If I understand the question correctly, another approach you could take would be to use a Drilldown question type with 2 levels, hide the 2nd dropdown, and then add JavaScript to the question that will automatically select the top answer in the 2nd dropdown when a selection is made in the 1st. This will give you the province's corresponding rain amount for use in piping.
To give it a try, first create a CSV that has 2 columns: Province and Rainfall.
Then, create a Drilldown question and set the number of choices to 2. Click to add answers and then upload the CSV file to the question.
Next, add the below to the question's JavaScript in the OnReady section so that the 2nd dropdown automatically selects its 1st option when a selection is made in the 1st dropdown:
var qid = this.questionId;
var sel1 = document.getElementById('QR~'+qid+'~1');
var sel2 = document.getElementById('QR~'+qid+'~2');
jQuery(sel1).on('change', function() {
sel2.options[1].selected = true;
});
Finally, add the below CSS to the Style section of the Look & Feel so that the 2nd dropdown is not displayed to the respondent.
div.Inner.BorderColor.DL > div > fieldset > div > table > tbody > tr:nth-child(2) {
display: none;
}
Later in the survey, you can pipe in the 2nd dropdown selection/Rainfall amount by using the below, updating for your QID:
${q://QID1/ChoiceGroup/SelectedAnswers/2}