Publications Published in Agricultural and Forest Meteorology

1. A new paradigm for assessing the role of agriculture in the climate system and in climate change. Pielke, Sr Roger A.; Adegoke, Jimmy O.; Chase, Thomas N.; Marshall, Curtis H.; Matsui, Toshihisa; Niyogi, Dev.
   Agricultural and Forest Meteorology:
   Notes
   This paper discusses the diverse climate forcings that impact agricultural systems, and contrasts the current paradigm of using global models downscaled to agricultural areas (a top-down approach) with a new paradigm that first assesses the vulnerability of agricultural activities to the spectrum of environmental risk including climate (a bottom-up approach). To illustrate the wide spectrum of climate forcings, regional climate forcings are presented including land-use/land-cover change and the influence of aerosols on radiative and biogeochemical fluxes and cloud/precipitation processes, as well as how these effects can be teleconnected globally. Examples are presented of the vulnerability perspective, along with a small survey of the perceived drought impacts in a local area, in which a wide range of impacts for the same precipitation deficits are found. This example illustrates why agricultural assessments of risk to climate change and variability and of other environmental risks should start with a bottom-up perspective.
   
   
   
2. Atmospheric aerosol light scattering and surface wetness influence the diurnal pattern of net ecosystem exchange in a semi-arid ponderosa pine plantation. Misson, Laurent; Lunden, Melissa; McKay, Megan; Goldstein, Allen H..
   Agricultural and Forest Meteorology: 2005
   Notes
   The diurnal variation of net ecosystem exchange (NEE) showed an unusual pattern at the Blodgett Forest Ameriflux site, with late afternoon NEE lower than early morning (indicating more uptake), while air temperature and atmospheric vapor pressure deficit were much higher. To investigate processes influencing this pattern, NEE was compared to several environmental variables during summer 2002. Unusual variations of NEE can be partly attributed to dew formation on the leaf surface. An empirical model is used to show that surface wetness reduced the net ecosystem uptake of CO2 during the morning by 11%. In addition, transport of air-pollution from the Central Valley to this site results in higher aerosol particle concentration, light extinction and light scattering during the afternoon than in the morning. Total irradiance was 11% lower during the afternoon than in the morning, while diffuse irradiance was 24% higher. The empirical model is used to show that the decrease in total radiation reduced photosynthesis during the afternoon, but the increase in diffuse radiation enhanced photosynthesis even more. Aerosol loading caused net uptake of CO2 by the forest to increase by 8% in the afternoon as a result of changes in direct and diffuse radiation.
   
   
   
3. Global dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences. Stanhill, Gerald; Cohen, Shabtai.
   Agricultural and Forest Meteorology: 2001
   Notes
   A number of studies show that significant reductions in solar radiation reaching the Earth’s surface have occurred during the past 50 years. This review analyzes the most accurate measurements, those made with thermopile pyranometers, and concludes that the reduction has globally averaged 0.51±0.05Wm−² per year, equivalent to a reduction of 2.7% per decade, and now totals 20Wm−2, seven times the errors of measurement. Possible causes of the reductions are considered. Based on current knowledge, the most probable is that increases in man made aerosols and other air pollutants have changed the optical properties of the atmosphere, in particular those of clouds. The effects of the observed solar radiation reductions on plant processes and agricultural productivity are reviewed. While model studies indicate that reductions in productivity and transpiration will be proportional to those in radiation this conclusion is not supported by some of the experimental evidence. This suggests a lesser sensitivity, especially in high-radiation, arid climates, due to the shade tolerance of many crops and anticipated reductions in water stress. Finally the steps needed to strengthen the evidence for global dimming, elucidate its causes and determine its agricultural consequences are outlined.
   
   
   
4. Impacts of future climate change on California perennial crop yields: Model projections with climate and crop uncertainties. Lobell, D. B.; Field, Christopher B.; Cahill, K.N.; Bonfils, Celine.
   Agricultural and Forest Meteorology: 2006
   Notes
   Most research on the agricultural impacts of climate change has focused on the major annual crops, yet perennial cropping systems are less adaptable and thus potentially more susceptible to damage. In regions where perennial crops are economically and culturally important, improved assessments of yield responses to future climate are needed to prioritize adaptation strategies. These impact assessments, in turn, must rely on climate and crop models that contain often poorly defined uncertainties. We evaluated the impact of climate change on six major perennial crops in California: wine grapes, almonds, table grapes, oranges, walnuts, and avocados. Outputs from multiple climate models were used to evaluate climate uncertainty, while multiple statistical crop models, derived by resampling historical databases, were used to address crop response uncertainties. We find that, despite these uncertainties, climate change in California is very likely to put downward pressure on yields of almonds, walnuts, avocados, and table grapes by 2050. Without CO2 fertilization or adaptation measures, projected losses range from 0 to >40% depending on the crop and the trajectory of climate change. Climate change uncertainty generally had a larger impact on projections than crop model uncertainty, although the latter was substantial for several crops. Opportunities for expansion into cooler regions were identified, but this adaptation would require substantial investments and may be limited by non-climatic constraints. Given the long time scales for growth and production of orchards and vineyards (30 years), climate change should be an important factor in selecting perennial varieties and deciding whether and where perennials should be planted.
   
   
   
5. Influences of recovery from clear-cut, climate variabiltiy, and thinning on the carbon balance of a young ponderosa pine plantation. Misson, Laurent; Tang, Jianwu; Xu, Ming; McKay, Megan; Goldstein, Allen.
   Agricultural and Forest Meteorology: 2005
   Notes
   From 1999 to 2002, the variations in carbon flux due to management practices (shrub removal, thinning) and climate variability were observed in a young ponderosa pine forest originated from clear-cutting and plantation in 1990. These measurements were done at the Blodgett Forest Ameriflux site located in the Sierra Nevada Mountains of California. Thinning in spring 2000 decreased the leaf area index (LAI) by 34% and added 496 g C m−2 of wood and leaf debris at the soil surface. Total ecosystem respiration was not significantly affected by thinning (1261 g C m−2 in 1999 and 1273 g C m−2 in 2000), while canopy photosynthesis decreased by 202 g C m−2. As a result the ecosystem shifted from a net sink of CO2 in 1999 (−201 g C m−2) to a small net source in 2000 (13 g C m−2). Woody and leaf debris resulting from thinning only accounted for maximum 1% and 7% of the total respiration flux, respectively. Thinning did not affect the relative proportion of the different components of respiration to an observable degree. Low soil water availability in summer 2001 and 2002 decreased the proportion of soil respiration to the total respiration. It also imposed limitations on canopy photosynthesis: as a result the ecosystem shifted from a sink to a source of carbon 1 month earlier than in a wetter year (1999). The leaf area index and biomass of the stand increased rapidly after the thinning. The ecosystem was again a sink of carbon in 2001 (−97 g C m−2) and 2002 (−172 g C m−2). The net carbon uptake outside the traditionally-defined growing season can be important in this ecosystem (NEE = −50 g C m−2 in 2000), but interannual variations are significant due to differences in winter temperatures.