Dale P. Kaiser

The 2007 Eastern US Spring Freeze: Increased Cold Damage in a Warming World?

ABSTRACT Plant ecologists have long been concerned with a seemingly paradoxical scenario in the relationship between plant growth and climate change: warming may actually increase the risk of plant frost damage. The underlying hypothesis is that mild winters and warm, early springs, which are expected to occur as the climate warms, may induce premature plant development, resulting in exposure of vulnerable plant tissues and organs to subsequent late-season frosts. The 2007 spring freeze in the eastern United States provides an excellent opportunity to evaluate this hypothesis and assess its large-scale consequences. In this article, we contrast the rapid prefreeze phenological advancement caused by unusually warm conditions with the dramatic postfreeze setback, and report complicated patterns of freeze damage to plants. The widespread devastation of crops and natural vegetation occasioned by this event demonstrates the need to consider large fluctuations in spring temperatures a real threat to terrestrial ecosystem structure and functioning in a warming climate.

More frequent cloud‐free sky and less surface solar radiation in China from 1955 to 2000

Newly available data from extended weather stations and time period reveal that much of China has experienced statistically significant decreases in total cloud cover and low cloud cover over roughly the last half of the Twentieth century. This conclusion is supported by our recent analysis of the more reliably observed frequency of cloud-free sky and overcast sky. The total cloud cover and low cloud cover have decreased 0.88% and 0.33% per decade, respectively, and cloud-free days have increased 0.60% and overcast days decreased 0.78% per decade in China from 1954-2001. Meanwhile, both solar radiation and pan evaporation have decreased in most parts of China, with solar radiation decreasing 3.1 W/m2 and pan evaporation decreasing 39 mm per decade. Combined with other evidences documented in previous studies, we conjectured that increased air pollution may have produced a fog-like haze that reflected/absorbed radiation from the sun and resulted in less solar radiation reaching the surface, despite concurrent upward trends in cloud-free skies over China.

Monitoring and Understanding Changes in Heat Waves, Cold Waves, Floods, and Droughts in the United States: State of Knowledge

Weather and climate extremes have been varying and changing on many different time scales. In recent decades, heat waves have generally become more frequent across the United States, while cold waves have been decreasing. While this is in keeping with expectations in a warming climate, it turns out that decadal variations in the number of U.S. heat and cold waves do not correlate well with the observed U.S. warming during the last century. Annual peak flow data reveal that river flooding trends on the century scale do not show uniform changes across the country. While flood magnitudes in the Southwest have been decreasing, flood magnitudes in the Northeast and north-central United States have been increasing. Confounding the analysis of trends in river flooding is multiyear and even multidecadal variability likely caused by both large-scale atmospheric circulation changes and basin-scale “memory” in the form of soil moisture. Droughts also have long-term trends as well as multiyear and decadal variability...

Decreasing cloudiness over China : An updated analysis examining additional variables

As preparation of the IPCCs Third Assessment Report takes place, one of the many observed climate variables of key interest is cloud amount. For several nations of the world, there exist records of surface-observed cloud amount dating back to the middle of the 20th Century or earlier, offering valuable information on variations and trends. Studies using such databases include Sun and Groisman (1999) and Kaiser and Razuvaev (1995) for the former Soviet Union, Angel1 et al. (1984) for the United States, Henderson-Sellers (1986) for Europe, Jones and Henderson-Sellers (1992) for Australia, and Kaiser (1998) for China. The findings of Kaiser (1998) differ from the other studies in that much of China appears to have experienced decreased cloudiness over recent decades (1954-1994), whereas the other land regions for the most part show evidence of increasing cloud cover. This paper expands on Kaiser (1998) by analyzing trends in additional meteorological variables for Chi na [station pressure (p), water vapor pressure (e), and relative humidity (rh)] and extending the total cloud amount (N) analysis an additional two years (through 1996).

Analysis of total cloud amount over China, 1951–1994

Trends in Chinese total cloud amount were analyzed for the period 1951–1994. Cloud data were obtained from a database of 6-hourly weather observations provided by the China Meteorological Administration (CMA) to the U.S. Department of Energys Carbon Dioxide Information Analysis Center (CDIAC) through a bilateral research agreement. Seasonal and annual means of midday (1400 Beijing Time (BT)) and midnight (0200 BT) observations were computed for each of 196 stations and over 8 specific regions of China. Linear regression analysis was used to characterize seasonal and annual trends in total cloud amount from 1951–1994. Decreasing trends in both midday and midnight cloud amount are observed over much of China; most stations in central, eastern, and northeastern China show statistically significant decreases of 1–3% sky cover per decade. These decreases in cloud amount are especially interesting in light of recent temperature trends observed over China. Several studies have shown significant increasing trends in daily minimum temperatures over China since 1951, especially in the northeastern part of the country, precisely where the strongest decreasing trends in total cloud amount are observed. Increases in cloud amount have been offered as a possible explanation for increasing minimum temperatures in other parts of the world; however, in China it seems that some mechanism(s) other than increasing cloud amount must be considered for understanding the observed increase in minimum temperatures.

Assessment of Reanalysis Daily Extreme Temperatures with China's Homogenized Historical Dataset during 1979-2001 Using Probability Density Functions

Abstract Using a recently homogenized observational daily maximum (TMAX) and minimum temperature (TMIN) dataset for China, the extreme temperatures from the 40-yr ECMWF Re-Analysis (ERA-40), the Japanese 25-year Reanalysis (JRA-25), the NCEP/Department of Energy Global Reanalysis 2 (NCEP-2), and the ECMWF’s ERA-Interim (ERAIn) reanalyses for summer (June–August) and winter (December–February) are assessed by probability density functions for the periods 1979–2001 and 1990–2001. For 1979–2001, no single reanalysis appears to be consistently accurate across eight areas examined over China. The ERA-40 and JRA-25 reanalyses show similar representations and close skill scores over most of the regions of China for both seasons. NCEP-2 generally has lower skill scores, especially over regions with complex topography. The regional and seasonal differences identified are commonly associated with different geographical locations and the methods used to diagnose these quantities. All the selected reanalysis products...

Assessment of the Effects of Climate Change on Federal Hydropower

As directed by Congress in Section 9505 of the SECURE Water Act of 2009 (Public Law 111-11), the US Department of Energy (DOE), in consultation with the federal Power Marketing Administrations (PMAs) and other federal agencies, including federal dam owners, has prepared a comprehensive assessment examining the effects of climate change on water available for hydropower at federal facilities and on the marketing of power from these federal facilities. This Oak Ridge National Laboratory report, referred to as the “9505 Assessment,” describes the technical basis for the report to Congress that was called for in the SECURE Water Act.

Detecting Extreme Events in Gridded Climate Data

Detecting and tracking extreme events in gridded climatological data is a challenging problem on several fronts: algorithms, scalability, and I/O. Successful detection of these events will give climate scientists an alternate view of the behavior of different climatological variables, leading to enhanced scientific understanding of the impacts of events such as heat and cold waves, and on a larger scale, the El Nio Southern Oscillation. Recent advances in computing power and research in data sciences enabled us to look at this problem with a different perspective from what was previously possible. In this paper we present our computationally efficient algorithms for anomalous cluster detection on climate change big data. We provide results on detection and tracking of surface temperature and geopotential height anomalies, a trend analysis, and a study of relationships between the variables. We also identify the limitations of our approaches, future directions for research and alternate approaches.