### 2.20.4.2. 14.4.2 Stress-Deciduous Offset Triggers[¶](#stress-deciduous-offset-triggers "Permalink to this headline")

Any one of the following three conditions is sufficient to initiate an offset period for the stress-deciduous phenology algorithm: sustained period of dry soil, sustained period of cold temperature, or daylength shorter than 6 hours. Offset triggering due to dry soil or cold temperature conditions is only allowed once the most recent onset period is complete. Dry soil condition is evaluated with an offset soil water index accumulator (\\({OSWI}\_{sum}\\), d). To test for a sustained period of dry soils, this control variable can increase or decrease, as follows:

(2.20.68)[¶](#equation-20-68 "Permalink to this equation")\\\[\\begin{split}OSWI\_{sum}^{n} =\\left\\{\\begin{array}{l} {OSWI\_{sum}^{n-1} +f\_{day} \\qquad \\qquad \\qquad {\\rm for\\; }\\Psi \_{s,3} \\le \\Psi \_{offset} } \\\\ {{\\rm max}\\left(OSWI\_{sum}^{n-1} -f\_{day} ,0\\right)\\qquad {\\rm for\\; }\\Psi \_{s,3} >\\Psi \_{onset} } \\end{array}\\right.\\end{split}\\\]

where \\({\\Psi}\_{offset} = -0.8 MPa\\) is the offset soil water potential threshold. An offset period is triggered if the previous onset period is complete and \\({OSWI}\_{sum}\\) \\(\\mathrm{\\ge}\\) \\({OSWI}\_{sum\\\_crit}\\), where \\({OSWI}\_{sum\\\_crit} = 15\\).

The cold temperature trigger is calculated with an offset freezing day accumulator (\\({OFD}\_{sum}\\), d). To test for a sustained period of cold temperature, this variable can increase or decrease, as follows:

(2.20.69)[¶](#equation-20-69 "Permalink to this equation")\\\[\\begin{split}OFD\_{sum}^{n} =\\left\\{\\begin{array}{l} {OFD\_{sum}^{n-1} +f\_{day} \\qquad \\qquad \\qquad {\\rm for\\; }T\_{s,3} \\le TKFRZ} \\\\ {{\\rm max}\\left(OFD\_{sum}^{n-1} -f\_{day} ,0\\right)\\qquad \\qquad {\\rm for\\; }T\_{s,3} >TKFRZ} \\end{array}\\right.\\end{split}\\\]

An offset period is triggered if the previous onset period is complete and \\({OFD}\_{sum} > {OFD}\_{sum\\\_crit}\\), where \\({OFD}\_{sum\\\_crit} = 15\\).

The offset counter is set at the initiation of the offset period: \\(t\_{offset} =86400\\cdot n\_{days\\\_ off}\\), where \\({n}\_{days\\\_off}\\) is set to a constant value of 15 days. The offset counter is decremented on each time step after initiation of the offset period, until it reaches zero, signaling the end of the offset period:

(2.20.70)[¶](#equation-20-70 "Permalink to this equation")\\\[t\_{offset}^{n} =t\_{offset}^{n-1} -\\Delta t\\\]

