Effects of anthropogenic intervention in the land hydrologic cycle on global sea level rise

Recent studies suggest that anthropogenic modification of land hydrology (e.g. through groundwater mining, dam building, irrigation, deforestation, wetlands drainage, and urbanization) could significantly impact sea-level rise, although the magnitude and sign of this effect have been widely debated. This paper attempts a comprehensive overview of the effects of human activities on land hydrology. Estimates are provided for the volumes of water associated with each of the major anthropogenic processes and the corresponding equivalent in sea level.Groundwater mining; and runoff from paved and built-up areas are two major sources of water added to the ocean. In contrast, storage of water behind dams, losses through percolation, and evapotranspiration from irrigated fields withhold water that would otherwise flow to the sea. The net effect of these processes holds back the equivalent of 0.8 +- 0.4 mm/yr from sea-level rise. This is a magnitude comparable to, but in the opposite direction from the currently observed sea-level rise of 1–2 mm/yr. These estimates are still preliminary, awaiting better documentation. Coupling of improved land hydrology models with GCMs will help in analysis of feedbacks, especially the partitioning of water among runoff, infiltration, and evaporation.     

GRACE observations of changes in continental water storage

Signatures between monthly global Earth gravity field solutions obtained from GRACE satellite mission data are analyzed with respect to continental water storage variability. GRACE gravity field models are derived in terms of Stokes' coefficients of a spherical harmonic expansion of the gravitational potential from the analysis of gravitational orbit perturbations of the two GRACE satellites using GPS high–low and K-band low–low intersatellite tracking and on-board accelerometry. Comparing the GRACE observations, i.e., the mass variability extracted from temporal gravity variations, with the water mass redistribution predicted by hydrological models, it is found that, when filtering with an averaging radius of 750 km, the hydrological signals generated by the world's major river basins are clearly recovered by GRACE. The analyses are based on differences in gravity and continental water mass distribution over 3- and 6-month intervals during the period April 2002 to May 2003. A background model uncertainty of some 35 mm in equivalent water column height from one month to another is estimated to be inherent in the present GRACE solutions at the selected filter length. The differences over 3 and 6 months between the GRACE monthly solutions reveal a signal of some 75 mm scattering with peak values of 400 mm in equivalent water column height changes over the continents, which is far above the uncertainty level and about 50% larger than predicted by global hydrological models. The inversion method, combining GRACE results with the signal and stochastic properties of a hydrological model as ‘a priori’ in a statistical least squares adjustment, significantly reduces the overall power in the obtained water mass estimates due to error reduction, but also reflects the current limitations in the hydrological models to represent total continental water storage change in particular for the major river basins.     

Climatic and anthropogenic factors affecting river discharge to the global ocean, 1951–2000

During the last half of the 20th century, cumulative annual discharge from 137 representative rivers (watershed areas ranging from 0.3 to 6300 × 10³ km²) to the global ocean remained constant, although annual discharge from about one-third of these rivers changed by more than 30%. Discharge trends for many rivers reflected mostly changes in precipitation, primarily in response to short- and longer-term atmospheric–oceanic signals; with the notable exception of the Parana, Mississippi, Niger and Cunene rivers, few of these “normal" rivers experienced significant changes in either discharge or precipitation. Cumulative discharge from many mid-latitude rivers, in contrast, decreased by 60%, reflecting in large part impacts due to damming, irrigation and interbasin water transfers. A number of high-latitude and high-altitude rivers experienced increased discharge despite generally declining precipitation. Poorly constrained meteorological and hydrological data do not seem to explain fully these “excess” rivers; changed seasonality in discharge, decreased storage and/or decreased evapotranspiration also may play important roles.     

Glacier mass balance of tropical Zongo glacier, Bolivia, comparing hydrological and glaciological methods

A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km², 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins.     

Agricultural irrigation demand under present and future climate scenarios in China

The anticipated change of climatic conditions within the next decades is thought to have far reaching consequences for agricultural cropping systems. The success of crop production in China, the world's most populous country, will also have effects on the global food supply. More than 30% of the cropping area in China is irrigated producing the major part of the agricultural production. To model the effects of climate change on irrigation requirements for crop production in China a high-resolution (0.25°, monthly time series for temperature, precipitation and potential evapotranspiration) gridded climate data set that specifically allows for the effects of topography on climate was integrated with digital soil data in a GIS. Observed long-term trends of monthly means as well as trends of interannual variations were combined for climate scenarios for the year 2030 with average conditions as well as ‘best case’ and ‘worst case’ scenarios.Regional cropping calendars with allowance for multiple cropping systems and the adaptation of the begin and length of the growing season to climatic variations were incorporated in the FAO water balance model to calculate irrigation amounts to obtain maximum yields for the period 1951–1990 and the climate scenarios.During the period 1951–1990 irrigation demand displayed a considerable variation both in temporal and spatial respects. Future scenarios indicate a varied pattern of generally increasing irrigation demand and an enlargement of the subtropical cropping zone rather than a general northward drift of all zones as predicted by GCM models. The effects of interannual variability appear to have likely more impact on future cropping conditions than the anticipated poleward migration of cropping zones.     

Future Benefits of Time-Varying Gravity Missions to Ocean Circulation Studies

A summary is offered of the potential benefits of future measurements of temporal variations in gravity for the understanding of ocean dynamics. Two types of process, and corresponding amplitudes are discussed: ocean basin scale pressure changes, with a corresponding amplitude of order 1 cm of water, or 1 mm of geoid height, and changes in along-slope pressure gradient, at cross-slope length scales corresponding to topographic slopes, with a corresponding amplitude of order 1 mm of water, or a maximum of about 0.01 mm of geoid. The former is feasible with current technology and would provide unprecedented information about abyssal ocean dynamics associated with heat transport and climate. The latter would be a considerable challenge to any foreseeable technology, but would provide an exceptionally clear, quantitative window on the dynamics of abyssal ocean currents, and strong constraints on ocean models. Both options would be limited by the aliassing effect of rapid mass movements in the earth system, and it is recommended that any future mission take this error source explicitly into account at the design stage. For basin-scale oceanography this might involve a higher orbit than GRACE or GOCE, and the advantages of exact-repeat orbits and multiple missions should be considered.     

水文、大气和海洋对钱德勒摆动的激发

分析计算了由陆地上土壤湿度和积雪水当量变化引起的水文变化对钱德勒摆动的激发作用，并将其和大气、海洋激发一起与天文观测激发作了比较．结果表明，虽然水文激发在钱德勒频带上的激发能量很小，只能解释观测激发的平均能量约10％，但是在大气激发的基础上增加水文变化的激发作用，显著提高了与观测激发的相干系数和置信度水平．因此，水文变化对钱德勒摆动的激发作用是值得重视的激发因素之一．     

Environmental change and water management in the Pyrenees: Facts and future perspectives for Mediterranean mountains

This paper analyses the effect of environmental changes observed in the 20th century on hydrology and water management in the southern Pyrenees, in terms of land use and climate. Moreover, a projected water-resource scenario for the 21st century is presented and discussed. Our results demonstrate that changes in precipitation, temperature, and snow accumulation, together with an increase in vegetation density in headwater regions, have led to a marked reduction in water availability in the region. Water resource managers have introduced major changes to dam operations to meet increasing water demand for irrigation purposes in lowland areas. Climatic and land-cover scenarios for the next century indicate that the sustainability of the equilibrium between available resources and water demand will be seriously threatened. These changes predicted for the Pyrenees may be representative of the changes that will occur within many other Mediterranean mountain sectors with similar climatic and socio-economic conditions.     

Geo-informational simulation of possible changes in Central Asian water resources

This study simulates water resources in the Tien Shan alpine basins to forecast how global and regional climate changes would affect river runoff. The model employed annual mean values for the major characteristics of the water cycle: annual air temperature, precipitation, evapotranspiration and river runoff. The simulation was based on 304 hydro-meteorological stations, 23 precipitation sites, 328 high altitudinal points with glaciological measurements, 123 stream-gauges, and 54 evaporation sites, and it took into account topography. The findings were simulated over Tien Shan relief using a 1:500,000 scale 100 m grid resolution Digital Elevation Model. An applicable GIS-based distributed River Runoff Model was implemented in regional conditions and tested in the Tien Shan basins. The annual evapotranspiration exceeds the river runoff in the Tien Shan watersheds particularly up to 3700 m. Hypothetical climate-change scenarios in the Tien Shan predict that by 2100 river runoff will increase by 1.047 times with an increase in air temperature averaging 3 °C and an increase in precipitation averaging 1.2 times the current levels. Change in precipitation, rather than temperature, is the main parameter determining river runoff in the Tien Shan. The maximum ratio for predicted river runoff could reach up to 2.2 and the minimum is predicted to be 0.55 times current levels. This possibly dramatic change in river runoff indicates on non-linear system response caused mainly by the non-linear response of evapotranspiration from air temperature and precipitation changes. In the frame of forecasted possible climate change scenarios the probability of river runoff growth amounts 83–87% and probability of this decline is 17–13% by 2100 in the Tien Shan River basins.     

Mars atmospheric water vapor abundance: 1991-1999, emphasis 1998-1999

Our ground-based measurements of martian atmospheric water vapor, made throughout Ls=34° to 249°, 24 September 1998 to 23 November 1999, during Mars year 24 (MY 24), show changes in Mars' humidity on hourly, daily, and seasonal timescales. We made concomitant measurement of nearby CO₂ bands, and when possible, results were corrected for aerosol extinction using aerosol optical depths derived from our own CO₂ analysis. Where there is spatial and temporal overlap, similar results are obtained for water vapor abundances and aerosol opacities as those observed from the Thermal Emission Spectrometer on Mars Global Surveyor. In addition some further discussion of our published earlier water vapor measurements (1991-1995) is included. Six results from this data set are: (1) the measured aerosol opacity in Mars atmosphere was variable but not greater than τ=1, with almost no clear atmosphere being observed, (2) measurements made with the slit crossing many hours of local time on Mars' Earth-facing disk show a diurnal pattern with highest abundances at mid-day and low abundance in very early morning and late afternoon for some but not all measurements, (3) water vapor abundance is patchy on hourly and daily time scales but follows the usual seasonal trends seen by instrumentation on the Mars Atmospheric Water Detector on the Viking Orbiters and by the Thermal Emission Spectrometer on Mars Global Surveyor, (4) there is a slight longitudinal correlation with the ground-ice observed by the Gamma Ray Spectrometer on Mars Odyssey, (5) there is evidence of the Low Southern Latitude Summer Minimum in our water vapor measurements but our data set for southern summer is limited, and (6) MY 24 appears to be wetter than MY 22 and MY 23.     

河外IRAS暗源大尺度分布的二维分析

本文对ＩＲＡＳ暗源表中４个选区内的ＩＲＡＳ星系的两点角相关函数，关联分维进行了计算。结果表明，所有选区内的星系呈现小角尺度上的成团。在较大角尺度上，分布可以用多级分形很好地表示。在更大角尺度上，用非归一星系对计数可以探测到密度分布中可能存在的典型尺度。当取４个选区的平均值作为ＩＲＡＳ星系在宇宙中分布情况的代表时，所得结果与用全天ＩＲＡＳ点源表和其他巡天资料得到的结果一致。     

Water vapor variability in the north polar region of Mars from Viking MAWD and MGS TES datasets

Atmospheric water vapor abundances in Mars’ north polar region (NPR, from 60° to 90°N) are mapped as function of latitude and longitude for spring and summer seasons, and their spatial, seasonal, and interannual variability is discussed. Water vapor data are from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Viking Orbiter (VO) Mars Atmospheric Water Detector (MAWD). The data cover three complete northern spring-summer seasons in 1977-1978, 2000-2001 and 2002-2003, and shorter periods of spring-summer seasons during 1975, 1999 and 2004. Long term interannual variability in the averaged NPR abundances may exist, with Viking MAWD observations showing twice as much water vapor during summer as the MGS TES observations more than 10 martian years (MY) later. While the averaged abundances are very similar in TES observations for the same season in different years, the spatial distributions in the early summer season do vary significantly year over year. Spatial and temporal variabilities increase between L_s ∼ 80-140°, which may be related to vapor sublimation from the North Polar Residual Cap (NPRC), or to changes in circulation. Spatial variability is observed on scales of ∼100 km and temporal variability is observed on scales of <10 sols during summer. During late spring the TES water vapor spatial distribution is seen to correlate with the low topography/low albedo region of northern Acidalia Planitia (270-360°E), and with the dust spatial distribution across the NPR during late spring-early summer. Non-uniform vertical distribution of water vapor, a regolith source or atmospheric circulation ‘pooling’ of water vapor from the NPRC into the topographic depression may be behind the correlation with low topography/low albedo. Sublimation winds carrying water vapor off the NPRC and lifting surface dust in the areas surrounding the NPRC may explain the correlation between the water vapor and dust spatial distributions. Correlation between water vapor and dust in MAWD data are only observed over low topography/low albedo area. Maximum water vapor abundances are observed at L_s = 105-115° and outside of the NPRC at 75-80°N; the TES data, however, do not extend over the NPRC and thus, this conclusion may be biased. Some water vapor appears to be released in plumes or ‘outbursts’ in the MAWD and TES datasets during late spring and early summer. We propose that the sublimation rate of ice varies across the NPRC with varying surface winds, giving rise to the observed ‘outbursts’ at some seasons.     

A new method of measuring the cluster peculiar velocity power spectrum

We propose to use spatial correlations of the kinetic Sunyaev–Zeldovich (KSZ) flux as an estimator of the peculiar velocity power spectrum. In contrast with conventional techniques, our new method does not require measurements of the thermal SZ signal or the X-ray temperature. Moreover, this method has the special advantage that the expected systematic errors are always subdominant to statistical errors on all scales and redshifts of interest. We show that future large sky coverage KSZ surveys may allow a peculiar velocity power spectrum estimates of an accuracy reaching ∼10 per cent.     

Pre-industrial-potential and Last Glacial Maximum global vegetation simulated with a coupled climate-biosphere model: diagnosis of bioclimatic relationships

The global climate–vegetation model HadSM3_TRIFFID has been used to estimate the equilibrium states of climate and vegetation with pre-industrial and last glacial boundary conditions. The present study focuses on the evaluation of the terrestrial biosphere component (TRIFFID) and its response to changes in climate and CO₂ concentration. We also show how, by means of a diagnosis of the distribution of plant functional types according to climate parameters (soil temperature, winter temperature, growing-degree days, precipitation), it is possible to get better insights into the strengths and weaknesses of the biosphere model by reference to field knowledge of ecosystems.The model exhibits profound changes between the vegetation distribution at the Last Glacial Maximum and today that are generally consistent with palaeoclimate data, such as the disappearance of the Siberian boreal forest (taiga), an increase in shrub cover in Europe and an increase of the subtropical desert area. The effective equatorial and sub-tropical tree area is reduced by 18%. There is also an increase in cover of wooded species in North-Western Africa and in Mexico. The analysis of bioclimatic relationships turns out to be an efficient method to infer the contributions of different climatic factors to vegetation changes, both at high latitudes, where the position of the boreal treeline appears in this model to be more directly constrained by the water stress than by summer temperature, and in semi-humid areas where the contributions of temperature and precipitation changes may partly compensate each other. Our study also confirms the major contribution of the decrease in CO₂ to environmental changes and carbon storage through its selective impact on gross primary productivity of C3 and C4 plants and a reduction by 25% of water-use efficiency. Specifically, the reduction in CO₂ concentration increases the amount of precipitation necessary to sustain at least 20% of grass fraction by 50 mm/year; the corresponding threshold for trees is increased by about 150 mm/year. As a consequence, a reduction in CO₂ concentration considerably widens the climatic range where grasses and shrubs dominate.     

Use of multi-point analysis and modelling to address cross-scale coupling in space plasmas: Lessons from Cluster

The properties of plasmas (in space) are fundamentally governed by both ‘cross-scale’ coupling and comparative temporal behaviour operating over the micro-, meso-, and (MHD-) fluid regimes: for example, under conditions of turbulence, during magnetic reconnection and in shocks and other plasma boundaries. These themes map to a number of related and overlapping, phenomena, where known phenomena play different roles in each theme. Detailed understanding of fundamental plasma processes therefore requires analysis of both theoretical models (to distinguish the collisionless from the collisional regimes) and multi-scale measurements (suitable to address issues of stationarity). In particular, the investigation of phenomena requires analysis techniques which can distinguish and quantify temporal behaviour and the multi-scale spatial behaviour. The analysis of existing, multi-point data sets has led to a number of data co-ordination methods, such as the four spacecraft analysis tools developed for cluster, and we consider examples here. Advanced analysis concepts may be investigated with suitable considerations of measurement quality:adequate sampling of phenomena (for example, to extract the necessary information on the mechanisms operating) requires suitable spacecraft configurations and directly relates to the measurement quality achievable. A particular issue is how to resolve temporal behaviour across the spatial regimes, so that the data set is suitably coordinated. With the addition of theoretical modelling (in the context of particular phenomena) both the space and laboratory plasma regimes may be compared and we give an example of nonlinear wave coupling across spatial scales in this context.     

Future desertification and climate change: The need for land-surface system evaluation improvement

In already drought-stressed areas and places with the potential for desertification as a result of greenhouse-induced change, high quality model-derived climate projections are essential for sustainable management. Today's challenge is how to select from the plethora of models and proposed new analyses the tools most likely to be valid for areas already water-stressed and those threatened by future surface moisture reduction. Here, the land-surface skills of models involved in the IPCC Fourth Assessment Report and new techniques of isotopic enrichment of components of evapotranspiration are analyzed. Both are found to have shortcomings. Surprisingly poor reporting of fundamental components of the land-surface system in standard model output was the largest challenge for widely accepted models. We show that very few of a large group (20) of today's climate models report land-surface water and energy budgets correctly in a well-controlled international experiment and that most fail basic conservation tests. Our analysis of a smaller (5) experiment suggests that isotopic techniques employed in arid zone irrigation management may not transition to evaluation and model improvement. Land-surface conditions important for policy are found to be poorly reported which raises questions about equal weighting given by international assessments to all models: good and bad.     

Potential causes of differences between ground and surface air temperature warming across different ecozones in Alberta, Canada

Analysis and modelling of temperature anomalies from 25 selected deep wells in Alberta show that the differences between GST (ground surface temperature) warming for the northern Boreal Forest ecozone and the combined Prairie Grassland ecozone and Aspen Parkland transition region to the south occur during the latter half of this century. This corresponds with recent changes in surface albedo resulting from permanent land development in the northern areas and also to increases in natural forest fires in the past 20 years. Differences between GST and SAT (surface air temperature) warming are much higher in the Boreal Forest ecozone than in the Prairie Grassland ecozone and Aspen Parkland transition region. Various hypotheses which could account for the existing differences between the GST and SAT warming in the different ecozones of Alberta, and western Canada in general, are tested. Analysis of existing data on soil temperature, hydrological piezometric surfaces, snowfall and moisture patterns, and land clearing and forest fires, indicate that large areas of Alberta, characterised by anomalous GST warming, have experienced widespread changes to the surface landscape in this century. It is postulated that this has resulted in a lower surface albedo with a subsequent increase in the absorption of solar energy. Heat flow modelling shows that, after climatic SAT warming, permanent clearing of the land is the most effective and likely cause of the observed changes in the GST warming. The greater GST warming in the Boreal Forest ecozone in the latter half of this century is related to landscape change due to land development and increasing forest fire activity. It appears to account for a portion of the observed SAT warming in this region through a positive feedback loop with the overlying air. The anthropogenic effect on regional climatic warming through 20th century land clearing and landscape alteration requires further study. In future, more accurate quantification of these various forcings will be necessary in order to distinguish between, and to detect, the variety of natural and anthropogenic influences and on climate.     

太阳表面磁场的分布与演化研究进展

太阳磁场、较差自转和内部对流使得日面磁场与磁活动在很大的时间尺度和空间尺度范围均表现得相当复杂.其中最有名的是太阳活动的11年周期,或22年磁周期.在较小时间尺度上,从几秒到几小时,有时太阳大气中会发生一些壮观的爆发事件,如耀斑、日珥爆发、日冕物质抛射等.所有这些形式的事件都与太阳磁场紧密关联.简单评述了太阳磁场起源与观测方法,重点论述了不同尺度太阳磁场的空间分布与演化,介绍了从太阳磁活动现象统计得到的有关太阳磁场的几个典型特征,同时讨论了进一步研究的方向.     

GRACE重力计划在揭示地球系统质量重新分布中的应用

2002年3月成功发射的美德合作卫星重力计划GRACE(Gravity Recovery And ClimateExperiment),即将提供空间分辨率约为200 km而时间分辨率为1个月的时变地球重力场模型序列。GRACE计划的星座由两颗相距约220 km,高度保持为300-500 km、倾角保持约90°的近极轨卫星组成。由于采用星载GPS和非保守力加速度计等高精度定轨技术,以及高精度的星一星跟踪数据反演地球重力场,在几百公里和更大空间尺度上, GRACE重力场的精度大大超过此前的卫星重力计划。根据GRACE时变重力场反演的地球系统质量重新分布,将对固体地球物理、海洋物理、气候学以及大地测量等应用有重要的意义。虽然其设计寿命只有5 yr,但研究表明GRACE的结果可用于研究北极冰长期时间尺度的变化,并进而研究极冰融化对全球气候变化,特别是对海平面长期变化的影响。在季节性时间尺度上,利用GRACE重力场反演的质量重新分布足以揭示平均小于1 cm的地表水变化,或小于1 mbar。的海底压强变化。除了巨大的社会效益和经济效益外,这些变化对了解地球系统的物质循环(主要是水循环)和能量循环有非常重要的意义。介绍GRACE重力场揭示的地球系统质量重新分布,为理解其地球物理应用提供必需的准备;同时针对我国大陆和沿海地区的地球物理应用提出初步的设想。