Download or read book Investigating Future Variation of Extreme Precipitation Events Over the Willamette River Basin Using Dynamically Downscaled Climate Scenarios written by Andrew Jason Halmstad and published by . This book was released on 2011 with total page 50 pages. Available in PDF, EPUB and Kindle. Book excerpt: One important aspect related to the management of water resources under future climate variation is the occurrence of extreme precipitation events. In order to prepare for extreme events, namely floods and droughts, it is important to understand how future climate variability will influence the occurrence of such events. Recent advancements in regional climate modeling efforts provide additional resources for investigating the occurrence of extreme events at scales that are appropriate for regional hydrologic modeling. This study utilizes data from three Regional Climate Models (RCMs), each driven by the same General Circulation Model (GCM) as well as a reanalysis dataset, all of which was made available by the North American Regional Climate Change Assessment Program (NARCCAP). A comparison between observed historical precipitation events and NARCCAP modeled historical conditions over Oregon's Willamette River basin was performed. This comparison is required in order to investigate the reliability of regional climate modeling efforts. Datasets representing future climate signal scenarios, also provided by NARCCAP, were then compared to historical data to provide an estimate of the variability in extreme event occurrence and severity within the basin. Analysis determining magnitudes of two, five, ten and twenty-five year return level estimates, as well as parameters corresponding to a representative Generalized Extreme Value (GEV) distribution, were determined. The results demonstrate the importance of the applied initial/boundary driving conditions, the need for multi-model ensemble analysis due to RCM variability, and the need for further downscaling and bias correction methods to RCM datasets when investigating watershed scale phenomena.
Download or read book Extreme Floods and Droughts under Future Climate Scenarios written by Momcilo Markus and published by MDPI. This book was released on 2019-11-28 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydroclimatic extremes, such as floods and droughts, affect aspects of our lives and the environment including energy, hydropower, agriculture, transportation, urban life, and human health and safety. Climate studies indicate that the risk of increased flooding and/or more severe droughts will be higher in the future than today, causing increased fatalities, environmental degradation, and economic losses. Using a suite of innovative approaches this book quantifies the changes in projected hydroclimatic extremes and illustrates their impacts in several locations in North America, Asia, and Europe.
Download or read book Evaluation of Physical Parameterizations for Atmospheric River Induced Precipitation and Application to Long term Reconstruction Based on Three Reanalysis Datasets in Western Oregon written by Kinya Toride and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Dynamically downscaled precipitation is often used for evaluating sub-daily precipitation behavior on a watershed-scale and for the input to hydrological modeling because of its increasing accuracy and spatiotemporal resolution. Despite these advantages, physical parameterizations in regional models and systematic biases due to the dataset used for boundary conditions greatly influence the quality of downscaled precipitation data. The present paper aims to evaluate the performance and the sensitivities of physical parameterizations of the Weather Research and Forecasting (WRF) model to simulate extreme precipitation associated with atmospheric rivers (ARs) over the Willamette watershed in Oregon. Also investigated was whether the optimized WRF configuration for extreme events can be used for long-term reconstruction using different boundary condition datasets. Three reanalysis datasets, the Twentieth Century Reanalysis version 2c (20CRv2c), the European Center for Medium-Range Weather Forecasts (ECMWF) twentieth century reanalysis (ERA20C), and the Climate Forecast System Reanalysis (CFSR), which have different spatial resolutions and dataset periods, were used to simulate precipitation at 4 km resolution. Sensitivity analyses showed that AR precipitation is most sensitive to the microphysics parameterization. Among 13 microphysics schemes investigated, the Goddard and the Stony-Brook University schemes performed the best regardless of the choice of reanalysis. Reconstructed historical precipitation with the optimized configuration showed better accuracies during the wet season than the dry season. With respect to simulations with CFSR, it was found that the optimized configuration for AR precipitation can be used for long-term reconstruction with small biases. However, systematic biases in the reanalysis datasets may still lead to uncertainties in downscaling precipitation in a different season with a single configuration.
Download or read book Winter Extreme Precipitation Along the North American West Coast written by Michael D. Warner and published by . This book was released on 2014 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most extreme precipitation events that occur along the North American west coast are associated with winter atmospheric river (AR) events, causing flooding, landslides, extensive property damage, and loss of life. The studies contained within this dissertation use a combination of NCDC precipitation observations, NCEP-NCAR reanalysis, a 10-model ensemble of historical and future CMIP5 climate model simulations, and an NCEP-NCAR reanalysis driven regionally downscaled WRF model simulation to characterize the synoptic evolution of AR events along the North American west coast, the spatial variability of precipitation along the coast and inland, and changes in AR intensity and frequency that are expected by the end of the 21st century. Most regional flooding events are associated with precipitation periods of 24 hours or less, and two-day precipitation totals identify nearly all major events. Precipitation areas of major events are generally narrow, roughly 200 km in width, and most are associated with ARs. Composite evolutions indicate negative anomalies in sea-level pressure and upper-level height in the central Pacific, high-pressure anomalies over the southwest U.S., large positive 850-hPa temperature anomalies along the coast and offshore, and enhanced precipitable water and integrated water vapor fluxes in southwest- to northeast-oriented swaths. A small subset of extreme precipitation events over the southern portion of the domain is associated with a very different synoptic evolution: a sharp trough in northwesterly flow and post-cold-frontal convection. High precipitable water values are more frequent during the summer but are not associated with heavy precipitation because of upper-level ridging over the eastern Pacific and weak onshore flow that limits upward vertical velocities. Global climate models have sufficient resolution to simulate synoptic features associated with AR events, such as high values of vertically integrated vapor transport (IVT) approaching the coast. Ten CMIP5 simulations are used to identify changes in ARs impacting the west coast of North America between historical (1970-1999) and end-of-century (2070-2099) representative concentration pathway (RCP) 8.5 runs. The most extreme ARs are identified in both time periods by the 99th percentile of IVT days along a north-south transect offshore of the coast. Integrated water vapor (IWV) and IVT are predicted to increase, while lower-tropospheric winds change little. Winter-mean precipitation along the West Coast increases by 11-18% (4-6% °C[superscript -1]) while precipitation on extreme IVT days increases by 15-39% (5-19% °C[superscript -1]). The frequency of IVT days above the historical 99th percentile threshold increases as much as 290% by the end of this century. There appear to be only very slight changes in annual AR climatology from historical to future time periods when considering the most extreme events (99th percentile). However, when evaluating by the number of future days exceeding the historical threshold, there are significant increases in extreme IVT events in all months, especially when the majority of events take place. The peaks in historical and future frequency occur in similar months given the amount of model variability. Extreme IVT events appear to be occurring slightly earlier in the season, particularly in the northern part of the domain, and these results are similar to other studies. Spatially, 10-model mean historical composites of IVT reveal canonical AR conditions. At locations farther south, there is less model agreement on what AR events should look like, both in spatial extent and intensity; whereas farther north, the various models agree more. The future composites indicate very little spatial change. The models behave similarly in both the historical and future runs, suggesting little change in dynamics. The future-historical difference plots highlight the largest changes expected in the future, namely increases in IVT intensity which are primarily associated with thermodynamic changes related to future IWV increases due to warming. The dynamically downscaled NCEP-NCAR reanalysis-driven WRF model, run with a 36-km resolution outer domain and a 12-km nest, contains more realistic terrain than most GCMs and highlights the spatial precipitation distribution over the Pacific Northwest. Winter precipitation in the Pacific Northwest correlates well with offshore daily IVT (as high as &sim0.8) with spatial signatures indicative of frequent coastal mid-latitude cyclones impacting the coast. However, the most extreme AR events did not correlate as highly as expected with daily precipitation (as high as ~ 0.4), despite ARs accounting for 8% or more of the total winter precipitation. When wind direction was taken into account, the correlations were much higher (~.7-0.8), indicating wind direction is an important factor when extreme precipitation occurs along the coast.
Download or read book Temporal Disaggregation of Daily Precipitation Data in a Changing Climate written by Karen Wey and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Shift of Precipitation Maxima on the Annual Maximum Series Using Regional Climate Model Precipitation Data written by Alejandro Riano and published by . This book was released on 2013 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ten regional climate models (RCMs) and atmosphere-ocean generalized model parings from the North America Regional Climate Change Assessment Program were used to estimate the shift of extreme precipitation due to climate change using present-day and future-day climate scenarios. RCMs emulate winter storms and one-day duration events at the sub-regional level. Annual maximum series were derived for each model pairing, each modeling period; and for annual and winter seasons. The reliability ensemble average (REA) method was used to qualify each RCM annual maximum series to reproduce historical records and approximate average predictions, because there are no future records. These series determined (a) shifts in extreme precipitation frequencies and magnitudes, and (b) shifts in parameters during modeling periods. The REA method demonstrated that the winter season had lower REA factors than the annual season. For the winter season the RCM pairing of the Hadley regional Model 3 and the Geophysical Fluid-Dynamics Laboratory atmospheric-land generalized model had the lowest REA factors. However, in replicating present-day climate, the pairing of the Abdus Salam International Center for Theoretical Physics' Regional Climate Model Version 3 with the Geophysical Fluid-Dynamics Laboratory atmospheric-land generalized model was superior. Shifts of extreme precipitation in the 24-hour event were measured using precipitation magnitude for each frequency in the annual maximum series, and the difference frequency curve in the generalized extreme-value-function parameters. The average trend of all RCM pairings implied no significant shift in the winter annual maximum series, however the REA-selected models showed an increase in annual-season precipitation extremes: 0.37 inches for the 100-year return period and for the winter season suggested approximately 0.57 inches for the same return period. Shifts of extreme precipitation were estimated using predictions 70 years into the future based on RCMs. Although these models do not provide climate information for the intervening 70 year period, the models provide an assertion on the behavior of future climate. The shift in extreme precipitation may be significant in the frequency distribution function, and will vary depending on each model-pairing condition. The proposed methodology addresses the many uncertainties associated with the current methodologies dealing with extreme precipitation.
Download or read book Extreme Precipitation and Runoff Under Changing Climate in Southern Maine written by and published by . This book was released on 2016 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: The quantification of extreme precipitation events is vitally important for designing and engineering water and flood sensitive infrastructure. Since this kind of infrastructure is usually built to last much longer than 10, 50, or even 100 years, there is great need for statistically sound estimates of the intensity of 10-, 50-, 100-, and 500-year rainstorms and associated floods. The recent assessment indicated that the intensity of the most extreme precipitation events (or the heaviest 1% of all daily events) have increased in every region of the contiguous states since the 1950s (Melillo et al. 2014). The maximum change in precipitation intensity of extreme events occurred in the northeast region reaching 71%. The precipitation extremes can be characterized using intensity-duration-frequency analysis (IDF). However, the current IDFs in this region were developed around the assumption that climate condition remains stationary over the next 50 or 100 years. To better characterize the potential flood risk, this project will (1) develop precipitation IDFs on the basis of both historical observations and future climate projections from dynamic downscaling with Argonne National Laboratory's (Argonne's) regional climate model and (2) develop runoff IDFs using precipitation IDFs for the Casco Bay Watershed. IDF development also considers non-stationary distribution models and snowmelt effects that are not incorporated in the current IDFs.
Download or read book Flood Frequency Analysis of Future Climate Projections for Cache Creek Watershed written by Ida Grace Fischer and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Effects of climate change on hydrologic flow regimes, particularly extreme events, necessitate modeling of future flows to best inform water resources management. Future flows may be simulated using global climate models (GCMs) and regional atmospheric models in tandem with watershed models. This research effort ran 13 simulations for possible future carbon emission scenarios (taken from the IPCC SRES A1FI, A1B, A2 and B1 families) over the 21st century (2010-2099) for the Cache Creek watershed in Northern California. Atmospheric data from GCMs, CCSM3 and ECHAM5, were dynamically downscaled to a 9 km by 9 km resolution using the Fifth-Generation Penn State/NCAR Mesoscale Model (MM5), a regional atmospheric model, before being input into the physically based Watershed Environmental Hydrology (WEHY) model. Ensemble mean and standard deviation of simulated flows describe the expected hydrologic system response. Frequency histograms and cumulative distribution functions characterize the range of hydrologic responses that may occur. The modeled flow results comprise a dataset suitable for time series and frequency analysis allowing for more robust system characterization. During the course of the 21st century the mean of annual maximum flows increases 24%, the variance 400% and the skewness 265%. The 100 -year flood grew 40% from 2010-2039 to 2070-2099. This change was more dramatic for the 200-year flood growing 227% from the beginning third to the last third of the 21st century. A comparison between frequency analysis results on simulated flows and those predicted by fitting the Log Pearson III and generalized extreme value distribution suggests that traditional distribution fitting misses the heavy tails seen in future simulated flows.
Download or read book Floods in a Changing Climate written by Ramesh S. V. Teegavarapu and published by Cambridge University Press. This book was released on 2012-11-22 with total page 289 pages. Available in PDF, EPUB and Kindle. Book excerpt: Provides measurement, analysis and modeling methods for assessment of trends in extreme precipitation events, for academic researchers and professionals.
Download or read book Anticipated Changes in Precipitation Events Over the 21st Century Using Community Climate System Model Version 4 written by Scott Tavish DeNeale and published by . This book was released on 2012 with total page 74 pages. Available in PDF, EPUB and Kindle. Book excerpt: Future global daily precipitation data from Community Climate System Model, version 4 (CCSM4) were analyzed to evaluate changes in a variety of precipitation parameters over the 21st century. Multiple ensemble members of 21st century Representative Community Pathways (RCP) radiative scenarios were included in the model to provide an array of potential future climate change results. Multiple ensembles of historic daily precipitation data from CCSM4 were compared with Global Precipitation Climatology Project (GPCP) V1DD daily precipitation data and Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) monthly precipitation data. Annual average and 95th percentile precipitation values were averaged from 1997-2005 among the datasets, and correlation coefficients (R) are relatively high (0.8796 and 0.8530 for average precipitation and 0.8820 for 95th percentile values) between CCSM4 and observational data. Analysis of mid and end-of-21st century changes in average and 95th precipitation values, reveals large increases in most locations and slight decreases across a few regions. Nearly identical spatial patterns exist between the parameters, though the magnitude of change varies. Magnitudes of change in 95th percentile values exceed those of average precipitation, but the relative change is spatially similar. Extreme indices R95T and DA95 indicate widespread increases in the annual contribution of total precipitation from extreme events with a simultaneous increase in frequency of such events, while some locations show decreases. Regional analysis of the four precipitation parameters results in similar findings but provides additional temporal information. Increasing changes in all parameters occur under with increases in radiative forcing. Division of daily precipitation into categories based on intensities reveals sharp increases in annual precipitation contribution from the most intense precipitation events and a subsequent decreasing contribution from less intense events. Under the highest radiative forcing scenario (RCP 8.5), temporal comparison between the annual contribution from the six precipitation categories and atmospheric carbon dioxide concentration yields R values of -0.979, -0.977, -0.753, 0.830, 0.971, and 0.969, respectively. These results indicate a direct relationship between anthropogenic greenhouse gas emissions and global precipitation trends, stressing the need to adapt to and mitigate impacts of climate change.
Download or read book Understanding Probable Maximum Precipitation and Safety of Water Management Infrastructures Under a Changing Climate written by Xiaodong Chen and published by . This book was released on 2017 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Large water management infrastructures, such as high hazard dams located upstream of population centers, are usually designed according to the Probable Maximum Precipitation (PMP) criteria that are traditionally derived using historical records of extreme precipitation. Given the observed climate change in the past century and projected climate change in the next century, it is questionable whether the historical storms and the PMPs they derive are a reliable representation of present or future climate. On the other hand, the linear relationship between precipitation and precipitable water as assumed in the traditional method has been questioned in several studies. As a solution, atmospheric numerical modeling has been explored for physics-based PMP estimations, but no physics-based method has been well developed up to now, which makes the current studies appear ad-hoc. In this study, we establish a numerical modeling framework (based on Weather Research and Forecasting model) for extreme precipitation simulation, which lays the foundation of model-based PMP estimation. Using this modeling framework, we examine model reconstruction of various extreme precipitation events since 1905 and find that only those extreme storms after the 1940s can be satisfactorily reconstructed. This lays the basis for storm selection in the physics-based PMP estimation. Through statistical analysis of atmospheric reanalysis data, we examine the relationship between extreme precipitation and the atmospheric conditions, which provides region-specific guidelines to the physics-based PMP estimation. In this physics-based approach, either wind fields (in the western US) or moisture availability (in the eastern US) should be considered to reasonably maximize the storm magnitude. We also develop a hybrid method that bridges the traditional the physics-based methods, so a smooth transition is made possible for engineering communities. As a demonstration, we applied this hybrid approach to estimate the PMPs in the US Pacific Northwest region. The hybrid PMP estimates during 1970-2016 are similar to the traditional values, but the future PMPs will increase by 50% ± 30% of the current level by 2099 under the RCP8.5 scenario. Most of the increase is caused by warming, which mainly affects moisture availability through increased sea surface temperature. The findings of the study will help to modernize current engineering practice of PMP estimation and to better quantify the failure risk of large water management infrastructures for present and future climate scenarios.
Download or read book Evaluation of Future Design Rainfall Extremes and Characteristics Using Multiple model and Multiple scenario Climate Change Models written by Celyn Dezmain and published by . This book was released on 2013 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Climate models are common tools for developing design standards in the hydrologic field; however, these models contain uncertainties in multi-model and scenario selections. Along with these uncertainties, biases can be attached to the models. Such biases and uncertainties can present difficulties in predicting future extremes. These hydrologic extremes are believed to be non-stationary in character. Only in the recent past have model users come to terms that the current hydrologic designs are no longer relevant due to their assumption of stationarity. This study describes a systematic method of selecting a best fit model in relationship to location and time, along with the use of that best fit model for evaluation of future extremes. Rain gage stations throughout Florida are used to collect daily precipitation data used in extreme precipitation and quantitative indices. Through these indices conclusions are made on model selection and future extremes, as they relate to hydrologic designs.
Download or read book Predicted 21st Century Changes in Seasonal Extreme Precipitation Events in the Parallel Climate Model written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Twenty-year return value of annual and seasonal maxima of daily precipitation are calculated from a set of transiently forced coupled general circulation model simulations. The magnitude and pattern of return values are found to be highly dependent on the seasonal cycle. A similar dependence is found for projected future changes in return values. The correlation between the spatial pattern of return value changes and mean precipitation changes is found to be low. Hence, the changes in mean precipitation do not provide significant information about changes in precipitation extreme values.
Download or read book The Future of Municipal Water Resources in the Willamette River Basin written by David Donald Dole and published by . This book was released on 2002 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Under current trends, municipal demand for water in Oregon's Willamette River Basin will double by 2050. Municipalities will have to develop new sources of water, in competition with agricultural and other established uses, as well as increased demand for water to support ecological values. Municipalities can, to a limited extent, turn to their currently dormant water rights, but executing these rights will displace other currently established uses of water or diminish flows for fish and wildlife. Recent listings of salmon and other fish under the Endangered Species Act greatly diminish the acceptability of making water-use decisions without accounting for their potential impacts on water quantity and quality throughout the basin. This paper adopts a basin-wide perspective to analyze the need for new development of new sources of municipal water in the basin, and the impact of increased municipal water demand on water resource management in the basin as a whole. The analysis employs a computer model that simulates the regulation of water rights across the basin. We develop scenarios for future demand and supply of water, and use the computer model to determine the resulting allocation of water across water rights in the basin. Results indicate that the state's three largest urban areas have adequate water resources, but many smaller municipalities will have to develop new sources. The analysis here indicates that eliminating summer releases from storage in the basin's federal reservoirs would not affect water availability at current municipal points of diversion.
Download or read book Modeling the Effects of Climate Change Forecasts on Streamflow in the Nooksack River Basin written by Susan E. Dickerson and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Nooksack River has its headwaters in the North Cascade Mountains and drains an approximately 2300 km2 watershed in northwestern Washington State. The timing and magnitude of streamflow in a high relief, snow-dominated drainage basin such as the Nooksack River basin is strongly influenced by temperature and precipitation. Forecasts of future climate made by general circulation models (GCMs) predict increases in temperature and variable changes to precipitation in western Washington, which will affect streamflow, snowpack, and glaciers in the Nooksack River basin. Anticipating the response of the river to climate change is crucial for water resources planning because municipalities, tribes, and industry depend on the river for water use and for fish habitat. I combined modeled climate forecasts and the Distributed-Hydrology-Soil-Vegetation Model (DHSVM) to simulate future changes to timing and magnitude of streamflow in the higher elevations of the Nooksack River, east of the confluence near Deming, Washington. The DHSVM is a physically based, spatially distributed hydrology model that simulates a water and energy balance at the pixel scale of a digital elevation model. I used recent meteorological and landcover data to calibrate and validate the DHSVM. Coarse-resolution GCM forecasts were downscaled to the Nooksack basin following the methods of previous regional studies (e.g., Palmer, 2007) for use as local-scale meteorological input to the calibrated DHSVM. Simulations of future streamflow and snowpack in the Nooksack River basin predict a range of magnitudes, which reflects the variable predictions of the climate change forecasts and local natural variability. Simulation results forecast increased winter flows, decreased summer flows, decreased snowpack, and a shift in timing of the spring melt peak and maximum snow water equivalent. Modeling results for future peak flow events indicate an increase in both the frequency and magnitudes of floods, but uncertainties are high for modeling the absolute magnitudes of peak flows. These results are consistent with previous regional studies which document that temperature-related effects on precipitation and melting are driving changes to snow-melt dominated basins (e.g., Hamlet et al., 2005; Mote et al., 2005; Mote et al., 2008; Adam et al., 2009).
Download or read book Extreme Floods and Droughts under Future Climate Scenarios written by Momcilo Markus and published by . This book was released on 2019 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydroclimatic extremes, such as floods and droughts, affect aspects of our lives and the environment including energy, hydropower, agriculture, transportation, urban life, and human health and safety. Climate studies indicate that the risk of increased flooding and/or more severe droughts will be higher in the future than today, causing increased fatalities, environmental degradation, and economic losses. Using a suite of innovative approaches this book quantifies the changes in projected hydroclimatic extremes and illustrates their impacts in several locations in North America, Asia, and Europe.
Download or read book Development of a Methodology for Probable Maximum Precipitation Estimation Over the American River Watershed Using the WRF Model written by Elcin Tan and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A new physically-based methodology for probable maximum precipitation (PMP) estimation is developed over the American River Watershed (ARW) using the Weather Research and Forecast (WRF-ARW) model. A persistent moisture flux convergence pattern, called Pineapple Express, is analyzed for 42 historical extreme precipitation events, and it is found that Pineapple Express causes extreme precipitation over the basin of interest. An average correlation between moisture flux convergence and maximum precipitation is estimated as 0.71 for 42 events. The performance of the WRF model is verified for precipitation by means of calibration and independent validation of the model. The calibration procedure is performed only for the first ranked flood event 1997 case, whereas the WRF model is validated for 42 historical cases. Three nested model domains are set up with horizontal resolutions of 27 km, 9 km, and 3 km over the basin of interest. As a result of Chi-square goodness-of-fit tests, the hypothesis that "the WRF model can be used in the determination of PMP over the ARW for both areal average and point estimates" is accepted at the 5% level of significance. The sensitivities of model physics options on precipitation are determined using 28 microphysics, atmospheric boundary layer, and cumulus parameterization schemes combinations. It is concluded that the best triplet option is Thompson microphysics, Grell 3D ensemble cumulus, and YSU boundary layer (TGY), based on 42 historical cases, and this TGY triplet is used for all analyses of this research. Four techniques are proposed to evaluate physically possible maximum precipitation using the WRF: 1. Perturbations of atmospheric conditions; 2. Shift in atmospheric conditions; 3. Replacement of atmospheric conditions among historical events; and 4. Thermodynamically possible worst-case scenario creation. Moreover, climate change effect on precipitation is discussed by emphasizing temperature increase in order to determine the physically possible upper limits of precipitation due to climate change. The simulation results indicate that the meridional shift in atmospheric conditions is the optimum method to determine maximum precipitation in consideration of cost and efficiency. Finally, exceedance probability analyses of the model results of 42 historical extreme precipitation events demonstrate that the 72-hr basin averaged probable maximum precipitation is 21.72 inches for the exceedance probability of 0.5 percent. On the other hand, the current operational PMP estimation for the American River Watershed is 28.57 inches as published in the hydrometeorological report no. 59 and a previous PMP value was 31.48 inches as published in the hydrometeorological report no. 36. According to the exceedance probability analyses of this proposed method, the exceedance probabilities of these two estimations correspond to 0.036 percent and 0.011 percent, respectively.
