The label on the burning house should probably say urban rather than wildland.
With a mean of 2.7°C drop, your graph indicates more like 17% loss in precipitation, not 7%.
Though the growing season of a crop is usually expressed in days, more accurate is growing degree days, where you add up the temperature above some base temperature, typically around 4°C. Because nuclear winter would not only shorten the growing season but also reduce average temperatures, it would doubly reduce the growing degree days. Did you take this into account?
More feedback:
The label on the burning house should probably say urban rather than wildland.
With a mean of 2.7°C drop, your graph indicates more like 17% loss in precipitation, not 7%.
Though the growing season of a crop is usually expressed in days, more accurate is growing degree days, where you add up the temperature above some base temperature, typically around 4°C. Because nuclear winter would not only shorten the growing season but also reduce average temperatures, it would doubly reduce the growing degree days. Did you take this into account?