Entire Period Of Record Research Articles

Global evaluation of gridded satellite precipitation products from the NOAA Climate Data Record program

AbstractThree satellite gridded daily precipitation datasets: PERSIANN-CDR, GPCP, and CMORPH, that are part of the NOAA/Climate Data Record (CDR) program are evaluated in this work. The three satellite precipitation products (SPPs) are analyzed over their entire period of record, ranging from over 20-year to over 35-year. The products inter-comparisons are performed at various temporal (daily to annual) and for different spatial domains in order to provide a detailed assessment of each SPP strengths and weaknesses. This evaluation includes comparison with in-situ data sets from the Global Historical Climatology Network (GHCN-Daily) and the US Climate Reference Network (USCRN). While the three SPPs exhibited comparable annual average precipitation, significant differences were found with respect to the occurrence and the distribution of daily rainfall events, particularly in the low and high rainfall rate ranges. Using USCRN stations over CONUS, results indicated that CMORPH performed consistently better than GPCP and PERSIANN-CDR for the usual metrics used for SPP evaluation (bias, correlation, accuracy, probability of detection, and false alarm ratio among others). All SPPs were found to underestimate extreme rainfall (i.e. above the 90th percentile) from about -20% for CMORPH to -50% for PERSIANN-CDR. Those differences in performance indicate that the use of each SPP has to be considered with respect to the application envisioned; from the long-term qualitative analysis of hydro-climatological properties to the quantification of daily extreme events for example. In that regard, the three satellite precipitation CDRs constitute a unique portfolio that can be used for various long-term climatological and hydrological applications.

Atmospheric measurements of the terrestrial O<sub>2</sub> : CO<sub>2</sub> exchange ratio of a midlatitude forest

Abstract. Measurements of atmospheric O2 have been used to quantify large-scale fluxes of carbon between the oceans, atmosphere and land since 1992 (Keeling and Shertz, 1992). With time, datasets have grown and estimates of fluxes have become more precise, but a key uncertainty in these calculations is the exchange ratio of O2 and CO2 associated with the net land carbon sink (αB). We present measurements of atmospheric O2 and CO2 collected over a 6-year period from a mixed deciduous forest in central Massachusetts, USA (42.537∘ N, 72.171∘ W). Using a differential fuel-cell-based instrument for O2 and a nondispersive infrared analyzer for CO2, we analyzed airstreams collected within and ∼5 m above the forest canopy. Averaged over the entire period of record, we find these two species covary with a slope of -1.081±0.007 mol of O2 per mole of CO2 (the mean and standard error of 6 h periods). If we limit the data to values collected on summer days within the canopy, the slope is -1.03±0.01. These are the conditions in which biotic influences are most likely to dominate. This result is significantly different from the value of −1.1 widely used in O2-based calculations of the global carbon budget, suggesting the need for a deeper understanding of the exchange ratios of the various fluxes and pools comprising the net sink.

Rainfall over the African continent from the 19th through the 21st century

Most of the African continent is semi-arid and hence prone to extreme variations in rainfall from year to year. The extreme droughts that have plagued the Sahel and eastern Africa are particularly well known. This article uses a markedly expanded and updated rainfall data set to examine rainfall variability in 13 sectors that cover most of the continent. Annual rainfall is presented for each sector; the March-to-May and October–November seasons are also examined for equatorial sectors. In each case, the article includes the longest and most comprehensive precipitation gauge series ever published. All time series cover at least a century and most cover roughly one and one-half centuries or more. Although towards the end of the 20th century there was a widespread trend towards more arid conditions, few significant trends are evident over the entire period of record. The largest were downward trends in the Sahel and western sectors of North Africa. In those regions, an abrupt reduction in rainfall occurred around 1968, but a synchronous change occurred many other parts of Africa. A recovery did occur in the Sahel, but to varying degrees across the east-west expanse of the region. Noteworthy is that the west-to-east rainfall gradient across the region appears to have weakened in recent decades. For the continent as a whole, another change began in the 1980s decade, with more arid conditions persisting at the continental scale until early in the twenty-first century. No other such period of dry conditions occurred within the roughly one and one-half centuries evaluated here. A notable change also occurred at the seasonal level. During the period 1980 to 1998 rainfall during March-to-May was well below the long-term mean throughout most of the area from 20° N to 35° S. At the same time rainfall was above the long-term mean in most of eastern sectors within this latitude span, indicating a change in the seasonality of rainfall of a large part of Africa.

Long-term and Two-period Analysis of Hydrologic Conditions of the South Edisto River

The U.S. Geological Survey (USGS) long-term daily streamflow record at station 02173000 in Bamberg County, South Carolina on the South Fork Edisto River (Latitude 33°23’35”, Longitude 81°08’00” NAD27) spans from 1932 to 2015 and was used for this study. The Nature Conservancy’s Indicators of Hydrologic Alteration (IHA) software was used to analyze the entire record of hydrologic data as ecologically relevant parameters and to categorize the flows. A two-period analysis was conducted to evaluate whether a significant difference could be observed in historic flow data from 1932–1985 (period one) compared to 1986–2015 (period two). An extreme low flow was defined as an initial low flow below 10% of daily flows for the period. Over the entire 76-year period of record, 51 years had at least one occurrence of extreme low flows. A median of 4 days per year had occurrences of extreme flows in period one in contrast to a median of 60 days per year during period two. Annual precipitation totals were not correlated with the number of days per year with extreme low flows. The two-period analysis showed significant differences between period one and period two for monthly mean flow for February, April, May, and August, as well as for 1-day and 30-day minima and maxima values. The analysis calculated the 7Q10 (the lowest stream flow for seven consecutive days that would be expected to occur once in ten years) at 4.4 cubic meters per second (cms), which was -10.9% different from the most recently published estimate. Results presented in this study have shown that spring and summer flows in the South Fork Edisto are statistically significantly lower in period two compared to period one.

Stream phosphorus dynamics of minimally impacted coastal plain watersheds

AbstractUnderstanding natural variation in stream phosphorus (P) concentrations over space and time is critical for understanding natural drivers of catchment behavior and establishing regulatory standards. Across minimally impacted benchmark streams (n = 81) in Florida, spatial variation in mean total P concentrations was large, indicating the importance of geologic controls on catchment solute dynamics. While this variation was significantly predicted by geographic regions, within regions we observed nearly comparable cross‐site variation, suggesting important finer‐scale heterogeneity in baseline catchment chemistry. Within‐site residual variation (unexplained by region or site) was as large as spatial variation, suggesting temporal variation in response to drivers such as flow may be critically important. To further explore timescales of P export variation, we collected long‐term, high‐frequency (subdaily) measurements of stream discharge (Q) and soluble reactive P (SRP) in 2 forested watersheds. We observed significant variation at annual, event, and diel timescales, all of which arise primarily from corresponding Q‐variation. Over the entire period of record, we generally observed a strong dilution signal, with SRP concentrations declining with increased Q. Despite significant SRP variation, flow variation was far larger and, thus, dominated temporal control on downstream flux. Within‐storm events, we observed strong and consistent clockwise SRP versus Q hysteresis, suggesting mobilization of proximal SRP stores. Diel variation exhibited mid‐afternoon concentration minima, Q‐controlled amplitude, and pronounced seasonal shifts in both magnitude and timing consistent with riparian evapotranspiration‐regulating lateral inputs of P‐rich groundwater. Such high‐resolution temporal signals allow identification of solute sources and provide insights into geologic and hydrologic drivers of solute variation.

Spatial and temporal variations in plant water-use efficiency inferred from tree-ring, eddy covariance and atmospheric observations

Abstract. Plant water-use efficiency (WUE), which is the ratio of the uptake of carbon dioxide through photosynthesis to the loss of water through transpiration, is a very useful metric of the functioning of the land biosphere. WUE is expected to increase with atmospheric CO2, but to decline with increasing atmospheric evaporative demand – which can arise from increases in near-surface temperature or decreases in relative humidity. We have used Δ13C measurements from tree rings, along with eddy covariance measurements from Fluxnet sites, to estimate the sensitivities of WUE to changes in CO2 and atmospheric humidity deficit. This enables us to reconstruct fractional changes in WUE, based on changes in atmospheric climate and CO2, for the entire period of the instrumental global climate record. We estimate that overall WUE increased from 1900 to 2010 by 48 ± 22 %, which is more than double that simulated by the latest Earth System Models. This long-term trend is largely driven by increases in CO2, but significant inter-annual variability and regional differences are evident due to variations in temperature and relative humidity. There are several highly populated regions, such as western Europe and East Asia, where the rate of increase of WUE has declined sharply in the last 2 decades. Our data-based analysis indicates increases in WUE that typically exceed those simulated by Earth System Models – implying that these models are either underestimating increases in photosynthesis or underestimating reductions in transpiration.

Hydroclimatic influences on non-stationary transit time distributions in a boreal headwater catchment

Understanding how water moves through catchments – from the time it enters as precipitation to when it exits via streamflow – is of fundamental importance to understanding hydrological and biogeochemical processes. A basic descriptor of this routing is the Transit Time Distribution (TTD) which is derived from the input–output behavior of conservative tracers, the mean of which represents the average time elapsed between water molecules entering and exiting a flow system. In recent decades, many transit time studies have been conducted, but few of these have focused on snow-dominated catchments. We assembled a 10-year time series of isotopic data (δ18O and δ2H) for precipitation and stream water to estimate the characteristics of the transit time distribution in a boreal catchment in northern Sweden. We applied lumped parameter models using a gamma distribution to calculate the Mean Transit Time (MTT) of water over the entire period of record and to evaluate how inter-annual differences in transit times relate to hydroclimatic variability. The best fit MTT for the complete 10-year period was 650 days (Nash–Sutcliff Efficiency = 0.65), while the best fit inter-annual MTT ranged from 300 days up to 1200 days. Whilst there was a weak negative correlation between mean annual total precipitation and the annual MTT, this relationship was stronger (r2 = 0.53, p = 0.02) for the annual rain water input. This strong connection between the MTT and annual rainfall, rather than snowmelt, has strong implications for understanding future hydrological and biogeochemical processes in boreal regions, given that predicted warmer winters would translate into a greater proportion of precipitation falling as rain and thus shorter MTT in catchments. Such a change could have direct implications for the export of solutes and pollutants.

Space–time variability of Indonesian rainfall at inter-annual and multi-decadal time scales

We investigated the space–time variability of wet (Nov–Apr) and dry (May–Oct) season rainfall over Indonesia, using monthly gridded rainfall data from the University of East Anglia Climatic Research Unit covering the period 1901–2012. Three complimentary techniques were employed—(1) principal component analysis to identify the dominant modes of variability, (2) wavelet spectral analysis to identify the spectral characteristics of the leading modes and their coherence with large scale climate variables and (3) Bayesian Dynamical Linear Model (BDLM) to quantify the temporal variability of the association between rainfall modes and climate variables. In the dry season when the Inter Tropical Convergence Zone (ITCZ) is to the north of the equator the leading two principal components (PCs) explain close to 50 % of the rainfall. In the wet season the ITCZ moves to the south and the leading PCs explain close to 30 % of the variance. El Nino Southern Oscillation (ENSO) is the driver of the leading modes of rainfall variability during both seasons. We find asymmetry in the teleconnections of ENSO to high and low rainfall years in the dry season. Furthermore, ENSO and the leading PCs of rainfall have spectral coherence in the inter-annual band (2–8 years) over the entire period of record and in the multi-decadal (8–16 years) band in post-1980 years. In addition, during the 1950–1980 period the second mode of variability in both seasons has a strong relationship with Pacific Decadal Oscillation. The association between ENSO and the leading mode of Indonesian rainfall has strengthened in recent decades, more so during dry season. These inter-annual and multi-decadal variability of Indonesian rainfall modulated by Pacific climate drivers has implications for rainfall and hydrologic predictability important for water resources management.

Snowpack variability and trends at long-term stations in northern Colorado, USA

Abstract. The individual measurements from snowcourse stations were digitized for six stations across northern Colorado that had up to 79 years of record (1936 to 2014). These manual measurements are collected at the first of the month from February through May, with additional measurements in January and June. This dataset was used to evaluate the variability in snow depth and snow water equivalent (SWE) across a snowcourse, as well as trends in snowpack patterns across the entire period of record and over two halves of the record (up to 1975 and from 1976). Snowpack variability is correlated to depth and SWE. The snow depth variability is shown to be highly correlated with average April snow depth and day of year. Depth and SWE were found to be significantly decreasing over the entire period of record at two stations, while at another station the significant trends were an increase over the first half of the record and a decrease over the second half. Variability tended to decrease with time, when significant.

Changes in volcanic hazard exposure in the Northwest USA from 1940 to 2100

This investigation frames volcano disaster potentialities for the US Pacific Northwest by assessing the interaction of the region’s growing population and affiliated housing development with volcanic hazards. Changes in human and residential exposure to the hazards are measured for a period of 1940 through 2100 by employing fine-scale (100 m) historical, current, and forecast demographic data derived from a spatial allocation model. Forecast population and housing unit density data from the model are based on societal change scenarios generated by Intergovernmental Panel on Climate Change. This ensemble approach reveals variations and uncertainties in the future hazard exposures, illustrating an envelope of volcano disaster possibilities. The demographic data are evaluated using a three-step, worst-case, downscaling approach by first calculating possible regional impacts before measuring volcano proximal and, thereafter, local hazard consequences. Results indicate that the Northwest regional study area is forecast to experience as much as a 445 % increase in total population and 1336 % amplification in housing unit counts from 1940 to 2100. The Mount Rainier proximal and local hazard analyses reveal the greatest overall increase in the total population and housing units for the entire period of record, whereas the Glacier Peak proximal and local hazard zone are forecast to experience the greatest percentage increase in population and housing units. These findings may be used by emergency managers, land planners, insurers, decision makers, and the public to discover changes in volcanic hazard risk and exposure within their communities, as well as assess potential mitigation and sustainability options.

Reliability and Cost Analysis of a Rainwater Harvesting System in Peri-Urban Regions of Greater Sydney, Australia

In large cities, rainwater tanks are used to save mains water, but in peri-urban and rural areas, rainwater tanks are used as a sole water supply for many households, as these regions often do not have any other means of water supply. This paper investigates the performance of a rainwater harvesting system (RWHS) in peri-urban regions of Greater Sydney, Australia. Considering the daily rainfall data over the entire period of record at ten different locations, it has been found that a 5 kL tank can meet 96% to 99% of the demand for toilet and laundry use depending on the location in Greater Sydney regions. However, in the driest year, a 5 kL tank can meet 69% to 99% of toilet and laundry demand depending on the location. Based on the results of life cycle cost analysis, it has been found that a 5 kL tank has the highest benefit–cost ratio (ranging from 0.86 to 0.97) among the eight possible tank sizes examined in this study. Interestingly, for a 5 kL tank, with a combined use (i.e., toilet, laundry and irrigation), the current water price in Sydney needs to be increased by 3% to 16% to achieve a benefit–cost ratio exceeding one. A set of regression equations are developed which can be used to estimate reliability using the average annual rainfall data at any arbitrary location in the peri-urban regions of Greater Sydney. The method presented in this paper can also be applied to other Australian states and other countries to estimate water savings and reliability of a RWHS using daily rainfall data.

Validating the BERMS in situ Soil Water Content Data Record with a Large Scale Temporary Network

Calibration and validation of soil moisture satellite products requires data records of large spatial and temporal extent and for diverse land cover types. Obtaining these data, especially for forests, can be challenging. These challenges can include the remoteness of the locations and expense of equipment. The Boreal Ecosystem Research and Monitoring Sites (BERMS) network in Saskatchewan, Canada, is a long‐term ecosystem network which includes five soil water content profile stations. These stations provide a critical but incomplete view of the soil water content patterns across a study domain of 10,000 square km; however, the representativeness of these observations for this purpose has not yet been evaluated. In coordination with the Canadian Experiment‐Soil Moisture 2010 (CANEX‐SM10), a temporary network of surface soil water content sensors was installed during the summer of 2010 to enhance the data resources of the BERMS network. This short term data record was then used as a basis for up‐scaling and validating the BERMS network. This large domain is approximately 1200 square km and provides a higher confidence because of the increased number of sampling sites. Using temporal stability analysis, this network verified that the BERMS network could be scaled to a satellite scale footprint with a root mean square error (RMSE) of 0.025 m3 m−3, and applied to the entire period of record.

Response to comments on ‘Influences of the Bermuda High and atmospheric moistening on changes in summer rainfall in the Atlanta, Georgia region, the United States’

ABSTRACTResearchers have come to differing conclusions about multi‐decadal changes in the position of the western ridge of the Bermuda High during the summer. This communication examines trends for 72 periods within the entire period of record (1948–2012), while also comparing variances in the Western Bermuda High Index (WBHI) and the latitudinal position of the western ridge. The western ridge has not moved significantly eastward or westward over either 1948–2012 or the past 60 years. The western ridge underwent a major westward shift from 1976 to 1977, but it did not stay in that western position during subsequent decades. Over the past 30–40 years, the western ridge has moved significantly eastwards and southwards. Finally, the WBHI, rather than the latitude of the western ridge, has had a definitive increase in variance over time and is the likely cause of increased summer rainfall variability in the southeastern United States.

Extrinsic regime shifts drive abrupt changes in regeneration dynamics at upper treeline in the Rocky Mountains, USA

Given the widespread and often dramatic influence of climate change on terrestrial ecosystems, it is increasingly common for abrupt threshold changes to occur, yet explicitly testing for climate and ecological regime shifts is lacking in climatically sensitive upper treeline ecotones. In this study, quantitative evidence based on empirical data is provided to support the key role of extrinsic, climate-induced thresholds in governing the spatial and temporal patterns of tree establishment in these high-elevation environments. Dendroecological techniques were used to reconstruct a 420-year history of regeneration dynamics within upper treeline ecotones along a latitudinal gradient (approximately 44-35 degrees N) in the Rocky Mountains. Correlation analysis was used to assess the possible influence of minimum and maximum temperature indices and cool-season (November-April) precipitation on regional age-structure data. Regime-shift analysis was used to detect thresholds in tree establishment during the entire period of record (1580-2000), temperature variables significantly Correlated with establishment during the 20th century, and cool-season precipitation. Tree establishment was significantly correlated with minimum temperature during the spring (March-May) and cool season. Regime-shift analysis identified an abrupt increase in regional tree establishment in 1950 (1950-1954 age class). Coincident with this period was a shift toward reduced cool-season precipitation. The alignment of these climate conditions apparently triggered an abrupt increase in establishment that was unprecedented during the period of record. Two main findings emerge from this research that underscore the critical role of climate in governing regeneration dynamics within upper treeline ecotones. (1) Regional climate variability is capable of exceeding bioclimatic thresholds, thereby initiating synchronous and abrupt changes in the spatial and temporal patterns of tree establishment at broad regional scales. (2) The importance of climate parameters exceeding critical threshold values and triggering a regime shift in tree establishment appears to be contingent on the alignment of favorable temperature and moisture regimes. This research suggests that threshold changes in the climate system can fundamentally alter regeneration dynamics within upper treeline ecotones and, through the use of regime-shift analysis, reveals important climate-vegetation linkages.

ICOADS Release 2.5: extensions and enhancements to the surface marine meteorological archive

AbstractRelease 2.5 of the International Comprehensive Ocean‐Atmosphere Data Set (ICOADS) is a major update (covering 1662–2007) of the world's most extensive surface marine meteorological data collection. Building on extensive national and international partnerships, many new and improved contributing datasets have been processed into a uniform format and combined with the previous Release 2.4. The new data range from early non‐instrumental ship observations to measurements initiated in the twentieth century from buoys and other automated platform types. Improvements to existing data include replacing preliminary Global Telecommunication System (GTS) receipts with more reliable, delayed mode reports for post‐1997 data, and in the processing and quality control (QC) of humidity observations. Over the entire period of record, spatial and temporal coverage has been enriched and data and metadata quality has been improved. Along with the observations, now updated monthly in near real time, Release 2.5 includes quality‐controlled monthly summary products for 2° latitude × 2° longitude (since 1800) and 1° × 1° boxes (since 1960), together with multiple options for access to the data and products. The measured and estimated data in Release 2.5 are subject to many technical changes, multiple archive sources, and historical events throughout the more than three‐century record. Some of these data characteristics are highlighted, including known unresolved errors and inhomogeneities, which may impact climate and other research applications. Anticipated future directions for ICOADS aim to continue adding scientific value to the observations, products, and metadata, as well as strengthen the cooperative enterprise through expanded linkages to international initiatives and organisations. Copyright © 2010 Royal Meteorological Society

Rapid 20th century warming in the Caribbean and impact of remote forcing on climate in the northern tropical Atlantic as recorded in a Guadeloupe coral

We have generated 104-year long (1895–1999) monthly δ 18O and Sr/Ca time series from a fast-growing Diploria strigosa coral core drilled off Guadeloupe Island, Lesser Antilles. Coral Sr/Ca reliably records interannual to decadal surface air temperature (SAT) variations in the region and shows a pronounced warming of approximately 1.5 °C since 1950, with the strongest warming (1.2 °C) occurring since 1975. This warming is also evident in SAT measured at Guadeloupe, which ends in 1951. Thus, our Sr/Ca series extends the air temperature record by 56 years. We find that the past few decades are the warmest years over the entire period of record. The accelerated warming since 1950 is accompanied by a pronounced decrease in regional precipitation. This dampens the warming signal indicated by coral δ 18O, which is too low (only 0.7–0.8 °C since 1951). Consistently, δ 18O sw estimated from the coral proxies also shows a strong decrease since 1950. Our data suggest an inverse relationship between SAT and precipitation (i.e. warmer and drier) for the latter half of the 20th century with the strongest trends since the mid-1970s. This is consistent with recent observational and model data, which report that while over the tropical oceans rainfall has increased due to an increase in sea surface temperatures, precipitation over land regions is reduced. A continuation of this warming and drying trend over Caribbean land regions would have severe societal consequences, especially in the context of anthropogenic warming. The El Niño Southern-Oscillation (ENSO) and the North Atlantic Oscillation (NAO) are the two major climate modes affecting large-scale SST variability in the northern tropical Atlantic. Both Sr/Ca and δ 18O show a close relationship to ENSO and the NAO. A quantitative comparison between extremes in mean March–May coral δ 18O and the Nino3 and NAO indices imply that climate variability in the northern tropical Atlantic is mainly forced by tropical Pacific and North Atlantic variability. Spectral analysis suggests that the relative importance of ENSO and the NAO is frequency dependent, with ENSO dominating at interannual, and the NAO dominating at interdecadal time scales.

A Homogeneous Record (1896–2006) of Daily Weather and Climate at Mohonk Lake, New York*

Abstract Reliable, long-term records of daily weather and climate are relatively rare but are crucial for understanding long-term trends and variability in extreme events and other climate metrics that are not resolvable at the monthly time scale. Here, the distinct features of a continuous, long-term (1896–2006) daily weather record from Mohonk Lake, New York, are highlighted. The site is optimal for daily climate analyses, since it has experienced negligible land-use change, no station moves, and has maintained methodological and instrumental consistency over the entire period of record. Unlike many sites, the site has always used maximum/minimum thermometers rather than shifting to the automated Maximum/Minimum Temperature Sensor. Notable results from the analysis of this record include 1) a warming trend driven largely by trends in maximum temperatures, especially during summer, 2) increasing diurnal temperature range during summer, and 3) a reduction in the number of freeze-days per year with little change in the length of the freeze-free season. These findings deviate from some regional level trends, suggesting there may be value in revisiting selected, consistently monitored, and maintained stations similar to Mohonk for focused analyses of regional climate change.

Trends in streamflow in the Yukon River Basin from 1944 to 2005 and the influence of the Pacific Decadal Oscillation

Summary Streamflow characteristics in the Yukon River Basin of Alaska and Canada have changed from 1944 to 2005, and some of the change can be attributed to the two most recent modes of the Pacific Decadal Oscillation (PDO). Seasonal, monthly, and annual stream discharge data from 21 stations in the Yukon River Basin were analyzed for trends over the entire period of record, generally spanning 4–6 decades, and examined for differences between the two most recent modes of the PDO: cold-PDO (1944–1975) and warm-PDO (1976–2005) subsets. Between 1944 and 2005, average winter and April flow increased at 15 sites. Observed winter flow increases during the cold-PDO phase were generally limited to sites in the Upper Yukon River Basin. Positive trends in winter flow during the warm-PDO phase broadened to include stations in the Middle and Lower Yukon River drainage basins. Increases in winter streamflow most likely result from groundwater input enhanced by permafrost thawing that promotes infiltration and deeper subsurface flow paths. Increased April flow may be attributed to a combination of greater baseflow (from groundwater increases), earlier spring snowmelt and runoff, and increased winter precipitation, depending on location. Calculated deviations from long-term mean monthly discharges indicate below-average flow in the winter months during the cold PDO and above-average flow in the winter months during the warm PDO. Although not as strong a signal, results also support the reverse response during the summer months: above-average flow during the cold PDO and below-average flow during the warm PDO. Changes in the summer flows are likely an indirect consequence of the PDO, resulting from earlier spring snowmelt runoff and also perhaps increased summer infiltration and storage in a deeper active layer. Annual discharge has remained relatively unchanged in the Yukon River Basin, but a few glacier-fed rivers demonstrate positive trends, which can be attributed to enhanced glacier melting. A positive trend in annual flow during the warm PDO near the mouth of the Yukon River suggests that small increases in flow throughout the Yukon River Basin have resulted in an additive effect manifested in the downstream-most streamflow station. Many of the identified changes in streamflow patterns in the Yukon River Basin show a correlation to the PDO regime shift. This work highlights the importance of considering proximate climate forcings as well as global climate change when assessing hydrologic changes in the Arctic.

Detecting the Timing of Morphologic Change Using Stage-Discharge Regressions: A Case Study at Fishtrap Creek, British Columbia, Canada

Nine submersible pressure transducers were installed at various locations in a study reach of Fishtrap Creek during the 2006 freshet. The channel morphology of the reach underwent a moderate change in 2006, due to the effects of the McLure forest fire which, in 2003, killed all of the riparian vegetation in the study reach and burned about 62% of the Fishtrap Creek watershed. By examining the changes in the rating relations between the water stage recorded by the pressure transducers and the discharge measured at a Water Survey of Canada gauging station located just downstream of the study reach, we were able to determine the timing of morphologic changes in the stream over the course of the freshet. Shifts in the rating curve were identified by first graphically analysing the stage-discharge relations, and then constructing stage discharge regressions for that part of the record for which the rating relation appeared to be stable. The residuals associated with the calculated rating equations were then computed for the entire period of record, and used to assess the temporal pattern of changes in the rating relation. The analysis shows that the largest changes in the rating relation occurred in the vicinity of the largest morphologic changes (as determined by analysis of repeated cross-sectional surveys) and that, in areas where the morphology was nearly stable, the rating relation remained relatively stable. The sensitivity of the rating relations to changes in the channel morphology suggests that deployment of submersible pressure transducers may be a suitable and cost-effective means for monitoring channel stability near existing gauging stations or stable control cross-sections where the rating relation is unlikely to change.

Distribution, Abundance, and Population Trends of Bull Trout in Idaho

AbstractBroad‐scale declines in populations of bull trout Salvelinus confluentus over the past century or more led the Idaho Department of Fish and Game to implement statewide no‐harvest regulations on bull trout in 1994 and ultimately led to a threatened listing under the U.S. Endangered Species Act in 1998. Despite this listing, quantitative evaluations of trends in abundance and estimates of population size over most of the species' historical range have not been made. We evaluated bull trout distribution, abundance, and trends in abundance using stratified sampling extrapolations of fish surveys (snorkeling and electrofishing) conducted at 2,521 survey sites (most distributed nonrandomly) across 77,447 km of stream. Bull trout were captured at 887 (35%) of the sites. Within the 262 local populations designated by the U.S. Fish and Wildlife Service within seven Idaho recovery units, the number of 70‐mm total length and larger bull trout was estimated at 1.13 million; this estimate was most likely biased low due to sampling limitations. Long‐term (>20 years) intrinsic rates of change (r) were negative for 10 of 16 bull trout populations up to 1994 (3 were significantly negative; 1 was significantly positive) and were positive for 14 of 17 populations after 1994 (1 was significantly negative; 5 were significantly positive). Over the entire period of record and all trend data sets, r averaged 0.01 ± 0.01 (mean ± 90% confidence interval), suggesting stability at a broad scale. During these same time periods, trends for other salmonids in much of the study area experienced similar declines through 1994 and increases after 1994, suggesting that environmental factors with influence over large geographical areas produced the recent positive trends. Once bull trout populations were detrended by use of linear regression residuals, there was little evidence of synchrony between populations. Our results suggest that despite declines from historical levels, bull trout in Idaho are presently widely distributed, relatively abundant, and apparently stable.