Impact of warm summers on the actual evapotranspiration from spring wheat grown on the eastern Canadian prairies

Abstract

Impact of warm summers on the actual evapotranspiration from spring wheat grown on the eastern Canadian prairies. Can. J. Soil Sci. 78: 171-179. How do warm summers (June-July-August) influence the actual evapotranspiration totals from cropped land sown to spring wheat on the eastern Canadian Prairies? The eastern Prairies is a semi-arid region where over 60% of the land is cultivated. Over a third of the cropped land is usually sown to spring wheat. A comparison of mean summer temperatures and modelled evapotranspiration, for the years 1988 to 1996, demonstrated that with the current environmental conditions and farming practices, warm summers have lower actual evapotranspiration totals from spring wheat than cool summers. The average daily actual evapotranspiration rate is generally higher in years with higher mean summer temperatures; however, the crop growth-period is shorter. The net effect is lower total actual evapotranspiration from spring wheat. This suggests that climate warming on the eastern Canadian Prairies, if the current trend continues and all other factors remain equal, will reduce, on average, the total actual evapotranspiration from spring wheat. A reduction in the growth-period actual evapotranspiration from lands sown to spring wheat will likely decrease the total actual evapotranspiration for the entire warm season as growth-period evapotranspiration currently makes up about three-quarters of the seasonal total. However, the magnitude and timing of the reduction is far from certain. The consequence for agriculture may be a reduction in the average spring wheat yield because yield is positively correlated with the actual evapotranspiration total from the crop. Key words:Modelling, crop growth-period, yield, climate warming Raddatz, R. L. et Shaykewich, C. F. 1998. Incidences des étés chauds sur l'évapotranspiration réelle du blé de printemps cultivé dans la partie orientale des Prairies canadiennes. Can. J. Soil Sci. 78: 171-179. Comment les étés chauds : juin, juillet, août, influent-ils sur l'évapotranspiration réelle totale des terres ensemencées en blé de printemps, dans l'est des provinces canadiennes des Prairies? Dans cette région semi-aride, plus de 60 % des terres sont en culture, dont plus d'un tiers est habituellement ensemencé en blé de printemps. En comparant les températures moyennes de l'été et l'évapotranspiration modélisée pour la péri-ode 1988 à 1996, on a pu constater que dans les conditions environnementales et selon les pratiques agricoles actuelles, les étés chauds produisent une évapotranspiration réelle totale effectivement plus basse à partir des cultures de blé de printemps que les étés frais. En effet, si l'évapotranspiration quotidienne réelle moyenne est généralement plus élevée en années de températures d'été moyennes élevées, en revanche la saison de végétation du blé est plus courte. Cette constatation suggère que le réchauffe-ment du climat dans cette région, si la tendance actuelle se maintient et tous autres facteurs demeurant égaux, provoquera en moyenne ...

Improvements to the accuracy of modelled soil water content from the Second Generation Prairie Agrometeorological Model

“…half of the growing season, the crop starts to senesce and the soil is typically at its driest level since crop water demand often exceeds water supply during this period on the Canadian Prairies (Ash et al 1992;Raddatz and Shaykewich 1998).…”

“…According to Shen et al (2002), r c for wheat increases with a decrease in either green leaf area or soil water content. During the second half of the growing season, the crop starts to senesce and the soil is typically at its driest level since crop water demand often exceeds water supply during this period on the Canadian Prairies (Ash et al 1992;Raddatz and Shaykewich 1998).…”

Determining the influence of agricultural land use on climate variables for the Canadian Prairies

“…Gameda et al () reported the most significant trends in the climate variables of interest occurred from mid‐June to mid‐July for their later data period and Betts et al () in their Table 2 listed the greatest changes between their earlier and later periods as the May 20–July 18 period of the growing season. According to the studies conducted by Raddatz and Shaykewich (), Raddatz and Cummine () and Shrestha et al () which assumed spring wheat to represent annual crops and perennial forages, end of May to end of June corresponded to the maximum positive growth rate stage and associated maximum positive rate of change in ET and specific humidity, and convective rainfall potential which in turn influence the temperature regime, cloud cover and rainfall potential. In our study, the greatest success in discriminating the trends in climate classes (i.e.…”

“…Agriculture, as a component of land use, has been shown to have a significant impact on local and regional climate and subsequently influences and shapes global climate (Adegoke et al , ; Betts et al , ; Desjardins et al , ; Raddatz, ). For example, Raddatz and Shaykewich () studied the impact of spring wheat on regional evapotranspiration (ET) over the growing season in Southern Manitoba. They reported that the seasonal trend in ET corresponded to that of the growth curve of spring wheat with maximum ET and peak growth occurring between mid‐June and mid‐July.…”

“…Such relationships have only been inferred by Betts et al () and Gameda et al (). Modelling has shown a relationship between crop growth stages and ET and convective potential (Raddatz and Shaykewich, ; Raddatz and Cummine, ; Shrestha et al , ) or increased cloud cover and decreasing Bowen Ratio to suggest increased ET due to increased crop cover (Shrestha et al , ; Betts et al , ). There is therefore a need to investigate a more direct link between the annual changes in agricultural land cover and the resulting climatology of the Canadian Prairies.…”