Generate variables to capture heat stress

Dear all
I have daily minimum and maximum temperature data from 697 weather stations across 311 districts.
For each district i in month m of year t, I need to aggregate the daily temperature data into two threshold-based heat stress variables which are (1) growing degree-days GDD and (2) stress degree-days or SDD.

The GDD and SDD variables are defined as follows
Array
Where T^low and T^high are the maximum and minimum temperature in ^oC for district i on day d of month m and year t.
T^low is the lower threshold and takes the value of 10, T^high is upper threshold and takes the value 30 and T^k takes the value 35

GDD_imt is heat accumulated within temperatures T^low and T^high and SDD_imt is heat accumulated above T^k.

Any suggestions how to implement these specifications?

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