How do I default the current year in a date parameter in a BI Publisher data model?

You can use the same sysdate function {$SYSDATE ()$} that's used to default a date in the parameter and specify the date format string as yyyy.

Here are the settings:

Attribute Name	Attribute Value
Name	p_year
Data Type	Date
Default Value	{$SYSDATE()$}
Parameter Type	Date
Display Label	Enter Year (YYYY Format)
Text Field Size	4
Options (Ignore User Timezone)	Checked
Date Format String	yyyy