Climate Science: Roger Pielke Sr. Research Group News

There is a very informative summary of a number of the issues raised on my website in a post on weblog The Resilient Earth by  Doug L. Hoffman on june 16 2009.  The post is titled

Seven Climate Models, Seven Different Answers 

The post is worth reading and their website should be bookmarked. The conclusion of their weblog states

“Earth’s climate system is amazingly complex and modeling is fraught with pitfalls and danger for even the most experienced computer scientists. No climate model predicted the current downturn in global temperatures, though many are now scrambling to predict possible decades of unchanging or cooling climate “within the general warming trend.” Still, climate science remains enthralled by its computerized playthings. I have to echo Professor Pielke’s question, how many years of wrong results are necessary before we reject the IPCC reports and the models they are based on?”

The plan to regulate CO2 by the EPA, and the intent of Congress and the President to introduce a “cap and trade” program for carbon emissions, in order to regulate climate, should require that the basis for these policy decisions be scientifcially robust.  It is essential to include all human climate forcings on climate (including land use/land change effects) in assessing the ability of their plans to actually alter climate.  They clearly have ignored doing this, and we will have a costly yet ineffective climate policy as a result.

A new study has appeared (and thanks to Willie Soon for alerting us to it!) which provides further quantitative documentation of the role of land use change as a first order climate forcing.

The paper is

Pitman, A.J., N. de Noblet-Ducoudré, F.T. Cruz, E.L. Davin, G.B. Bonan, V. Brovkin, M. Claussen, C. Delire, L. Ganzeveld, V. Gayler, B.J.J.M. van den Hurk, P.J. Lawrence, M.K. van der Molen, C. Müller, C.H. Reick, S.I. Seneviratne, B. J. Strengers, and A. Voldoire, 2009: Uncertainties in climate responses to past land cover change: first results from the LUCID intercomparison study, Geophys. Res. Lett., doi:10.1029/2009GL039076, in press. [“Land-Use and Climate, IDentification of robust impacts” (LUCID)].

The abstract reads

“Seven climate models were used to explore the biogeophysical impacts of human induced land cover change (LCC) at regional and global scales. The imposed LCC led to statistically significant decreases in the northern hemisphere summer latent heat flux in three models, and increases in three models. Five models simulated statistically significant cooling in summer in near-surface temperature over regions of LCC and one simulated warming. There were few significant changes in precipitation. Our results show no common remote impacts of LCC. The lack of consistency among the seven models was due to: 1) the implementation of LCC despite agreed maps of agricultural land, 2) the representation of crop phenology, 3) the parameterisation of albedo, and 4) the representation of evapotranspiration for different land cover types. This study highlights a dilemma: LCC is regionally significant, but it is not feasible to impose a common LCC across multiple models for the next IPCC assessment.”

This is the type of study that was recommended in the 2005 National Research Council report

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp.

The conclusions in the Pitman et al 2009 article include the text

 ”In conclusion, LUCID results suggest that the statistically significant impacts of past LCC are restricted to regions of LCC….Thus, the IPCC 5th Assessment Report (AR5) should implement LCC since it is regionally significant, recognizing it will cause divergence over regions of LCC in the models.”

“LUCID did not identify any region, remote from LCC, where there are impacts that approach statistical significance or where several models agree on a remote teleconnection pattern.”

“We recognise several limitations in our results. First, fixed SSTs may damp global-scale teleconnections resulting from LCC if they exist. LUCID plans fully-coupled experiments in the future. Second, we note that others have found teleconnections with fixed SSTs; we suggest that by using multiple realizations and the modified t-test to exclude changes that are caused by model variability and by using multiple models our
results are more robust than earlier studies that used a single model. Third, we imposed small LCCs in the tropics and it is arguably more likely that global scale teleconnections would be triggered from this region (Werth and Avissar, 2002). Clearly, including future LCC in climate projections (Feddema et al., 2005) is necessary but is not possible to implement in a common way for AR5. Finally, our simulations only included the biogeophysical effects of LCC on climate. Additional impacts may have occurred had we included changes in land-atmosphere exchange of greenhouse gases, reactive trace gases and aerosols as a function of LCC.”

This is a very important study.

The failure to find a a long distance connection, however, needs further scrutiny. The finding of a “no common remote impacts of LCC” does not mean this teleconnection does not exist, since they also report that there is a “lack of consistency among the seven models”.  Thus, in addition to the other shortcomings that the authors list with respect to teleconnections, if there are significant real world teleconnections, but they are not spatially coherent among the models due to their lack of consistency, the analysis proceedure they used will incorrectly conclude that there is no long range effect of LCC when there really is. This issue needs  further exploration in order to remove this limitation in their excellent preliminary investigation.

For further papers on the importance of land use change in climate assessments, see, for example,

Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, P.C. Frumhoff, S.T. Jackson, L. Joyce, P. Kauppi, J. Katzenberger, K.G. MacDicken, R. Neilson, J.O. Niles, D. dutta S. Niyogi, R.J. Norby, N. Pena, N. Sampson, and Y. Xue, 2003: The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy. Climate Policy, 3, 149-157.

Pielke Sr., R.A., J.O. Adegoke, T.N. Chase, C.H. Marshall, T. Matsui, and D. Niyogi, 2007: A new paradigm for assessing the role of agriculture in the climate system and in climate change. Agric. Forest Meteor., Special Issue, 132, 234-254.

I am pleased to announce another peer reviewed paper with the senior author, Professor Chris Castro, on the faculty of the University of Arizona.

Castro, C.L. A. Beltrán-Przekurat, and R.A. Pielke Sr., 2009: Spatiotemporal variability of precipitation, soil moisture, and vegetation greenness in North America within the recent observational record. J. Hydrometeor., accepted.

The abstract reads

“Dominant spatiotemporal patterns of precipitation, modeled soil moisture, and vegetation are determined in North America within the recent observational record (late 20th century on). These data are from a gridded U.S.-Mexico precipitation product, retrospective long-term integrations of two land surface models, and satellite-derived vegetation greenness. The analysis procedure uses two statistical techniques. First, all the variables are normalized according to the Standardized Precipitation Index procedure. Second, dominant patterns of spatiotemporal variability are determined using multi-taper method, singular value decomposition for interannual and longer timescales. The dominant spatiotemporal patterns of precipitation generally conform to known and distinct Pacific SST forcing in the cool and warm seasons. Two specific timescales in precipitation at 9 years and 6-7 years correspond to significant variability in soil moisture and vegetation, respectively. The 9 year signal is related to precipitation in late fall to early winter, while the 6-7 year signal is related to early summer precipitation. Canonical correlation analysis is additionally used to confirm that strong covariability between land surface variables and precipitation exists at these specific times of the year. Both signals are strongest in the central and western U.S., and are consistent with prior global modeling and paleoclimate studies which have investigated drought in North America.”

As writtnen in the paper

“The main goal of the present study is to determine the dominant spatiotemporal patterns of precipitation that force long-term variability in soil moisture and vegetation.”

This study is a very significant advancement in our understanding the role of sea surface temperatures in the Pacific Ocean on precipitation and other weather variables in the central and western United States. It also reinforces that it is the regional atmospheric and ocean circulations, not a global average surface temperature trend, that dominate regional climate patterns such as drought and floods.

There was an article on January 26, 2005 in the Sydney Morning Herald titled Climate change: settlers 50,000 years ago blamed which provides another example of the major role of land surface processes (and the human conversion of the landscape) on the climate system (and thanks to Tom Grahame for alerting us to this!).

Excerpts from this news article read

“Settlers who came to Australia 50,000 years ago and set fires that burned off natural flora and fauna may have triggered a cataclysmic weather change that turned the continent’s interior into the dry desert it is today, United States and Australian researchers say.”

“Their study, reported in the latest issue of the journal, Geology, supports arguments that early settlers literally changed the landscape of the continent with fire.”

“The implications are that the burning practices of early humans may have changed the climate of the Australian continent by weakening the penetration of monsoon moisture into the interior,” Gifford Miller of the University of Colorado at Boulder, who led the study, said in a statement.”

“Miller’s study suggests that large fires could have altered the plant population enough to decrease the exchange of water vapour with the atmosphere, stopping clouds from forming.”

“The researchers, working with John Magee of the Australian National University in Canberra, used computerised global climate simulations to show that if there were some forest in the middle of Australia, it would lead to a monsoon with twice as much rain as the current pattern.”

A Science peer reviewed article by Gifford Miller closely related this subject is

Miller, G. H. et al, 2005: Ecosystem Collapse in Pleistocene Australia and a Human Role in Megafaunal Extinction: Science 8 July 2005: Vol. 309. no. 5732, pp. 287 - 290 DOI: 10.1126/science.1111288

The abstract reads

“Most of Australia’s largest mammals became extinct 50,000 to 45,000 years ago, shortly after humans colonized the continent. Without exceptional climate change at that time, a human cause is inferred, but a mechanism remains elusive. A 140,000-year record of dietary 13C documents a permanent reduction in food sources available to the Australian emu, beginning about the time of human colonization; a change replicated at three widely separated sites and in the marsupial wombat. We speculate that human firing of landscapes rapidly converted a drought-adapted mosaic of trees, shrubs, and nutritious grasslands to the modern fire-adapted desert scrub. Animals that could adapt survived; those that could not, became extinct.”

With the much smaller human populations at that time, it should not be surprising that there is an even greater effect on today’s climate by human conversion of the landscape.

The significant new paper on the role of human caused landscape change on the climate system is now available (I weblogged on this paper on April 24 2009; see). There is also an excellent news article on this paper published June 1 2009 by Sid Perkins on Science News.

The article is

Kumiko Takata, Kazuyuki Saitoa and Tetsuzo Yasunari, 2009: Changes in the Asian monsoon climate during 1700–1850 induced by preindustrial cultivation PNAS published online June 1, 2009, doi:10.1073/pnas.0807346106.

The abstract reads

“Preindustrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an atmospheric general circulation model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked and was consistent with the observational changes derived from examining the Himalayan ice cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/ use change was the major source of disturbances to the climate during that period. This report will set forward quantitative examination of the actual impacts of land cover/use changes on Asian monsoons, relative to the impact of greenhouse gases and aerosols, viewed in the context of global warming on the interannual, decadal, and centennial time scales.”

Excerpts from the paper read

“Changing the land cover/use from forest to croplands can affect the global and regional climate through changes in the energy and water balance at the earth’s surface…. Among the various effects of vegetation change, 2 factors have been shown to have a major influence on the energy and water balance: (i) an increase in surface albedo leading to a reduction in solar energy absorption at the surface and (ii) a decrease in surface roughness, resulting in low-level wind speed intensification. As a consequence, the partitioning of turbulent heat fluxes into its sensible and latent heat fluxes would subsequently affect the planetary boundary layer and deep cumulus convection and, hence, the large-scale atmospheric phenomena…”

To this list of effects of changing land cover/use can be added the change of fraction of the surface turbulent fluxes fluxes of heat into its sensible and latent heat form even if th solar energy absorption were the same. 

This paper is very important since it was able to eliminate the human additions of well mixed greenhouse gases as a major forcing yet showed that humans still had a very significant effect on the climate change.

Since human land management continues to substantially alter the global landscape (e.g. see Feddema et al 2005), any climate policy whose goal is to mitigate and adapt to human caused climate change must include land cover/use change as a first order effect. The recent IPCC and CCSP failed to do this.
 

An excellent new paper is “in press” for Geophysical Research Letters (GRL) which documents the major role of regional atmospheric/ocean circulation pattern changes on regional multi-decadal climate variability (e.g. see What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?).

This paper supports the finding that long term variations in atmospheric/ocean circulations (such as the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation, ENSO, etc)  cause regional changes in temperatures over this time period, and that these changes have a significant natural cause. Such a perspective supports the views of Joe D’Aleo (see); Bill Gray (see); and Roy Spencer (see). [also see].  [Added June 2 2009: Joe D'Aleo alerted me to another paper on this topic: Francis, J. A., and E. Hunter (2007), Drivers of declining sea ice in the Arctic winter: A tale of two seas, Geophys. Res. Lett., 34, L17503, doi:10.1029/2007GL030995.]

The paper is

Chylek Petr, Chris K. Folland, Glen Lesins, Manvendra K. Dubeys, and Muyin Wang: 2009: “Arctic air temperature change amplification and the Atlantic Multidecadal Oscillation”. Geophysical Research Letters (in press).

The abstract reads

“Understanding Arctic temperature variability is essential for assessing possible future melting of the Greenland ice sheet, Arctic sea ice and Arctic permafrost. Temperature trend reversals in 1940 and 1970 separate two Arctic warming periods (1910-1940 and 1970-2008) by a significant 1940-1970 cooling period. Analyzing temperature records of the Arctic meteorological stations we find that (a) the Arctic amplification (ratio of the Arctic to global temperature trends) is not a constant but varies in time on a multi-decadal time scale, (b) the Arctic warming from 1910-1940 proceeded at a significantly faster rate than the current 1970-2008 warming, and (c) the Arctic temperature changes are highly correlated with the Atlantic Multi-decadal Oscillation (AMO) suggesting the Atlantic Ocean thermohaline circulation is linked to the Arctic temperature variability on a multi decadal time scale.”

Text in this paper includes

“In the following analysis we confirm that the Arctic has indeed warmed during the 1970-2008 period by a factor of two to three faster than the global mean in agreement with model predictions but the reasons may not be entirely anthropogenic. We find that the ratio of the Arctic to global temperature change was much larger during the years 1910-1970.”

“We consequently propose that the AMO is a major factor affecting inter-decadal variations of Arctic temperature and explaining [the] high value of the Arctic to global temperature trend ratio during the cooling period of 1940-1970.”

“Our analysis suggests that the ratio of the Arctic to global temperature change varies on [a] multi-decadal time scale. The commonly held assumption of a factor of 2-3 for the Arctic amplification has been valid only for the current warming period 1970-2008. The Arctic region did warm considerably faster during the 1910-1940 warming compared to the current 1970-2008 warming rate (Table 1). During the cooling from 1940-1970 the Arctic amplification was extremely high, between 9 and 13. The Atlantic Ocean thermohaline
circulation multi-decadal variability is suggested as a major cause of Arctic temperature variation. Further analyses of long coupled model runs will be critical to resolve the influence of the ocean thermohaline circulation and other natural climate variations on Arctic climate and to determine whether natural climate variability will make the Arctic more or less vulnerable to anthropogenic global warming.”

 There is a news article on the recent excellent MacAlpine research group papers

McAlpine, C.A., J. Syktus, J.G. Ryan, R.C. Deo, G.M. McKeon, H.A. McGowan, and S.R. Phinn, 2009:A continent under stress: interactions, feedbacks and risks associated with impact of modified land cover on Australia’s Climate. Global Change Biology, in press. doi: 10.1111/j.1365-2486.2009.01939.x

Deo, R. C., J. I. Syktus, C. A. McAlpine, P. J. Lawrence, H. A. McGowan, and S. R. Phinn, 2009: Impact of historical land cover change on daily indices of climate extremes including droughts in eastern Australia, Geophys. Res. Lett., 36, L08705, doi:10.1029/2009GL037666.

which have been weblogged on at Climate Science (see and see).

The news article in New Scientist on May 16 2009 is titled Land clearances turned up the heat on Australian climate and reads

“DEFORESTATION by European settlers may be to blame for making Australia’s drought longer, hotter and dryer than it would be otherwise.

The “big dry”, Australia’s 11-year drought, has been blamed on greenhouse gases and natural variability. To see if deforestation played a part, Clive McAlpine of the University of Queensland in Brisbane and colleagues used a climate model to simulate Australian conditions from the 1950s to 2003. They then compared the impact of today’s fragmented vegetation, obtained from satellite images, with that of 1788, prior to European settlement.

Over much of south-east Australia, where the drought has hit hardest, less that 10 per cent of the original vegetation remains. The team’s model showed that this land clearance has increased the length of droughts in the area by one to two weeks per year. In years of extreme drought, the loss of vegetation caused the number of days above 35 °C to increase by six to 18 days, and the number of dry days to increase by five to 15 days (Geophysical Research Letters, in press).

“Land clearing may be having a similar impact on the drought as greenhouse gases,” says McAlpine. Reforestation could minimise future droughts, he adds.

“It’s a nice piece of work,” says Andy Pitman of the University of New South Wales in Sydney, but he adds that the modelling needs to be confirmed.”

This excellent article highlights the role of land use change as a first order climate forcing. This climate forcing was inadequately reported on in the recent IPCC and CCSP climate assessments.

Our research group and collaborating colleagues have published several papers with major findings with respect to climate science. This weblog lists several of these findings, along with the peer reviewed papers in which they are based on:

• A conservative estimate of the warm bias resulting from measuring the temperature near the ground is around 0.21°C per decade (with the nighttime minimum temperature contributing a large part of this bias). Since land covers about 29% of the Earth’s surface, the warm bias due to just this one effect explains about 30% of the IPCC estimate of global warming. In other words, consideration of this one bias in temperature would reduce the IPCC trend to about 0.14°C per decade; still a warming, but not as large as indicated by the IPCC. [based on Lin, X., R.A. Pielke Sr., K.G. Hubbard, K.C. Crawford, M. A. Shafer, and T. Matsui, 2007: An examination of 1997-2007 surface layer temperature trends at two heights in Oklahoma. Geophys. Res. Letts., 34, L24705, doi:10.1029/2007GL031652; Klotzbach, P.J., R.A. Pielke Sr., R.A. Pielke Jr., and J.R. Christy, 2009: An alternative explanation for differential temperature trends at the surface and in the lower troposphere. J. Geophys. Res., submitted.] - for other uncertainties and biases in the monitoring of multi-decadal global average surface temperature trends; see).

• From observations of the spatial distribution of the human input of aerosols in the atmosphere in the lower latitudes, the aerosol effect on atmospheric circulations (through their diabatic heating effect on the three dimensional pressure field), can be 60 times greater than the effect due to the radiative heating effect of the human addition of well-mixed greenhouse gases [based on Matsui, T., and R.A. Pielke Sr., 2006: Measurement-based estimation of the spatial gradient of aerosol radiative forcing. Geophys. Res. Letts., 33, L11813, doi:10.1029/2006GL025974].

• Extensive peer-reviewed research has shown that the focus on just carbon dioxide as the dominate human climate forcing is too narrow. We have found that natural variations are still quite important, and moreover, the human influence is significant, but it involves a diverse range of first-order climate forcings, including, but not limited to the human input of CO2 [ based on Rial, J., R.A. Pielke Sr., M. Beniston, M. Claussen, J. Canadell, P. Cox, H. Held, N. de Noblet-Ducoudre, R. Prinn, J. Reynolds, and J.D. Salas, 2004: Nonlinearities, feedbacks and critical thresholds within the Earth’s climate system. Climatic Change, 65, 11-38; Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S. Running, 2002: The influence of land-use change and landscape dynamics on the climate system- relevance to climate change policy beyond the radiative effect of greenhouse gases. Phil. Trans. A. Special Theme Issue, 360, 1705-1719.

The acceptance of CO2 as a pollutant by the EPA , yet it is a climate forcing not a traditional atmospheric pollutant, opens up a wide range of other climate forcings which the EPA could similarly regulate (e.g., land use, water vapor). These other forcings, such as land-use change and from atmospheric pollution aerosols, may have a greater effect on our climate than the effects that have been claimed for CO2.

Our peer reviewed papers have not been refuted by any subsequent peer reviewed articles. Interested climate scientists are invited to contact me, if they are interested in posting a guest weblog as to what scientific reasons exist to reject any of the findings listed above.

Thanks to Jos de Laat of KNMI for alerting us to the paper

Paeth, H., K. Born, R. Girmes, R. Podzun, and D. Jacob, 2009: Regional Climate Change in Tropical and Northern Africa due to Greenhouse Forcing and Land Use Changes. J. Climate, 22, 114–132.

The abstract reads

“Human activity is supposed to affect the earth’s climate mainly via two processes: the emission of greenhouse gases and aerosols and the alteration of land cover. While the former process is well established in state-of-the-art climate model simulations, less attention has been paid to the latter. However, the low latitudes appear to be particularly sensitive to land use changes, especially in tropical Africa where frequent drought episodes were observed during recent decades. Here several ensembles of long-term transient climate change experiments are presented with a regional climate model to estimate the future pathway of African climate under fairly realistic forcing conditions. Therefore, the simulations are forced with increasing greenhouse gas concentrations as well as land use changes until 2050. Three different scenarios are prescribed in order to assess the range of options inferred from global political, social, and economical development. The authors find a prominent surface heating and a weakening of the hydrological cycle over most of tropical Africa, resulting in enhanced heat stress and extended dry spells. In contrast, the large-scale atmospheric circulation in upper levels is less affected, pointing to a primarily local effect of land degradation on near-surface climate. In the model study, it turns out that land use changes are primarily responsible for the simulated climate response. In general, simulated climate changes are not concealed by internal variability. Thus, the effect of land use changes has to be accounted for when developing more realistic scenarios for future African climate.”

Important findings from this paper include the text

 ”….most investigations of future African climate change have been focused on the impact of increasing greenhouse gas (GHG) concentrations, which usually satisfy the effect of warmer tropical oceans but neglect the role of land cover changes (Pielke et al. 2002). Several of the GHG induced experiments from global climate models predict a northward extension of moisture advection into the Sahel zone and more humid conditions (Kamga et al. 2005; Hoerling et al. 2006), but still with little agreement between different climate models (Hulme et al. 2001; Maynard and Royer 2004; Coppola and Giorgi 2005; Cook and Vizy 2006; Paeth et al. 2008)…..”

“….Hence, the question arises whether the classical procedure of the IPCC, namely, the assessment of anthropogenic climate change by prescribing rising GHG and aerosol concentrations, is sufficient for the prediction of future African climate (Pielke et al. 2002). Another important factor for climate change, particularly in the low latitudes, may be the changing land cover in the form of land use changes owing to human activity like agriculture, shifting cultivation, pasture, urbanization, and transport infrastructure (Feddema et al. 2005). On the other hand, land cover changes as a natural response to climate change, like, for example, albedo changes in high latitudes, may be crucial in the extratropical regions. Regional studies for the United States, China, and Europe have shown that urbanization, land use changes, and vegetation loss may enhance the amplitude of near-surface warming considerably by up to a factor of 2 (Zhao and Pitman 2002). In tropical Africa, however, the effect on the hydrological cycle would be more relevant.”

“Several authors have suggested that the prevailing droughts during the second half of the twentieth century
were at least partly caused by land cover changes in tropical and subtropical Africa (Zeng and Neelin 2000; Pielke 2001; Semazzi and Song 2001; Zeng et al. 2002).”

This paper clearly documents a failure of the 2007 IPCC reports to include the assessment of the role of all first order climate forcings on the climate system.
 

We have a new paper which provides further insight into land-atmosphere interactions.

It is

Alfieri, J., Xiao, X., Niyogi, D., Pielke, Sr., R. A., Chen, F., LeMone, M. A., 2009: Satellite-based modeling of transpiration and evaporation of grasslands and croplands in the Southern Great Plains, USA. Global and Planetary Change. 67, 78.86

The abstract reads

“Data from the 2002 International H2O Project (IHOP_2002), which was conducted during May and June 2002 in the Southern Great Plains of the United States, was used to validate a remote sensing-based Vegetation Transpiration Model (VTM). The VTM is based on the linkage between transpiration and photosynthesis, and has been successfully tested over forest landscapes. This study is the first evaluation of the VTM model over grasslands. Since grasslands represent a significant proportion of the Earth’s terrestrial surface, this research marks an important step toward applying a satellite-based transpiration model over a landscape that plays a critical role in numerous biogeochemical cycles on both regional and global scales. Comparison of the model output with observer transpiration showed the VTM tended to overestimate transpiration under sparely vegetated conditions and overestimate transpiration when the vegetation was full. These results indicate that explicitly incorporating the effects of LAI into the VTM could improve model estimates of transpiration; they also underscore the importance of soil evaporation in grassland environments and consequently the need for a companion soil evaporation model that works with the VTM.”

As we write in the Introduction

“Evapotranspiration (ET), the combined transport of moisture from the land surface to the atmosphere by soil evaporation and vegetation transpiration (TR), is a fundamental process linking numerous hydrologic, atmospheric, and ecological processes. Globally, nearly two-thirds of the precipitations that falls over land is returned to the atmosphere via ET (Baumgartner and Reichel,1975); thus, ET is clearly an important component of the water cycle and hydrologic processes. Furthermore, as an integral component of the surface energy budget, ET is also linked to a variety of atmospheric processes (Pielke et al., 1998, 2007) ranging from the development of mesoscale circulation patterns (Hanesaik et al., 2004; Raddatz, 2007) to the evolution of the atmospheric boundary layer (LeMone et al., 2002, 2007a) and the development of convective storms (Pielke, 2001). The TR component of ET is closely connected to many ecological and biogeochemical processes ranging from nitrogen cycling (Schulze et al., 1994) to carbon uptake through photosynthesis (Farquhar and Sharkey, 1982).”