Recent research suggests that the characteristics of precipitation are changing with a warming global climate. This study uses two traditional measures of precipitation, amount and frequency, in ...addition to two metrics that have not been widely used in hydroclimatological research, the Gini coefficient (GC) and the Lorenz asymmetry coefficient (LAC), to analyse change and variability in precipitation characteristics across the United States from 1949 through 2018. The GC quantifies the inequity of an accumulating variable across individual contributors. For this study, the GC was used to quantify equity in the accumulating distribution of daily precipitation amounts through an annual timeframe. The LAC quantifies the relative magnitude of individual contributors which were primarily responsible for inequity in an accumulating distribution. For this analysis, the LAC assesses the relative magnitude of precipitation events (light, heavy) primarily responsible for occurrences of inequity in the temporal distribution of precipitation. Time series analysis of regionally averaged values of precipitation amount, precipitation frequency, GC, and LAC values suggest change in the hydroclimate for many regions across the United States, including a trend towards greater inequity in the temporal distribution of precipitation. The more recent trends and variability of the four precipitation characteristics were statistically examined for relationships with time series of two key atmospheric features – total column water vapour (moisture availability) and the 850 hPa–500 hPa lapse rate (static stability). Results of this study show that change and variability in the atmospheric characteristics likely help explain the observed trends and variability of several precipitation characteristics across the United States.
This study uses two traditional measures of precipitation, amount and frequency, in addition to two metrics that have not been widely used in hydroclimatological research, the Gini coefficient (GC) and the Lorenz asymmetry coefficient (LAC), to analyse change in precipitation characteristics across the United States from 1949 through 2018. Results show change in the hydroclimate for many regions across the United States, including a trend towards greater inequity in the temporal distribution of precipitation.
Spatially homogenous precipitation regions were delineated for the contiguous United States using a gridded data set of daily precipitation. Seasonal means (1981-2010) of four variables, together ...characterizing seasonal precipitation, were computed and subjected to a principal component analysis (PCA). PCA reduced the original 30,665 grid cells by sixteen precipitation variables (four variables, four seasons) in the data set. The standardized scores of the three retained principal components, which together retain 78.4 percent of the original data set's variance, were then subjected to three agglomerative hierarchical clustering techniques. Using an objective method, several cluster solutions were examined, and the average linkage thirteen-cluster solution was deemed optimal. The average linkage solution was then subjected to a k-means partitioning technique under the premise that objects are not considered for reassignment during agglomerative hierarchical cluster procedures. The result is fifteen precipitation regions across the contiguous United States. Results indicate that the regions successfully minimize intraregion variability and maximize interregion variability when compared to the nine climate regions defined by the United States National Centers for Environmental Information. It is therefore suggested that the regions defined by this work will better serve research aimed at an improved understanding of long-term hydroclimate change and variability at regional to synoptic scales across the United States.
Changes in the frequency of cold and warm synoptic weather types within eastern North America indicate the occurrence of a cool season climate shift in the late 1990s. This aligns with the timing of ...shifts toward earlier spring ice out on freshwater lakes within the region and less frequent cold air mass passage over the North American Great Lakes. While a preliminary shift occurred in the early 1980s, a pronounced shift toward more frequent warm weather types during November through April occurred after 1997, when prominent warming of the lower atmosphere over the region began. The late 1990s’ climate shift appears linked to middle atmospheric circulation change associated with phase changes for two influential low-frequency climate teleconnections originating within the Atlantic and Pacific Oceans, the Atlantic Multidecadal Oscillation and the Interdecadal Pacific Oscillation. The climate shift, approximately 20 years after warming within the global climate system commenced, further illustrates the importance of climate system variability within anthropogenically driven climate change.
Hurricanes and flood-related events cause more direct economic damage than any other type of natural disaster. In the United States, that damage totals more than USD 1 trillion in damages since 1980. ...On average, direct flood losses have risen from USD 4 billion annually in the 1980s to roughly USD 17 billion annually from 2010 to 2018. Despite flooding’s tremendous economic impact on US properties and communities, current estimates of expected damages are lacking due to the fact that flood risk in many parts of the US is unidentified, underestimated, or available models associated with high quality assessment tools are proprietary. This study introduces an economic-focused Environmental Impact Assessment (EIA) approach that builds upon an our existing understanding of prior assessment methods by taking advantage of a newly available, climate adjusted, parcel-level flood risk assessment model (First Street Foundation, 2020a and 2020b) in order to quantify property level economic impacts today, and into the climate adjusted future, using the Intergovernmental Panel on Climate Change’s (IPCC) Representative Concentration Pathways (RCPs) and NASA’s Global Climate Model ensemble (CMIP5). This approach represents a first of its kind—a publicly available high precision flood risk assessment tool at the property level developed completely with open data sources and open methods. The economic impact assessment presented here has been carried out using residential buildings in New Jersey as a testbed; however, the environmental assessment tool on which it is based is a national scale property level flood assessment model at a 3 m resolution. As evidence of the reliability of the EIA tool, the 2020 estimated economic impact (USD 5481 annual expectation) was compared to actual average per claim-year NFIP payouts from flooding and found an average of USD 5540 over the life of the program (difference of less than USD 100). Additionally, the tool finds a 41.4% increase in average economic flood damage through the year 2050 when environmental change is included in the model.
ABSTRACT
Extreme precipitation studies commonly link anomalies to specific episodes of drought or flooding, while studies of precipitation volatility typically employ statistical measures of ...variability. This study addresses the concept of an extreme precipitation reversal (EPR), defined as an unusually wet or dry period that precedes a large precipitation anomaly of opposite sign, or more specifically the difference in the percentiles of precipitation for consecutive periods. The focus of this study is EPRs over the past 121 years for the hydrologically critical winter season across the Western United States. Results show that EPR values are of a greater magnitude during the second half of the historical record than during the first half, indicating increased volatility in extreme winter‐to‐winter precipitation. Historically, the direction of reversals (wet‐to‐dry or dry‐to‐wet) corresponds to a similar reversal in the nature of the El Niño‐Southern Oscillation (ENSO) phenomenon, although EPRs are not systematically aligned with extreme ENSO reversals. While a greater frequency and intensity of winter season EPRs in recent years is potentially problematic for water managers, the relationship with ENSO may afford proactive management and mitigation of the impacts.
The nine climate regions of the United States (a) and the Northwest and West region climate divisions (b)(http://www.ncdc.noaa.gov/monitoring‐references/maps/us‐climate‐regions.php).
The North American Great Lakes influence surface weather downwind, distinctly in winter when southward migrating cold air passes over relatively warm lakes. Study of the synoptic atmospheric patterns ...favorable for lake effects has focused on lake-effect snowfall, the most impactful effect of the lakes. Although the patterns are conducive to lake effects, they might not actually yield discernible modification of downwind surface weather. This study uses historical daily data (1964-1965 through 2017-2018) of weather types to detect cool season (November-April) modification of cold, dry air upwind of the Great Lakes to cool, moist air downwind of the eastern (Erie, Ontario) and western (Michigan, Superior) lakes. A spatial arrangement of weather types across the region is shown to identify individual days characterized by a lake effect. The frequency of lake effects increased through the first one third of the record, but it has since decreased, most profoundly since a change point in the late 1990s and more prominently for the eastern lakes. At stations immediately downwind of the lakes, the result is a changed cool season hydroclimate, with fifty-four-year declines in lake-effect precipitation amount and frequency and in the percentages of seasonal precipitation amount and frequency attributed to lake effects.
ABSTRACT
An air mass approach was used to identify episodes of cool season cold‐air damming (CAD) within the central Appalachian Mountains region of the eastern United States. Daily air mass type ...data were used to identify days on which moist polar (MP) air was regionally evident east of the mountains, while non‐MP air was in place at nearby stations west of the mountains. Over a 35‐year study period, 219 CAD days were identified (>6 per year) with the annual frequency exhibiting no trend but suggesting that El Niño (La Niña) coincides with a greater (lesser) frequency of CAD days in winter (December–February). Synoptic atmospheric composites reveal west‐to‐east migration of a parent anticyclone to a classic position along the border of the northeastern United States and southeastern Canada. This coincides with a pattern of amplifying and slowly eastward‐moving 500 hPa height anomalies characterized by positive (negative) values over eastern (western) North America that are signalled a few days in advance by the index representing the Pacific‐North American teleconnection pattern. Confinement of the CAD below the 850 hPa level is evident in the synoptic wind field, while the composite vertical profile of the atmosphere within the CAD environment further depicts the shallow nature of the surface‐based cool, moist air. Northeasterly winds at the surface veer to southeasterly within a few hundred metres above the surface, and then southwesterly at less than one km above the surface, at the 850 hPa level. The air mass approach to CAD identification appears to successfully identify regional occurrences of synoptically forced CAD, although it likely does not detect local and/or diabatically forced CAD.
An air mass approach is used to identify occurrences of synoptically‐forced cold‐air damming (CAD) within the central Appalachian Mountains region of the eastern United States. Results indicate that El Niño (La Niña) coincides with a greater (lesser) frequency of winter CAD days. CAD days coincide with amplifying and eastward‐moving 500 hPa height anomalies characterized by positive (negative) values over eastern (western) North America that are signaled a few days in advance by the index representing the Pacific‐North American teleconnection pattern.
Recent research suggests that the characteristics of precipitation, particularly extremes and variability, are changing with a warming global climate. This study demonstrates a budding approach to ...analyzing the temporal uniformity of precipitation using daily data for the Mid-Atlantic region of the eastern United States over the period 1950 to 2017. The Gini coefficient (GC) assesses the equity of a distribution of an accumulated quantity across individual contributors. In this study, the GC characterizes the equity with which daily precipitation events contributed to seasonal and annual precipitation amounts through the study period. The Lorenz asymmetry coefficient (LAC) expresses the relative magnitude of precipitation events (heavy, light) that were primarily responsible for instances of inequity. Time series analysis of precipitation amount, wet-day frequency, wet-day GC values, and wet-day LAC values for each of 158 stations within the Mid-Atlantic region and for the region as a whole reveal ongoing change in the hydroclimate. Over the 68 yr study period, the region experienced increases in annual precipitation amount and wet-day frequency, while precipitation became less evenly distributed across precipitation events. The results suggest that extreme precipitation events are becoming more prevalent. Heavier and lighter events are in creasing at the expense of moderate events.
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