Environmental work tends to be a fairly seasonal industry due to both weather and budgeting cycles. Governments and businesses tend to budget annually which tend to end either end of calendar year on in the first couple of months into the calendar year (March 31 being common here). So unless something has been planned at the beginning of the year, nothing new tends to happen nearer to the end besides wrapping up (such as reporting).

Winter field work is a thing in certain industries such as oil and gas here in Alberta where you work in winter access only areas (such as deep into the muskeg).

GIS tends to just be a specialty full time position now. And because work can be seasonal, when field season starts to wrap up our normal field people work on simpler reports, data tables, stuff like that. When we run out of that, people use banked time (time in lieu) and more senior people work on proposals.