Winter Extreme Precipitation Research Articles

Future changes in the influence of the NAO on Mediterranean winter precipitation extremes in the EC-Earth3 large Ensemble: The prominent role of internal variability

One of the largest uncertainties in future climate projections is the interplay between internally generated and externally forced changes. This study investigates the changes in the link between the North Atlantic Oscillation (NAO) and Mediterranean winter extreme rainfall and dry days by the end of the 21st century compared to present day. We compare two different future pathways and estimate the extent to which the NAO imprint is affected by the global warming level using the latest EC-Earth3 large ensemble historical and future experiments. It is shown that the expected range of winter extremes changes due to internal and unpredictable fluctuations of the NAO largely overcomes the signal associated with externally-forced NAO variations. The NAO is found to exert a similar control on European climate variability, regardless of the amount of warming. For most of the Mediterranean region, magnitude and even sign of projected changes in the NAO-congruent precipitation indices vary substantially across the individual ensemble members according to the corresponding evolution of the NAO. Internal variability provides an average basin-wide contribution of up to 90% or more to the total NAO-driven variability in SSP1–1.9, and of about 80% in SSP5–8.5. Sub-regionally, the anthropogenic component of the NAO link is more evident over the Iberian Peninsula and parts of the central Mediterranean. This emphasises the role of internal variability and related uncertainty in determining the future impact of the NAO via the large spread in the circulation responses. However, the NAO is found to exert a weaker influence on the extreme precipitation total variability in both future scenarios given their future marked increase in total intensity and variance as opposed to the negligible NAO-related trends. Opposite conclusions are drawn for dry days, which are projected to decrease in the future, especially in the northern Mediterranean. Thus, this study also highlights how the variability of future extreme precipitation intensity in the Mediterranean basin will be less dependent on the principal mode of internal climate variability, posing further challenges for prediction and adaptation to weather-related hazards.

Underlying physical mechanisms of winter precipitation extremes over India's high mountain region

AbstractExtreme precipitation events (EPEs) are among the most pervasive weather hazards in the western Himalayan region (WHR), posing widespread damage to life, infrastructure, and agriculture. This study investigates the synoptic and large‐scale characteristics linked to winter precipitation extremes over the WHR. EPEs are identified as events surpassing the 95th percentile threshold. A composite analysis is employed using two reanalyses—the fifth‐generation European Centre for Medium‐Range Weather Forecasts Reanalysis (ERA5) and the Indian Monsoon Data Assimilation and Analysis (IMDAA)—to elucidate the synoptic conditions conducive to EPEs. Our findings suggest that EPEs in the WHR are linked to an intensified subtropical westerly jet, characteristically shifted to south than normal. Enhanced kinetic energy in the upper troposphere, attributed to increased baroclinic instability, reinforces moisture convergence and strengthens synoptic‐scale circulation, triggering deep convection and supporting EPEs. Notably, the interplay of pronounced Rossby waves sinking over the WHR and regional orography significantly modulates the intensity of western disturbances (WDs). Employing clustering analysis, we observed that the strongest EPEs are linked to anomalous vorticity in the upper to middle troposphere, together with deep convection via strengthened WDs, suggesting the potential role of large‐scale influences. Using Lagrangian method, we identify that the Arabian Sea is the primary moisture source for EPEs in the WHR. We further delved into the role of large‐scale connections and EPEs through quasi‐resonant amplification (QRA) analysis. The findings unveil distinct QRA fingerprints in meridional temperature gradients along with notably magnified, quasi‐stationary midlatitude planetary waves characterized by zonal wave numbers 6/7/8 (baroclinic waves) contributing to EPEs. Overall, our results highlight the underlying physical mechanisms for winter precipitation extremes, emphasizing QRA's role in amplifying planetary waves and promoting EPEs, underscoring the WHR's vulnerability to evolving climatic conditions.

Analyzing urban influence on extreme winter precipitation through observations and numerical simulation of two South China case studies

This study investigates the impact of urbanization on extreme winter rainfall in the South China Greater Bay Area (GBA) through the analysis of hourly station observations and simulations using the Weather Research and Forecasting Model with the Single Layer Urban Canopy Model (WRF-SLUCM). Data from 2008 to 2017 reveal that urban areas in the GBA experience lower 99th percentile hourly winter rainfall intensity compared to surrounding rural regions. However, urban locations exhibit higher annual maximum hourly rainfall (Rmax) and very extreme rainfall events (99.99th percentile) in winter, suggesting a positive influence of urbanization on extreme winter precipitation. A case study further underscores the role of the Urban Heat Island (UHI) effect in enhancing extreme rainfall intensity and probability in the GBA urban areas. Additionally, two extreme cases were dynamically downscaled using WRF-SLUCM, involving four parallel experiments: replacing urban land use with cropland (Nourban), using historical urban land use data from 1999 (99LS), projecting near-future urban land use for 2030 (30LS), and considering 2030 urban land use without anthropogenic heat (AH) (30LS-AH0). Synoptic analysis demonstrates that cold air intrusion suppresses the GBA UHI in Case 2013 but not in Case 2015. Reduced evaporation and humidity induced by urban surfaces significantly decrease urban precipitation in Case 2013. In contrast, the persistent UHI in Case 2015 enhances local convection and land–ocean circulation, leading to increased moisture flux convergence and amplified urban precipitation intensity and probability in 30LS compared to Nourban. This amplification is primarily attributed to AH, while the change in 99LS remains insignificant. These findings suggest that urban influences on extreme precipitation in the GBA persist during winter, particularly when the UHI effect is maintained.

Winter extreme precipitation over the Tibetan Plateau influenced by Arctic sea ice on interdecadal timescale

The Tibetan Plateau (TP) and the Arctic are the most sensitive regions to global climate change. However, the interdecadal varibility of winter extreme precipitation over the TP and its linkage with Arctic sea ice are still unclear. In this study, the characteristics and mechisnems of the TP extreme precipitation (TPEP) influenced by Arctic sea ice on interdecadal timescale are studied based on the daily precipitation, monthly sea ice concentration and ERA5 reanalysis data from 1980 to 2018. We found that the dominant mode of the TPEP in winter mostly exhibits a uniform spatial variation on the interdecadal timescale, with an opposite weak variation in the southeastern TP, and the Arctic sea ice concentration (SIC) before 2002 are larger than that after 2003. The interdecadal variation of TPEP is affected by two teleconnection wave trains regulated by the Barents and Kara Sea ice. In the light ice years, a remarkable positive geopotential height (HGT) anomaly appears over the Barents‒Kara Sea and a remarkable negative HGT anomaly is located over the Lake Baikal. Two wave trains originating over the Barents‒Kara Sea can be observed. The southern branch forms a wave train through the North Atlantic along the subtropical westerly jet stream, showing a ‘+ − + − +’ pattern of HGT anomalies from Arctic to the TP. Negative HGT anomaly controls the western TP, which creates dynamic and water vapor conditions for the TPEP. The northern branch forms a wave train through the Lake Baikal and the southeast of the TP, showing a ‘+ − +’ HGT anomaly distribution. Positive HGT anomaly controls the southeastern TP, which is not conducive to precipitation in the region. When the SIC in the Barents‒Kara Sea increases, the situation is opposite. The above analysis also reveals the reason for the difference in the east‒west distribution of the TPEP.

Characteristics of mean and extreme precipitation in Ny Ålesund, Arctic

The intensification of precipitation in the Arctic can impact the ecosystem by altering the freshwater flux, albedo, sea ice, and permafrost stability. In a location like the Arctic with a harsh environment, precipitation observations are difficult to make. In the present study, precipitation characteristics are investigated using precipitation records from Ny Ålesund, Svalbard, where the longest record of precipitation in the Atlantic sector of the Arctic is available. Precipitation is expected to increase with the warming of the atmosphere; however, significant trends in precipitation are only observed during fall (0.36 mm/decade). Even though a strong temperature increase was noticed in winter, the precipitation trend was not significant. Precipitation is separated into weak and extreme events to gain more insight into its characteristics. Again, fall was characterised by a significant positive trend in weak precipitation (150 × 10−3mm/decade), while extreme winter precipitation displayed a positive trend during 2000–2019 (4.13 mm/decade). Further analysis indicated that winter extreme precipitation followed a 2-CC relationship while the precipitation during fall followed 2-CC/1-CC scaling for mean/extreme events. The atmospheric circulation pattern during the extreme events resembles the Scandinavian pattern, characterised by high MSLP anomalies over northwestern Europe. While widespread evaporation was noticed over the North Atlantic during extreme events, vertically integrated moisture divergence indicated West Spitzbergen Current (WSC) could be a possible moisture source for extreme precipitation events during winter.

Winter heavy precipitation events over Northern Europe modulated by a weaker NAO variability by the end of the 21st century

We use an ensemble of models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) to analyse the number of days with extreme winter precipitation over Northern Europe and its relationship to the North Atlantic Oscillation (NAO), for the historical period 1950–2014 and two future 21st-century scenarios. Here we find that over Northern Europe, the models project twice more extreme precipitation days by the end of the 21st century under the high-emission scenario compared to the historical period. We also find a weakening of the NAO variability in the second half of the 21st century in the high greenhouse gas emission scenario compared to the historical period, as well as an increasing correlation between extreme winter precipitation events and the NAO index in both future scenarios. Models with a projected decrease in the NAO variability across the 21st century show a positive trend in the number of days with extreme winter precipitation over Northern Europe. These results highlight the role played by NAO in modulating extreme winter precipitation events.

Western disturbances alter the trend of winter precipitation and its extremes over Northwest Himalayas: Kashmir Himalaya.

The perception of spatio-temporal variability of winter precipitation covering dominant water resources and environment over Kashmir Himalaya is a pre-eminent perspective under current social interests. The main objectives of the study are, firstly, to unriddle the whole (1980-2020) and post-2000 trend in the winter season precipitation (WP), frequency of low-pressure systems (Lp-S), and western disturbances (WDs) to understand the footprints of climate change over the region; secondly, to evaluate the spatio-temporal variability of winter precipitation under the dominance of global teleconnection indices, using both station and reanalysis datasets. Modified Mann-Kendell test and a linear regression model were utilized to extract the trend and significance in WP, Lp-S, and WDs. The results reveal that WP shows an insignificant decreasing trend (1980-2020), with an increasing trend post-2000, while a decreasing trend is seen during post-2000 in the frequency of Lp-S and WDs. The contribution of WP to annual precipitation shows decadal variability with a decreasing trend post-2000. The anatomy of winter extreme precipitation days has shown a decreasing trend (1980-2020), with a robust coupled increasing trend with WP post-2000. The dynamics of ten severe WD-based extreme precipitation events show that a cyclonic circulation and trough connects the Arabian Sea and the Himalayas, bringing additional moisture to the study region and resulting in extreme precipitation. The cogency of global teleconnections on the variability of WP shows that a pattern with positive phase of NAO, ENSO, and a negative phase in Siberian high intensifies the WD-based precipitation. The study discovers its applicability for the regional forecast system in predicting the winters.

ENSO Diversity and the Simulation of Its Teleconnections to Winter Precipitation Extremes Over the US in High Resolution Earth System Models

AbstractAccounting for the diversity in El Niño Southern Oscillation (ENSO)'s spatial pattern, with the novel ENSO longitudinal index (ELI), we evaluate the simulation of its teleconnections to US winter precipitation extremes by seven global high‐resolution (HR) Earth System Models (ESM). Six (four) HR ESMs simulate the observed increase in precipitation extremes over Southwest US (Southeast US) during ELI‐defined El Niño events better than their low‐resolution counterparts, which are low‐biased. The stronger ENSO‐dependence over the Southwest US and Southeast US in those models is associated with an improved simulation of moisture flux into the regions and/or storm track activity there. HR ESMs, however, generally overestimate the increase in precipitation extremes over the Pacific‐Northwest during La Niña events. Model bias there is associated with bias in moisture transport into the region during La Niña events, which is amplified by the enhanced vertical mass fluxes in HR.

Spatial coherence patterns of extreme winter precipitation in the U.S.

Extreme precipitation events have a significant impact on life and property. The U.S. experiences huge economic losses due to severe floods caused by extreme precipitation. With the complex terrain of the region, it becomes increasingly important to understand the spatial variability of extreme precipitation to conduct a proper risk assessment of natural hazards such as floods. In this work, we use a complex network-based approach to identify distinct regions exhibiting spatially coherent precipitation patterns due to various underlying climate mechanisms. To quantify interactions between event series of different locations, we use a nonlinear similarity measure, called the edit-distance method, which considers not only the occurrence of the extreme events but also their intensity, while measuring similarity between two event series. Using network measures, namely, degree and betweenness centrality, we are able to identify the specific regions affected by the landfall of atmospheric rivers in addition to those where the extreme precipitation due to storm track activity is modulated by different mountain ranges such as the Rockies and the Appalachians. Our approach provides a comprehensive picture of the spatial patterns of extreme winter precipitation in the U.S. due to various climate processes despite its vast, complex topography.

The Unprecedented Character of California's 20th Century Enhanced Hydroclimatic Variability in a 600‐Year Context

AbstractRecently, year‐to‐year swings in California winter precipitation extremes have resulted in drought, wildfires, and floods causing billions of dollars in damage. These recent precipitation swings represent an increasing trend in variability of California's hydroclimate over the past decades. Here, we put this trend in a longer‐term context using tree‐ring‐based precipitation, streamflow, and snow water equivalent reconstructions. We show that the statewide rise in hydroclimate variability in the 20th century is driven by an increasing trend in the magnitude of wet extremes. A prior period of strong variability in the 16th century, in contrast, is related to an increasing trend in the magnitude of dry extremes. Our results are consistent with climate model simulations that suggest an increasingly volatile future for California's hydroclimate and highlight the importance of collaboration between scientists and water resource managers to incorporate this increased variability into their decision‐making and planning, acknowledging higher risks for compound events.

Study on Change of the Glacier Mass Balance and Its Response to Extreme Climate of Urumqi Glacier No.1 in Tianshan Mountains in Recent 41 Years

Glaciers are susceptible indicators of climate change and crucial parts of the world’s water cycle. In the context of global warming, we took the Urumqi Glacier No.1 (UG1) as an example, which is situated at the source of the Urumqi River on the northern slope of the Tianshan Mountains, Xinjiang, combined with the climate data of Daxigou Meteorological Station from 1980 to 2020, and the change of glacier mass balance and its response to extreme climate are discussed. The results suggest that the glacier mass balance of UG1 showed a downward trend over the studied 41-year period, and the mass loss increased. The cumulative glacier mass balance value was −19,776 mm w.e., and the average annual value was −482 mm w.e.a−1. The Mann-Kendall trend test showed that the change point occurred around 1994, and the mass balance of UG1 became more negative after 1994. In the same period, the changing mass balance trend of UG1 was not the same in different seasons. The inter-annual variation of summer mass balance was drastic, showing a marked downward trend; the inter-annual change of winter mass balance was small, showing a slight uptrend. The changing of extreme climate indices where UG1 is located showed that only TX90p and TX10p changed observably from 1980 to 2020, and the extreme precipitation indices changed evidently and had been on the rise. The changing trend of extreme climate indices indicated that the temperature was rising, the warming was significant, and the precipitation was increasing. During 1980–2020, the glacier mass balance was substantially correlated with the extreme temperature indices (TX90p, TXx) but not with the extreme precipitation indices. Analyzing on a seasonal scale, the summer mass balance was memorably correlated with the extreme temperature indices (TX90p, TX10p, TXx), and the correlation coefficient between winter mass balance and the extreme precipitation index R95p and winter precipitation was in the range 0.36~0.40 (p < 0.05). According to the correlation between glacier mass balance and extreme climate indices, the summer mass balance was mainly affected by temperature, and the winter mass balance was affected primarily by precipitation.

Diagnostic evaluation of extreme winter rainfall events over the Arabian Peninsula using high‐resolution weather research and forecasting simulations

AbstractThe sensitivity of different cumulus physical parameterization schemes for simulating extreme winter precipitation events over the Arabian Peninsula (AP) is investigated using a high‐resolution weather research and forecasting (WRF) model. For winters in 2001–2016, the following three parameterization schemes are examined: (i) Kain–Fritsch (KF), (ii) Betts–Miller–Janjić (BMJ), and (iii) Grell–Freitas (GF). The simulation results suggest that the AP extreme winter rainfall events are best simulated using the KF, followed by the BMJ, in terms of spatial distribution and intensity. The spatial pattern correlation coefficient between the model‐simulated and observed rainfall is highest with KF (0.94), followed by BMJ (0.91) and GF (0.76). These results are attributed to a better representation of the moisture transport associated with upper‐tropospheric cyclonic circulation and potential vorticity intrusions. By contrast, the GF scheme fails to simulate moisture convergence and updrafts, leading to an unrealistic representation of cloud hydrometeors and an improper organization of convection and associated extreme rainfall intensities. Meanwhile, the KF and BMJ also successfully simulate the dynamics and thermodynamics of extreme rainfall events that are usually driven by synoptic forcing. The study results suggest that the choice of cumulus parameterization schemes in the WRF model is critical for reliable simulation of extreme rainfall in the hyperarid AP region.

Extreme Winter Precipitation Regimes in Eastern North America: Synoptic-Scale and Thermodynamic Environments

Abstract We define extreme precipitation regimes (EPRs) during the eastern North American winter based on widespread and persistent heavy precipitation, using ERA5 precipitation data from 1979 to 2020. We find 62 EPRs and analyze their synoptic-scale and thermodynamic environments. EPRs impact most of eastern North America with heavy precipitation, especially from Louisiana to Quebec, and generally last for 5–8 days. They are associated with an anomalously strong 500-hPa trough–ridge over western–eastern North America that travels slowly eastward, favoring intrusions of moist, tropical air into eastern North America, and a strong baroclinic zone from the central United States to Atlantic Canada. They are also characterized by high frequencies of cyclones in the midwestern United States, anticyclones over eastern Canada and the subtropical Atlantic, and atmospheric rivers (ARs) in eastern North America. Precipitation is maintained by large moisture influxes, primarily from the Gulf of Mexico and Caribbean Sea, from the EPR start to the time midway through the EPR period. The influxes are often associated with ARs feeding into cyclones, where the moisture falls as precipitation. We also categorize EPRs based on the spatial anomaly correlation (AC) of synoptic-scale weather patterns between individual EPRs and the EPR composite. High AC EPRs have similar but stronger 500-hPa features over North America, greater moisture flux from the Gulf of Mexico and inland precipitation over eastern North America, farther inland cyclone track, higher frequency of subtropical Atlantic anticyclones, and lower EPR-to-EPR variability than low AC EPRs. Significance Statement Cool-season extreme precipitation regimes (EPRs) often lead to flooding and other impacts and represent a significant forecast challenge. We define and analyze EPRs during the eastern North American winter to obtain a better understanding of their associated meteorological conditions. We also categorize EPRs into two distinct categories to capture the variability among EPRs. EPRs generally last 5–8 days and are associated with slowly moving large-scale weather patterns favoring intrusions of moist, tropical air into eastern North America, a strong temperature contrast, and frequent cyclones in the midwestern United States with anticyclones to the north and south. The intrusions of moist, tropical air are often associated with atmospheric rivers (ARs) that deposit their moisture in cyclones as precipitation.

Lagrangian Analysis of Moisture Sources of Precipitation in the Tianshan Mountains, Central Asia

AbstractThe moisture sources of precipitation in the Tianshan Mountains, one of the regions with the highest precipitation in Central Asia during 1979–2017 are comprehensively and quantitatively summarized by using a Lagrangian moisture source detection technique. Continental sources provide about 93.2% of the moisture for precipitation in the Tianshan Mountain, while moisture directly from the ocean is very limited, averaging only 6.8%. Central Asia plays a dominant role in providing moisture for all sub‐regions of the Tianshan Mountains. For the Western Tianshan, moisture from April to October comes mainly from Central Asia (41.4%), while moisture from November to March is derived primarily from Western Asia (45.7%). Nearly 13.0% of moisture to precipitation for Eastern Tianshan in summer originates from East and South Asia, and the Siberia region. There is a significant decreasing trend in the moisture contribution of local evaporation and Central Asia in the Eastern Tianshan during winter. The contribution of moisture from Europe to summer precipitation in the Central and Eastern Tianshan and the contribution of the North Atlantic Ocean to summer precipitation in the Northern, Central, and Eastern Tianshan also exhibit a decreasing trend. The largest increase in moisture in Western Tianshan stems from West Asia during extreme winter precipitation months. Europe is also an important contributor to extreme precipitation in the Northern Tianshan. The moisture from East and South Asia and Siberia during extreme precipitation months in both winter and summer is significantly enhanced in the Eastern Tianshan.

Retrospective sub-seasonal forecasts of extreme precipitation events in the Arabian Peninsula using convective-permitting modeling

This work demonstrates the potential of extreme cool-season precipitation forecasts in the Arabian Peninsula (AP) at sub-seasonal time scales, identifies regions and periods of forecast opportunity, and investigates the predictability of synoptic-scale forcing at sub-seasonal time scales. To this end, we simulate 18 extreme precipitation events using the convective-permitting Weather Research and Forecasting (CP-WRF) model with lateral boundary forcing from the European Centre of Medium-range Weather Forecasts sub-seasonal to seasonal reforecasts (ECMWF S2S reforecasts). The simulations are initiated at one-, two-, and three-week lead times. At all lead times, the CP-WRF improves the mean accumulated precipitation in the extratropical synoptic regimes over the west coastal and central AP and the central Red Sea compared to ECMWF S2S reforecasts as evaluated against the Global Precipitation Measurement Final (GPMF) and King Abdullah University of Science and Technology reanalysis (KAUST-RA) precipitation products. Based on categorical statistics with a threshold of 20 mm accumulated precipitation over 7 days, the CP-WRF skillfully forecasts the precipitation over Jeddah, the west coast of AP, and the central Red Sea up to three-week lead time. The relative operating characteristic curve reconfirmed the high forecast skill of the CP-WRF, with an area under the curve above 0.5 in most of the events at all lead times. Finally, the correlation coefficients between the ECMWF S2S reforecast and ECMWF reanalysis interim 500 hPa geopotential heights are higher in the events associated with an extratropical synoptic regime than in those associated with a tropical synoptic regime, regardless of lead time. Therefore, the convective-permitting model can potentially improve the accuracy of extreme winter precipitation forecasts at two-and three-week lead times over Jeddah, the west coast of AP, and the central Red Sea in the extratropical synoptic regime.

Preceding winter Okhotsk Sea ice as a precursor to the following winter extreme precipitation in South China

The winter extreme precipitation over South China (SC) experiences a large year-to-year variability, causing uncertainty in its prediction. Here, we find that the boreal winter sea ice concentration (SIC) in the Okhotsk Sea can serve as a precursor to the following winter's extreme precipitation frequency (EPF) over SC, which has important implications for its prediction. Further analysis reveals that the Okhotsk Sea SIC anomalies help to reinforce North Pacific Oscillation-like atmospheric variability over the North Pacific, which induces the development of El Niño-Southern Oscillation (ENSO)-like SST anomalies in the equatorial eastern Pacific. The ENSO may act as a “power amplifier” to boost the impact of the Okhotsk Sea winter SIC anomalies on the following winter EPF over SC via a positive atmosphere–ocean feedback process. Our findings suggest that the Okhotsk Sea SIC may act as a potential precursor for the winter EPF over SC leading by about 1 year, and further improve our understanding of extratropical-tropical interactions and aid predictability of winter extreme precipitation over SC.

Extreme austral winter precipitation events over the South-American Altiplano: regional atmospheric features

Extreme austral winter precipitation events over the South-American Altiplano: regional atmospheric features

Investigating the Linkage between Extreme Rainstorms and Concurrent Synoptic Features: A Case Study in Henan, Central China

Extraordinary floods are linked with heavy rainstorm systems. Among various systems, their synoptic features can be quite different. The understanding of extreme rainstorms by their causative processes may assist in flood frequency analysis and support the evaluation of any changes in flood occurrence and magnitudes. This paper aims to identify the most dominant meteorological factors for extreme rainstorms, using the ERA5 hourly reanalysis dataset in Henan, central China as a case study. Past 72 h extreme precipitation events are investigated, and six potential factors are considered in this study, including precipitable water (PW), the average temperature (Tavg) of and the temperature difference (Tdiff) between the value at 850 hPa and 500 hPa, relative humidity (RH), convective available potential energy (CAPE), and vertical wind velocity (Wind). The drivers of each event and the dominant factor at a given location are identified using the proposed metrics based on the cumulative distribution function (CDF). In Henan, central China, Wind and PW are dominant factors in summer, while CAPE and Wind are highly related factors in winter. For Zhengzhou city particularly, Wind is the key driver for summer extreme rainstorms, while CAPE plays a key role in winter extreme precipitation events. It indicates that the strong transport of water vapor in summer and atmospheric instability in winter should receive more attention from the managers and planners of water resources. On the contrary, temperature-related factors have the least contribution to the occurrence of extreme events in the study area. The analysis of dominant factors can provide insights for further flood estimations and forecasts.

Water vapor isotopes indicating rapid shift among multiple moisture sources for the 2018–2019 winter extreme precipitation events in southeastern China

Abstract. In the East Asian monsoon region, winter extreme precipitation events occasionally occur and bring great social and economic losses. From December 2018 to February 2019, southeastern China experienced a record-breaking number of extreme precipitation events. In this study, we analyzed the variation in water vapor isotopes and their controlling factors during the extreme precipitation events in Nanjing, southeastern China. The results show that the variations in water vapor isotopes are closely linked to the change in moisture sources. Using a water vapor d-excess-weighted trajectory model, we identified the following five most important moisture source regions: South China, the East China Sea, the South China Sea, the Bay of Bengal, and continental regions (northwestern China and Mongolia). Moreover, the variations in water vapor d excess during a precipitation event reflect rapid shifts in the moisture source regions. These results indicate that rapid shifts among multiple moisture sources are important conditions for sustaining wintertime extreme precipitation events over extended periods.

Trends of winter precipitation extremes over Northwest Himalaya

ABSTRACT The intensity and frequency of extreme precipitation events are of great concern for water resources over the Indian Himalayas, where climate change is rapidly progressive. The long-term trends of extreme precipitation events have been examined during the winter season (November to April; 1996–2016) using the data of 10 observatories maintained by the Snow and Avalanche Study Establishment (SASE) over the Northwest Himalaya (NWH) region. The extreme events are categorized into seven indices, which are 90th and 95th percentiles, rainy days, and maximum 1-d, 3-d, 5-d and total accumulated precipitation. The analysis shows increasing trends for all seven indices for the peak month of February for all Himalayan ranges and altitudes. The rainy days are significantly increased at a 95% confidence level in the Pir-Panjal Range. The teleconnection study reveals that the negative correlation between the North Atlantic Oscillation and winter precipitation extremes is critical for the inter-monthly precipitation behaviours over the NWH.