Journal of Hydrologic Engineering

Climatic variables that are used as inputs in hydrologic models often have large measurement uncertainties that are mostly ignored in hydrologic applications because of lack of appropriate tools. This study develops a set of algorithms to engage uncertainty information in three of the most common statistical procedures applied on climatic data, namely correlation (BaNCorr), principal component analysis (VBaNPCA), and regression (VNRVM). These new algorithms are developed within a common framework of Bayesian learning, and together they provide a comprehensive tool to account for uncertainty in various stages of model development. The developed algorithms are first tested and compared with traditional methods and state-of-the-art algorithms on synthetic data. Practical application of the proposed algorithms is demonstrated by developing a seasonal prediction model for all India summer monsoon rainfall by using sea surface temperature (SST) data and associated measurement errors as inputs. The results suggest that incorporating measurement errors in hydrologic models improves their prediction performance and provides better assessment of their predictive capabilities.

Because of the complexity and rapidly occurring changes in the dynamics of human demography and water demands, it is difficult to assess the future adequacy of limited freshwater resources. The planning of water resources largely depends on the meteorological variables (precipitation and evaporation) in terms of their distribution in space and time. Considering precipitation and evaporation as natural input and output without any human intervention for water-resources systems that can be perceived to represent the potential water-resources availability of an area, an uncertainty study was carried out for different water-resources regions in Texas. The entropy method was used for measuring the uncertainty in meteorological variables. It was observed that critical water-deficit regions based on meteorological variables are mostly located in the western part of Texas. The Mann-Kendall test was employed to understand the trend in precipitation, evaporation, and the meteorological excess index (MEI) in deficit and surplus water-resources zones. It was observed that increasing trends exist in both precipitation and evaporation at most of the grids, but the increasing trend of evaporation is more than precipitation in some of the water-resources zones, which is likely to make the deficit regions even more deficient and critical.

The National Weather Service (NWS) maintains a collection of computer models used to perform various functions for managing the rivers of the United States. One function of the NWS's river forecast centers is to provide long-term resource forecasts for the main river basins in the United States. By using singular value decomposition (SVD) analysis, the research presented here identifies a new sea surface temperature (SST) index which demonstrates significant, long-lead covariance with streamflow in the Colorado River Basin. This index is compared with other existing climate indices by using the nonparametric rank sum test and by also using the index in a forecasting scenario.

The question addressed in this study was: do the number and magnitude of dry and wet spells occur in a scale invariant manner in the state of Texas or not? To answer this question, a large set of monthly precipitation data from 75 grid points spread across Texas was employed to investigate the spatial variability in the scaling properties of number and magnitude of dry and wet spells. No coherent regional differences were found. Using a power-law analysis, time-scale properties of dry and wet spells were examined, and power-law coefficients were related to the various truncation levels. A linear relationship was found between fractal dimensions of the numbers of dry and wet spells, whereas power-law coefficients of the magnitude remained constant for all truncation levels. Also, significant low-frequency patterns of precipitation were found when the wavelet transform was used. Generally, interannual cycles were found to be significant for the state of Texas. Low-frequency cycles had no distinguishable impacts on the grid point precipitation values where significant deviations from the power law occurred.

Land surfaces are spatially inhomogeneous at the spatial scales of vegetation canopies to watersheds or even continents. The spatial heterogeneity strongly affects heat, momentum, and vapor exchange at the land surface. It is necessary to consider the spatial heterogeneity of land surface properties in the land surface process modeling that is required for regional hydroclimate models. The main objective of this study is to develop a stochastic upscaling methodology for land surface process modeling for heterogeneous landscapes. Fokker-Planck equation (FPE) as a probabilistic model for land surface processes is formulated in a one-dimensional probability domain for land surface temperature. The numerical solutions of the FPE are validated by Monte Carlo simulations. The validation results are quite encouraging and point toward potential use of this model as a land surface hydrologic model for the two-way nonlinear coupling with a regional atmospheric model to represent the subgrid variability of the land surface processes. Furthermore, in this study, a sensitivity analysis using the FPE was performed to investigate the sensitivity of the spatial variability of land surface temperature to the variance of land surface parameters.

It is necessary to have historical atmospheric data at fine time and spatial grid resolutions as input to watershed-scale models of the Mekong River Basin to perform water balance studies over the basin. However, such historical atmospheric data are not available at the desired fine time-space scales for various reasons in this region. Therefore, it is necessary to reconstruct the atmospheric data over the Mekong River Basin at a fine spatial resolution (approximately 20 km) by means of a regional coupled atmospheric-hydrologic model from the available historical global atmospheric data that have a very coarse resolution (approximately 285 km). The coarse resolution (approximately 285 km) reanalysis of atmospheric data for 1956–2006 from the U.S. National Center for Atmospheric Research (NCAR) and the U.S. National Center for Environmental Prediction (NCEP) were used for the reconstruction of the fine resolution (approximately 20 km) historical atmospheric data over the basin. To incorporate the complex topographical and land surface features of this basin, a regional, fully coupled atmospheric-hydrologic hydro-climate model of the Mekong River Basin, called “RegHCM-Mekong,” was developed for the dynamic downscaling. The coarse time-space resolution NCEP-NCAR historical atmospheric data were then downscaled by RegHCM-Mekong to produce meteorological information on rainfall, air temperature, specific humidity, wind velocity, solar radiation, and net radiation at 0.2 degrees spatial resolution (approximately 20 km) and at hourly intervals over the whole Mekong River Basin during a historical period. After a bias correction of the RegHCM-Mekong-downscaled data (by means of Global Precipitation Climatology Project (GPCP) data), the RegHCM-Mekong-reconstructed historical rainfall fields were successfully validated through comparisons against available point-location observations. The comparisons against the interpolated spatial maps of historical precipitation showed satisfactory results.

The future projections of climate change by means of global climate models of the Earth provide fundamental coarse-grid-resolution hydroclimate data for studies of the effect of climate change on water resources. This paper reports on a study that was performed during 2001–2006, in which the climate change simulations of the coupled global climate model of the Canadian Center for Climate Modeling and Analysis were downscaled by a regional hydroclimate model of Peninsular Malaysia (RegHCM-PM) to the scale of the subregions and watersheds of Peninsular Malaysia (PM), to assess the effect of future climate change on its water resources. On the basis of the simulations of hydroclimatic conditions during the historical period of 1984–1993 and future periods of 2025–2034 and 2041–2050, this report concludes that the overall mean monthly streamflow is approximately the same during both the future period, and the historical period for most of the watersheds of Peninsular Malaysia, except Kelantan and Pahang. In those two watersheds, a significant increase occurs in the overall mean monthly streamflow during the future period. In the future, high flow conditions will be magnified in the Kelantan, Terengganu, Pahang, and Perak River watersheds during the wet months, whereas low monthly flows will be significantly lower in the Selangor and Klang watersheds during the dry months.

This paper presents the improved performance of a regional climate model for the Japan region when a fully coupled boundary layer model and an areally averaged land–surface flow model are employed. It also describes results from the application of the regional climate model to the region for climate-change prediction. An integrated regional-scale hydrological-atmospheric model (IRSHAM) was developed for the Japan region that consisted of a 60-km resolution large-domain model nesting a 20-km resolution small-domain model. The small-domain model was equipped with two-way interaction between the areally averaged land–surface parameterization and the first layer of the atmospheric model. A historical period was then simulated by IRSHAM for local precipitation and other hydrological processes. Simulation results showed a significant improvement in the monsoon-affected regional distribution of monthly precipitation in the Japan region. The simulation results correlated with their counterparts observed at the Tsukuba ground station, showing that IRSHAM performed well in predicting daily meteorological changes. IRSHAM performed another run to simulate local-scale effects of the climate change caused by a doubling of the ${\mathrm{CO}}_2$ concentration based on Meteorological Research Institute general circulation model (GCM) I data. IRSHAM successfully downscaled GCM-I outputs to project local-scale changes in temperature and precipitation over the Japan region.

To establish a basinwide water management plan for the Tigris-Euphrates (TE) watershed, it is necessary to perform rigorous water balance studies of the whole watershed—at least for critical historical drought and flood conditions and under various water resources development scenarios. Water-balance studies over the watershed require climatic and hydrologic data sets, corresponding to historical critical flood and drought periods, at fine time and spatial grid resolutions provide the necessary hydroclimatic information. The Regional Hydroclimate Model of the Tigris-Euphrates (RegHCM-TE) and the associated geographic information system (GIS) were developed to downscale large-scale atmospheric data sets over the TE watershed and to reconstruct the aforementioned climatic and land hydrologic data sets at fine spatial and time increments. In RegHCM-TE, the earth system over the TE watershed is modeled as a fully coupled system of atmospheric processes aloft coupled with the atmospheric boundary layer, land-surface processes, surface and subsurface hydrologic processes, and the interactions among the various hydrologic and atmospheric processes. The parameters of the model are estimated by using existing global and local GIS data. By using the large-scale global historical atmospheric databases as its initial and boundary conditions, RegHCM-TE has been used to reconstruct historical hydroclimate data at a grid size of 15 km over the TE watershed, for which only very sparse hydrologic observations were available. RegHCM-TE and its model validation are described in this paper.

Several case studies of the Tigris-Euphrates (TE) river basin were performed to investigate the effects of various water resource utilizations on dynamic water balances of the watershed. A daily dynamic water balance model was developed to simulate water resource conditions corresponding to four utilization scenarios in the TE watershed: (1) pre-1970 natural conditions; (2) current levels of water resource development/utilization in Syria and Iraq while maintaining pre-1970 conditions in Turkey (i.e., natural, unobstructed flows from Turkey); (3) scenarios involving constant-discharge water release from the Turkish sector downstream on the basis of estimations of future water utilization in the Turkish sector of the TE watershed; and (4) minimum time-varying water releases from Turkey to meet current irrigation water demands in the downstream region. All water balance simulations reconstructed atmospheric and hydrologic conditions during historical critical drought and flood periods. Irrigation demands were estimated by using the Food and Agricultural Organization of the United Nations (FAO) method, with reconstructed atmospheric and crop distribution data derived from satellite observations. Operations of 15 major dams in the Syrian and Iraqi sectors of the TE watershed were dynamically simulated under several different flow regimes regulated and unregulated by the upstream country, Turkey. This study illustrates that irrigation water demands in Iraq and Syria can be effectively met by various constant-discharge water releases from the Turkish sector. Also, if the seasonality of irrigation water demands in the lower TE region is considered when scheduling water releases from Turkey, these releases can be decreased while still meeting the current irrigation water demands of downstream countries. Water diversion from the Tigris to the Euphrates through the Samarra-Thartar complex may provide significant freedom to optimize water allocation in this region. Additionally, because of the arid climate in the lower TE river basin, a considerable amount of water evaporates from the reservoirs. The analyses indicate that storing water in the upstream region seems to be more effective in reducing reservoir water evaporation compared to storing water in the downstream region because the small surface area-to-storage volume of the upstream TE reservoirs and the cooler climate in the upstream sector of the watershed.

The Mesopotamian Marshlands used to be the largest wetland ecosystem in the Middle East and western Eurasia. These marshlands once covered more than 15,000–20,000 sq km with permanent lakes and marshes, seasonal marshes, and temporary marshes. Although the recent restoration efforts returned the marshes back to approximately 39% of their original spatial extent, the artificial drainage works have significantly reduced the marshes during the late 1980s and 1990s. The water resources development/utilization in the upstream regions of the Tigris-Euphrates (TE) River Basin has been considered as one of the causes for the damage of the marshland ecosystem. To assess the hydrologic conditions in the Mesopotamian Marshes under various water utilization scenarios, a marshland hydrologic model for the Hawr Al Hammar Marshes near the downstream end of the TE River Network has been developed in conjunction with the regional hydro-climate model of Tigris-Euphrates (RegHCMTE) Watershed and the water resources system model of the Euphrates-Tigris River Basin. This marshland hydrologic model accounts for rainfall, evapotranspiration, surface water inflows and outflows, and soil water inflows and outflows. In this paper, the marshland hydrologic model for the Hawr Al Hammar Marshes is described, and the reconstruction of historical marshland hydrologic data over Hawr Al Hammar Marshes by using the coupled TE modeling system is presented. By using the developed Mesopotamia Marsh model, the impact of various water resources utilization alternatives in the TE Basin on the hydrology of the Hawr Al Hammar marshes is quantified. The simulation results reveal that by treating the TE Basin as one hydrologic unit, where water is transferred from the Tigris to the Euphrates River to meet the irrigation water demands in the basin for various release scenarios from the Turkish sector, it is possible to sustain the Al Hammar Marshes at their pre-dam-construction (pre-1970) conditions in the TE Basin under severe hydro-climate conditions of the historical critical dry period.