Spring Drought Research Articles

A study on the predictability of the transition day from the dry to the rainy season over South Korea

This study was conducted to evaluate the prediction accuracies of THe Observing system Research and Predictability EXperiment (THORPEX) Interactive Grand Global Ensemble (TIGGE) data at six operational forecast centers using the root-mean square difference (RMSD) and Brier score (BS) from April to July 2012. And it was performed to test the precipitation predictability of ensemble prediction systems (EPS) on the onset of the summer rainy season, the day of withdrawal in spring drought over South Korea on 29 June 2012 with use of the ensemble mean precipitation, ensemble probability precipitation, 10-day lag ensemble forecasts (ensemble mean and probability precipitation), and effective drought index (EDI). The RMSD analysis of atmospheric variables (geopotential-height at 500 hPa, temperature at 850 hPa, sea-level pressure and specific humidity at 850 hPa) showed that the prediction accuracies of the EPS at the Meteorological Service of Canada (CMC) and China Meteorological Administration (CMA) were poor and those at the European Center for Medium-Range Weather Forecasts (ECMWF) and Korea Meteorological Administration (KMA) were good. Also, ECMWF and KMA showed better results than other EPSs for predicting precipitation in the BS distributions. It is also evaluated that the onset of the summer rainy season could be predicted using ensemble-mean precipitation from 4-day leading time at all forecast centers. In addition, the spatial distributions of predicted precipitation of the EPS at KMA and the Met Office of the United Kingdom (UKMO) were similar to those of observed precipitation; thus, the predictability showed good performance. The precipitation probability forecasts of EPS at CMA, the National Centers for Environmental Prediction (NCEP), and UKMO (ECMWF and KMA) at 1-day lead time produced over-forecasting (under-forecasting) in the reliability diagram. And all the ones at 2∼4-day lead time showed under-forecasting. Also, the precipitation on onset day of the summer rainy season could be predicted from a 4-day lead time to initial time by using the 10-day lag ensemble mean and probability forecasts. Additionally, the predictability for withdrawal day of spring drought to be ended due to precipitation on onset day of summer rainy season was evaluated using Effective Drought Index (EDI) to be calculated by ensemble mean precipitation forecasts and spreads at five EPSs.

A universal meteorological method to identify potential risk of wind erosion on heavy-textured soils

Abstract The climate of Central Europe, mainly winter seasons with no snow cover at lower altitudes and a spring drought as well, might cause erosion events on heavy-textured soils. The aim of this paper is to define a universal method to identify the potential risk of wind erosion on heavy-textured soils. The categorization of potential wind erosion risk due to meteorological conditions is based on: (i) an evaluation of the number of freeze-thaw episodes forming bare soil surfaces during the cold period of year; and (ii), an evaluation of the number of days with wet soil surfaces during the cold period of year. In the period 2001–2012 (from November to March), episodes with temperature changes from positive to negative and vice versa (thaw-freeze and freeze-thaw cycles) and the effects of wet soil surfaces in connection with aggregate disintegration, are identified. The data are spatially interpolated by GIS tools for areas in the Czech Republic with heavy-textured soils. Blending critical categories is used to locate potential risks. The level of risk is divided into six classes. Those areas identified as potentially most vulnerable are the same localities where the highest number of erosive episodes on heavy-textured soils was documented.

Impacts of climate change on regional hydrological regimes of the Wujiang River watershed in the Karst area, Southwest China

Abstract Background The impacts of climate change on streamflow in the Wujiang River watershed of Guizhou Province, Southwest China, were investigated by using a monthly distributed hydrological model and the two–parameter climate elasticity of streamflow approach. Results Results showed two different approaches obtained almost identical results in term of precipitation elasticity of streamflow, which is about 1.42 across different emission scenarios. Precipitation is the primary factor controlling runoff generation. However, the effects of temperature on the streamflow cannot be neglected with evidences of opposite signs of future precipitation and streamflow; the slight decline of streamflow is associated with an increase of precipitation and a higher temperature. Conclusion While the magnitudes of annual mean streamflow responses are minor, there would be a seasonal shift: drier spring and wetter summer would potentially result in the increasing frequency of spring drought events and summer flooding, and would produce serious challenge for water resources planning and management for Southwest China.

Long-term multifactorial climate change impacts on mesofaunal biomass and nitrogen content

Rising atmospheric CO2 concentration accompanied by temperature increases and altered precipitation patterns calls for assessment of long-term effects of these climatic changes on soil organisms that are essential for ecosystem functioning.In a long-term, full-factorial climate change field experiment, with factors elevated atmospheric CO2 concentration, warming and prolonged summer drought, we assessed the responses of Collembola, oribatid and mesostigmatic mites and enchytraeid worms after 8 years of treatment. Both the biomasses and N content of oribatid and mesostigmatic mites increased at elevated CO2, or tended do so. In contrast, enchytraeid N content decreased at elevated CO2. Soil microbial biomass N pool and litter C:N ratio also increased with elevated CO2, which suggests that mite biomasses are more coupled to microbial biomass, whereas enchytraeid biomass to a larger extent is governed by litter nitrogen concentration, i.e. litter quality. Structural equation modelling confirmed the positive coupling between soil microbial N content and oribatid biomass and further between oribatid and mesostigmatic biomass. The SEM also revealed a negative relationship between microbial N content and enchytraeid biomass.The biomass of all mesofaunal groups was reduced by spring drought, especially when combined with warming. Enchytraeid and especially collembolan biomass suffered greater drought declines than mite biomasses.We conclude that under long-term elevated CO2 exposure, energy and elements will to a larger extent pass through decomposer organisms such as oribatid mites, which are based on food sources with relatively high nitrogen content.After eight years of repeated spring drought events, soil mesofauna did not show signs of adaptation to acute stress effects imposed by drought. However, Collembola and enchytraeids were more drought-sensitive than mites, and although the soil temperature increase in warmed treatments was very modest, warming exacerbated the drying of soil and thus also the negative drought impact on soil mesofauna.

Exploring Growth Variability and Crown Vitality of Sessile Oak (Quercus Petraea) in the Czech Republic

Unraveling climatic effects on growth of oak - Europe’s most ecologically and economically important forest species - has been the subject of many recent studies; however, more insight based on field data is necessary to better understand the relationship between climate and tree growth and to adapt forest management strategies to future climate change. In this report, we explore the influence of temperature, precipitation and drought variability on the productivity and vitality of oak stands in the Czech Highlands. We collected 180 cores from mature oaks (Quercus petraea) at four forest stands in the Czech Drahany Highlands. Standard dendromethods were used for sample preparation, ring width measurements, cross-dating, chronology development, and the assessment of growth-climate response patterns. Crown vitality was also evaluated, using the modified ICP Forests methodology. Late spring precipitation totals between May and June as well as the mean July temperature for the year of ring formation were found to be the most important factors for oak growth, whereas crown condition was significantly affected by spring and summer drought. This study is rep-resentative for similar bio-ecological habitats across Central Europe and can serve as a dendroclima-tological blueprint for earlier periods for which detailed meteorological information is missing

Soil layer displacing plough with a corn stalk collector – Part 2: Construction of a watertable underground

Fuxin, a major corn production area, is located in Liaoning province, P. R. of China. The annual precipitation in this area is only 450 mm, mostly during summer. The area receives less rainfall in spring seeding season every year. Droughts in spring are common. We constructed an artificial perched watertable by burying corn stalks. The results showed that before watertable construction, the soil penetration resistance was 5.0 MPa below 200 mm depth. After construction, that became 1.0 MPa down to 400 mm depth. The watertable construction evened out available N, P2O5 and K2O and organic matter in all layers. Therefore, when the top soil and the subsoil were displaced, a deficiency of any chemical element for plants would not be caused.

Development of DArT-based PCR markers for selecting drought-tolerant spring barley.

The tolerance of spring barley (Hordeum vulgare L.) cultivars to spring drought is an important agronomic trait affecting crop yield and quality in Poland. Therefore, breeders require new molecular markers to select plants with lower spring drought susceptibility. With the advent of genomic selection technology, simple molecular tools may still be applicable to screen material for markers of the most important traits and in-depth genome scanning. In previous studies, diversity arrays technology (DArT)-based genetic maps were constructed for F2 populations of Polish fodder and malt barley elite breeding lines, and 15 and 18 quantitative trait loci (QTLs) related to spring drought tolerance were identified, respectively. In this paper, we show the results of a conversion of 30 DArT markers corresponding to 11 QTLs into simple sequence repeat (SSR) and sequence tagged site (STS) markers. Twenty-two polymorphic markers were obtained, including 13 DArT-based SSRs. Additionally, 31 SSR markers, located in close proximity to the DArT markers, were selected from the GrainGenes database and tested. Further analyses of 24 advanced breeding lines with different drought tolerances confirmed that five out of the 30 converted markers, as well as three out of the 31 additional SSR markers, were effective in marker-assisted selection for drought tolerance. The possible function of clones related to these markers in drought tolerance is discussed.Electronic supplementary materialThe online version of this article (doi:10.1007/s13353-015-0273-x) contains supplementary material, which is available to authorized users.

Recent changes in extreme precipitation and drought over the Songhua River Basin, China, during 1960–2013

Based on ten indices of extreme precipitation and one drought index (composite index, CI), the trends in extreme events were investigated using a Mann–Kendall non-parametric method at 39 stations in the Songhua River Basin (SHB) during 1960–2013. The regionally averaged wet-day precipitation (PRCPTOT) increased at a rate of 1.65mm/year (R2=0.28, P=0.13), in which 82% of the stations experienced increases, but only 4 stations showed significant positive trends. The annual R95 and R99 exhibited slight upward trends at rates of 1.37 (R2=0.21, P=0.27) and 1.28mm/year (R2=0.23, P=0.23) over the last 54years; however, there were not significant trends in R95 and R99 at the 0.05 level. PRCPTOT, R95 and R99 showed similar spatial trends, in which positive trends mainly occurred in the northern and southeastern basins. The trends in the maximum 1-day precipitation (RX1day) and maximum 5-day precipitation (RX5day) do not show a prevalent trend (approximately 50% of the stations have a positive trend and the remaining stations have a negative trend). The simple daily intensity index (SDII) significantly decreased at an annual rate of 0.02mm/d during 1960–2013 (R2=0.66, P<0.01); spatially, 49% of the stations experienced statistically significant decreases at the 0.05 level based on the Mann–Kendall non-parametric test. The regionally averaged heavy (R10mm) and very heavy precipitation days (R20mm) and consecutive wet days (CWD) showed no significant trends during the past 54years; however, several individual extreme precipitation events, such as the flood of 1998 in the SHB, were well detected by these indices. The regionally averaged consecutive dry days (CDD) significantly increased (R2=0.79, P<0.01) at a rate of 0.22days/year from 1960 to 2013. All of the stations exhibited statistically significant increases in CDD, excluding the Tongyu station in the western basin. The monthly RX5day values were highest in summer, from June to August, in the SHB; a peak occurred in July (67.5mm) in the SHB during 1960–2013. The CI peaked in July, with the highest value of 0.2 in the SHB during 1960–2013. However, the two lowest CI values occurred in spring and fall, with values of −0.56 and −0.41, respectively. During April and May, when most of the spring drought events occur, a prevalent trend does not exist; moreover, almost no stations have statistically significant CI increases. In August and September, respectively 79% and 97% of the stations exhibited a CI negative trend, but only 2 and 6 stations showed significant decreases at the 0.05 level. The increasing extreme climate events present a challenge for local water resources management.

The yield response of oilseed rape to plant population density

SUMMARYEight winter oilseed rape and two spring oilseed rape field experiments were performed in the UK in harvest years 2009–12. Each experiment consisted of at least one hybrid and one open-pollinated variety grown at five seed rates from 10 or 20 seeds/m2 to 160 or 200 seeds/m2. Linear plus exponential curves were used to describe the yield response to seed rate and to calculate economically optimal seed rates. Plant counts were then used to derive optimal plant population densities. These ranged from &lt;10 to 39 plants/m2 for six winter oilseed rape experiments between 73 and &gt;155 plants/m2 in two winter oilseed rape experiments with severe spring droughts, and from 47 to 65 plants/m2 for spring oilseed rape. Optimal plant population densities were lower for hybrid than for open-pollinated varieties, due to a combination of the higher cost of hybrid seed and, for some experimental sites, hybrid varieties compensating better for low plant populations. Across all sites, sowing winter oilseed rape at 30 seeds/m2 rather than common commercial rates of 70 seeds/m2 for hybrids and 100 seeds/m2 for open-pollinated varieties would have increased average gross margin by £29/ha. Sowing spring oilseed rape at 70 seeds/m2 rather than commonly used rates of 120 or 150 seeds/m2 would have increased average gross margin by £64/ha.

Projecting streamflow in the Tangwang River basin (China) using a rainfall generator and two hydrological models

To estimate the impacts of future climate change on streamflow in the Tangwang River basin (TRB) in northeastern China, 2 hydrological models, the Soil and Water Assessment Tool and the Hydro-Informatic Modeling System, were used. These models are driven by future (2021-2050) local rainfall and temperature scenarios downscaled from global climate model (GCM) simulations from the fifth phase of the Coupled Model Intercomparison Project under 2 emission scenarios (Representative Concentration Pathway [RCP] 4.5 and RCP8.5). The downscaling of rainfall is done with the help of a multisite stochastic rainfall generator (MSRG), which extends the 'Richardson type' rainfall generator to a multisite approach using a modified series-independent and spatial-correlated random numbers method by linking its 4 parameters to large-scale circulations using least-squares regressions. An independent validation of the MSRG shows that it successfully preserves the major daily rainfall characteristics for wet and dry seasons. Relative to the reference period (1971-2000), the annual and wet season (April to October) streamflow during the future period (2021-2050) would decrease overall, which indicates that water resources and the potential flood risk would decline in the TRB. The slightly increased dry season (November to March) streamflow would, to some extent, contribute to the 'spring drought' over this region. Although rainfall is projected to remain un changed in the wet season and the whole year, the increased total evapotranspiration due to the increase in temperature would lead to a decline in total streamflow for this basin. The projected streamflow changes from multiple GCMs in this paper could provide a glimpse into a very plausible future for the water resource management community, and would hence provide valuable references for the sustainable management of water and forest ecosystems under a changing climate.

Ability of various tree species to acclimation in urban environments probed with the JIP-test

Urban trees are often affected by water deficit. Therefore, the choice of suitable tree species for urban forestry should include their ability to cope with drought stress. In our examination, we used a physiological method based on chlorophyll-a fluorescence to evaluate the performance of urban trees of eight species and cultivars in dry June and moderate September 2008. The following taxa were examined: Tilia cordata Mill. ‘Greenspire’, Tilia×europaea L. ‘Pallida’, Acer campestre L., Quercus rubra L., Gleditsia triacanthos L., Pyrus calleryana Decne ‘Chanticleer’, Platanus×hispanica Mill. ex Münchh. ‘Acerifolia’ and Ginkgo biloba L. Our investigation showed different ability to acclimation to drought in examined taxa. Gleditsia triacanthos, Pyrus calleryana and Platanus×hispanica ‘Acerifolia’ seem to be more resistant to long periods of water deficit. On the contrary, tree species from typical mesotic forests and species of northern part of deciduous forest zone are more susceptible to prolonged drought in late spring. When the drought becomes more severe, trees adjust their photosynthetic apparatus activity to poor water availability by increasing dissipation of excess light energy absorbed. Additionally, we found that, independently of climatic conditions and habitat characteristics, some parameters of chlorophyll-a fluorescence change during the leaf maturity stage.

根系固土主导力学因素初探与差异性评价

PDF HTML阅读 XML下载 导出引用 引用提醒 根系固土主导力学因素与差异性评价 DOI: 10.5846/stxb201403050375 作者: 作者单位: 内蒙古农业大学,内蒙古农业大学,内蒙古农业大学,内蒙古农业大学,内蒙古自治区灌溉排水发展中心 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目(51064021);内蒙古基金重点项目(2010ZD16) Mechanical factors influencing soil-reinforcement by roots and identifying appropriate plant species for erosion control Author: Affiliation: Inner Mongolia Agriculture University,Inner Mongolia Agriculture University,Inner Mongolia Agricultural 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:为了探究影响根系固土的主导力学因素,并为侵蚀区固土抗蚀植物种的筛选提供部分依据。以3-4年生(4年生为主)5种内蒙古干旱、半干旱地区常见的水土保持植物:柠条(Caragana microphylla Lam.)、沙柳(Salix psammophila C.wang et Ch.Y.Yang)、沙地柏(Sabina vulgaris Ant.)、白沙蒿(Artemisia sphaerocephala Krasch.)、沙棘(Hippophae rhamnoides Linn.)为研究对象,针对春季土壤干旱和夏季暴雨(土壤湿润)两种自然条件,对影响5种植物根系固土的10项指标进行主成分分析。结果表明,根系抗拉力学特性是影响植物根系固土的主导力学因素,其次为根-土界面摩阻特性,最后是根-土复合体抗剪特性。在此基础上,从根系力学特性的角度出发,运用层次分析法对两个时期5种植物根系固土能力的差异性进行评价。在评价过程中,为了保证评价数据完整性,减小专家主观因素所带来的误差,使评价结果更具科学性,该文将两个时期主成分分析所得3个力学特性的方差贡献率作为权重。评价结果显示,根系固土指数为:春季土壤干旱时期,柠条(0.834) > 沙柳(0.330) > 沙地柏(-0.066) > 白沙蒿(-0.206) > 沙棘(-0.864);夏季暴雨时期分别为,柠条(0.876)>沙地柏(0.218) > 沙柳(0.065) > 白沙蒿(-0.404) > 沙棘(-0.755)。5种植物中,柠条根系的抗拉力学特性显著优于其他植物,可作为干旱、半干旱地区固土抗蚀的重要参考树种。 Abstract:Influenced by the physiological and genetic characteristics of plants, the mechanical properties of roots differ significantly, with the result that species vary in their ability to resist soil erosion. The selection of species to reinforce soil and prevent erosion is the key to improving not only soil and water conservation, but also vegetation and ecological restoration. Research to identify suitable plant species is still in its early stages, and studies addressing many issues are urgently needed. Caragana microphylla Lam, Salix psammophila C.wang & Ch.Y.Yang, Sabina vulgaris Ant, Artemisia sphaerocephala Krasch, and Hippophae rhamnides Linn are common plants used in soil and water conservation projects in the arid and semi-arid regions of Inner Mongolia. Rainfall is concentrated in summer with short-duration and high-intensity. The mechanical properties of roots differ significantly with growth period and soil moisture conditions. In order to study the mechanical factors influencing soil-reinforcement by roots and identify suitable anti-erosion plant species for this area, root tensile strength, root-soil surface friction, and root-soil composite shear strength of five plant species were studied. During the spring drought period and summer wet period, ten indicators of efficacy in erosion prevention (root-soil composite cohesion, root-soil composite equivalent friction angle, root-soil interface sheer strength, cumulative surface area, interface friction coefficient, representative root elasticity modulus, representative root constitutive properties, taproot tensile strength, lateral branch root tensile strength, length of cumulative root length) of the five species at the age of 3-4 (mainly 4) years were measured. The data were then analyzed using principal component analysis (PCA) with SAS9.0 software. The PCA results indicate that tensile mechanical strength had the greatest influence on soil reinforcement, followed by root-soil surface friction, and then root-soil composite shear strength. Based on these mechanical factors, the performance of the five species was evaluated. In order to maintain the integrity of the data and reduce uncertainty caused by subjective expert assessments, the variance contribution to the PCA of each of the three mechanical characteristics was used as to weight an analytic hierarchy process (AHP). The results showed the soil-reinforcement indices in the drought period were ranked Caragana microphylla Lam (0.834) > Salix psammophila C.wang et Ch.Y.Yang (0.303) > Sabina vulgaris Ant (-0.066) > Artemisia sphaerocephala Krasch (-0.206) > Hippophae rhamnides Linn (-0.864), while in the wet period they were ranked Caragana microphylla Lam (0.876) > Sabina vulgaris Ant (0.218) > Salix psammophila C.wang et Ch.Y.Yang (0.065) > Artemisia sphaerocephala Krasch (-0.404) > Hippophae rhamnides Linn (-0.755). The results suggest that species with better root tensile strength should be chosen reinforce soil and prevent erosion. Of the five species, Caragana microphylla Lam is the preferred soil-reinforcement and anti-erosion plant in arid and semi-arid regions due to its high root tensile strength. 参考文献 相似文献 引证文献

Impacts of drought on grape yields in Western Cape, South Africa

Droughts remain a threat to grape yields in South Africa. Previous studies on the impacts of climate on grape yield in the country have focussed on the impact of rainfall and temperature separately; meanwhile, grape yields are affected by drought, which is a combination of rainfall and temperature influences. The present study investigates the impacts of drought on grape yields in the Western Cape (South Africa) at district and farm scales. The study used a new drought index that is based on simple water balance (Standardized Precipitation Evapotranspiration Index; hereafter, SPEI) to identify drought events and used a correlation analysis to identify the relationship between drought and grape yields. A crop simulation model (Agricultural Production Systems sIMulator, APSIM) was applied at the farm scale to investigate the role of irrigation in mitigating the impacts of drought on grape yield. The model gives a realistic simulation of grape yields. The Western Cape has experienced a series of severe droughts in the past few decades. The severe droughts occurred when a decrease in rainfall occurred simultaneously with an increase in temperature. El Nino Southern Oscillation (ENSO) appears to be an important driver of drought severity in the Western Cape, because most of the severe droughts occurred in El Nino years. At the district scale, the correlation between drought index and grape yield is weak (r≈−0.5), but at the farm scale, it is strong (r≈−0.9). This suggests that many farmers are able to mitigate the impacts of drought on grape yields through irrigation management. At the farm scale, where the impact of drought on grape yields is high, poor yield years coincide with moderate or severe drought periods. The APSIM simulation, which gives a realistic simulation of grape yields at the farm scale, suggests that grape yields become more sensitive to spring and summer droughts in the absence of irrigation. Results of this study may guide decision-making on how to reduce the impacts of drought on food security in South Africa.

Effects of stand composition and tree size on resistance and resilience to drought in sessile oak and Scots pine

The IPCC previsions for the upcoming decades include an increase in frequency and intensity of drought events in several regions worldwide, including Northern Europe. Drought significantly affects forest ecosystems through decreased productivity, increased vulnerability to biotic disturbances and increased subsequent mortality. How forest ecosystems maintain resistance and resilience to drought events are important questions. Our study aimed to assess whether species mixture or an individual tree size within a stand alters a given tree’s resilience and resistance to drought. A retrospective study of tree-ring widths allowed us to calculate resistance, resilience and recovery indices for five recent drought events: 1976, the 1990–1992 period, 2003, 2006 and 2010. These drought events were selected based on the SPEI (Standardized Precipitation Evapotranspiration Index) drought index. Our study sample consisted of 108 individual sessile oak (Quercus petraea (Matt.)) or Scots pine (Pinus sylvestris L.) trees sampled in 2012 and 2013 (Orleans forest, central France) in pure and mixed stands, divided into three diameter classes corresponding to three sizes: large, medium and small trees. Scots pine performed better than sessile oak during the 1990–1992 and 2010 droughts while the contrary was observed for the 2003 and 2006 droughts. They performed equally in 1976. We suggest that the differing sensitivity of the two species to spring and summer drought explained this result. In our study, stand composition had no effect on resilience or resistance for either species. The size effect in oaks was unclear as small oaks displayed either a better performance or a worse performance than large oaks. Small pines displayed better resistance and resilience than pines of a larger size. This work stressed the importance of taking into account stand composition and trees size as well as soil and climatic conditions for each drought events to achieve a better understanding of the diversity of responses to climatic variations among forest ecosystems.

Predicting East African spring droughts using Pacific and Indian Ocean sea surface temperature indices

Abstract. In eastern East Africa (the southern Ethiopia, eastern Kenya and southern Somalia region), poor boreal spring (long wet season) rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers implement disaster risk reduction measures while guiding climate-smart adaptation and agricultural development. Building on recent research that links more frequent East African droughts to a stronger Walker circulation, resulting from warming in the Indo–Pacific warm pool and an increased east-to-west sea surface temperature (SST) gradient in the western Pacific, we show that the two dominant modes of East African boreal spring rainfall variability are tied to SST fluctuations in the western central Pacific and central Indian Ocean, respectively. Variations in these two rainfall modes can thus be predicted using two SST indices – the western Pacific gradient (WPG) and central Indian Ocean index (CIO), with our statistical forecasts exhibiting reasonable cross-validated skill (rcv ≈ 0.6). In contrast, the current generation of coupled forecast models show no skill during the long rains. Our SST indices also appear to capture most of the major recent drought events such as 2000, 2009 and 2011. Predictions based on these simple indices can be used to support regional forecasting efforts and land surface data assimilations to help inform early warning and guide climate outlooks.

The Copula Function-Based Probability Characteristics Analysis on Seasonal Drought &amp; Flood Combination Events on the North China Plain

Drought &amp; flood events, especially the drought &amp; flood combination events (DFCEs) on the North China Plain (NCP), known as an important grain production region in China, constitute a serious threat to China’s food security. Studies on DFCEs in this region are of great significance for the rational allocation of water resources and the formulation of integrated response strategy for droughts and floods. In this study, L-moments theory and bivariate copula method were used to evaluate the probability characteristics of seasonal DFCEs (continuous drought, continuous flood, and alternation between drought and flood) on the NCP, based on the daily precipitation data (1960–2012) at 19 meteorological stations. Results indicate the following: (1) On the NCP, the precipitation in summer accounts for 56.45%–72.02% of mean annual precipitation, and the precipitation in autumn and spring come second. The winter precipitation is the smallest (less than 4%); (2) The best-fit distribution for precipitation anomaly percentages in spring, summer and autumn are Generalized Normal (GNO), Generalized Logistic (GLO) and Pearson III (P-III) in sub-region I, respectively. While in sub-region II, they are respectively the P-III, P-III and Generalized Extreme-Value (GEV); (3) Compared with the Gumbel copula and Clayton copula, Frank copula is more suitable for spring-summer and summer-autumn precipitation anomaly percentage sequences on the NCP; (4) On the time scale, continuous drought respectively dominate in spring-summer DFCEs and in summer-autumn DFCEs on the NCP. Summer-autumn DFCEs prevail in sub-region I with the average probability value 0.34, while spring-summer DFCEs dominate in sub-region II, of which average probability value is 0.42; (5) On the spatial scale, most areas where the probability of continuous drought in spring-summer and spring drought &amp; summer flood is relatively high are located in the northwest, northeast, and coastal parts of sub-region II; all the events with high probability of continuous drought in summer-autumn and summer flood &amp; autumn drought occurred at the central part in the northwest of sub-region II.

Exploration of drought evolution using numerical simulations over the Xijiang (West River) basin in South China

Summary The knowledge of drought evolution characteristics may aid the decision making process in mitigating drought impacts. This study uses a macro-scale hydrological model, Variable Infiltration Capacity (VIC) model, to simulate terrestrial hydrological processes over the Xijiang (West River) basin in South China. Three drought indices, namely standardized precipitation index (SPI), standardized runoff index (SRI), and soil moisture anomaly index (SMAI), are employed to examine the spatio-temporal and evolution features of drought events. SPI, SRI and SMAI represent meteorological drought, hydrological drought and agricultural drought, respectively. The results reveal that the drought severity depicted by SPI and SRI is similar with increasing timescales; SRI is close to that of SPI in the wet season for the Liu River basin as the high-frequency precipitation is conserved more by runoff; the time lags appear between SPI and SRI due to the delay response of runoff to precipitation variability for the You River basin. The case study in 2010 spring drought further shows that the spatio-temporal evolutions are modulated by the basin-scale topography. There is more consistency between meteorological and hydrological droughts for the fan-like basin with a converged river network. For the west area of the Xijiang basin with the high elevation, the hydrological drought severity is less than meteorological drought during the developing stage. The recovery of hydrological and agricultural droughts is slower than that of meteorological drought for basins with a longer mainstream.

Spatial and temporal distribution of West Nile virus in horses in Israel (1997-2013)--from endemic to epidemics.

With the rapid global spread of West Nile virus (WNV) and the endemic state it has acquired in new geographical areas, we hereby bring a thorough serological investigation of WNV in horses in a longstanding endemic region, such as Israel. This study evaluates the environmental and demographic risk factors for WNV infection in horses and suggests possible factors associated with the transition from endemic to epidemic state. West Nile virus seroprevalence in horses in Israel was determined throughout a period of more than a decade, before (1997) and after (2002 and 2013) the massive West Nile fever outbreak in humans and horses in 2000. An increase in seroprevalence was observed, from 39% (113/290) in 1997 to 66.1% (547/827) in 2002 and 85.5% (153/179) in 2013, with persistent significantly higher seroprevalence in horses situated along the Great Rift Valley (GRV) area, the major birds' migration route in Israel. Demographic risk factors included age and breed of the horse. Significantly lower spring precipitation was observed during years with increased human incidence rate that occurred between 1997–2007. Hence, we suggest referring to Israel as two WNV distinct epidemiological regions; an endemic region along the birds' migration route (GRV) and the rest of the country which perhaps suffers from cyclic epidemics. In addition, weather conditions, such as periods of spring drought, might be associated with the transition from endemic state to epidemic state of WNV.

Inundation and precipitation effects on growth and flowering of the high marsh species Juncus gerardii

Accelerated sea level rise threatens coastal wetland plant communities where coastal development restricts transgression, and inundation increases and declining sediment supplies limit the capacity of coastal wetlands to build in elevation. Juncus gerardii Loisel., black needle rush, is a high latitude cosmopolitan plant species and, within salt marshes of the U.S. mid-Atlantic and New England coasts, it occupies a narrow belt along the marsh-upland border. Examination of historic aerial photography, vegetation resurveys, and peat composition analysis for U.S. Northeastern marshes have shown vegetation change patterns indicative of increased inundation, including decline of J. gerardii. To interpret loss patterns for J. gerardii in southern New England, we conducted a factorial experiment to establish its sensitivity to inundation and drought. A strong relationship was found between inundation and growth for J. gerardii, which together with marsh elevation and water level data, suggests that growth is reduced by current flooding patterns. Examination of J. gerardii flowering also indicates that floret and inflorescence density vary with inundation, suggesting that negative impacts of sea level rise on Juncus may extend to seed production. Late spring and summer drought impacted neither J. gerardii growth nor its flowering, implying that J. gerardii is insensitive to below-average precipitation or drought during this time of year. We conclude that current inundation patterns are incompatible with robust growth for J. gerardii, and recommend conservation actions be focused on the marsh-upland border to facilitate the upslope migration of J. gerardii and other transitional high marsh plant species.

Post-fire forest dynamics and climate variability affect spatial and temporal properties of spruce beetle outbreaks on a Sky Island mountain range

The spruce beetle (Dendroctonus rufipennis) is known for extensive outbreaks resulting in high spruce mortality, but several recent outbreaks in the western United States have been among the largest and most severe in the documentary record. In the Pinaleño Mountains of southeast Arizona, U.S.A., an outbreak in the mid-1990s resulted in 85% mortality of Engelmann spruce >7cm diameter. To put this outbreak into historical perspective, we used dendrochronology to examine the effects of host species’ distribution and growth rates on spruce beetle outbreak initiation, frequency and size over three centuries. We used multiproxy records of understory spruce growth release, snag death dates, failed attack scars, and historical records to identify 12 distinct outbreak events over a 319-year period of reconstruction. Outbreaks were defined by spatial criteria, affecting 25% or more of sites, instead of mortality-based criteria that could not be assessed in older outbreak events. We also tested outbreak associations with summer temperature and spring drought as they relate to thresholds associated with larval development and host stress, respectively. In the decades following fire exclusion in adjacent mixed-conifer forest, the area occupied by Engelmann spruce and corkbark fir doubled in size, coinciding with the first wide-spread outbreaks in the reconstructed period and a doubling of outbreak duration. Outbreaks lagged spruce establishment by 40–90years depending on forest type and time since fire, and were correlated significantly with several years of antecedent warm summer temperatures followed by up to a decade of persistent spring drought. Mean annual growth increment, a factor associated with host susceptibility, was significantly higher in recently colonized mixed-conifer forest than in historically spruce- and fir-dominated sites. Increasing size and severity of outbreaks appears to have been influenced by host range expansion due to fire exclusion, coupled with increasing incidence of warm summer temperatures associated with persistent spring water stress. The combined effects of expansion of spruce into mixed-conifer forest and climatic trend toward warmer, drier conditions have the potential to promote extensive spruce beetle outbreaks across the host range of the western United States.