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Literature Review Kathryn Westerman Oliver Smith Enrique Hernandez Megan Fowler.

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Presentation on theme: "Literature Review Kathryn Westerman Oliver Smith Enrique Hernandez Megan Fowler."— Presentation transcript:

1 Literature Review Kathryn Westerman Oliver Smith Enrique Hernandez Megan Fowler

2 A Technique to Detect Microclimatic Inhomogeneities in Historical Records of Screen-Level Air Temperature  New method developed to detect biases in screen- level temperature records at Standard Climate Stations.  Errors due to: vegetation changes, land development, irrigation/crops, and maintenance of site/instruments.  Hurst rescaling used to transform time series to detect previously unaccounted for errors.  Typical biases are thought to be too small to effect large scale climate data, but effects on individual records can be significant, potentially rendering some historical data sets useless for micro/local scale studies.

3 Analysis of the Impacts of Station Exposure on the U.S. Historical Climatology Network Temperatures and Temperature Trends  82.5% of USHCN stations classified based on NOAA’s rating system.  Poor siting leads to over estimations of min temperatures, and under estimations of max temperatures, resulting in a substantial difference in diurnal temperature trends.  Major portion of bias due to siting classification rather than geographic distribution of stations.  Changes may occur over time at initially well-sited locations that go undocumented, leading to new biases.

4 The Effect of Irrigation on Regional Temperatures: A Spatial and Temporal Analysis of Trends in California, 1934 – 2002  Regression analysis of temperature and irrigation changes for stations in California revealed the most impact on maximum temperatures from June-August and little impact on minimum temperatures.  Over 68 years, average temperatures were 2 degrees different at irrigated sites versus non-irrigated.  Daily min temperatures were found to be much higher at non-irrigated stations in California, but this is attributed to urbanization.

5 Microclimate Exposures of Surface-Based Weather Stations: Implications for the Assessment of Long- Term Temperature Trends  Exposures of 57 USHCN sites surveyed did not meet standards endorsed by WMO.  Problems include proximity to obstructions, patchy land surfaces, combinations of issues.  USHCN stations with problems similar to those listed above should not be included in climate determinations, and possibly replaced with COOP stations.

6 On the Reliability of the U.S. Surface Temperature Record  71 stations fall under the right exposure while 454 fall under unacceptable exposure to the elements  Of the good cited station only 30% had up to date equipment, 75% of poor cited stations had updated equipment.  Results found show that stations placed in warm sectors tend to show a slight warming bias but nothing that can contribute to bad data.  No evidence found that poor siting of station has negatively influenced data over the united states  Further investigation needed.

7 Documentation of Uncertainties and Biases Associated with Surface Temperature Measurement Sites for Climate Change Assessment  Undesirable instrument exposure associated with both anthropogenic and natural influences resulted in large variations in the measurements of temperature.  The exact effect at individual stations may vary somewhat depending on local environmental or climate factors such as the amount of direct sunlight on the shelter, and this adjustment for instrumentation transition should be reevaluated.  A station may have been initially located at what might be considered a good environment only to have that environment change over time.

8 Land Use/Land Cover Change Effects on Temperature Trends at U.S. Climate Normals Stations  Alterations in land use/land cover (LULC) near observation stations can influence temperature.  Trends of min, max, and average temperatures at 366 US Climate Stations were analyzed and results indicated relatively few significant temperature trends before periods of greatest LULC change.  After the period of greatest LULC change was observed, 95% of stations that exhibited significant trends displayed warming.

9 Evaluation of Temperature Differences for Paired Stations of the U.S. Climate Reference Network  Adjustments recommended to remove biases introduced by differences between stations due to time of observation, temperature instrumentation, latitude, and elevation.  Daily, monthly, and annual min, max and mean temperatures were compared for 5 pairs of stations.  Significant differences were found for all pairs.  Adjustments for latitude and elevation contributed to larger differences in annual mean temperature for 4 out of 5 stations.

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