Hi everyone,
Can someone help me and suggest what statistic method is best to use to find out and show if there is a shift in rainfall from one month to another or to show if the rainfall is getting prolonged.
I have rainfall from 1975 to 2015, and my study area has 2 monsoon and 2 inter-monsoon periods. One monsoon and one inter-monsoon periods have the highest rainfall while the other monsoon and inter-monsoon periods have low rainfalls. I wanted to see if the convectional rainfall in the inter-monsoon period is shifting or getting prolonged into the drier monsoon period using statistics.
Thank you for your suggestions,
Regards,
Majid.
Dear Majid,
Hi,
You can try climatol r-cran package in R program to make Walter-Leith climatic diagram.
Best,
Saeed
Please refer to the links below
https://rdrr.io/cran/climatol/man/diagwl.html
https://rdrr.io/cran/iki.dataclim/man/plotWalterLieth.html
Best wishes,
Saeed
This could be very tricky. I've researched rainfall data of some stations in Berlin, Germany with hourly data to show how climate change has impact on storm events, causing floods.
You might have the problem to identfy the each for your study interesting event.
I started to define one single event by sum the hourly data until the hourly rainfall drops to zero. For me, this was the best method and worked well. I eliminated all events below a specific threshold, and I got a database with significant rain events with following entities: start, duration, precipitation, max intensity per hour.
Meteorologists grouping the events over 3 decades. With your data it would be 1975 to 2004 and 1985 to 2014. Maybe it works with shorter intervals too.
Dear Saeed,
Thank you for your reply.
But i don't have temperature data for most of my rainfall stations. Only 2 stations I have temperature data for, and this data is only from 1995 to 2018. So I dont know if this can work.
Dear Steffen Krei ,
Thank you for your reply,
Unfortunately I don't have hourly data, I have daily mean rainfall. so what can be done with daily mean rainfall?
Majid,
thank you for following up.
I understood your question that you want to research the change in time of the beginning of a monsoon season. In my example, I had to identify rainfall events, lasting from few minutes up to days.
If you want to research monsoon and intermonsoon periods, you have to identify the start and end of each period. Daily data would probably good enough for your research. I don’t know how long the shifts from intermonsoon to monsoon lasts in your area. If you can identify a specific day in each year, perfect. If not try to identify the specific week. Try to set a threshold to identify the periods.
you’ll getting data for monsoon 1 at station xyz with following entities per year: start (day x of the year, duration in days, sum rainfall, ...)
then you are able to show on axis x the year and on axis y the start of monsoon 1. A linear regression shows a shift over the years. You can put every entity on axis y.
If the dataset is not clear and showing no correlation, group the years. Meteorologists working with an 30year average. For your research might work a 5y average or maybe 10y. You can also try overlapping periods.
best regards
Steffen
Dear Steffen Krei,
Thank you for your reply.
In my study area there are 2 monsoons, the North East monsoon which is from Nov - March and the South West monsoon from May - Sept, then there is 2 inter-monsoons in April and October. The area is affected mostly by the NEM. So I have around 20 stations and some of the stations are located around urban areas, I wanted to see if the rainfall is shifting or getting prolonged between the monsoon and inter-monsoon periods, specially the convectional rainfall in the inter-monsoon in April, and see if its shifting into the SWM. And then if there is any shift then I can see where this shift is happening and if urban land use is a cause in this change. Therefore I wanted to find what is the best method and statistics to show and find this shift, graphs alone is not enough.
I see the suggestion you have made, I will look into this and try it out. If you have any other advice or suggestion I would appreciate it.
Regards,
Majid.
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