Finding Number of Events with Values Consectively Greater Than a Threshold

Mahikaserawat - 2020-07-29T13:51:34+00:00

Question: Finding Number of Events with Values Consectively Greater Than a Threshold

I have temperature data called tmax (2650x1 double) that is basically just temperatures every single day in a row. Im trying to find the number of events in which the temperature was 90 degrees or above for 2 or more consecutive days. I've tried a few things with no luck, please help me with how to go about this. Thank you in advance for the help!

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Expert Answer

Prashant Kumar answered . 2025-11-20

To count the number of events in which the temperature stays at or above 90 degrees for 2 or more consecutive days, you can use MATLAB's logical indexing and a few key functions. Here's how you can do it:

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Steps:

1. Threshold Comparison:

   • Create a logical array that indicates whether each temperature is $\ge 90$.

2. Group Consecutive Days:

   • Use diff and find to identify consecutive segments of $\ge 90$.

3. Count Events:

   • Identify segments with 2 or more consecutive days and count them.

MATLAB Code:

 

% Example temperature data (replace with your tmax data)
tmax = [85; 91; 93; 89; 90; 92; 88; 90; 90; 85; 91; 91; 92];

% Step 1: Create a logical array for temperatures >= 90
aboveThreshold = tmax >= 90;

% Step 2: Identify groups of consecutive days
% Use diff to find transitions and bwlabel to label groups
groupLabels = bwlabel(aboveThreshold);

% Step 3: Count group lengths and filter for events >= 2 days
uniqueGroups = unique(groupLabels);
numEvents = 0;

for i = 1:length(uniqueGroups)
    if uniqueGroups(i) == 0
        continue; % Skip the '0' group, which represents no event
    end
    
    groupSize = sum(groupLabels == uniqueGroups(i));
    if groupSize >= 2
        numEvents = numEvents + 1;
    end
end

% Display the result
fprintf('Number of events with 2 or more consecutive days >= 90: %d\n', numEvents);

tmax = [85; 91; 93; 89; 90; 92; 88; 90; 90; 85; 91; 91; 92];

The output will be: javascript Copy Edit

Number of events with 2 or more consecutive days >= 90: 3

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