An investigation on reference crop evapotranspiration trend from 1975 to 2005 in Iran

Evapotranspiration is one of the most important factors in agriculture and the hydrological cycle that can be influenced by global warming and climatic changes. In this study, the trend of reference crop evapotranspiration (ET0) computed by penman Penman-Monteith equation and surveyed in 42 synoptic weather stations during last 3 decades (1975–2005). Nonparametric statistical test, Kendall's rank correlation (or τ test) was used to determine ET0 trends. Although, downward and upward trends were observed, increasing trends had more frequency. Spatial analysis of results indicated upward trends especially in the boundary parts of the country while, no significant trends were distributed in central parts. In addition, correlation analysis between ET0 trend and other climatic parameters trend (the trend of mean temperature, mean of minimum temperature, and mean of maximum temperature, mean of relative humidity, mean of wind speed and mean of sunshine duration) showed that wind is the most effective parameter on ET0. Iran losses more than 70% of annual precipitation by ET0. It is obvious that in this country where there are many limitations for water resources management, increase in ET0 could lead to more problems. Copyright © 2011 Royal Meteorological Society

[1]  D. Hernández-Ramírez,et al.  FRACTALITY OF MONTHLY EXTREME MINIMUM TEMPERATURE , 2003 .

[2]  Ulrike Lohmann,et al.  Can aerosols spin down the water cycle in a warmer and moister world? , 2004 .

[3]  R. Modarres,et al.  Rainfall trends in arid and semi-arid regions of Iran , 2007 .

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

[5]  V. Singh,et al.  Trends in reference crop evapotranspiration over Iran , 2011 .

[6]  G. Florides,et al.  Global warming and carbon dioxide through sciences. , 2009, Environment international.

[7]  T. McVicar,et al.  Wind speed climatology and trends for Australia, 1975–2006: Capturing the stilling phenomenon and comparison with near‐surface reanalysis output , 2008 .

[8]  Yagob Dinpashoh,et al.  Study of reference crop evapotranspiration in I.R. of Iran , 2006 .

[9]  Liu Yunfeng,et al.  Climatic change on the Tibetan Plateau: Potential Evapotranspiration Trends from 1961–2000 , 2006 .

[10]  T. Jiang,et al.  Analysis of spatial distribution and temporal trend of reference evapotranspiration and pan evaporation in Changjiang (Yangtze River) catchment , 2006 .

[11]  Ling Tong,et al.  Analysis of impacts of climate variability and human activity on streamflow for a river basin in arid region of northwest China , 2008 .

[12]  Yantai Gan,et al.  Phenological trends in winter wheat and spring cotton in response to climate changes in northwest China , 2008 .

[13]  Gerald Stanhill,et al.  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 , 2001 .

[14]  H. Tabari,et al.  Recent trends of mean maximum and minimum air temperatures in the western half of Iran , 2011 .

[15]  Hossein Dehghanisanij,et al.  Assessment of evapotranspiration estimation models for use in semi-arid environments , 2004 .

[16]  Claude N. Williams,et al.  Radiosonde‐based trends in precipitable water over the Northern Hemisphere: An update , 2009 .

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

[18]  Edward T. Linacre,et al.  A simple formula for estimating evaporation rates in various climates, using temperature data alone , 1977 .

[19]  R. Allen,et al.  History and Evaluation of Hargreaves Evapotranspiration Equation , 2003 .

[20]  Thomas Rötzer,et al.  Annual and spatial variability of the beginning of growing season in Europe in relation to air temperature changes , 2002 .

[21]  Narendra Singh Raghuwanshi,et al.  Temporal Trends in Estimates of Reference Evapotranspiration over India , 2009 .

[22]  M. Dastorani,et al.  Drought Monitoring by Reconnaissance Drought Index (RDI) in Iran , 2011 .

[23]  M. Roderick,et al.  A simple pan‐evaporation model for analysis of climate simulations: Evaluation over Australia , 2006 .

[24]  M. Roderick,et al.  Pan Evaporation Trends and the Terrestrial Water Balance. I. Principles and Observations , 2009 .

[25]  V. P. D. Silva.  On climate variability in Northeast of Brazil , 2004 .

[26]  Axel Thomas,et al.  Spatial and temporal characteristics of potential evapotranspiration trends over China , 2000 .

[27]  Ali Rahimikhoob,et al.  Estimation of evapotranspiration based on only air temperature data using artificial neural networks for a subtropical climate in Iran , 2010 .

[28]  M. Maugeri,et al.  Trends of Minimum and Maximum Daily Temperatures in Italy from 1865 to 1996 , 2000 .

[29]  Davar Khalili,et al.  Regional classification for dryland agriculture in southern Iran , 2002 .

[30]  M. R. Kousari,et al.  An investigation of the Iranian climatic changes by considering the precipitation, temperature, and relative humidity parameters , 2011 .

[31]  Mike Hulme,et al.  Evaporation and potential evapotranspiration in India under conditions of recent and future climate change , 1997 .

[32]  M. Hulme,et al.  Precipitation measurements and trends in the twentieth century , 2001 .

[33]  M. R. Kousari,et al.  Minimum, maximum, and mean annual temperatures, relative humidity, and precipitation trends in arid and semi-arid regions of Iran , 2011 .

[34]  William O. Pruitt,et al.  Adaptation of the Thornthwaite scheme for estimating daily reference evapotranspiration , 2004 .