Soumyajit Sen | IIT Bombay (original) (raw)

Papers by Soumyajit Sen

An unsteady state mass transfer model of unstirred dead-end ultrafiltration module has been devel... more An unsteady state mass transfer model of unstirred dead-end ultrafiltration module has been developed in the present study. The dynamic membrane surface concentration is evaluated using a modified self-consistent field theory, which enables the development of an algorithm to incorporate the contribution of solute adsorption in the membrane surface concentration dynamics. Knowing the corrected membrane surface concentration, permeate flux and permeate side concentration is determined using osmotic pressure model and flux-rejection relation as predicted by irreversible thermodynamics. The time evolution of all the different process variables is achieved by solving two component balance equations developed at the membrane surface and in the solution phase respectively. The basic feature of the model is the incorporation of adsorbed fraction in the unsteady state membrane surface concentration. For the validation of the proposed model, experiments were conducted with Bovine Serum Albumin (BSA)/water as feed in a standard unstirred batch ultrafiltration module fitted with Polyethersulfone (PES) membrane of 30 kDa molecular weight cut-off (MWCO). The model predicted flux and the permeate concentration were found to be in good agreement with the experimental data.

The impact of climate change on the temporal and spatial distribution of precipitation, temperatu... more The impact of climate change on the temporal and spatial distribution of precipitation, temperature, evapotranspiration and surface runoff in the Volta Basin (400 000 km 2 ) of West Africa is investigated. Trend analysis shows clear positive trends with high levels of significance for temperature time series. Precipitation time series show both positive and negative trends, although most significant trends are negative. In the case of river discharge, a small number of (mostly positive) significant trends for the wet season are observed. High resolution regional climate simulation using explicit dynamic downscaling of the IS92a ECHAM4 global climate scenario indicates a slight increase in total annual precipitation of 5%, but also a significant decrease (up to 70%) of precipitation in April, which marks the transition from the dry season to the rainy season. The total duration of the rainy season is shortened. The simulated dry season temperature increase is around 1°C, while in the rainy season an increase of up to 2°C is projected. Expected temperature increase is smallest in the coastal areas and increases towards the north of the basin. An increase in mean annual surface runoff by 18% is anticipated. Predicted changes in precipitation, temperature, evapotranspiration and surface runoff show strong regional differences.

Geochimica Et Cosmochimica Acta, 2011

To determine where and when glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in lakes ... more To determine where and when glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in lakes are produced, we collected descending particles in Lake Lucerne (Switzerland) using two sediment traps (at 42 and 72 m water depth) with a monthly resolution from January 2008 to late March 2009. Suspended particulate matter (SPM) was monthly filtered from the water column at three different depths. The potential application of GDGTs in palaeoenvironmental and palaeoclimatic reconstructions was investigated by comparing core lipids and their relative GDGT distribution, with lake water temperatures throughout the year. Fluxes of GDGTs and their concentrations in the water column vary according to a seasonal pattern, showing a similar trend in the SPM and sediment traps. Fluxes and concentrations of isoprenoid GDGTs increase with depth, maximum values being observed in the deeper part of the water column, indicating production of isoprenoid GDGTs by Thaumarchaeota in the deep (˜50 m), aphotic zone of Lake Lucerne. The flux-weighted averages of the proxies TEX86 (0.27) and BIT (0.03) based on the total extracted GDGTs are similar at both trap depths. A sediment core from the same location showed that in the first few centimetres of the core TEX86 and BIT values of 0.29 and 0.07, respectively, are similar to those recorded for descending particles and SPM, indicating that the sedimentary TEX86 records the annual mean temperature of deeper waters in Lake Lucerne. TEX86 values are slightly higher below 20 cm in the core. This offset is interpreted to be caused by the present-day trophic state of the lake, which probably resulted in a deeper niche of the Thaumarchaeota. Branched GDGTs represent only a minor fraction of the total GDGTs in the lake and their origin remains unclear. Our data reveal that GDGTs in lakes have a large potential for palaeoclimatic studies but indicate that knowledge of the system is important for accurate interpretation.

Climatic Change, 2008

Daily stage data measured at the closing section of the Po River (Northern Italy), collected from... more Daily stage data measured at the closing section of the Po River (Northern Italy), collected from historical archives of the “Hydrological Office of the Po River—Parma”, allowed to estimate daily discharges for the period 1807–1916, therefore to extend the time series of Po River discharges for 110 years before the actually published time series. This paper provides a detailed description of the stage–discharge conversion and of the tests performed for checking homogeneity of reconstructed data. In particular, monthly discharge data were compared with approximated catchment-average data of precipitation and evapotranspiration for the period 1831–2003, which were estimated, respectively, from monthly data of local precipitation (at Milan, Turin and Parma) and local air temperature (at Milan and Turin). It emerges that estimated values of precipitation, evapotranspiration and discharge provide a coherent picture of the hydrological dynamics in the basin throughout the study period. Specifically, an apparent progressive depletion of basin reservoirs is observed since 1920, i.e., when concomitant sudden changes (regime shifts) occurred in precipitation (downward shift) and evapotranspiration (upward shift). The 1920-shift is amongst the likely causes of the fact that prolonged drought periods as those observed in the 1940s and since 2003 are not observed in the pre-shift period, when accumulation of reservoirs occurred. The increase in peak-flow discharges observed in recent decades, with values well above the maximum discharge estimated for the nineteenth century as well as for the early twentieth century, is apparently the result of the massive levee works along the river network that were completed in the 1960s. On decadal time scales, discharge variability is found to essentially reflect the changes in precipitation patterns. In particular, peaks of comparable magnitude are found in the 128-month (∼11 years) wavelet spectra of precipitation and discharge. Furthermore, concurrent changes are observed in the persistence (i.e., autocorrelation) of precipitation and discharge data. Since the red-noise background spectrum of discharge is much lower than that of precipitation, river discharge is the likely hydrological variable to be preferred for assessing the basin’s response to the background climatic variability occurring at the decadal and multi-decadal time scales, notwithstanding the fact that changes in water management and other anthropogenic impacts can be important on long time scales. Concerning the seasonal to interannual response to climatic forcing, a robust dependence of wintertime precipitation and discharges on the state of the NAO was observed. This dependence results in stronger (weaker) precipitation and higher (lower) discharges during negative (positive) anomalies of the NAO index.

The Texas Water Development Board collected suspended sediment samples across the state of Texas ... more The Texas Water Development Board collected suspended sediment samples across the state of Texas for approximately 60 years. Until this research, no comprehensive analysis of the data had been conducted. This study compiles the suspended sediment data along with corresponding streamflow and rainfall. GIS programs are developed which characterize watersheds corresponding to the sediment gauging stations. The watersheds are characterized according to topography, climate, soils, and land use. All of the data is combined to form several SAS data sets which can subsequently be analyzed using regression. Annual data for all of the stations across the state are classified temporally and spatially to determine trends in the sediment yield. In general, the suspended sediment load increases with increasing runoff but no correlation exists with rainfall. However, the annual average rainfall can be used to classify the watersheds according to climate, which improves the correlation between sediment load and runoff. The watersheds with no dams have higher sediment loads than watersheds with dams. Dams in the drier parts of Texas reduce the sediment load more than dams in the wetter part of the state. Sediment rating curves are developed separately for each basin in Texas. All but one of the curves fall into a band which varies by about two orders of magnitude. The study analyzes daily time series data for the Lavaca River near Edna station. USGS data are used to improve the sediment rating curve by the addition of physically related variables and interaction terms. The model can explain an additional 41% of the variability in sediment concentration compared to a simple bivariate regression of sediment load and flow. The TWDB daily data for the Lavaca River near Edna station are used to quantify temporal trends. There is a high correlation between sediment load and flowrate for the Lavaca River. The correlation can be improved by considering a flow-squared term and by considering seasonal effects. Typically, sediment concentration is the highest during the warmest months. The infrequent high flows carry a large, disproportionate amount of sediment.

This paper describes a procedure grouping streamflow patterns across Turkey that exhibit similar ... more This paper describes a procedure grouping streamflow patterns across Turkey that exhibit similar annual flow behaviors. Streamflow information is the integrated response of the river basin, such as topography, soil and vegetation to external impacts such as climate. A regionalization of annual data is carried out using kmeans analysis. Streamflow series from 80 gauging stations were chosen to characterize geographic differences in year to year streamflow variability. The eight-cluster solutions of k-means analysis are stable and interpretable with reference to spatial and temporal variations. It was shown that western Turkey is dominated by a relatively large cluster, indicating strong influences of the Mediterranean dynamics. The resultant map was given at the 8-cluster level, showing the spatial variability of homogeneous streamflow regions.

Advances in Atmospheric Sciences, 2010

General circulation models (GCMs) are often used in assessing the impact of climate change at glo... more General circulation models (GCMs) are often used in assessing the impact of climate change at global and continental scales. However, the climatic factors simulated by GCMs are inconsistent at comparatively smaller scales, such as individual river basins. In this study, a statistical downscaling approach based on the Smooth Support Vector Machine (SSVM) method was constructed to predict daily precipitation of the changed climate in the Hanjiang Basin. NCEP/NCAR reanalysis data were used to establish the statistical relationship between the larger scale climate predictors and observed precipitation. The relationship obtained was used to project future precipitation from two GCMs (CGCM2 and HadCM3) for the A2 emission scenario. The results obtained using SSVM were compared with those from an artificial neural network (ANN). The comparisons showed that SSVM is suitable for conducting climate impact studies as a statistical downscaling tool in this region. The temporal trends projected by SSVM based on the A2 emission scenario for CGCM2 and HadCM3 were for rainfall to decrease during the period 2011–2040 in the upper basin and to increase after 2071 in the whole of Hanjiang Basin.

Theoretical and Applied Climatology, 2010

Statistical models for rainfall downscaling based on multiple linear regression techniques have b... more Statistical models for rainfall downscaling based on multiple linear regression techniques have been developed and tested in the Andean Region of west Argentina, an extended mountainous region where three different rain regimes predominate and rainfall has great spatial and temporal variability. The verification procedure was focused on the model’s ability to reproduce observed rainfall trends in recent decades. In the northwest of Argentina, domain of the tropical summer rain regime, the monthly rainfall variance accounted for by downscaling models was 77% on average and models reproduced satisfactorily the negative linear trend observed in the last two decades of the past century. In the arid central-west Argentina, a region of rapid transition between two different rain regimes, model performance was rather poor (an average of 50% of explained variance), even so models were able to capture outstanding differences in the linear trend between the northern and southern sectors of the region. In the southwest of Argentina, domain of the mid-latitude winter rain regime, the monthly variance accounted for by downscaling models was 71% on average and models were capable to reproduce a singular change in the onset of the rainy season that occurred during the 1990s. The results achieved demonstrate that it is feasible to establish significant and useful statistical relationships between atmospheric variables and rainfall at monthly and river basin scales, even for a topographically complex region like western Argentina.

Water Resources Research, 2010

Annual maximum peak discharge time series from 572 stations with a record of at least 75 years in... more Annual maximum peak discharge time series from 572 stations with a record of at least 75 years in the eastern United States are used to examine flood peak distributions from a regional perspective. The central issues of this study are (1) “mixtures” of flood peak distributions, (2) upper tail properties of flood peaks, (3) scaling properties of flood peaks, (4)

Scarce water resources of the semi-arid eastern Mediterranean are facing significant changes in t... more Scarce water resources of the semi-arid eastern Mediterranean are facing significant changes in the forthcoming decades due to their vulnerability to climate change. Particularly in the snow-melt driven watersheds of the Taurus Mountains, prospected changes in temperature and rain/snowfall dynamics will influence snow accumulation and melt dynamics, significantly affecting runoff generation processes. One of the most productive agricultural areas under irrigation in the eastern Mediterranean, the Seyhan Plain, has the potential to be impacted by the alterations to runoff and water availability. Given this lack of understanding of the potential impacts, a study was initiated linking remote sensing based data products, geospatial data analysis, hydro-meteorological time series analysis and hydrological modeling in order to quantify and assess the effect of climate change on water resources. The research presented here shows how improved spatial precipitation data and remotely sensed snow cover distribution as well as spatial data on temperature variability were used to provide information on spatio-temporal snow dynamics and pattern in the upper Seyhan river basin (21720 km2). Since only insufficient precipitation data were available for this region, improved rainfall estimates (IRE), blending satellite precipitation estimates with available stations, were used to develop a spatial precipitation data set for the period from 1975 to 2006 at a 10-days interval. Linking precipitation data to field based snow depth measurements and spatial snow cover identified from multi-temporal metrics based on 57 Envisat MERIS images recorded between March 2003 and September 2005, spatially aggregated total water volumes in the snow pack in selected basins were estimated. In addition, areas of expected cold air pooling were identified in order to improve the temperature station data which are considered important for reliable snow modeling. All hydro-meteorological time series were processed for trend analyses. To quantify whether trends are significant or not a signal to noise ratio (SNR) was calculated as the ratio between the trend and the standard deviations of the anomalies. Using the provided data sets, the distributed, process-oriented J2000 model was utilized to identify runoff generation mechanisms. The model exercises indicate that runoff mechanisms are strongly controlled by snow melt in spring, but also that there is a significant decrease in groundwater recharge comparing the periods 1975-1988 and 1989-2003 which might be associated with land use changes in upper reaches. Evaluating the major water cycle components in the context of climatic trends, it can be shown that i.e. the onset of snow melt will appear earlier in spring which needs to be into account for the management of water resources in the Seyhan River basin.

Assessing the impacts of land use change, especially the role of vegetation, on hydrological resp... more Assessing the impacts of land use change, especially the role of vegetation, on hydrological response from the plot to the catchment scale has become one of the widespread issues of scientific concern,in recent decades. The continuous expansion of urban areas, the dramatic changes in land-cover and land-use patterns and the climate change which have taken place on a global scale explain this increasing interest. Although scientists have long recognized that changes in land use and land cover are important factors affecting water circulation and the spatial-temporal variations in the distribution of water resources, little is known about the quantitative relation between land use/coverage characteristics and runoff generation or processes. Therefore, a better understanding of how land-use changes impact watershed hydrological processes will become a crucial issue for the planning, management, and sustainable development of water resources. In the past decades, abandonment of marginal agricultural land has been a widespread phenomenon in Portugal, as well as in many other countries of Europe, especially in the Mediterranean countries. The abandonment of arable land typically leads to natural succession and to the development of shrub and woodland. Shrubs like Cytisus spp.usually establish in study area. A Quercus pyrenaica Willd. wood generally appears after a long time, about 3 or 4 decades. The general aim of this work is to analyse the temporal evolution of water supplies in a Côa basins (located between 41°00'' N and 40°15'' N and 7°15'' W and 6°55'' W Greenwich)and relate its behaviour with changes undergone by the plant cover and by the main climatic variables (temperatures and precipitation). To achieve this goal, dynamics on the land use and land cover were estimated after the second half of the 20th century. The hydrological response under different land uses and plant covers were monitored during 2005 and 2006, using small permanently establish bounded runoff plots (8×2 m) that drain to a modified Gerlach trough. Regarding the hydrological analysis at basin scale, a study of the temporal evolution of the monthly and annual discharges (Dam3) was made at two measuring stations, between 1956 and 1999. During this period the river was not subjected to the effects of large reservoir and its data on discharges can be considered representative of the natural functioning under a natural regimen. After 2000, the Côa river functioning was submitted to the effect of a large dam. For the analysis of temperatures and precipitation, the monthly and annual series recorded between 1956 and 1999 were used. To check the degree of significance of the trend with a certain level of confidence and to detect correlations among observed variables, a non-parametric test and Pearson coefficient were applied. The obtained results show that an important increase occurred on plant covers between 1960 and 2000; scrub plant communities became the most extensive land cover and the most important vegetation type. When a permanent vegetated cover is dominant surface runoff are very well controlled at plot scale. The major part of rainfall is infiltrated. On a catchment scale, the temporal evolution of the annual discharges has been negative and statistically significant (p-value < 0.05). The correlation coefficient between rainfall and discharges was quite significant for the studied period, which means that river discharges are very sensitive to rainfall amount. Nevertheless, the relationship between the variables seems to have a significant change throughout the analysed period, which is confirmed by the observation of temporal trend in residuals, the product of the year-by-year correlation between rainfall and discharge, and time. In general, residuals behaviour are clearly positive before the 80`s and negative after this date. This temporal variability could be related with changes occurred in land use and land cover.

The GRACE gravity field solutions have been used in several studies to provide some constraint on... more The GRACE gravity field solutions have been used in several studies to provide some constraint on how terrestrial water storage in Australia is changing, especially given the recent drought that has afflicted much of the country for most of the past decade. In this study we look at four regions of Australia, and compare/contrast how GRACE describes the behaviour of the terrestrial water storage. These areas are the Murray-Darling River Basin (MDRB) in the southeast corner of Australia, one of the primary agricultural regions that have been seriously afflicted by the drought, monsoonal Northern Australia, which has seen an increase in terrestrial water storage, the southwest corner of Western Australia (SWWA), another area of regional agricultural importance and the Lake Eyre district, an area that is usually extremely dry, but experiences occasional flooding. We make use of the mascon solutions from the Goddard Space Science Laboratory, and apply principle component analysis to identify the most important spatial and temporal trend variability in the GRACE solutions. These are in turn compared to other datasets, namely ground truth data such as groundwater levels and river gauges from various government agencies (e.g. the Western Australian Department of Water), as well as precipitation data from the Tropical Rainfall Measuring Mission. Loss of mass, interpreted as a decrease in stored terrestrial water, is identified from the GRACE time series for the MRDB and SWWA, while an increase is seen in the monsoonal north, with significant mass fluctuations noted around Lake Eyre which are correlated with flooding events in other parts of Australia, e.g. Queensland.

Hydrological Sciences Journal-journal Des Sciences Hydrologiques, 2011

A critical discussion of recent studies that analysed the effects of climate change on the water ... more A critical discussion of recent studies that analysed the effects of climate change on the water resources of the River Nile Basin (RNB) is presented. First, current water-related issues on the RNB showing the particular vulnerability to environmental changes of this large territory are described. Second, observed trends in hydrological data (such as temperature, precipitation, river discharge) as described in the recent literature are presented. Third, recent modelling exercises to quantify the effects of climate changes on the RNB are critically analysed. The many sources of uncertainty affecting the entire modelling chain, including climate modelling, spatial and temporal downscaling, hydrological modelling and impact assessment are also discussed. In particular, two contrasting issues are discussed: the need to better recognize and characterize the uncertainty of climate change impacts on the hydrology of the RNB, and the necessity to effectively support decision-makers and propose suitable adaptation strategies and measures. The principles of a code of good practice in climate change impact studies based on the explicit handling of various sources of uncertainty are outlined. Citation Di Baldassarre, G., Elshamy, M., van Griensven, A., Soliman, E., Kigobe, M., Ndomba, P., Mutemi, J., Mutua, F., Moges, S., Xuan, J.-Q., Solomatine, D. & Uhlenbrook, S. (2011) Future hydrology and climate in the River Nile basin: a review. Hydrol. Sci. J. 56(2), 199–211.Une discussion critique des études récentes qui ont analysé les effets du changement climatique sur les ressources en eau du bassin du Nil (RNB) est présentée. Premièrement, les problèmes actuels liés à l'eau dans le RNB montrant la vulnérabilité particulière de ce vaste territoire aux changements environnementaux sont décrits. Deuxièmement, les tendances observées dans les données hydrologiques (comme la température, les précipitations, le débit des rivières) sont présentées, telles qu'elles sont décrites dans la littérature récente. Troisièmement, les exercices récents de modélisation quantitative des effets des changements climatiques dans le RNB sont analysés de manière critique. Les nombreuses sources d'incertitude qui affectent toute la chaîne de modélisation, incluant la modélisation du climat, la descente d’échelles spatiale et temporelle, la modélisation hydrologique, et l’évaluation des impacts sont également discutées. En particulier, deux questions contrastées sont discutées: la nécessité de mieux identifier et caractériser l'incertitude des impacts du changement climatique sur l'hydrologie du RNB, et la nécessité de soutenir efficacement les décideurs et de proposer des stratégies d'adaptation et des mesures appropriées. Les principes d'un code de bonnes pratiques dans les études d'impact du changement climatique sont décrits, qui reposent sur le traitement explicite des diverses sources d'incertitude.

River Research and Applications, 2005

Analysis of water discharge and sediment flux data as measured in the Longchuanjiang Basin in the... more Analysis of water discharge and sediment flux data as measured in the Longchuanjiang Basin in the Lower Jinsha tributary over the past few decades has been undertaken. The results of this study indicate that the lower reaches of the Longchuanjiang River produce relatively less runoff but higher sediment loads than the upper reaches. This can be attributed to the differences in climate, the dissected terrain and the sparse vegetation cover of the downstream river. Temporal series analysis suggests a significant increase in sediment flux, notably in the lower reaches of the river. The available data suggest the increasing sediment flux is a result of climate variations and a series of human activities such as land-use changes, mainly through deforestation and agricultural expansion. Other activities, such as road construction, urban expansion, building-material excavation and largescale terrace construction and afforestation, have also contributed to the significant increase in the sediment flux. However, the Longchuanjiang Basin as a whole has a low sediment yield (<1000 t km À2 a À1 ), despite severe soil erosion in the catchment. This is a result of sediment deposition in the numerous reservoirs, constructed since the 1950s. Runoff in the dry season has also significantly declined due to increasing water consumption. These profound changes in the hydrological regime will have significant implications for effective soil erosion and water management. Further studies in the region are necessary to address the impact of these human activities on hydro-geomorphological processes and, particularly, water discharge and sediment flux. Figure 6. Annual rainfall (black line), water discharge and sediment flux (grey lines) over the past 40 years in Xiaohekou and Huangguayuan stations. Thin lines represent actual values and thick line is a 5-year running mean 236 X. X. LU

This study investigated spatial and temporal patterns of trends of the precipitation maxima (defi... more This study investigated spatial and temporal patterns of trends of the precipitation maxima (defined as the annual/seasonal maximum precipitation) in the Yangtze River basin for 1960-2005 using Mann-Kendall trend test, and explored association of changing patterns of the precipitation maxima with large-scale circulation using NCEP/ NCAR reanalysis data. The research results indicate changes of precipitation maxima from relative stable patterns to the significant increasing/decreasing trend in the middle 1970s. With respect to annual variability, the rainy days are decreasing and precipitation intensity is increasing, and significant increasing trend of precipitation intensity was detected in the middle and lower Yangtze River basin. Number of rain days with daily precipitation exceeding 95th and 99th percentiles and related precipitation intensities are in increasing tendency in summer. Large-scale atmospheric circulation analysis indicates decreasing strength of East Asian summer monsoon during 1975-2005 as compared to that during 1961-1974 and increasing geopotential height in the north China, South China Sea and west Pacific regions, all of which combine to negatively impact the northward propagation of the vapor flux. This circulation pattern will be beneficial for the longer stay of the Meiyu front in the Yangtze River basin, leading to more precipitation in the middle and lower 0022-1694/$ -see front matter ª 2007 Published by Elsevier B.V. a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l

Natural Hazards, 2009

Drought is one of the most harmful natural hazards in Gansu Province in Northwest China. The chan... more Drought is one of the most harmful natural hazards in Gansu Province in Northwest China. The changes of precipitation affect the severity of drought. In order to recognize the trend of precipitation and understand the effect of rainfall change on water resources management and drought severity, Mann–Kendall test was used. Standardized Precipitation Index (SPI) was calculated to reconstruct the drought at different time scales and analyze the frequency of drought occurrence in the recent 50 years. The results show that the SPI is applicable in Gansu Province. The number of severe droughts differs among regions: it is more obvious as a 3-month drought in the Yellow River Basin and the Yangtze River Basin than in the Inland River Basin, and other droughts at 6-, 9-, and 12-month time scales have the same effect in the three regions. Mann–Kendall test results show that there is an upward trend in the summer periods and a downward trend in the autumn-winter-spring intervals ranging from 10.5 mm/10 years to −37.4 mm/10 years, which affect the local water resources management, droughts mitigation, and agriculture decision making. This situation poses challenges for future study.

Stochastic Environmental Research and Risk Assessment, 2010

Climate projections for the Huaihe River Basin, China, for the years 2001–2100 are derived from t... more Climate projections for the Huaihe River Basin, China, for the years 2001–2100 are derived from the ECHAM5/MPI-OM model based on observed precipitation and temperature data covering 1964–2007. Streamflow for the Huaihe River under three emission scenarios (SRES-A2, A1B, B1) from 2010 to 2100 is then projected by applying artificial neural networks (ANN). The results show that annual streamflow will change significantly under the three scenarios from 2010 to 2100. The interannual fluctuations cover a significant increasing streamflow trend under the SRES-A2 scenario (2051–2085). The streamflow trend declines gradually under the SRES-A1B scenario (2024–2037), and shows no obvious trend under the SRES-B1 scenario. From 2010 to 2100, the correlation coefficient between the observed and modeled streamflow in SRES-A2 scenario is the best of the three scenarios. Combining SRES-A2 scenario of the ECHAM5 model and ANN might therefore be the best approach for assessing and projecting future water resources in the Huaihe basin and other catchments. Compared to the observed period of streamflows, the projected periodicity of streamflows shows significant changes under different emission scenarios. Under A2 scenario and A1B scenario, the period would delay to about 32–33a and 27–28a, respectively, but under B1 scenario, the period would not change, as it is about 5–6a and the observed period is about 7–8a. All this might affect drought/flood management, water supply and irrigation projects in the Huaihe River basin.

Stochastic Environmental Research and Risk Assessment, 2011

Conventional statistical downscaling techniques for prediction of multi-site rainfall in a river ... more Conventional statistical downscaling techniques for prediction of multi-site rainfall in a river basin fail to capture the correlation between multiple sites and thus are inadequate to model the variability of rainfall. The present study addresses this problem through representation of the pattern of multi-site rainfall using rainfall state in a river basin. A model based on K-means clustering technique coupled with a supervised data classification technique, namely Classification And Regression Tree (CART), is used for generation of rainfall states from large-scale atmospheric variables in a river basin. The K-means clustering is used to derive the daily rainfall state from the historical daily multi-site rainfall data. The optimum number of clusters in the observed rainfall data is obtained after application of various cluster validity measures to the clustered data. The CART model is then trained to establish relationship between the daily rainfall state of the river basin and the standardized, dimensionally-reduced National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis climatic data set. The relationship thus developed is applied to the General Circulation Model (GCM)-simulated, standardized, bias free large-scale climate variables for prediction of rainfall states in future. Comparisons of the number of days falling under different rainfall states for the observed period and the future give the change expected in the river basin due to global warming. The methodology is tested for the Mahanadi river basin in India.

Journal of Hydrology, 2007

The Danjiangkou reservoir lies in the upper Hanjiang basin and is the source of water for the mid... more The Danjiangkou reservoir lies in the upper Hanjiang basin and is the source of water for the middle route of the South-to-North Water Diversion Project (SNWDP) in China. Any significant change in the magnitude or timing of runoff from the Danjiangkou reservoir induced by changes in climatic variables would have significant implications for the economic prosperity of the area in the Hanjiang basin as well as for the South-to-North Water Diversion Project. In this paper the following issues are investigated: (1) Temporal trends of annual and seasonal precipitation and temperature from 1951 to 2003 in the Hanjiang basin are analyzed using the Mann-Kendall and the linear regression methods; spatial distributions of precipitation and temperature are interpolated by the inverse distance weighted interpolation method. (2) Temporal trends of runoff, precipitation and temperature from 1951 to 2003 in the Danjiangkou reservoir, an upper stream basin of the Hanjiang River, are further tested. (3) To assess the impact of climate change on water resources and predict the future runoff change in the Danjiangkou reservoir basin, a two-parameter water balance model is used to simulate the hydrological response for the climate change predicted by GCMs for the region for the period of 2021-2050. a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j h y d r o l