U41B-01 INVITED
Drought Studies For Mexico
Drought constitutes one of the major threats for a number of socioeconomic sectors in Mexico. Meteorological drought occurs in various temporal and spatial scales that range from a few weeks in the tropical Mexico to decades in northern Mexico. Historically, these long term droughts have had a negative impact, not only in economic activities, but in the lives of Mexicans as well. In general, short term droughts over central southern Mexico are related to El Niño conditions. However, drought may also occur when an anomalously low number of easterly waves reach the Caribbean and Mexico. El Niño and easterly wave activity may be related by the intensification of the Caribbean Low Level Jet. However, the role of this form of transient activity as a drought trigger in Mexico has not been explored in depth. The present analysis explores the possibility of more than one form of forcing to explain drought in Mexico on various spatial and temporal scales, as well as in various regions. Such approach to the study of drought may prove useful to diagnose why certain general circulation models are unable of reproducing drought patterns over Mexico.
U41B-02
Drought and Patterns of Circulation Inferred From Tree-Ring Data in Western North America
Tree-ring data are excellent proxies for climate in western North America and have been used to reconstruction a variety of hydroclimatic variables. This study takes advantage of a network of PDSI reconstructions and reconstructions of Colorado River streamflow to examine drought in the upper Colorado River basin over the past five centuries, with a focus on multidecadal periods of drought. The upper Colorado River basin is located in a zone that is transitional with respect to a number of circulation features, including ENSO. As a result, the circulation patterns that lead to drought in this region have not been well identified. This study uses the PSDI reconstruction network as the basis for a set of indices that describes major spatial patterns of drought across western North America. These drought pattern indices are compared to Colorado River reconstructed flow to investigate widespread hydroclimatic patterns during periods of drought in the basin over past centuries. Since hydroclimatic patterns, such as the winter moisture dipole between the northwestern and southwestern US, may be indicators of ocean/atmospheric conditions, these proxy-based indices derived may be useful for documenting the association between upper Colorado River basin drought and ocean/atmosphere circulation in the past.
U41B-03
Long-term Drought in the North-Western Interior of North America and Linkages to ENSO, PDO and AMO
The subhumid climate of North America's western interior extends to high latitudes in the rainshadow of the
western Cordillera. Higher temperatures in this region in recent decades are consistent with global warming
scenarios that also include increased summer aridity. This drier climate most likely will result from a greater
frequency of severe or prolonged drought. The instrumental observation of climate, extending only to late 19th
century at a few sites, provides a limited perspective on long-term hydroclimatic variability. Most drivers of the
variation in hydroclimate have a periodicity that approaches or exceeds the length of instrumental records. Among
sources of paleo-climatic data, tree-rings are among the best proxies of summer and annual hydroclimate and
drought.
In the Tree-Ring Lab at the University of Regina, we have developed a network of more than 60 moisture-sensitive
tree-ring chronologies spanning the western interior from the island forests of eastern Montana, up the foothills
of the Canadian Rockies and across the boreal forest of Alberta, Saskatchewan and the Northwest Territories.
Most of the tree-ring samples are from open-canopy forests sites at dry sites, where available soil moisture
controls tree growth. This tree-ring network enables us to examine the variability of hydroclimate over the past
250-750 years and 19 degrees of latitude. Correlations between principal components and global SSTs and SLP
reveal responses of tree growth to ENSO, PDO and AMO. This comparative wavelet analysis indicates that
moisture variability at interannual (2-7 yr) and decadal to interdecadal (15-25 yr) timescales is strongly linked to
SSTs in the Pacific Ocean (i.e. ENSO and PDO), while multidecadal variability (30-70 yr) is mainly related to the
AMO. These forcings of hydroclimate and their interactions modulate to a great extent the moisture variability in
this region at various temporal and spatial scales.
The application of our paleo-drought records to water resource management in western Canada is one aspect of
the knowledge translation strategy at the Prairie Adaptation Research Collaborative; PARC supports
collaborations among scientists and decision makes to address adaptation to climate change. An important
finding of our tree-ring research with management implications is the distinct hydroclimatic cycles with
wavelengths that are near or just beyond the length of gauge records. Also the non-stationarity of linkages
between drought and SSTs indicates that forcing of hydroclimatic variability identified from the analysis of
instrumental records may apply only to recent decades. Western water policy, use and management practices
have evolved during a period of fairly reliable water supplies and under assumptions of relatively abundant water
and stationary hydroclimate. The low frequency cycling of hydroclimate will underlie the trends imposed by global
warming: lower summer stream flows, falling lake levels, and increasingly frequent soil and surface water
deficits. Between cycles and trends, our experience with practitioners is that they more comfortable with historical
and proxy data records derived from tangible archives as opposed to simulated shifts in future climate. Thus the
tree-ring reconstructions of streamflow and drought serve to expand the perspective of water managers beyond
the range of conventional experience and databases before they are asked to comprehend and apply scenarios
of the hydroclimate of the mid 21st century.
http:www.parc.ca/urtreelab
U41B-04
Simulation of ENSO Forcings on U.S. Drought by the HadCM3 Coupled Climate Model
The ability of the HadCM3 coupled ocean - atmosphere general circulation model to represent the mechanisms linking the El Niño Southern Oscillation (ENSO) and drought in the U.S. is investigated. Rotated principal components analyses of a self-calibrating Palmer Drought Severity Index (scPDSI) data are used to identify the dominant modes of summer drought variability in the observed climate record (1901-2002), and in a 250-year period of a HadCM3 control run. A similar mode of drought variability is identified in both data sets that is correlated with ENSO variability: a monopolar pattern across the continental interior, centred in the southern states. HadCM3 successfully reproduces the displacement of the mid-latitude jet streams during ENSO events, a mechanism related to U.S. drought variability, but the model appears to be less realistic in its simulation of the influence of Rossby wave teleconections on drought, possibly due to errors in its simulation of ENSO in the equatorial Pacific. Despite this, we conclude that HadCM3's simulation of the link between ENSO and U.S. drought is sufficiently realistic for it to be used in further studies of U.S. drought variability.
U41B-05
Meteorological drought episodes over Mexico region
The occurrence of drought in Mexico has brought to light the large vulnerability of the northern part of this country to water shortages. However, it is not clear what produces a meteorological drought spanning for more than one year. Based on gridded monthly precipitation data for the one hundred years, the spatial structure of significant deficit in precipitation is documented. Low frequency variations in precipitation are also examined to identify potential forcing mechanisms associated to circulation anomalies over North America region, such as the Hadley Cell. This hypothesis though, is not able to fully contrast the difference in precipitation between the 1950s and the 1930s drought episodes. Remote mechanisms related to transient activity such as easterly waves may be important to explain some of the regional aspects of drought over northern Mexico.
U41B-06
Pacific Ocean Sea Surface Temperatures and Their Relationship to North American Fire Danger and Drought Variability
In this study, gridded sea surface temperatures (SST) in the Pacific Ocean are analyzed in relation to monthly North American wildland fire danger and drought. Wildland fire danger is the sum of constant danger and variable danger factors affecting the inception, spread and resistance to control, and subsequent fire damage; often expressed as a relative number indicating the severity of wildland fire danger. Temperature, relative humidity and precipitation are integrated meteorological inputs for the computation of fire danger indices. The drought index used in this study is the Standardized Precipitation Index (SPI) based upon monthly precipitation totals. While it is known that SSTs can influence anomaly patterns of these meteorological elements, it is of interest to examine patterns and variability of fire danger and precipitation anomalies as related to SST patterns. These results provide direct benefit to fire agencies by identifying key regions of potential predictability and areas most likely to be impacted by ocean influence using a decision-support tool (fire danger) common in fire management. In the analysis, positive matrix factorization is used to relate monthly SST, fire danger computed from the 32-km North American Regional Reanalysis for the period 1980-2005, and SPI based upon the approximate 4-km monthly SPI dataset. The fire danger index used in the analysis is the energy release component (ERC) that is the computed total heat released per unit area within the flaming front at the head of an advancing fire, and is a heavily utilized index in fire management. While some studies have focused on and found SST relationships to fire occurrence and drought regionally, this analysis is unique in that 1) fire danger (ERC) spatial patterns are examined for the first time; and 2) drought is analyzed using gridded data as opposed to point-specific or climate division domains. Results of this study suggest several climate modes that indicate an inter-relationship between drought, fire danger, and Pacific SSTs.
U41B-07
Regional and Large-Scale Climate Influences on Tree-Ring Reconstructed Null Zone Position in San Francisco Bay
A new network of 36 moisture sensitive tree-ring chronologies has been developed in and near the drainage basins of the Sacramento and San Joaquin Rivers. The network is based entirely on blue oak (Quercus douglasii), which is a California endemic found from the lower forest border up into the mixed conifer zone in the Coast Ranges, Sierra Nevada, and Cascades. These blue oak tree-ring chronologies are highly correlated with winter-spring precipitation totals, Sacramento and San Joaquin streamflow, and with seasonal variations in salinity and null zone position in San Francisco Bay. Null zone is the non-tidal bottom water location where density-driven salinity and river-driven freshwater currents balance (zero flow). It is the area of highest turbidity, water residence time, sediment accumulation, and net primary productivity in the estuary. Null zone position is measured by the distance from the Golden Gate of the 2 per mil bottom water isohaline and is primarily controlled by discharge from the Sacramento and San Joaquin Rivers (and ultimately by winter-spring precipitation). The location of the null zone is an estuarine habitat indicator, a policy variable used for ecosystem management, and can have a major impact on biological resources in the San Francisco estuary. Precipitation-sensitive blue oak chronologies can be used to estimate null zone position based on the strong biogeophysical interaction among terrestrial, aquatic, and estuarine ecosystems, orchestrated by precipitation. The null zone reconstruction is 626-years long and provides a unique long term perspective on the interannual to decadal variability of this important estuarine habitat indicator. Consecutive two-year droughts (or longer) allow the null zone to shrink into the confined upper reaches of Suisun Bay, causing a dramatic reduction in phytoplankton production and favoring colonization of the estuary by marine biota. The reconstruction indicates an approximate 10 year recurrence interval between these consecutive two-year droughts and null zone maxima. Composite analyses of the Palmer drought index over North America indicate that the drought and wetness regimes associated with maxima and minima in reconstructed null zone position are largely restricted to the California sector. Composite analyses of the 20th century global sea surface temperature (SST) field indicate that wet years over central California with good oak growth, high flows, and a seaward position for the null zone (minima) are associated with warm El Nino conditions and a "Pineapple Express" SST pattern. The composite SST pattern is not as strong during dry years with poor growth, low flows, and a landward position of the null zone (maxima), but the composite warm SST anomaly in the eastern North Pacific during maxima would be consistent with a persistent ridge and drought over western North America.
U41B-08
Climate Reconstruction and Historical Fire Regime in Cerro El Mohinora, Chihuahua, Mexico
Tree rings constitute one of the most important sources of low and high frequency resolution for climate reconstruction for the last millennium. Chronologies of total ring width, earlywood, and latewood were developed from a Douglas-fir in a mixed conifer stand in Cerro El Mohinora, Chihuahua, Mexico. The tree-ring chronology extended back in time for 349 years (1657 - 2005) showing a high sensibility to climate variability. Therefore, total ring width indices were used as a proxy of the climate variability in the area. Intensive droughts were observed in the periods 1695-1715, 1753-1760, 1786-1792, 1798-1806, 1819-1830, 1841-1870, 1890-1899, 1906-1912, 1924-1941, 1971-1977, and 1994- 2005. The most prolonged droughts took place in the periods 1695-1715, 1841-1870, 1924-1941, and 1994-2005. Pluvials were less frequent in this reconstruction and were observed for the 1680s, 1900s, and 1970s. Pine species were sampled for fire frequency studies at the upper and lower watershed of Cerro El Mohinora. The fire frequency reconstruction extended from 1800 to 2005 for the upper watershed, and fire years were detected in 1999, 1988, 1971, 1967, 1964, 1950, 1945, 1923, 1904, 1889, 1882, 1873, 1862, 1853, and 1837. At the lower watershed fire frequency was reconstructed from 1900 to 2005. Fires were present for the years 1995, 1988, 1985, 1971, 1945, 1943, 1933, 1923, and 1900. Common fire years for upper and lower elevations were observed in 1988, 1971, 1945, and 1923. The fire year of 1971 affected the whole watershed and could be related to the severe drought prevailing in that decade. Preliminary results show a good correspondence between prolonged dry conditions and presence of fires, but further analysis remain to be done.