Historical changes in hydroclimatic characteristics in four Lower Colorado River sub-basins are examined using the Mann-Kendall test for trends and Kendall's tau-b test for statistical association to better understand the processes taking place in these arid watersheds. During the historical record of 1906-2007, in general, temperatures have increased and streamflows have decreased while there has been no change in precipitation. Streamflow was found to have statistical association with annual maximum temperatures, El Nino/Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). Using this knowledge, two-year and five-year streamflow predictions are made using climate data to force a statistical model. We find no predictive skill at the two-year range but significant (alpha =.05) predictive skill in two of the basins at the five-year range. The dominant climate predictor for the Paria River Basin is ENSO and for the Little Colorado River Basin it is temperature.

Global flood forecasting can benefit developing countries and ungauged regions that lack observational data, computational infrastructure, and human capacity for streamflow modeling. Many technical challenges exist to provide flood predictions on a global scale. First, existing land surface forecasts use coarse resolution grid cells, which provide limited information when used for flood forecasting at local scales. There is, so far, no modeling system that can provide rapid and accurate global flood predictions with low cost. Second, accurate flood predictions often require integrating interdisciplinary models, data sources, and analysis routines into a workflow. Limited accessibility, reusability, and interoperability of models restrict integrated modeling from producing more reliable results. Web services have been demonstrated as an effective way for data and model sharing because of the capability of enabling communication among heterogeneous applications over the internet. However, publishing models or analysis routines as web services is still challenging and, hence, is not commonly done. To address the above challenges, I present a computational system for global streamflow prediction, using existing, well-established open source software tools, that quickly downscales the runoff generated from such coarse grid-based land surface models (LSMs) onto high-resolution vector-based stream networks then routes the results using a vector-based river routing model. A set of experiments are conducted to demonstrate the feasibility and credibility of this approach. I also present a tool to publish complex environmental models as web services by adopting the OpenGMS Wrapper System (OGMS-WS) and Docker. The streamflow prediction system is deployed as a web service using this tool, and the service is used to analyze the historical streamflow tendency in Bangladesh. Next, I present a ready-to-use tool called Tethys WPS Server, which provides a simplified and formalized way to expose web app functionality as standardized Open Geospatial Consortium (OGC) Web Processing Services (WPS) alongside a web app's graphical user interface. Three Tethys web apps are developed to demonstrate how web app functionality(s) can be exposed as WPS using Tethys WPS Server, and to show how these WPS can be coupled to build a complex modeling web app. In sum, this dissertation explores new computational approaches and software tools to advance global streamflow prediction and integrated environmental modeling.

The growing pressure on the world‘s fresh water resources is enforced by population growth that leads to conflicts between demands for different purposes. A main concern on water use is the conflict between the environment and other purposes like hydropower, irrigation for agriculture and domestic and industry water supply, where total flows are diverted without releasing water for ecological conservation. As a consequence, some of the common problems related to water faced by many countries are shortage, quality deterioration and flood impacts. Hence, utilization of integrated water resources management in a single system, which is built up by river basin, is an optimum way to handle the question of water. However, in many areas, when planning for balancing water demands major gaps exist on baseline knowledge of water resources. In order to bridge these gaps, hydro-logical models are among the available tools used to acquire adequate understanding of the characteristics of the river basin. Apart from forecasting and predicting the quantity and quality of water for decision makers, some models could also help in predicting the impacts of natural and anthropogenic changes on water resources and also in quantifying the spatial and temporal availability of the resources. However, main challenges lie in choosing and utilizing these models for a specific basin and managerial plan. In this study, an analysis of the different types of models and application of a selected model to characterize the Awash River basin, located in Ethiopia, is presented. The results from the modeling procedure and the performance of the model are discussed. The different possible sources of uncertainties in the modeling process are also discussed. The results indicate dissimilar predictions in using different methods; hence proper care must be taken in selecting and employing available methods for a specific watershed prior to presenting the results to decision makers. / QC 20110516

General Circulation Models (GCMs) are tools designed to simulate time series of climate variables globally, accounting for effects of greenhouse gases in the atmosphere. They attempt to represent the physical processes in the atmosphere, ocean, cryosphere and land surface. They are currently the most credible tools available for simulating the response of the global climate system to increasing greenhouse gas concentrations, and to provide estimates of climate variables (e.g. air temperature, precipitation, wind speed, pressure etc.) on a global scale. GCMs demonstrate a significant skill at the continental and hemispheric spatial scales and incorporate a large proportion of the complexity of the global system; they are, however, inherently unable to represent local subgrid-scale features and dynamics. The spatial scale on which a GCM can operate (e.g., 3.75° longitude x 3.75° latitude for Coupled Global Climate Model, CGCM2) is very coarse compared to that of a hydrologic process (e.g., precipitation in a region, streamflow in a river etc.) of interest in the climate change impact assessment studies. Moreover, accuracy of GCMs, in general, decreases from climate related variables, such as wind, temperature, humidity and air pressure to hydrologic variables such as precipitation, evapotranspiration, runoff and soil moisture, which are also simulated by GCMs. These limitations of the GCMs restrict the direct use of their output in hydrology. This thesis deals with developing statistical downscaling models to assess climate change impacts and methodologies to address GCM and scenario uncertainties in assessing climate change impacts on hydrology. Downscaling, in the context of hydrology, is a method to project the hydrologic variables (e.g., rainfall and streamflow) at a smaller scale based on large scale climatological variables (e.g., mean sea level pressure) simulated by a GCM. A statistical downscaling model is first developed in the thesis to predict the rainfall over Orissa meteorological subdivision from GCM output of large scale Mean Sea Level Pressure (MSLP). Gridded monthly MSLP data for the period 1948 to 2002, are obtained from the National Center for Environmental Prediction/ National Center for Atmospheric Research (NCEP/NCAR) reanalysis project for a region spanning 150 N -250 N in latitude and 800 E -900 E in longitude that encapsulates the study region. The downscaling model comprises of Principal Component Analysis (PCA), Fuzzy Clustering and Linear Regression. PCA is carried out to reduce the dimensionality of the larger scale MSLP and also to convert the correlated variables to uncorrelated variables. Fuzzy clustering is performed to derive the membership of the principal components in each of the clusters and the memberships obtained are used in regression to statistically relate MSLP and rainfall. The statistical relationship thus obtained is used to predict the rainfall from GCM output. The rainfall predicted with the GCM developed by CCSR/NIES with B2 scenario presents a decreasing trend for non-monsoon period, for the case study. Climate change impact assessment models developed based on downscaled GCM output are subjected to a range of uncertainties due to both ‘incomplete knowledge’ and ‘unknowable future scenario’ (New and Hulme, 2000). ‘Incomplete knowledge’ mainly arises from inadequate information and understanding about the underlying geophysical process of global change, leading to limitations in the accuracy of GCMs. This is also termed as GCM uncertainty. Uncertainty due to ‘unknowable future scenario’ is associated with the unpredictability in the forecast of socio-economic and human behavior resulting in future Green House Gas (GHG) emission scenarios, and can also be termed as scenario uncertainty. Downscaled outputs of a single GCM with a single climate change scenario represent a single trajectory among a number of realizations derived using various GCMs and scenarios. Such a single trajectory alone can not represent a future hydrologic scenario, and will not be useful in assessing hydrologic impacts due to climate change. Nonparametric methods are developed in the thesis to model GCM and scenario uncertainty for prediction of drought scenario with Orissa meteorological subdivision as a case study. Using the downscaling technique described in the previous paragraph, future rainfall scenarios are obtained for all available GCMs and scenarios. After correcting for bias, equiprobability transformation is used to convert the precipitation into Standardized Precipitation Index-12 (SPI-12), an annual drought indicator, based on which a drought may be classified as a severe drought, mild drought etc. Disagreements are observed between different predictions of SPI-12, resulting from different GCMs and scenarios. Assuming SPI-12 to be a random variable at every time step, nonparametric methods based on kernel density estimation and orthonormal series are used to determine the nonparametric probability density function (pdf) of SPI-12. Probabilities for different categories of drought are computed from the estimated pdf. It is observed that there is an increasing trend in the probability of extreme drought and a decreasing trend in the probability of near normal conditions, in the Orissa meteorological subdivision. The single valued Cumulative Distribution Functions (CDFs) obtained from nonparametric methods suffer from limitations due to the following: (a) simulations for all scenarios are not available for all the GCMs, thus leading to a possibility that incorporation of these missing climate experiments may result in a different CDF, (b) the method may simply overfit to a multimodal distribution from a relatively small sample of GCMs with a limited number of scenarios, and (c) the set of all scenarios may not fully compose the universal sample space, and thus, the precise single valued probability distribution may not be representative enough for applications. To overcome these limitations, an interval regression is performed to fit an imprecise normal distribution to the SPI-12 to provide a band of CDFs instead of a single valued CDF. Such a band of CDFs represents the incomplete nature of knowledge, thus reflecting the extent of what is ignored in the climate change impact assessment. From imprecise CDFs, the imprecise probabilities of different categories of drought are computed. These results also show an increasing trend of the bounds of the probability of extreme drought and decreasing trend of the bounds of the probability of near normal conditions, in the Orissa meteorological subdivision. Water resources planning requires the information about future streamflow scenarios in a river basin to combat hydrologic extremes resulting from climate change. It is therefore necessary to downscale GCM projections for streamflow prediction at river basin scales. A statistical downscaling model based on PCA, fuzzy clustering and Relevance Vector Machine (RVM) is developed to predict the monsoon streamflow of Mahanadi river at Hirakud reservoir, from GCM projections of large scale climatological data. Surface air temperature at 2m, Mean Sea Level Pressure (MSLP), geopotential height at a pressure level of 500 hecto Pascal (hPa) and surface specific humidity are considered as the predictors for modeling Mahanadi streamflow in monsoon season. PCA is used to reduce the dimensionality of the predictor dataset and also to convert the correlated variables to uncorrelated variables. Fuzzy clustering is carried out to derive the membership of the principal components in each of the clusters and the memberships thus obtained are used in RVM regression model. RVM involves fewer number of relevant vectors and the chance of overfitting is less than that of Support Vector Machine (SVM). Different kernel functions are used for comparison purpose and it is concluded that heavy tailed Radial Basis Function (RBF) performs best for streamflow prediction with GCM output for the case considered. The GCM CCSR/NIES with B2 scenario projects a decreasing trend in future monsoon streamflow of Mahanadi which is likely to be due to high surface warming. A possibilistic approach is developed next, for modeling GCM and scenario uncertainty in projection of monsoon streamflow of Mahanadi river. Three GCMs, Center for Climate System Research/ National Institute for Environmental Studies (CCSR/NIES), Hadley Climate Model 3 (HadCM3) and Coupled Global Climate Model 2 (CGCM2) with two scenarios A2 and B2 are used for the purpose. Possibilities are assigned to GCMs and scenarios based on their system performance measure in predicting the streamflow during years 1991-2005, when signals of climate forcing are visible. The possibilities are used as weights for deriving the possibilistic mean CDF for the three standard time slices, 2020s, 2050s and 2080s. It is observed that the value of streamflow at which the possibilistic mean CDF reaches the value of 1 reduces with time, which shows reduction in probability of occurrence of extreme high flow events in future and therefore there is likely to be a decreasing trend in the monthly peak flow. One possible reason for such a decreasing trend may be the significant increase in temperature due to climate warming. Simultaneous occurrence of reduction in Mahandai streamflow and increase in extreme drought in Orissa meteorological subdivision is likely to pose a challenge for water resources engineers in meeting water demands in future.