Evidence for decadal variation in global terrestrial evapotranspiration between 1982 and 2002: 2. Results

[1] Terrestrial evapotranspiration (ET) cools the surface and moistens the atmosphere near the Earth's surface. Variations in this important climate factor have major environmental and socioeconomic impacts. How terrestrial ET has varied in the past and what caused the variations, however, have remained quite uncertain. These issues are addressed by calculating monthly global ET from 1982 to 2002 at 1120 globally distributed stations, using a modified Penman-Monteith method that was developed in the first part of the two-part paper. Our analyses show that ET has a significant decadal variation (∼10%) regionally and globally. Over the period analyzed ET for global land increased by 0.6 W m−2 per decade equal to 1.2 W m−2 (about 2.2% in relative value) or 15 mm yr−1 in water flux during the study period. We show that long-term variations of ET in humid areas such as the tropics, Europe, and humid areas of Asia are primarily controlled by variations in incident solar radiation Rs connected to changes in cloudiness and aerosols. However, soil water supply, estimated here by RH, and connected to precipitation, is the dominant factor in controlling long-term variations of ET in arid areas. A correlation analysis demonstrates that the dependence of ET on Rs switches to negative in dry regions. Furthermore, its dependence on relative humidity switches from negative in moist regions to positive in dry regions. Its dependence on normalized difference vegetation index is uniformly positive.

[1]  R. Dickinson,et al.  Evidence for decadal variation in global terrestrial evapotranspiration between 1982 and 2002: 1. Model development , 2010 .

[2]  Martin Wild,et al.  Global dimming and brightening: A review , 2009 .

[3]  L. Leslie,et al.  Multidecadal variability of Eastern Australian dust and Northern New Zealand sunshine: Associations with Pacific climate system , 2009 .

[4]  Taotao Qian,et al.  Changes in Continental Freshwater Discharge from 1948 to 2004 , 2009 .

[5]  M. Mccabe,et al.  Closing the terrestrial water budget from satellite remote sensing , 2009 .

[6]  R. Dickinson,et al.  Clear Sky Visibility Has Decreased over Land Globally from 1973 to 2007 , 2009, Science.

[7]  M. Roderick,et al.  Pan Evaporation Trends and the Terrestrial Water Balance. II. Energy Balance and Interpretation , 2009 .

[8]  Shunlin Liang,et al.  Estimation of Daytime Net Radiation from Shortwave Radiation Measurements and Meteorological Observations , 2009 .

[9]  S. Seneviratne,et al.  A regional perspective on trends in continental evaporation , 2009 .

[10]  Shunlin Liang,et al.  Estimation of Surface Net Radiation from Solar Shortwave Radiation Measurements , 2008, IGARSS 2008 - 2008 IEEE International Geoscience and Remote Sensing Symposium.

[11]  Theo Chidiezie Chineke,et al.  Equations for estimating global solar radiation in data sparse regions , 2008 .

[12]  Biao Wang,et al.  Data Quality Assessment and the Long-Term Trend of Ground Solar Radiation in China , 2008 .

[13]  D. B. Jadhav,et al.  Observational evidence of solar dimming: Offsetting surface warming over India , 2007 .

[14]  P. Ciais,et al.  Changes in climate and land use have a larger direct impact than rising CO2 on global river runoff trends , 2007, Proceedings of the National Academy of Sciences.

[15]  Michael L. Roderick,et al.  On the attribution of changing pan evaporation , 2007 .

[16]  Olivier Boucher,et al.  Projected increase in continental runoff due to plant responses to increasing carbon dioxide , 2007, Nature.

[17]  Martin Wild,et al.  Trends in aerosol radiative effects over Europe inferred from observed cloud cover, solar “dimming,” and solar “brightening” , 2007 .

[18]  Steven W. Running,et al.  Evaluating water stress controls on primary production in biogeochemical and remote sensing based models , 2007 .

[19]  Stephen G. Warren,et al.  A Survey of Changes in Cloud Cover and Cloud Types over Land from Surface Observations, 1971–96 , 2007 .

[20]  A. Evan,et al.  Arguments against a physical long‐term trend in global ISCCP cloud amounts , 2007 .

[21]  W. J. Shuttleworth,et al.  Putting the "vap" into evaporation , 2007 .

[22]  Ming Xu,et al.  Steady decline of east Asian monsoon winds, 1969–2000: Evidence from direct ground measurements of wind speed , 2006 .

[23]  P. D’Odorico,et al.  Evidence of optimal water use by vegetation across a range of North American ecosystems , 2006 .

[24]  Wilfried Brutsaert,et al.  Indications of increasing land surface evaporation during the second half of the 20th century , 2006 .

[25]  Zhanqing Li,et al.  Estimation of evaporative fraction from a combination of day and night land surface temperatures and NDVI: A new method to determine the Priestley-Taylor parameter , 2006 .

[26]  Xiangao Xia,et al.  Analysis of downwelling surface solar radiation in China from National Centers for Environmental Prediction reanalysis, satellite estimates, and surface observations , 2006 .

[27]  W. Brutsaert,et al.  Complementary relationship between daily evaporation in the environment and pan evaporation , 2006 .

[28]  Kevin E. Trenberth,et al.  Recent Trends in Cloudiness over the United States: A Tale of Monitoring Inadequacies. , 2006 .

[29]  Kazuaki Kawamoto,et al.  Importance of aerosols in satellite‐derived estimates of surface shortwave irradiance over China , 2006 .

[30]  R. Betts,et al.  Detection of a direct carbon dioxide effect in continental river runoff records , 2006, Nature.

[31]  Y. Qian,et al.  More frequent cloud‐free sky and less surface solar radiation in China from 1955 to 2000 , 2005 .

[32]  Edwin W. Pak,et al.  An extended AVHRR 8‐km NDVI dataset compatible with MODIS and SPOT vegetation NDVI data , 2005 .

[33]  M. El-Metwally,et al.  Sunshine and global solar radiation estimation at different sites in Egypt , 2005 .

[34]  C. Long,et al.  From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth's Surface , 2005, Science.

[35]  E. Dutton,et al.  Do Satellites Detect Trends in Surface Solar Radiation? , 2004, Science.

[36]  Thomas C. Brown,et al.  Trends in pan evaporation and actual evapotranspiration across the conterminous U.S.: Paradoxical or complementary? , 2004 .

[37]  M. Roderick,et al.  Changes in Australian pan evaporation from 1970 to 2002 , 2004 .

[38]  Martin Wild,et al.  On the consistency of trends in radiation and temperature records and implications for the global hydrological cycle , 2004 .

[39]  Wang Zhiwei,et al.  Variation of drought over northern China during 1950–2000 , 2003 .

[40]  C. Tucker,et al.  Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999 , 2003, Science.

[41]  M. Roderick,et al.  The cause of decreased pan evaporation over the past 50 years. , 2002, Science.

[42]  A. Huete,et al.  Overview of the radiometric and biophysical performance of the MODIS vegetation indices , 2002 .

[43]  I. C. Prentice,et al.  Climatic Control of the High-Latitude Vegetation Greening Trend and Pinatubo Effect , 2002, Science.

[44]  J. Szilágyi.  Modeled areal evaporation trends over the conterminous United States , 2001 .

[45]  Thomas C. Peterson,et al.  Evaporation changes over the contiguous United States and the former USSR: A reassessment , 2001 .

[46]  J. Lawrimore,et al.  Pan Evaporation Trends in Dry and Humid Regions of the United States , 2000 .

[47]  H. Suehrcke,et al.  On the relationship between duration of sunshine and solar radiation on the earth’s surface: Ångström’s equation revisited , 2000 .

[48]  Randal D. Koster,et al.  A Simple Framework for Examining the Interannual Variability of Land Surface Moisture Fluxes , 1999 .

[49]  M. B. Parlange,et al.  Hydrologic cycle explains the evaporation paradox , 1998, Nature.

[50]  C. Tucker,et al.  Increased plant growth in the northern high latitudes from 1981 to 1991 , 1997, Nature.

[51]  H. Mooney,et al.  Modeling the Exchanges of Energy, Water, and Carbon Between Continents and the Atmosphere , 1997, Science.

[52]  T. Peterson,et al.  Evaporation losing its strength , 1995, Nature.

[53]  P. Jarvis.  The Interpretation of the Variations in Leaf Water Potential and Stomatal Conductance Found in Canopies in the Field , 1976 .

[54]  C. Priestley,et al.  On the Assessment of Surface Heat Flux and Evaporation Using Large-Scale Parameters , 1972 .

[55]  J. Monteith.  Evaporation and environment. , 1965, Symposia of the Society for Experimental Biology.

[56]  H. L. Penman.  Natural evaporation from open water, bare soil and grass , 1948, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.