Kelly T. Redmond

Surface Climate and Streamflow Variability in the Western United States and Their Relationship to Large‐Scale Circulation Indices

A statistical analysis was undertaken to determine the nature and magnitude of the relationship of precipitation, temperature and streamflow in the western United States to large-scale atmospheric circulation patterns. The Southern Oscillation Index (SOI) was used as an indicator of the El Nino/Southern Oscillation (ENSO) and the PNA index as an indicator of the Pacific//North America pattern. These indices were correlated with surface climate data and split sample analyses were conducted to determine climate response during the extreme phases of each index. October–March precipitation was shown to be most strongly correlated with SOI averaged over the July–November period. The analysis showed that there are two centers of opposite association with the SOI. During low values of the SOI (ENSO events) precipitation is low in the Pacific northwest and high in the desert southwest. Correlations between SOI and temperature were greatest in the Pacific northwest. The split sample analysis also revealed statistically significant differences in precipitation occurring during extremes of the SOI. The PNA pattern was related to precipitation and temperature over a concurrent time period. Especially strong associations were noted in the Pacific northwest for both precipitation and temperature. Streamflow showed associations with SOI similar to precipitation.

ENSO and Hydrologic Extremes in the Western United States

Frequency distributions of daily precipitation in winter and daily stream flow from late winter to early summer, at several hundred sites in the western United States, exhibit strong and systematic responses to the two phases of ENSO. Most of the stream flows considered are driven by snowmelt. The Southern Oscillation index (SOI) is used as the ENSO phase indicator. Both modest (median) and larger (90th percentile) events were considered. In years with negative SOI values (El Nino), days with high daily precipitation and stream flow are more frequent than average over the Southwest and less frequent over the Northwest. During years with positive SOI values (La Nina), a nearly opposite pattern is seen. A more pronounced increase is seen in the number of days exceeding climatological 90th percentile values than in the number exceeding climatological 50th percentile values, for both precipitation and stream flow. Stream flow responses to ENSO extremes are accentuated over precipitation responses. Evidence suggests that the mechanism for this amplification involves ENSO-phase differences in the persistence and duration of wet episodes, affecting the efficiency of the process by which precipitation is converted to runoff. The SOI leads the precipitation events by several months, and hydrologic lags (mostly through snowmelt) delay the stream flow response by several more months. The combined 6-12-month predictive aspect of this relationship should be of significant benefit in responding to flood (or drought) risk and in improving overall water management in the western states.

Climate and Salmon Restoration in the Columbia River Basin: The Role and Usability of Seasonal Forecasts

Abstract The Pacific Northwest is dependent on the vast and complex Columbia River system for power production, irrigation, navigation, flood control, recreation, municipal and industrial water supplies, and fish and wildlife habitat. In recent years Pacific salmon populations in this region, a highly valued cultural and economic resource, have declined precipitously. Since 1980, regional entities have embarked on the largest effort at ecosystem management undertaken to date in the United States, primarily aimed at balancing hydropower demands with salmon restoration activities. It has become increasingly clear that climatically driven fluctuations in the freshwater and marine environments occupied by these fish are an important influence on population variability. It is also clear that there are significant prospects of climate predictability that may prove advantageous in managing the water resources shared by the long cast of regional interests. The main thrusts of this study are 1) to describe the cli...

Methodology and Results of Calculating Central California Surface Temperature Trends: Evidence of Human-Induced Climate Change?

Abstract A procedure is described to construct time series of regional surface temperatures and is then applied to interior central California stations to test the hypothesis that century-scale trend differences between irrigated and nonirrigated regions may be identified. The procedure requires documentation of every point in time at which a discontinuity in a station record may have occurred through (a) the examination of metadata forms (e.g., station moves) and (b) simple statistical tests. From this “homogeneous segments” of temperature records for each station are defined. Biases are determined for each segment relative to all others through a method employing mathematical graph theory. The debiased segments are then merged, forming a complete regional time series. Time series of daily maximum and minimum temperatures for stations in the irrigated San Joaquin Valley (Valley) and nearby nonirrigated Sierra Nevada (Sierra) were generated for 1910–2003. Results show that twentieth-century Valley minimum...

Gulf of California Sea Surface Temperatures and the North American Monsoon: Mechanistic Implications from Observations

Abstract Perhaps the most regular and predictable weather pattern in North America is the North American (NA) or Mexican monsoon. Occurring in summer, it delivers about 35% and 45% of Arizonas and New Mexicos annual precipitation, respectively, and about 60% of northern Mexicos. While recent studies have linked strong NA monsoons to summer drought in the U.S. Midwest, the sequence of events that produce the NA monsoon remain unclear. This empirical study builds on the findings of many other studies that implicate the Gulf of California [(GOC) or simply the gulf] as the dominant moisture source for the monsoon. It examines six monsoon seasons in detail, and quantitatively relates GOC sea surface temperatures (SST) to the timing, amount, and regional extent of monsoon rainfall. This six season study is based on satellite measurements of rainfall [using the Special Sensor Microwave Imager (SSM/I)] and GOC SST at high spatial and temporal resolution. Key findings include the following. 1) Monsoon rainfall ...

Temporal variations in frost‐free season in the United States: 1895–2000

[1] A newly available data set of daily temperature observations was used to study the temporal variability of the frost-free season, based on an inclusive 0°C threshold, for 1895-2000 in the conterminous United States. A national average time series of the length of the frost-free season is characterized by 3 distinct regimes. The period prior to 1930 was notable for decreasing frost-free season length from 1895 to a minimum around 1910, followed by a marked increase in length of about 1 week from 1910 to 1930. During 1930-1980, frost-free season length was near the period average with relatively little decadal-scale variability. Since 1980, frost-free season length has increased by about 1 week. The national average increase in frost-free season length from the beginning to the end of the 20th Century is about 2 weeks. Frost-free season length has increased much more in the western U.S. than in the eastern U.S.

Winter orographic precipitation ratios in the Sierra Nevada - Large-scale atmospheric circulations and hydrologic consequences

The extent to which winter precipitation is orographically enhanced within the Sierra Nevada of California varies from storm to storm, and season to season, from occasions when precipitation rates at low and high altitudes are almost the same to instances when precipitation rates at middle elevations (considered here) can be as much as 30 times more than at the base of the range. Analyses of large-scale conditions associated with orographic precipitation variations during storms and seasons from 1954 to 1999 show that strongly orographic storms most commonly have winds that transport water vapor across the range from a more nearly westerly direction than during less orographic storms and than during the largest overall storms, and generally the strongly orographic storms are less convectively stable. Strongly orographic conditions often follow heavy precipitation events because both of these wind conditions are present in midlatitude cyclones that form the cores of many

Classification of Regional Climate Variability in the State of California

A novel approach is presented to objectively identify regional patterns of climate variability within the state of California using principal component analysis on monthly precipitation and temperature data from a network of 195 climate stations statewide and an ancillary gridded database. The confluence of large-scale circulation patterns and the complex geography of the state result in 11 regional modes of climate variability within the state. A comparison between the station and gridded analyses reveals that finescale spatial resolution is needed to adequately capture regional modes in complex orographic and coastal settings. Objectively identified regions can be employed not only in tracking regional climate signatures, but also in improving the understanding of mechanisms behind regional climate variability and climate change. The analysis has been incorporated into an operational tool called the California Climate Tracker.

Managing climate change refugia for climate adaptation

Refugia have long been studied from paleontological and biogeographical perspectives to understand how populations persisted during past periods of unfavorable climate. Recently, researchers have applied the idea to contemporary landscapes to identify climate change refugia, here defined as areas relatively buffered from contemporary climate change over time that enable persistence of valued physical, ecological, and socio-cultural resources. We differentiate historical and contemporary views, and characterize physical and ecological processes that create and maintain climate change refugia. We then delineate how refugia can fit into existing decision support frameworks for climate adaptation and describe seven steps for managing them. Finally, we identify challenges and opportunities for operationalizing the concept of climate change refugia. Managing climate change refugia can be an important option for conservation in the face of ongoing climate change.

THE DEPICTION OF DROUGHT

AUGUST 2002 AMERICAN METEOROLOGICAL SOCIETY | T his issue of BAMS contains several articles that emphasize how we describe the status of drought. Interest in this topic has risen because of a combination of natural and human factors. The Southwest–southern Great Plains drought of 1995–96 led to the establishment of the Western Drought Coordination Council (WDCC) by the Western Governors Association. The subsequent National Drought Policy Commission (NDPC) expanded on WDCC recommendations distilled from the western experience. Both groups emphasized climate monitoring as a necessity. In May 1999, drought in an area of tremendous climatic significance—Washington, D.C.—led to the establishment of the Drought Monitor. A small cadre of climatologists, originally in the West—the Climate Prediction Center, the National Climatic Data Center (NCDC), and the National Drought Mitigation Center— were involved in every step in this sequence, and participation has gradually grown since. The Drought Monitor is both a product and an activity. An extended e-mail “conversation” takes place for about 2–3 days each week, and the results are assimilated by the “author of the week” into a consensus product in the form of a national map. During a typical week about 15–20 out of a total distribution of around 140 individuals participate, mostly from affected areas. The article by Svoboda et al. captures the flavor of the Drought Monitor very well. The discussions, ranging widely as conditions and issues unfold, have proven to be a rich source of provocative thought. It is from these and numerous earlier WDCC discussions, and other experiences over the prior 15 years, that the personal perspective has been acquired to offer the observations and comments that follow.