Decrease In Summer Precipitation Research Articles

Contrasted changes of sea-surface salinity in the southern and northern Okinawa Trough since the mid-Holocene

A reconstruction of sea-surface salinity (SSS) in the southern Okinawa Trough (OT) since 6800 cal. yr BP has been presented in this study. We found that the SSS record increased gradually from the middle to late Holocene, indicating reduced summer precipitation in Taiwan. Our results also suggest regional patterns of SSS with SSS increasing in the southern OT and decreasing in the northern OT since the mid-Holocene. Observational data indicate that the SSS in the southern and northern OT are strongly affected by fluvial discharge from Taiwan and the Changjiang River, linked to summer precipitation in South and Central Eastern China, respectively. The contrasting changes in SSS from the OT since the mid-Holocene suggest different spatial patterns of precipitation, with decreasing summer precipitation in South China and increasing summer precipitation in central-eastern China due to the weakened East Asian Summer Monsoon (EASM) and solar insolation. The delayed seasonal transitions of the EASM, with a longer Meiyu stage and a shorter midsummer stage from the mid-Holocene to late Holocene, are consistent with the delayed northward migration of the westerlies in the late Holocene.

Assessing the hydroclimate changes in Western Himalayas during the Little Ice Age

The Little Ice Age (LIA) was a period of most recent glacial advancement and had pronounced cooling effect in the North Atlantic region. Synchronous hydroclimate changes are also reported from the Himalayas, however owing to the heterogeneity within the proxy reconstructions, their relationship with LIA cooling is unclear. Varied topography, huge glacial mass, and multiple moisture sources (both from the Indian Summer Monsoon (ISM) and the Westerlies) makes understanding of the impact of LIA cooling on this region ambiguous. In this study, we review and assess the existing paleoclimatic proxy records for a comprehensive analysis of the regional response of the Western Himalayas to LIA cooling. Using the existing meteorological reanalysis data for back trajectory analysis for the last 20 years, the Western Himalayan region was classified into three different zones based on the relative percentage of moisture-bearing-wind-source contribution. The upper Western Himalayas receive most of the moisture from the Westerlies, both Middle and Lower Western Himalayas receive majority of rainfall from the ISM, with a relatively higher contribution of Westerlies in the Lower Western Himalayas. Comparison of reconstructions using Principal Component Analysis reveal consistent high moisture conditions during the LIA, with increased winter precipitation and decreased summer precipitation coherently in all the records. Spectral analysis of the available proxy records and various climate forcing for LIA cooling show similar dominant frequency, attesting that the LIA cooling drove the hydroclimate changes in the Western Himalayan region. External forcings such as decreased solar activity and increased volcanic activity caused cooling, influenced the Inter Tropical Convergence Zone, and resulted in weaker summer rainfall during the LIA. Synchronous changes in the North Atlantic Oscillations and El Niño–Southern Oscillation records with precipitation records suggest a link between “monsoon breaks” and enhanced Westerly intensity and an intensified winter precipitation in this region.

Multidecadal Oceanic Modulation of Summer Precipitation in North China in 1200-Year Global Climate Simulations

Abstract The multidecadal decrease of precipitation in North China since the 1960s has caused a significant impact on the ecological environment and social development. It has become a key concern for meteorologists and national decision-makers to understand what is driving this. To better understand the oceanic impact on the interdecadal variation of summer precipitation in North China, we analyze two 1200-yr global climate simulations from state-of-the-art coupled models with an explainable convolutional neural network (CNN). The accuracy of the CNN model in correctly diagnosing the increased and decreased summer precipitation anomaly in North China reaches 98% and 96.6% in two CMIP6 models, respectively. We find that a sea surface temperature anomaly (SSTA) in the northern Pacific, associated with the Pacific decadal oscillation (PDO), and an SSTA in the northern Atlantic, associated with the Atlantic multidecadal oscillation (AMO), play essential roles in the interdecadal variation of summer precipitation in North China. The modulations of the PDO and AMO on summer precipitation in North China are consistent with the results derived from limited observations and simulations, which means these mechanisms are robust. In particular, when the PDO is in a negative phase and the AMO is in a positive phase, the positive anomaly of precipitation and the associated circulation anomalies are intensified. This study also confirms that with the explainable deep learning method, a convolutional neural network can be used to identify multidecadal variability in North China summer precipitation, although limited datasets such as observational records make it more challenging to apply deep learning methods.

Distinct Impacts of Two Types of Developing El Niño–Southern Oscillations on Tibetan Plateau Summer Precipitation

El Niño–Southern Oscillation (ENSO) has remarkable impacts on Tibetan Plateau (TP) summer precipitation. However, recently identified ENSO spatial diversity brings complexity to these impacts. This study investigates the distinct impacts of the Eastern Pacific (EP) and Central Pacific (CP) ENSOs on TP summer precipitation based on numerous precipitation data and satellite-observed and reanalyzed circulation data. The results show that the EP El Niño and the CP La Niña have opposite effects on summer precipitation in the southwestern TP, with significant decreases and increases, respectively, indicating a trans-type inversion. In contrast, the CP El Niño causes significant decreases in summer precipitation in the central-eastern TP. No significant anomaly occurs during the EP La Niña. Moisture budget and circulation analyses suggest that these distinct precipitation characteristics can be attributed to different atmospheric teleconnections, which provide varying vertical motion and moisture conditions. The EP El Niño triggers an atmospheric response similar to the Indian Summer Monsoon–East Asian Summer Monsoon teleconnection, and the CP La Niña generates a teleconnection in the opposite phase. In contrast, the CP El Niño mainly causes a teleconnection resembling the East Asian–Pacific pattern. This study may deepen our understanding of ENSO impacts on TP summer precipitation and have implications for regional climate predictions.

Modelling the effect of aerosol and greenhouse gas forcing on the South Asian and East Asian monsoons with an intermediate-complexity climate model

Abstract. The South Asian and East Asian summer monsoons are globally significant meteorological features, creating a strongly seasonal pattern of precipitation, with the majority of the annual precipitation falling between June and September. The stability the monsoons is of extreme importance for a vast range of ecosystems and for the livelihoods of a large share of the world's population. Simulations are performed with an intermediate-complexity climate model in order to assess the future response of the South Asian and East Asian monsoons to changing concentrations of aerosols and greenhouse gases. The radiative forcing associated with absorbing aerosol loading consists of a mid-tropospheric warming and a compensating surface cooling, which is applied to India, Southeast Asia, and eastern China both concurrently and independently. The primary effect of increased absorbing aerosol loading is a decrease in summer precipitation in the vicinity of the applied forcing, although the regional responses vary significantly. The decrease in precipitation is not ascribable to a decrease in the precipitable water and instead derives from a reduction in the precipitation efficiency due to changes in the stratification of the atmosphere. When the absorbing aerosol loading is added in all regions simultaneously, precipitation in eastern China is most strongly affected, with a quite distinct transition to a low precipitation regime as the radiative forcing increases beyond 60 W m−2. The response is less abrupt as we move westward, with precipitation in southern India being least affected. By applying the absorbing aerosol loading to each region individually, we are able to explain the mechanism behind the lower sensitivity observed in India and attribute it to remote absorbing aerosol forcing applied over eastern China. Additionally, we note that the effect on precipitation is approximately linear with the forcing. The impact of doubling carbon dioxide levels is to increase precipitation over the region while simultaneously weakening the circulation. When the carbon dioxide and absorbing aerosol forcings are applied at the same time, the carbon dioxide forcing partially offsets the surface cooling and reduction in precipitation associated with the absorbing aerosol response. Assessing the relative contributions of greenhouse gases and aerosols is important for future climate scenarios, as changes in the concentrations of these species has the potential to impact monsoonal precipitation.

Contribution of external forcing to summer precipitation trends over the Qinghai–Tibet Plateau and Southwest China

In the past 60 years, the global climate has undergone both rapid warming and a brief warming hiatus, while regional precipitation patterns in China have also experienced diverse and complex changes. Specifically, the factors behind the opposing trends in summer precipitation between two adjacent regions—Southwest China and the Qinghai–Tibet Plateau—are particularly intricate. After evaluating the historical runs from CMIP6 models, the authors assessed the contributions of various external forcing factors that simulated the summer precipitation trends observed over the Qinghai–Tibet Plateau and Southwest China from 1961 to 2014. The findings show that, compared to other forcing factors, greenhouse gases had a significant impact on the increase in summer precipitation over the Qinghai–Tibet Plateau, while aerosols played an important role in the decrease in summer precipitation in Southwest China.摘要在过去的60年中, 全球气候经历了快速变暖和短暂的变暖停滞, 而中国的区域降水也经历了多样而复杂的变化. 本文分析了1961年至2014年外强迫因子对青藏高原和中国西南地区夏季降水趋势的影响. 观测数据显示, 青藏高原的夏季降水呈增加趋势, 而中国西南地区的夏季降水呈减少趋势, 这两个相邻地区的夏季降水变化趋势相反. 利用CMIP6数据, 本文研究了不同外强迫因子对两个区域夏季降水趋势的影响. 结果表明, 温室气体对青藏高原夏季降水的增加具有显著影响, 而气溶胶在中国西南地区夏季降水减少中起主要作用.

Potential changes in climate indices in Alberta under projected global warming of 1.5–5 °C

Study regionAlberta province, Canada Study focusThe global average surface temperature has continuously warmed at an unprecedentedly rapid rate since the mid-20th century. Employing CMIP6 (Coupled Model Intercomparison Project Phase 6) climate projections, this study suggested a comprehensive framework with state-of-the-art techniques and evaluated potential changes in climate indices under the GMT changes of + 1.5 °C, + 2 °C, + 3 °C, + 4 °C, and + 5 °C in Alberta, Canada. New hydrological insights for the regionMain finding of this study is that a significant warming trend in annual mean temperature was projected from all of the selected CMIP6 climate projections in Alberta while there was no distinct trend in annual precipitation. Under the GMT changes from + 1.5 °C to + 5 °C, extreme cold temperature indices were warming at a larger rate in response to the GMT warming. In particular, the warming rate of the annual coldest minimum temperature in Alberta was 2.5 times faster than GMT warming. In addition, a potential decrease in summer precipitation was projected under the GMT warming, leading to a drier and warmer summer in the central and southern parts of Alberta. Furthermore, more extreme drought conditions were projected in Alberta under the GMT warming, indicating that the extreme drought conditions are likely to become more common in Alberta along with the GMT warming.

Southern hemisphere monsoonal system during superinterglacial stages: MIS5e, MIS11c and MIS31

The current study investigates changes in Austral Summer Monsoon based on numerical experiments conducted with the coupled ICTP-CGCM model. The interannual variability and intensity of the monsoonal system have been analyzed from vorticity indices and air-sea interaction in Africa, Australia and South America. We focus on interglacial stages MIS5e (127 ka), MIS11c (409 ka) and MIS31 (1072 ka). Results show orbitally-driven decreased summer precipitation and slightly shifted monsoon onset and demise with respect to present day conditions. Sensitivity experiments indicate that monsoons are forced not only by the dominant effect of insolation, but also by remote teleconnections, such as the equatorial Atlantic and Pacific ocean basins. During those interglacial stages, cooling occurs in the Southern Hemisphere whereas Northern Hemisphere substantially warms. This induces meridional displacement of oceanic subtropical high pressure systems and the equatorial convergence zone. Regionally, these mechanisms contribute to droughts over the Amazon and northeastern Brazil, northern Australia and southern Africa. Monsoonal rainfall shows different responses to precessional forcing, as well as the relationship between the monsoon and Niño 3.4 differs among the interglacial stages. Results also indicate a weaker influence of the equatorial Pacific Ocean on the Austral summer monsoon for the MIS31 interglacial stage as compared to current climate conditions across Africa and Australia. On the other hand, South America monsoon is strongly influenced by Niño 3.4 and tropical Atlantic.

Climate Change Characteristics of Typical Grassland in the Mongolian Plateau from 1978 to 2020

Typical grassland is the core of the Mongolian Plateau grassland belt, and is also an important ecological barrier in the north of China. It is of great significance to explore the real-time changes in grassland climate for the prevention and control of climate disasters, and for ecological protection. In this study, the spatial and temporal variation of temperature, precipitation and maximum wind speed in typical Mongolian Plateau grassland were studied using observation data from 16 meteorological stations from 1978 to 2020, using the linear trend method, cumulative anomaly method, Mann-Kendall test, sliding t-test and Morlet wavelet analysis. The results show that: (1) The typical grassland temperature has been increasing at a rate of 0.4 °C/10a (p < 0.001) over the past 40 years, with the most significant warming in spring and summer; a sudden change from low to high temperature occurred in 1992; the annual average temperature gradually increased from northeast to southwest, with significant warming in the southwest. (2) Annual precipitation decreased slightly at a rate of −2.39 mm/10a, with the most significant decrease in summer precipitation; a sudden change from more to less precipitation occurred in 1998; spatially, precipitation decreased gradually from east to west, with significant moisture reduction in its northern part. (3) The maximum wind speed decreased significantly at a rate of −0.33m/s/10a (p < 0.001), with the most pronounced decrease in spring; the maximum wind speed changed abruptly from strong to weak around 1991; spatially, the annual average maximum wind speed decreased gradually from northwest to southeast and northeast, with the most pronounced decrease in the south and northeast. (4) The wavelet analysis shows that the typical grassland area will still be in a warm, low-rainfall and weak-wind stage in the coming years. Using the above analysis, the typical grassland climate of the Mongolian Plateau has shown a clear trend of warm and dry, weak wind in the past 40 years.

South Asian black carbon is threatening the water sustainability of the Asian Water Tower

Long-range transport of black carbon from South Asia to the Tibetan plateau and its deposition on glaciers directly enhances glacier melt. Here we find South Asian black carbon also has an indirect effect on the plateau’s glaciers shrinkage by acting to reduce the water supply over the southern Tibetan plateau. Black carbon enhances vertical convection and cloud condensation, which results in water vapor depletion over the Indian subcontinent that is the main moisture flux source for the southern Tibetan plateau. Increasing concentrations of black carbon causes a decrease in summer precipitation over the southern Tibetan plateau, resulting in 11.0% glacier deficit mass balance on average from 2007 to 2016; this loss rises to 22.1% in the Himalayas. The direct (accelerated melt) and indirect (mass supply decrease) effects of black carbon are driving the glacial mass decline of the so-called “Asian Water Tower”.

Projected changes in mean annual cycle of temperature and precipitation over the Czech Republic: Comparison of CMIP5 and CMIP6

The multi-model ensembles like CMIP5 or CMIP6 provide a tool to analyze structural uncertainty of climate simulations. Currently developed regional and local climate change scenarios for the Czech Republic assess the uncertainty based on state-of-the-art Global Climate Model (GCM) and Regional Climate Model (RCM) ensembles. Present study focuses on multi-model spread of projected changes in long-term monthly means and inter-annual variability of monthly mean minimum, mean and maximum daily air temperature and monthly mean precipitation. We concentrate in more detail on the simulation of CNRM-ESM2-1, the driving GCM for the convection permitting ALADIN-Climate/CZ simulation contributing to the local scenarios in very high resolution. For this GCM, we also analyze a mini-ensemble with perturbed initial conditions to evaluate the range of internal climate variability. The results for the Czech Republic reveal minor differences in model performance in the reference period whereas quite substantial inter-generation shift in projected future change towards higher air temperature and lower summer precipitation in CMIP6 comparing to CMIP5. One of the prominent features across GCM generations is the pattern of summer precipitation decrease over central Europe. Further, projected air temperature increase is higher in summer and autumn than in winter and spring, implying increase of thermal continentality of climate. On the other hand, slight increase of winter precipitation and tendency towards decrease of summer precipitation lead to projected decrease of ombric continentality. The end of 21st century projections also imply higher probability of dry summer periods, higher precipitation amounts in the cold half of the year and extremely high temperature in summer. Regarding the CNRM-ESM2-1, it is often quite far from the multi-model median. Therefore, we strictly recommend to accompany any analysis based on the simulation of nested Aladin-CLIMATE/CZ with proper uncertainty estimate. The range of uncertainty connected to internal climate variability based on one GCM is often quite large in comparison to the range of whole CMIP6 ensemble. It implies that when constructing climate change scenarios for the Central Europe region, attention should be paid not only to structural uncertainty represented by inter-model differences and scenario uncertainty, but also to the influence of internal climate variability.

Large increases of multi-year droughts in north-western Europe in a warmer climate

Three consecutive dry summers in western Europe (2018–2019–2020) had widespread negative impacts on society and ecosystems, and started societal debate on (changing) drought vulnerability and adaptation measures. We investigate the occurrence of multi-year droughts in the Rhine basin, with a focus on event probability in the present and in future warmer climates. Additionally, we investigate the temporally compounding physical drivers of multi-year drought events. A combination of multiple reanalysis datasets and multi-model large ensemble climate model simulations was used to provide a robust analysis of the statistics and physical processes of these rare events. We identify two types of multi-year drought events (consecutive meteorological summer droughts and long-duration hydrological droughts), and show that these occur on average about twice in a 30 year period in the present climate, though natural variability is large (zero to five events can occur in a single 30 year period). Projected decreases in summer precipitation and increases in atmospheric evaporative demand, lead to a doubling of event probability at 1 ^circC additional global warming relative to present-day and an increase in the average length of events. Consecutive meteorological summer droughts are forced by two, seemingly independent, summers of lower than normal precipitation and higher than normal evaporative demand. The soil moisture response to this temporally compound meteorological forcing has a clear multi-year imprint, resulting in a relatively larger reduction of soil moisture content in the second year of drought, and potentially more severe drought impacts. Long-duration hydrological droughts start with a severe summer drought followed by lingering meteorologically dry conditions. This limits and slows down the hydrological recovery of soil moisture content, leading to long-lasting drought conditions. This initial exploration provides avenues for further investigation of multi-year drought hazard and vulnerability in the region, which is advised given the projected trends and vulnerability of society and ecosystems.

Mechanisms of Reduced Mid‐Holocene Precipitation in Arid Central Asia as Simulated by PMIP3/4 Models

AbstractWe investigated the precipitation changes in mid‐latitude arid central Asia (ACA, including Central Asia and Xinjiang) and the related mechanisms in the mid‐Holocene using the output from the Paleoclimate Modeling Intercomparison Project phases 3 and 4 (PMIP3/4). The annual precipitation in ACA was decreased in the mid‐Holocene compared with the preindustrial period, consistent in direction with reconstruction records. Such change was mainly due to deficient winter and spring (December‐May) precipitation in the mid‐Holocene. The decrease in incoming solar radiation in the mid‐Holocene winter and spring caused stronger surface and tropospheric cooling in the northern low latitudes. It reduced the meridional temperature gradient in the troposphere, thereby weakening the westerly winds and related transport of water vapor. More importantly, the cooling weakened the local water cycle in ACA. Finally, the precipitation decreased over almost all of ACA. In the mid‐Holocene summer (June‐August), the meridional temperature gradient and related westerly winds were also reduced. It was mainly caused by stronger surface and tropospheric warming in the northern mid‐ to high latitudes. The stronger warming was due to increased summer incoming solar radiation in the mid‐Holocene. This process differed from that occurred in winter and spring. Therefore, the water vapor transport was weakened, and the summer precipitation was deficient in northern ACA. At the same time, strengthened descending motions contributed to the decrease in summer precipitation in most parts of Central Asia. On the contrary, intensified ascending motions increased summer precipitation in southeastern Xinjiang.

Recent decrease in summer precipitation over the Iberian Peninsula closely links to reduction in local moisture recycling

Abstract. The inherently dry summer climate of the Iberian Peninsula (IP) is undergoing drought exacerbated by more intense warming and reduced precipitation. Although many studies have studied changes in summer climate factors, it is still unclear how the changes in moisture contribution from the sources lead to the decrease in summer precipitation. This study investigates the differences in the IP precipitationshed from 1980 to 1997 and 1998 to 2019 using the Water Accounting Model-2layers with ERA5 data, and assesses the role of local moisture recycling and external moisture in reducing summer precipitation. Our findings indicate that the moisture contributions from the local IP, and from the west and the east of the precipitationshed, contributed 1.7, 3.6 and 1.1 mm per month less precipitation after 1997 than before 1997, accounting for 26 %, 57 % and 17 % of the main source supply reduction, respectively. The significant downward trend of the IP local moisture recycling closely links to the disappearance of the wet years after 1997 as well as the decrease in local contribution in the dry years. Moreover, the feedback between the weakened local moisture recycling and the drier land surface can exacerbate the local moisture scarcity and summer drought.

Impact of Rainfall Variability and Land Use Change on River Discharge in South Cameroon

Climate change, variability and anthropogenic forcings such as land use change are the main forcings of river discharge variability. However, an understanding of their simultaneous impacts on river discharge remains limited in some parts of the world. To shed light on this issue, the objective of this article is to investigate the effects of rainfall variability and land use change on river discharge in the Nyong basin (at Olama and Mbalmayo gauging stations) and some of its sub-basins (So’o and Mefou) over the long period 1950–2018. To achieve this goal, hydro-meteorological data of the Nyong basin and sub-basins were analyzed using the Pettitt test. Likewise, land use changes in the basin and sub-basins were also analyzed using supervised classifications of Landsat satellite images of the basins at different periods (1973, 2000 and 2018). On the annual scale, rainfall has decreased statistically over the studied basins. In the large basins (Olama and Mbalmayo), this decrease in rainfall is synchronous with that of discharges, while it is concomitant with an increase in the Mefou (small basin). After the ruptures within time series identified in the annual modules, the extreme discharges (maximum and minimum) decreased in Olama; in Mbalmayo, the maximum discharges remained stable while the minimum discharges decreased. On the other hand, the maximum and minimum discharges have significantly increased in the Mefou. The stability of maximum discharges at Mbalmayo and the increase in extremes on the Mefou in a context where the precipitation that generates the discharge has decreased can be attributed to land use change. These changes are essentially marked by an increase in impervious areas and a reduction in forest cover. On the seasonal scale, the impact of precipitation in the dry season is visible on the flows of the rainy seasons that follow them on the large basins (Olama and Mbalmayo). Between the decades 1970–1990 and 2000–2010, there was respectively a significant increase, then a decrease in summer precipitation, which impacted the autumn discharges in the same direction. Conversely, between the same intervals, there was a significant decrease, then a slight increase in winter precipitation. The impact of winter precipitation on the spring discharge is more visible during the first period only (1970–1990). During the second period, winter precipitation seems to have more of an impact on the runoff for the same season. In the Mefou sub-basin, the precipitation plays an essentially amplifying role in the increase in discharge in the seasons during which they occur. Those having experienced an increase, or a maintenance of precipitation (summer and spring) recorded the most significant increases in discharges. These results could be useful for long-term planning on the demand and use of water, as well as flood management in the basins

Future urban heat island influence on precipitation

Urbanization and global warming are two of the major human impacts on the environment. The Urban Heat Island (UHI) effect can change precipitation patterns. Global warming also leads to changes in precipitation and especially an increase in intensity and frequency of extreme precipitation. With urbanization expected to grow in the future, the role of UHI in a warmer climate is an important research question. We present results from 20-year long regional convection-permitting model simulations that include the UHI effect, run for historical and future climates for two megacities, Paris and Shanghai. In the warmer future climate, urban-induced precipitation is found to decrease compared to the historical climate, for both mean and extreme precipitation, with large uncertainties due to natural variability. The mean precipitation increase due to UHI in Paris is 2.2± 1.4% and 1.8 ± 1.3% for historical and future conditions, respectively. Shanghai has slightly weaker mean precipitation change than Paris at present and no change in the future. The future reduction of the urban effect is found to be caused by a decrease in summer precipitation for both cities. Interannual variability in precipitation due to UHI is larger for Shanghai than Paris. The UHI effect on extreme precipitation is also reduced in the future climate and the area with precipitation increase is more concentrated. The general increase in extreme precipitation due to global warming, in combination with the precipitation redistribution due to UHI, underline the importance for future urban planning to mitigate damage caused by extreme precipitation events.

Millennial-scale variability of Indian summer monsoon constrained by the western Bay of Bengal sediments: Implication from geochemical proxies of sea surface salinity and river runoff

The Indian summer monsoon (ISM) is critical to billions of people living in the region. In this study, high-resolution major element composition and Globigerinoides ruber sensu stricto (G. ruber s.s.) δ18O measurements of a sediment core collected from the western Bay of Bengal indicated a high sensitivity of the study site to monsoonal climate variability related to climatic changes on a timescale of millennia (Younger Dryas and Heinrich Stadials) in the North Atlantic during the last 80 kyr. High G. ruber s.s. δ18O and ice volume-corrected ocean surface water δ18O and increased Ca/Ti ratios during Younger Dryas and Heinrich Stadials HS1–6 indicate the decreased summer monsoonal rainfall in the Indian peninsula during these periods. The increases of G. ruber s.s. δ18O records in the western Bay of Bengal during Younger Dryas and Heinrich Stadials were similar in previous records of G. ruber s.s. δ18O in the northern Bay of Bengal and stalactite δ18O in northern India. This implies that the decreased precipitation during these periods may have been induced by the southward migration of the northern boundary of Intertropical Convergence Zone (ITCZ) over the Indian peninsula during Younger Dryas and Heinrich Stadials. Previous records of δ18O values in the Andaman Sea located in the eastern Bay of Bengal showed no remarkable decrease of summer precipitation during HS1 and 5. These differences may be explained by the different migration trends of summer ITCZ position in the eastern Bay of Bengal versus western Bay of Bengal during HS1 and 5.

Cross-sphere modelling to evaluate impacts of climate and land management changes on groundwater resources

Climate change affects both water resources and agricultural production. With rising temperatures and decreasing summer precipitation, it is expected that agricultural production will be increasingly limited by drought. Where surface- or groundwater resources are available for irrigation, an increase in water withdrawals for irrigation is to be expected. Therefore, quantitative approaches are required to anticipate and manage the expected conflicts related to increased water abstraction for irrigation. This project aims to investigate how agricultural production, water demand for irrigation, runoff and groundwater dynamics are affected by future climate change and how climate change impacts combined with changes in agricultural water use affect groundwater dynamics. To answer these research questions, a comprehensive, loosely coupled model approach was developed, combining models from three disciplines: an agricultural plant growth model, a hydrological model and a hydrogeological model. The model coupling was implemented and tested for an agricultural area located in Switzerland in which groundwater plays a significant role in providing irrigation water. Our suggested modelling approach can be easily adapted to other areas.The model results show that yield changes are driven by drought limitations and rising temperatures. However, an increase in yield may be realized with an increase in irrigation. Simulation results show that the water requirement for irrigation without climate protection (RCP8.5) could increase by 40% by the end of the century with an unchanged growing season and by up to 80% with varietal adaptations. With climate change mitigation (RCP2.6) the increase in water demand for irrigation would be limited to 7%. The increase in irrigation (+12 mm) and the summer decrease in recharge rates (~20 mm/month) with decreasing summer precipitation causes a lowering of groundwater levels (40 mm) in the area in the late summer and autumn. This impact may be accentuated by an intensification of irrigation and reduced by extensification.

Building a local climate reference dataset: Application to the Abruzzo region (Central Italy), 1930–2019

AbstractReliable secular time series of essential climatic variables are a fundamental element for the assessment of vulnerability, impact and adaptation to climate change. Here, we implement a readily portable procedure for building an upgradable long‐term homogeneous climate dataset using monthly and daily observations of temperature and precipitation over a given area of interest, exemplified here with Abruzzo, a region in Central Italy characterized by complex orography. We process the dataset according to a preliminary ranking of stations based on data quantity and quality, and we exploit the Climatol algorithm for inhomogeneity correction. The corrected time series show trends in broad agreement with external databases (CRU, Berkeley Earth, E‐OBS), and highlight the importance of relying on a local network for a better representation of gradients and variability over the territory. We estimate that maximum (TX) and minimum temperature (TN) increased by ~1.6 and ~2.2°C/century, respectively, over the period 1930–2019, while in the recent decades 1980–2019 we found an accelerated trend of ~5.7 and ~3.9°C/century. Precipitation (RR) decreased by ~10%/century in 1930–2019, while it has been increasing at a rate of ~26%/century in 1980–2019. The Köppen–Geiger climate classification is sensitive to the increase of precipitation in the recent decades, which is attributable to decreased summer precipitation overcompensated by more rain in late spring and early autumn. The cold climate types are retreating upwards along the slopes of the mountain ranges. Over the period 1980–2019, extreme values are also displaying significant trends. Every 2 years, there is one less frost day (TN <0°C) and one more summer day (TX >25°C) in the Apennines area, while there is one more tropical night (TN >20°C) in the Adriatic coastal area. Precipitation extremes are increasing, especially along the coast, with rain accumulated in the rainiest days increasing at a rate of 1–2%/year.

Trait characterization of genetic resources reveals useful variation for the improvement of cultivated Nordic red clover

AbstractRed clover (Trifolium pratense L.) is the most important forage legume in the Nordic region, but its utilization is limited by poor persistency. The improvement of cultivated red clover can potentially take advantage of the numerous wild populations and landraces conserved in gene banks; however, there is often limited information available on the phenotypic and genetic characteristics of this material. We characterized 48 populations conserved at NordGen for a number of traits and compared them to commercial cultivars. The material was evaluated in field trials at four locations over two years and in an experiment under controlled conditions. Considerable variation was identified, with stem length, growth type and flowering date having the highest broad sense heritabilities. Traits related to plant size were strongly associated with late flowering and upright growth and differed between landraces/cultivars on the one hand and wild populations on the other. There was a large genotype by environment interaction on winter survival, which only partially correlated with freezing tolerance under controlled conditions. A majority of gene bank accessions exceeded the commercial cultivars in winter survival and freezing tolerance and can therefore be a genetic resource for future improvement of these traits. The phenotypic variation among accessions was associated with two main axes of climatic variation at the collection site. Petiole length of young plants under controlled conditions as well as plant size in the field increased with increasing summer temperature and decreasing summer precipitation, while number of leaves and an apparent vernalization requirement, recorded under controlled conditions, increased with decreasing annual and winter temperature. We discuss the implications these results have for collection, conservation and utilization of red clover genetic resources in the Nordic region.