Ellen M. Douglas

Trends in floods and low flows in the United States: impact of spatial correlation

Trends in flood and low flows in the US were evaluated using a regional average Kendalls S trend test at two spatial scales and over two timeframes. Field significance was assessed using a bootstrap methodology to account for the observed regional cross-correlation of streamflows. Using a 5% significance level, we found no evidence of trends in flood flows but did find evidence of upward trends in low flows at the larger scale in the Midwest and at the smaller scale in the Ohio, the north central and the upper Midwest regions. A dramatically different interpretation would have been achieved if regional cross-correlation had been ignored. In that case, statistically significant trends would have been found in all but two of the low flow analyses and in two-thirds of the flood flow analyses. We show that the cross-correlation of flow records dramatically reduces the effective number of samples available for trend assessment. We also found that low flow time series exhibit significant temporal persistence. Even when the serial correlation was removed from the time series, significant trends in low flow series were apparent, though the number of significant trends decreased.

Geospatial Indicators of Emerging Water Stress: An Application to Africa

Abstract This study demonstrates the use of globally available Earth system science data sets for water assessment in otherwise information-poor regions of the world. Geospatial analysis at 8 km resolution shows that 64% of Africans rely on water resources that are limited and highly variable. Where available, river corridor flow is critical in augmenting local runoff, reducing impacts of climate variability, and improving access to freshwater. A significant fraction of cropland resides in Africas driest regions, with 39% of the irrigation nonsustainable. Chronic overuse and water stress is high for 25% of the population with an additional 13% experiencing drought-related stress once each generation. Paradoxically, water stress for the vast majority of Africans typically remains low, reflecting poor water infrastructure and service, and low levels of use. Modest increases in water use could reduce constraints on economic development, pollution, and challenges to human health. Developing explicit geospatial indicators that link biogeophysical, socioeconomic, and engineering perspectives constitutes an important next step in global water assessment.

Changes in moisture and energy fluxes due to agricultural land use and irrigation in the Indian Monsoon Belt

[1] We present a conceptual synthesis of the impact that agricultural activity in India can have on land-atmosphere interactions through irrigation. We illustrate a ‘‘bottom up’’ approach to evaluate the effects of land use change on both physical processes and human vulnerability. We compared vapor fluxes (estimated evaporation and transpiration) from a pre-agricultural and a contemporary land cover and found that mean annual vapor fluxes have increased by 17% (340 km 3 ) with a 7% increase (117 km 3 ) in the wet season and a 55% increase (223 km 3 ) in the dry season. Two thirds of this increase was attributed to irrigation, with groundwater-based irrigation contributing 14% and 35% of the vapor fluxes in the wet and dry seasons, respectively. The area averaged change in latent heat flux across India was estimated to be 9 Wm 2 . The largest increases occurred where both cropland and irrigated lands were the predominant contemporary land uses. Citation: Douglas, E. M., D. Niyogi, S. Frolking, J. B. Yeluripati, R. A. Pielke Sr.,

Probable Maximum Precipitation Estimation Using Multifractals: Application in the Eastern United States

Probable maximum precipitation (PMP) is the conceptual construct that defines the magnitude of extreme storms used in the design of dams and reservoirs. In this study, the value and utility of applying multifractal analysis techniques to systematically calculate physically meaningful estimates of maximum precipitation from observations in the eastern United States is assessed. The multifractal approach is advantageous because it provides a formal framework to infer the magnitude of extreme events independent of empirical adjustments, which is called the fractal maximum precipitation (FMP), as well as an objective estimate of the associated risk. Specifically, multifractal (multiscaling) behavior of maximum accumulated precipitation at daily (327 rain gauges) and monthly (1400 rain gauges) timescales, as well as maximum accumulated 6-hourly precipitable water fluxes for the period from 1950 to 1997 were characterized. Return periods for the 3-day FMP estimates in this study ranged from 5300 to 6200 yr. The multifractal parameters were used to infer the magnitude of extreme precipitation consistent with engineering design criterion (e.g., return periods of 10 6 yr), the design probable maximum precipitation (DPMP). The FMP and DPMP were compared against PMP estimates for small dams in Pennsylvania using the standard methodology in engineering practice (e.g., National Weather Service Hydrometeorological Reports 51 and 52). The FMP estimates were usually, but not always, found to be lower than the standard PMP (FMP/PMP ratios ranged from 0.5 to 1.0). Furthermore, a high degree of spatial variability in these ratios points to the importance of orographic effects locally, and the need for place-based FMP estimates. DMP/PMP ratios were usually greater than one (0.96 to 2.0), thus suggesting that DPMP estimates can provide a bound of known risk to the standard PMP.

Is Precipitation in Northern New England Becoming More Extreme? Statistical Analysis of Extreme Rainfall in Massachusetts, New Hampshire, and Maine and Updated Estimates of the 100-Year Storm

The objective of this study was to investigate the presence of trends in extreme precipitation. (denoted MAXP and defined as the annual maximum daily precipitation depth) time series for coastal northern New England and to assess changes in the magnitude of the socalled “100-year storm”. MAXP depths from 48 stations with long, continuous records in Maine, New Hampshire and Massachusetts were analyzed. At those same stations, the number of daily precipitation depths ≥ 2 inches (denoted as GT2in) was also quantified for each year. The seasonally-averaged MAXP was found to be fairly uniform throughout the year, but the frequency of MAXP is highest during August through October, the typical hurricane season in New England. The presence of trends in MAXP and GT2in was evaluated over four time frames (1954-2005, 1954-2008, 1970-2005 and 1970-2008) using two statistical methods (linear regression and the Mann-Kendall trend test) and at two scales (“at-site” and regional). The trend analysis over the time period 1954-2005 indicated that MAXP was amazingly stationary; however, a trend in GT2in was found at some stations. More trends in both MAXP and GT2in were present in the time period 1954-2008. The majority of stations in southern NH and eastern MA showed evidence of trends in MAXP (but not GT2in) for the time period 1970-2008. The fact that the number of trends in MAXP increased despite the shorter record length suggests a strong increase in the magnitude of extreme precipitation in northern coastal New England in the last few decades. The stationarity of the 1954-2005 record was confirmed by the regional trend analysis as was the presence of stronger trends in coastal stations when the record was extended through 2008. Most stations that had trends in MAXP also had trends in GT2in. The Generalized Extreme Value (GEV) distribution was used to estimate 100-yr precipitation depth quantiles for the 1954-2005 record which were then compared to TP-40 100year, 24-hour precipitation depths. Estimates for stations along coastal MA, NH and ME all exceeded 7 inches and exceeded TP-40 by one inch or more. Stations in northeastern MA, southeastern NH and southern ME exceeded 8 inches and also exceeded TP-40 estimates by more than 2 inches. These findings indicate that TP-40 under-represents coastal storm depths. This study as well as recent record-breaking events in northern New England strongly suggests the need for updating of design storm estimates. Furthermore, extreme precipitation events of longer than 1-day duration have caused large-scale flooding in the region over the last decade. The magnitude of longer duration storms (particularly 2-day storms) may also be increasing, calling for engineered infrastructure that can accommodate increases in both storm magnitude

Coastal flooding, climate change and environmental justice: identifying obstacles and incentives for adaptation in two metropolitan Boston Massachusetts communities

We explored the possible future impacts of increased coastal flooding due to sea level rise and the potential adaptation responses of two urban, environmental justice communities in the metropolitan Boston area of Massachusetts. East Boston is predominantly a residential area with some industrial and commercial activities, particularly along the coastal fringe. Everett, a city to the north of Boston, has a diversified industrial and commercial base. While these two communities have similar socioeconomic characteristics, they differ substantially in the extent to which residents would be impacted by increased coastal flooding. In East Boston, a large portion of residents would be flooded, while in Everett, it is the commercial/industrial districts that are primarily vulnerable. Through a series of workshops with residents in each community, we found that the target populations do not have an adaptation perspective or knowledge of any resources that could assist them in this challenge. Furthermore, they do not feel included in the planning processes within their communities. However, a common incentive for both communities was an intense commitment to their communities and an eagerness to learn more and become actively engaged in decisions regarding climate change adaptation. The lessons that can be applied to other studies include 1) images are powerful tools in communicating concepts, 2) understanding existing cultural knowledge and values in adaptation planning is essential to the planning process and 3) engaging local residents at the beginning of the process can create important educational opportunities and develop trust and consensus that is necessary for moving from concept to implementation.

Climatology of Daily Precipitation and Extreme Precipitation Events in the Northeast United States

AbstractThis study examines U.S. Northeast daily precipitation and extreme precipitation characteristics for the 1979–2008 period, focusing on daily station data. Seasonal and spatial distribution, time scale, and relation to large-scale factors are examined. Both parametric and nonparametric extreme definitions are considered, and the top 1% of wet days is chosen as a balance between sample size and emphasis on tail distribution. The seasonal cycle of daily precipitation exhibits two distinct subregions: inland stations characterized by frequent precipitation that peaks in summer and coastal stations characterized by less frequent but more intense precipitation that peaks in late spring as well as early fall. For both subregions, the frequency of extreme precipitation is greatest in the warm season, while the intensity of extreme precipitation shows no distinct seasonal cycle. The majority of Northeast precipitation occurs as isolated 1-day events, while most extreme precipitation occurs on a single day ...

Climate Change, Justice, and Adaptation among African American Communities in the Chesapeake Bay Region

AbstractIn this paper, the authors present results from a study of climate change and community adaptation, focusing on two African American communities on the Eastern Shore of the Chesapeake Bay. These two communities are representative of small, resource-poor communities that are particularly prone to increased flooding, storms, and erosion accompanying climate change. The authors frame their research within a focus on distributive and procedural justice, including considerations of the role of adaptation capacity and vulnerability. They use methods from cognitive–environmental anthropology and psychometrics to ground a participatory and multidisciplinary approach that emphasizes community participation and the sharing of scientific and program information on climate change and adaptation. Their results suggest that community members have a holistic understanding of climate change, recognize a wide range of potential community and individual impacts, face specific vulnerabilities, and are organized thro...

An analysis of the allocation of Yakima River water in terms of sustainability and economic efficiency

Decades of agricultural growth has led to the over appropriation of Yakima water and the ecological integrity of the Basin has been compromised. We evaluate the impact of current water allocation on the natural flow regime of the Yakima River using the Indicators of Hydrologic Alteration/Range of Variability Analysis and by quantifying indicators of ecosurplus and ecodeficit. We analyze the sustainability of the current water allocation scheme based on a range of sustainability criteria, from weak to strong to environmentally sustainable. Economic efficiency is assessed by describing the current allocation framework and suggesting ways to make it more efficient. Our IHA/RVA analysis suggests that the allocation of water in the Yakima River has resulted in a highly altered flow regime. Ecodeficit is far in excess of ecosurplus. We conclude that this allocation scheme is weakly sustainable, if sustainable at all, in its current framework. The allocation of water is also not economically efficient and we suggest that a reallocation of water rights may be necessary in order to achieve this objective. The creation of water markets to stimulate voluntary water rights transactions is the best way to approach economic efficiency. The first step would be to extend beneficial use requirements to include instream flows, which would essentially allow individuals to convert offstream rights into instream rights. The Washington trust water rights program was implemented as a means of creating a water market, which has contributed to the protection of instream flows, however more needs to be done to create an ideal water rights market so that rights migrate to higher valued uses, many of which are met instream. However, water markets will likely not solve the Yakimas water allocation problems alone; some degree of regulation may still be necessary.

Use of Visible Geostationary Operational Meteorological Satellite Imagery in Mapping Reference and Potential Evapotranspiration over Florida

John R. Mecikalski1, David M. Sumner2, Jennifer M. Jacobs3, Chandra S. Pathak4, Simon J. Paech5, and Ellen M. Douglas6 1University of Alabama in Huntsville, Huntsville, Alabama 2U. S. Geological Survey (USGS), Orlando, Florida 3University of New Hampshire, Durham, New Hampshire 4South Florida Water Management District, West Palm Beach, Florida 5University of Alabama in Huntsville, Huntsville, Alabama 6University of Massachusetts, Boston, Massachusetts USA