The future for global water assessment
Harding, R.J. ; Weedon, G.P. ; Lanen, H.A.J. van; Clark, D.B. - \ 2014
Journal of Hydrology 518 (2014). - ISSN 0022-1694 - p. 186 - 193.
multimodel ensemble - bias correction - climate - precipitation - model - runoff - impact - 20th-century - temperature - drought
The global water cycle is a fundamental component of our climate and Earth system. Many, if not the majority, of the impacts of climate change are water related. We have an imperfect description and understanding of components of the water cycle. This arises from an incomplete observation of some of the stores and fluxes in the water cycle (in particular: precipitation, evaporation, soil moisture and groundwater), problems with the simulation of precipitation by global climate models and the wide diversity of global hydrological models currently in use. This paper discusses these sources of errors and, in particular, explores the errors and advantages of bias correcting climate model outputs for hydrological models using a single large catchment as an example (the Rhine). One conclusion from this analysis is that bias correction is necessary and has an impact on the mean flows and their seasonal cycle. However choice of hydrological model has an equal, if not larger effect on the quality of the simulation. The paper highlights the importance of improving hydrological models, which run at a continental and global scale, and the importance of quantifying uncertainties in impact studies.
Benchmark products for land evapotranspiration: LandFlux-EVAL multi-data set synthesis
Mueller, B. ; Hirschi, M. ; Jimenez, C. ; Ciais, P. ; Dirmeyer, P.A. ; Dolman, A.J. ; Fisher, J.B. ; Jung, M. ; Ludwig, F. ; Maignan, F. - \ 2013
Hydrology and Earth System Sciences 17 (2013). - ISSN 1027-5606 - p. 3707 - 3720.
reanalysis data - soil-moisture - global-scale - surface - climate - trends - model - 20th-century - variability - evaporation
Land evapotranspiration (ET) estimates are available from several global datasets. Here, monthly global land ET synthesis products, merged from these individual datasets over the time periods 1989–1995 (7 yr) and 1989–2005 (17 yr), are presented. The 5 merged synthesis products over the shorter period are based on a total of 40 distinct datasets while those over the longer period are based on a total of 14 datasets. In the individual datasets, ET is derived from satellite and/or in-situ observations (diagnostic datasets) or calculated via land-surface models (LSMs) driven with observationsbased forcing and atmospheric reanalyses. Statistics for four merged synthesis prod10 ucts are provided, one including all datasets and three including only datasets from one category each (diagnostic, LSMs, and reanalyses). The multi-annual variations of ET in the merged synthesis products display realistic responses. They are also consistent with previous findings of a global increase in ET between 1989 and 1997 (1.15mmyr-2 in our merged product) followed by a decrease in this trend (-1.40mmyr-2), although 15 these trends are relatively small compared to the uncertainty of absolute ET values. The global mean ET from the merged synthesis products (based on all datasets) is 1.35mm per day for both the 1989–1995 and 1989–2005 products, which is relatively low compared to previously published estimates. We estimate global runoff (precipitation minus ET) to 34 406 km3 per year for a total land area of 130 922 km2. Precipitation, 20 being an important driving factor and input to most simulated ET datasets, presents uncertainties between single datasets as large as those in the ET estimates. In order to reduce uncertainties in current ET products, improving the accuracy of the input variables, especially precipitation, as well as the parameterizations of ET are crucial.
What could have caused pre-industrial biomass burning emissions to exceed current rates?
Werf, G.R. van der; Peters, W. ; Leeuwen, T.T. van; Giglio, L. - \ 2013
Climate of the Past 9 (2013)1. - ISSN 1814-9324 - p. 289 - 306.
rain-forest fires - past 2 millennia - amazonian forests - southern africa - trace gases - model tm5 - land-use - carbon - 20th-century - climate
Recent studies based on trace gas mixing ratios in ice cores and charcoal data indicate that biomass burning emissions over the past millennium exceeded contemporary emissions by up to a factor of 4 for certain time periods. This is surprising because various sources of biomass burning are linked with population density, which has increased over the past centuries. We have analysed how emissions from several landscape biomass burning sources could have fluctuated to yield emissions that are in correspondence with recent results based on ice core mixing ratios of carbon monoxide (CO) and its isotopic signature measured at South Pole station (SPO). Based on estimates of contemporary landscape fire emissions and the TM5 chemical transport model driven by present-day atmospheric transport and OH concentrations, we found that CO mixing ratios at SPO are more sensitive to emissions from South America and Australia than from Africa, and are relatively insensitive to emissions from the Northern Hemisphere. We then explored how various landscape biomass burning sources may have varied over the past centuries and what the resulting emissions and corresponding CO mixing ratio at SPO would be, using population density variations to reconstruct sources driven by humans (e.g., fuelwood burning) and a new model to relate savanna emissions to changes in fire return times. We found that to match the observed ice core CO data, all savannas in the Southern Hemisphere had to burn annually, or bi-annually in combination with deforestation and slash and burn agriculture exceeding current levels, despite much lower population densities and lack of machinery to aid the deforestation process. While possible, these scenarios are unlikely and in conflict with current literature. However, we do show the large potential for increased emissions from savannas in a pre-industrial world. This is mainly because in the past, fuel beds were probably less fragmented compared to the current situation; satellite data indicates that the majority of savannas have not burned in the past 10 yr, even in Africa, which is considered "the burning continent". Although we have not considered increased charcoal burning or changes in OH concentrations as potential causes for the elevated CO concentrations found at SPO, it is unlikely they can explain the large increase found in the CO concentrations in ice core data. Confirmation of the CO ice core data would therefore call for radical new thinking about causes of variable global fire rates over recent centuries
SST and circulation trend biases cause an underestimation of European precipitation trends
Haren, R. van; Oldenborgh, G.J. van; Lenderink, G. ; Collins, M. ; Hazeleger, W. - \ 2013
Climate Dynamics 40 (2013)1-2. - ISSN 0930-7575 - p. 1 - 20.
neerslag - klimaatverandering - statistische analyse - temperatuur - mariene gebieden - europa - atlantische oceaan - precipitation - climatic change - statistical analysis - temperature - marine areas - europe - atlantic ocean - air-flow influences - climate-change - model projections - united-kingdom - local climate - 20th-century - simulations - extremes
Clear precipitation trends have been observed in Europe over the past century. In winter, precipitation has increased in north-western Europe. In summer, there has been an increase along many coasts in the same area. Over the second half of the past century precipitation also decreased in southern Europe in winter. An investigation of precipitation trends in two multi-model ensembles including both global and regional climate models shows that these models fail to reproduce the observed trends. In many regions the model spread does not cover the trend in the observations. In contrast, regional climate model (RCM) experiments with observed boundary conditions reproduce the observed precipitation trends much better. The observed trends are largely compatible with the range of uncertainties spanned by the ensemble, indicating that the boundary conditions of RCMs are responsible for large parts of the trend biases. We find that the main factor in setting the trend in winter is atmospheric circulation, for summer sea surface temperature (SST) is important in setting precipitation trends along the North Sea and Atlantic coasts. The causes of the large trends in atmospheric circulation and summer SST are not known. For SST there may be a connection with the well-known ocean circulation biases in low-resolution ocean models. A quantitative understanding of the causes of these trends is needed so that climate model based projections of future climate can be corrected for these precipitation trend biases.
A generic method for hydrological drought identification across different climate regions
Huijgevoort, M.H.J. van; Hazenberg, P. ; Lanen, H.A.J. van; Uijlenhoet, R. - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 2437 - 2451.
environment simulator jules - conterminous united-states - soil-moisture - model description - multimodel ensemble - land-surface - 20th-century - precipitation - temperature - definition
The identification of hydrological drought at global scale has received considerable attention during the last decade. However, climate-induced variation in runoff across the world makes such analyses rather complicated. This especially holds for the drier regions of the world (both cold and warm), where, for a considerable period of time, zero runoff can be observed. In the current paper, we present a method that enables to identify drought at global scale across climate regimes in a consistent manner. The method combines the characteristics of the classical variable threshold level method that is best applicable in regions with non-zero runoff most of the time, and the consecutive dry days (period) method that is better suited for areas where zero runoff occurs. The newly presented method allows a drought in periods with runoff to continue in the following period without runoff. The method is demonstrated by identifying droughts from discharge observations of four rivers situated within different climate regimes, as well as from simulated runoff data at global scale obtained from an ensemble of five different land surface models. The identified drought events obtained by the new approach are compared to those resulting from application of the variable threshold level method or the consecutive dry period method separately. Results show that, in general, for drier regions, the threshold level method overestimates drought duration, because zero runoff periods are included in a drought, according to the definition used within this method. The consecutive dry period method underestimates drought occurrence, since it cannot identify droughts for periods with runoff. The developed method especially shows its relevance in transitional areas, because, in wetter regions, results are identical to the classical threshold level method. By combining both methods, the new method is able to identify single drought events that occur during positive and zero runoff periods, leading to a more realistic global drought characterization, especially within drier environments.
Filling the white space on maps of European runoff trends: estimates from a multi-model ensemble
Stahl, K. ; Tallaksen, L.M. ; Hannaford, J. ; Lanen, H.A.J. van - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 2035 - 2047.
north-atlantic oscillation - soil-moisture - streamflow - climate - precipitation - 20th-century - catchments - impact - flood - discharge
An overall appraisal of runoff changes at the European scale has been hindered by "white space" on maps of observed trends due to a paucity of readily-available streamflow data. This study tested whether this white space can be filled using estimates of trends derived from model simulations of European runoff. The simulations stem from an ensemble of eight global hydrological models that were forced with the same climate input for the period 1963–2000. The derived trends were validated for 293 grid cells across the European domain with observation-based trend estimates. The ensemble mean overall provided the best representation of trends in the observations. Maps of trends in annual runoff based on the ensemble mean demonstrated a pronounced continental dipole pattern of positive trends in western and northern Europe and negative trends in southern and parts of eastern Europe, which has not previously been demonstrated and discussed in comparable detail. Overall, positive trends in annual streamflow appear to reflect the marked wetting trends of the winter months, whereas negative annual trends result primarily from a widespread decrease in streamflow in spring and summer months, consistent with a decrease in summer low flow in large parts of Europe. High flow appears to have increased in rain-dominated hydrological regimes, whereas an inconsistent or decreasing signal was found in snow-dominated regimes. The different models agreed on the predominant continental-scale pattern of trends, but in some areas disagreed on the magnitude and even the direction of trends, particularly in transition zones between regions with increasing and decreasing runoff trends, in complex terrain with a high spatial variability, and in snow-dominated regimes. Model estimates appeared most reliable in reproducing observed trends in annual runoff, winter runoff, and 7-day high flow. Modelled trends in runoff during the summer months, spring (for snow influenced regions) and autumn, and trends in summer low flow were more variable – both among models and in the spatial patterns of agreement between models and the observations. The use of models to display changes in these hydrological characteristics should therefore be viewed with caution due to higher uncertainty.
An ecohydrological sketch of climate change impacts on water and natural ecosystems for the Netherlands: bridging the gap between science and society
Witte, J.P.M. ; Runhaar, J. ; Ek, R. van; Hoek van der, D.C.J. ; Bartholomeus, R.P. ; Batelaan, O. ; Bodegom, P.M. van; Wassen, M.J. ; Zee, S.E.A.T.M. van der - \ 2012
Hydrology and Earth System Sciences 16 (2012). - ISSN 1027-5606 - p. 3945 - 3957.
ecohydrologie - ecosystemen - klimaatverandering - modellen - kaarten - ecohydrology - ecosystems - climatic change - models - maps - habitat distribution models - terrestrial ecosystems - vegetation - soil - balance - flow - co2 - precipitation - biodiversity - 20th-century
For policy making and spatial planning, information is needed about the impacts of climate change on natural ecosystems. To provide this information, commonly hydrological and ecological models are used. We give arguments for our assessment that modelling only is insufficient for determining the impacts of climate changes on natural ecosystems at regional scales. Instead, we proposed a combination of hydrological simulations, a literature review and process-knowledge on climate-hydrology-vegetation interactions, to compile a sketch map that indicates climate change effects on a number of ecosystems in the Netherlands.Soon after a first version of our sketch map was published by a Dutch professional journal, copies appeared in policy documents, and also in a commercial and popular atlas of the Netherlands. Moreover, the map led to a question in the Dutch parliament about the sustainability of bog reserves under the future climate. Apparently, there was an urgent need for the information provided by the map.
For policy making and spatial planning, information is needed about the impacts of climate change on natural ecosystems. To provide this information, commonly hydrological and ecological models are used. We give arguments for our assessment that modelling only is insufficient for determining the impacts of climate changes on natural ecosystems at regional scales. Instead, we proposed a combination of hydrological simulations, a literature review and process-knowledge on climate-hydrology-vegetation interactions, to compile a sketch map that indicates climate change effects on a number of ecosystems in the Netherlands. Soon after a first version of our sketch map was published by a Dutch professional journal, copies appeared in policy documents, and also in a commercial and popular atlas of the Netherlands. Moreover, the map led to a question in the Dutch parliament about the sustainability of bog reserves under the future climate. Apparently, there was an urgent need for the information provided by the map. The map shows that climate change will presumably have the largest influence on ecosystems in the Netherlands that depend on precipitation as the major water source, like heathlands, dry grasslands, rain-fed moorland pools and raised bogs. Also highly susceptible are fens in reserves surrounded by deeply drained polders, because such fens depend on the inlet of surface water, of which quality is likely to deteriorate upon climate change. While the map is indicative for directions of change, in view of the uncertainties of our study, no conclusions should be drawn that may have far-reaching consequences, such as giving up certain nature targets that might no longer be feasible in the future climate. Instead, we advise to anticipate the potential threats from climate change by taking a number of adaptation measures that enhance the robustness of nature reserves. To improve climate change projections on hydrology and ecosystems, future research should especially focus on feedbacks of vegetation on the water balance, on processes that directly influence plant performance and on the ecological effects of weather extremes.
Agriculture, livelihoods and climate change in the West African Sahel
Sissoko, K. ; Keulen, H. van; Verhagen, A. ; Tekken, V. ; Battaglini, A. - \ 2011
Regional Environmental Change 11 (2011)suppl. 1. - ISSN 1436-3798 - p. S119 - S125.
burkina-faso - level - rainfall - drought - 20th-century - dynamics - farm
The West African Sahel is a harsh environment stressed by a fast-growing population and increasing pressure on the scarce natural resources. Agriculture is the main source of livelihood of the majority of the people living in the area. Increases in temperature and/or modifications in rainfall quantities and distribution will substantially impact on the natural resource on which agriculture depends. The vulnerability of livelihoods based on agriculture is increased and most likely exacerbate and accelerate the current ‘downward spiral’ of underdevelopment, poverty and environmental degradation. Notably, droughts, a short rainy season and/or very low rainfall will be felt by current systems. To cope with the difficult climatic situation, farm households have developed a range of strategies including selling of animals and on-farm diversification or specialization. At regional level, early warning systems including an operational agro-meteorological information system already provide farmers with crucial information. Substantial political, institutional and financial efforts at national and international level are indispensable for the sustenance of millions of lives. In terms of development, priority needs to be given to adaptation and implementation of comprehensive programs on water management and irrigation, desertification control, development of alternative sources of energy and the promotion of sustainable agricultural practices by farmers
The influence of interpolation and station network density on the distributions and trends of climate variables in gridded daily data
Hofstra, N. ; New, M. ; McSweeney, C. - \ 2010
Climate Dynamics 35 (2010)5. - ISSN 0930-7575 - p. 841 - 858.
regional climate - extreme precipitation - future changes - model - rainfall - europe - 20th-century - temperature - events
We study the influence of station network density on the distributions and trends in indices of area-average daily precipitation and temperature in the E-OBS high resolution gridded dataset of daily climate over Europe, which was produced with the primary purpose of Regional Climate Model evaluation. Area averages can only be determined with reasonable accuracy from a sufficiently large number of stations within a grid-box. However, the station network on which E-OBS is based comprises only 2,316 stations, spread unevenly across approximately 18,000 0.22A degrees grid-boxes. Consequently, grid-box data in E-OBS are derived through interpolation of stations up to 500 km distant, with the distance of stations that contribute significantly to any grid-box value increasing in areas with lower station density. Since more dispersed stations have less shared variance, the resultant interpolated values are likely to be over-smoothed, and extreme daily values even more so. We perform an experiment over five E-OBS grid boxes for precipitation and temperature that have a sufficiently dense local station network to enable a reasonable estimate of the area-average. We then create a series of randomly selected station sub-networks ranging in size from four to all stations within the E-OBS interpolation search radii. For each sub-network realisation, we estimate the grid-box average applying the same interpolation methodology as used for E-OBS, and then evaluate the effect of network density on the distribution of daily values, as well as trends in extremes indices. The results show that when fewer stations have been used for the interpolation, both precipitation and temperature are over-smoothed, leading to a strong tendency for interpolated daily values to be reduced relative to the "true" area-average. The smoothing is greatest for higher percentiles, and therefore has a disproportionate effect on extremes and any derived extremes indices. For many regions of the E-OBS dataset, the station density is sufficiently low to expect this smoothing effect to be significant and this should be borne in mind by any users of the E-OBS dataset.
The Peasantries of the Twenty-First Century: the Commoditisation Debat revisited
Ploeg, J.D. van der - \ 2010
The Journal of Peasant Studies 37 (2010)1. - ISSN 0306-6150 - p. 1 - 30.
agrarian change - rural-development - agriculture - labor - land - food - commercialization - differentiation - 20th-century - capitalism
This article examines the re-emergence of the peasantry. It argues that farming is increasingly being restructured in a peasant-like way. This restructuring is an actively constructed response to the agrarian crisis that has grown out of five decades of state-induced modernisation and is currently being accelerated by the financial crisis and the generalised economic depression. Through a process of restructuring that is both multi-dimensional and multi-level farmers are reconstituting themselves into peasants (although important features of operating as peasants have never been completely absent), a process that is occurring as much in developed countries as in developing ones. At more or less the same time theoretical concepts of the peasantry and the peasant way of farming are being rediscovered and revisited. Earlier debates are highly relevant for understanding the current situation of a generalised crisis and the responses that are being triggered among farmers. The rediscovery of the peasant as theoretically meaningful concept reflects the socio-material re-emergence of the peasantry, and helps to explain the particular features of this process. The article concludes by arguing that the reconstitution of the peasantry is strategic to future world food security
Glacier extent in a Novaya Zemlya fjord during the Little Ice Age inferred from glaciomarine sediment records
Zeeberg, J.J. ; Forman, S.L. ; Polyak, L. - \ 2003
Polar Research 22 (2003)2. - ISSN 0800-0395 - p. 385 - 394.
north-atlantic - 20th-century - barents - russia
Glacier activity at Russkaya Gavan', north-west Novaya Zemlya (Arctic Russia), is reconstructed by particle size analysis of three fjord sediment cores in combination with 14C and 210Pb dating. Down-core logging of particle size variation reveals at least two intervals with sediment coarsening during the past eight centuries. By comparing them with reconstructions of summer temperature and atmospheric circulation, these intervals are interpreted to represent two cycles of glacier advance and retreat sometime during ca. AD 1400¿1700 and AD 1700¿present. Sediment accumulation thus appears to be sensitive to century-scale fluctuations of the Barents Sea climate. The identification of two glacier cycles in the glaciomarine record from Russkaya Gavan' demonstrates that during the "Little Ice Age" major glacier fluctuations on Novaya Zemlya occurred in broad synchrony with those in other areas around the Barents Sea.
Fifty years of crop protection, 1950-2000
Zadoks, J.C. - \ 2002
NJAS Wageningen Journal of Life Sciences 50 (2002)2. - ISSN 1573-5214 - p. 181 - 193.
gewasbescherming - geschiedenis - nederland - plant protection - history - netherlands - 20th-century - pesticides - irrigation - rice
We detected the presence of fructosamine in human and bovine semen. In seminal plasma of healthy normozoospermic men (N = 17) fructosamine was found in 53% of the cases (fru+). In fru+ semen samples the concentration of fructosamine was (mean ± S.E.M., N = 9) 0.45 ± 0.09 mmol/L and varied from 0.15 to 0.75 mmol/L. It was 3–12 times lower than in blood serum of healthy men. In semen of infertile men (N = 57) fructosamine was present only in 21% of the cases and its concentration was lower than in fertile men i.e. (mean ± S.E.M., N = 12) 0.27 ± 0.007 mmol/L. In bulls (N = 98) fructosamine was found in semen of 82% of animals. In fru+ semen samples the concentration of fructosamine was (mean ±S.E.M., N = 80) 0.77 ± 0.12 mmol/L and varied from 0.30 to 1.15 mmol/L. We did not find any correlation between the concentration of fructosamine on one hand, and that of fructose and glucose on the other hand, in either human or bull semen. The difference in the frequency of fructosamine appearance in semen of fertile and infertile men suggests that fructosamine may be in some way involved in the process of fertisation.