scholarly journals Prediction of Summer Maximum and Minimum Temperature over the Central and Western United States: The Roles of Soil Moisture and Sea Surface Temperature

2006 ◽  
Vol 19 (8) ◽  
pp. 1407-1421 ◽  
Author(s):  
Eric J. Alfaro ◽  
Alexander Gershunov ◽  
Daniel Cayan
Keyword(s):  
United States ◽  
Soil Moisture ◽  
Short Range ◽  
Large Scale ◽  
Severity Index ◽  
Time Frame ◽  
Western United States ◽  
Drought Severity ◽  
Explanatory Variables ◽  
Predictive Skill

Abstract A statistical model based on canonical correlation analysis (CCA) was used to explore climatic associations and predictability of June–August (JJA) maximum and minimum surface air temperatures (Tmax and Tmin) as well as the frequency of Tmax daily extremes (Tmax90) in the central and western United States (west of 90°W). Explanatory variables are monthly and seasonal Pacific Ocean SST (PSST) and the Climate Division Palmer Drought Severity Index (PDSI) during 1950–2001. Although there is a positive correlation between Tmax and Tmin, the two variables exhibit somewhat different patterns and dynamics. Both exhibit their lowest levels of variability in summer, but that of Tmax is greater than Tmin. The predictability of Tmax is mainly associated with local effects related to previous soil moisture conditions at short range (one month to one season), with PSST providing a secondary influence. Predictability of Tmin is more strongly influenced by large-scale (PSST) patterns, with PDSI acting as a short-range predictive influence. For both predictand variables (Tmax and Tmin), the PDSI influence falls off markedly at time leads beyond a few months, but a PSST influence remains for at least two seasons. The maximum predictive skill for JJA Tmin, Tmax, and Tmax90 is from May PSST and PDSI. Importantly, skills evaluated for various seasons and time leads undergo a seasonal cycle that has maximum levels in summer. At the seasonal time frame, summer Tmax prediction skills are greatest in the Midwest, northern and central California, Arizona, and Utah. Similar results were found for Tmax90. In contrast, Tmin skill is spread over most of the western region, except for clusters of low skill in the northern Midwest and southern Montana, Idaho, and northern Arizona.

Long lead statistical forecasts of area burned in western U.S. wildfires by ecosystem province

2002 ◽  
Vol 11 (4) ◽  
pp. 257 ◽  
Author(s):  
Anthony L. Westerling ◽  
Alexander Gershunov ◽  
Daniel R. Cayan ◽  
Tim P. Barnett
Keyword(s):  
Soil Moisture ◽  
Large Scale ◽  
Forecast Model ◽  
Severity Index ◽  
Fire Season ◽  
Drought Severity ◽  
Canonical Correlations ◽  
Area Burned ◽  
Wildfire Season ◽  
Random Guess

A statistical forecast methodology exploits large-scale patterns in monthly U.S. Climatological Division Palmer Drought Severity Index (PDSI) values over a wide region and several seasons to predict area burned in western U.S. wildfires by ecosystem province a season in advance. The forecast model, which is based on canonical correlations, indicates that a few characteristic patterns determine predicted wildfire season area burned. Strong negative associations between anomalous soil moisture (inferred from PDSI) immediately prior to the fire season and area burned dominate in most higher elevation forested provinces, while strong positive associations between anomalous soil moisture a year prior to the fire season and area burned dominate in desert and shrub and grassland provinces. In much of the western U.S., above- and below-normal fire season forecasts were successful 57% of the time or better, as compared with a 33% skill for a random guess, and with a low probability of being surprised by a fire season at the opposite extreme of that forecast.

scholarly journals How Wet and Dry Spells Evolve across the Conterminous United States Based on 555 Years of Paleoclimate Data

2018 ◽  
Vol 31 (16) ◽  
pp. 6633-6647 ◽  
Author(s):  
Michelle Ho ◽  
Upmanu Lall ◽  
Edward R. Cook
Keyword(s):  
United States ◽  
Large Scale ◽  
Viterbi Algorithm ◽  
Severity Index ◽  
Climate Forcing ◽  
Drought Severity ◽  
Spatial Features ◽  
Dry Spells ◽  
Temporal And Spatial ◽  
Wet Spells

Abstract Evolving patterns of droughts and wet spells in the conterminous United States (CONUS) are examined over 555 years using a tree-ring-based paleoclimate reconstruction of the modified Palmer drought severity index (PDSI). A hidden Markov model is used as an unsupervised method of classifying climate states and quantifying the temporal evolution from one state to another. Modeling temporal variability in spatial patterns of drought and wet spells provides the ability to objectively assess and simulate historical persistence and recurrence of similar patterns. The Viterbi algorithm reveals the probable sequence of states through time, enabling an examination of temporal and spatial features and associated large-scale climate forcing. Distinct patterns of sea surface temperature that are known to enhance or inhibit rainfall are associated with some states. Using the current CONUS PDSI field the model can be used to simulate the space–time PDSI pattern over the next few years, or unconditional simulations can be used to derive estimates of spatially concurrent PDSI patterns and their persistence and intensity across the CONUS.

Statistical Model for Forecasting Monthly Large Wildfire Events in Western United States

2007 ◽  
Vol 46 (7) ◽  
pp. 1020-1030 ◽  
Author(s):  
Haiganoush K. Preisler ◽  
Anthony L. Westerling
Keyword(s):  
United States ◽  
Statistical Model ◽  
Spatial Scales ◽  
Severity Index ◽  
Fire Danger ◽  
Western United States ◽  
Drought Severity ◽  
Large Fire ◽  
Confidence Bounds ◽  
Regression Techniques

Abstract The ability to forecast the number and location of large wildfire events (with specified confidence bounds) is important to fire managers attempting to allocate and distribute suppression efforts during severe fire seasons. This paper describes the development of a statistical model for assessing the forecasting skills of fire-danger predictors and producing 1-month-ahead wildfire-danger probabilities in the western United States. The method is based on logistic regression techniques with spline functions to accommodate nonlinear relationships between fire-danger predictors and probability of large fire events. Estimates were based on 25 yr of historic fire occurrence data (1980–2004). The model using the predictors monthly average temperature, and lagged Palmer drought severity index demonstrated significant improvement in forecasting skill over historic frequencies (persistence forecasts) of large fire events. The statistical models were particularly amenable to model evaluation and production of probability-based fire-danger maps with prespecified precisions. For example, during the 25 yr of the study for the month of July, an area greater than 400 ha burned in 3% of locations where the model forecast was low; 11% of locations where the forecast was moderate; and 76% of locations where the forecast was extreme. The statistical techniques may be used to assess the skill of forecast fire-danger indices developed at other temporal or spatial scales.

scholarly journals Evidence for Increasingly Variable Drought Conditions in the United States Since 1895

2015 ◽  
Author(s):  
Sierra Rayne ◽  
Kaya Forest
Keyword(s):  
United States ◽  
Severity Index ◽  
The United States ◽  
Time Frame ◽  
Drought Severity ◽  
The Pacific ◽  
Rapid Changes ◽  
Increasing Trend ◽  
End Members ◽  
Short Time

Annual and summertime trends towards increasingly variable values of the Palmer Drought Severity Index (PDSI) over a sub-decadal period (five years) were investigated within the contiguous United States between 1895 and the present. For the contiguous U.S. as a whole, there is a significant increasing trend in the five-year running minimum-maximum ranges for the annual PDSI (aPDSI5yr(min|max range)). During this time frame, the averageaPDSI5yr(min|max range)has increased by about one full unit, indicating a substantial increase is drought variability over short time scales across the United States. The end members of the runningaPDSI5yr(min|max range)highlight even more rapid changes in the drought index variability within the past 120 years. This increasing variability in theaPDSI5yr(min|max range)is driven primarily by changes taking place in the Pacific and Atlantic Ocean coastal climate regions, climate regions which collectively comprise one-third the area of the contiguous U.S. Overall, interannual drought patterns are becoming more extreme and difficult to predict, posing a challenge to agricultural and other water-resource related planning efforts.

scholarly journals Influence of the Pacific Decadal Oscillation on Winter Precipitation and Drought during Years of Neutral ENSO in the Western United States

2007 ◽  
Vol 22 (1) ◽  
pp. 116-124 ◽  
Author(s):  
Gregory B. Goodrich
Keyword(s):  
United States ◽  
Pacific Northwest ◽  
Pacific Decadal Oscillation ◽  
Severity Index ◽  
Winter Precipitation ◽  
Western United States ◽  
Drought Severity ◽  
The Pacific ◽  
Area Of Influence ◽  
Hydroclimatic Variables

Abstract The influence of the Pacific decadal oscillation (PDO) on important hydroclimatic variables during years of neutral ENSO for 84 climate divisions in the western United States is analyzed from 1925 to 1998. When the 34 neutral ENSO years are split by cold (12 yr) and warm (22 yr) PDOs, the resulting winter precipitation patterns are spatially similar to those that occur during years of La Niña–cold PDO and, to a lesser extent, years of El Niño–warm PDO, respectively, although the characteristic ENSO dipole is not evident. The PDO influence is similar when the winter Palmer drought severity index is analyzed, although the core area of influence moves from the Southwest to the northern Rockies. Correlations between Niño-3.4 SSTs and the hydroclimatic variables reverse sign when the neutral ENSO years are split by PDO phase. The greatest difference between correlations occurs in the characteristic dipole between the Pacific Northwest and the desert Southwest. Since seasonal forecast guidance based on ENSO conditions in the tropical Pacific often yields a forecast of “equal chances” during years of neutral ENSO, forecasters may be able to improve their forecasts for the southwestern United States depending on if the PDO is known to be in the cold (drier than normal) or warm (wetter than normal) phase. However, this can be difficult to implement considering the current uncertainty of the phase of the PDO.

scholarly journals Variability of Cloudiness over Mountain Terrain in the Western United States

2017 ◽  
Vol 18 (5) ◽  
pp. 1227-1245 ◽  
Author(s):  
Edwin Sumargo ◽  
Daniel R. Cayan
Keyword(s):  
United States ◽  
Large Scale ◽  
Spatial Scales ◽  
High Elevation ◽  
Empirical Orthogonal Functions ◽  
Western United States ◽  
Spatial And Temporal Variability ◽  
Regional Patterns ◽  
Cloud Albedo

Abstract This study investigates the spatial and temporal variability of cloudiness across mountain zones in the western United States. Daily average cloud albedo is derived from a 19-yr series (1996–2014) of half-hourly Geostationary Operational Environmental Satellite (GOES) images. During springtime when incident radiation is active in driving snowmelt–runoff processes, the magnitude of daily cloud variations can exceed 50% of long-term averages. Even when aggregated over 3-month periods, cloud albedo varies by ±10% of long-term averages in many locations. Rotated empirical orthogonal functions (REOFs) of daily cloud albedo anomalies over high-elevation regions of the western conterminous United States identify distinct regional patterns, wherein the first five REOFs account for ~67% of the total variance. REOF1 is centered over Northern California and Oregon and is pronounced between November and March. REOF2 is centered over the interior northwest and is accentuated between March and July. Each of the REOF/rotated principal components (RPC) modes associates with anomalous large-scale atmospheric circulation patterns and one or more large-scale teleconnection indices (Arctic Oscillation, Niño-3.4, and Pacific–North American), which helps to explain why anomalous cloudiness patterns take on regional spatial scales and contain substantial variability over seasonal time scales.

A collaborative model for large-scale riparian restoration in the western United States

2014 ◽  
Vol 23 (2) ◽  
pp. 143-148 ◽  
Author(s):  
J. Daniel Oppenheimer ◽  
Stacy K. Beaugh ◽  
Julie A. Knudson ◽  
Peter Mueller ◽  
Nikki Grant-Hoffman ◽  
...  
Keyword(s):  
United States ◽  
Large Scale ◽  
Western United States ◽  
Riparian Restoration ◽  
Collaborative Model

Flash Drought Characteristics by Different Severities in Humid Subtropical Basins: A Case Study in the Gan River Basin, China

2021 ◽  
pp. 1-44
Author(s):  
Yuqing Zhang ◽  
Qinglong You ◽  
Guangxiong Mao ◽  
Changchun Chen ◽  
Xin Li ◽  
...  
Keyword(s):  
Soil Moisture ◽  
River Basin ◽  
Vapour Pressure Deficit ◽  
Severity Index ◽  
Drought Severity ◽  
Rapid Decline ◽  
Drought Risk ◽  
Drought Event ◽  
Drought Period ◽  
Drought Intensity

AbstractIt is essential to assess flash drought risk based on a reliable flash drought intensity (severity) index incorporating comprehensive information of the rapid decline (“flash”) in soil moisture towards drought conditions and soil moisture thresholds belonging to the “drought” category. In this study, we used the Gan River Basin as an example to define a flash drought intensity index that can be calculated for individual time steps (pentads) during a flash drought period over a given grid (or station). The severity of a complete flash drought event is the sum of the intensity values during the flash drought. We explored the spatial and temporal characteristics of flash droughts with different grades based on their respective severities. The results show that decreases in total cloud cover, precipitation, and relative humidity, as well as increases in 500 hPa geopotential height, convective inhibition, temperature, vapour pressure deficit, and wind speed can create favorable conditions for the occurrence of flash droughts. Although flash droughts are relatively frequent in the central and southern parts of the basin, the severity is relatively high in the northern part of the basin due to longer duration. Flash drought severity shows a slightly downward trend due to decreases in frequency, duration, and intensity from 1961 to 2018. Extreme and exceptional flash droughts decrease significantly while moderate and severe flash droughts trend slightly upward. Flash drought severity appears to be more affected by the interaction between duration and intensity as the grade increases from mild to severe. The frequency and duration of flash droughts are higher in July to October. The southern part of the basin is more prone to moderate and severe flash droughts, while the northern parts of the basin are more vulnerable to extreme and exceptional flash droughts due to longer durations and greater severities than other parts. Moderate, severe, extreme, and exceptional flash droughts occurred approximately every 3-6, 5-15, 10-50, and 30-200 year intervals, respectively, based on the copula analysis.

The dendroecology and climatic impacts for old-growth white pine and hemlock on the extreme slopes of the Berkshire Hills, Massachusetts, U.S.A.

2000 ◽  
Vol 78 (7) ◽  
pp. 851-861 ◽  
Author(s):  
Marc D Abrams ◽  
Saskia van de Gevel ◽  
Ryan C Dodson ◽  
Carolyn A Copenheaver
Keyword(s):  
United States ◽  
20Th Century ◽  
Tree Ring ◽  
Palmer Drought Severity Index ◽  
Severity Index ◽  
Drought Severity ◽  
White Pine ◽  
Old Growth ◽  
Hardwood Species ◽  
Drought Severity Index

Dendrochronological techniques were used to investigate the dynamics of an old-growth forest on the extreme slope (65%) at Ice Glen Natural Area in southwestern Massachusetts. The site represented a rare opportunity to study the disturbance history, successional development, and responses to climatic variation of an old-growth hemlock (Tsuga canadensis (L.) Carr) - white pine (Pinus strobus L.) - northern hardwood forest in the northeastern United States. Hemlock is the oldest species in the forest, with maximum tree ages of 305-321 years. The maximum ages for white pine and several hardwood species are 170-200 years. There was continuous recruitment of hemlock trees from 1677 to 1948. All of the existing white pine was recruited in the period between 1800 and 1880, forming an unevenly aged population within an unevenly aged, old-growth hemlock canopy. This was associated with large increases in the Master tree-ring chronologies, indicative of major stand-wide disturbances, for both hemlock and white pine. Nearly all of the hardwood species were also recruited between 1800 and 1880. After 1900, there was a dramatic decline in recruitment for all species, including hemlock, probably as a result of intensive deer browsing. White pine and hemlock tree-ring growth during the 20th century was positively correlated with the annual Palmer drought severity index (r = 0.61 and 0.39, respectively). This included reduced growth during periods of low Palmer drought severity index values, the drought years of 1895-1922, and dramatic increases during periods of high Palmer drought severity index values in the 1970s and 1990s. Significant positive and negative correlations of certain monthly Palmer drought severity index values with 20th century tree-ring chronologies also exist for white pine and hemlock using response function analysis. The results of this study suggest that old-growth forests on extreme sites in the eastern United States may be particularly sensitive to direct and indirect allogenic factors and climatic variations and represent an important resource for studying long-term ecological and climatic history.Key words: age structure, radial growth analysis, disturbance, climate, fire, tree rings.

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