Changes In Seasonal Precipitation Research Articles

Response of phytoplankton to an experimental fish culture in net cages in a subtropical reservoir.

This study aimed to evaluate nutrients concentration and spatial-temporal changes in phytoplankton biovolume during an experimental fish culture in net cages in a lateral arm of Salto Caxias reservoir, Brazil. Two sampling stations were placed in the affected lateral arm and other two in a cageless lateral arm. Neither abiotic variables nor phytoplankton biovolume presented significant differences between the treatments. Only temporal changes were confirmed by the analysis performed. Both lateral arms were classified as oligotrophic, reflecting low influence of the net cages. Phytoplankton growth seems to be limited by nitrogen. Biovolume values were, in general, low and five major functional groups were recognized (E, F, G, K and P). In summer higher biovolume values were observed and representatives of Chlorophyceae and Cyanobacteria belonging to the functional groups F and K, respectively, were the most important. In winter phytoplankton was mainly composed by Bacillariophyceae taxa from P group. G group was also restricted to winter and E group occurred in winter and summer. The variations recorded in phytoplankton structure appear to have been mainly influenced by seasonal changes in temperature, precipitation and nutrients availability. The effects of net cages on the abiotic variables and phytoplankton biovolume appear to have been small, probably due to the small number of net cages employed and the system dilution capacity. However, a permanent monitoring of phytoplankton is recommended, since this environment has a carrying capacity, from which the trophic state may increase.

Projections of high resolution climate changes for South Korea using multiple-regional climate models based on four RCP scenarios. Part 2: precipitation

Precipitation changes over South Korea were projected using five regional climate models (RCMs) with a horizontal resolution of 12.5 km for the mid and late 21st century (2026-2050, 2076- 2100) under four Representative Concentration Pathways (RCP) scenarios against present precipitation (1981-2005). The simulation data of the Hadley Centre Global Environmental Model version 2 coupled with the Atmosphere-Ocean (HadGEM2-AO) was used as boundary data of RCMs. In general, the RCMs well simulated the spatial and seasonal variations of present precipitation compared with observation and HadGEM2-AO. Equal Weighted Averaging without Bias Correction (EWA_NBC) significantly reduced the model biases to some extent, but systematic biases in results still remained. However, the Weighted Averaging based on Taylor’s skill score (WEA_Tay) showed a good statistical correction in terms of the spatial and seasonal variations, the magnitude of precipitation amount, and the probability density. In the mid-21st century, the spatial and interannual variabilities of precipitation over South Korea are projected to increase regardless of the RCP scenarios and seasons. However, the changes in area-averaged seasonal precipitation are not significant due to mixed changing patterns depending on locations. Whereas, in the late 21st century, the precipitation is projected to increase proportionally to the changes of net radiative forcing. Under RCP8.5, WEA_Tay projects the precipitation to be increased by about +19.1, +20.5, +33.3% for annual, summer and winter precipitation at 1-5% significance levels, respectively. In addition, the probability of strong precipitation (≥ 15 mm d-1) is also projected to increase significantly, particularly in WEA_Tay under RCP8.5.

Use of beta regression for statistical downscaling of precipitation in the Campbell River basin, British Columbia, Canada

Summary Impacts of global climate change on water resources systems are assessed by downscaling coarse scale climate variables into regional scale hydro-climate variables. In this study, a new multisite statistical downscaling method based on beta regression (BR) is developed for generating synthetic precipitation series, which can preserve temporal and spatial dependence along with other historical statistics. The beta regression based downscaling method includes two main steps: (1) prediction of precipitation states for the study area using classification and regression trees, and (2) generation of precipitation at different stations in the study area conditioned on the precipitation states. Daily precipitation data for 53 years from the ANUSPLIN data set is used to predict precipitation states of the study area where predictor variables are extracted from the NCEP/NCAR reanalysis data set for the same interval. The proposed model is applied to downscaling daily precipitation at ten different stations in the Campbell River basin, British Columbia, Canada. Results show that the proposed downscaling model can capture spatial and temporal variability of local precipitation very well at various locations. The performance of the model is compared with a recently developed non-parametric kernel regression based downscaling model. The BR model performs better regarding extrapolation compared to the non-parametric kernel regression model. Future precipitation changes under different GHG (greenhouse gas) emission scenarios also projected with the developed downscaling model that reveals a significant amount of changes in future seasonal precipitation and number of wet days in the river basin.

Dynamically-downscaled probabilistic projections of precipitation changes: A Canadian case study

In this study, plausible changes in annual and seasonal precipitation over Ontario, Canada in response to global warming are investigated through a regional climate modeling approach. A high-resolution regional climate model ensemble based upon the Providing REgional Climates for Impacts Studies (PRECIS) model is developed to help explore the possible outcomes of future climate. A Bayesian hierarchical model is then employed to quantify the uncertainties involved in the modeling results and obtain probabilistic projections of precipitation changes at grid point scales. The results show that the projected changes in annual precipitation exhibit a certain degree of spatial variability with the median changes mostly bounded by 0% and 20%, implying that the annual precipitation over Ontario is more likely to increase in the context of global warming. Specifically, the mean changes in annual precipitation for 2030s and 2050s would be ~7.5%, while the annual precipitation for 2080s is likely to increase by an average of ~12.5%. By contrast, the spatial variability of seasonal precipitation changes is more significant, especially for the changes in spring precipitation which may vary from −40% in south and 50% in north. It is reported that there would be a continuous increasing trend in winter, spring, and autumn precipitation from 2030s to 2080s by 5–30%, but summer precipitation is likely to decrease by 5% or even higher to the end of this century. Furthermore, our results suggest that the larger the biases in historical simulations, the more uncertain the future projections will be.

Isotopic reconstructions of habitat change surrounding the extinction of Oreopithecus, the last European ape.

Oreopithecus bambolii was the last hominoid to survive in Europe. The purpose of this investigation was to reconstruct, through stable isotope analyses, Oreopithecus' habitat, subsistence behavior, and changes in habitat that may have led to its extinction. Carbon and oxygen stable isotopes from inorganic carbonate in tooth enamel from Oreopithecus and its contemporaneous faunas from localities in Tuscany and Sardinia were sampled. Also the fauna from localities in Tuscany shortly after Oreopithecus went extinct were sampled. Results indicated that Oreopithecus, compared with most modern hominoids, inhabited forests that probably had a more open canopy. At Tuscan localities, Oreopithecus yields some of the highest carbon isotope values but some of the lowest oxygen, suggesting a diet that may have included tubers or aquatic vegetation. Relatively higher oxygen values in Sardinia suggested that its diet included arboreal foods as well. Among modern and fossil hominoids, Oreopithecus only resembled chimpanzees living outside of rainforests. It also resembled Ardipithecus in carbon isotope values, suggesting possible similarities in feeding strategies concordant with shared skeletal features between Oreopithecus and early hominins. Isotope values from post-Oreopithecus faunas indicated a shift to more forested conditions, unlike other hominoid extinctions associated with loss of forest. Isotopic reconstructions of Oreopithecus' habitat and changes associated with its extinction indicated that its paleoecology was unique among hominoids. However, these reconstructions also suggested that like other hominoids, Oreopithecus was susceptible to changes in seasonality of precipitation, and it may have used wetlands as a buffer to seasonal regimes. Am J Phys Anthropol 160:254-271, 2016. © 2016 Wiley Periodicals, Inc.

Multiple water isotope proxy reconstruction of extremely low last glacial temperatures in Eastern Beringia (Western Arctic)

Precipitation isotopes are commonly used for paleothermometry in high latitude regions. Here we present multiple water isotope proxies from the same sedimentary context – perennially frozen loess deposits in the Klondike Goldfields in central Yukon, Canada, representing parts of Marine Isotope Stages (MIS) 4, 3 and 2 – allowing us to uniquely corroborate fractionations and temperature conversions during these Late Pleistocene cold stages. We include new and existing proxy data from: relict wedge ice, a direct archive for snowmelt; relict pore ice, an archive for bulk soil water integrating year-round precipitation; and hydrated volcanic glass shards and fossil plant waxes, which are also thought to integrate year-round precipitation but are subject to large fractionations. In some cases, our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean, new transfer functions calibrated specifically for northern North America (δDprecip = 3.1‰·°C−1 × T – 155‰; and δ18Oprecip = 0.41‰·°C−1 × T – 20.2‰), and novel insights on the apparent net fractionation correction for Eastern Beringian steppe-tundra plant waxes (εwax/precip = −59 ± 10‰). The snowmelt origin of wedge ice ensures a relatively constrained winter-spring seasonality of contributing precipitation, as supported by the consistency between water isotope measurements from Late Holocene wedge ice and modern winter-spring precipitation. Wedge ice dating to the transitional MIS 3/2 is isotopically depleted relative to modern spring-winter precipitation by an amount that indicates a temperature depression of ∼14 ± 5 °C below modern. The soil water origin of pore ice, and other proxies integrating year-round precipitation from soil water, allows for a more variable precipitation seasonality. The isotopic composition of modern pore ice is consistent with mean annual precipitation. However, the isotopic composition of pore ice during MIS 3/2 converges on wedge ice values, signalling an increase in the ratio of cold-to-warm-season precipitation integrated by pore ice during glacial times, possibly due to drier summers as supported by the fossil record and climate model simulations. In the study region, water isotope proxies integrating year-round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality, as detected here, and thus are best interpreted as upper bound estimates. Based on these proxies, we estimate that annual temperatures during MIS 4, 3/2 and 2 were depressed below the modern climate to a maximum of ∼18 °C, 16 °C and 21 °C ± 4–5 °C, respectively. Our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate, and may be particularly important for studies of the major climate transformations over glacial-interglacial timescales.

Timing and associated climate change of a 2 °C global warming

ABSTRACTTowards a better insight into the timing and climate change associated with a 2 °C global warming above pre‐industrial levels in the 21st century, here we perform an analysis of all pertinent experiments within the framework of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Considering equally all available CMIP5 models, the probability of crossing the 2 °C target before the year 2100 is 26, 86, and 100% for the Representative Concentration Pathways 2.6 (RCP2.6), 4.5 (RCP4.5), and 8.5 (RCP8.5) scenarios, respectively, with the median years of 2054 for RCP4.5 and 2042 for RCP8.5. A 2 °C global warming would not be felt equally round the globe: stronger warming occurs over land than over the ocean, and the strongest warming occurs in the Arctic. Almost all temperature changes are larger than natural internal variability. Global average signal‐to‐noise ratios (S/N) of annual and seasonal temperature changes are in the range 3.2–5.0, and the largest values occur at low latitudes due to the lower background variability. Precipitation tends to increase at high latitudes but decrease in the subtropics, while all changes are smaller than natural internal variability except in parts of the high northern latitudes. The S/N of annual (seasonal) precipitation changes averages only 0.2 (no more than 0.1) for the globe.

Impact of climate change on precipitation patterns: a comparative approach

ABSTRACTAssessment of the impact of climate change on future precipitation scenarios is critical for water resources planning and development. Despite the advances reported in climate modelling, it remains a challenge to adequately develop approaches for impact assessment that can be easily interpreted by a wide range of decision makers in the society. The future scenarios are customarily projected with a range of uncertainties. Based on a case study, this article first discusses the complementarity of different statistical tools that are relevant for assessing the impact of climate change. Then, it reports a probabilistic method, which shows promising applicability. Specifically, we address the effect of climate change over the entire range of monthly precipitation and the number of precipitation events (>3 mm) across the Texas Gulf watershed. We consider daily precipitation series released by the North American Regional Climate Change Assessment Program for historical (1971–2000) and future (2041–2070) periods. The precipitation series are bias‐corrected and are then analysed using different statistical methods, including trends and pooled analyses. Subsequently, we present a probabilistic approach that is capable of depicting the plausible effects of climate change in time and space. Finally, we infer temporal changes in seasonal precipitation across the watershed, which suggest meaningful spatial disparity. The probabilistic approach may serve as a complementary tool that seems to be relevant for a holistic interpretation of critical changes in precipitation patterns under climate change.

中亚热带森林更新方式对土壤磷素的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 中亚热带森林更新方式对土壤磷素的影响 DOI: 10.5846/stxb201506071150 作者: 作者单位: 福建师范大学地理科学学院,福建师范大学地理科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金面上项目（31270584）；国家自然科学基金重点项目（31130013） Effect of forest regeneration on soil phosphorus in mid-subtropical area Author: Affiliation: School of Geographical Science, Fujian Normal University,School of Geographical Science, Fujian Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了深入了解磷（P）在中亚热带森林生态系统内的有效性，在三明市梅列区陈大采育场黄坑工区，选择天然林采伐后采取不同更新方式的多种森林，以米槠天然林为对照，研究森林不同更新方式对中亚热带森林土壤全磷、有效磷及可溶性有机磷的影响。结果显示：在0-100 cm土层，（1）土壤全磷平均含量大小顺序依次为米槠天然林（NF）（0.49±0.09）g/kg，米槠轻度干扰人促更新林（LAR）（0.35±0.04）g/kg，米槠强度干扰人促更新林（HAR）（0.34±0.03）g/kg，马尾松人工林（PIM）（0.32±0.02）g/kg，杉木人工林（CUL）（0.3±0.03）g/kg，人促更新林比人工林高，NF显著高于其它的林分（P < 0.05）；（2）土壤有效磷（NaHCO3提取）平均含量大小顺序依次为NF（0.41±0.39）mg/kg，LAR（0.26±0.2）mg/kg，HAR（0.23±0.16）mg/kg，PIM（0.17±0.05）mg/kg，CUL（0.13±0.06）mg/kg，NF显著高于其它林分，LAR显著比人工林高（P < 0.05）。（3）在0-10 cm土层，各林分可溶性有机磷含量在夏季最高，冬季最低，温度和降水量的季节变化是影响其重要因子之一；同一季节，人促更新林比人工林高，NF显著高于人工林（P <0.05）。结果表明，全磷、有效磷和可溶性有机磷含量随人为干扰强度的增强呈降低趋势，其与年凋落物量和土壤有机碳储量呈显著正相关，与土壤容重呈显著负相关，全磷和有效磷在土壤剖面呈表聚性特征。相比于人工林经营，采取人促天然更新的方式，更有利于中亚热带森林养分的贮存和转化，有利于森林的长期经营和管理。 Abstract:To better understand the availability of phosphorus (P) in mid-subtropical forest ecosystems, various forests that originated from natural tree felling were selected in the Huangkeng work area of the Chenda state-owned forestry farm, and the effect of different regeneration patterns on soil total, available, and dissolved organic P were studied. The results indicated that, in the 0-100 cm soil layer, (1) Average soil total P content from highest to lowest was (0.49±0.09) g/kg in the Castanopsis carlesii forest (NF), (0.35±0.04) g/kg in the mild disturbance forest with natural regeneration (LAR), (0.34±0.03) g/kg in the intensive disturbance forest with natural regeneration (HAR), (0.32±0.02) g/kg in the Pinus massoniana plantation (PIM), and (0.3±0.03) g/kg in the Cunninghamia lancealata plantation. Natural regeneration forests had higher total P than plantations, and total P for NF was significantly higher than that of the plantations (P < 0.05). (2) Average soil available P content (NaHCO3 extraction) from highest to lowest was (0.41±0.39) mg/kg for NF, (0.26±0.2) mg/kg for LAR, (0.23±0.16) mg/kg for HAR, (0.17±0.05) mg/kg for PIM, and (0.13±0.06) mg/kg for CUL. Available P of LAR was significantly higher than that of plantations (P < 0.05). (3) In the 0-10 cm soil layer, dissolved organic P content was highest in summer and lowest in winter for every forest type, which was probably caused by seasonal changes in temperature and precipitation. In the same season, dissolved organic P from NF was significantly higher than that of plantations (P < 0.05), and dissolved organic P is natural regeneration forests was higher than in plantations. Correlation analysis showed total P, available P, and dissolved organic P were significantly positively correlated with litterfall and soil organic carbon storage, but had a significant negative correlation with soil bulk density, and exhibited a declining trend with increasing human disturbance. Total P and available P in the soil profile exhibited characteristics of surface accumulation. Compared to plantation management, natural forest regeneration was more conducive to storage and transformation of nutrients, and for the long-term management of the mid-subtropical forests. 参考文献 相似文献 引证文献

Impacts of ENSO and ENSO Modoki+A regimes on seasonal precipitation variations and possible underlying causes in the Huai River basin, China

Spatiotemporal patterns of seasonal precipitation changes across the Huai River basin, China, were analyzed, using daily precipitation data from 35 meteorological stations for the period of 1961–2010. Seasonal precipitation changes in related to Eastern Pacific Warming (EPW), Central Pacific Warming (CPW), and Eastern Pacific Cooling (EPC) were investigated. Impacts of canonical ENSO (c-ENSO) and ENSO Modoki+A (EM+A) on seasonal precipitation variations were evaluated. Water vapor transport patterns were also examined to determine the possible mechanisms causing the impacts of ENSO regimes on seasonal precipitation changes. Results indicated that: (1) EPC is the main driver for the increase of spring and autumn precipitation and autumn/spring precipitation tends to decrease during CPW/EPW, respectively. However, EPW and CPW can result in an increase of the summer precipitation amount in the middle and upper basin, and EPC causes an increase of the spring precipitation amount, which may amplify flood risk in the basin; (2) c-ENSO regimes tend to increase the precipitation amount during spring and autumn, especially for the winter precipitation amount. However, c-ENSO and EM+A cause distinctly different impacts on the summer and autumn precipitation: a decrease of summer and autumn precipitation is observed during the EM+A periods while an increase during the c-ENSO periods; (3) In summer and spring, water vapor transport during the c-ENSO periods is more active than during the EM+A periods. Further, water vapor flux is more abundant during the warm episodes of c-ENSO events in spring and summer than during the cold episodes of c-ENSO, and hence higher spring and summer precipitation across the basin. Results of this study may help to understand the causes underlying spatiotemporal patterns of seasonal precipitation and can help in developing measures for the mitigation of floods and droughts hazards in a changing climate.

Radiative properties of clouds over a tropical Bolivian glacier: seasonal variations and relationship with regional atmospheric circulation

ABSTRACTAt low latitudes, strong seasonal changes in cloud cover and precipitation largely control the mass balance of glaciers. Measurements of shortwave and longwave radiation fluxes reaching Zongo glacier, Bolivia (16°S, 5060 m asl), were analysed from 2005 to 2013 to investigate cloud radiative properties. Cloud shortwave attenuation and longwave emission were greater in the wet summer season (DJF) than in the dry winter season (JJA) probably because most DJF clouds were low warm cumulus associated with local convection, whereas JJA clouds were frequently altostratus associated with extra‐tropical perturbations. Solar irradiance was high all year round and cloud radiative forcing on down‐welling fluxes was strongly negative, with monthly averages ranging from ‐60 to ‐110 W m−2 from the dry to the wet season, respectively. In the wet season, high extraterrestrial solar irradiance and low shortwave transmissivity caused very negative cloud forcing despite the high longwave emissivity of convective clouds. Reanalysis of wind and geopotential height anomalies and outgoing longwave radiation satellite data were used to characterize the regional atmospheric circulation causing thick cloud covers (10% thickest clouds) during the dry (JJA), transition (SON), and wet (DJF) seasons. Around 87% (80%) of cloud events in JJA (SON) occurred during the incursion of low‐level southern wind from southern South America to the Bolivian Andes, which caused 2–3 days of cold surge episodes in the Cordillera Real. Around 13% of cloudy days in JJA were associated with high‐level low‐pressure conditions over the Chilean coast around 45°S, including cut‐off lows. In SON, 20% of cloudy days were associated with summer conditions, characterized by an active Bolivian High and moist air advection from the Amazon basin. In the wet season, only 46% of thick cloud events were associated with low‐level southern wind incursions, the other events being associated with the South American Monsoon.

Reconstruction of seasonal precipitation in Hawai'i using high-resolution carbon isotope measurements across tree rings

Determination of carbon isotope (δ13C) values of tree-ring tissue is a well-established method to reconstruct past climate variability at annual resolution, but such records are limited in tropical latitudes due to the lack of well-defined annual growth bands. Recent work has demonstrated the potential for high-resolution, intra-ring δ13C records to help define ring boundaries in tropical environments and provide additional climate information at sub-annual resolution. Here we present a high-resolution, intra-ring carbon isotope (δ13C) record of the Hawaiian endemic species Sophora chrysophylla (also known as “māmane”) in order to assess the ability to extract seasonal climate information from these drought tolerant trees. Tree cores were sampled from high-elevation māmane trees growing on the west side of Mauna Kea, Big Island. Across our entire dataset (1986–2008), we identified a notable decreasing linear trend in the δ13C record of 0.061‰/year that can be attributed to changes in the δ13C value of atmospheric CO2 and pCO2 concentration associated with fossil fuel burning. Correcting for these affects yields a nearly flat δ13C record with a slope of −0.0075‰/year, suggesting no long-term trends in climate across the study period. We observe a quasi-periodic change in the δ13C values [Δ(δ13C)] measured within each ring that averages 1.09±0.50‰ (±1σ, n=23) in amplitude. These variations are interpreted as the intra-annual isotopic signal in tree photosynthesis. The δ13C variability correlates with the visible ring structure of the sample, suggesting the presence of annual growth rings at this tropical high elevation site.We applied these data to a model that relates the Δ(δ13C) value to seasonal changes in precipitation in order to reconstruct annual changes in total summer (May through October) and winter (November through April) precipitation at the site. Across the 23-year record (1986–2008; n=579 δ13C measurements), reconstructed values for the ratio of summer to winter precipitation, total summer precipitation, and total winter precipitation correlate well with rainfall data collected from a nearby weather station (r=0.65, 0.36, and 0.70, respectively). These results support application of this model to reconstruct inter-annual changes in seasonal precipitation from long-term tree-ring chronologies. They also demonstrate the potential of using māmane δ13C for future long-term climate reconstructions.

Effects of precipitation change and neighboring plants on population dynamics of Bromus tectorum.

Shifting precipitation patterns resulting from global climate change will influence the success of invasive plant species. In the Front Range of Colorado, Bromus tectorum (cheatgrass) and other non-native winter annuals have invaded grassland communities and are becoming more abundant. As the global climate warms, more precipitation may fall as rain rather than snow in winter, and an increase in winter rain could benefit early-growing winter annuals, such as B. tectorum, to the detriment of native species. In this study we measured the effects of simulated changes in seasonal precipitation and presence of other plant species on population growth of B. tectorum in a grassland ecosystem near Boulder, Colorado, USA. We also performed elasticity analyses to identify life transitions that were most sensitive to precipitation differences. In both study years, population growth rates were highest for B. tectorum growing in treatments receiving supplemental winter precipitation and lowest for those receiving the summer drought treatment. Survival of seedlings to flowering and seed production contributed most to population growth in all treatments. Biomass of neighboring native plants was positively correlated with reduced population growth rates of B. tectorum. However, exotic plant biomass had no effect on population growth rates. This study demonstrates how interacting effects of climate change and presence of native plants can influence the population growth of an invasive species. Overall, our results suggest that B. tectorum will become more invasive in grasslands if the seasonality of precipitation shifts towards wetter winters and allows B. tectorum to grow when competition from native species is low.

Great Basin hydrology, paleoclimate, and connections with the North Atlantic: A speleothem stable isotope and trace element record from Lehman Caves, NV

We present a record of speleothem stable isotope (δ18O, δ13C) and trace element (Mg/Ca, Sr/Ca) variations from Lehman Caves, Nevada for an interval of time (139–128 ka) that encompasses the penultimate glacial termination, Termination II (T-II). Additional growth phases provide data from about 123 ka, a time that correlates with Marine Isotope Stage (MIS) 5e, and about 84 ka and between 82 and 81 ka (MIS 5a). Chronologies from two new stalagmites are anchored by thirty-six uranium–thorium dates. We also present new trace element data from stalagmite LC-2, which has a previously published uranium–thorium chronology and stable isotope record of T-II (Shakun et al., 2011). Our T-II δ18O record broadly replicates that of the Shakun et al. (2011) and Lachniet et al. (2014) records of this time, recording low values from 139 to 135 ka followed by an approximately 3.5‰ increase over an extended interval between 134 and 129 ka. This rise in δ18O values occurs during Heinrich Stadial 11 and the associated Weak Monsoon Interval observed in Chinese caves; our record broadly follows the marine termination, rising boreal summer insolation, and the rise in atmospheric CO2. We infer that this shift results from temperature increase due to increasing atmospheric CO2 and potentially a change in moisture source or precipitation seasonality from greater influence of the North American Monsoon accompanying summer insolation increase. It is also plausible that the melting of the ice sheet itself may have contributed to both temperature and precipitation seasonality changes. Trace element ratios and δ13C values are largely decoupled from δ18O values, showing minimal variation between 139 and 130 ka, for the duration of the Chinese Weak Monsoon Interval. However, these values increase sharply between 130 and 128 ka, which we interpret as increased prior calcite precipitation driven by a transition from wet to dry conditions. This abrupt drying event coincides within dating uncertainties with the abrupt strengthening of the East Asian summer monsoon, which marks the end of both the Weak Monsoon Interval and Heinrich Stadial 11. Our records demonstrate a link between North Atlantic climate and Great Basin moisture during this time that is consistent with the interpretation of data from the last glacial period and may result from abrupt shifts in Atlantic Meridional Overturning Circulation affecting the strength of the Aleutian Low.

Climate, dust, and fire across the Eocene-Oligocene transition, Patagonia

The Eocene-Oligocene transition (EOT) is typically interpreted as a time of drastic global cooling and drying associated with massive growth of a glacial icecap in Antarctica and the shift to an “icehouse” climate. The effects of this transition on the terrestrial environments, floras, and faunas of the Southern Hemisphere, however, have been unclear. Here we document simultaneous changes in fire regime and plant community in Patagonia, Argentina. Decreases in the concentration of magnetite in loessites from the Eocene-Oligocene Vera Member of the Sarmiento Formation correlate with decreases in the fraction of burnt palm phytoliths as well as more consistently palm-dominated phytolith assemblages. Association of magnetite and burnt palm phytoliths suggests intense wildfires, which appear to have been suppressed for ∼200 k.y. shortly after the EOT. The disappearance of fire-related characteristics near the EOT is possible if changes in regional wind patterns—consistent with observed changes in sediment particle sizes—caused changes in seasonal precipitation. These results imply a more important role for fire in structuring Eocene-Oligocene landscapes than previously thought.

Understanding Uncertainties in Future Projections of Seasonal Tropical Precipitation

Abstract Projected changes in regional seasonal precipitation due to climate change are highly uncertain, with model disagreement on even the sign of change in many regions. Using a 20-member CMIP5 ensemble under the RCP8.5 scenario, the intermodel uncertainty of the spatial patterns of projected end-of-twenty-first-century change in precipitation is found not to be strongly influenced by uncertainty in global mean temperature change. In the tropics, both the ensemble mean and intermodel uncertainty of regional precipitation change are found to be predominantly related to spatial shifts in convection and convergence, associated with processes such as sea surface temperature (SST) pattern change and land–sea thermal contrast change. The authors hypothesize that the zonal-mean seasonal migration of these shifts is driven by 1) the nonlinear spatial response of convection to SST changes and 2) a general movement of convection from land to ocean in response to SST increases. Assessment of tropical precipitation model projections over East Africa highlights the complexity of regional rainfall changes. Thermodynamically driven moisture increases determine the magnitude of the long rains (March–May) ensemble mean precipitation change in this region, whereas model uncertainty in spatial shifts of convection accounts for almost all of the intermodel uncertainty. Moderate correlations are found across models between the long rains precipitation change and patterns of SST change in the Pacific and Indian Oceans. Further analysis of the capability of models to represent present-day SST–rainfall links, and any relationship with model projections, may contribute to constraining the uncertainty in projected East Africa long rains precipitation.

Seasonal hydrologic responses to climate change in the Pacific Northwest

AbstractIncreased temperatures and changes in precipitation will result in fundamental changes in the seasonal distribution of streamflow in the Pacific Northwest and will have serious implications for water resources management. To better understand local impacts of regional climate change, we conducted model experiments to determine hydrologic sensitivities of annual, seasonal, and monthly runoff to imposed annual and seasonal changes in precipitation and temperature. We used the Variable Infiltration Capacity (VIC) land‐surface hydrology model applied at 1/16° latitude‐longitude spatial resolution over the Pacific Northwest (PNW), a scale sufficient to support analyses at the hydrologic unit code eight (HUC‐8) basin level. These experiments resolve the spatial character of the sensitivity of future water supply to precipitation and temperature changes by identifying the seasons and locations where climate change will have the biggest impact on runoff. The PNW exhibited a diversity of responses, where transitional (intermediate elevation) watersheds experience the greatest seasonal shifts in runoff in response to cool season warming. We also developed a methodology that uses these hydrologic sensitivities as basin‐specific transfer functions to estimate future changes in long‐term mean monthly hydrographs directly from climate model output of precipitation and temperature. When principles of linearity and superposition apply, these transfer functions can provide feasible first‐order estimates of the likely nature of future seasonal streamflow change without performing downscaling and detailed model simulations.

Precipitation changes in wet and dry seasons over the 20th century simulated by two versions of the FGOALS model

Seasonal precipitation changes over the globe during the 20th century simulated by two versions of the Flexible Global Ocean-Atmosphere-Land System (FGOALS) model are assessed. The two model versions differ in terms of their AGCM component, but the remaining parts of the system are almost identical. Both models reasonably reproduce the mean-state features of the timings of the wet and dry seasons and related precipitation amounts, with pattern correlation coefficients of 0.65–0.84 with observations. Globally averaged seasonal precipitation changes are analyzed. The results show that wet seasons get wetter and the annual range (precipitation difference between wet and dry seasons) increases during the 20th century in the two models, with positive trends covering most parts of the globe, which is consistent with observations. However, both models show a moistening dry season, which is opposite to observations. Analysis of the globally averaged moisture budget in the historical climate simulations of the two models shows little change in the horizontal moisture advection in both the wet and dry seasons. The globally averaged seasonal precipitation changes are mainly dominated by the changes in evaporation and vertical moisture advection. Evaporation and vertical moisture advection combine to make wet seasons wetter and enhance the annual range. In the dry season, the opposite change of evaporation and vertical moisture advection leads to an insignificant change in precipitation. Vertical moisture advection is the most important term that determines the changes in precipitation, wherein the thermodynamic component is dominant and the dynamic component tends to offset the effect of the thermodynamic component.

Spatial distribution of oxygen-18 and deuterium in stream waters across the Japanese archipelago

Abstract. The spatial distribution of oxygen and hydrogen isotopic composition (δ18O and δ2H) of stream waters across Japan was clarified with a data set by compiling sample data obtained from 1278 forest catchments during the summer of 2003. Both δ18O and δ2H values showed positive correlations with the mean annual air temperature and annual evapotranspiration, and negative correlations with latitude and elevation. Deuterium excess (d-excess) values in stream waters were higher on the Sea of Japan side, and lower on the Pacific Ocean side, of the Japanese archipelago. The d-excess in precipitation was generally higher in winter and lower in summer in Japan. The Sea of Japan side experiences a great deal of snowfall, and seasonal changes in monthly precipitation are rather small. In contrast, the Pacific Ocean side experiences a large amount of rainfall during summer with low levels of precipitation during the winter. Therefore, the lower d-excess in stream waters on the Pacific Ocean side reflects summer precipitation, and the higher values on the Sea of Japan side are affected by delayed recharge from snowmelt. The isoscapes of stream water connote not only spatially integrated but also temporally integrated isotope signals of precipitation and provide a framework for addressing applied hydrological, ecological, or meteorological research questions at regional scales, such as the effects of climate change.

Precipitation trends and variability from 1950 to 2000 in arid lands of Central Asia

Climate warming will cause differences in precipitation distribution and changes in hydrological cycle both at regional and global scales. Arid lands of Central Asia (ALCA), one of the largest arid regions at the middle latitudes in the world, is likely to be strongly influenced by climate warming. Understanding the precipitation variations in the past is an important prerequisite for predicting future precipitation trends and thus managing regional water resources in such an arid region. In this study, we used run theory, displacement, extreme deviation theory, precipitation concentration index (PCI), Mann-Kendall rank correlation and climatic trend coefficient methods to analyze the precipitation in wet and dry years, changes in precipitation over multiple-time scales, variability of precipitation and its rate of change based on the monthly precipitation data during 1950–2000 from 344 meteorological stations in the ALCA. The occurrence probability of a single year with abundant precipitation was higher than that of a single year with less precipitation. The average duration of extreme drought in the entire area was 5 years, with an average annual water deficit of 34.6 mm (accounting for 11.2% of the average annual precipitation over the duration). The occurrence probability of a single wet year was slightly higher than that of a single dry year. The occurrence probability of more than 5 consecutive wet years was 5.8%, while the occurrence probability of more than 5 consecutive dry years was 6.2%. In the center of the study area, the distribution of precipitation was stable at an intra-annual timescale, with small changes at an inter-annual timescale. In the western part of the study area, the monthly variation of precipitation was high at an inter-annual timescale. There were clear seasonal changes in precipitation (PCI=12–36) in the ALCA. Precipitation in spring and winter accounted for 37.7% and 24.4% of the annual precipitation, respectively. There was a significant inter-annual change in precipitation in the arid Northwest China (PCI=24–34). Annual precipitation increased significantly (P=0.05) in 17.4% of all the meteorological stations over the study period. The probability of an increase in annual precipitation was 75.6%, with this increase being significant (P=0.05) at 34.0% of all the meteorological stations. The average increasing rate in annual precipitation was 3.9 mm/10a (P=0.01) in the ALCA. There were significant increasing trends (P=0.01) in precipitation in Kazakhstan, Kyrgyzstan and Tajikistan, with rates of 2.6, 3.1 and 3.7 mm/10a, respectively.