<p>It is hard  to help unless you clarify what methods have you tried. However, I would suggest to explore reanalysis weather models, as they are the most accurate source of estimated weather conditions worldwide in the past.</p>

<p>A recommended reanalysis is ERA-interim, starting in 1979 so it gives you  39 years, if you really need 40 you can use JRA-55 that starts on 1955.</p>

<p>The <a href="https://climexp.knmi.nl/selectfield_rea.cgi?id=someone@somewhere" rel="nofollow noreferrer">KNMI Climate Explorer</a> is a great way to retrieve and plot data from those models.</p>

<p>If you get in there you can set it to plot monthly mean temperatures for a given location. Here is an example of somewhere in SW Canada:
<a href="https://i.sstatic.net/Q80GW.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Q80GW.png" alt="enter image description here"></a></p>

<p>That will produce a plot like this:
<a href="https://i.sstatic.net/gUxP4.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/gUxP4.png" alt="enter image description here"></a></p>

<p>Were you can click the "raw data" to get the raw values, and that will produce an output like this:</p>

<p><a href="https://i.sstatic.net/cW4VZ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cW4VZ.png" alt="enter image description here"></a></p>

<p>Where each row is a year and each column is a month. So you can pick the column of the month of your interest and compute the trend from that.</p>

<p>Does it makes sense?</p>

CC BY-SA 3.0
2018-02-27T18:38:16.157Z
Yes, I'm sorry for my lack of detail, I was probably too cautious to don't be sent to the statistics forum. Yes I'm using NARR data (validated with some weather stations), I averaged the daily temperatures for each area according to each of the periods I have (which are not true months, but based on dates according to the bird migration) and from that I want to estimate a trend for each of them.
MSS
CC BY-SA 3.0
2018-02-27T18:47:15.913Z
@MSS That sounds as a reasonable methodology. So, what do you mean with "But using different methods I got different results". Which different methods? How different are the results?
Camilo Rada
CC BY-SA 3.0
2018-02-27T19:03:03.513Z
I used the Sen's slope, the Mann-Kendal test (adjusted for autocorrelated data), Zhang method (from package ZYP in R)  models gls (from package nlme, not able to remove the autocorrelation of the residuals), ARIMAX and with all of them I get different results. Only ARIMAX was able to remove the correlation in the residuals. Which method would you trust more?
MSS
CC BY-SA 3.0
2018-02-27T19:09:03.140Z
The problem with ARIMAX was that when I looked at the overall period trend (76 days) this was negative for the Arctic! (not much, but negative)
MSS
CC BY-SA 3.0
2018-02-27T19:42:56.283Z
I'm not familiar with those methods. But it would be informative if you add to your question a plot with the source data (mean temp of the period of the year of interest versus year).  If there is no significant trend, maybe there IS no trend, and it is pointless to try to use a statistical method to find the significance of the trend. Keep in mind that NARR data have uncertainties, and any trend that lay within that uncertainty won't have any significance.
Camilo Rada
CC BY-SA 3.0
2018-02-27T17:24:18.677Z
2018-02-27T17:33:59.707Z
2018-02-27T17:33:59.707Z
Camilo Rada
<p>I'm calculating warming trends in specific places and periods of time, that are related to the time a migratory bird spends in a stopover. But using different methods I got different results and I'm trying to figure out which is the most accurate. I know it will depend on location, so my sites are Southeast Canada and the Arctic. How much warming is possible in 40 years for example in a period covering only one month in spring, like May? What would be a good value to compare my results? spring temperature warming trend?</p>

<p>There's a lot of fluctuation in temperatures, so when averaging them I get no changes, including in the Arctic, which cannot be true. I looked at trends of the maximum temperatures and they are increasing, also investigated the anomalies, but I would like to have an advice.</p>

CC BY-SA 3.0
2018-02-27T13:19:41.710Z
What? _"so my sites are Southeast Canada and the Arctic. How much warming is possible in 40 years for example in one month in spring"_ are you asking for 40 years or a month in spring?
Eevee
CC BY-SA 3.0
2018-02-27T13:57:37.597Z
Perhaps warming of May average temperature in 40 years?
Communisty
CC BY-SA 3.0
2018-02-27T15:54:29.047Z
Thank you for your suggestion @Communisty, do you think this also works if I have only 15 days and I want to estimate a warming trend?
MSS
CC BY-SA 3.0
2018-02-27T16:01:16.747Z
If you pick only a specific location and/or small portion of a year the  overall trend can be very different from the global average.
Communisty
CC BY-SA 3.0
2018-02-27T16:30:34.323Z
A meteorologist would most like be able to give you a better answer.  For your month of interest you look at either the average of the daily maxima over time, or the average of each daily maximum minus the daily minimum over time.
Fred
<climate-change><climate><temperature>
How much warming there was over time for a specific month?
MSS
# How much warming there was over time for a specific month?

(Asked by: username_0 on 2018-02-27)

I'm calculating warming trends in specific places and periods of time, that are related to the time a migratory bird spends in a stopover. But using different methods I got different results and I'm trying to figure out which is the most accurate. I know it will depend on location, so my sites are Southeast Canada and the Arctic. How much warming is possible in 40 years for example in a period covering only one month in spring, like May? What would be a good value to compare my results? spring temperature warming trend?

There's a lot of fluctuation in temperatures, so when averaging them I get no changes, including in the Arctic, which cannot be true. I looked at trends of the maximum temperatures and they are increasing, also investigated the anomalies, but I would like to have an advice.

**Tags:** climate-change, climate, temperature

> **Comments:**
> **username_1**: What? _"so my sites are Southeast Canada and the Arctic. How much warming is possible in 40 years for example in one month in spring"_ are you asking for 40 years or a month in spring?  
> **username_2**: Perhaps warming of May average temperature in 40 years?  
> **username_0**: Thank you for your suggestion @username_2, do you think this also works if I have only 15 days and I want to estimate a warming trend?  
> **username_2**: If you pick only a specific location and/or small portion of a year the  overall trend can be very different from the global average.  
> **username_3**: A meteorologist would most like be able to give you a better answer.  For your month of interest you look at either the average of the daily maxima over time, or the average of each daily maximum minus the daily minimum over time.  

---

## 1 answers

### Answer by username_4 on 2018-02-27. Score: 1

It is hard to help unless you clarify what methods have you tried. However, I would suggest to explore reanalysis weather models, as they are the most accurate source of estimated weather conditions worldwide in the past.

A recommended reanalysis is ERA-interim, starting in 1979 so it gives you 39 years, if you really need 40 you can use JRA-55 that starts on 1955.

The [KNMI Climate Explorer](https://climexp.knmi.nl/selectfield_rea.cgi?id=someone@somewhere) is a great way to retrieve and plot data from those models.

If you get in there you can set it to plot monthly mean temperatures for a given location. Here is an example of somewhere in SW Canada:
[![enter image description here](https://i.sstatic.net/Q80GW.png)](https://i.sstatic.net/Q80GW.png)

That will produce a plot like this:
[![enter image description here](https://i.sstatic.net/gUxP4.png)](https://i.sstatic.net/gUxP4.png)

Were you can click the "raw data" to get the raw values, and that will produce an output like this:

[![enter image description here](https://i.sstatic.net/cW4VZ.png)](https://i.sstatic.net/cW4VZ.png)

Where each row is a year and each column is a month. So you can pick the column of the month of your interest and compute the trend from that.

Does it makes sense?

> **Comments:**
> **username_0**: Yes, I'm sorry for my lack of detail, I was probably too cautious to don't be sent to the statistics forum. Yes I'm using NARR data (validated with some weather stations), I averaged the daily temperatures for each area according to each of the periods I have (which are not true months, but based on dates according to the bird migration) and from that I want to estimate a trend for each of them.  
> **username_4**: @username_0 That sounds as a reasonable methodology. So, what do you mean with "But using different methods I got different results". Which different methods? How different are the results?  
> **username_0**: I used the Sen's slope, the Mann-Kendal test (adjusted for autocorrelated data), Zhang method (from package ZYP in R)  models gls (from package nlme, not able to remove the autocorrelation of the residuals), ARIMAX and with all of them I get different results. Only ARIMAX was able to remove the correlation in the residuals. Which method would you trust more?  
> **username_0**: The problem with ARIMAX was that when I looked at the overall period trend (76 days) this was negative for the Arctic! (not much, but negative)  
> **username_4**: I'm not familiar with those methods. But it would be informative if you add to your question a plot with the source data (mean temp of the period of the year of interest versus year).  If there is no significant trend, maybe there IS no trend, and it is pointless to try to use a statistical method to find the significance of the trend. Keep in mind that NARR data have uncertainties, and any trend that lay within that uncertainty won't have any significance.  

---

