Spring Rainfall Research Articles

Impact of the Anomalous Latent Heat Flux Over the Kuroshio Extension on Western North American Rainfall in Spring: Interannual Variation and Mechanism

The Kuroshio and its extension (KE) significantly influences regional climate through meridional heat transport from the tropical ocean. In this study, the observational and reanalysis datasets are used to investigate the impact of the latent heat flux (LHF) over the KE region on downstream rainfall and the underlying mechanism. The result shows a “seesaw” structure in rainfall anomaly, dominating the Western Canada and the southwestern North America with a correlation coefficient of 0.77 between the two modes. In strong LHF years, strengthened LHF favors to enhance precipitation in the Western Canada and reduce that in the southwestern North America. This is primarily associated with an anomalous cyclonic circulation over the KE region, which enhances southwesterly precipitation and latent heating in the middle troposphere. The heating excites an anomalous cyclonic circulation to its west and an anticyclonic circulation to its east, helping to reinforce the existing anomalous cyclonic circulation in turn and form a positive feedback. The conditions associated with La Niña events favor to above processes. To the upper troposphere, the deepened anomalous cyclonic circulation due to enhanced eddy activities and atmospheric baroclinic instability over the KE strengthens subtropical westerly jet stream and thereby extends eastward on the 200 hPa level. Correspondingly, an elongated zonally lower level cyclonic circulation anomaly across the North Pacific leads to a moisture convergence in the Western Canada, which is mainly resulted from the anomalous positive vorticity advection over the left side of the exit region of the jet stream. The opposite circumstance occurs in weak LHF years, presenting an opposed anomalous circulation and rainfall pattern.

Seasonal Evolution of Anomalous Rainband over East China Regulated by Sea Surface Temperature Anomalies in the Northern Hemisphere

AbstractSeasonal evolution of rainband over East China is evident and shows remarkable year-to-year variations. The present study identified two dominant interannual modes of the seasonal evolution of rainband over East China from 1981 to 2018: (1) the sudden change pattern, in which the anomalous rainfall changes abruptly from boreal spring to summer, especially over South China; and (2) the northward migration pattern, which shows a gradual poleward migration of the anomalous rainband over East China with the East Asian summer monsoon (EASM). Both of them are regulated by the sea surface temperature anomalies (SSTAs) in the Northern Hemisphere from spring to summer. In the sudden change pattern, the SSTAs in the Pacific modulate spring rainfall over South China via the ENSO–EASM teleconnection. By contrast, the North Atlantic SSTAs change the mid-latitude wave train and modify summer rainfall over South and North China, in conjunction with the anomalous tropical circulation due to the Indian SSTAs. In the northward migration pattern, the North Pacific SSTAs alter spring rainfall over South China by varying the low-level western North Pacific subtropical high and the zonal land–sea thermal contrast over East Asia. Afterward, the ENSO-like SSTAs induce a Pacific–Japan teleconnection and shift the anomalous rainband northward to the Yangtze-Huai River and North China in summer. The seasonal switch of the SSTAs regulating these two modes is physically linked from boreal spring to summer. This mechanism provides potential seasonal predictability of the seasonal evolution of the anomalous rainband over East China.

Interdecadal Variation of Early Spring Rainfall Over the Southeastern Edge of the Tibetan Plateau

AbstractThis study investigates the interdecadal variation in early spring rainfall over the southeastern edge of the Tibetan Plateau (SEETP) during 1979–2015 and its possible causes using mainly Asian Precipitation–Highly‐Resolved Observational Data Integration Toward Evaluation daily precipitation data set, ERA5 reanalysis data and the atmospheric general circulation model ECHAM6. A significant interdecadal change in early spring rainfall over the SEETP occurred with its node around 1998/1999. The early spring rainfall over the SEETP was heavier in 1979–1998 than in 1999–2015, reflecting a reduction in moderate and heavy rain during the early spring. The covariability of the Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), and Indian Ocean Basin Mode (IOBM) is an important driver of the interdecadal decrease in early spring rainfall over the SEETP. When the PDO is in a cold phase, and the AMO and IOBM are in positive phases, an anomalous cyclone is excited over the Bay of Bengal‐western Pacific in the lower to middle troposphere. Anomalous easterly winds on the north flank of the anomalous cyclone lead to the interdecadal decrease in early spring rainfall over the SEETP by reducing water vapor transport from the Indian Ocean and producing divergence over the SEETP. This diagnosis of the key physical process linking the associated sea surface temperature anomalies with the interdecadal variation in early spring rainfall over the SEETP is supported by numerical experiments.

Atmospheric Wet Deposition of PCDD/Fs in the Ambient Air

ABSTRACT Wet deposition is an important mechanism for removing air pollutants from the atmosphere. The total PCDD/Fs-WHO2005-TEQ wet deposition from 2018–2020 was investigated for Beijing and Tianjin City in this study. In addition, the gas-particle partitioning of wet deposition, the total PCDD/Fs-WHO2005-TEQ concentrations in the rain, the PM2.5-bound total PCDD/Fs-WHO2005-TEQ content, and the PM2.5 concentration were also studied for Beijing and Tianjin City, respectively. Between 2018 to 2020, as a whole, the average seasonal variations in PCDD/F wet deposition fluxes in spring, summer, fall, and winter were 50.50, 41.47, 23.03 and 16.76 pg WHO2005-TEQ m–2 month–1, respectively, while in Tianjin, they were 35.30, 42.40, 13.37, and 14.77 pg WHO2005-TEQ m–2 month–1, respectively. Because the two cities have more rainfall in spring and summer than they do in fall and winter, rainfall has a significant influence on the wet deposition flux. In regard to PCDD/Fs-WHO2005-TEQ in the rain, in Beijing, the average total PCDD/Fs-WHO2005-TEQ concentration in the rain in spring, summer, fall, and winter were 1.70, 0.39, 1.42, and 1.52 pg WHO2005-TEQ L–1, respectively, while those in Tianjin, were 1.73, 0.42, 1.35, and 1.88 pg WHO2005-TEQ L–1, respectively. The above results show that the total PCDD/Fs-WHO2005-TEQ concentrations in the rain are significantly lower in summer, which is mainly due to the fact that in summer, the total PCDD/Fs-WHO2005-TEQ concentrations in the air are lower, and the proportion of the gas phase is increased. When the total PCDD/Fs-WHO2005-TEQ concentrations in the air are washed away by a heavy rainfall, the PCDD/F concentrations are diluted.

Wpływ cyrkulacji atmosferycznej na opady w Tatrach oraz Czarnohorze = Influence of atmospheric circulation on precipitation in Tatra and Chornohora Mts.

While significant increases in air temperature are being observed in the context of climate change, precipitation characteristics, indicators and indices seem to be changing in a more regionally-variable manner. High-mountain areas prove particularly subject to fluctuations and changes of climate, given that mountains serve as barriers to masses of air flowing over them, with the result that atmospheric precipitation totals are high in the context of the so-called orographic rainfall. Overall, the Chornohora represents the highest range anywhere in Ukraine’s Carpathian Mts, as there are six peaks over 2000 m a.s.l. capable of serving as a barrier running NW-SE. Nevertheless, the main ridge of the High Tatras (of the Slovakia-Poland borderland) is even higher and runs W-E. Each massif is some 30 km in length, while the two ranges are separated by a distance of almost 350 km. Main drainage divides run along the highest ridges here, with the Tatras separating the drainage basins of the Vistula and Danube, while the Chornohora represent a divide between the Prut and Tysa basins. The aim here has been to present characteristics of atmospheric precipitation in Tatra and Chornohora Mts. as these are seen to relate to atmospheric circulation. To this end, the dependent relationship between intensity of precipitation and atmospheric circulation was examined exhaustively, with changes in the latter considered from the point of view of intensity of precipitation in the massifs under study, and with trends for precipitation over the study period also looked for.The Niedźwiedź (2017) classification of types of atmospheric circulation was applied, with annual values calculated for circulation indicators P (a W-E inflow), S (a S-N inflow) and C (a cyclonic/anticyclonic inflow). Overall, the study drew on 1961‑2015 daily precipitation data from the north-eastern slope of Chornohora Mts. (as represented by Ukraine’s Pozhyzhevska weather station, PO, 1451 m a.s.l.), as well as the north slope of the Tatra Mts. (as represented by Poland’s Hala Gasienicowa weather station, HG, 1520 m a.s.l.).An air inflow from western directions was found to have prevailed over 28% of the days in the average year (Fig. 1). The most frequent types involved here were: Ka (12%), Bc (10%), Wc (10%) and Wa (8%). During the summer months (JJA), it is the Ka and Bc types that are even more frequent (present on approx. 15% of summer days). Types Wc and Wa in turn occur more frequently in winter (DJF) – respectively 13% and 12% of the time. In autumn, these types reach a level of occurrence around 10%.At 1712 mm, the average annual rainfall total for Tatra Mts is higher than that for the Chornohora (on 1446 mm). While the seasonal distribution of rainfall in spring and autumn looks almost the same in the two massifs, winter brings more precipitation in the Chornohora, while summer is a wetter season in the Tatras (Fig. 2). Largest amounts of precipitation nevertheless fall in the warm half-year, in the circumstances of N+NEa advection, cyclonic situations and under arctic, polar-marine or polar-marine transformed air masses (Figs. 3 and 4).The largest changes over time are to be observed for the zonal inflow index (P) and the cyclonic index (C). The P index points to increased numbers of days with a western circulation, while the C index confirms the domination of anticyclonic circulation (Fig. 5). The trend for annual rainfall totals is an upward one overall in both regions, but in neither does this achieve statistical significance (Fig. 6). Equally, there is a downward trend line for numbers of days featuring precipitation (RRdays) in the cases of both the Chornohora and Tatra ranges (equal to -7.3 days/10 years and -7.59 days/10 years respectively) (Fig. 7). On the other hand, the trend for numbers of days with higher rainfall, e.g. with RRdays>10mm is upward for the Chornohora (at +1.23 days/10 years), but downward for the Tatra Mts (at -0.6 days/10 years) (Fig. 8).

The Seasonal Rainfall Forecast in Nanning City in 2019 with the Method of Trend Comparison Ratio (TCR)

In this paper, the monthly rainfall statistical data of Nanning City, Capital of Guangxi Zhuang Autonomous Region, China, from 2006 to 2018, were collected. On the basis of qualitative analysis of the rainfall seasonal changing law, the non-linear seasonal rainfall forecast model on Nanning City with the method of Trend Comparison Ratio (TCR) was established by the statistical analysis software Office Excel 2013. The model was used to predict the rainfall in spring, summer, autumn and winter in Nanning in 2019. The results were: 286.41 mm, 695.79 mm, 292.20 mm and 118.11 mm, respectively. It was also found that the predicted results were consistent with the seasonal distribution characteristics, annual distribution characteristics and the trend of historical rainfall time series fluctuation, through the qualitative analysis of figures. Compared with the actual measured rainfall data of Nanning City in 2019 in the China Statistical Yearbook (2020), the predicted values are basically consistent with the measured values.

Comparison of seasonal climate in China during the cold and warm phases of ENSO

El Niño-Southern Oscillation (ENSO) events have serious impacts on weather patterns, agriculture and ecosystems, and play an important role in predicting regional and global climate. A 2-tailed Student’s t-test was used to analyze the differences of seasonal air temperature and rainfall between ENSO years (El Niño/La Niña years) and non-ENSO years in China, and the results indicate that summer temperature was lower, and winter, spring and autumn rainfall was higher in El Niño years, while in La Niña years, winter temperature was lower and summer rainfall was higher in China as a whole. There were significant regional differences in seasonal temperature and rainfall between ENSO and non-ENSO years. In El Niño years, summer temperatures in most regions of China were lower than those in non-ENSO years. Summer and autumn rainfall was higher in the mid-lower reaches of the Yangtze River but lower in North China, and winter rainfall was lower in southern China. In La Niña years, winter temperatures were lower in the mid-lower reaches of the Yangtze River and South China, and summer rainfall was higher in Northeast China, North China, the mid-lower reaches of the Yangtze River and Southwest China than those in non-ENSO years. We conclude that the impacts of ENSO on rainfall are more obvious than those on temperature, and the responses of seasonal temperature and rainfall to El Niño are more obvious than those to La Niña events in China.

Dryness over the U.S. Southwest, a Springboard for Cold Season Pacific SST to Influence Warm Season Drought over the U.S. Great Plains

AbstractAlthough the influence of sea surface temperature (SST) forcing and large-scale teleconnection on summer droughts over the U.S. Great Plains has been suggested for decades, the underlying mechanisms are still not fully understood. Here we show a significant correlation between low-level moisture condition over the U.S. Southwest in spring and rainfall variability over the Great Plains in summer. Such a connection is due to the strong influence of the Southwest dryness on the zonal moisture advection to the Great Plains from spring to summer. This advection is an important contributor for the moisture deficit during spring to early summer, and so can initiate warm season drought over the Great Plains. In other words, the well-documented influence of cold season Pacific SST on the Southwest rainfall in spring, and the influence of the latter on the zonal moisture advection to the Great Plains from spring to summer, allows the Pacific climate variability in winter and spring to explain over 35% of the variance of the summer precipitation over the Great Plains, more than that can be explained by the previous documented west Pacific–North America (WPNA) teleconnection forced by tropical Pacific SST in early summer. Thus, this remote land surface feedback due to the Southwest dryness can potentially improve the predictability of summer precipitation and drought onsets over the Great Plains.

Pteridium aquilinum performance is driven by climate, soil and land-use in Southwest Asia

Growing anthropogenic impacts on natural and semi-natural ecosystems have created a network of degraded sites throughout the world. These disturbed ecosystems are often colonized by invasive plants such as Pteridium aquilinum, which is one of the most widespread plants worldwide. In northern Iran, P. aquilinum is often found invading newly-created habitats formed after anthropogenic disturbance. This study aimed to assess the relationship between P. aquilinum performance and a range of environmental factors (soils, climate, topography and land-use) in northern Iran. In fifteen sites dominated by P. aquilinum, that spanned the regional distribution of P. aquilinum, we measured its cover, density and biomass. Pteridium aquilinum was found to occur in a variety of land-uses including abandoned agricultural lands, degraded forests and upland rangelands. The performance of P. aquilinum varied significantly between the sites and it performed better in a moderate-Mediterranean climate. Variation partitioning confirmed the importance of climate followed by soil and land-use in explaining the performance of P. aquilinum. Topographic variables did not show any significant effect on P. aquilinum. Both temperature and rainfall affected P. aquilinum performance. Density was correlated positively with early-spring rainfall whereas biomass and cover were found to have positive correlation with temperature. There was also a gradient of soil texture/pH/N/P influencing P. aquilinum. Frond density and biomass were correlated positively with sand content, N and P, but negatively with pH, lime and bulk density. Thus, soil conditions alongside temperature in spring and early summer could explain P. aquilinum cover, but for density, rainfall in early spring was the most important factor, suggesting that in northern Iran P. aquilinum performance appears to be intermediate compared to responses reported for temperate (temperature-controlled) and tropical climates (rainfall-controlled).

Relación entre la variabilidad climática y el crecimiento radial de Pinus montezumae Lamb. en Coyuca de Catalán, Guerrero

Introduction: Understanding the dendroclimatic potential of a species allows us to reconstruct the climate variability in the latitudes and altitudes of its distribution. Objective: To determine the potential of Pinus montezumae Lamb. to reconstruct climatic variables. Materials and methods: A total of 80 samples were extracted with a Pressler increment borer and dated, allowing growth rates to be generated. Average monthly rainfall and minimum and maximum temperature were obtained, and a response function analysis between growth rates and climate data was conducted. Results and discussion: Dated samples represented 75 % of the total. The COFECHA program indicated a correlation between series of r = 0.57 (P < 0.01) and a mean sensitivity of 0.31; P. montezumae is sufficiently sensitive to record climate variability. Three chronologies (standard, residual and arstan) covering 228 years (1790-2017) were generated for each of the three growth rates (total ring, early and latewood). The response function analysis showed that it is possible to reconstruct the spring rainfall and the May-July maximum temperature based on the total ring (r = 0.66; P < 0.01) and latewood (r = 0.35; P < 0.01) indices, respectively. Conclusion: Statistical parameters indicate that P. montezumae is an adequate proxy source for climate variability reconstruction studies.

Effect of Cultivar Resistance and Soil Management on Spatial-Temporal Development of Verticillium Wilt of Olive: A Long-Term Study.

Verticillium wilt, caused by Verticillium dahliae, challenges olive cultivation and an Integrated Disease Management (IDM) approach is the best-suited tool to combat it. Since 1998, an IDM strategy in an orchard (called Granon, Spain) of the susceptible cv. Picual was conducted by increasing planting density with moderately resistant cv. Frantoio, chemical weed control, and replanting of dead olives with cv. Frantoio following soil solarization. The Verticillium wilt epidemic in Granon orchard was compared to the epidemic in a non-IDM orchard (called Ancla, Spain) with plowed soil and dead Picual olives replanted with the same cultivar. Field evaluations (2012–2013) showed an incidence and severity of the disease as Picual–Ancla > Picual–Granon > Frantoio–Granon. The spatiotemporal dynamics of the Verticillium epidemics from 1998 to 2010 were monitored with digital images using SIG. The annual tree mortalities were 5.6% for Picual olives in Ancla orchard, and 3.1 and 0.7% for Picual and Frantoio olives in Granon orchard, respectively. There was a negative relationship between the mortality of olive trees (%) by the pathogen and the height (m) above sea level. The annual mortality of cv. Picual olives was positively correlated with spring rainfalls. The Index of Dispersion and beta-binomial distribution showed aggregation of Verticillium-dead olives. In conclusion, this IDM strategy considerably reduced the disease in comparison with traditional agronomic practices.

Anatomy of the Indian Summer Monsoon and ENSO relationships in state-of-the-art CGCMs: role of the tropical Indian Ocean

Indian Summer Monsoon (ISM) rainfall and El Nino-Southern Oscillation (ENSO) exhibit an inverse relationship during boreal summer, which is one of the roots of ISM interannual variability and its seasonal predictability. Here we document how current climate and seasonal prediction models simulate the timing and amplitude of this ISM-ENSO teleconnection. Many Coupled General Circulation Models (CGCMs) do simulate a simultaneous inverse relationship between ENSO and ISM, though with a large spread. However, most of them show significant negative correlations before ISM, which are at odd with observations. Consistent with this systematic error, simulated Nino-3.4 Sea Surface Temperature (SST) variability has erroneous high amplitude during boreal spring and ISM rainfall variability is also too strong during the first part of ISM. The role of the Indian Ocean (IO) in modulating the ISM-ENSO relationships is further investigated using dedicated experiments with the SINTEX-F2 CGCM. Decoupled tropical Pacific and IO experiments are conducted to assess the direct relationship between ISM and IO SSTs on one hand, and the specific role of IO feedback on ENSO on the other hand. The direct effect of IO SSTs on ISM is weak and insignificant at the interannual time scale in the Pacific decoupled experiment. On the other hand, IO decoupled experiments demonstrate that El Nino shifts rapidly to La Nina when ocean–atmosphere coupling is active in the whole IO or only in its western part. This IO negative feedback is mostly active during the decaying phase of El Nino, which is accompanied by a basin-wide warming in the IO, and significantly modulates the length of ENSO events in our simulations. This IO feedback operates through a modulation of the Walker circulation over the IO, which strengthens and shifts eastward an anomalous anticyclone centered on the Philippine Sea and associated easterly wind anomalies in the equatorial western Pacific during boreal winter. In turn, these atmospheric anomalies lead to a fast ENSO turnabout via oceanic adjustement processes mediated by eastward propagating upwelling Kelvin waves. An experiment in which only the SouthEast Indian Ocean (SEIO) is decoupled, demonstrates that the equatorial SST gradient in the IO during boreal winter plays a fundamental role in the efficiency of IO feedback. In this experiment, simulated ISM-ENSO lead-lag correlations match closely the observations. This success is associated with removal of erroneous SEIO SST variability during boreal winter in the SEIO decoupled experiment. Finally, it is illustrated that most CMIP5 CGCMs exhibit similar SST errors in the SEIO during boreal winter in addition to an exagerated SEIO SST variability during boreal fall.

Adaptation to climate change in irrigated agriculture in Uzbekistan*

AbstractIn recent years, climate change in Central Asia, especially in Uzbekistan, has resulted in sharp alternation of dry and wet years. In such conditions, agriculture has turned into the most vulnerable sector. Agricultural producers have not been able to adapt to such variations of climatic conditions. Traditional irrigation approaches and agronomic operations are becoming unacceptable against the background of severe droughts or heavy rains. Moreover, intra‐annual distribution of precipitation and air temperature has changed. Especially in agriculture, increased rainfall in spring and summer and decreased rainfall in autumn and winter has had a negative impact.In 2013, the Global Water Partnership initiated the Water, Climate, and Development Programme for Caucasus and Central Asia. In the Fergana Valley of Uzbekistan, a project was implemented to study the possibility of agriculture adaptation to climate change within the framework of this programme. This article presents an analysis of long‐term data received from 1960 to 2014 on air temperature and precipitation. As a result of these studies, it has been determined that we can forecast the current year's weather conditions if we find a similar year in recent years. For the Fergana Valley of Uzbekistan, it has been established that we have a stable spring, when winter is cold with heavy precipitation, and we have a cold spring and summer with high precipitation, when we have a warm winter with low precipitation. Past experience has shown that the use of water for irrigation, taking into account climatic conditions, has a significant impact on reducing irrigation water and increasing crop yields.

The influence of soil tillage system on Salsola kali L. emergence during the fallow period within cereal fields

AbstractWith the move towards conservation agriculture, we have seen an increase in weeds such as Salsola kali L., well known as Russian thistle, which are wind spread over fallow land. The emergence of this weed species seemed erratic, perhaps connected to climate conditions and management techniques. In order to shed some light on this issue, we carried out a field experiment over 3 years to monitor Russian thistle density in fallow plots, comparing three tillage systems. This study provides an insight about the limitations of assuming no‐tillage techniques within a cropping system that include fallow in the rotation sequence. Our results show that no‐tillage systems are more vulnerable to S. kali. Low spring rain leads to high S. kali density, especially in no‐tillage plots. High spring rainfall reduced the emergence in all tillage systems because of soil water saturation. Minimum tillage technique served to maintain control over this species even in weather conditions that favoured its emergence in other systems. In order to reduce the need for herbicide in fallow lands under conservation systems, we recommend the implementation of minimum tillage to combat Russian thistle infestation.

Application of high-frequency spring discharge data: a case study of Mathamali spring rejuvenation in the Garhwal Himalaya

Abstract Water scarcity is becoming the biggest threat to the global population due to unpredictable rainfall, glaciers melt, and other anthropogenic activities. This study focuses on the analysis of monitored high-frequency continuous spring discharge and rainfall data in the contact and fracture type Mathamali spring located in the Garhwal Himalaya. Discharge from the spring and its storage behavior has been studied by analyzing recession components and flow duration curves. Analyzed discharge data revealed that the spring can generate maximum volume during monsoon as compared to winter due to aquifer properties and tendencies to store and transmit water. Springshed intervention practices were implemented in early April 2017. The measured average flow was 16.9 lpm but soon after the interventions, the average flow increased by 2.6 times. The minimum average spring flow was 2.3 lpm which increased by 5 times whereas the average maximum flow increased by 1.8 times. Post-intervention, storage duration has increased by 16%, decaying from 143 lpm (peak flow) to 12.7 lpm (baseflow). The preliminary findings from this spring can be considered as a check for establishing benchmarks for sustainable development of springsheds, climate change adaptation, and development plans to cope up with growing water insecurity in the rural Himalayas.

Impact of extreme weather conditions on European crop production in 2018.

Extreme weather increases the risk of large-scale crop failure. The mechanisms involved are complex and intertwined, hence undermining the identification of simple adaptation levers to help improve the resilience of agricultural production. Based on more than 82 000 yield data reported at the regional level in 17 European countries, we assess how climate affected the yields of nine crop species. Using machine learning models, we analyzed historical yield data since 1901 and then focus on 2018, which has experienced a multiplicity and a diversity of atypical extreme climatic conditions. Machine learning models explain up to 65% of historical yield anomalies. We find that both extremes in temperature and precipitation are associated with negative yield anomalies, but with varying impacts in different parts of Europe. In 2018, Northern and Eastern Europe experienced multiple and simultaneous crop failures—among the highest observed in recent decades. These yield losses were associated with extremely low rainfalls in combination with high temperatures between March and August 2018. However, the higher than usual yields recorded in Southern Europe—caused by favourable spring rainfall conditions—nearly offset the large decrease in Northern European crop production. Our results outline the importance of considering single and compound climate extremes to analyse the causes of yield losses in Europe. We found no clear upward or downward trend in the frequency of extreme yield losses for any of the considered crops between 1990 and 2018.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

Effects of tillage systems on wheat and weed water relationships over time when growing together, in semiarid conditions

AbstractWater availability directly influences interactions and competition between weeds and crops. This article is based on the idea that relative water content (RWC) indicates the water uptake within plants and that it is possible to explain the water relationships between plants that are growing together. A field experiment carried out for 3 years (2013–2014, 2014–2015 and 2015–2016) compared the short‐term effects of years and tillage systems on wheat grain yield, weed density, wheat‐RWC, weed‐RWC and soil water content (SWC), at tillering and flowering stages in a winter wheat monoculture system. The three tillage treatments were conventional tillage (CT), minimum tillage (MT) and no‐tillage (NT). Wheat grain yield was low all years of study, because of low interannual rainfall, and we did not observe differences between tillage systems. Weed density was also affected by year and not by tillage systems. Lowest winter rainfall (73.4 mm from Nov to Feb) in the last year of the study (2015–2016), decreased the weed density in all tillage systems. Despite the rainfall variability over the 3 years of study, the NT system presented higher weed density (73 plants/m2) than MT and CT systems (39.83 and 46.33 plants/m2). We also observed a higher number of weed species for the NT system, facilitated by a high soil water storage in this system. The wheat‐RWC, at tillering stage, varied with years and tillage systems; we found that high winter rainfall (2013–2014) led to higher values in CT (64.5%) compared with MT (52.9%) and NT plots (52.9%). Weed‐RWC values did not vary and SWC was greater in NT than in CT and MT. At flowering stage, the year (2015–2016) with highest spring rainfall favoured higher wheat‐RWC in NT (56.9%) compared with CT (48.3%). However, the lowest spring rainfall coincided with the lowest weed‐RWC, (18% in NT plots) and SWC was always higher in NT soils. The results showed that climatic conditions affected the water competence dynamics between weeds and wheat in different ways. Seemingly, weeds can tolerate a lack of water availability until crop tillering stage independently of tillage system; however, the competition for water was not a problem as crops overcame the high weed density by flowering stage.

Comparison of cyanobacterial communities in temperate deserts: A cue for artificial inoculation of biological soil crusts

The topsoil cyanobacteria in biological soil crusts (BSCs) play a vital role in stabilizing soil surface of disturbed habitats in water and nutrient-poor ecosystems. Currently, artificial inoculation of BSCs is considered as an effective approach to restore habitats and accelerate ecosystem regeneration. Understanding the character of cyanobacterial communities is the necessary prerequisite to explore the artificial inoculation of BSCs. For this reason, cyanobacterial communities in BSCs were compared between two mid-latitute temperate deserts with distinct precipitation patterns. The results showed that Oscillatoriales and Nostocales dominated crusts in the Tengger desert with majority of rainfall in summer and early autumn while Oscillatoriales dominated crusts in the Kyzyl kum desert with more rainfall in winter and early spring. Moreover, filamentous Microcoleus vaginatus overwhelmingly dominated all the crusts in both deserts with Mastigocladopsis sp. and Chroococcidiopsis spp. as the dominant heterocystous cyanobacteria. Of note, genus Wilmottia kept a relative stable and high abundance in both deserts. The top two abundantly shared cyanobacteria (> 1% of total sequences) were M. vaginatus and Mastigocladopsis sp. in both deserts, while 16 genera with significant variances were found between the two deserts (P <0.05). Total variations of cyanobacterial communities across the deserts were largely explained by a combination of biotic factors (microbial biomass C and N) and abiotic factors (soil pH, soil water content, soil water holding capacity, and soil available potassium). Compared to better-developed crusts, cyanobacterial abundance was higher in cyanobacterial crusts. BSC type and/or geographic location significantly affected cyanobacterial Shannon diversity without significantly influencing species richness. Our data suggest that the basic and major groups (e.g. M. vaginatus, Wilmottia spp., Mastigocladopsis sp., and Chroococcidiopsis spp.), and the abundantly shared phylotypes which showed significant difference in cyanobacterial communities between deserts, should be focused on to further explore the artificial inoculation of BSCs in temperate drylands.

Monitoring Residual Soil Moisture and Its Association to the Long-Term Variability of Rainfall over the Upper Blue Nile Basin in Ethiopia

Monitoring soil moisture and its association with rainfall variability is important to comprehend the hydrological processes and to set proper agricultural water use management to maximize crop growth and productivity. In this study, the European Space Agency’s Climate Change Initiative (ESA CCI) soil moisture product was applied to assess the dynamics of residual soil moisture in autumn (September to November) and its response to the long-term variability of rainfall in the Upper Blue Nile Basin (UBNB) of Ethiopia from 1992 to 2017. The basin was found to have autumn soil moisture (ASM) ranging from 0.09–0.38 m3/m3, with an average of 0.26 m3/m3. The ASM time series resulted in the coefficient of variation (CV) ranging from 2.8%–28% and classified as low-to-medium variability. In general, the monotonic trend analysis for ASM revealed that the UBNB had experienced a wetting trend for the past 26 years (1992–2017) at a rate of 0.00024 m3/m3 per year. A significant wetting trend ranging from 0.001 to 0.006 m3/m3 per year for the autumn season was found. This trend was mainly showed across the northwest region of the basin and covers about 18% of the total basin area. The spatial patterns and variability of rainfall and ASM were also found to be similar, which implies the strong relationship between rainfall and soil moisture in autumn. The spring and autumn season rainfall explained a considerable portion of ASM in the basin. The analyses also signified that the rainfall amount and distribution impacted by the topography and land cover classes of the basin showed a significant influence on the characteristics of the ASM. Further, the result verified that the behavior of ASM could be controlled by the loss of soil moisture through evapotranspiration and the gain from rainfall, although changes in rainfall were found to be the primary driver of ASM variability over the UBNB.

Plant invasion depresses native species richness, but control of invasive species does little to restore it

ABSTRACT Background Invasive plants are associated with the decline of native plant richness, but the impact of removal of invasives on native plant richness is often unknown. Aims We investigated whether the presence of the introduced plant Centaurea solstitialis (Asteraceae) was correlated with reduced native plant richness; whether rain in late spring, when C. solstitialis is virtually the only plant actively growing, increased its cover; and whether native species richness increased following the control of C. solstitialis. Methods From 2011 to 2017 in a grassland in Sonoma County, California, USA, we treated 20 1-m2 plots in C. solstitialis-invaded patches with chemical and mechanical removal. We monitored cover of all plants in those plots, plus 20 invaded untreated and 20 uninvaded plots, for a total of 60 plots in two blocks. Results Native plant richness was lower in invaded than in non-invaded plots. More late spring rainfall resulted in greater C. solstitialis cover in the following year. Native species richness in the six years after initial removal was slightly higher in removal plots than in untreated control plots. Conclusions Centaurea solstitialis removal alone results in modest benefits for native plant species richness. Managing this invasive requires more resources in years with more late spring rainfall.