekly oscillation (QBWO) are prominent components of the intraseasonal oscillations over the tropical Indo-Pacific Ocean. This study examines the tropical cyclone (TC) genesis over the Bay of Bengal (BOB) and the South China Sea (SCS) on an intraseasonal scale in May–June during 1979–2021. Results show that the convection associated with the two types of intraseasonal oscillations simultaneously modulates TC genesis in both ocean basins. As the MJO/QBWO convection propagated, TCs form alternately over the two basins, with a significant increase (decrease) in TC genesis frequency in the convective (nonconvective) MJO/QBWO phase. Based on the anomalous genesis potential index associated with the MJO/QBWO, an assessment of the influence of various factors on TC genesis is further assessed. Middle-level relative humidity and lower-level relative vorticity play key roles in the MJO/QBWO modulation on TC genesis. The MJO primarily enhances large-scale cross-equatorial moisture transport, resulting in significant moisture convergence, while the QBWO generally strengthens the monsoon trough and induces the retreat of the western North Pacific subtropical high, increasing the regional lower-level relative vorticity. The potential intensity and vertical wind shear make small or negative contributions. This study provides insights into the neighboring basin TC relationship at intraseasonal scales, which has a potential to improve the short-term prediction of regional TC activity. Significance Statement The Madden–Julian oscillation (MJO) and the quasi-biweekly oscillation (QBWO) are two types of intraseasonal tropical atmospheric oscillations. The development of tropical cyclones (TCs) is often accompanied by intraseasonal convection. This study highlights the distinct roles of MJO and QBWO in TC genesis over the South Asian marginal seas (e.g., Bay of Bengal and South China Sea). The QBWO can co-regulate TC genesis along with the background of the MJO, where the large-scale MJO mainly provides moisture, while the small-scale QBWO mainly contributes to vorticity. These findings provide useful information for subseasonal TCs forecasting. There are many developing countries along the South Asian marginal seacoast; therefore, further research on regional TC climate would help effectively reduce casualties and property damage.

Temporal and spatial patterns of hydroclimate variability related to the Pacific Decadal Oscillation in Michigan, USA

ABSTRACT Teleconnections play an influential role in driving atmospheric circulation and hydroclimatic variability at regional and global scales. While hydroclimatic conditions are associated with the Pacific Decadal Oscillation (PDO) throughout North America, to date there has been limited study on the influence of the PDO on the hydroclimate of Michigan. Using statistical analyses, this study quantified the mean monthly streamflow, precipitation and temperature characteristics in climate divisions and stream gage stations in both the Upper and Lower Peninsulas of Michigan during the warm (+) and cool (-) phases of the PDO from 1967 to 2018. Streamflow is greater statewide during PDO+ phases compared to during PDO- phases, and most prominent from August to February. During the peak month of streamflow difference by PDO phase, November, there was a streamflow increase of nearly 26% during PDO+ phases compared to the long-term mean. In relation, mean monthly precipitation increased (decreased) statewide from August to November during PDO+ (PDO-) phases, with decreased (increased) monthly precipitation from December to July. This study advances our understanding of the PDO’s influence on hydroclimatic variability in Michigan, presenting novel results at intra-seasonal scales in this highly impactful and populated region.

Impact of Pacific blocking on the intraseasonal winter sea ice seesaw between the Bering and Okhotsk Seas

The winter sea ice cover (SIC) over the Bering Sea (BS) and Okhotsk Sea (OS) shows significant co-variability. In particular, a clear seesaw-like variability can be observed on an intraseasonal scale between the two seas. However, the mechanism by which the atmospheric circulation affects them is unclear and further insight is needed. In this study, based on reanalysis data from 1979 to 2019, we use composite analyses to examine the physical processes of atmospheric blocking that affect the intraseasonal seesaw SIC changes between OS and BS. The investigation reveals that Pacific blocking (PB) events can enhance the existing intraseasonal seesaw variation of the OS and BS SIC in winter. Based on the maximum core position of the anticyclonic center, we divide PB events into two subgroups: western PB and eastern PB. In addition, considering average zonal shifting speed, we further classify them into three subgroups: westward shifting PB, quasi-stationary PB and eastward shifting PB. Composite results show that the changes of SIC and surface air temperature (SAT) show different asymmetric characteristics for the different PB subgroups. Of the five PB regimes, the quasi-stationary PB is associated with the greatest reduction in SIC in the BS over its lifetime, both in magnitude and duration. Furthermore, we find that the local sea surface temperature (SST) anomaly upstream of the quasi-stationary PB, both during and prior to its onset, exhibits a significant dipole mode, along with a positive anomaly in the 300-hPa zonal wind. The SST dipole could serve as a precursor climatic background condition, likely triggering the occurrence of quasi-stationary PB and subsequently leading to intense SIC changes.

Analysis of Diurnal Sea Surface Temperature Variability in the Tropical Indian Ocean

Based on the 30-year global hourly sea surface temperature (SST) dataset (MLSST) produced by the National Marine Environmental Forecasting Center, Ministry of Natural Resources of China, we analyzed the variability of diurnal sea surface temperature amplitude (DSST) of the tropical Indian Ocean at multiple time scales, as well as its influencing factors. The results show that the DSST in the Arabian Sea, Bay of Bengal, and equatorial Indian Ocean exhibits a bimodal seasonal variation with a semi-annual cycle, while the DSST in the southern Indian Ocean shows an annual cycle. The seasonal variation of DSST is mainly influenced by factors such as sea surface wind speed, shortwave solar radiation, and precipitation. The DSST in the equatorial Indian Ocean is generally higher during El Niño years compared to La Niña years. At the intraseasonal scale, the large standard deviation of DSST in boreal winter is mainly distributed in the southern hemisphere, while the large standard deviation of DSST in boreal summer shifts northward. The intraseasonal variation amplitude of DSST in boreal winter of the tropical Indian Ocean is greater than that in boreal summer. The DSST in the tropical Indian Ocean exhibits significant variation characteristics at multi-time scales. This study provides reference for numerical simulation of air-sea interaction patterns in the tropical Indian Ocean, as well as improvement of short-term climate prediction.

Distinctly Different Dynamical Processes in Maintaining the Intraseasonal NAO+ and NAO−

AbstractPositive feedback between high‐frequency eddies and low‐frequency processes is believed to play an essential role in the NAO evolution. In this study, however, it is found that the previously well‐studied upscale forcing to the intraseasonal scale window is mostly limited during the phase NAO−, but almost disappears during NAO+. The maintenance of the intraseasonal NAO+ is by a strong barotropic instability of the basic flow, which has been overlooked previously. The divergence of the Reynolds stress tensor that decelerates the basic flow is found to account for this asymmetry. For NAO−, there also exist strong interactions between the basic flow and the intraseasonal component, but the energy transfer is in a dipolar form, which, if integrated over space, contributes insignificantly as a whole. These new findings from a dynamics viewpoint shed insight deeper into NAO, a climate mode playing a key role in the Northern Hemisphere warming.

Study of the Dynamical Relationships between PM2.5 and PM10 in the Caribbean Area Using a Multiscale Framework

The Caribbean basin is a geographical area with a high prevalence of asthma due to mineral dust. As such, it is crucial to analyze the dynamic behavior of particulate pollutants in this region. The aim of this study was to investigate the relationships between particulate matter with aerodynamic diameters less than or equal to 2.5 and 10 μm (PM2.5 and PM10) using Hilbert–Huang transform (HHT)-based approaches, including the time-dependent intrinsic correlation (TDIC) and time-dependent intrinsic cross-correlation (TDICC) frames. The study utilized datasets from Puerto Rico from between 2007 and 2010 to demonstrate the relationships between two primary particulate matter concentration datasets of air pollution across multiple time scales. The method first decomposes both time series using improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) to obtain the periodic scales. The Hilbert spectral analysis identified two dominant peaks at a weekly scale for both PM types. High amplitude contributions were sustained for long and continuous time periods at seasonal to intra-seasonal scales, with similar trends in spectral amplitude observed for both types of PM except for monthly and intra-seasonal scales of six months. The TDIC method was used to analyze the resulting modes with similar periodic scales, revealing the strongest and most stable correlation pattern at quarterly and annual cycles. Subsequently, lagged correlations at each time scale were analyzed using the TDICC method. For high-frequency PM10 intrinsic mode functions (IMFs) less than a seasonal scale, the value of the IMF at a given time scale was found to be dependent on multiple antecedent values of PM2.5. However, from the quarterly scale onward, the correlation pattern of the PM2.5-PM10 relationship was stable, and IMFs of PM10 at these scales could be modeled by the lag 1 IMF of PM2.5. These results demonstrate that PM2.5 and PM10 concentrations are dynamically linked during the passage of African dust storms.

Combined impact of summer NAO and northern Russian shortwave cloud radiative effect on Eurasian atmospheric circulation

Based on ERA-Interim and CERES_SYN1deg Ed4.1 datasets, the combined influence of summer North Atlantic Oscillation (SNAO) and positive shortwave cloud radiative effect (SWCRE) events in northern Russia on Eurasian atmospheric circulation is investigated at the intraseasonal scale. The impact of the SNAO on the position of the North Atlantic storm track is modified combined with the Ural anticyclone anomaly contributed by positive northern Russian SWCRE anomalies, which could affect the summer stationary wave pattern. During positive northern Russian SWCRE events under SNAO+, the upstream wave train enhanced by the southward Ural anticyclone anomaly is easily trapped by the northward South Asian jets, thus propagating to low latitudes and causing extreme heat events in East Asia. Under SNAO-, the wave train propagates in the British–Baikal Corridor pattern along polar front jet towards the Far East, slowing down the dramatic melting of sea ice in the Laptev and East Siberian seas. Summer positive SWCRE events in northern Russian act as a bridge by promoting the emergence of the Ural anticyclone anomaly, influencing extreme weather in East Asia and Arctic sea ice variability.

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.

Unravelling δ13C signal in Scots pine trees for climate change and tree physiology studies

Stable carbon isotope composition (δ13C) recorded in trees responds sensitively to the changing environmental conditions and thus provides a powerful tool for paleoenvironmental reconstructions. The retrospective interpretation of tree δ13C signal depends on comprehensive understanding of how environmental and physiological signals are recorded in δ13C during photosynthesis and how the δ13C signal is modified after photosynthesis. This thesis aims to improve the understanding of photosynthetic and post-photosynthetic isotope fractionation processes, and to examine the suitability of tree ring δ13C for intra-seasonal reconstructions of intrinsic water use efficiency (iWUE). The former goal was studied by combining compound-specific isotope analysis of organic matter with isotope discrimination models and online δ13C measurements of leaf CO2 fluxes for field-grown mature Scots pine (Pinus sylvestris L.). The latter was achieved via comparing 18-year-long intra-seasonal iWUE chronologies estimated from laser ablation derived tree ring δ13C, gas exchange and eddy covariance data. Mesophyll conductance and time-integral effect of leaf assimilates had a clear impact on the intra-seasonal dynamics of leaf sugar δ13C. No significant use of reserves was observed for biomass growth of needles, stem or roots of Scots pine. Unlike sucrose, leaf bulk matters had a significant δ13C offset from new assimilates, leading to a distorted environmental signal documented in their δ13C. The reliability of tree ring δ13C data for intra-seasonal iWUE reconstructions was supported by an agreement of intra-seasonal patterns across the iWUE estimation methods. These results broaden our knowledge of the less well-known photosynthetic and post-photosynthetic isotopic fractionation processes, demonstrate the benefits of analysing sucrose δ13C for understanding plant physiological responses, and show that the tree ring δ13C based iWUE reconstructions can be extended to intra-seasonal scale. This information not only helps to better unravel δ13C signal in trees, but also improves reliable reconstructions of environmental and physiological signals from tree ring δ13C.

Estimating intraseasonal intrinsic water-use efficiency from high-resolution tree-ring δ13 C data in boreal Scots pine forests.

Intrinsic water-use efficiency (iWUE), a key index for carbon and water balance, has been widely estimated from tree-ring δ13 C at annual resolution, but rarely at high-resolution intraseasonal scale. We estimated high-resolution iWUE from laser-ablation δ13 C analysis of tree-rings (iWUEiso ) and compared it with iWUE derived from gas exchange (iWUEgas ) and eddy covariance (iWUEEC ) data for two Pinus sylvestris forests from 2002 to 2019. By carefully timing iWUEiso via modeled tree-ring growth, iWUEiso aligned well with iWUEgas and iWUEEC at intraseasonal scale. However, year-to-year patterns of iWUEgas , iWUEiso , and iWUEEC were different, possibly due to distinct environmental drivers on iWUE across leaf, tree, and ecosystem scales. We quantified the modification of iWUEiso by postphotosynthetic δ13 C enrichment from leaf sucrose to tree rings and by nonexplicit inclusion of mesophyll and photorespiration terms in photosynthetic discrimination model, which resulted in overestimation of iWUEiso by up to 11% and 14%, respectively. We thus extended the application of tree-ring δ13 C for iWUE estimates to high-resolution intraseasonal scale. The comparison of iWUEgas , iWUEiso , and iWUEEC provides important insights into physiological acclimation of trees across leaf, tree, and ecosystem scales under climate change and improves the upscaling of ecological models.

A modeling study of hydrographic and flow variability along the river-influenced coastal ocean off central Chile

The coast of central Chile has multiple rivers with a marked seasonal discharge variability. Few studies have addressed primarily the seasonal variability of river plume extension and vertical structure. Here, we have analyzed the effects of multiple river outflows on the hydrography (salinity and density) and meridional transports off central Chile. This study is focused on synoptic and intraseasonal scales of variability using eight years of semi-realistic model outputs. Our results reveal that the plume spreading is much broader during winter than spring. Wind-driven changes in plume shapes modulate the geostrophic component of the flow field off Biobío and Itata rivers in winter (spring) after downwelling (upwelling) favorable winds. The geostrophic flow was important off Mataquito and Maule rivers after upwelling-favorable winds, primarily in spring. The stratification in winter was mostly associated with the freshwater content in all coastal regions and showed a rapid response to the wind stress forcing. The mixing through wind stress decreased in spring, modifying the stratification and uncoupling the wintertime variability between stratification and freshwater.

Coping with Central European climate – xylem adjustment in seven non-native conifer tree species

The introduction of tree species raises the question of whether they find suitable conditions in their secondary range and whether they can successfully adapt to the new conditions in the context of an unstable climate. Stem secondary growth of trees and the changes in xylem cell structure make it possible to trace the adaptation process to the new climate on an inter- and intra-seasonal scale. The objective of this study was to determine whether the seven non-native conifer species in Central Europe differ in climate sensitivity and to what extent late frost and spring-summer drought can influence xylem changes. In our study, we investigated the growth pattern and xylem cell structure modifications of seven introduced conifer species Pseudotsuga menziesii, Pinus strobus, Tsuga canadensis, Abies grandis, Pinus banksiana, Pinus rigida, Pinus nigra, growing under uniform conditions in Poland. To determine species-specific temporal variations in climate sensitivity, we used stationary and non-stationary correlations of ring width with daily climate variables: mean, minimum, and maximum temperatures, precipitation sum, and SPEI, supported by a pointer-year analysis. Changes in xylem structure (frost rings and intra-annual density fluctuations) were analyzed using light and fluorescence microscopy. Warming of the winter-spring period benefits both southern European and North American introduced conifers, as reflected in the extended responsiveness period. However, as the growing season warms and the risk of late frosts increases, the potential for acclimatization of non-native species decreases, especially with respect to their juvenile growth phase. Negative precipitation and evapotranspiration balance at spring-summer period can lead to reduced growth and anomalies in earlywood xylem structure, commonly referred to as intra annual density fluctuations. P. strobus, the species that loses both frost-induced cambium damage and drought-induced xylem anomalies in summer is the fastest growing non-native species, along with P. menziesii. Although the results presented here show the potential and the limitations in the acclimatization of coniferous species, the obvious limitations related to local environmental conditions and the different ages of the trees make us cautious in generalizing the conclusions. Therefore, we call for the creation of a pan-European dendro-network of sites of non-native coniferous species.

Analysis of Intraseasonal Oscillation Features of Winter Cold Precipitation Events in Southern China

Based on the daily minimum air temperature (Tmin) data and the daily precipitation data from the NCC/CMA combined with the NCEP/DOE reanalysis data, the intraseasonal features and circulations of the winter cold precipitation events (CPEs) in southern China under the influence of strong Madden–Julian oscillation (MJO) were explored. The results show that: (1) Winter temperatures in southern China are characterized by intraseasonal oscillations (ISOs) of 10–30-d and 30–60-d, with six CPEs under strong MJO all occurring during these two intraseasonal scales in cooling phases. The invasion of cold air coupled with the availability of appropriate moisture conditions in southern China is more conducive to the CPEs. (2) A cyclone and anticyclone lying to the east of the Ural Mountains and the northwest of Lake Baikal at 925-hPa gradually move southeastward. The merging of the low-frequency (LF) blocking highs over the Ural Mountains and the North Pacific Ocean at 500-hPa leads to the contraction and southward movement of the LF cold vortex. The following anomalous northerly winds steer the cold air towards southern China. The cold advection is the dominant term in the cooling process, while the adiabatic cooling accompanied with ascending motion is also beneficial to the cooling process. (3) MJO has some effect on the LF blocking highs and the cold vortex in the mid-high latitudes and induces the CPEs over southern China. The joint effect of mid-high and low latitudes on the 30–60-d intraseasonal oscillation scale can have a significant impact on the cooling and precipitation processes of CPEs.

Intra-seasonal rainfall and piped water revenue variability in rural Africa

Rainfall patterns influence water usage and revenue from user payments in rural Africa. We explore these dynamics by examining monthly rainfall against 4,888 records of rural piped water revenue in Ghana, Rwanda, and Uganda and quantifying revenue changes over 635 transitions between dry and wet seasons.Results show operators experience revenue variability at regional and intra-seasonal scales. Revenues fall by an average of 30 percent during the wettest months of the year in climate regimes with consistent wet season rainfall. However, seasonally stable revenues are observed in areas where consecutive dry days are common during the wet season, potentially reflecting a dependency on reliable services. We also find changes in tariff level, waterpoint connection type, and payment approach do not consistently prevent or increase seasonal revenue variability.Local revenue generation underpins delivery of drinking water services. Where rainfall patterns remain consistent, piped water operators can expect to encounter seasonal revenue reductions regardless of whether services are provided on or off premises and of how services are paid for. Revenue projections that assume consistent volumetric demand year-round may lead to shortfalls that threaten sustainability and undermine the case for future investment. Intra-seasonal rainfall analysis can enhance rural piped water revenue planning by offering localised insight into demand dynamics and revealing where climate variability may increase dependency on reliable services.

Tropical and Polar Oceanic Influences on the Cold Extremes in East Asia: Implications of the Cold Surges in 2020/2021 Winter

East-Asia winter cooling and the associated atmospheric and oceanic influences were investigated based on the wintertime daily temperature and circulation fields during 1950–2020. Both the case study on the 2020/2021 cold surge and the large-sample clustering in the recent 71 winters extracted similar circulation signatures for East-Asia cooling, which are featured by the blocking-related anticyclonic circulation in North Eurasia, large-scale mid-to-high-latitude wave trains, decrease in the sea surface temperature (SST) in tropical Pacific, and the sea-ice cover (SIC) reduction in the Barents and Kara Seas (BKS). From the joint clustering of Eurasian circulation and temperature, two circulation modes that have a cooling effect on East Asia account for 41% of winter days. One of the two modes is characterized by the cyclonic circulation over Northeast Asia coupled with a southward-extending negative-phase Arctic Oscillation (AO−), whose cooling effect is mainly concentrated in central Siberia. The other cooling mode, featuring an anticyclonic circulation over the Urals and AO+ in middle-to-high latitudes, has a relatively stronger cooling effect on lower latitudes, including Mongolia and North China. In general, the occurrences of the mode with warming/cooling effect on East Asia show an overall downward/upward trend. The two cooling modes are significantly influenced by the La Niña-type SST anomaly and reduced SIC in BKS through large-scale wave trains, of which the tropical oceanic forcing mainly acts as a climatic background. Furthermore, the polar forcing is more tightly bound to internal atmospheric variability. Therefore, the tropical SST tends to exert impact over a seasonal scale, but the SIC influence is more significant below the intraseasonal scale; moreover, the synergy between the tropical and polar oceanic forcing can increase the East-Asia cooling days by 3–4% and cold extremes by 5%, mainly through enhancing the AO-related circulation mode.

Evaluation of diverse-based precipitation data over the Amazon Region

The skill of the diverse-based precipitation products is investigated in comparison with the observed-derived HYBAM and with GoAmazon and TRMM-LBA field campaigns data. The performance of eight remote sensing-based datasets (CHIRPS, MSWEP, TRMM, CMORPH, IMERG, PERSIANN-CDR, PERSIANN-CCS-CDR, and PERSIANN-CCS) is evaluated from 1998 to 2009 considering different timescales (diurnal, intraseasonal, and seasonal) for the Amazon Basin (AB). To compare the rainfall products, we applied cluster analysis, the Seasonality Index, the Kling-Gupta Efficiency metric, categorical indices, spectral analysis, and composing technique. Overall, the databases poorly represent the precipitation in the northwest of the AB (NWAB), a region with a lack of in situ measurements. CHIRPS underestimates NWAB precipitation at the seasonal scale, while at the intraseasonal timescale most databases do not adequately represent the precipitation anomalies in the NWAB, except for MSWEP. The PERSIANN-CCS-CDR product overestimates precipitation and extreme rainfall, while CMORPH overestimates the number of no rain events. At the diurnal timescale, most databases overestimate nighttime precipitation and underestimate it in the afternoon. Although there is no single database more suitable for the AB at all timescales, CHIRPS, MSWEP, and PERSIANN-CDR are the most accurate databases at seasonal timescale, while at the intraseasonal scale MSWEP would be the most appropriate. The estimates that combine reanalysis data, surface measurements, and infrared and microwave satellite data through more sophisticated techniques, such as artificial neural networks, can improve the representation of the rainfall in the AB, especially at the diurnal timescale.