Shafiqul Islam - Academia.edu (original) (raw)

Papers by Shafiqul Islam

Proceedings of the 19th ACM SIGKDD international conference on Knowledge discovery and data mining, 2013

The development of disastrous flood forecasting techniques able to provide warnings at a long lea... more The development of disastrous flood forecasting techniques able to provide warnings at a long lead-time (5-15 days) is of great importance to society. Extreme Flood is usually a consequence of a sequence of precipitation events occurring over from several days to several weeks. Though precise shortterm forecasting the magnitude and extent of individual precipitation event is still beyond our reach, long-term forecasting of precipitation clusters can be attempted by identifying persistent atmospheric regimes that are conducive for the precipitation clusters. However, such forecasting will suffer from overwhelming number of relevant features and high imbalance of sample sets. In this paper, we propose an integrated data mining framework for identifying the precursors to precipitation event clusters and use this information to predict extended periods of extreme precipitation and subsequent floods. We synthesize a representative feature set that describes the atmosphere motion, and apply a streaming feature selection algorithm to online identify the precipitation precursors from the enormous feature space. A hierarchical

Remote Sensing of Environment, 2008

We present a new formulation to derive evaporative fraction (EF) and evapotranspiration (ET) maps... more We present a new formulation to derive evaporative fraction (EF) and evapotranspiration (ET) maps from remotely sensed data without auxiliary relationships or site-specific relationships. This formulation is based on Granger's complementary relationship and Priestley-Taylor's equation. The proposed model eliminates the wind function and resistance parameters commonly applied to ET calculation by including a relative evaporation parameter (ET/Epot). By combining this relative evaporation parameter, Granger's complementary relationship and Priestley-Taylor equation, we obtain a simple equation to estimate ET. We tested and validated the proposed formulation over the Southern Great Plains (SGP) region of the United States for seven clear sky days during March-October 2003. MODIS Atmospheric and Land products were the only source of data used in this study. Estimates of ET show an overall root mean square error and bias of 33.89 and −10.96 Wm − 2 , respectively. Our results suggest that the proposed approach is robust and valid for a wide range of atmospheric and surface conditions.

Water Resources Research, 1988

This paper presents the multidimensional representation of the cumulative rainfall process and de... more This paper presents the multidimensional representation of the cumulative rainfall process and derives a closed-form expression for the mean and space-time covariance functions. A parameter estimation procedure is developed. Sensitivity analysis provides useful information for ...

Water Resources Research, 1989

Science, 2002

High levels of arsenic in well water are causing widespread poisoning in Bangladesh. In a typical... more High levels of arsenic in well water are causing widespread poisoning in Bangladesh. In a typical aquifer in southern Bangladesh, chemical data imply that arsenic mobilization is associated with recent inflow of carbon. High concentrations of radiocarbon-young methane indicate that young carbon has driven recent biogeochemical processes, and irrigation pumping is sufficient to have drawn water to the depth where dissolved arsenic is at a maximum. The results of field injection of molasses, nitrate, and low-arsenic water show that organic carbon or its degradation products may quickly mobilize arsenic, oxidants may lower arsenic concentrations, and sorption of arsenic is limited by saturation of aquifer materials.

Remote Sensing of Environment, 2004

Remote sensing cannot provide a direct measurement of evapotranspiration (ET) but it can provide ... more Remote sensing cannot provide a direct measurement of evapotranspiration (ET) but it can provide a reasonably good estimate of Evaporative Fraction (EF), defined as the ratio of ET and available energy. Recent studies have successfully estimated EF using a contextual interpretation ...

Journal of Geophysical Research: Atmospheres, 2000

Several recent studies have shown that a remarkably wide variety of natural systems display fluct... more Several recent studies have shown that a remarkably wide variety of natural systems display fluctuations that may be characterized by long-range power-law correlations. Such correlations hint toward fractal geometry of the underlying dynamical system. Existence and ...

International Journal of Remote Sensing, 2003

In-situ observation, climate reanalyses, and satellite remote sensing are used to study the annua... more In-situ observation, climate reanalyses, and satellite remote sensing are used to study the annual cycle of turbulent latent heat flux (LHF) in the Agulhas Current system. We assess if the datasets do represent the intense exchange of moisture that occurs above the Agulhas Current and the Retroflection region, especially the new reanalyses as the former, the National Centers for Environmental Prediction Reanalysis 2 (NCEP2) and the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis second-generation reanalysis (ERA-40) have lower sea and less distinct surface temperature (SST) in the Agulhas Current system due to their low spatial resolution thus do not adequately represent the Agulhas Current LHF. We use monthly fields of LHF, SST, surface wind speed, saturated specific humidity at the sea surface (Qss), and specific humidity at 10 m (Qa). The Climate Forecast System Reanalysis (CFSR), the European Centre for Medium-Range Weather Forecast fifth generation (ERA-5), and the Modern-Era Retrospective analysis for Research and Applications version-2 (MERRA-2) are similar to the air-sea turbulent fluxes (SEAFLUX) and do represent the signature of the Agulhas Current. ERA-Interim underestimates the LHF due to lower surface wind speeds than other datasets. The observation-based National Oceanography Center Southampton (NOCS) dataset is different from all other datasets. The highest LHF of 250 W/m 2 is found in the Retroflection in winter. The lowest LHF (~100 W/m 2) is off Port Elizabeth in summer. East of the Agulhas Current, Qss-Qa is the main driver of the amplitude of the annual cycle of LHF, while it is the wind speed in the Retroflection and both Qss-Qa and wind speed in between. The difference in LHF between product are due to differences in Qss-Qa wind speed and resolution of datasets.

Global and Planetary Change, 2009

Water resources and agricultural applications require the knowledge of evapotranspiration (ET) ov... more Water resources and agricultural applications require the knowledge of evapotranspiration (ET) over a range of spatial and temporal scales. Due to paucity of surface based hydro-meteorological stations, the spatial resolution of ET estimates is fairly coarse and is not particularly suitable or reliable for hydrologic modeling, water resources planning and decision making. An ET estimation algorithm has been developed by combining data from satellite and ground observations. The method extends the applicability of a commonly used energy balance formulation of ET and utilizes the contextual relationship between remotely sensed surface temperature and vegetation index. The required parameters are derived from the Advanced Very High Resolution Radiometer (AVHRR) aboard NOAA-14 satellite. First, the Evaporative Fraction (EF) is estimated by utilizing the relationship between a vegetation index and radiometric surface temperature observed from AVHRR for each day. Then spatio-temporal interpolation and filtering techniques are applied to obtain daily EF values for cloudy pixels to produce the EF map for the entire region. Daily Actual ET (DAET) maps are derived from these EF maps and net radiation maps obtained from ground-based observations. The comparisons between satellite derived DAET and ground measurements showed overall low bias and rootmean-square-error for both clear and cloudy days at South Florida in 1998 and 1999. The proposed satellitebased DAET (SatDAET) algorithm has its EF component primarily estimated from satellite data and the resulting DAET has been validated using multi-year ground observations over the South Florida region. The SatDAET algorithm appears to be robust and has the potential to provide near real-time land surface evapotranspiration monitoring over large heterogeneous areas at a very fine spatial and temporal resolution.

Geophysical Research Letters, 2006

We have identified a dipole in annual precipitation across eastern North America (ENA) east of 10... more We have identified a dipole in annual precipitation across eastern North America (ENA) east of 100°W between 30°N and 60°N. This dipole appears to create spatially coherent opposing variations in precipitation with a separation of the two regions around 45°N. Annual average precipitation over ENA appears to be stable and unimodal, suggesting that the amount of overall precipitation variability is a small fraction of the mean and is largely determined by similar large scale processes. Analysis of regional average time series at interannual (3-7 year) and decadal (10-16 year) scales indicates that the dipole over the ENA region is most clearly discernible at the decadal scale. Linear regression analysis between global sea surface temperatures (SSTs) and precipitation over the two subregions in ENA suggests that SST variations in several areas of the oceans tend to be associated with opposite precipitation anomalies in the two subregions of ENA.

Comptes Rendus Geoscience, 2005

Written on invitation of the Editorial Board. ... Over the last several decades, much of populati... more Written on invitation of the Editorial Board. ... Over the last several decades, much of population of Bangladesh and West Bengal switched their water supply from surface water to groundwater. Tragically, much of the region's groundwater is dangerously contaminated ...

Canadian Journal of Remote Sensing, 2004

L'estimation précise des flux d'énergie de surface est essentielle pour diverses applic... more L'estimation précise des flux d'énergie de surface est essentielle pour diverses applications hydrologiques, météorologiques, agricoles et écologiques. Au cours des années, une grande variété de systèmes instrumentaux et de méthodologies d'estimation ont été développés ...

Bulletin of the World Health Organization, 2012

Atmospheric Environment, 1994

Dominant degrees of freedom of surface ozone pollution dynamics have been determined in Cairo and... more Dominant degrees of freedom of surface ozone pollution dynamics have been determined in Cairo and Qena/ Egypt during the period 2001-2003. The results showed that the dominant degrees of freedom are 2 for both Cairo and Qena. Indicating that there are two dominant variables affecting surface ozone concentrations in the both two cities. The appointment of these two factors requires applying photochemical models and other measurements of surface ozone precursors. Temperature and wind speed were found to maybe the main two parameters affecting SOC in the two cities.

The IPCC AR4 report projects that atmospheric moisture transport and convergence are likely to in... more The IPCC AR4 report projects that atmospheric moisture transport and convergence are likely to increase over the central and northern regions of North America, resulting in a widespread increase in annual precipitation over this region of the continent. However, the uncertainty around projected changes in regional precipitation among the models used in the assessment and between the various emissions scenarios is large. In general circulation models, changes in global mean evaporation closely balance changes in precipitation. This is not true locally where changes in the large-scale atmospheric transport of water vapor produce significant regional variability. Identifying the primary atmospheric controls on the large-scale transport of moisture is therefore crucial for reducing the uncertainty in regional estimates of precipitation over North America. Most studies of regional surface climate anomalies focus on winter when the global or regional teleconnection patterns such as the Pacific North America (PNA) pattern and North Atlantic Oscillation (NAO) are most active. Few studies examine climate variability in seasons other than winter. Yet, observational evidence suggests that fall is the only season in which the total precipitation and stream flow have increased across the central U.S. over the last several decades. This apparent oversight motivates our diagnostic study to identify the dominant mechanism that controls the moisture flux into the central United States on decadal and longer scales in fall and how it differs from winter. In this study, we create an index of the moisture flux over the central United States from the Gulf of Mexico using observations to identify the signature of a remote forcing on the moisture flux in fall and winter and relate it to trends and decadal variations in precipitation. We then repeat the analysis using model data from the climate of the 20th century runs of the IPCC AR4 experiments to assess how well the models capture the observed trends and decadal variations in the moisture transport and how this effects the model trends in precipitation. The results indicate that the large-scale teleconnections associated with the dominant mode of the meridional moisture flux variability in fall and winter is quite different. In fall, the leading mode of the meridional moisture flux includes a trend and a 12-15 year signal. In winter, the timescale is approximately 20 years and exhibits no trend. The analysis of the associated 300mb stream function anomalies indicates that the fall moisture flux is associated with a wave train that originates in the western tropical Pacific near Indonesia that spans the Pacific North America and north Atlantic regions. In winter, the leading pattern of the moisture flux variability appears to be associated with the PNA teleconnection. The difficulty of the AR4 models in reproducing the observed modes of fall and winter moisture flux and precipitation is discussed.

ABSTRACT An algorithm is developed for estimation of actual evapotranspiration (ET) for all sky c... more ABSTRACT An algorithm is developed for estimation of actual evapotranspiration (ET) for all sky conditions using primarily remote sensing data. Our approach is based on an extension of the Priestley-Taylor equation, a contextual interpretation of remotely sensed surface temperature and vegetation index, and estimation of net radiation from remotely sensed data. For cloud free days, net radiation is computed using MODIS-Terra data and a simple sinusoidal model to obtain the diurnal variation of radiation. If a particular day is cloudy for a MODIS-Terra pixel, we use data from MODIS-Aqua which has a different orbital pass time. If a pixel is cloudy for Terra and Aqua overpass times, then a set of regression relationships are used to estimate net radiation and surface temperature. For cloudy days, the algorithm first computes the shortwave radiation using a regression model between clear sky shortwave radiation and cloud fraction. Then, net radiation is computed using a linear regression model between estimated shortwave radiation for cloudy days. Surface temperature is estimated using regression model between calculated net radiation and cloud cover. Once the surface temperature is estimated, a contextual interpretation of surface temperature and vegetation index is used to obtain ET. Results from calibration and validation of the proposed ET estimation algorithm for all sky conditions over the Southern Great Plains will be presented.

Journal of Applied Meteorology, 1993

Water Policy, 2020

The question of how to govern and manage transboundary river basin for competing and often confli... more The question of how to govern and manage transboundary river basin for competing and often conflicting demands due to limited supplies continues to be an issue of concern, conflict, and cooperation. A key novelty of this paper is the use of the Water Diplomacy Framework (WDF) to address supply-demand mismatch using the notion of collaborative problem-solving and joint fact-finding. It builds on innovative applications of game-theoretic approaches and uses equity and sustainability as guiding principles to address the supply-demand mismatch. Five different bankruptcy methods (net benefit ranges between US$17,462M to US$18,201M) and the Nash Bargaining Solution (net benefit ranges between US$18,132M to US$19,216M) are used to resolve supply-demand mismatch in the Indus basin among four provinces within Pakistan. The maximum total benefit generated from the Nash Bargaining Solution is 5.5% higher compared to the best bankruptcy method. Moving from the non-cooperative and rule-based ban...

Geophysical Research Letters, 2006

International Journal of Climatology, 1998

ABSTRACT An analytical approach is presented to study the effects of spatial heterogeneity of lan... more ABSTRACT An analytical approach is presented to study the effects of spatial heterogeneity of land surface parameters in climate models. This approach does not use any parametric probability density functions for land surface parameters and attempts to account for the effects of subgrid heterogeneity by using grid-level parameters and correlation between parameters. The adequacy of the approach is illustrated by using the influence of spatial variability in soil wetness and temperature on evaporation. It is shown that both the stability of the lower atmosphere and the surface soil wetness conditions could introduce non-linearity in the estimation of grid-scale evaporation. For stable and near neutral conditions, the heterogeneity in surface temperature plays an important role in the estimation of grid-level latent heat flux. The heterogeneous effect of soil wetness is found to be important when the soil is under moisture constraint. With increasing soil wetness, heterogeneous effects of soil wetness diminish and become negligible as we approach saturation. It appears that effects of temperature and soil moisture heterogeneity effects are an order of magnitude larger compared with correlative effects of temperature and soil moisture for a range of soil wetness and temperature conditions. The subtle difficulties associated with non-linear and coupled influence of soil wetness and atmospheric stability on evaporation preclude the use of any simple aggregation procedure to represent subgrid-scale effects in climate models.

Proceedings of the 19th ACM SIGKDD international conference on Knowledge discovery and data mining, 2013

The development of disastrous flood forecasting techniques able to provide warnings at a long lea... more The development of disastrous flood forecasting techniques able to provide warnings at a long lead-time (5-15 days) is of great importance to society. Extreme Flood is usually a consequence of a sequence of precipitation events occurring over from several days to several weeks. Though precise shortterm forecasting the magnitude and extent of individual precipitation event is still beyond our reach, long-term forecasting of precipitation clusters can be attempted by identifying persistent atmospheric regimes that are conducive for the precipitation clusters. However, such forecasting will suffer from overwhelming number of relevant features and high imbalance of sample sets. In this paper, we propose an integrated data mining framework for identifying the precursors to precipitation event clusters and use this information to predict extended periods of extreme precipitation and subsequent floods. We synthesize a representative feature set that describes the atmosphere motion, and apply a streaming feature selection algorithm to online identify the precipitation precursors from the enormous feature space. A hierarchical

Remote Sensing of Environment, 2008

We present a new formulation to derive evaporative fraction (EF) and evapotranspiration (ET) maps... more We present a new formulation to derive evaporative fraction (EF) and evapotranspiration (ET) maps from remotely sensed data without auxiliary relationships or site-specific relationships. This formulation is based on Granger's complementary relationship and Priestley-Taylor's equation. The proposed model eliminates the wind function and resistance parameters commonly applied to ET calculation by including a relative evaporation parameter (ET/Epot). By combining this relative evaporation parameter, Granger's complementary relationship and Priestley-Taylor equation, we obtain a simple equation to estimate ET. We tested and validated the proposed formulation over the Southern Great Plains (SGP) region of the United States for seven clear sky days during March-October 2003. MODIS Atmospheric and Land products were the only source of data used in this study. Estimates of ET show an overall root mean square error and bias of 33.89 and −10.96 Wm − 2 , respectively. Our results suggest that the proposed approach is robust and valid for a wide range of atmospheric and surface conditions.

Water Resources Research, 1988

This paper presents the multidimensional representation of the cumulative rainfall process and de... more This paper presents the multidimensional representation of the cumulative rainfall process and derives a closed-form expression for the mean and space-time covariance functions. A parameter estimation procedure is developed. Sensitivity analysis provides useful information for ...

Water Resources Research, 1989

Science, 2002

High levels of arsenic in well water are causing widespread poisoning in Bangladesh. In a typical... more High levels of arsenic in well water are causing widespread poisoning in Bangladesh. In a typical aquifer in southern Bangladesh, chemical data imply that arsenic mobilization is associated with recent inflow of carbon. High concentrations of radiocarbon-young methane indicate that young carbon has driven recent biogeochemical processes, and irrigation pumping is sufficient to have drawn water to the depth where dissolved arsenic is at a maximum. The results of field injection of molasses, nitrate, and low-arsenic water show that organic carbon or its degradation products may quickly mobilize arsenic, oxidants may lower arsenic concentrations, and sorption of arsenic is limited by saturation of aquifer materials.

Remote Sensing of Environment, 2004

Remote sensing cannot provide a direct measurement of evapotranspiration (ET) but it can provide ... more Remote sensing cannot provide a direct measurement of evapotranspiration (ET) but it can provide a reasonably good estimate of Evaporative Fraction (EF), defined as the ratio of ET and available energy. Recent studies have successfully estimated EF using a contextual interpretation ...

Journal of Geophysical Research: Atmospheres, 2000

Several recent studies have shown that a remarkably wide variety of natural systems display fluct... more Several recent studies have shown that a remarkably wide variety of natural systems display fluctuations that may be characterized by long-range power-law correlations. Such correlations hint toward fractal geometry of the underlying dynamical system. Existence and ...

International Journal of Remote Sensing, 2003

In-situ observation, climate reanalyses, and satellite remote sensing are used to study the annua... more In-situ observation, climate reanalyses, and satellite remote sensing are used to study the annual cycle of turbulent latent heat flux (LHF) in the Agulhas Current system. We assess if the datasets do represent the intense exchange of moisture that occurs above the Agulhas Current and the Retroflection region, especially the new reanalyses as the former, the National Centers for Environmental Prediction Reanalysis 2 (NCEP2) and the European Centre for Medium-Range Weather Forecast (ECMWF) reanalysis second-generation reanalysis (ERA-40) have lower sea and less distinct surface temperature (SST) in the Agulhas Current system due to their low spatial resolution thus do not adequately represent the Agulhas Current LHF. We use monthly fields of LHF, SST, surface wind speed, saturated specific humidity at the sea surface (Qss), and specific humidity at 10 m (Qa). The Climate Forecast System Reanalysis (CFSR), the European Centre for Medium-Range Weather Forecast fifth generation (ERA-5), and the Modern-Era Retrospective analysis for Research and Applications version-2 (MERRA-2) are similar to the air-sea turbulent fluxes (SEAFLUX) and do represent the signature of the Agulhas Current. ERA-Interim underestimates the LHF due to lower surface wind speeds than other datasets. The observation-based National Oceanography Center Southampton (NOCS) dataset is different from all other datasets. The highest LHF of 250 W/m 2 is found in the Retroflection in winter. The lowest LHF (~100 W/m 2) is off Port Elizabeth in summer. East of the Agulhas Current, Qss-Qa is the main driver of the amplitude of the annual cycle of LHF, while it is the wind speed in the Retroflection and both Qss-Qa and wind speed in between. The difference in LHF between product are due to differences in Qss-Qa wind speed and resolution of datasets.

Global and Planetary Change, 2009

Water resources and agricultural applications require the knowledge of evapotranspiration (ET) ov... more Water resources and agricultural applications require the knowledge of evapotranspiration (ET) over a range of spatial and temporal scales. Due to paucity of surface based hydro-meteorological stations, the spatial resolution of ET estimates is fairly coarse and is not particularly suitable or reliable for hydrologic modeling, water resources planning and decision making. An ET estimation algorithm has been developed by combining data from satellite and ground observations. The method extends the applicability of a commonly used energy balance formulation of ET and utilizes the contextual relationship between remotely sensed surface temperature and vegetation index. The required parameters are derived from the Advanced Very High Resolution Radiometer (AVHRR) aboard NOAA-14 satellite. First, the Evaporative Fraction (EF) is estimated by utilizing the relationship between a vegetation index and radiometric surface temperature observed from AVHRR for each day. Then spatio-temporal interpolation and filtering techniques are applied to obtain daily EF values for cloudy pixels to produce the EF map for the entire region. Daily Actual ET (DAET) maps are derived from these EF maps and net radiation maps obtained from ground-based observations. The comparisons between satellite derived DAET and ground measurements showed overall low bias and rootmean-square-error for both clear and cloudy days at South Florida in 1998 and 1999. The proposed satellitebased DAET (SatDAET) algorithm has its EF component primarily estimated from satellite data and the resulting DAET has been validated using multi-year ground observations over the South Florida region. The SatDAET algorithm appears to be robust and has the potential to provide near real-time land surface evapotranspiration monitoring over large heterogeneous areas at a very fine spatial and temporal resolution.

Geophysical Research Letters, 2006

We have identified a dipole in annual precipitation across eastern North America (ENA) east of 10... more We have identified a dipole in annual precipitation across eastern North America (ENA) east of 100°W between 30°N and 60°N. This dipole appears to create spatially coherent opposing variations in precipitation with a separation of the two regions around 45°N. Annual average precipitation over ENA appears to be stable and unimodal, suggesting that the amount of overall precipitation variability is a small fraction of the mean and is largely determined by similar large scale processes. Analysis of regional average time series at interannual (3-7 year) and decadal (10-16 year) scales indicates that the dipole over the ENA region is most clearly discernible at the decadal scale. Linear regression analysis between global sea surface temperatures (SSTs) and precipitation over the two subregions in ENA suggests that SST variations in several areas of the oceans tend to be associated with opposite precipitation anomalies in the two subregions of ENA.

Comptes Rendus Geoscience, 2005

Written on invitation of the Editorial Board. ... Over the last several decades, much of populati... more Written on invitation of the Editorial Board. ... Over the last several decades, much of population of Bangladesh and West Bengal switched their water supply from surface water to groundwater. Tragically, much of the region's groundwater is dangerously contaminated ...

Canadian Journal of Remote Sensing, 2004

L'estimation précise des flux d'énergie de surface est essentielle pour diverses applic... more L'estimation précise des flux d'énergie de surface est essentielle pour diverses applications hydrologiques, météorologiques, agricoles et écologiques. Au cours des années, une grande variété de systèmes instrumentaux et de méthodologies d'estimation ont été développés ...

Bulletin of the World Health Organization, 2012

Atmospheric Environment, 1994

Dominant degrees of freedom of surface ozone pollution dynamics have been determined in Cairo and... more Dominant degrees of freedom of surface ozone pollution dynamics have been determined in Cairo and Qena/ Egypt during the period 2001-2003. The results showed that the dominant degrees of freedom are 2 for both Cairo and Qena. Indicating that there are two dominant variables affecting surface ozone concentrations in the both two cities. The appointment of these two factors requires applying photochemical models and other measurements of surface ozone precursors. Temperature and wind speed were found to maybe the main two parameters affecting SOC in the two cities.

The IPCC AR4 report projects that atmospheric moisture transport and convergence are likely to in... more The IPCC AR4 report projects that atmospheric moisture transport and convergence are likely to increase over the central and northern regions of North America, resulting in a widespread increase in annual precipitation over this region of the continent. However, the uncertainty around projected changes in regional precipitation among the models used in the assessment and between the various emissions scenarios is large. In general circulation models, changes in global mean evaporation closely balance changes in precipitation. This is not true locally where changes in the large-scale atmospheric transport of water vapor produce significant regional variability. Identifying the primary atmospheric controls on the large-scale transport of moisture is therefore crucial for reducing the uncertainty in regional estimates of precipitation over North America. Most studies of regional surface climate anomalies focus on winter when the global or regional teleconnection patterns such as the Pacific North America (PNA) pattern and North Atlantic Oscillation (NAO) are most active. Few studies examine climate variability in seasons other than winter. Yet, observational evidence suggests that fall is the only season in which the total precipitation and stream flow have increased across the central U.S. over the last several decades. This apparent oversight motivates our diagnostic study to identify the dominant mechanism that controls the moisture flux into the central United States on decadal and longer scales in fall and how it differs from winter. In this study, we create an index of the moisture flux over the central United States from the Gulf of Mexico using observations to identify the signature of a remote forcing on the moisture flux in fall and winter and relate it to trends and decadal variations in precipitation. We then repeat the analysis using model data from the climate of the 20th century runs of the IPCC AR4 experiments to assess how well the models capture the observed trends and decadal variations in the moisture transport and how this effects the model trends in precipitation. The results indicate that the large-scale teleconnections associated with the dominant mode of the meridional moisture flux variability in fall and winter is quite different. In fall, the leading mode of the meridional moisture flux includes a trend and a 12-15 year signal. In winter, the timescale is approximately 20 years and exhibits no trend. The analysis of the associated 300mb stream function anomalies indicates that the fall moisture flux is associated with a wave train that originates in the western tropical Pacific near Indonesia that spans the Pacific North America and north Atlantic regions. In winter, the leading pattern of the moisture flux variability appears to be associated with the PNA teleconnection. The difficulty of the AR4 models in reproducing the observed modes of fall and winter moisture flux and precipitation is discussed.

ABSTRACT An algorithm is developed for estimation of actual evapotranspiration (ET) for all sky c... more ABSTRACT An algorithm is developed for estimation of actual evapotranspiration (ET) for all sky conditions using primarily remote sensing data. Our approach is based on an extension of the Priestley-Taylor equation, a contextual interpretation of remotely sensed surface temperature and vegetation index, and estimation of net radiation from remotely sensed data. For cloud free days, net radiation is computed using MODIS-Terra data and a simple sinusoidal model to obtain the diurnal variation of radiation. If a particular day is cloudy for a MODIS-Terra pixel, we use data from MODIS-Aqua which has a different orbital pass time. If a pixel is cloudy for Terra and Aqua overpass times, then a set of regression relationships are used to estimate net radiation and surface temperature. For cloudy days, the algorithm first computes the shortwave radiation using a regression model between clear sky shortwave radiation and cloud fraction. Then, net radiation is computed using a linear regression model between estimated shortwave radiation for cloudy days. Surface temperature is estimated using regression model between calculated net radiation and cloud cover. Once the surface temperature is estimated, a contextual interpretation of surface temperature and vegetation index is used to obtain ET. Results from calibration and validation of the proposed ET estimation algorithm for all sky conditions over the Southern Great Plains will be presented.

Journal of Applied Meteorology, 1993

Water Policy, 2020

The question of how to govern and manage transboundary river basin for competing and often confli... more The question of how to govern and manage transboundary river basin for competing and often conflicting demands due to limited supplies continues to be an issue of concern, conflict, and cooperation. A key novelty of this paper is the use of the Water Diplomacy Framework (WDF) to address supply-demand mismatch using the notion of collaborative problem-solving and joint fact-finding. It builds on innovative applications of game-theoretic approaches and uses equity and sustainability as guiding principles to address the supply-demand mismatch. Five different bankruptcy methods (net benefit ranges between US$17,462M to US$18,201M) and the Nash Bargaining Solution (net benefit ranges between US$18,132M to US$19,216M) are used to resolve supply-demand mismatch in the Indus basin among four provinces within Pakistan. The maximum total benefit generated from the Nash Bargaining Solution is 5.5% higher compared to the best bankruptcy method. Moving from the non-cooperative and rule-based ban...

Geophysical Research Letters, 2006

International Journal of Climatology, 1998

ABSTRACT An analytical approach is presented to study the effects of spatial heterogeneity of lan... more ABSTRACT An analytical approach is presented to study the effects of spatial heterogeneity of land surface parameters in climate models. This approach does not use any parametric probability density functions for land surface parameters and attempts to account for the effects of subgrid heterogeneity by using grid-level parameters and correlation between parameters. The adequacy of the approach is illustrated by using the influence of spatial variability in soil wetness and temperature on evaporation. It is shown that both the stability of the lower atmosphere and the surface soil wetness conditions could introduce non-linearity in the estimation of grid-scale evaporation. For stable and near neutral conditions, the heterogeneity in surface temperature plays an important role in the estimation of grid-level latent heat flux. The heterogeneous effect of soil wetness is found to be important when the soil is under moisture constraint. With increasing soil wetness, heterogeneous effects of soil wetness diminish and become negligible as we approach saturation. It appears that effects of temperature and soil moisture heterogeneity effects are an order of magnitude larger compared with correlative effects of temperature and soil moisture for a range of soil wetness and temperature conditions. The subtle difficulties associated with non-linear and coupled influence of soil wetness and atmospheric stability on evaporation preclude the use of any simple aggregation procedure to represent subgrid-scale effects in climate models.