Redistribution Of Precipitation Research Articles

Precipitation response to aerosol–radiation and aerosol–cloud interactions in regional climate simulations over Europe

Abstract. The effect of aerosols on regional climate simulations presents large uncertainties due to their complex and non-linear interactions with a wide variety of factors, including aerosol–radiation (ARI) and aerosol–cloud (ACI) interactions. These interactions are strongly conditioned by the meteorological situation and type of aerosol, but, despite their increase, only a limited number of studies have covered this topic from a regional and climatic perspective. This contribution thus aims to quantify the impacts on precipitation of the inclusion of ARI and ACI processes in regional climate simulations driven by ERA20C reanalysis. A series of regional climatic simulations (for the period 1991–2010) for the Euro-CORDEX domain were conducted including ARI and ARI + ACI (ARCI), establishing as a reference a simulation where aerosols were not included interactively (BASE). The results show that the effects of ARI and ACI on time-mean spatially averaged precipitation over the whole domain are limited. However, a spatial redistribution of precipitation occurs when the ARI and ACI processes are introduced into the model, as well do changes in the precipitation intensity regimes. The main differences with respect to the base-case simulations occur in central Europe, where a decrease in precipitation is associated with a depletion in the number of rainy days and clouds at low level (CLL). This reduction in precipitation presents a strong correlation with the ratio PM2.5∕PM10, since the decrease is especially intense during those events with high values of that ratio (pointing to high levels of anthropogenic aerosols) over central Europe. The precipitation decrease occurs for all ranges of precipitation rates. On the other hand, the model produces an increase in precipitation over the eastern Mediterranean basin associated with an increase in clouds and rainy days when ACIs are implemented. Here, the change is caused by the high presence of PM10 (low PM2.5∕PM10 ratios, pointing to natural aerosols). In this case, the higher amount of precipitation affects only days with low rates of precipitation. Finally, there are some disperse areas where the inclusion of aerosols leads to an increase in precipitation, especially for moderate and high precipitation rates.

庐山日本柳杉林下穿透雨时空分布特征

林冠是降水到达地面前的第一个作用层，其对降水的再分配作用，导致穿透雨的数量和空间分布具有很大的变异性，这既阻碍了对其的精确评估，也常常被认为是水文模型中蒸发量化的不确定来源之一。在庐山自然保护区日本柳杉（Cryptomeria japonica）人工林内设置了面积30 m×30 m的样地，机械布置了37个截面面积为314.15 cm²穿透雨收集器，于2017年生长季（4-9月）共监测21次降雨事件下穿透雨量。分析林冠下穿透雨率及其时空分布特征和影响因素。日本柳杉林下穿透雨率变化范围为2%-222%，平均穿透雨率为80%，穿透雨率随着林外次降雨量的增加而逐渐增大，降雨量达到28 mm时穿透雨率趋于最大值，之后变化规律复杂未见稳定，二者之间最优拟合关系为二次多项式；与叶面积指数呈显著负相关，叶面积指数小于4.5时对穿透雨率的影响显著。不同叶面积指数下，穿透雨率达到最大时的林外降雨量不同。穿透雨率的空间变异系数的变化范围为15%-114%，随林外降雨量的增加而减小，并在林外次降雨量大于20 mm以后，逐渐趋于稳定，二者之间以对数函数关系式拟合。观测点位的时间变异系数随着叶面积指数的增加而增大。叶面积指数小于5，降雨量小于20 mm时，降雨量是影响穿透雨空间变异性的关键因素。;Precipitation redistribution is one of the most important effect of canopy interception, which caused the large variations of the quantity and spatial distribution of throughfall rain. This hinders both the accurate assessment of interception and is often considered to be one of the uncertain sources of evaporation quantification in hydrological models. A total of 37 gauges (cross-sectional area of 314.15 cm²) were mechanically arranged within a 30 m×30 m sample plot of Cryptomeria japonica stands in Mount Lu national natural reserve. During the 2017 growing season (April-September), a total of 21 rainfall events were monitored for rainfall. The results showed that the range of throughfall percentage varied between 2% and 222%, and the mean value was 80%. When the rainfall reaches 28 mm, the penetration rain rate tends to the maximum, and then the change law is complicated and not stable. The best fitting relationship between rainfall and throughfall could be described with a quadratic polynomial. Penetrating rain rate was significantly negatively correlated with the leaf area index. When the leaf area index was less than 4.5, the impact on the penetration rain rate was significant. Under different leaf area indexes, the rainfall outside the forest is different when the penetration rain rate reaches the maximum. The spatial variation coefficient of the penetration rain rate varies from 15% to 114%, which decreases with the increase of the rainfall outside the forest, and gradually stabilizes after the secondary rainfall outside the forest is greater than 20 mm. Logarithmic function relationship fitting. The coefficient of time variation of the observation points increases with the increase of the leaf area index.

Влияние импульсного ионно-плазменного воздействия и электронного облучения на механические свойства сплава Инконель 718

The effect of pulsed ion-plasma irradiation in the Plasma Focus installation and irradiation with 20 MeV electrons at the Miсrotron-ST accelerator on the mechanical properties of the precipitation-hardening Inconel 718 alloy obtained by the method of selective laser fusion has been studied. It was found that ion-plasma and electron irradiation does not affect the properties of the alloy, which is explained by the small thickness of the modified layer during PF irradiation and insufficiently high electron fluence for the manifestation of radiation-stimulated processes of redistribution and dissolution of dispersed precipitates of the strengthening phases. The results obtained indicate a high resistance to crack propagation and the absence of a tendency of the studied alloy to embrittlement.

The Condition Of Atmospheric Precipitation in the Zones of Large Lakes of Kazakhstan

Numerous studies indicate that climate change will lead to unfavorable redistribution of atmospheric precipitation. Those where there are enough of them, for example, in the northern and middle latitudes, there will be more precipitation, and where they are lacking, there will be generally less precipitation. The central continental regions are likely to become even drier, and the interannual variability of precipitation increases sharply. Some natural systems (glaciers, rivers, lakes, etc.) are likely to undergo significant changes, which can cause irreversible losses in their ecosystems. There are many lakes in the Republic of Kazakhstan, different in size, with different quality and quantity of water. From an economic point of view, lakes are among the most important sources of natural resources. Given the ever-increasing impacts of climate change, an assessment of the change in the amount of atmospheric precipitation is necessary in the analysis, forecasting and regulation of the quality of surface waters. In this regard, in work the features of the temporal distribution of precipitation in 6 water basins, where the monitoring lakes of Kazakhstan are located. The main purpose of the study is to analyze spatio-temporal variability of the precipitation condition in the zones of large lakes in Kazakhstan. The results obtained indicate the variability of anomalies in the amount of atmospheric precipitation in the zones of large lakes in Kazakhstan over the past decades. In the inter-basin section, annual precipitation has generally increased. In the Ertissky, Balkash-Alakol, Nura-Sarysu, Esil basins, there was a tendency to increase the annual precipitation - by 1.5 ... 3.6% /10 years. A decrease in the annual amount of precipitation is observed in the territory of the Shu-Talas and Zhaiyk-Caspian basins - 0.8%/10 years and 0.9% /10 years, respectively. The obtained trends are statistically significant only for the Esil and Nura-Sarysu basins.

Numerical simulation of intense precipitation in Moscow region: a case study of a heavy rainfall event on June 30, 2017

This paper considers physical and synoptic mechanisms of an extreme rainfall on June 30, 2017 in the central part of European Russia, which was the maximum of daily precipitation sum in Moscow (65 mm) since 1970. Based on meteorological observations, radar data, and ERA5 reanalysis data, we show that the rainfall was associated with three mesoscale convective systems (MCSs) that formed in the warm sector of a cyclone in a strip of anomalously high moisture content in the considered region, which developed further due to advection and evaporation. A numerical simulation with mesoscale model COSMO shows a significant contribution to the precipitation intensity of evaporation from the Earth’s surface: a 10-times decrease in soil the moisture in the initial conditions leads to a 3-times decrease in the amount of precipitation and its intensity. Additionally, we consider urban-induced effects on this rainfall event by switching on and off urban parametrization TERRA_URB. The application of the urban surface parametrization has not changed the average amount of precipitation in Moscow region. It causes, however, a redistribution of precipitation sums within it.

Microstructure, Substructure and Mechanical Properties of 9CrNB Steel after Tempering

This paper deals with the analysis of microstructure and substructure of 9CrNB steel, after normalization at temperature of 1070 °C and tempering at 790 °C / 240 min. The tube was second time tempered at the following temperatures and holding times: 760 °C / 30 min (A1), 760 °C / 120 min (C1), 800 °C / 30 min (G1) and 800 °C / 120 min (I1). Microstructure after tempering consists of tempered martensite and bainite with lath morphology, while inhomogeneous redistribution of precipitates is visible. Substructure analysis of state A1 and I1 show, that a relatively large number of irregular, rod-shaped and oval carbide particles, often arranged in clusters, were precipitated at the primary original austenite grain boundaries. In case of state A1, the average size of these carbide particles is 300 nm and in case of state I1 the average size is 350 nm. A relatively large number of rod-shaped and oval shaped particles were found at the interface of the tempered martensite and bainite mainly in the form of clusters and also inside the tempered bainite with higher particle distribution. In the case of the state A1, they reached an average size of 150 nm. In some regions of substructure of the state I1, the fine carbide particles with an average size of 200 nm and coarse carbide particles with an average size of 400 nm were presented within the areas of tempered bainite. Particles were identified by EDX analysis and by selection electron diffraction. The mechanical properties after tempering were evaluated and compared with properties of P91 and P92 steel.

Mechanical Behavior and Strengthening Mechanisms in Precipitation-Strengthened Aluminum Alloy with Gradient Structure Induced by Sliding Friction Treatment

The flat surfaces of a 7075 aluminum (Al) alloy plate were processed by sliding friction treatment (SFT), which is a technique for surface nanocrystallization of metals and alloys. The aim of this study was to investigate the microstructural evolution, mechanical behavior and strengthening mechanisms in this SFTed precipitation-strengthened Al alloy. The SFT resulted in a gradient structure (GS) with an effective depth of ~ 800 µm, and a nanostructured layer was formed within a depth of ~ 30 µm from the surface. Increasing boundary spacing and decreasing misorientation angle between boundaries were found with increasing depth from the surface, which was accompanied by a decrease in hardness from ~ 2436 MPa in the topmost surface layer to ~ 1568 MPa in the undeformed coarse grain (CG) matrix. Moreover, the GS revealed a prominent precipitate redistribution induced by the SFT. The GS revealed higher strength and especially exhibited a higher work-hardening rate at low strain (e < 0.026) than the CG, attributed to a novel coupling of dislocations, boundaries and precipitates. Grain boundary strengthening, dislocation strengthening, precipitation strengthening and synergetic strengthening in the GS were quantitatively evaluated based on sufficient discussion.

Linking meteorological patterns shift to hydrological extremes in a lake watershed across the mid-high latitude transition region

Climate transition at different scales complicates the dynamics of catchment water cycle. Examination of meteorological pattern shift enables us to have a deeper insight of the mechanism in hydrological extremes. Lake Hulun, the largest freshwater lake in Northern China, plays an important role in maintaining the regional ecological sustainability. The abrupt decrease of water level in the lake after 2000 has resulted in serious impacts on the lake’s ecosystem. This paper presents a systematic analysis by linking meteorological dynamics with hydrological extremes based on the long-term precipitation, river discharge, and evapotranspiration (ET) data in the Lake Hulun watershed, which is a transition zone from desert to wetland and to permafrost along the Mongolia–China borderline. The results indicate that signals of large-scale precipitation variations can be well identified by using the Empirical Orthogonal Function (EOF). Spatially, the precipitation in the Lake Hulun watershed is dominated by two leading EOF patterns at the basin scale. The two leading patterns present complementary features of the high value centers in space. The amplitudes evolution of the leading patterns of EOF reveal that the redistribution of precipitation that occurred more in the middle flat plain and less in the mountain regions of the watershed triggers a big effect on the increasing ET and weakening runoff production due to the spatial heterogeneity in hydrological processes. Such effects are echoed by the trend patterns in precipitation and ET. The mechanism of the precipitation pattern shift is also confirmed by the large scale meteorological variations in geopotential and water vapor transport. Therefore, the change in the leading patterns of precipitation and the effects in ET triggered by the pattern shift in precipitation are the major causes of decrease in watershed runoff and the hydrological extremes in the terminal lake.

Impact of Afforestation on Atmospheric Recharge to Groundwater in a Semiarid Area

AbstractWhile the global forest area is generally decreasing, various afforestation projects have been implemented, including the large‐scale Three‐North Afforestation Program (TNAP) and the Conversion of Cropland to Forest Program in China, under which 0.63 million square kilometers of trees have been planted. The large‐scale land use and cover change (LUCC) would affect the redistribution of precipitation and change the water cycle, especially groundwater recharge. The chloride mass balance (CMB) between precipitation and soil water/groundwater is the most widely used technique to estimate the recharge in arid and semiarid areas. However, in the case of decreased recharge following LUCC, a new equilibrium of water and chloride flux is not easily reached and the identification of steady state is the premise to use CMB. This study provided a method to assess the steady state by comparing the history of LUCC and chloride cumulative age at sampling depth and by checking the breaks in the slope of the line for cumulative chloride and soil water. The case study in the Mu Us Sandy Land, affected by the TNAP, shows that soil profiles beneath sparse grassland, shrubland, and woodland have reached steady state. However, new equilibrium has not been reached in the soil profiles beneath the dense shrubland. The estimated recharge rates beneath the plantations represent reductions from 33% to &gt;90% relative to the surrounding bare sandy land (50–54 mm/year). The results highlight the unfavorable effects of some afforestation and ecological rehabilitation approaches in arid and semiarid areas on regional groundwater resources.

Evolution of microstructure and mechanical properties during tempering of M50 steel with Bainite/Martensite duplex structure

The evolution of microstructure and mechanical properties during tempering of M50 steel with bainite/martensite (B/M) duplex structure have been investigated. The microstructural observation shows that the redistribution of carbon atoms and precipitation of transition carbides in the B/M duplex specimens are slightly decreased during the initial stage of tempering, as compared with the fully martensitic specimens. After tempering of 550 °C, not only finer ferrite packets are obtained, but also the precipitation of nano-scale carbides is enhanced for the B/M duplex specimens. The mechanical characterization indicates that the hardness is decreased while the impact toughness is significantly improved when tempering temperature increases to 300 °C. When the tempering temperature increases to 550 °C, due to the decomposition of retained austenite (RA) and precipitation of alloy carbides, the hardness exhibits an obvious improvement while the toughness first decreases and then increases. The impact toughness of the B/M duplex specimens is higher than that of the fully martensitic specimens during the whole tempering process, although they have the same tendency varying with tempering temperature. Furthermore, the final wear resistance is significantly improved in the austempered specimens due to the enhanced precipitation during tempering.

The impacts of a warming climate on winter mid-latitude cyclones in the NARCCAP model suite

The North American Regional Climate Change Assessment Program (NARCCAP) represents the next step in investigating the behavior of weather phenomena in current and future climate. Specifically, variations in mid-latitude cyclone tracks attributable to a warming climate have potential socio-economic consequences via the redistribution of precipitation on regional spatial scales. This manuscript assesses the impacts of a warming climate on cyclone tracks in the NARCCAP model suite. Specifically, cyclones are generated from eight 33-year simulations for the twentieth Century (1968–2000) and eight 33-year simulations for the A2 greenhouse scenario (2068–2100). To provide comparison, cyclone tracks are also generated from the Climate Forecast System Reanalysis (CFSR) and ERA Interim (ERA_INT) reanalysis datasets from 1979 to 2016. The results support that the NARCCAP model suite is capable of producing a reasonable cyclone frequency and intensity climatology when compared with the reanalysis datasets. Comparison of the ensemble twentieth Century cyclone (20C) tracks with the ensemble A2 cyclone tracks demonstrate a zonally-oriented poleward shift in cyclone track frequency in response to a warming climate. Intensity differences were regionally oriented, with cyclones being more intense in the A2 relative to the twentieth Century scenarios west of the Appalachians, suggesting cyclones acquire greater latent heat from warmer western Atlantic/Gulf of Mexico moisture sources in A2. A sector analysis revealed a higher total frequency of cyclones in both reanalysis datasets relative to either NARCCAP scenario. For intense cyclones, the NARCCAP model simulations produced more frequent cyclones in the Great Lakes and East Coast sectors. In contrast, reanalysis produced a higher frequency of weak cyclones for all sectors except Atlantic Canada. In addition, NARCCAP simulations were found to be capable of reproducing the broadness of intensity distributions in the reanalysis datasets, likely due to the fine spatial gridding in the NARCCAP models. Sector analysis for frequency and intensity affirmed the ensemble results, with individual model simulations showed a reduction in frequency for all sectors except the Canadian Maritimes for A2 relative to 20C. For intensity, cyclones were once again overall more intense for the upper Midwest/Great Lakes sector for A2 relative to 20C. The results of this research demonstrates the ability for regional climate models to be used to assess changes in synoptic-scale phenomena in a warming climate. Future work will focus on assessing cyclone structure including changes in moisture transport, precipitation, and the low-level jet.

The effects of gap size and litter species on colonization of soil fauna during litter decomposition in Pinus massoniana plantations

Litter decomposition is a major component of the nutrient cycle in forest ecosystems. It is generally accepted that higher initial quality and litter mixture contribute to increased mass loss, and the effects of soil fauna on litter decomposition is context-dependent. Meanwhile, the formation of gaps alters the hydrological and thermal conditions of the forest through the redistribution of light and precipitation, ultimately influencing the distribution and activity of the soil biota. Previous studies have focused on the effects of either litter species or forest gaps on soil microbes. However, the combined effects of litter species and gap size on the composition and structure of the soil fauna during litter decomposition have not been thoroughly examined. By analyzing litter collected over the course of one year from a Pinus massoniana plantation, shifts in the soil fauna, including indicator groups and guilds based on feeding habits, were correlated with changes of litter substrate, gap size, and incubation time. It was also observed that mesofauna (including microarthropods, nematodes, etc.) were more susceptible to these examined factors than macrofauna. Furthermore, litter type has higher influence on the abundance and richness of soil fauna than litter diversity. In general, small to intermediate sized gaps improved soil fauna diversity, richness, and functional diversity of indicator taxa. The relative abundance of guilds varied with gap size, litter species, and incubation time. The relative abundance of carnivores increased with gap size, whereas fungivores and detritivores increased with incubation time. The observed relative abundance of herbivores was higher in P. massoniana leaf litter than in Cinnamomum camphora and mixed-species leaf litters. Overall, the data presented here indicated that the creation of small to intermediate sized gaps will increase the diversity of soil fauna and accelerate litter mass loss in P. massoniana plantations. The subsequent effects on the return of bioavailable nutrients and soil carbon storage require additional long-term studies.

Late Holocene monsoon precipitation changes in southern China and their linkage to Northern Hemisphere temperature

Observations and models suggest a latitudinal redistribution of precipitation as a result of ongoing global climatic warming. However, the dynamic link between temperature and regional precipitation in the course of natural climatic variability during the current interglacial period remains unclear, especially in the monsoon regions of China. Here we present a reconstruction of a ∼5 year-resolution summer monsoon rainfall record for the past 3200 years, based on 622 pairs of δ18O and δ13C and 29 230Th dates from a stalagmite (Wu37) from Wulu Cave in southern China. A close similarity between the δ18O and δ13C records on centennial to decadal timescales suggests that calcite δ18O is most likely a proxy associated with monsoon precipitation. The record reveals that the Little Ice Age (650 - 100 yr B.P.) was a relatively humid period, with two centennial-scale wet events, compared with the Medieval Warm Period (1050 - 650 yr B.P.). In contrast with previous observations in India and northern China, monsoon precipitation variations indicated by our record and other cave records nearby were inversely related to changes in Northern Hemisphere (NH) temperature over the past two millennia, in particular to variations in the thermal gradient between the Northern and Southern hemispheres. This suggests that NH temperature has an important influence on summer precipitation in southern China, via the interhemispheric thermal gradient and land-ocean thermal contrast. In addition, we find that variations of monsoon rainfall in southern China on multi-centennial to centennial timescales are inversely correlated with observed rainfall in the core monsoon region of India and in the northern fringe of the Asian summer monsoon region in China. This spatial pattern of rainfall variability can be interpreted as a result of the migration of the intertropical convergence zone that is likely dominated by the interhemispheric thermal gradient via cross-equatorial airflows.

A Novel ENSO Monitoring Method using Precipitable Water Vapor and Temperature in Southeast China

Southeast China, a non-core region influenced by the El Niño–Southern Oscillation (ENSO), has been seldom investigated before. However, the occurrence of ENSO will affect the redistribution of precipitation and the temperature (T) spatial pattern on a global scale. This condition will further lead to flood or drought disasters in Southeast China. Therefore, the method of monitoring the occurrence of ENSO is important and is the focus of this paper. The spatiotemporal characteristics of precipitable water vapor (PWV) and T are first analyzed during ENSO using the empirical orthogonal function (EOF). The results showed that a high correlation spatiotemporal consistency exist between PWV and T. The response thresholds of PWV and T to ENSO are determined by moving the window correlation analysis (MWCA). If the sea surface temperature anomaly (SSTA) at the Niño 3.4 region exceeded the ranges of (−1.17°C, 1.04°C) and (−1.15°C, 1.09°C), it could cause the anomalous change of PWV and T in Southeast China. Multichannel singular spectral analysis (MSSA) is introduced to analyze the multi-type signals (tendency, period, and anomaly) of PWV and T over the period of 1979–2017. The results showed that the annual abnormal signal and envelope line fluctuation of PWV and T agreed well in most cases with the change in SSTA. Therefore, a standard PWV and T index (SPTI) is proposed on the basis of the results to monitor ENSO events. The PWV and T data derived from the grid-based European Center for Medium-Range Weather Forecasting (ECMWF) reanalysis products and GNSS/RS stations in Southeast China were used to validate the performance of the proposed SPTI. Experimental results revealed that the time series of average SPTI calculated in Southeast China corresponded well to that of SSTA with a correlation coefficient of 0.66 over the period of 1979–2017. The PWV values derived from the Global Navigation Satellite System (GNSS) and radiosonde data at two specific stations (WUHN and 45004) were also used to calculate the SPTI. The results showed that the correlation coefficients between SPTI and SSTA were 0.73 and 0.71, respectively. Such results indicate the capacity of the proposed SPTI to monitor the ENSO in Southeast China.

Inconsistent changes in global precipitation seasonality in seven precipitation datasets

Changes in precipitation seasonality or redistribution of precipitation could exert significant influences on regional water resources availability and the well-being of the ecosystem. However, due to the nonuniform distribution of precipitation stations and intermittency of precipitation, precise detection of changes in precipitation seasonality on the global scale is absent. This study identifies and inter-compares trends in precipitation seasonality within seven precipitation datasets during the past three decades, including two gauge-based datasets derived from the Climatic Research Unit (CRU) and the Global Precipitation Climatology Centre (GPCC), one remote sensing-retrieval obtained from Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Climate Data Record (PERSIANN-CDR), three reanalysis datasets obtained from National Centers for Environmental Prediction reanalysis II (NCEP2), European Centre for Medium-Range Weather Forecasts Interim Reanalysis (ERA-Interim), and Modern Era Reanalysis for Research and Applications Version 2 (MERRA2), and one precipitation dataset merged from above three types, Multi-Source Weighted Ensemble Precipitation Version 1.2 (MSWEP_V1.2). Values of two indices representing the precipitation seasonality, the normal seasonality index (SI) and the dimensionless seasonality index (DSI), are estimated for each land grid in each precipitation dataset. The results show that DSI is more sensitive to changes in the temporal distribution of precipitation as it considers both annual amount and monthly fluctuations of precipitation, compared to SI that only considers monthly fluctuations of precipitation. There are large differences in precipitation seasonality at annual and climatologic scales between precipitation datasets for both SI and DSI. Within the seven precipitation datasets, PERSIANN-CDR SI and DSI show high precipitation seasonality while CRU SI, and ERA-Interim and MERRA2 DSI show the low precipitation seasonality in all continental regions. During 1988–2013, PERSIANN-CDR, NCEP2 and ERA-Interim show more widespread, statistically significant trends in precipitation seasonality than other four precipitation datasets. PERSIANN-CDR and NCEP2 show statistically significant decreases in SI over Middle East and Central Asia, while ERA-Interim, MERRA2 and MSWEP_V1.2 SI increase over Central and South Africa. Increases in SI over the most of South America are significant. Regions of Canada/Greenland/Iceland, East and South Africa show significant increases in precipitation seasonality, while South Europe/Mediterranean and Central Africa show significant decreases in precipitation seasonality in most datasets. Although time series of seasonality indices values fluctuate correlatively in recent three decades, there are no regions on which all precipitation datasets show a consistent, statistically significant, positive or negative trend in indices of precipitation seasonality. These inconsistent changes in precipitation seasonality within various precipitation datasets imply the importance of choosing dataset when studying changes in regional precipitation seasonality.

Snow Depth Patterns in a High Mountain Andean Catchment from Satellite Optical Tristereoscopic Remote Sensing

AbstractObtaining detailed information about high mountain snowpacks is often limited by insufficient ground‐based observations and uncertainty in the (re)distribution of solid precipitation. We utilize high‐resolution optical images from Pléiades satellites to generate a snow depth map, at a spatial resolution of 4 m, for a high mountain catchment of central Chile. Results are negatively biased (median difference of −0.22 m) when compared against observations from a terrestrial Light Detection And Ranging scan, though replicate general snow depth variability well. Additionally, the Pléiades dataset is subject to data gaps (17% of total pixels), negative values for shallow snow (12%), and noise on slopes &gt;40–50° (2%). We correct and filter the Pléiades snow depths using surface classification techniques of snow‐free areas and a random forest model for data gap filling. Snow depths (with an estimated error of ~0.36 m) average 1.66 m and relate well to topographical parameters such as elevation and northness in a similar way to previous studies. However, estimations of snow depth based upon topography (TOPO) or physically based modeling (DBSM) cannot resolve localized processes (i.e., avalanching or wind scouring) that are detected by Pléiades, even when forced with locally calibrated data. Comparing these alternative model approaches to corrected Pléiades snow depths reveals total snow volume differences between −28% (DBSM) and +54% (TOPO) for the catchment and large differences across most elevation bands. Pléiades represents an important contribution to understanding snow accumulation at sparsely monitored catchments, though ideally requires a careful systematic validation procedure to identify catchment‐scale biases and errors in the snow depth derivation.

МНОГОЛЕТНЯЯ ДИНАМИКА АТМОСФЕРНЫХ ОСАДКОВ НА ЧЕРНОМОРСКОМ ПОБЕРЕЖЬЕ КАВКАЗА

Long-term changes in the amount of precipitation on the Black Sea coast of the Caucasus according to data of the hydro-meteorological stations Anapa, Tuapse and Sochi are considered. The observation data analysis of for the selected periods revealed an increase in the average yearly precipitation from the beginning of the twentieth to the beginning of the twenty-first centuries for all hydro-meteorological stations with a slight decrease in the coefficient of variation. Seasonal changes in precipitation regime are pronounced in the region. The highest increase in seasonal precipitation was noted at the Anapa hydro-meteorological station for winter, then for spring and autumn. At the Tuapse and Sochi hydro-meteorological stations also tended to increase precipitation in spring and autumn, but was noted a slight decrease in winter in the modern period. At the same time, for all seasons such growth is provided mainly by an increase in the minimum seasonal values (for all stations), as well as maximum ones in spring (for all stations) and autumn (hydro-meteorological station Anapa). In modern period relative to the twentieth century it is possible to note a slight decrease in the coefficient of variation in winter and spring (for all hydro-meteorological stations), and an increase in summer (for hydro-meteorological stations Anapa and Tuapse). The redistribution of precipitation by seasons was revealed from the beginning of the twentieth to the beginning of the twentyfirst centuries. The most significant changes affected the hydro-meteorological station Tuapse: the share of autumn and spring precipitation increased from 25 to 31 % and from 18 to 22 %, respectively, while the share of summer precipitation decreased from 26 to 18 %. The share of winter precipitation increased from the first to the third selected periods (from 30 to 35 %), after which it decreased to 29 % in the modern period.

Growing-season temperature and precipitation are independent drivers of global variation in xylem hydraulic conductivity.

Stem xylem-specific hydraulic conductivity (KS ) represents the potential for plant water transport normalized by xylem cross section, length, and driving force. Variation in KS has implications for plant transpiration and photosynthesis, growth and survival, and also the geographic distribution of species. Clarifying the global-scale patterns of KS and its major drivers is needed to achieve a better understanding of how plants adapt to different environmental conditions, particularly under climate change scenarios. Here, we compiled a xylem hydraulics dataset with 1,186 species-at-site combinations (975 woody species representing 146 families, from 199 sites worldwide), and investigated how KS varied with climatic variables, plant functional types, and biomes. Growing-season temperature and growing-season precipitation drove global variation in KS independently. Both the mean and the variation in KS were highest in the warm and wet tropical regions, and lower in cold and dry regions, such as tundra and desert biomes. Our results suggest that future warming and redistribution of seasonal precipitation may have a significant impact on species functional diversity, and is likely to be particularly important in regions becoming warmer or drier, such as high latitudes. This highlights an important role for KS in predicting shifts in community composition in the face of climate change.

Systematic precipitation redistribution following a strong hurricane landfall

The 2017 and 2018 Atlantic hurricane seasons poignantly illustrated the dangers tropical cyclones pose to US, Central American, and Caribbean coastlines. In particular, Hurricane Maria inflicted widespread damage, including catastrophic defoliation, to Puerto Rico, altering surface heat fluxes and possibly modifying precipitation patterns. This study assesses whether defoliation-driven changes to surface energy fluxes redistribute precipitation in the months following a powerful hurricane landfall. Remote sensing analyses of Maria-related vegetation reduction and recovery from Puerto Rico were adapted to the Georgia coastline. In this novel methodology, the resulting landscape evolution, characterized by an instantaneous vegetation reduction with a gradual recovery, was assimilated into the Weather Research and Forecasting model at a convection-allowing a 3-km grid spacing for the 1 June–1 August 2017 period. The experiment revealed that Maria-scale defoliation reduced precipitation by 14% during the month following landfall within a 50 × 50 km zone containing the hypothetical landfall location. A maximum deficit of 20.0% was reached 4 weeks after landfall. For June 2017, the modeled 14% deficit would have shifted the precipitation total from the 61st to the 47th percentile for years 1981–2016. Meanwhile, precipitation totals were unchanged on the domain scale. The near-landfall drying was also evident in three less-severe defoliation simulations, suggesting that systematic precipitation redistribution near the landfall location is possible following storms considerably weaker than Hurricane Maria. Analyses of the temperature and wind fields suggest that coastal kinematic flow is altered by the introduction of a thermally driven pressure gradient in the defoliated zone.

Higher temporal evapotranspiration estimation with improved SEBS model from geostationary meteorological satellite data

Evapotranspiration (ET) is a key variable in hydrologic cycle that directly affects the redistribution of precipitation and surface balance. ET measurements with high temporal resolution are required for coupling with models of highly dynamic processes, e.g., hydrological and land surface processes. The Haihe River Basin is the focus of China’s industrial base and it is one of the three major grain-producing regions within the country. However, this area is facing serious water resource shortages and water pollution problems. The present study used geostationary satellite remote sensing data, in situ meteorological observations, and the surface energy balance system (SEBS) model with a new kB−1 parameterization to estimate 3-hourly and daily energy and water fluxes in the Haihe River Basin. The results of the SEBS model were validated with point-scale data from five observation flux towers. Validation showed that 3-hourly and daily ET derived from the SEBS model performed well (R2 = 0.67, mean bias = 0.027 mm/h, RMSE = 0.1 mm/h). Moreover, factors influencing ET were also identified based on the results of this study. ET varies with land cover type and physical and chemical properties of the underlying surface. Furthermore, ET is also controlled by water availability, radiation, and other atmospheric conditions. It was found that ET had strong correlation with the normalized difference vegetation index (NDVI). Specifically, daily ET fluctuated with the NDVI when the NDVI was <0.29, and ET increased rapidly as the NDVI increased from 0.29 to 0.81. For NDVI values >0.81, indicating a state of saturation, the rate of increase of ET slowed. This research produced reliable information that could assist in sustainable management of the water resources and in improved understanding of the hydrologic cycle of the Haihe River Basin.