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The last 12 months have provided further evidence of the potential for cascading ecological and socio-political crises that were warned of 12 months ago. Then a consensus statement from the Regional Action on Climate Change Symposium warned: “the Earth’s climatic, ecological, and human systems are converging towards a crisis that threatens to engulf global civilization within the lifetimes of children now living.” Since then, the consequences of a broad set of extreme climate events (notably droughts, floods, and fires) have been compounded by interaction with impacts from multiple pandemics (including COVID-19 and cholera) and the Russia–Ukraine war. As a result, new connections are becoming visible between climate change and human health, large vulnerable populations are experiencing food crises, climate refugees are on the move, and the risks of water, food, and climate disruption have been visibly converging and compounding. Many vulnerable populations now face serious challenges to adapt. In light of these trends, this year, RACC identifies a range of measures to be taken at global and regional levels to bolster the resilience of these populations in the face of such emerging crises. In particular, at all scales, there is a need for globally available local data, reliable analytic techniques, community capacity to plan adaptation strategies, and the resources (scientific, technical, cultural, and economic) to implement them. To date, the rate of growth of the support for climate change resilience lags behind the rapid growth of cascading and converging risks. As an urgent message to COP27, it is proposed that the time is now right to devote much greater emphasis, global funding, and support to the increasing adaptation needs of vulnerable populations.

The COVID-19 pandemic illustrates how the impacts of climate change are beginning to converge with other developing challenges with a likely peak with global population, requiring more integrated responses locally, regionally and globally.

This study investigated atmospheric water cycles over several time scales to understand the maintenance processes that control heavy precipitation over the islands of the Maritime Continent. Large island regions can be divided into land, coastal, and ocean areas based on the characteristics of both the hydrologic cycle and the diurnal variation in precipitation. Within the Maritime Continent, the major islands of Borneo and New Guinea exhibit different hydrologic cycles. Large-scale circulation variations, such as the seasonal cycle and the Madden–Julian oscillation, have a lesser effect on the hydrologic cycle over Borneo than over New Guinea because the effects depend on their shapes and locations. The impact of diurnal variations on both regional-scale circulation and water exchange between land and coastal regions is pronounced over both islands. The recycling ratio of precipitation, which can be related to stronger diurnal variation in the atmospheric water cycle that results from enhanced evapotranspiration over tropical rain forests, is higher over Borneo than over New Guinea.

This paper reviews the recent studies on the uplift of the Tibet-Himalaya mountains (TH) and its association with the human origin and evolution through the climate and ecosystem changes in Afro-Eurasian continents.

The Indian subcontinent receives most of its annual precipitation due to Indian summer (June, July, August and September) monsoon. Southeastern coastal region of the India receives significant amount of precipitation due to the northeast monsoon (October and November). Over northern Indian region almost one-third of annual precipitation is received during winter (December, January and February) by eastward moving extratropical cyclone called ‘western disturbances (WDs)’ in Indian meteorological parlance. Various studies are conducted to understand the Indian summer and northeast monsoons. However, the dynamics and characterization of winter precipitation is not well understood except with reference to the western disturbances (WDs). In this study, wintertime dynamics associated with large-scale flows and WDs influencing winter precipitation is proposed and termed ‘Indian winter monsoon’. In addition, winter precipitation – the Indian winter monsoon – is proposed as eastward traveling WDs embedded in the large-scale subtropical westerlies over the Indian sub-continent. During winter (December, January and February) upper level subtropical westerly jet moves southwards and passes over the Indian sub-continent and provides associated precipitation over the northern Indian region. With concurrent research and changing global context, increased understanding of the Indian winter monsoon is imperative. Equally important is the behavior of WDs showing different patterns in the Peninsular India and the Himalaya particularly during the Holocene. During the Little Ice Age (LIA), it appears that high frequency of El Nino events was responsible for drier conditions in the core monsoon zone but generated more monsoon “breaks” over the Himalaya and thus the climatic conditions in the core Indian summer monsoon area were generally opposite to those in the foothills of the Himalaya during the Holocene period. During this period, a higher frequency of El Nino events might have restricted transport of warm water to the North Atlantic Ocean and brought about a cooling of adjacent continents including Central Asia and this may have amplified the extent of snow over Asia during the winter, and may even have been accounted for early snow in the region at the expanse of reduction in the Indian summer monsoon strength. Thus, this study delineates the Indian winter monsoon at intraseasonal-sub seasonal-interannual-paleoclimate scale and provides comprehensive details on defining the Indian winter monsoon and makes an attempt to understand the WDs particularly from mid-Holocene onwards as well.

Cyclonic storms associated with the midlatitude Subtropical Westerly Jet (SWJ), referred to as Western Disturbances (WDs), play a critical role in the meteorology of the Indian subcontinent. WDs embedded in the southward propagating SWJ produce extreme precipitation over northern India and are further enhanced over the Himalayas due to orographic land-atmosphere interactions. During December, January, and February, WD snowfall is the dominant precipitation input to establish and sustain regional snowpack, replenishing regional water resources. Spring melt is the major source of runoff to northern Indian rivers and can be linked to important hydrologic processes from aquifer recharge to flashfloods. Understanding the dynamical structure, evolution-decay, and interaction of WDs with the Himalayas is therefore necessary to improve knowledge which has wide ranging socioeconomic implications beyond short-term disaster response including cold season agricultural activities, management of water resources, and development of vulnerability-adaptive measures. In addition, WD wintertime precipitation provides critical mass input to existing glaciers and modulates the albedo characteristics of the Himalayas and Tibetan Plateau, affecting large-scale circulation and the onset of the succeeding Indian Summer Monsoon. Assessing the impacts of climate variability and change on the Indian subcontinent requires fundamental understanding of the dynamics of WDs. In particular, projected changes in the structure of the SWJ will influence evolution-decay processes of the WDs and impact Himalayan regional water availability. This review synthesizes past research on WDs with a perspective to provide a comprehensive assessment of the state of knowledge to assist both researchers and policymakers, and context for future research.

We analysed the long-term trend and interannual variability in summer (JJA) precipitation over eastern Siberia (90°–140°E, 50°–70°N) for the period 1979–2007. An increasing trend in summer precipitation was observed over large areas (Yenisei and Lena river basins) of eastern Siberia. Summer mean 850-hPa geopotential height decreased from Siberia to the marginal seas north of Siberia, with the largest decreases occurring over the northern part of eastern Siberia, while increasing trends were found around Mongolia, inducing a significant increase in westerly moisture flux and its convergence over eastern Siberia. Empirical orthogonal function (EOF) analysis of detrended summer precipitation revealed the leading modes of the interannual variability. The first leading mode (EOF1) represents interannual variation around the central Siberian Plateau and the middle reaches of the Lena river basin, related to the enhancement of a low-level cyclonic circulation centred on 65°N, 100°E around eastern Siberia. The circulation pattern of EOF1 closely matches the trend pattern over Siberia, indicating that a deeper quasi-stationary trough appears with increasing frequency in recent decades. The second leading mode (EOF2) shows a dipole pattern between the middle reaches of the Lena river basin and the western part of the Central Siberian Plateau. Wet summers in the Lena river basin are related to a stationary trough centred at around 60°N, 130°E. These leading patterns are related to the change in position of the stationary trough and the ridge of the wave train structure along the Arctic polar jet across the northern Eurasian continent.

The atmospheric circulation patterns that were responsible for the heavy flooding that occurred in Thailand in 2011 are examined. This paper also investigates the interannual variation in precipitation over Indochina over a 33-yr period from 1979–2011, focusing on the role of westward-propagating tropical cyclones (TCs) over the Asian monsoon region. Cyclonic anomalies and more westward-propagating TCs than expected from the climatology of the area were observed in 2011 along the monsoon trough from the northern Indian subcontinent, the Bay of Bengal, Indochina, and the western North Pacific, which contributed significantly to the 2011 Thai flood. The strength of monsoon westerlies was normal, which implies that the monsoon westerly was not responsible for the seasonal heavy rainfall in 2011. Similar results were also obtained from the 33-yr statistical analysis. The 5-month total precipitation over Indochina covaried interannually with that along the monsoon trough. In addition, above-normal precipitation over Indochina was observed when enhanced cyclonic circulation with more westward-propagating TCs along the monsoon trough was observed. Notably, the above-normal precipitation was not due to the enhanced monsoon westerly over Indochina. Therefore, the 2011 Thai flood was caused by the typical atmospheric circulation pattern for an above-normal precipitation year. It is noteworthy that the effect of sea surface temperature (SST) forcing over the western North Pacific and the Niño-3.4 region on total precipitation during the summer rainy season over Indochina was unclear over the 33-yr period.

Characteristics of low pressure systems (LPSs) responsible for submonthly-scale (7–25 days) intraseasonal oscillation (ISO) in rainfall over Bangladesh and their impact on the amplitude of active peaks are investigated for 29 summer monsoon seasons. Extreme and moderate active peaks are obtained based on the amplitude of 7–25-day-filtered rainfall series. By detecting the LPSs that formed over the Indian monsoon region, it was found that about 59% (62%) of extreme (moderate) active peaks of rainfall are related to LPSs. These LPSs have horizontal scale of about 600 km and vertical scale of about 9 km. For the extreme active peak, the locations of the LPS centers are clustered significantly over and around Bangladesh, accompanied by the maximum convergence in the southeast sector of the LPSs. After their formation, they tend to remain almost stationary over and around Bangladesh. In contrast, for the moderate active peak, the LPS centers are located over the Ganges Plain around 85°E, and the maximum convergence of the LPSs occurs around their centers. This difference in the convergence fields is closely associated with the geographical features to the north and east of Bangladesh and the horizontal scale of the LPSs. These features suggest that the amplitude of the active peaks in the submonthly-scale ISO is modulated by small differences in the locations of the LPS centers. These findings suggest that improved predictions of both genesis location and the tracks of the LPSs are crucial to forecasting seasonal rainfall over Bangladesh.

The objectives of this study are to diagnose and prevent environmental problems that threaten urban sustainability, the impact of changes in lifestyle (diet, domestic sanitation, and motorization), and production style (agriculture, industry, and services) with the rapid urbanization on regional nitrogen (N) flows, and the water environment was quantitatively evaluated. The megacity Shanghai was chosen as a case study to investigate the temporal changes in nitrogen flow during 1980-2008 by a multidisciplinary approach (a field survey, a regional nitrogen mass balance model, input-output analysis, etc.). Although the total potential nitrogen load in Shanghai has decreased in the 2000s and water pollution problems seem to have improved, the problem has shifted and expanded to affect a wider area through the food/product chain and water/air movement. Further effective solutions that aim at material cycles are necessary and have to be implemented on a large scale.

A series of 60-year numerical experiments starting from 1851 was conducted using a global climate model coupled with an aerosol-cloud-radiation model to investigate the response of the Asian summer monsoon to variations in the secondary organic aerosol (SOA) flux induced by two different estimations of biogenic volatile organic compound (BVOC) emissions. One estimation was obtained from a pre-existing archive and the other was generated by a next-generation model (the Model of Emissions of Gases and Aerosols from Nature, MEGAN). The use of MEGAN resulted in an overall increase of the SOA production through a higher rate of gasto-particle conversion of BVOCs. Consequently, the atmospheric loading of organic carbon (OC) increased due to the contribution of SOA to OC aerosol. The increase of atmospheric OC aerosols was prominent in particular in the Indian subcontinent and Indochina Peninsula (IP) during the pre- and early-monsoon periods because the terrestrial biosphere is the major source of BVOC emissions and the atmospheric aerosol concentration diminishes rapidly with the arrival of monsoon rainfall. As the number of atmospheric OC particles increased, the number concentrations of cloud droplets increased, but their size decreased. These changes represent a combination of aerosol-cloud interactions that were favorable to rainfall suppression. However, the modeled precipitation was slightly enhanced in May over the oceans that surround the Indian subcontinent and IP. Further analysis revealed that a compensating updraft in the surrounding oceans was induced by the thermally-driven downdraft in the IP, which was a result of surface cooling associated with direct OC aerosol radiative forcing, and was able to surpass the aerosolcloud interactions. The co-existence of oceanic ascending motion with the maximum convective available potential energy was also found to be crucial for rainfall formation. Although the model produced statistically significant rainfall changes with locally organized patterns, the suggested pathways should be considered guardedly because in the simulation results, 1) the BVOC-induced aerosol direct effect was marginal; 2) cloud-aerosol interactions were modeldependent; and 3) Asian summer monsoons were biased to a nonnegligible extent.

The role of extratropical waves in the excitation of tropical waves on submonthly timescales is explored along the Indian Ocean Intertropical Convergence Zone (ITCZ) during the austral summer using Japanese Reanalysis products and NOAA outgoing longwave radiation data. The analysis period is DecemberŰFebruary of 1979/1980 to 2008/2009. The submonthly tropical waves are regarded as a type of Rossby wave propagating along the mean monsoon westerly flow. They play an important role in modulating the Indian Ocean ITCZ convection. The linkage between the tropical and extratropical waves, which is responsible for the formation and strengthening of tropical waves, is examined. Composite analysis results linked to the tropical wave train development show that the midlatitude Rossby wave train progresses eastward and northeastward from the South Atlantic into the subtropical Indian Ocean. As a trough and ridge that form part of the midlatitude wave train approach the southern Africa-southwest Indian Ocean (SWIO) region, a southwest-northeast-oriented wave train is subsequently established, originating from this feature, and is strengthened across the tropical Indian Ocean. The midlatitude wave propagation toward the subtropics induces the growth of the trough and ridge over the SWIO. Wave activity flux diagnostics indicate that the amplified trough and ridge over the SWIO act as an energy source for northeastward amplification of the tropical waves through the wave energy dispersion process. The results suggest that the propagation of the midlatitude wave toward the SWIO is the fundamental mechanism behind the development of the tropical waves along the Indian Ocean ITCZ.

Copyright © 2013 John Wiley & Sons, Ltd. Borneo is the third largest island in the world and famous for its majestic rainforests (Figure 1a). Southeast Asian tropical forests have the highest relative deforestation rate in the world (Canadell et al., 2007). More than 80% of the total land area of Borneo was covered with pristine forest in the 1950s; however, the high deforestation rate (1.7%year ), which is almost double that of the already intense deforestation rate of the whole Southeast Asian region, has resulted in the current estimation of forest cover being ~50% (Langner et al., 2007) (Figure 1b). Since 1965, production of tropical hardwood timber in Borneo sharply increased and reached a plateau and maximum in the early 1980s (Brookfield and Byron, 1990). Although the recent and rapid decline in timber production has been evident throughout Borneo owing to over-logging, over the past decades, more timber was exported from Borneo than from tropical Africa and Latin America combined (Curran et al., 2004). The land cover area categorized as ‘degraded forest and regrowth’, ‘cultivation forest mosaic’ and ‘dry/wet bare soil; grasslands; agriculture’ reached up to 33 million ha, ~45% of the total area of Borneo (Langner et al., 2007). Tropical forests are a major source of global hydrologic fluxes, and thus, this forest cover change has potential to significantly alter the global and regional climate and hydrologic cycling (Nobre et al., 1991;Kanae et al., 2001; Avissar andWerth, 2005). Because tropical rainforests exist where ecosystem water resources are greatest, the hydrologic changes could significantly alter ecological patterns and processes (Malhi et al., 2009; Phillips et al., 2009; Kumagai and Porporato, 2012), in turn affecting feedback to the atmosphere (Meir et al., 2006; Bonan, 2008). It is a matter of course that the drastic deforestation and forest degradation in Borneo should be anticipated to impact the regional hydro-climate; in fact, the long-term daily grid precipitation datasets (APHRODITE’s Water Resources, available via http://www.chikyu.ac.jp/precip/, Yatagai et al., 2012) over Borneo showed a significant decline in precipitation over the period 1951–2007 (Figure 1c). An abrupt decline in precipitation in the late 1980s can be seen (Figure 1c), which was consistent with a time when deforestation, i.e. logging for timber production, might have become intensive (Brookfield and Byron, 1990; Curran et al., 2004). Furthermore, it should be noted that such a decreasing trend in precipitationmight cause frequent extreme droughts and subsequent fires, resulting in more severe deforestation and forest degradation (van Nieuwstadt and Sheil, 2005; Wooster et al., 2012). A spatial distribution of atmospheric moisture convergence averaged over 1998–2010 in the eastern Pacific Ocean (built using a reanalyzed and gridded four-dimensional meteorology dataset, Japanese 25-year ReAnalysis and the JapanMeteorologicalAgencyClimateDataAssimilation System available via http://jra.kishou.go.jp/JRA-25/index_en.html) suggests less moisture convergence and divergence over Borneo compared with other regions (Figure 2a). On the other hand, the Tropical Rainfall Measuring Mission satellite measurements from 1998 to 2010 (NASA Goddard Earth Sciences Data and Information Services Center, available via http://disc.sci.gsfc.nasa.gov/ about-us) showed a larger amount of precipitation above islands of the maritime continent in the western Pacific Ocean compared with sea areas

Regional material flows are strongly influenced by human diets. To diagnose and prevent environmental problems that threaten urban sustainability, the impact of human diet changes with rapid urbanization on the regional nitrogen (N) and phosphorus (P) flows were quantitatively evaluated. A survey of day-to-day activities was conducted of 450 individuals surveyed (adults over 18 years old) in three representative areas (the central district, the new district, and the suburban/rural areas) of Shanghai, a megacity which has attracted worldwide attention. The lifestyle (eating habits, domestic sanitation, drainage facilities, etc.) pattern was determined and the potential N and P loads from human diets on the environment were calculated. The daily potential nitrogen and phosphorus loads from human diets was 19.36 g-N, 1.80 g-P in the central district, 16.48 g-N, 1.52 g-P in the new district, and 13.04 g-N, 1.20 g-P in the suburban/rural areas of Shanghai. Respondents in all three areas, especially those in the suburban/rural areas reported a preference for increasing the intake of animal-derived as well as processed foods, which means that the potential N and P load from human diets to the environment will increase further. In addition, most respondents consider industrial wastewater discharge as the main cause of eutrophication of waterbodies, though in recent years water pollution caused by domestic wastewater has increased rapidly, but this has received much less attention. Environment-friendly eating habits and improvements in the environmental awareness will be required.

If sustainability entails maintaining wellbeing over time, including environmental, economic, and social dimensions at local to global scales, Asia is its proving ground. The region is characterized by diverse climate, ecosystem, and social-historical conditions. It contains more than 60% of the global population, accounts for one-third of global GDP, consumes more than 60% of global materials, is a growing emitter of greenhouse gases, and is undergoing rapid demographic change and economic growth [1 ]. Moreover, Urbanization (see Figure 1) and industrialization have increased resource extraction, processing, transport, and consumption and waste generation, transforming local and regional environments at a pace and scale that is unprecedented in modern history. At the same time, significant disparities of wealth both within and between countries intensify social and ecological vulnerability to the potential impacts of climate change. This article suggests the region requires well-integrated researches by global environmental change (GEC) research community and sustainable development (SD) research community, and proposes formation of a special Future Asia (Futue Earth in Asia) network within the Future Earth initiative for global sustainability.

This study investigates spatiotemporal characteristics of the diurnal cycle (DC) of rainfall over Sarawak in northwest Borneo Island, associated with large-scale intraseasonal disturbances represented by the Madden–Julian oscillation (MJO). This is accomplished using a dense hourly rain gauge network and satellite data. The spatial pattern of the DC is classified into two major groups, coastal and interior regions, based on remarkable differences in rainfall peak times and amplitudes. Amplitudes of the DC and daily rainfall amount increase in active MJO phases at all sites, but the MJO has a stronger effect in the coastal region than the interior region. This modulation of rainfall by the MJO disturbance is largely attributed to rainfall frequency in the interior region, but to both frequency and intensity of rainfall in the coastal region. The low-level westerly wind anomaly enhances convergence, the land–sea breeze, and a midnight rainfall peak in the coastal region during the active MJO phase. Analysis of moisture flux divergence and moist static instability suggests the different dynamics of this modulation of the DC between coastal and interior regions.

[1] Using both a coupled atmosphere-ocean general circulation model (GCM) and an atmospheric GCM, we investigate the effects of the Tibetan Plateau (TP) on the onset of the South Asian summer monsoon by conducting simulations with and without the TP. In the coupled GCM, the presence of the TP causes the monsoon onset to occur approximately 15 days later in the Arabian Sea (AS) and India (ID) and approximately 10 days earlier in the Bay of Bengal (BB). These changes are attributed to different atmospheric circulation patterns and different conditions within the adjacent oceans, such as the AS and the BB. When the TP is included, lower sea surface temperatures (SSTs) in the AS contribute to a stable lower atmosphere, which suppresses convection over the AS and ID in May. In contrast, low pressure over South Asia, caused by the TP, induces a southwesterly toward the BB that transports a substantial amount of water vapor to the BB. This flow results in an earlier monsoon in the BB. Without the TP, higher SSTs that are formed in the AS in May destabilize the lower atmosphere and create a depression, resulting in an earlier onset of the monsoon over the AS and ID. Consequently, the cyclonic circulation spreads abruptly to the BB, and precipitation begins to increase over the BB. Therefore, the air-sea interaction in the adjacent ocean under the influence of the TP strongly modulates the onset of the South Asian summer monsoon. This modulation was verified by the atmospheric GCM experiments.

The Tropical Ocean-Global Atmosphere (TOGA) program sought to determine the predictability of the coupled ocean-atmosphere system. The World Climate Research Programme's (WCRP) Global Ocean-Atmosphere-Land System (GOALS) program seeks to explore predictability of the global climate system through investigation of the major planetary heat sources and sinks, and interactions between them. The Asian-Australian monsoon system, which undergoes aperiodic and high amplitude variations on intraseasonal, annual, biennial and interannual timescales is a major focus of GOALS. Empirical seasonal forecasts of the monsoon have been made with moderate success for over 100 years. More recent modeling efforts have not been successful. Even simulation of the mean structure of the Asian monsoon has proven elusive and the observed ENSO-monsoon relationships has been difficult to replicate. Divergence in simulation skill occurs between integrations by different models or between members of ensembles of the same model. This degree of spread is surprising given the relative success of empirical forecast techniques. Two possible explanations are presented: difficulty in modeling the monsoon regions and nonlinear error growth due to regional hydrodynamical instabilities. It is argued that the reconciliation of these explanations is imperative for prediction of the monsoon to be improved. To this end, a thorough description of observed monsoon variability and the physical processes that are thought to be important is presented. Prospects of improving prediction and some strategies that may help achieve improvement are discussed.

To examine the influence of both crop cultivation and surface air temperatures (SATs) on annual global isoprene and monoterpene emissions, which can lead to the formation of secondary organic aerosols (SOAs), we simulated, on a monthly basis, the annual emissions of volatile organic compounds (VOCs) during the period 1854–2000. The model estimates were based on historical climate data such as SATs, and downward solar radiation (DSR) reproduced with an atmospheric-ocean circulation model, as well as a time series of the global distribution of cropland (to test the hypothesis that conversion of forests into croplands lowers emissions). The simulations demonstrated that global SAT, DSR, the combination of SAT and DSR, and the expansion of cropland all affected emissions. The effect of cropland expansion (i.e., forest conversion) on annual emissions during this period was larger for isoprene (~7% reduction on a global scale) than for monoterpenes (~2% reduction), mainly because of the reduction in broadleaf evergreen forests (BEFs) in Southeast Asia, which have the highest and most constant emissions of isoprene and where both temperature and radiation are high all year round. The reduction in the Amazon region and in parts of Africa, which are other primary sources of annual global isoprene emissions, but where the conversion of BEF to cropland has been much smaller than in Southeast Asia, was less remarkable, probably because the broadleaf deciduous forests and C4 grasslands in these areas have lower and seasonal emissions; hence, their conversion has less effect. On the other hand, the difference in the emission factors (ε) between cropland and the other vegetation types was much lower for monoterpenes than for isoprene, although the ε for cropland was generally the lowest for both compounds. Thus, the expansion of cropland also contributed to the reduction in monoterpene emissions to some degree, but had less effect. A ~5% increase in emissions due to rising SAT was more than offset by the decrease in isoprene emissions and a concurrent ~2% reduction caused by a decrease in DSR. Overall, annual global isoprene emissions in 2000 were lower than in 1854 by 13 TgC yr−1, whereas annual global monoterpene emissions were higher by 2.3 TgC yr−1.

This study examines wave disturbances on submonthly (6–30-day) timescales over the tropical Indian Ocean during Southern Hemisphere summer using Japanese Reanalysis (JRA25-JCDAS) products and National Oceanic and Atmospheric Administration outgoing longwave radiation data. The analysis period is December–February for the 29 years from 1979/1980 through 2007/2008. An extended empirical orthogonal function (EEOF) analysis of daily 850-hPa meridional wind anomalies reveals a well-organized wave-train pattern as a dominant mode of variability over the tropical Indian Ocean. Daily lagged composite analyses for various atmospheric variables based on the EEOF result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the Indian Ocean Intertropical Convergence Zone (ITCZ). The wave train is oriented in a northeast–southwest direction from Sumatra toward Madagascar. The waves have zonal wavelengths of about 3,000–5,000 km and exhibit westward and southwestward phase propagation. Individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of Sumatra into Madagascar. Meanwhile, eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern Indian Ocean. This could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern Indian Ocean along the mean monsoon westerly flow. In addition, the waves modulate the ITCZ convection. Correlation statistics show the average behavior of the wave disturbances over the tropical Indian Ocean. These statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis. The waves appear to be connected to the monsoon westerly flow. The waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow. This suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical Indian Ocean. The horizontal structure of the wave train may be interpreted as that of a mixture of equatorial Rossby waves and mixed Rossby-gravity wavelike gyres.

The India Meteorological Department (IMD) gridded rainfall dataset, the 47 Bangladesh gauge rainfall observations and the Tropical Rainfall Measuring Mission (TRMM) 3B42V6 satellite data are used in the present analysis. The nearest neighbour interpolation scheme is used, wherein the interpolated values are computed from a weighted sum of observations. The Bangladesh daily gauge measured rainfall is interpolated into regular grids of 0.5° × 0.5° resolution every day from January 1988 to December 2007 and appended with the daily gridded dataset of the IMD over the Indian region. A similar resolution dataset of 0.5° × 0.5° for the TRMM-3B42V6 data from January 1998 to December 2007 is created from the original data of 0.25° × 0.25° resolution. To produce a merged rainfall product, all the gridded datasets are merged. The merging of datasets is done in such a way as to include the highest rainfall at each grid point from the three products. Based on the three available sets of daily observations (IMD dataset (1° × 1°), TRMM-3B42 (0.25° × 0.25°) and 46 daily station observations over Bangladesh), a dataset of 0.5° × 0.5° resolution on a daily scale is generated. The focus of this study is to compare the TRMM-3B42V6 rainfall data over the Ganga, Brahmaputra and Meghna (GBM) domain with observed point gauge data, and assess the possibility of using them for application in real time flood forecasting as well as to serve as a comparison tool for the baseline simulation of high resolution atmospheric models aimed at flood forecasting and climate change projections. Copyright © 2012 Royal Meteorological Society

Terrestrial evaporation is essential to the global hydrological cycle and climate systems. It is a complicated energy and mass transfer process that involves radiation, conduction, diffusion, convection, and surface–atmosphere interactions. The energetic and diffusive controls on evaporation were combined in the contemporary theory (e.g. the Penman–Monteith equation), in which surface–atmosphere interfacial transfer coefficients were adopted and parameterized semi-empirically or empirically to achieve a solution to evaporation. The solution achieved through this parameterization leaves unsolvable uncertainty. Thus, the theory of evaporation remains diagnostic rather than predictive. Here we show that terrestrial evaporation can be predicted without parameterization. Terrestrial evaporation, as a mechanical and thermodynamic process, follows Hamilton's principle in the macro-state. With surface temperature as a generalized coordinate of the Hamiltonian, and incorporating equilibrium evaporation, we present a nonparametric solution in a simple analytical form. We used observational data collected at 26 eddy covariance sites to test the effectiveness and the generality of the solution. Results showed good agreements between the estimated and the observed values, by an absolute difference of 10.3 ± 20.2 W m−2 for latent heat flux (evaporation) and −11.8 ± 21.0 W m−2 for sensible heat flux, for all the tested sites. Further examination demonstrated that the proposed approach achieved the performance compatible to the Penman–Monteith approach. We anticipate our analysis to be a starting point for more sophisticated investigation into the complex nature of terrestrial evaporation. Its simplicity should have potential value in applications, in addition to contributing to fundamental theory.

BACKGROUND: To diagnose problems that threaten regional sustainability and to devise appropriate treatment measures in China's agro-ecosystems, a study was carried out to quantify the nitrogen (N) flow in China's typical agro-ecosystems and develop potential solutions to the increasing environmental N load. RESULTS: The analysis showed that owing to human activity in the agro-ecosystems of Changjiang River Basin the mean total input of anthropogenic reactive N (i.e.chemical fertiliser, atmospheric deposition and bio-N fixation) increased from 4.41 x 10(9) kg-N in 1980 to 7.61 x 10(9) kg-N in 1990 and then to 1.43 x 10(10) kg-N in 2000, with chemical fertiliser N being the largest contributor to N load.Field investigation further showed that changes in human behaviour and rural urbanisation have caused rural communities to become more dependent on chemical fertilisers.In rural regions, around 4.17 kg-N of per capita annual potential N load as excrement was returned to farmlands and 1.38 kg-N directly discharged into river systems, while in urbanised regions, around 1.00 kg-N of per capita annual potential N load as excrement was returned to farmlands and 5.62 kg-N discharged into river systems in urban areas. CONCLUSION: The findings of the study suggest that human activities have significantly altered the N cycle in agro-ecosystems of China.With high population density and scarce per capita water resources, non-point source pollution from agro-ecosystems continues to put pressure on aquatic ecosystems.Increasing the rate of organic matter recycling and fertiliser efficiency with limited reliance on chemical fertilisers might yield tremendous environmental benefits. (C) 2011 Society of Chemical Industry

This study identifies intraseasonal oscillations in summer precipitation over northern Eurasia using multi-channel singular spectrum analysis (MSSA) and a gridded daily precipitation data set for northern Eurasia. The analysis period is June–August of 1979–2002. Empirical orthogonal function analysis was first performed on 8-day low-pass-filtered precipitation anomalies at 2.5° grid resolution for northern Eurasia; MSSA was then carried out on the ten leading principal components (PCs). Three quasi-periodic oscillations with timescales of 45, 15, and 9 days were identified. The spatiotemporal structures of precipitation oscillations were defined by composite analysis based on the reconstructed time series of the spatiotemporal PCs obtained from the MSSA. The composite life cycle of each mode was classified into eight phase categories. The 45-day oscillation is characterised by a slow eastward progression of a broad east/west contrastive pattern which is associated with a replacement of elongated dry and wet zones across northern Eurasia. The 15-day oscillation shows a regular eastward phase propagation of precipitation anomalies with a tripole structure across the domain. The eastward displacement of dry and wet zones occurs in association with this oscillation. Spatiotemporal behaviours of the precipitation anomalies associated with the 9-day oscillation are similar to those of the 15-day oscillation, but the spatial scale of this oscillation is somewhat smaller. To explore the connections between the oscillations of precipitation and large-scale atmospheric circulation patterns, a similar composite method was applied to 300-hPa geopotential height anomalies over the Northern Hemisphere. The circulation patterns responsible for the 45-day oscillation are characterised by a wave train extending across the northeastern Atlantic/northern Eurasian sector. The wave train, with zonal wavenumbers of 3–4, indicates slow eastward moving and quasi-stationary features. The circulation patterns linked to the 15-day oscillation exhibit an eastward propagating wave train extending from northeastern Europe into the North Pacific/North American sector. In spatial scale, this wave train has zonal wavenumbers of 5–6. The wave trains associated with the 9- and 15-day oscillations have similar behaviour patterns over northern Eurasian. However, the 9-day wave train has a comparatively smaller spatial scale with zonal wavenumbers of 6–7. Therefore, the intraseasonal oscillations of precipitation are connected to the well-organised wave trains that extend from the Euro-Atlantic region to northern Eurasia, suggesting that the oscillation on each intraseasonal time scale must be produced by propagation of the corresponding wave train. Copyright © 2011 Royal Meteorological Society

This study investigated the impacts of historical land use/cover changes (LUCC), from forest to cultivated land, on the seasonal cycle of the hydroclimate over the Indian subcontinent and southern China. The mechanism of these impacts was studied by conducting numerical experiments using an atmospheric general circulation model MIROC3.2 coupled with the land surface scheme MATSIRO and historical global land use/cover changes between 1700 and 1850. A previous study found a decrease in summer (JJA) precipitation over the Indian subcontinent and southern China induced by extended cultivation between 1700 and 1850. We further found that evapotranspiration in the Indian subcontinent notably decreased, particularly in the spring, while that in southern China discernibly decreased throughout the year. The difference in the changes in evapotranspiration in the spring over both regions could be explained by the amount of precipitation during the dry season. In the Indian subcontinent, the marked decrease in evapotranspiration in May due to LUCC caused the decrease in precipitation during the same season. However, in southern China, the decrease of precipitation from March to April was contributed rather by the decrease of water vapor flux convergence due to atmospheric circulation changes than by the decrease of evapotranspiration.

Downward shortwave flux at the surface over China was derived from sunshine duration data using parameters of Jordan sunshine recorders. The sunshine duration data were obtained as routine meteorological data and ad- justed as necessary for the eects of topography, station surroundings, altitude, and atmospheric turbidity. Calculated flux was verified by in situ observations. Daily flux was calculated at more than 190 stations in China, Climatic maps (statistical period: 1971-2000) of surface solar radiation were produced and have been made public. The sunshine duration-based shortwave flux was used to check satellite observation-based datasets. Two ver- sions of satellite-based surface radiation budget datasets (SRB 2.0 and SRB 3.0) from NASA's Langley Research Center were investigated. Compared with the SRB 2.0 dataset, the SRB 3.0 dataset showed improved shortwave flux, especially over western China and the Tibetan Plateau.

This paper evaluates the performance of eight state-of-art IPCC-AR4 coupled atmosphere-ocean general circulation models in their representation of regional characteristics of atmospheric water balance over South Asia. The results presented here are the regional climate change scenarios of atmospheric water balance components, precipitation, moisture convergence and evaporation (P, C and E) up to the end of the twenty-second century based on IPCC AR4 modelling experiments conducted for (A1B) future greenhouse gas emission scenario. The AOGCMs, despite their relatively coarse resolution, have shown a reasonable skill in depicting the hydrological cycle over the South Asian region. However, considerable biases do exist with reference to the observed atmospheric water balance and also inter-model differences. The monsoon rainfall and atmospheric water balance changes under A1B scenario are discussed in detail. Spatial patterns of rainfall change projections indicate maximum increase over northwest India in most of the models, but changes in the atmospheric water balance are generally widespread over South Asia. While the scenarios presented in this study are indicative of the expected range of rainfall and water balance changes, it must be noted that the quantitative estimates still have large uncertainties associated with them.

Intraseasonal oscillation (ISO) of rainfall during the summer monsoon season (June–August) and its plausible effect on interannual variation (IAV) of total summer monsoon rainfall over Bangladesh are examined using daily rainfall data from 25 rain-gauge stations for 20 years (1981–2000). Submonthly scale (7–25 days) ISO is a dominant mode of summer rainfall fluctuation over Bangladesh. In the active (suppressed) ISO phases, a cyclonic (anticyclonic) circulation anomaly develops at the low-level troposphere from northeastern India to Bangladesh, and an anticyclonic (cyclonic) circulation anomaly appears over the Bay of Bengal, accompanied by the enhancement of westerly/southwesterly (easterly/southeasterly) moisture flux anomalies over Bangladesh. The IAV of total summer monsoon rainfall is significantly correlated with that of the rainfall variance, mainly in the submonthly scale, suggesting that the ISO activity controls the IAV of the total summer monsoon rainfall. Moreover, the spatial patterns of atmospheric circulation and convection associated with the ISO and the IAV are quite similar to each other around the monsoon trough, especially from northeastern India to Bangladesh. In wet monsoon years, more frequent strong submonthly scale ISOs and a larger number of rainy days related to the active ISO phase are evident compared with that of dry monsoon years. Climatologically, Bangladesh is one of the most predominant areas of submonthly scale ISO; however, 30–60-day ISO is not prominent. These characteristic features probably allow the submonthly scale ISO to modulate the total seasonal rainfall and the spatial patterns of circulation and convection over and near Bangladesh. Copyright © 2010 Royal Meteorological Society

This study examined the impact of changes in land surface conditions on regional climate over Indochina using a high-resolution regional climate model. Anthropogenically induced land surface changes are going on in this part of tropical Southeast Asia. Because a previous study suggested that deforestation in this area affected September precipitation, we chose September as the study period. We performed a control simulation (CTL) driven by reanalysis data combined with current land use and predicted soil moisture data. The CTL reproduced the spatial distribution of total precipitation well. In addition, it also simulated a distinct diurnal cycle of precipitation that was previously reported in observational studies. Two sensitivity experiments, assuming wetter and drier land surface conditions over the Khorat Plateau (northeast Thailand) compared with the current land surface condition, were conducted and examined the impact of land surface changes on precipitation. The results indicated that drier land surface conditions increased precipitation over the disturbed region. A pronounced increase in precipitation was found only during nighttime, which coincided with the peak in the climatological diurnal precipitation cycle. Climatologically, the diurnal peak in precipitation occurs from evening to early morning over the Khorat Plateau. Drier conditions intensified the diurnal variation of precipitable water associated with the thermally induced local circulation responsible for a horizontal gradient of near-surface temperature. The effects of land use and land cover changes in the tropics are shown to be strongly related to the diurnal precipitation cycle. Copyright © 2010 Royal Meteorological Society

The Yellow River, the main source of water for the North and Northwest China, showed a marked decrease in runoff during the 1990s compared to that in the 1980s. Since the basin is extensive, covering many different climatic zones with various land uses, the hydrological processes are very complex. It is necessary to develop and verify a detailed water budget in order to understand changes in the hydrological processes within the basin. In this paper, we describe a hydrological model that considers five categories of land use. The calibration and verification of the model were carried out at two independent watersheds (Tangnaihai, 120 000 km 2 and Lushi, 6400 km 2 ). The results from the model represent the hydrographs and annual runoffs at two gauge stations over a relatively long-term period (18 years at Tangnaihai and 21 years at Lushi). The model was applied to other watersheds of the Yellow River basin above Huayuankou station, and water budget components in each region were analysed. The results indicate only a small change in evapotranspiration, but a marked decrease in precipitation, which was significant in all of the analysed areas except the Lanzhou-Toudaoguai inter-watershed area. Water use for agricultural irrigation was stable throughout the entire simulation period. A numerical experiment of water conservation for the whole basin above Huayuankou station demonstrated that if the number of irrigation days was reduced by 20, 40 or 60%, the amount of water used could be reduced by 26Ð6, 52Ð 1o r 80Ð7%, compared to the current situation. Copyright  2010 John Wiley & Sons, Ltd.

Convective variability at submonthly time scales (7–25 days) over the Yangtze and Huaihe River basins (YHRBs) and associated large-scale atmospheric circulation during the mei-yu season were examined using interpolated outgoing longwave radiation (OLR) and NCEP–NCAR reanalysis data for 12 yr having active submonthly convective fluctuation over the YHRBs within the period 1979–2004. Correlations between convection anomalies over the YHRBs and upper-level streamfunction anomalies at every grid point show two contrasting patterns. One pattern exhibits high correlations along the northern to eastern peripheries of the Tibetan Plateau (defined as the NET pattern), whereas the other has high correlations across the Tibetan Plateau (defined as the AT pattern). Composite analysis of the NET pattern shows slow southward migration of convection anomalies from the northeastern periphery of the Tibetan Plateau to southern China, in relation to southward migration of the mei-yu front caused by simultaneous amplification of upper- and low-level waves north of the YHRBs. In the AT pattern, convection anomalies migrate eastward from the western Tibetan Plateau to the YHRBs. A low-level vortex is created at the lee of the plateau by eastward-moving upper-level wave packets and associated convection from the plateau. Rossby wave trains along the Asian jet characterize the upper-level circulation anomalies in the two patterns. The basic state of the Asian jet during the mei-yu season differs between the two patterns, especially around the Tibetan Plateau. The Asian jet has a northward arclike structure in NET years, while a zonal jet dominates in AT years. These differences could alter the Rossby wave train propagation route. Furthermore, the larger zonal wavenumber of AT waves (∼7–8) than of NET waves (∼6) means faster zonal phase speed relative to the ground in the AT pattern than in the NET pattern. These differences likely explain the meridional amplification of waves north of the YHRBs in the NET pattern and the eastward wave movement across the plateau in the AT pattern.

The atmospheric water balance over dierent domains within the South Asian monsoon region has been studied using moisture convergence ðCÞ computed from JRA-25, ERA-40 and NCEP/NCAR reanalysis datasets, GPCP precipitation data ðPÞ and evaporation data ðEÞ as a residual of these two parameters. The seasonal clima- tology of P, C, and E for the selected regions shows generally large contribution of E to P. The inter-annual characteristics of P, C and E over selected key domains within the South Asian monsoon region have also been examined for both the early (June and July: JJ) and late summer (August and September: AS) monsoon periods from 1979 to 2000. The spatial and temporal characteristics of the hydrological cycle and the contribution of E and C to P are discussed in detail. One important aspect on the seasonal timescale is that from the dry regions in the northwest to the central and the wettest northeast regions, the monthly variations of E or C are large during the monsoon months specific to those regions. However, the interannual variability of P over each domain is not necessarily influenced by the same criteria like C or E, which influences the mean seasonal precipitation. It is also evident that the structure of variability for early (JJ) and late (AS) summer precipitation is dierent over the South Asian monsoon region. Over northwest India E is dominant on the seasonal timescale, but C contributes higher to interannual variability of P. On the other hand, over central India C is dominant during early summer (JJ) on the seasonal timescale, but E contributes higher to P variability on the interannual timescale, and during late summer (AS) E is dominant on the seasonal timescale, but C contributes higher to P variability on the inter- annual timescale. Over northeast India, C is dominant on the seasonal timescale, but E contributes higher to in- terannual variability of P. The importance of land-atmosphere interaction over each domain is discussed. The regionality in the mechanism of precipitation generation and its contribution to the India summer monsoon precipitation variability are also discussed in detail. The role of evaporation variability of precipitation is stronger over the Bay of Bengal sector and the role of convergence on the interannual variability of precipitation is stronger over the Arabian Sea sector.

We address the long-term decrease in September rainfall over the Indochina Peninsula. Distinct long-term decreases in rainfall along the monsoon trough across the Indochina Peninsula have been observed. We performed long-term simulations and discuss the effects of long-term changes in both the local surface conditions and large-scale circulation. Using a 30-year simulation for September for the period from 1966 to 1995 with land-use conditions fixed at present-day values and neglecting the recorded deforestation, we successfully simulated the observed long-term decrease in rainfall. We therefore conclude that the weakening tropical-cyclone activity over the Indochina Peninsula region is probably responsible for the decrease in rainfall. Copyright © 2008 Royal Meteorological Society

In this study we have investigated atmospheric water balance over South Peninsular India and Sri Lanka during the months October to December (OND) using computed moisture convergence (C) and residual evaporation (E) from National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and Global Precipitation and Climatology Project (GPCP) precipitation data. The interannual signatures of OND precipitation, moisture convergence and evaporation over the South Peninsular India and Sri Lanka have been captured. The spatial and temporal characteristics of the hydrological cycle and the contribution of evaporation (E) and convergence (C) to precipitation (P) are discussed in detail. Over the South Peninsular India and Sri Lanka, evaporation (E) dominates during the entire monsoon months (OND). However, the interannual variability of precipitation over the domain is not necessarily influenced by the same criteria which influences the mean seasonal precipitation. The moisture from the Indian Ocean (IO) sector also modulates the precipitation over this region on a year-to-year basis. It has been noted that the positive northeast monsoon rainfall (NEMR) is associated with El Nino coupled with IO dipole, but negative NEMR is weakly associated only with La Nina over South Peninsular India and Sri Lanka. There also exists a significant land-atmospheric interaction over the region in modulating the hydrological cycle on a year-to-year basis. Copyright © 2008 Royal Meteorological Society

High-resolution Tropical Rainfall Measuring Mission (TRMM) rainfall data for six wet seasons (December–March) were used to investigate the time and space structure of the diurnal cycle of rainfall over and around New Guinea, a major island of the Maritime Continent. The diurnal cycle shows a systematic modulation associated with intraseasonal variability in the large-scale circulation pattern, with regimes associated with low-level easterlies or westerlies over the island. Lower-tropospheric easterly (westerly) wind components correspond to periods of inactive (active) convection over the islands that are associated with the passage of intraseasonal atmospheric disturbances such as the Madden–Julian oscillation (MJO). A striking feature is the diurnal rainfall that develops over the central mountain ranges in the evening and propagates toward the southwest (northeast) of the island with an inferred phase speed of about 2–3 m s−1 under low-level easterly (westerly) flow. In the case of the easterly regime, diurnal rainfall is strongly concentrated over the southwestern part of the island, inhibited from spreading offshore southwest of New Guinea. Under the westerly regime, in contrast, the rainfall area spread far and wide along the low-level westerlies from the island toward the Pacific Ocean. Significant offshore rainfall propagation extending from the island appears during the night over the north-northeastern coast and moves with a phase speed of about 7–8 m s−1, reaching the open ocean the following day. Possible processes for controlling the variability in diurnal rainfall through the interaction between large-scale circulation and previously denoted complex local circulation over the island are discussed.

To clarify the interannual variability of winter surface air temperature (SAT) over Asia and the surrounding oceans, the authors applied principal component analysis to normalized monthly SATs. The first mode represents the Asian north–south dipole pattern with a node over the Tibetan Plateau. This component has close relationships to the Arctic Oscillation and cold surge variability around Southeast Asia, showing decadal oscillation with signal changes in 1988 and 1997. The second mode is the inner-Asian mode with a center to the north of the Tibetan Plateau. This component connects to fluctuations of not only the western Siberian high but also the Icelandic low, which is associated with the pattern of the polar vortex over Eurasia. A recent warming trend and possible relationship to solar activity are also shown. The modes of Asian SAT variability associated with ENSO are extracted as the north–south dipole mode over the tropical western Pacific and Japan (the third mode) and Silk Road mode (the fourth mode). The two independent modes appear to be caused by different sea surface temperature (SST) anomalies over the western Pacific and Indian Ocean and their associated atmospheric Rossby wave responses: the atmospheric wave trains over both the north and south of the Tibetan Plateau in the third mode, and the atmospheric wave train that propagates toward the Silk Road via Greenland in the fourth mode.

We examined the decreasing trend in rainfall during the late summer monsoon season (September) in Thailand from 1951 to 2000 and associated changes in tropical cyclone (TC) activity. Thailand receives significant rainfall from May to October and experiences two rainy peaks in late May to early June and in September. A previous study reported a decreasing trend in September rainfall in Thailand and, based on a regional climate model, suggested that the trend was associated with local deforestation. However, the long-term trend may also be affected by changes in large-scale circulation. Thus, the purpose of this study was to investigate changes in large-scale circulation associated with the decreasing rainfall trend.Westward-propagating TCs from the South China Sea and the western North Pacific brought most of the rainfall over Thailand in September. TCs include tropical depressions, tropical storms, severe tropical storms, typhoons, and residual lows. 70% of the rainfall amount in September was estimated to be associated with TCs.The 50-year time-series of September rainfall over Thailand showed a significant decreasing trend. TC activity defined by 700-hPa relative vorticity, showed a weakening trend over the Indochina Peninsula. TC tracks also suggested the weakening of TC activity over this area. The long-term trend in rainfall during the late summer monsoon season was closely associated with changes in TC activity over the Indochina Peninsula; these changes were likely caused by changes in the major course of TCs. Concurrent with the changes in TC tracks, there was a change in the TC steering current around the Philippines archipelago and Taiwan. This led to the TC activity over the Indochina Peninsula being inactive, probably resulting in the long-term decrease in rainfall over Thailand.

This study focuses on the reproducibility of the climatic change in the early summer rainfall in East Asia (Mei-yu rainband) by the Pseudo Climate Simulation (PCS) using a regional climate model. In the PCS, the lateral boundary condition is given by the composite of six hourly reanalysis data and the difference between two decadal climate means. The daily variation on the lateral boundary of the PCS is similar to that of the control hindcast in one decade, but its climate is the same as the other decadal mean. The PCS accurately reproduces the change in the Mei-yu rainband over Southern China between the 1960s and the 1990s, suggesting that the climatic features of the Mei-yu rainband are controlled by the climatic change in a large-scale circulation.The PCS reduces the uncertainty caused by the interannual variability in case of the downscaling of global warming projected by the General Circulation Models (GCMs) even if the number of sample years is the same as that in the conventional dynamical downscaling. The PCS can also exclude model biases in the present climatology reproduced by each GCM.