Summer Precipitation Events Research Articles

Ecohydrological Dynamics and Temporal Water Origin in a European Mediterranean Vineyard

ABSTRACTViticulture is an essential sector in agriculture as wine production plays a vital role in the socio‐economic life of many countries, especially in the Mediterranean area. Grapevines are a valuable, long‐lived species able to grow in hot and dry regions. We currently do not know whether rain‐fed grapevines entirely rely on deep soil water or make substantial use of shallow water from summer precipitation events. Without knowing this, we poorly understand what fraction of summer precipitation inputs contributes to grapevine transpiration. This has implications for how we quantify grapevine‐relevant precipitation budgets and for predicting the impacts of climate change on grape and wine production. We investigated grapevine water use in a vineyard in the Chianti region, central Italy. During the growing season of 2021, we monitored precipitation and soil moisture at 30‐ and 60‐cm depth. We collected over 250 samples for stable isotope analysis from rainfall, soil, and plants. Since traditional plant water sampling is problematic for grapevines, we collected samples from shoots, leaves, and condensed leaf transpiration after sealed plastic bags were wrapped around a shoot. We use these alternative plant samples to reconstruct the isotopic signal in the xylem water and infer the plant's seasonal water origin throughout the growing season. The analysis of the seasonal origin of water revealed that, throughout the growing season, soil water and plant water received disproportional contributions by rain that had fallen in the winter, even when compensating for the Mediterranean climate of the area. Only in late summer did the grapevines use substantial amounts of summer rainfall, whose contribution occasionally became dominant. These results provide a better understanding of ecohydrological interactions and uptake dynamics in valuable socio‐economic agroecosystems such as vineyards.

Forecast accuracy and physics sensitivity in high-resolution simulations of precipitation events in summer 2022 by the Korean Integrated Model

Forecast accuracy and physics sensitivity in high-resolution simulations of precipitation events in summer 2022 by the Korean Integrated Model

Formation mechanisms of persistent extreme precipitation events over the eastern periphery of the Tibetan Plateau: Synoptic conditions, moisture transport and the effect of steep terrain

The eastern periphery of the Tibetan Plateau (EPTP) is prone to frequent and severe Persistent Extreme precipitation (PEP) events in summer. Given the complexity of weather systems and the intricate nature of terrain over this region, the generation and development mechanisms of the PEP in the EPTP remain to be determined. In this study, the formation and persistence mechanisms are further explored from the perspective of the general features of large-scale circulations, moisture source diagnosis and the influence of steep topography by using a thermal-dynamical diagnosis method, a mesoscale numerical simulation and a Lagrangian identification of the main moisture sources. The results show that during PEP events, the corresponding atmospheric circulation systems are characterized by an anomalous Rossby wave train at middle levels, an intensified westerly jet, an eastward extension of the South Asian high and a westward extension of the western Pacific subtropical high, all of which are possible to facilitate the development of potential instability and anticyclonic convergence of water vapor transport. The evaporative moisture sources from the Southeastern Asia (SEA), Bay of Bengal (BOB), and Southern China Sea (SCS) are remarkably enhanced during PEP events, with a contribution of 56.44%, which is 28.5% higher than the climatic mean. The further sensitive experiment indicates that the steep terrain could enhance the continuous transport of positive potential vorticity and the downward propagation of upper-level isentropic potential vorticity disturbances, thereby playing an essential role in the triggering and development of PEP events.

An Index for Snowmelt-Induced Landslide Prediction for Zavoj Lake, Serbia

In February 1963, a huge landslide (ca. 1,950,000 m3) blocked the Visočica River and, thus, formed Zavoj Lake. The primary objective of this research was to investigate the importance of snowmelt in relation to landslide occurrence and to define the critical climatic conditions that may trigger massive winter landslides. We used monthly precipitation and average monthly maximum temperature data from meteorological and precipitation stations in the Visočica River basin (Dojkinci) and in the immediate proximity of Lake Zavoj (Pirot, Dimitrovgrad and Topli Do) as data inputs to the Snow-Melt Landslide (SML) index. It considers the summed monthly precipitation for previous months that continuously have an average maximum temperature below 0 °C. According to this method, the event at Zavoj Lake stands out among all other precipitation and snowmelt values for the past 72 years. After applying the SML index, all stations showed values of >300 mm for February 1963, which we consider as the threshold value for potential landslides appearance. In addition to meteorological data, we applied the SML index to data from the Coordinated Regional Downscaling Experiment (CORDEX) regional climate model outputs for the region from 2022 to 2100. As expected, climate change will have influenced the temperature values, especially during the winter. Conversely, the study area is experiencing drastic changes in land use caused by depopulation, leading to a reduced risk of winter landslides in the Visočica basin. We suggest that future climatic conditions in the area will make it more likely to experience extreme summer precipitation events, which might trigger large landslides. The SML method can be implemented for all landscapes that experience snowy winters, providing information in a timely manner so that local residents can react properly when the probability of landslide occurrence rises. The SML index, grounded in essential meteorological principles, provides a tailor-made, data-driven methodology applicable across varied geographical settings. Its utility extends to mitigating hydro-meteorological hazards on scales ranging from local to national scales, offering diverse and effective early warning solutions.

A comparative analysis of the attribution of extreme summer precipitation in south and north parts of the East China monsoon region—with the year 2020 as an example

AbstractIn summer 2020, several watersheds in China monsoon region experienced historically unusually heavy precipitation. The flooding associated with these heavy precipitation events led to devastating impacts on human life, infrastructure, agriculture and economy. Using historical climate simulations from the HadGEM3‐GA6 and CMIP6 models under influences of natural and/or anthropogenic forcings, we conducted a comparative study on the attribution of extremely heavy precipitation events in summer 2020 in the mid‐lower reaches of the Yangtze River and the mid‐lower reaches of the Yellow River‐Hai River Basin which locates respectively in the south and north parts of the East China monsoon region. The potential contributions of anthropogenic forcings to monthly‐scale extreme precipitation and daily maximum precipitation (RX1day) were examined. The results suggest that human activities have decreased the probability of month‐scale extreme precipitation events in the south part of the East China monsoon region. For RX1day extreme precipitation events, anthropogenic factors have increased their probability in both regions. However, the influence of anthropogenic forcings on month‐scale extreme precipitation events in the north part of the East China monsoon region is not robust among the two attribution systems. Further analyses indicated that anthropogenic aerosols (AER) make both month‐scale extreme precipitation events and extreme RX1day less likely to occur in summer 2020, and greenhouse gases (GHG) increase the likelihood of both. GHG influences on Rx1day overwhelm AER influences, leading to an increase of the probability of Rx1day similar to the 2020 events in both regions. In contrast, the decrease in the probability of month‐scale precipitation in the south part of the East China monsoon region is predominantly due to aerosol forcing. The model projections show that the likelihood of both monthly and daily extreme precipitation events in both regions will increase in the future. Accordingly, the recurrence period of extreme precipitation events will be shortened by the end of the 21st century, which is more significant under the high‐emission scenario.

Population dynamics in Taiwan from the Neolithic to early historic periods (5000–100 cal BP): Linking cultural developments and environmental change

To reconstruct population dynamics in Taiwan between 5000 and 100 cal BP, we analysed spatial-temporal changes in archaeological site abundance and size (area). The results suggest that population growth was discontinuous throughout the study region and that the main spatial differences in population trends were between eastern/northern and western Taiwan. Comparison of settlement data shows that population trends in Taiwan and different regions in continental China were partly parallel. We contrast these data with political, economic, settlement, and climatic developments in continental China, when considering possible factors that influenced these demographic relationships. In addition, we examined published palaeoenvironmental time series from the broader study region to explore human-environment interactions. This revealed that proxy records of human activities (agriculture, deforestation) correlate with the derived trends in site abundance and area. Furthermore, we hypothesise that the inferred sparse settlement in eastern Taiwan during 2700–1800 cal BP is related to climate change. An increase in seasonal rainfall and high-intensity precipitation events in late summer and autumn, due to long-term changes in summer monsoon precipitation and El Niño–Southern Oscillation intensity, likely resulted in unfavourable hydrological conditions for crop cultivation in this part of the study region.

High‐resolution in situ stable isotope measurements reveal contrasting atmospheric vapour dynamics above different urban vegetation

AbstractWe monitored stable water isotopes in liquid precipitation and atmospheric water vapour (δv) using in situ cavity ring‐down spectroscopy (CRDS) over a 2 month period in an urban green space area in Berlin, Germany. Our aim was to better understand the origins of atmospheric moisture and its link to water partitioning under contrasting urban vegetation. δv was monitored at multiple heights (0.15, 2 and 10 m) in grassland and forest plots. The isotopic composition of δv above both land uses was highly dynamic and positively correlated with that of rainfall indicating the changing sources of atmospheric moisture. Further, the isotopic composition of δv was similar across most heights of the 10 m profiles and between the two plots indicating high aerodynamic mixing. Only at the surface at ~0.15 m height above the grassland δv showed significant differences, with more enrichment in heavy isotopes indicative of evaporative fractionation especially after rainfall events. Further, disequilibrium between δv and precipitation composition was evident during and right after rainfall events with more positive values (i.e., values of vapour higher than precipitation) in summer and negative values in winter, which probably results from higher evapotranspiration and more convective precipitation events in summer. Our work showed that it is technically feasible to produce continuous, longer‐term data on δv isotope composition in urban areas from in situ monitoring using CRDS, providing new insights into water cycling and partitioning across the critical zone of an urban green space in Central Europe. Such data have the potential to better constrain the isotopic interface between the atmosphere and the land surface and to thus, improve ecohydrological models that can resolve evapotranspiration fluxes.

Meteorological Analysis on Extremely Depleted 18O Rainfall Events during the Summer in Adelaide, Australia

Abstract The transport of atmospheric water vapor plays a crucial role in the production of precipitation and the variation of precipitation isotopic composition (δ18Op). This study investigates three precipitation events with extremely depleted heavy isotopes in the summer of Adelaide, Australia. Using fundamental water vapor diagnosis and moisture calculation method, this research analyzes the impact of rainout degrees along moisture transport paths, atmospheric circulation patterns, water vapor sources, and moisture transport on the extreme depletion of precipitation isotopes in the study area. The purpose of this study is to reveal the direct cause of extremely depleted δ18Op at the hourly time scale. The results show the diversity and complexity of δ18Op variation in summer precipitation events in Adelaide. The rainout caused by local and upstream large precipitation may be the main reason for extremely low values of δ18Op. The phenomenon of subcloud secondary evaporation, which is driven by the interaction between relatively low humidity and high temperature at near-surface levels, plays a pivotal role in the entire precipitation process. This mechanism is particularly pronounced during the onset or cessation of precipitation events, thereby resulting in the observed enrichment of δ18Op values. The oxygen stable isotopic composition of water vapor (δ18Oa) would usually become higher, when the air mass mixes with new moisture with relatively high δ18Oa, suppressing the influence of the previous rainout.

Moisture Source Analysis of Two Case Studies of Major Extreme Precipitation Events in Summer in the Iberian Peninsula

Extreme summer precipitation events commonly affect the Iberian Peninsula (IP), and studying the moisture sources that generate intense precipitation is extremely important. Therefore, this study analyzed the moisture sources of two major extreme precipitation events in summer in the IP. The events occurred on 18 September 1999 and 7 September 1989, and the anomalies of the associated meteorological variables are shown with respect to a 30-year reference period (1985–2014). A Lagrangian approach is used for determining the moisture source pattern using only the precipitating particles that reach the target region. In this research a dynamic downscaling methodology is applied using the WRF-ARW model forced using the ERA5 reanalysis and then the WRF-ARW outputs used to force the Lagrangian dispersion model FLEXPART-WRF. Specifically, the first event was associated with an atmospheric river favoring strong moisture transport from remote sources and the second event was caused by local convergence of moisture under the influence of a cut-off low system. For the 18 September 1999 case study, the major contribution to moisture reaching the target region was associated with the central and eastern North Atlantic, with values of up to approximately 32%. In addition, the moisture source pattern exhibited a strong anomaly in the climatological pattern. However, the origin of the moisture sources associated with the case of 7 September 1989 was mainly the western Mediterranean Sea, with a contribution of up to 40% or higher. Finally, Northwest Africa and precipitation recycling processes over the IP contributed approximately 16% to the moisture supply for this event.

Contrasting Ocean–Atmosphere Dynamics Mediate Flood Hazard across the Mississippi River Basin

Abstract The Mississippi River basin drains nearly one-half of the contiguous United States, and its rivers serve as economic corridors that facilitate trade and transportation. Flooding remains a perennial hazard on the major tributaries of the Mississippi River basin, and reducing the economic and humanitarian consequences of these events depends on improving their seasonal predictability. Here, we use climate reanalysis and river gauge data to document the evolution of floods on the Missouri and Ohio Rivers—the two largest tributaries of the Mississippi River—and how they are influenced by major modes of climate variability centered in the Pacific and Atlantic Oceans. We show that the largest floods on these tributaries are preceded by the advection and convergence of moisture from the Gulf of Mexico following distinct atmospheric mechanisms, where Missouri River floods are associated with heavy spring and summer precipitation events delivered by the Great Plains low-level jet, whereas Ohio River floods are associated with frontal precipitation events in winter when the North Atlantic subtropical high is anomalously strong. Further, we demonstrate that the El Niño–Southern Oscillation can serve as a precursor for floods on these rivers by mediating antecedent soil moisture, with Missouri River floods often preceded by a warm eastern tropical Pacific (El Niño) and Ohio River floods often preceded by a cool eastern tropical Pacific (La Niña) in the months leading up peak discharge. We also use recent floods in 2019 and 2021 to demonstrate how linking flood hazard to sea surface temperature anomalies holds potential to improve seasonal predictability of hydrologic extremes on these rivers.

Evaluation of Alpine-Mediterranean precipitation events in convection-permitting regional climate models using a set of tracking algorithms

We here inter-compare four different tracking algorithms by applying them onto the precipitation fields of an ensemble of convection-permitting regional climate models (cpRCMs) and on high-resolution observational datasets of precipitation. The domain covers the Alps and the northern Mediterranean and thus we here analyse heavy precipitation events, that are renowned for causing hydrological hazards. In this way, this study is both, an inter-comparison of tracking algorithms as well as an evaluation study of cpRCMs in the Lagrangian frame of reference. The tracker inter-comparison is performed by comparison of two case studies as well as of climatologies of cpRCMs and observations. We find that that all of the trackers produce qualitatively equal results concerning characteristic track properties. This means that, despite of quantitative differences, equivalent scientific conclusions would be drawn. This result suggests that all trackers investigated are reliable analysis tools of atmospheric research. With respect to the model ensemble evaluation, we find an encouraging performance of cpRCMs in comparison to radar-based observations. In particular prominent hotspots of heavy precipitation events are well-reproduced by the models. In general most characteristic properties of precipitation events have positive biases. Assuming the under-catchment of precipitation in observations in a domain of such complex orography, this result is to be expected. Only the mean area of tracks is underestimated, while their duration is overestimated. Mean precipitation rate is estimated well, while maximum precipitation rate is overestimated. Furthermore, geometrical and rain volume are overestimated. We find that models overestimate the occurrence of precipitation events over all mountain chains, whereas over plain terrain in summer precipitation events are seen underestimated. This suggests that, despite the convection-permitting resolution, thermally driven thunderstorms are either not triggered or their dynamics still under-resolved. Eventually we find that biases in the spatio-temporal properties of precipitation events appear reduced when evaluating cpRCMs against Doppler radar-based and rain gauge-adjusted observational datasets of comparable spatial resolution, strengthening their role in evaluation studies.

Emerging solute-induced mineralization in Arctic rivers under climate warming

Permafrost degradation under a warming climate is accelerating the hydrological processes in Arctic river basins. However, corresponding changes in river mineralization, riverine solute exports and their potential influencing factors are not fully understood. In this study, we selected six major Arctic rivers (Ob, Yenisei, Lena, Kolyma, Yukon and Mackenzie Rivers) with different permafrost extents, meteorological conditions and hydrological regimes to reveal the changes in river mineralization and riverine solute exports using ArcticGRO sampling data from 2003 to 2019. Our results indicate that solute-induced river mineralization has already been observed in the Lena, Yukon and Mackenzie Rivers during 2003–2019. The annual flux of total dissolved solids (TDS; a key parameter of drinking water quality), calculated by the Load Estimator (LOADEST) program, from these six rivers was approximately 295.24 ± 12.50 Tg, with the Ob, Kolyma and Yukon Rivers exhibiting significant increasing trends (p < 0.05) at rates of 4.38 Tg/10 yr, 1.62 Tg/10 yr and 3.03 Tg/10 yr, respectively. Climate-induced changes in hydrological regimes regulate riverine solute exports, with relatively higher TDS concentrations in the groundwater-dominated winter low-flow season and lower TDS concentrations under the dilution of groundwater by snowmelt spring floods and summer precipitation events. The riverine solute fluxes with higher TDS concentrations (e.g., those of the Yukon and Mackenzie Rivers) increased more rapidly (~0.14 Tg/km3) with changes in river discharge; however, the TDS concentrations were more sensitive to climate warming in continuous permafrost-dominated colder basins (i.e., the Kolyma and Lena River basins) than in other relatively warmer basins. Our results suggest that riverine solute exports are likely affected by permafrost thaw-induced changes in hydrogeological processes, which are tightly associated with increases in active layer thickness and enhanced groundwater discharge to rivers. Under a warming climate, riverine solute exports in Arctic rivers are expected to increase with intensifying groundwater–surface water exchanges.

Wetland position in the landscape: Impact on water storage and flood buffering

AbstractOn‐going climatic changes and land‐use changes may impact water storage dynamics within wetlandscapes (defined as the entire hydrological catchments of interconnected wetland systems). These dynamics are closely linked to many wetland ecosystem services including flood buffering, nutrient retention and biodiversity support. Here, we investigate if and how current water storage dynamics can differ between wetlands within the same wetlandscape. Based on continuous monitoring of water levels in multiple wetlands throughout a growing season (spring, summer, autumn) in Vattholma, Sweden, we show that there are two distinct storage behaviours depending on the position of the wetland within the landscape. Headwater wetland regions were active in temporary storage of surplus water from regular summer rains while water levels of downstream wetlands dropped to seasonal low values without responding to individual summer precipitation events. Thereby, the downstream wetlands maintained capacity to buffer extreme floods. We also found that headwater wetlands were associated with complex and patchy inundation, which causes habitat conditions to vary over short time scales both within and among these wetlands, in contrast to the prolonged low‐water state of the downstream wetlands. These differences between headwater‐downstream wetlands imply that the functionality of an entire wetlandscape cannot be assessed by simple extrapolation of data from monitoring stations that typically are located downstream of headwater regions. Increased understanding of these differences can support wetland management practices that target location‐specific nature‐based solutions and ecosystem services.

Relationships Between Rapid Urbanization and Extreme Summer Precipitation Over the Sichuan–Chongqing Area of China

China has undergone rapid urbanization over the past few decades, and accordingly, changes have occurred in the extreme precipitation events. However, few studies have focused on the relationships between rapid urbanization and extreme precipitation events in southwest China, particularly in the Sichuan–Chongqing area, which has a complex topography and has experienced rapid urbanization over the past few decades. This is the first study to analyze the impact of urbanization on the amount, frequency, and intensity of extreme summer (June–August) precipitation events over the past 30 years. Our results indicate that extreme precipitation events primarily occurred in the urban-dominated Sichuan basin, particularly during the fast urbanization development stage (FUDS) of 1994–2015. Extreme precipitation amounts and intensities increased during the FUDS, implying the greater probability of individual precipitation events developing into heavy or extreme events in a particular area. In addition, the probability distribution functions of the occurrence and volume of strong convective events significantly increased during the FUDS. Finally, the annual increase in urban-scale land surface air temperature, increase in wet convection, and changes in wind speed are identified as essential factors leading to extreme precipitation events in this region.

Modelling temporal variability of in situ soil water and vegetation isotopes reveals ecohydrological couplings in a riparian willow plot

Abstract. The partitioning of water fluxes in the critical zone is of great interest due to the implications for understanding water cycling and quantifying water availability for various ecosystem services. We used the tracer-aided ecohydrological model EcH2O-iso to use stable water isotopes to help evaluate water, energy, and biomass dynamics at an intensively monitored study plot under two willow trees, a riparian species, in Berlin, Germany. Importantly, we assessed the value of in situ soil and plant water isotope data in helping to quantify xylem water sources and transit times, with coupled estimates of the temporal dynamics and ages of soil and root uptake water. The willows showed high water use through evapotranspiration, with limited percolation of summer precipitation to deeper soil layers due to the dominance of shallow root uptake (&gt;80 % in the upper 10 cm, 70 %–78 % transpiration/evapotranspiration). Lower evapotranspiration under grass (52 %–55 % transpiration/evapotranspiration) resulted in higher soil moisture storage, greater soil evaporation, and more percolation of soil water. Biomass allocation was predominantly foliage growth (57 % in grass and 78 % in willow). Shallow soil water age under grass was estimated to be similar to under willows (15–17 d). Considering potential xylem transit times showed a substantial improvement in the model's capability to simulate xylem isotopic composition and water ages and demonstrates the potential value of using in situ data to aid ecohydrological modelling. Root water uptake was predominately derived from summer precipitation events (56 %) and had an average age of 35 d, with xylem transport times taking at least 6.2–8.1 d. By evaluating isotope mass balances along with water partitioning, energy budgets, and biomass allocation, the EcH2O-iso model proved a useful tool for assessing water cycling within the critical zone at high temporal resolution, particularly xylem water sources and transport, which are all necessary for short- and long-term assessment of water availability for plant growth.

The Quasi-Biweekly Oscillation of Summer Rainfall in Southern China and Its Relationship With the Geopotential Height Anomaly Over the North Atlantic Ocean

Summer precipitation in East Asia has significant quasi-biweekly (10–30-day) oscillation characteristics. By using gauge-based precipitation and ERA-Interim reanalysis data, the basic mode of the quasi-biweekly oscillation of summer precipitation in East Asia and the related circulation from 1979 to 2012 were analyzed. It was found that the middle and lower reaches of the Yangtze River and its south in China were among the key areas for the 10- to 30-day oscillation of summer precipitation. After selecting typical summer precipitation events with 10- to 30-day oscillation characteristics in key areas and conducting composite analysis, it is found that in the dry (wet) phase of quasi-biweekly precipitation in southern China, it is controlled by quasi-biweekly anticyclone (cyclone) at 500 hPa above the key area. During the evolution of quasi-biweekly precipitation, the ridge of the Northwest Pacific Subtropical High is located between 20 and 22°N latitude, and there is no significant variability in the large-scale background circulation. Furthermore, composite analysis of the precursory signal at 500 hPa during quasi-biweekly precipitation in southern China found that there was an obvious quasi-biweekly geopotential height anomaly over the North Atlantic Ocean almost 30 days before the peak day of quasi-biweekly precipitation. While the quasi-biweekly geopotential height anomaly at 500 hPa in the North Atlantic propagates eastward, it also leads the cold air to transport southward. Cold air from high latitudes and warm air from low latitudes converge in southern China, which affects the quasi-biweekly oscillation of precipitation. Hysteresis synthesis of precipitation based on 500 hPa geopotential height’s quasi-biweekly oscillation events over the North Atlantic Ocean comes to almost the same conclusion. Therefore, the 500 hPa geopotential height quasi-biweekly anomaly in the North Atlantic may have important prediction significance for an extended-range forecast of summer rainfall in China.

Tree ring anatomy indices of Pinus tabuliformis revealed the shifted dominant climate factor influencing potential hydraulic function in western Qinling Mountains

Trees can adjust xylem anatomical structure related with potential hydraulic functions to cope with climate variability. We therefore need a better understanding of how climate variability constrains wood anatomy and tree radial growth. Pinus tabuliformis dominates natural forests and plantations over the western Qinling Mountains, which is one of the ecologically vulnerable areas in China. Here, we investigated the response of P. tabuliformis tree-ring anatomical structure to climate variability by applying wood anatomy analysis, and evaluated the influences of anatomical traits on potential hydraulic functions and the climate significance of intra-annual density fluctuations (IADFs). We found that with the increasing temperature from spring to summer, the negative effect of temperature on the formation and enlargement of earlywood and transition-wood tracheids was gradually enhanced. However, spring precipitation not only had a direct and positive influence on the formation of earlywood, but also had a delaying impact on the transition-wood cell enlargement. Besides, the smaller earlywood tracheid size of P. tabuliformis could be a substantially characteristic reflecting spring drought. The contribution of lumen diameter on conduit wall reinforcement was dominated in earlywood, while the contribution of cell wall thickness was greater than that of lumen diameter in latewood. The different contributions of anatomical traits on conduit wall reinforcement would further affect the response of potential hydraulic function to climate. IADFs of P. tabuliformis could be a potential indicator to reflect the abnormal summer precipitation events in the western Qinling Mountains. IADFs with strong and weak intensity indicated years with high and low rates of change in mid-summer precipitation, respectively. Future warmer and drier climate in the western Qinling Mountains will likely result in the production of smaller tracheids to ensure hydraulic safety, which means the stronger drought resistant of P. tabuliformis in the future. In this study, we linked the xylem anatomy and potential hydraulics functions with intra-seasonal climate variability in the context of climate warming and drying, and proposed some xylem anatomical indices reflecting potential drought events.

Case studies of atmospheric moisture sources in the source region of the Yellow River from a Lagrangian perspective

AbstractIn this study, atmospheric moisture source regions and transport pathways, which substantially affect extreme summer precipitation events in the source region of the Yellow River (SRYR) of China were investigated using the Lagrangian Flexible Particle Dispersion Model (FLEXPART). Based on the 24‐hour cumulative precipitation data from the China Meteorological Data Service Center, 2012 and 2015 were selected to represent wet and dry years during the period 2007–2016, respectively. The results indicate that potential moisture sources include the northern Tibetan Plateau, the Bay of Bengal, the southern edge of the Himalayas, Sichuan Basin, and the SRYR. In the wet year, moisture from the southern branch was transported along two pathways: (a) moisture from the Arabian Sea was carried by the Somalia jet and entered the SRYR through the Indian Peninsula and Bay of Bengal, and (b) moisture from the South China Sea entered the SRYR through the Sichuan Basin. In the dry year, the moisture primary originated from the northern branch. Moisture from the eastern European Plain or northern Africa was carried by the westerly jet and entered the SRYR. It is estimated that the ratios of moisture from the northern and southern branches contributing to the precipitation in the SRYR were 22.1 and 15.9% in the wet year, while they were 52.9 and 8.4% in the dry year, respectively. Internal moisture recycling contributed ~22.0% to precipitation in the wet year and 11.0% in the dry year. In this study, the transport trajectories of moisture contributing to extreme precipitation events in the SRYR are delineated. The results indicate that the northern branch is the primary contributor of moisture in the SRYR.

Predictability of moisture flux anomalies indicating central European extreme precipitation events

AbstractForecasting heavy precipitation has an important role in mitigating floods and associated hazards, but it remains one of the main challenges in operational meteorology. Our previous study confirmed the close connection between large‐scale extreme precipitation events and anomalous moisture fluxes in central Europe. In this study, we introduce a variable accounting for the accumulated ascending moisture flux, which could potentially support extreme precipitation event forecasts. The variable reflects the total amount of transported water vapour in combination with extra high upward vertical velocity, which are important factors required for extreme precipitation occurrence. Looking at ERA‐Interim forecasts, we aim to determine a practical predictability and forecast skill of accumulated ascending moisture flux and compare it with the forecast skill of precipitation. While the predictability of moisture flux itself is satisfactory, generally less accurate forecasts of the vertical velocity negatively affect the predictability of accumulated ascending moisture flux, especially in the case of summer precipitation events with prevailing northern moisture flux. Nevertheless, the forecast of the proposed variable was adequate and stable up to 6 days in advance in all cases of maximum events that produced major central European summer floods. There were no such stable forecasts for less extreme events or false‐alarm precipitation extremes. Thus, we hypothesize that the calculation of the accumulated ascending moisture flux from numerical weather prediction could be useful as a supporting tool in extreme precipitation warnings in central Europe.

How Do Extreme Summer Precipitation Events Over Eastern China Subregions Change?

AbstractIn this study, observations from the CN05.1 daily data set and K‐means clustering were used to capture spatiotemporal characteristics of extreme precipitation events (EPEs) during summer over eastern China subregions from 1961 to 2018. Five subregions including South China (SC), the Yangtze River Basin (YRB), the HeTao Area (HTA), North China (NC), and Northeast China (NEC) are identified, which is distinct from previous studies. There were significant rates of EPEs transfer from the YRB‐type to SC‐type (18%), HTA‐type to YRB‐type (16%), HTA‐type to NC‐type (22%), and NC‐type to NEC‐type (25%), and the associated processes of synoptic evolution are addressed. Within these types of regional EPEs, intrinsic relationships exist that have not been recorded by previous studies. The intraseasonal evolution of summer EPEs shows a northward migration of the rainbelt influenced by the East Asian summer monsoon system. Moreover, temporal variations of regional EPEs from interannual timescales to long‐term trends are examined.