The global-scale impacts of climate change on water resources and flooding under new climate and socio-economic scenarios

This paper presents a preliminary assessment of the relative effects of rate of climate change (four Representative Concentration Pathways - RCPs), assumed future population (five Shared Socio-economic Pathways - SSPs), and pattern of climate change (19 CMIP5 climate models) on regional and global exposure to water resources stress and river flooding. Uncertainty in projected future impacts of climate change on exposure to water stress and river flooding is dominated by uncertainty in the projected spatial and seasonal pattern of change in climate. There is little clear difference in impact between RCP2.6, RCP4.5 and RCP6.0 in 2050, and between RCP4.5 and RCP6.0 in 2080. Impacts under RCP8.5 are greater than under the other RCPs in 2050 and 2080. For a given RCP, there is a difference in the absolute numbers of people exposed to increased water resources stress or increased river flood frequency between the five SSPs. With the ‘middle-of-the-road’ SSP2, climate change by 2050 would increase exposure to water resources stress for between approximately 920 and 3400 million people under the highest RCP, and increase exposure to river flood risk for between 100 and 580 million people. Under RCP2.6, exposure to increased water scarcity would be reduced in 2050 by 22-24%, compared to impacts under the RCP8.5, and exposure to increased flood frequency would be reduced by around 16%. The implications of climate change for actual future losses and adaptation depend not only on the numbers of people exposed to changes in risk, but also on the qualitative characteristics of future worlds as described in the different SSPs. The difference in ‘actual’ impact between SSPs will therefore be greater than the differences in numbers of people exposed to impact.

Modeling plant transpiration under limited soil water: comparison of different plant and soil hydraulic parameterizations and preliminary implications for their use in land surface models

Accurate estimates of how soil water stress affects plant transpiration are crucial for reliable land surface model (LSM) predictions. Current LSMs generally use a water stress factor, β, dependent on soil moisture content, θ, that ranges linearly between β = 1 for unstressed vegetation and β = 0 when wilting point is reached. This paper explores the feasibility of replacing the current approach with equations that use soil water potential as their independent variable, or with a set of equations that involve hydraulic and chemical signaling, thereby ensuring feedbacks between the entire soil–root–xylem–leaf system. A comparison with the original linear θ-based water stress parameterization, and with its improved curvi-linear version, was conducted. Assessment of model suitability was focused on their ability to simulate the correct (as derived from experimental data) curve shape of relative transpiration versus fraction of transpirable soil water. We used model sensitivity analyses under progressive soil drying conditions, employing two commonly used approaches to calculate water retention and hydraulic conductivity curves. Furthermore, for each of these hydraulic parameterizations we used two different parameter sets, for 3 soil texture types; a total of 12 soil hydraulic permutations. Results showed that the resulting transpiration reduction functions (TRFs) varied considerably among the models. The fact that soil hydraulic conductivity played a major role in the model that involved hydraulic and chemical signaling led to unrealistic values of β, and hence TRF, for many soil hydraulic parameter sets. However, this model is much better equipped to simulate the behavior of different plant species. Based on these findings, we only recommend implementation of this approach into LSMs if great care with choice of soil hydraulic parameters is taken

Illustration of micro-scale advection using grid-pattern mini-lysimeters

Twenty-five small soil-filled perspex boxes arranged in a square, with dwarf sunflowers growing in them, were used to study micro-scale advection. Hydrological heterogeneity was introduced by applying two different amounts of irrigation water (low-irrigation, L, versus high-irrigation, H). The nine central boxes (4 H, 4 L and I bare box) were precision weighing lysimeters, yielding diurnal measurements of evaporation. After the onset of soil water stress, a large difference in latent heat flux (up to 4-fold) was observed between the lysimeters of the H and L treatments, mainly caused by large differences between H and L stomatal conductance values. This resulted in micro-advection, causing H soil-sunflower systems to evaporate well above equilibrium latent heat flux. The occurrence of micro-advective enhancement was reflected in large values of the Priestley-Taylor constant (often larger than 2.0) and generally negative values of sensible heat flux for the H treatment. (c) 2005 Elsevier B.V. All rights reserved.

"Ever-growing Amman", Jordan: Urban expansion, social polarisation and contemporary urban planning issues

Amman the primate capital city of the Hashemite Kingdom of Jordan currently has a population in excess of 2 million, but in 1924 it consisted of little more than a collection of dwellings and some 2000-3000 inhabitants. The present paper sets out to document and explain the phenomenal expansion of "ever-growing Amman". The physical geography of the urban region and the early growth of the city are considered at the outset and this leads directly to consideration of the highly polarised social structuring that characterises contemporary Amman. In doing this, original data derived from the recent Greater Amman Municipality's Geographical Information System are presented. In this respect, the essential modernity of the city is exemplified. The employment and industrial bases of the city and a range of pressing contemporary issues are then considered, including transport and congestion, the provision of urban water under conditions of water stress and privatisation, and urban and regional development planning for the city. The paper concludes by emphasizing the growing regional and international geopolitical salience of the city of Amman at the start of the 21st century. (C) 2008 Elsevier Ltd. All rights reserved.

Effects of prolonged conditioning on dormancy and germination of Striga hermonthica

The impact of environment on the germination biology of Striga hermonthica was studied in the laboratory by conditioning seeds at various water potentials and urea concentrations at 17.5 to 37.5°C for up to 133 days. The experimental results presented in this research are related to the effects of temperature, water potential and urea nitrogen concentration during conditioning on subsequent germination percentage of S. hermonthica. Maximum germination in S. hermonthica seeds was observed at conditioning temperatures of 20 to 25°C within the range investigated of 17.5 to 37.5°C. Water stress and also urea during conditioning suppressed maximum germination. However, the conditioning temperature ranges at which maximum germination percentages occur vary with water stress and also urea concentration. In the presence of a high concentration of urea (3.16 mM), temperatures required for maximum germination narrowed to between 17.5 to 20°C. The optimum period of conditioning decreased with increase in water stress and also urea concentration similar to previous reports. The implications of these findings on Striga hermonthica field infestations have been investigated and being reported in another paper. Germination was greatly suppressed by conditioning environments including 3.16 mM urea and at 37.5°C. At the high concentration of 3.16 mM, temperatures required for maximum germination narrowed to between 17.5 and 20°C. Optimum conditioning period decreased with water stress and with increase in urea concentration.

Modelling effects of prolonged conditioning on dormancy and germination of Striga hermonthica

The impact of environment on the germination biology of the parasite was studied in the laboratory with seeds conditioned at various water potentials, urea concentrations and at 17.5 to 37.5°C for up to 133 days. Maximum germination was observed at 20 to 25°C. Water stress and urea suppressed maximum germination. The final percentage germination response to period of conditioning showed a non-linear relationship and suggests the release of seeds from dormancy during the initial period and later on dormancy induction. Germination percentage increased with increase in conditioning period to a threshold and remained stable for variable periods followed by a decline with further extension of conditioning time. The decline in germination finally terminated in zero germination in most treatments before the end of experimentation. The investigated factors of temperature, water potential and urea showed clear effects on the expression of dormancy pattern of the parasite. The effects of water potential and urea were viewed as modifying a primary response of seeds to temperature during conditioning. The changes in germinability potential during conditioning were consistent with the hypothesis that dormancy periods are normally distributed within seed populations and that loss of primary dormancy precedes induction of secondary dormancy. Hence an additive mathematical model of loss of primary dormancy and induction of secondary as affected by environment was developed as: G = {[Φ-1 (Kp+ (po+pnN+pwW) (T-Tb) t)]-[Φ-1 (Ks+ ((swW+sa)+sorT)t)]}[Φ-1(aT2+bT+c+cwW)].

Adaptation and yield of pigeonpea in different environments in Tanzania

Pigeonpea is grown in wide range of cropping systems and environments, both in East Africa and internationally. An important feature of adaptation to these diverse systems and environments is the timing of flowering and maturity. Most traditional cultivars grown in Tanzania are medium to late flowering types (> 150 days), although extra-early flowering cultivars are now available. The aim of the present investigation was to measure biomass (BY) and seed (SY) yield of a set of phenologically diverse cultivars to determine their adaptation to contrasting environments in Tanzania. Ten cultivars, from extra-early (60 days) to late (> 180 days) flowering, were planted at six locations varying in mean temperature, photoperiod and rainfall. Days to flowering (DTF) and maturity, and above-ground BY and SY at maturity, were measured. A stress index (ETr:ETm ratio, 100 = no stress) was computed for each site. Rainfall and the stress index at the different sites varied from 322 to 1297 mm and 57 to 89, respectively. Among cultivars, DTF varied from 55 to 320 days, the stress index from 3 to 98, BY from 700 to 25,000 kg ha(-1), and SY from 0 to 4000 kg ha(-1). The highest yielding environment was at Selian, where mean temperatures were favourable (19 degrees C) and no stress occurred. At all sites there was an optimum DTF, which for SY varied from < 100 to 150 days. The best adapted cultivars were ICP 7035, ICPL 90094, Kat 50 and QP37, which were all medium flowering (c. 150 day) types. Extra-early cultivars such as ICPL 86005 also showed considerable potential, especially in short-season environments. (c) 2004 Elsevier B.V. All rights reserved.

Towards a THz osmometer

This work discusses the use of a THz-transient spectrometer for the measurement of tissue water content. The relation of both mammalian- and plant-cell water content to the osmotic potential is discussed. The process of equilibration of tissue water potential with the water potential of water vapor in an osmometer cuvette is described. Observation of the THz transmittance through the water vapor provides a measure of the water activity and water potential in the sample. The possibility of performing dielectric relaxation measurements of the liquid water in the tissue at THz frequencies directly and the use of proline as marker of water stress in tissue are discussed.

Cultivating C4 crops in a changing climate: sugarcane in Ghana

Over the next few decades, it is expected that increasing fossil fuel prices will lead to a proliferation of energy crop cultivation initiatives. The environmental sustainability of these activities is thus a pressing issue—particularly when they take place in vulnerable regions, such as West Africa. In more general terms, the effect of increased CO2 concentrations and higher temperatures on biomass production and evapotranspiration affects the evolution of the global hydrological and carbon cycles. Investigating these processes for a C4 crop, such as sugarcane, thus provides an opportunity both to extend our understanding of the impact of climate change, and to assess our capacity to model the underpinning processes. This paper applies a process-based crop model to sugarcane in Ghana (where cultivation is planned), and the São Paulo region of Brazil (which has a well-established sugarcane industry). We show that, in the Daka River region of Ghana, provided there is sufficient irrigation, it is possible to generate approximately 75% of the yield achieved in the São Paulo region. In the final part of the study, the production of sugarcane under an idealized temperature increase climate change scenario is explored. It is shown that doubling CO2 mitigates the degree of water stress associated with a 4 °C increase in temperature.

Pre-conditioning the epigenetic response to high vapor pressure deficit increases the drought tolerance of Arabidopsis thaliana

Epigenetic modification of the genome via cytosine methylation is a dynamic process that responds to changes in the growing environment. This modification can also be heritable. The combination of both properties means that there is the potential for the life experiences of the parental generation to modify the methylation profiles of their offspring and so potentially to ‘pre-condition’ them to better accommodate abiotic conditions encountered by their parents. We recently identified high vapor pressure deficit (vpd)-induced DNA methylation at two gene loci in the stomatal development pathway and an associated reduction in leaf stomatal frequency.1 Here, we test whether this epigenetic modification pre-conditioned parents and their offspring to the more severe water stress of periodic drought. We found that three generations of high vpd-grown plants were better able to withstand periodic drought stress over two generations. This resistance was not directly associated with de novo methylation of the target stomata genes, but was associated with the cmt3 mutant’s inability to maintain asymmetric sequence context methylation. If our finding applies widely, it could have significant implications for evolutionary biology and breeding for stressful environments.

The impacts of climate change across the globe: a multi-sectoral assessment

The overall global-scale consequences of climate change are dependent on the distribution of impacts across regions, and there are multiple dimensions to these impacts.This paper presents a global assessment of the potential impacts of climate change across several sectors, using a harmonised set of impacts models forced by the same climate and socio-economic scenarios. Indicators of impact cover the water resources, river and coastal flooding, agriculture, natural environment and built environment sectors. Impacts are assessed under four SRES socio-economic and emissions scenarios, and the effects of uncertainty in the projected pattern of climate change are incorporated by constructing climate scenarios from 21 global climate models. There is considerable uncertainty in projected regional impacts across the climate model scenarios, and coherent assessments of impacts across sectors and regions therefore must be based on each model pattern separately; using ensemble means, for example, reduces variability between sectors and indicators. An example narrative assessment is presented in the paper. Under this narrative approximately 1 billion people would be exposed to increased water resources stress, around 450 million people exposed to increased river flooding, and 1.3 million extra people would be flooded in coastal floods each year. Crop productivity would fall in most regions, and residential energy demands would be reduced in most regions because reduced heating demands would offset higher cooling demands. Most of the global impacts on water stress and flooding would be in Asia, but the proportional impacts in the Middle East North Africa region would be larger. By 2050 there are emerging differences in impact between different emissions and socio-economic scenarios even though the changes in temperature and sea level are similar, and these differences are greater in 2080. However, for all the indicators, the range in projected impacts between different climate models is considerably greater than the range between emissions and socio-economic scenarios.

Effects of restricted water availability and increased temperature on the grain filling, drying and quality of winter wheat

Experiments in controlled environments examined the effects of the timing and severity of drought, and increased temperature, on grain development of Hereward winter wheat. Environmental effects on grain specific weight, protein content, Hagberg Falling Number, SDS-sedimentation volume, and sulphur content were also studied. Drought and increased temperature applied before the end of grain filling shortened the grain filling period and reduced grain yield, mean grain weight and specific weight. Grain filling was most severely affected by drought between days 1-14 after anthesis. Protein content was increased by stresses before the end of grain growth, because nitrogen harvest index was less severely affected than was dry matter harvest index. Hagberg Falling Number was increased to the greatest extent by stresses applied 15-28 days after anthesis. Treatment effects on grain sulphur content were similar to those on protein content, such that N:S ratio was not significantly affected by drought nor temperature stresses. The effects of restricted water on grain yield and quality were linearly related to soil moisture between 44 and about 73% field capacity (FC) from days 15-28. Drought stress (but not temperature stress) before the end of grain filling decreased SDS-sedimentation volume relative to drought applied later. (C) 2003 Elsevier Science Ltd. All rights reserved.

Effects of restricted water availability and increased temperature on the grain filling, drying and quality of winter wheat

Experiments in controlled environments examined the effects of the timing and severity of drought, and increased temperature, on grain development of Hereward winter wheat. Environmental effects on grain specific weight, protein content, Hagberg Falling Number, SDS-sedimentation volume, and sulphur content were also studied. Drought and increased temperature applied before the end of grain filling shortened the grain filling period and reduced grain yield, mean grain weight and specific weight. Grain filling was most severely affected by drought between days 1-14 after anthesis. Protein content was increased by stresses before the end of grain growth, because nitrogen harvest index was less severely affected than was dry matter harvest index. Hagberg Falling Number was increased to the greatest extent by stresses applied 15-28 days after anthesis. Treatment effects on grain sulphur content were similar to those on protein content, such that N:S ratio was not significantly affected by drought nor temperature stresses. The effects of restricted water on grain yield and quality were linearly related to soil moisture between 44 and about 73% field capacity (FC) from days 15-28. Drought stress (but not temperature stress) before the end of grain filling decreased SDS-sedimentation volume relative to drought applied later. (C) 2003 Elsevier Science Ltd. All rights reserved.

MODIS-based vegetation index has sufficient sensitivity to indicate stand-level intra-seasonal climatic stress in oak and beech forests

Context: Variation in photosynthetic activity of trees induced by climatic stress can be effectively evaluated using remote sensing data. Although adverse effects of climate on temperate forests have been subjected to increased scrutiny, the suitability of remote sensing imagery for identification of drought stress in such forests has not been explored fully. Aim: To evaluate the sensitivity of MODIS-based vegetation index to heat and drought stress in temperate forests, and explore the differences in stress response of oaks and beech. Methods: We identified 8 oak and 13 beech pure and mature stands, each covering between 4 and 13 MODIS pixels. For each pixel, we extracted a time series of MODIS NDVI from 2000 to 2010. We identified all sequences of continuous unseasonal NDVI decline to be used as the response variable indicative of environmental stress. Neural Networks-based regression modelling was then applied to identify the climatic variables that best explain observed NDVI declines. Results: Tested variables explained 84–97% of the variation in NDVI, whilst air temperature-related climate extremes were found to be the most influential. Beech showed a linear response to the most influential climatic predictors, while oak responded in a unimodal pattern suggesting a better coping mechanism. Conclusions: MODIS NDVI has proved sufficiently sensitive as a stand-level indicator of climatic stress acting upon temperate broadleaf forests, leading to its potential use in predicting drought stress from meteorological observations and improving parameterisation of forest stress indices.

On the influence of stratospheric water vapor changes on the tropospheric circulation

Observations suggest that the mixing ratio of water vapour in the stratosphere has increased by 20–50% between the 1960s and mid-1990s. Here we show that inclusion of such a stratospheric water vapour (SWV) increase in a state-of-the-art climate model modifies the circulation of the extratropical troposphere: the modeled increase in the North Atlantic Oscillation (NAO) index is 40% of the observed increase in NAO index between 1965 and 1995, suggesting that if the SWV trend is real, it explains a significant fraction of the observed NAO trend. Our results imply that SWV changes provide a novel mechanism for communicating the effects of large tropical volcanic eruptions and ENSO events to the extratropical troposphere over timescales of a few years, which provides a mechanism for interannual climate predictability. Finally, we discuss our results in the context of regional climate change associated with changes in methane emissions.