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Dry Years (dry + year)
Selected AbstractsLong-term carbon exchange in a sparse, seasonally dry tussock grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2004John E. Hunt Abstract Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m,2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was <0.2 by early summer. The maximum daily net CO2 uptake rate was only 1.5 g C m,2 day,1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m,2 was lost to the atmosphere. During the wet year, 41 g C m,2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall. The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m,3) to the driest value obtained (0.04 m3 m,3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term. [source] Sources of stream sulphate in headwater catchments in Otter Creek Wilderness, West Virginia, USAHYDROLOGICAL PROCESSES, Issue 4 2001Ross D. Fitzhugh Abstract Upland forested catchments in the Appalachian Plateau region receive among the greatest rates of atmospheric sulphur (S) deposition in the eastern USA, although coal mines and S-bearing minerals in bedrock may also contribute to stream acidity in this region. Watershed mass balance and stable S isotopic values (,34S) of sulphate (SO42,) were used to assess the contributions to stream SO42, from atmospheric and lithogenic sources at Yellow Creek (YC), a headwater catchment on the Appalachian Plateau in West Virginia. Oxygen isotopic values (,18O) of water were used to study catchment hydrology. Stream output of SO42, was c. 60% of atmospheric S deposition during a relatively dry year, whereas atmospheric S input was nearly balanced by stream output during a year with above normal amounts of precipitation. The temporal patterns and values of ,34S were similar between bulk precipitation and stream water at two upper elevation sites. At the lowest elevation site, stream ,34S values were similar to bulk precipitation values during the dormant season but were slightly lower than precipitation during the low-flow summer, probably as the result of a greater proportion of stream water being derived from deep hydrological flowpaths that have contacted S-bearing minerals with low ,34S values in coal seams. Stream ,34S values at YC were significantly higher than at Coal Run, a catchment containing abandoned coal prospects and having a greater amount of S-bearing minerals than YC. Results suggested that lithogenic S is a relatively minor source and that atmospheric deposition is the principal source of stream SO42,, and thus stream acidity, at YC. Copyright © 2001 John Wiley & Sons, Ltd. [source] Double-nesting behaviour and sexual differences in breeding success in wild Red-legged Partridges Alectoris rufaIBIS, Issue 4 2009FABIÁN CASAS Double-nesting behaviour, a rare breeding system in which females lay in two nests, one incubated by herself and the other one by her mate, could be considered an intermediate stage in the evolutionary trend from biparental to uniparental care of single clutches. We examined the occurrence and success of double-nesting behaviour in Red-legged Partridges Alectoris rufa in Central Spain. Clutch size and hatching success were recorded, as well as the variation in these between years and between incubating sexes. Participation in incubation was higher for females (94.76%) than males (41.0%), and the proportion of incubating males varied markedly between years, with no incubating males in one dry year and approximately 50% of males incubating in other years. There was significant variation among years and between sexes in laying date, clutch size and hatching success. Clutch size decreased with later laying date in males and females. The probability of clutch loss to predation differed between sexes, being much higher for nests incubated by females. Our results suggest that both rainfall and predation influence the occurrence and success of double-nesting. [source] Spatial differences in breeding success in the pied avocet Recurvirostra avosetta: effects of habitat on hatching success and chick survivalJOURNAL OF AVIAN BIOLOGY, Issue 4 2006Szabolcs Lengyel I studied the breeding biology of pied avocets Recurvirostra avosetta in natural habitats (alkaline lakes), and in semi-natural sites (dry fishpond, reconstructed wetlands) in Hungary to relate habitat selection patterns to spatial and temporal variation in breeding success. Colonies were initiated earlier in semi-natural sites than in natural habitats, and earlier on islands than on the mainland. Hatching success was higher on islands than on the mainland, in semi-natural sites than in natural habitats, in colonies of at least 15 pairs than in smaller colonies, and for nests initiated earlier than later within a colony. Fledging success was higher in the wet years (1999,2000) than in the dry year (1998), decreased strongly by season in both habitats and increased with average daily temperature in the first week post-hatch in 1999,2000. Most pairs hatching young in semi-natural sites attempted to lead their chicks to feeding areas in natural habitats, whereas no such movement occurred in the opposite direction. Chick mortality due to predation was high during brood movements and only 23% of the pairs moving their young produced fledglings, compared to 43% for pairs remaining in semi-natural sites and 68% for pairs hatching and rearing young in natural habitats (total n=192 broods). These results suggest that semi-natural sites were more suitable for nesting, whereas natural habitats were more suitable for chick-rearing. The opposing trends in habitat-related breeding success between nesting and chick-rearing suggest sub-optimal habitat selection by Pied Avocets due to an incorrect assessment of the potential for successful reproduction of semi-natural sites, which may thus function as ecological traps. [source] Interactions between Drought and O3 Stress in Forest TreesPLANT BIOLOGY, Issue 1 2006R. Matyssek Abstract: Temperature increase and altered precipitation are facets of "Global Change", along with enhanced tropospheric ozone (O3) and CO2 levels. Both O3 and drought may curtail the probably limited capacity of "extra" carbon fixation in forest trees under a CO2 -enriched atmosphere. In view of the exceptionally dry year of 2003 in Central Europe, this mini-review highlights O3/drought interactions in biochemical and ecophysiological responses of trees. Such interactions appear to vary, depending on the genotype and factorial scenarios. If O3 perturbs stomatal regulation, tolerance to both drought and persisting O3 exposure may be weakened, although drought preceding O3 stress may "harden" against O3 impact. Stomatal closure under drought may shield trees against O3 uptake and injury, which indeed was the case in 2003. However, the trees "tuning" between O3 uptake and defence capacity is crucial in stress tolerance. Defence may be constrained due to limited carbon fixation, which results from the trade-off with O3 exclusion upon stomatal closure. Drought may cause a stronger reduction in stem growth than does ozone on an annual basis. [source] Carbon isotope discrimination and wood anatomy variations in mixed stands of Quercus robur and Quercus petraeaPLANT CELL & ENVIRONMENT, Issue 8 2001S. Ponton Abstract The two most common oak species in western Europe, Quercus robur and Quercus petraea, display different ecological behaviours, particularly with respect to their responses to drought. The ecophysiological basis of this niche difference is not understood well. Here we test the hypothesis that these two species present distinct water use efficiencies (WUEs), using the carbon isotope discrimination approach. Leaves and 13 dated ring sequences were sampled in 10 pairs of adult trees growing side by side. Carbon isotope composition was measured on cellulose extracts. In addition, relationships between carbon isotope discrimination and wood anatomy were assessed at the tree level. Quercus robur displayed a 1·0, larger isotopic discrimination than Q. petraea, and therefore a lower intrinsic WUE (,13%). This interspecific difference of isotopic discrimination was quite stable with time and independent of tree radial growth and climate fluctuations. A strong positive correlation was observed between average tree values of earlywood vessel surface area and 13C isotopic discrimination. This correlation was even higher with 13C of the 1976 dry year (r = 0·86). These observations led to the hypothesis that hydraulic properties of xylem could exert a constraint on leaf gas exchange, resulting in a larger WUE for individuals with smaller vessel cross-section area. [source] The role of successional stage and small-scale disturbance for establishment of pioneer grass Corynephorus canescensAPPLIED VEGETATION SCIENCE, Issue 3 2010Okka Tschöpe Abstract Question: Which mechanisms promote the maintenance of the protected pioneer grass Corynephorus canescens in a mosaic landscape? Which are the interactive effects of small-scale disturbances, successional stage and year-to-year variation on early establishment probabilities of C. canescens? Location: Brandenburg, NE Germany. Methods: We measured emergence and survival rates over 3 yr in a sowing-experiment conducted in three successional stages (C. canescens -dominated site, ruderal forb site and pioneer forest) under two different regimes of mechanical ground disturbance (disturbed versus undisturbed control). Results: Overall, disturbance led to higher emergence in a humid year and to lower emergence in a very dry year. Apparently, when soil moisture was sufficient, the main factor limiting C. canescens' establishment was competition, while in the dry year, water became the limiting factor. Survival rates were not affected by disturbance. In humid years, C. canescens emerged in higher numbers in open successional stages while in the dry year, emergence rates were higher in late stages, suggesting an important role of late successional stages for the persistence of C. canescens. Conclusions: Our results suggest that small-scale disturbances can promote germination of C. canescens. However, disturbances should be carefully planned. The optimal strategy for promoting C. canescens is to apply disturbances just before seed dispersal and not during dry years. At the landscape scale, a mosaic of different vegetation types is beneficial for the protected pioneer grass as facilitation by late-successional species may be an important mechanism for the persistence of C. canescens, especially in dry years. [source] Superficial lizards in cold climates: Nest site choice along an elevational gradientAUSTRAL ECOLOGY, Issue 7 2009J. SEAN DOODY Abstract Embryonic conditions may limit the distributions of egg-laying ectotherms, and recent research suggests that nesting mothers of wide-ranging species may use a number of factors to compensate for differing climates. However, while variation in temporal factors across environmental gradients are common or pervasive (i.e. seasonal timing of nesting), similar evidence for spatial factors is rare (e.g. aspect, openness and depth of nest sites). I tested the idea that a wide-ranging lizard, the Australia water dragon (Physignathus lesueurii), uses nest depth to counter climate differences along a temperature cline at their cold-end range margin. Two measures of nest depth were significantly, inversely related to elevation across six populations spanning 700 m. Elevation explained 83,86% of the variation in nest depth. These findings support a thermal compensatory mechanism for this pattern, although soil moisture compensation is plausible. My results directly support a recent, untested prediction that the evolution of viviparity in reptiles is preceded by a behavioural shift towards increasingly superficial nest sites in cold climates, followed by selection for increased egg retention to avoid temperature extremes. However, in the present study egg desiccation rates increased with increasing elevation in a dry year, suggesting that increased egg retention may evolve in response to lethal hydric conditions, rather than lethal temperatures. When considered alongside recent research, the present study indicates that water dragons possess several mechanisms for adjusting to climate change. [source] Factors Affecting Population Assessments of Desert TortoisesCONSERVATION BIOLOGY, Issue 5 2000Jerome E. Freilich With a wide geographic range and more living individuals than any other listed land animal, biologists have needed to detect population trends against a "noisy" background of strong annual changes. We obtained annual population estimates of desert tortoises over 6 consecutive years at a 2.59-km2 plot in Joshua Tree National Park, California. Our estimates, based on weekly spring surveys, varied substantially, particularly between wet and dry years. Concurrently, we followed 10 radiotagged animals for 3 years to corroborate the surveys. Population density was determined separately for each year and for all years combined. Our best population estimate was an average of 67 adult tortoises, three times more than the density reported in a 1978 survey of the same site. Annual mortality was low ( <10%), and the animals showed extreme site fidelity. Apparent changes in population size were most strongly related to the animals' varying susceptibility to capture. In dry years, home ranges decreased, captures decreased, and effort required to find each tortoise nearly doubled. Our data confirm that tortoises are likely to be undercounted during dry years and call into question earlier studies conducted during droughts. Resumen: Las tortugas del desierto han sido tema de controversia desde que fueron enlistadas como amenazadas en 1990. Con un amplio rango de distribución geográfica y más individuos vivos que cualquier otro animal terrestre enlistado, los biólogos han necesitado detectar tendencias poblacionales contra un trasfondo "ruidoso" de cambios anuales fuertes. Obtuvimos estimaciones de la población anual de tortugas del desierto por seis años consecutivos en un cuadrante de 2.59 Km2 en el Parque Nacional Joshua Tree de California. Nuestras estimaciones, basadas en sondeos semanales de primavera, variaron sustancialmente, particularmente al comparar años lluviosos con años secos. Al mismo tiempo, monitoreamos por tres años a 10 animales marcados con radiotransmisores para corroborar los sondeos. La densidad poblacional estuvo determinada por separado para cada año y para todos los años combinados. Nuestras mejores estimaciones de densidad poblacional fueron en promedio de 67 adultos, tres veces más que la densidad reportada en un sondeo de 1978 en el mismo sitio. La mortalidad anual fue baja ( <10%) y los animales mostraron una fidelidad extrema por el sitio. Los cambios aparentes en el tamaño poblacional estuvieron más fuertemente relacionados con la variación en la susceptibilidad de captura de los animales. En años secos, el rango de hogar disminuyó, las capturas disminuyeron, y el esfuerzo requerido para encontrar cada tortuga fue de casi el doble. Nuestros datos confirman que las tortugas son probablemente mal contadas ( menos) durante los años de seca y ponen en duda estudios previos realizados durante secas. [source] Computer simulation of the population dynamics of Panonychus ulmi and applications to integrated pest management,EPPO BULLETIN, Issue 1 2000M. Sobala Panonychus ulmi is a serious pest of apple orchards, especially in hot dry years. To improve quantitative insight into its population dynamics, and as a tool for forecasting optimal dates for visual assessment of abundance and of integrated pest management strategies, an age- and stage-structured temperature-dependent predator,prey model for P. ulmi and two of its natural enemies, Typhlodromus pyri and Amblyseius potentillae, has been developed. [source] Soil and atmospheric water deficits and the distribution of New Zealand's indigenous tree speciesFUNCTIONAL ECOLOGY, Issue 2 2001Leathwick J. R. Summary 1.,An extensive data set describing the composition of New Zealand's remaining indigenous forests was used to estimate the degree of correlation between measures of both soil and atmospheric water deficit and the distribution of common tree species. 2.,For most species, regression models incorporating measures of air saturation deficit in early autumn, as well as an annual integral of root zone water deficit, provided the best explanation of spatial distribution. This accords strongly with the mechanistic effects of air saturation deficits on transpiration from trees, and the hydraulic risks experienced by trees under high evaporative demand. 3.,Adjustment of root zone water deficits to account for reductions in rainfall in dry years substantially improved model predictions. This suggests that extreme climatic events, such as the El Niño phase of the Southern Oscillation, are likely to have strongly influenced the historic composition of forests in New Zealand's drier eastern lowlands. [source] Atmospheric impact of bioenergy based on perennial crop (reed canary grass, Phalaris arundinaceae, L.) cultivation on a drained boreal organic soilGCB BIOENERGY, Issue 3 2010NARASINHA J. SHURPALI Abstract Marginal organic soils, abundant in the boreal region, are being increasingly used for bioenergy crop cultivation. Using long-term field experimental data on greenhouse gas (GHG) balance from a perennial bioenergy crop [reed canary grass (RCG), Phalaris arundinaceae L.] cultivated on a drained organic soil as an example, we show here for the first time that, with a proper cultivation and land-use practice, environmentally sound bioenergy production is possible on these problematic soil types. We performed a life cycle assessment (LCA) for RCG on this organic soil. We found that, on an average, this system produces 40% less CO2 -equivalents per MWh of energy in comparison with a conventional energy source such as coal. Climatic conditions regulating the RCG carbon exchange processes have a high impact on the benefits from this bioenergy production system. Under appropriate hydrological conditions, this system can even be carbon-negative. An LCA sensitivity analysis revealed that net ecosystem CO2 exchange and crop yield are the major LCA components, while non-CO2 GHG emissions and costs associated with crop production are the minor ones. Net bioenergy GHG emissions resulting from restricted net CO2 uptake and low crop yields, due to climatic and moisture stress during dry years, were comparable with coal emissions. However, net bioenergy emissions during wet years with high net uptake and crop yield were only a third of the coal emissions. As long-term experimental data on GHG balance of bioenergy production are scarce, scientific data stemming from field experiments are needed in shaping renewable energy source policies. [source] Abiotic constraints on the establishment of Quercus seedlings in grasslandGLOBAL CHANGE BIOLOGY, Issue 2 2003Brett T. Danner Abstract High evaporative demand and periodic drought characterize the growing season in midwestern grasslands relative to deciduous forests of the eastern US, and predicted climatic changes suggest that these climatic extremes may be exacerbated. Despite this less than optimal environment for tree seedling establishment, deciduous trees have expanded into adjacent tallgrass prairie within the last century leading to a dramatic land cover change. In order to determine the role of light and temperature on seedling establishment, we assessed carbon and water relations and aboveground growth of first-year Quercus macrocarpa seedlings exposed to one of three conditions: (1) intact tallgrass prairie communities (control), (2) aboveground herbaceous biomass removed (grass removal), and (3) shade plus biomass removal to reduce light (PFD) to levels typical of the grassland-forest ecotone (shade). In the 2000 growing season, precipitation was 35% below the long-term average, which had a significant negative effect on oak seedling carbon gain at midseason (photosynthesis declined to 10% of maximum rates). However, net photosynthesis and stomatal conductance in the shade treatment was ca. 2.5 and 1.5 times greater, respectively, than in control treatment seedlings during this drought. During this period, leaf and air temperatures in control seedlings were similar whereas leaf temperatures in the shade treatment remained below air temperature. A late-season recovery period, coincident with decreased air temperatures, resulted in increased net photosynthesis for all seedlings. Increased photosynthetic rates and water relations in shaded seedlings compared to seedlings in full sun suggest that, at least in dry years, high light and temperature may negatively impact oak seedling performance. However, high survival rates for all seedlings indicate that Q. macrocarpa seedlings are capable of tolerating both present-day and future climatic extremes. Unless historic fire regimes are restored, forest expansion and land cover change are likely to continue. [source] El Niño Southern Oscillation link to the Blue Nile River Basin hydrologyHYDROLOGICAL PROCESSES, Issue 26 2009Wossenu Abtew Abstract The objective of this study is to evaluate the relationships of El Niño Southern Oscillation (ENSO) indices and the Blue Nile River Basin hydrology using a new approach that tracks cumulative ENSO indices. The results of this study can be applied for water resources management decision making to mitigate drought or flood impacts with a lead time of at least few months. ENSO tracking and forecasting is relatively easier than predicting hydrology. ENSO teleconnections to the Blue Nile River Basin hydrology were evaluated using spatial average basin rainfall and Blue Nile flows at Bahir Dar, Ethiopia. The ENSO indices were sea surface temperature (SST) anomalies in region Niño 3·4 and the Southern Oscillation Index (SOI). The analysis indicates that the Upper Blue Nile Basin rainfall and flows are teleconnected to the ENSO indices. Based on event correspondence and correlation analysis, high rainfall and high flows are likely to occur during La Niña years and dry years are likely to occur during El Niño years at a confidence level of 90%. Extreme dry and wet years are very likely to correspond with ENSO events as given above. The great Ethiopian famine of 1888,1892 corresponds to one of the strongest El Niño years, 1888. The recent drought years in Ethiopia correspond to strong El Niño years and wet years correspond to La Niña years. In this paper, a new approach is proposed on how to classify the strength of ENSO events by tracking consecutive monthly events through a year. A cumulative SST index value of ,5 and cumulative SOI value of , ,7 indicate strong El Niño. A cumulative SST index value of ,,5 and cumulative SOI index of ,7 indicate strong La Niña. Copyright © 2009 John Wiley & Sons, Ltd. [source] Hydrologic comparison between a forested and a wetland/lake dominated watershed using SWATHYDROLOGICAL PROCESSES, Issue 10 2008Kangsheng Wu Abstract The Soil and Water Assessment Tool (SWAT) is a physically-based hydrologic model developed for agricultural watersheds, which has been infrequently validated for forested watersheds, particularly those with deep overwinter snow accumulation and abundant lakes and wetlands. The goal of this study was to determine the applicability of SWAT for modelling streamflow in two watersheds of the Ontonagon River basin of northern Michigan which differ in proportion of wetland and lake area. The forest-dominated East Branch watershed contains 17% wetland and lake area, whereas the wetland/lake-dominated Middle Branch watershed contains 26% wetland and lake area. The specific objectives were to: (1) calibrate and validate SWAT models for the East Branch and Middle Branch watersheds to simulate monthly stream flow, and (2) compare the effects of wetland and lake abundance on the magnitude and timing of streamflow. Model calibration and validation was satisfactory, as determined by deviation of discharge D and Nash and Sutcliffe coefficient values E that compared simulated monthly mean discharge versus measured monthly mean discharge. Streamflow simulation discrepancies occurred during summer and fall months and dry years. Several snow melting parameters were found to be critical for the SWAT simulation: TIMP (snow temperature lag factor) and SMFMX and SMFMN (melting factors). Snow melting parameters were not transferable between adjacent watersheds. Differences in seasonal pattern of long-term monthly streamflow were found, with the forest-dominated watershed having a higher peak flow during April but a lower flow during the remainder of the year in comparison to the wetland and lake-dominated watershed. The results suggested that a greater proportion of wetland and lake area increases the capacity of a watershed to impound surface runoff and to delay storm and snow melting events. Representation of wetlands and lakes in a watershed model is required to simulate monthly stream flow in a wetland/lake-dominated watershed. Copyright © 2007 John Wiley & Sons, Ltd. [source] Simulation of the intraseasonal and the interannual variability of rainfall over West Africa with RegCM3 during the monsoon periodINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2010M. B. Sylla Abstract Intraseasonal and interannual variability of rainfall is simulated using the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM3) over West Africa. The intraseasonal variability of rainfall showing three distinct phases and the monsoon jump is well reproduced in the simulation. In addition, the regional model shows that while the monsoon rainbelt moves to the Sahel, the African Easterly Jet (AEJ) undergoes a northward migration and a weakening from June to August, when the core is at its northernmost location. This coexists with the appearance and the strengthening of the Tropical Easterly Jet (TEJ), the development and increased activity of the African Easterly Waves (AEWs), and the intensification and northward shift of the ascent between the AEJ and the TEJ core levels and axis. Similarly, the simulated interannual variability of rainfall over West Africa, the Guinea region, and the Sahel, as well as the variability of atmospheric features during contrasting wet and dry years, is also well captured. In fact, in the simulation during dry years the AEWs activity is decreased while the AEJ is strengthened and migrates southward, the TEJ becomes weaker, and the ascent between the levels of the AEJ and the TEJ decreases. The simulated rainfall variability and the behavior of the related features during the rainy season and during contrasting wet and dry years are in line with previous studies that used observations and reanalysis. We conclude that this model performance is of sufficient quality for application to the study of climate processes and mechanisms over West Africa. Copyright © 2009 Royal Meteorological Society [source] Pre-rainy season moisture build-up and storm precipitation delivery in the West African SahelINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2008J. Bayo Omotosho Abstract The salient differences between the years of above and below normal precipitation, particularly within the long period of 1972,1990 with persistently decreasing Sahelian rainfall, are investigated for Kano, a Nigerian station within the Sahel. Daily rainfall data from 1916 to 2000, storm records from 1951 to 2000 and radiosonde data for three dry and three wet years are used in this study. Results confirm previous findings that the African Easterly Jet (AEJ) located in the 700,600 mb layer is stronger during the dry than in wet years. Significantly, however, it is shown that during the wet years, there is stronger and deeper early season (April,June) build-up of moisture below the AEJ. Furthermore, throughout the period from April to August, the middle troposphere was almost always drier than normal during the dry years and moist than normal in the wet years. Consequent upon these, the storms, which deliver almost all the rainfall in the Sahel, produce at least 150% more precipitation during the wet than in the dry years, though the June to September or annual total number of storms differs by only about 30%. Finally, during the dry years, the onset of rainfall is found to be generally very late compared to the long-term mean, with shorter length of the rainy season. Copyright © 2007 Royal Meteorological Society [source] Global analysis of runs of annual precipitation and runoff equal to or below the median: run magnitude and severityINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 5 2005Murray C. Peel Abstract Fluctuations of wet and dry years have long been investigated in the climatology and hydrology literature. In this, the second of two papers investigating runs of consecutive dry years, the magnitude, also known as the intensity, and severity (length × magnitude) of dry runs are investigated. In the first paper the length of dry runs was investigated. Periods of consecutive dry years are associated with drought and the attendant physical and economic stresses that are placed on society. Run magnitudes of consecutive years equal to or below the median were analysed for 3863 precipitation and 1236 runoff stations from around the world. For both annual precipitation and runoff, run magnitude was found to be predominately related to interannual variability and to a lesser extent skewness. Run magnitude of annual runoff was observed to be greater than that for annual precipitation, due to annual runoff having a higher coefficient of variation than annual precipitation. Continental differences in run magnitude of annual runoff were observed and were consistent with continental differences in interannual variability reported previously. Annual run severity was also investigated and found to be independent of run length and strongly related to run magnitude. These findings differ from previously published work; this difference is primarily due to the methodology of comparing run metrics between stations (used in this paper) rather than at a station (previous research). The relationships between run magnitude, severity and interannual variability highlight the importance of adequately reproducing interannual variability within global climate models for future modelling of drought scenarios, as well as having economic implications for drought relief and management policy-making. Copyright © 2005 Royal Meteorological Society. [source] Evolution and features of global land June,August dry/wet periods during 1920,2000INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 12 2004Neng Shi Abstract Dry/wet features for the globe and the Northern and Southern Hemispheres are investigated in terms of 1920,2000 June,August (JJA) global land precipitation data. The weighted mean JJA precipitation anomaly index and the weighted mean JJA dry/wet area index are used to describe the extent of global dryness/wetness. It is pointed out that 1988 (1930) was the globally wettest (driest) year in 1920,2000, and 1954 (1976) was the second wettest (driest). The dryness/wetness of the globe and Northern and Southern Hemispheres has shown distinctive interdecadal changes: during the 1920s, global dryness occurred in JJA frequently; from the 1920s to the 1940s global wetness occurred infrequently in JJA; the 1950s,1960s was a period of frequent global JJA wetness; and the 1970s to 2000 was a period of frequent global JJA dryness/wetness, with the number of dry years greater than that of wet years. The dry/wet features of the Northern Hemisphere are comparatively consistent with those of the globe, but there is no obvious relation between JJA mean precipitation anomalies of the two hemispheres. The analyses of the simultaneous and last winter sea-surface temperature anomalies of global dry/wet years reveal that there is clear correlation of JJA global dry/wet change with sea-surface temperature variations and El Niño,southern oscillation (ENSO) events. Global JJA dryness occurs when the summer ENSO (El Niño) is weaker, and global JJA wetness occurs when the summer ENSO is strong. The largest difference between the last winter sea-surface temperature fields for global dry and wet years is that the sea-surface temperature in the North Pacific and North Atlantic for wet years is substantially higher than that for dry years. Copyright © 2004 Royal Meteorological Society [source] Global analysis of runs of annual precipitation and runoff equal to or below the median: run lengthINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2004Murray C. Peel Abstract The investigation of fluctuations of wet and dry years has a long history in the climatology and hydrology literature. In this, the first of two papers investigating runs of consecutive dry years, the lengths (persistence) of dry runs are investigated. In the second paper the magnitude/intensity and severity (length × magnitude) of dry runs will be investigated. Consecutive dry years are associated with drought, which is a significant physical and economic phenomenon that imposes great stress on ecosystems and societies. Run lengths of consecutive years equal to or below the median were analysed for 3863 precipitation and 1236 runoff stations from around the world. Run lengths were found to be similar across all continents and Köppen climate zones, expect for tropical and arid North Africa (Sahel), which showed a distinct bias toward longer run lengths than any other region of the world. Generally, the run length observed in annual runoff was found to be similar to that observed in annual precipitation for the same location. Both annual precipitation and runoff data were found to be well described by the lag-one autoregressive (AR(1)) model or by white noise. The influence of the El Niño,southern oscillation on run lengths was not observed to be significant. The presence of decadal and multi-decadal oscillations was weakly observed in the results of the precipitation runs analysis. The faintness of the decadal and multi-decadal oscillation signal may be due to the sample sizes not being long enough and/or the runs analysis not being sensitive enough to detect their presence. Copyright © 2004 Royal Meteorological Society [source] The effect of large-scale circulation on precipitation and streamflow in the Gulf of California continental watershedINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 7 2003Luis Brito-Castillo Abstract The interannual variability of summer and winter rainfall and streamflow in the Gulf of California continental watershed is compared. Varimax-rotated empirical orthogonal function (EOF) analysis is applied to 15 streamflow series, in the period from 1960 to 1990, and two regions are defined: a central region and a southern region. Results show that in both regions, between 1944 and 1999, the long-term rainfall variability is well explained by the long-term streamflow variability in both seasons, the result being statistically significant at the 95% level. We conclude that regional streamflows in that period are climate driven. This conclusion is reinforced when we show that the large-scale circulation (700 hPa heights) explains: (i) wet and dry conditions in both regions; (ii) conditions of wet and dry years with the same signal of El Niño and La Niña events; and (iii) long-term periods in association with the Pacific decadal oscillation (PDO). When the PDO is in its warm phase, summers are likely to be dry with an El Niño event and wet with a La Niña event. In the cool phase of the PDO, summers are influenced by more localized events (i.e. the position of the subtropical continental ridge). In winter, warm and cool phases of the PDO are likely to be associated with wet and dry winters respectively. Copyright © 2003 Royal Meteorological Society [source] Urban and industrial water use in the Krishna Basin, India,IRRIGATION AND DRAINAGE, Issue 4 2009Daniel J. Van Rooijen Bassin Krishna; utilisation urbaine de l'eau; utilisation industrielle de l'eau; modélisation Abstract Regional urbanization and industrial development require water that may put additional pressure on available water resources and threaten water quality in developing countries. In this study we use a combination of census statistics, case studies, and a simple model of demand growth to assess current and future urban and industrial water demand in the Krishna Basin in southern India. Water use in this "closed" basin is dominated by irrigation (61.9 billion cubic metres (BCM) yr,1) compared to a modest domestic and industrial water use (1.6 and 3.2 BCM yr,1). Total water diversion for non-irrigation purposes is estimated at 7,8% of available surface water in the basin in an average year. Thermal power plants use the majority of water used by industries (86% or 2.7 BCM yr,1), though only 6.8% of this is consumed via evaporation. Simple modelling of urban and industrial growth suggests that non-agricultural water demand will range from 10 to 20 BCM by 2030. This is 14,28% of basin water available surface water for an average year and 17,34% for a year with 75% dependable flow. Although water use in the Krishna Basin will continue to be dominated by agriculture, water stress, and the fraction of water supplies at risk of becoming polluted by urban and industrial activity, will become more severe in urbanized regions in dry years. Copyright © 2008 John Wiley & Sons, Ltd. L'urbanisation régionale et le développement industriel demandent de l'eau, ce qui peut augmenter la pression sur les ressources en eau disponibles dans les pays en développement. Dans cette étude nous utilisons une combinaison de données de recensement, des études de cas et un modèle simple de croissance de la demande pour évaluer la demande en eau urbaine et industrielle actuelle et future dans le bassin Krishna en Inde du sud. Les usages de l'eau dans ce bassin « fermé » sont dominés par l'irrigation (61.9 milliards de m3/an) alors que les usages domestiques et industriels sont modestes (1.6 et 3.2 milliards de m3/an). L'eau utilisée en dehors de l'irrigation est estimée à 7 ,8% de l'eau de surface disponible dans le bassin en année moyenne. Les centrales thermiques utilisent la plus grosse partie de l'eau allouée aux industries (86% ou 2.7 milliards de m3/an) bien que seulement 6.8% de cette quantité soit consommé par évaporation. Une modélisation simple de la croissance urbaine et industrielle suggère que la demande non-agricole d'eau variera de 10 à 20 milliards de m3/an d'ici à 2030. C'est 14,28% de l'eau de surface disponible du bassin en année moyenne et 17,34% de l'écoulement garanti à 75%. Bien que l'utilisation de l'eau dans le bassin Krishna continue à être dominée par l'agriculture, la tension sur l'eau peut devenir plus sévère en année sèche dans les régions urbanisées avec en outre le risque d'une pollution par l'activité urbaine et industrielle. Copyright © 2008 John Wiley & Sons, Ltd. [source] Resource variability, aggregation and direct density dependence in an open context: the local regulation of an African elephant populationJOURNAL OF ANIMAL ECOLOGY, Issue 1 2008Simon Chamaillé-Jammes Summary 1An emerging perspective in the study of density dependence is the importance of the spatial and temporal heterogeneity of resources. Although this is well understood in temperate ungulates, few studies have been conducted in tropical environments where both food and water are limiting resources. 2We studied the regulation of one of the world's largest elephant populations in Hwange National Park, Zimbabwe. The study period started in 1986 when the population was released from culling. Using census data we investigated changes in elephant abundance with respect to rainfall and density across the entire park and across waterholes. 3The population more than doubled since culling stopped. The population increased continuously during the first 6 years, and then fluctuated widely at about 30 000 individuals. Immigration processes must have been involved in the increase of the population size. 4Population growth rates were negatively related to previous population density by a convex relationship, and negatively related to the ratio of previous population density on annual rainfall by a linear relationship. However, only this latter model (i.e. assuming a fluctuating carrying capacity related to annual rainfall) produced realistic dynamics. Overall, population decreased during dry years when the elephant density was high. 5During dry years there were fewer waterholes retaining water during the dry season and consequently elephant numbers at waterholes increased, while their aggregation level across waterholes decreased. On the long-run elephant numbers increased only at the less crowded waterholes. 6We suggest that the interaction between population size and the available foraging range determined by the number of active waterholes during the dry season controls the park population. 7Our results emphasize the need to understand how key-resource areas cause resource-based aggregation, which ultimately influences the strength of density dependence. More specifically, this study suggests that climate variability strongly affects local elephant population dynamics through changes in surface-water availability. Finally, as dispersal is likely to be an important driver of the dynamics of this population, our results support views that a metapopulation framework should be endorsed for elephant management in open contexts. [source] Post-dispersal fate of seeds in the Monte desert of Argentina: patterns of germination in successive wet and dry yearsJOURNAL OF ECOLOGY, Issue 6 2000Luis Marone Summary 1,Patterns of seed germination of grass and forb species were studied in open Prosopis woodland of the central Monte desert (Argentina) during several years, to test the hypotheses that (i) seed germination is positively affected by both rainfall and protection afforded by vegetation cover (a facilitative effect), (ii) the number of surviving plants is positively influenced by rainfall but negatively affected by established vegetation (a competitive effect), and (iii) seed loss from soil banks owing to germination is lower than that caused by granivorous animals. 2,Forb species germinated during restricted periods, either in early autumn or in spring. Grasses, however, germinated throughout the growing season, but because seedlings could not be identified to species level, it was impossible to discern whether different species germinated in particular seasons, or if all grasses germinated in all seasons. Grass and forb germination were generally of similar magnitude, but grass germination increased by an order of magnitude during a summer of unusually abundant rainfall related to an El Niño Southern Oscillation (ENSO) event. 3,Overall, the spatial distribution of neither germinating seeds nor surviving plants could be explained by interactions with established vegetation (facilitation and competition effects, respectively). An alternative explanation may be provided by the distribution of forb and grass seeds in the soil. 4,Seed loss owing to germination was low in both dry and rainy years. For forbs, such loss totalled <,1% of soil-seed reserves, and no forb species suffered losses >,4%. Total grass-seed loss to germination was usually <,0.5%, and the 5% reached in 1997,98 corresponded to an interruption of a prolonged drought by unusually abundant rainfall associated with a reduced seed bank. 5,Grass-seed loss caused by germination was one to two orders of magnitude lower than that reported due to autumn-winter granivory in the central Monte desert. [source] Nitrogen Sources and Sinks Within the Middle Rio Grande, New Mexico,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 4 2007Gretchen P. Oelsner Abstract:, Relationships between discharge, land use, and nitrogen sources and sinks were developed using 5 years of synoptic sampling along a 300 km reach of the Rio Grande in central New Mexico. Average river discharge was higher during 2001 and 2005 "wet years" (15 m3/s) than during the drought years of 2002-04 "dry years" (8.9 m3/s), but there were no differences in nitrogen loading from wastewater treatment plants (WWTPs) which were the largest and most consistent source of nitrogen to the river (1,330 kg/day). Average total dissolved nitrogen (TDN) concentrations remained elevated for 180 km downstream of the Albuquerque WWTP averaging 1.2 mg/l in wet years and 0.52 mg/l in dry years. Possible explanations for the constant elevated TDN concentrations downstream of the major point source include reduced nitrogen retention capacity, minimal contact with riparian or channel vegetation, large suspended sediment loads, and low algal biomass. Somewhat surprisingly, agricultural return flows had lower average nitrogen concentrations than river water originally diverted to agriculture in both wet (0.81 mg/l) and dry years (0.19 mg/l), indicating that the agricultural system is a sink for nitrogen. Lower average nitrogen concentrations in the river during the dry years can be explained by the input of agricultural returns which comprise the majority of river flow in dry years. [source] AN ORGANIZED SIGNAL IN SNOWMELT RUNOFF OVER THE WESTERN UNITED STATES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2000D. H. Peterson ABSTRACT: Daily-to-weekly discharge during the snowmelt season is highly correlated among river basins in the upper elevations of the central and southern Sierra Nevada (Carson, Walker, Tuolumne, Merced, San Joaquin, Kings, and Kern Rivers). In many cases, the upper Sierra Nevada watershed operates in a single mode (with varying catchment amplitudes). In some years, with appropriate lags, this mode extends to distant mountains. A reason for this coherence is the broad scale nature of synoptic features in atmospheric circulation, which provide anomalous insolation and temperature forcing that span a large region, sometimes the entire western U.S. These correlations may fall off dramatically, however, in dry years when the snowpack is spatially patchy. [source] Fire disturbance and forest structure in old-growth mixed conifer forests in the northern Sierra Nevada, CaliforniaJOURNAL OF VEGETATION SCIENCE, Issue 6 2007R. Matthew Beaty Abstract Question: This study evaluates how fire regimes influence stand structure and dynamics in old-growth mixed conifer forests across a range of environmental settings. Location: A 2000-ha area of mixed conifer forest on the west shore of Lake Tahoe in the northern Sierra Nevada, California. Methods: We quantified the age, size, and spatial structure of trees in 12 mixed conifer stands distributed across major topographic gradients. Fire history was reconstructed in each stand using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing the fire history with the age, size, and spatial structure of trees in a stand. Results: There was significant variation in species composition among stands, but not in the size, age and spatial patterning of trees. Stands had multiple size and age classes with clusters of similar aged trees occurring at scales of 113 - 254 m2. The frequency and severity of fires was also similar, and stands burned with low to moderate severity in the dormant season on average every 9,17 years. Most fires were not synchronized among stands except in very dry years. No fires have burned since ca. 1880. Conclusions: Fire and forest structure interact to perpetuate similar stand characteristics across a range of environmental settings. Fire occurrence is controlled primarily by spatial variation in fuel mosaics (e.g. patterns of abundance, fuel moisture, forest structure), but regional drought synchronizes fire in some years. Fire exclusion over the last 120 years has caused compositional and structural shifts in these mixed conifer forests. [source] Long-term influence of manure and mineral nitrogen applications on plant and soil 15N and 13C values from the Broadbalk Wheat Experiment,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 11 2008Mehmet Senbayram The Broadbalk Wheat Experiment at Rothamsted Research in the UK provides a unique opportunity to investigate the long-term impacts of environmental change and agronomic practices on plants and soils. We examined the influence of manure and mineral fertiliser applications on temporal trends in the stable N (15N) and C (13C) isotopes of wheat collected during 1968,1979 and 1996,2005, and of soil collected in 1966 and 2000. The soil ,15N values in 1966 and 2000 were higher in manure than the mineral N supplied soil; the latter had similar or higher ,15N values than non-fertilised soil. The straw ,15N values significantly decreased in all N treatments during 1968 to 1979, but not for 1996,2005. The straw ,15N values decreased under the highest mineral N supply (192,kg,N,ha,1,year,1) by 3, from 1968 to 1979. Mineral N supply significantly increased to straw ,13C values in dry years, but not in wet years. Significant correlations existed between wheat straw ,13C values with cumulative rainfall (March to June). The cultivar Hereward (grown 1996,2005) was less affected by changes in environmental conditions (i.e. water stress and fertiliser regime) than Cappelle Desprez (1968,1979). We conclude that, in addition to fertiliser type and application rates, water stress and, importantly, plant variety influenced plant ,13C and ,15N values. Hence, water stress and differential variety response should be considered in plant studies using plant ,13C and ,15N trends to delineate past or recent environmental or agronomic changes. Copyright © 2008 John Wiley & Sons, Ltd. [source] Sampling Techniques Influence Understory Plant Trajectories After Restoration: An Example from Ponderosa Pine RestorationRESTORATION ECOLOGY, Issue 4 2003Julie E. Korb Abstract Although there is no one correct technique for sampling vegetation, the sampling design chosen may greatly influence the conclusions researchers can draw from restoration treatments. Considerations when designing vegetation sampling protocol include determining what sampling attributes to measure, the size and shape of the sampling plot, the number of replicates and their location within the study area, and the frequency of sampling. We installed 20 point-intercept transects (50-m long), 8 belt transects (10 × 50 m), 10 adapted Daubenmire transects (four 0.5 × 2-m plots), and 4 modified-Whittaker plots (20 × 50 m with smaller nested plots) in treatment and control units to measure understory herbaceous response in a forest restoration experiment that tested different treatments. Point-intercept transects on average recorded at least twice as much plant cover as did adapted Daubenmire transects and modified-Whittaker plots taken at the same location for all control and treatment units. Point-intercept transects and adapted Daubenmire plots on average captured fewer rare and exotic species in the control and treatment units in comparison with the belt transects and modified-Whittaker plots. Modified-Whittaker plots captured the highest species richness in all units. Early successional understory response to restoration treatments was likely masked by the response of the herbaceous community to yearly climatic variation (dry vs. wet years). Species richness and abundance were higher in wet years than dry years for all control and treatment units. Our results illustrate that sampling techniques can greatly influence perceptions of understory plant trajectories and therefore the interpretation of whether restoration goals have been achieved. In addition, our results suggest that restoration monitoring needs to be conducted for a sufficient length of time so that restoration treatment responses can be detected. [source] Effects of diseases on the growth and yield of spring linseed (Linum usitatissimum), 1988,1998ANNALS OF APPLIED BIOLOGY, Issue 3 2000S A M PERRYMAN Summary In spring linseed field experiments with fungicides at Rothamsted from 1988 to 1998, substantial yield losses assoeiated with diseases occurred in three years and slight losses could be associated with diseases in other years. These yield losses were related to decreases in yield components (thousand grain weights and number of capsules). Leaf browning was observed each year and percentage leaf area with browning was the disease factor most consistently related to yield losses (in five years). Yield loss relationships for these five years suggested that for each 10% increase in percentage leaf area with browning there was a yield loss of 0.10 to 0.18 t ha,1. Stem browning, lesions on capsules and powdery mildew were associated with yield losses in two years, three years and one year, respectively. Yield losses were greatest in years when the period of flowering and early capsule development in June and July was wetter than average; the predominant disease was grey mould (Botrytis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola) was most important in 1997 and 1998. Observed yield losses were small in hot, dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae) were the predominant diseases. [source] | |||||||||||||||||||||||||||||||||||||