in c#, calendar selectionchanged event
, check the selected date range and select the value in dropdown
If (Calendar1.SelectedDate.Month>=1 &&Calendar1.SelectedDate.Month<=3)
dropdownlist.SelectedValue="Winter";
else If (Calendar1.SelectedDate.Month>=4 &&Calendar1.SelectedDate.Month<=6)
dropdownlist.SelectedValue="Summer"
else If (Calendar1.SelectedDate.Month>=7 &&Calendar1.SelectedDate.Month<=9)
dropdownlist.SelectedValue="Cold"
Updated solution:
So you meant to say you will decide the date and the season. So have a table with 3 columns SeasonName, StartDate, EndDate. Then whenever you select a value in calendar, query the name from this table.
Select seasonName from tbl where @dt between startdate and Enddate