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Two different formulations are considered for calculating vapour pressure ed from relative humidity RH (%) and temperature (°C); one uses mean temperature T
formula
3
and the other uses the min and max temperature (Tmin, Tmax) (Allen et al. 1994)
formula
4
The aerodynamic resistance ra is calculated from the 10 m wind speed U10 (ms−1) using
formula
5
which includes a logarithmic correction for wind height (Hough et al. 1996), and surface resistance rs is calculated using
formula
6
where A =0.7L, L is leaf area index (LAI), rsc is crop resistance and rss is bare soil resistance (100 sm−1) (Hough et al. 1996). MORECS monthly values of rsc and LAI for short grass are used (Hough et al. 1996) (Table 2).
Table 2

Monthly leaf area index (LAI) and crop resistance for Current (rsc_M) and Future (rsc_F) periods, for short grass. LAI and rsc_M are from MORECS, and rsc_F is calculated from rsc_M using Equation (7)

MonthLAICurrent crop resistance rsc_MFuture crop resistance rsc_F
January 2.0 80 168 
February 2.0 80 168 
March 3.0 60 126 
April 4.0 50 105 
May 5.0 40 84 
June 5.0 60 126 
July 5.0 60 126 
August 5.0 70 147 
September 4.0 70 147 
October 3.0 70 147 
November 2.5 80 168 
December 2.0 80 168 
MonthLAICurrent crop resistance rsc_MFuture crop resistance rsc_F
January 2.0 80 168 
February 2.0 80 168 
March 3.0 60 126 
April 4.0 50 105 
May 5.0 40 84 
June 5.0 60 126 
July 5.0 60 126 
August 5.0 70 147 
September 4.0 70 147 
October 3.0 70 147 
November 2.5 80 168 
December 2.0 80 168 
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