H21G-0815
Impact assessment of climate change to salinity in brackish lake: A case study with SWAT model and regression curve
Salinity of a brackish lake is kept by superb balance of amounts of seawater and freshwater, and many aquatic lives make their habitat in a brackish lake. Salinity is one of the most important factors for aquatic lives in a brackish lake and changes in water yields from a river by climate changes should influence salinity in the lake and aquatic lives. However, there is little information about influences to watershed and brackish lake by climate change. Thus, as a first step of the study, we tried to show some information about them by using SWAT model and regression curve made by observed monthly water yields and salinity in the lake. The Hii River basin is in the eastern part of Shimane Prefecture, Japan. About 80 % of the land use in the basin is forest and 10 % is paddy fields. As the Hii River dominates about 75 % of watershed area flowing into the brackish lake called Shinji, it is considered that water quality and quantity of the river will affect the Lake a lot. As high reproducibility of the model was confirmed in the basin, the model was used for scenario analysis on monthly changes in water yields and salinity in the lake by climate changes. It was cleared that water yields would decrease from the basin outlet when amount of rainfall decreased. Then, salinity of brackish lake would increase (maximum about 30 % increase). As well, water yields would decrease about 4-5 % in yearly average when only temperature would increase. Then, salinity of the lake would increase a few percentages in yearly average. Moreover, water yields would increase every month but March when amount of rainfall would increase. Then, salinity of the lake would decrease, especially in February, August and October.
H21G-0816
Possible Scenarios of Impacts of Climatic Change on Potential Evapotranspiration in the Watershed of the Conchos River, Mexico
The watershed of the Conchos River is the main watershed of the state of Chihuahua, Mexico, and it is the main source of water of the watershed of the Grande river downstream El Paso, Texas. Such part of the watershed of the Grande River is also the border between Mexico and the United States of America, from El Paso-Ciudad Juarez up to Brownsville-Matamoros. It is very important for the state of Chihuahua and Mexico as a whole, to construct possible scenarios of the effects of the global climatic change in the potential evapotranspiration in such watershed and to construct likely scenarios which results will help to define an integrated watershed management to mitigate those global climate change impacts. The results of a recent study sponsored by the alliance between WWF-Fundacion Gonzalo Rio Arronte, are presented in the paper. The study was conducted to construct possible scenarios on the effects of the global climatic change on the potential evapotranspiration in the watershed of the Conchos River in Mexico. Three watershed characteristic meteorological stations were selected to conduct such study. The predictions of change of the surface air temperature and the change of the rainfall produced by the global climatic change, by the end of the XXI Century, were those published by the Hadley Center. The results show that air temperature increment of one degree centigrade increases evapotranspiration values between 3 and 3.5% with respect current values. As a consequence moisture deficiency increases from 9% to 40%. With an air temperature increment of three degrees centigrades, the potential evapotranspiration increases between 8.8% and 10% increasing moisture deficiency from 27.5% up to 116%. The expected rainfall increment values show a negligible contribution for the potential evapotranspiration reduction in the Rio Conchos watershed. These results conclude that immediate actions need to be taken to mitigate climate change impacts all along the watershed.
H21G-0817
Yearly Streamflow Discharge Analysis Using Functional Regression Models
Earlier spring runoff from snow melt in western North America has been suggested from analysis of both river discharge and snowpack data. This work takes a different approach to detecting evidence of earlier spring onset using a new semi-metric based on yearly streamflow discharge records. New methods of time series analysis for functional data (Ramsay and Silverman, 2005) are presented to analyze the inverse yearly cumulative discharge functions. An algorithm is developed for estimation of a functional regression model that incorporates autocorrelated errors. A framework for choosing the model structure is provided using a functional extension of a model selection criterion. Further, a diagnostic for assessing autocorrelation in the errors is provided. Results based on the analysis of streamflow records for Water Years 1951-2005 from the South Fork of the Boise River are used to illustrate the new techniques.
H21G-0818
Exploring Patterns of Hydrological Drought from Proxy Data in Wabi Shebele river basin, East Africa
Quite often, in developing countries,many watersheds are totally ungauged or havestreamflow records for a short period of time. This problem may be compounded with inconsistency in hydrometric measurement and storage thatimpairs the quality of data retrieved.In time series analysis short lengthdata is not much different than none, thus precluding a clear understanding of the temporal hydrological phenomenon. Hence most conclusions drawn from such a data suffer a similar unreliability. Signature of water stress can be identified in tree rings. This investigation attempts to explore the potential of this proxy data for hydrological drought reconstruction in Wabi Shebele basin, a transboudary river basin in East Africa. Using Incremental corer and disk sampler, 31 cored and 17 disk samples of tree rings were collected at various sites and from different species in the riparian environment. The residual tree ring series has a good correlation with historical streamflow in the dry season. A long term seasonal hydrological drought series is reconstructed from the proxy record and temporally disaggregated. Possible improvement of the reconstructed series due to supplementary attributes from climatic and remotely sensed vegetation characteristics of the catchment is also analysed. The reconstructed series mimics well the hydrological drought series established from gauged historical flows. Patterns of drought in the study area are investigated by cross wavelet analysis.
H21G-0819
Streamflow Reconstructions and Periods of Drought in the Upper Green River Basin, Wyoming, USA
The upper Green River represents a vital water supply region for southwestern Wyoming and Upper / Lower Colorado River Compact states. Rapid development in the southwestern U.S. (e.g., Las Vegas, Phoenix) combined with the recent drought has greatly stressed the water supply system of the Colorado River. This has resulted in increased interest in the Colorado River Compact and related "Law of the River." The current research developed proxy records (streamflow) derived from tree ring chronologies. These streamflow reconstructions provide an effective way to analyze patterns of drought over a period of time extending beyond any instrumental record in the upper Green River Basin (GRB). Six new tree ring chronologies were developed in the foothills of the Wind River Mountain Range, along the eastern boundary of the upper GRB. The six new chronologies consisted of three Douglas fir (Pseudotsuga menziesii) and three limber pine (Pinus flexilis) sites. The newly developed tree ring chronologies and existing chronologies around the region were used in developing the streamflow reconstructions. Nine streamflow reconstructions were developed for both headwater stations (utilizing unimpaired streamflow records) and stations lower in the basin (utilizing naturalized streamflow records). Traditionally, streamflow reconstructions have been limited to large rivers, but reconstructing headwater stream records provides information to water users high in the basin as well as providing spatial variations in streamflow variability across the river basin. All upper basin reconstructions extended back to the year 1615. The most downstream station in the upper GRB (Green River, near Greendale, UT) was extended to 1439. The coefficient of variance (R2) for this reconstruction is 0.65. Different modes of drought were identified for the Green River, near Greendale, UT reconstruction. Annual extremes (wet and dry) and persistent wet and dry (drought) periods were identified. The wet and dry periods identified were analyzed and compared with long term trends in the reconstructed streamflow record.
H21G-0820
Fluvial responses to environmental perturbations since the Last Glacial Maximum
The numerical model HydroTrend, that produces daily time series of water discharge and sediment load to the ocean, is applied to three Mediterranean drainage basins to: (i) simulate the water and sediment flux changes over time and (ii) determine the impact of potential forcing factors on sediment and water fluxes and how this impact varied through time. Climate (precipitation, temperature and glacier equilibrium line) and drainage basin (basin elevation, drainage area and reservoir) reconstructions of the Po, Rhone and Tet river basins over the last 21 000 Cal. years B.P. are used as input to the model. Although these rivers are located in the same climatic region and drain into the same sedimentary basin, there are predictable differences in the delivered sediment fluxes due to shelf geometry and more local climatic effects. Simulated sediment fluxes for the Po, Rhone and Tet rivers during the late Pleistocene were considerably higher compared to Holocene pristine sediment flux, with a factor 3.5, 2.4 and 2.4 respectively. For the Po and the Rhone rivers, deglaciation in the late Pleistocene is the main factor, responsible for these higher sediment fluxes. Drainage basin area change due to sea level rise is the main cause of decrease in sediment flux for the Tet River and to a certain extent for the Po River. Man-made reservoirs reduced sediment flux to the ocean for the Po, Rhone and Tet rivers over the last 3 - 6 decades with a factor of 1.3, 3.8 and 2.4 respectively. Fluvial responses to climate and basin variations are reflected in the peak flood discharge and sediment concentration curves, where present day water peak flood curves for all the three rivers are the highest in the last 21 000 Cal. years B.P. However, their associated sediment concentration curves show opposite results because of diminishing glacial area and the impact of reservoirs. The Tet River has the ability to generate hyperpycnal plumes although the occurrence frequency changes over time. Prior to 15 500 Cal. years B.P. the river system area was extended due to the low sea level, causing a less favorable regime to generate hyperpycnal events. Presently sediment trapping due to man made reservoirs alters the river ability to generate hyperpycnal events.
H21G-0821
Improving Forecasts of Flood Risk by Incorporating Climate Variability Into Bulletin 17B LP3 Model
The current techniques for flood frequency analysis presented in Bulletin 17B assume annual maximum floods are stationary; meaning the distribution of flood flows is not significantly affected by climatic trends or long-term cycles (i.e. decadal variations). In light of growing evidence that streamflows are nonstationary and are impacted by climate variability, the Bulletin 17B techniques should be modified. The effects of climatic cycles occurring over a shorter time frame, such as El Niño-Southern Oscillation (ENSO), are averaged into flood risk estimates made using the procedures of Bulletin 17B. However, the effects of ENSO are likely to affect the magnitude of annual maximum streamflows, and thus would impact flood risk in a given year. In order to improve estimates/forecasts obtained using the Bulletin 17B LP3 model, the effects of climate variability associated with ENSO events may be incorporated into updated estimates of the mean, and perhaps the standard deviation, by regressing the LP3 parameters on a climatic index such as sea surface temperature (SST) anomalies. In this study, the regression model is applied to unimpaired annual maximum streamflow datasets for gauging stations across the contiguous United States to obtain a one-year ahead forecast of the mean. For stations where the regression analysis yields significant results, the forecasted flood risk is compared with that obtained using the existing Bulletin 17B LP3 model.
H21G-0822
Probabilistic Impact Assessment of Domestic Rainwater Harvesting in Urban Slums: West Africa Case Study
Urban populations now exceed rural populations worldwide, creating unique challenges in providing basic services, especially in developing countries where informal or illegal settlements grow in peri-urban areas. West Africa is an acute example of the problems created by rapid urban growth, with high levels of urban poverty and low water and sanitation access rates. Although considerable effort has been made in providing improved water access and urban services to slum communities, research indicates that clean water access rates are not keeping up with urbanization rates in several areas of the world and that rapidly growing slum communities are beginning to overwhelm many prior water improvements projects. In the face of these challenges, domestic rainwater harvesting is proposed as a technologically appropriate and economically viable option for enhancing water supplies to urban slum households. However, assessing the reliability, potential health impacts, and overall cost-effectiveness of these systems on a regional level is difficult for several reasons. First, long daily rainfall records are not readily available in much of the developing world, including many regions of sub-Saharan Africa. Second, significant uncertainties exist in the relevant cost, water use, and health data. Third, to estimate the potential future impacts at the regional scale, various global change scenarios should be investigated. Finally, in addition to these technical challenges, there is also a need to develop relatively simple and transparent assessment methods for informing policy makers. A procedure is presented for assessment of domestic rainwater harvesting systems using a combination of scenario, sensitivity, and trade-off analyses. Using data from West Africa, simple stochastic weather models are developed to generate rainfall sequences for the region, which are then used to estimate the reliability of providing a range of per capita water supplies. Next, a procedure is proposed for quantifying the health impacts of improved water supplies, and sensitivity analysis of cost and health data provides an indication of cost- effectiveness. Climate change impacts are assessed via weather model parameter adjustment according to statistical downscaling of general circulation model output. Future work involving the interpolation of model parameters to ungaged sites, incorporation of additional global change scenarios (e.g., population, emissions), and extension of the procedure to a full Monte Carlo analysis will be discussed as time allows.
H21G-0823
Characterizing the 2007 California Drought Using an Aggregate Drought Index
The Aggregate Drought Index (ADI) (Keyantash and Dracup, 2004) was developed as a tool to describe the intensity of drought across multiple hydrologic reservoirs. The ADI is a principal-components based index, which examines water shortages and abundances with regards to precipitation, evaporation, streamflow, reservoir storage, soil moisture, and alpine snowpack. In this regard, the ADI aggregates water deficiencies commonly segregated into meteorological, hydrological, and agricultural forms of drought. The ADI will be used to quantify drought severity in three California climate divisions from circa 1970 through the record dry conditions of water year 2007.
H21G-0824
Scenario Planning for Water Resources: a Forward-looking Approach Combining Science, Demographic Trends and Policy
Although there has been much written about the use of scenario analysis for long-term planning, particularly with respect to the decisions facing firms, the extant literature has few examples of scenarios explicitly applied to water resource issues. Fewer still have considered short-fuse events such as floods and failure of water retention and conveyance structures in the context of longer-term scenarios for water resources planning. We report progress on an effort to develop a unified framework for constructing scenarios for water resource management. We place particular emphasis on semi-arid environments and forces external to the traditional water management process such as high-impact weather and climate events or unforeseen changes in government institutions that may drive unanticipated change in environmental systems. Most water resource scenarios are typically based on high, medium and low projections of demographics (gpcd), climate (precipitation, temperature), and perhaps institutional variables (conveyance infrastructure, legal issues). We discuss the relative merits of this with other approaches including: probabalistic scenarios, which explicitly weight the likelihood of different outcomes; anticipatory scenarios, which consider how to achieve or avoid some subjective future state; strategic scenarios, which seeks to identify the inconsistencies between disciplines in the way the environmental models are constructed
H21G-0825
A formal framework of scenario creation and analysis of extreme hydrological events
We are presenting a formal framework for a hydrological risk analysis. Different measures of risk will be introduced, such as average annual loss or occurrence exceedance probability. These are important measures for e.g. insurance companies to determine the cost of insurance. One key aspect of investigating the potential consequences of extreme hydrological events (floods and draughts) is the creation of meteorological scenarios that reflect realistic spatial and temporal patterns of precipitation that also have correct local statistics. 100,000 years of these meteorological scenarios are used in a calibrated rainfall-runoff-flood-loss-risk model to produce flood and draught events that have never been observed. The results of this hazard model are statistically analyzed and linked to socio-economic data and vulnerability functions to show the impact of severe flood events. We are showing results from the Risk Management Solutions (RMS) Europe Flood Model to introduce this formal framework. http://www.rms.com