The first thing you should do is to address the real purpose of your question. The reason there are different "drought indices" is because there are different types of drought. And these different types mean different things. You can't really make a good choice until you can state why you want to make the classification. Are you talking about agricultural drought in which there is moisture deficit in the root zone of particular crops? Are you talking about a hydrologic drought in which there is a runoff deficit? Are you talking about a climatological drought in which there's simply a rainfall deficit, etc. Are you trying to determine whether a particular year is a "drought year" in order to classify against a particular criterion in order to determine insurance compensation or trigger government action?

You could also browse the National Drought Mitigation Center's website and see how this is dealt with in the U.S. But be careful because droughts in different parts of the world can have different characteristics and definitions because of differences in climatology and impact.

http://drought.unl.edu

Hi Xiaodong,

We hydrogeologist people use annual moisture index to classify climate year by year. There are few methods for calculating annual moisture index, but the most popular one is Thornthwaite and Hare (1955). Annual moisture index is actually a ratio of annual cumulative precipitation and potential evaporation. You could use this to classify annual climate. For more, follow the paper Thornthwaite (1948), and Thornthwaite and Hare (1955). Hope this will help.

Thanks

Shubhra Pk 

Based on data presented, Imwould not include 2016 as light drought. However, relying only on annual rainfall can be problemmatic in identifying drought years. Indicators as native plants, crops, water supplies, severe wildfires in some areas, wells going dry, etc. The distribution of rainfall throughout year and during growing season can make a big difference. Since evapotranspiration during growing season is a big demand, you may want to consider analyzing those separately when discussing possibility of drought.

I am not aware of any official categories for drought, and drought conditions may be specific or relative to conditions, as a drought in a xeric climate and soils may be different from a drought in a mesic conditions. From your annual rainfall data, and that alone, I think you can say 2015 is a dry year, but without analyzing the seasonal data of rainfall, I would not automatically assume its a drought. Likewise, it is also possible to have an average or even wet year with unusual rainfall distribution, and end up with seasonal drought. And in some instances, a severe or extreme drought may take more than one average rainfall year to replenish water supplies.

Various climate and management agencies develop drought criteria that fits the circumstances. They may use streamflow, reservoir levels, water levals in aquifer, plant or crop indicators, rainfall, ET demand, etc.

The first thing you should do is to address the real purpose of your question. The reason there are different "drought indices" is because there are different types of drought. And these different types mean different things. You can't really make a good choice until you can state why you want to make the classification. Are you talking about agricultural drought in which there is moisture deficit in the root zone of particular crops? Are you talking about a hydrologic drought in which there is a runoff deficit? Are you talking about a climatological drought in which there's simply a rainfall deficit, etc. Are you trying to determine whether a particular year is a "drought year" in order to classify against a particular criterion in order to determine insurance compensation or trigger government action?

You could also browse the National Drought Mitigation Center's website and see how this is dealt with in the U.S. But be careful because droughts in different parts of the world can have different characteristics and definitions because of differences in climatology and impact.

http://drought.unl.edu

Greetings,

If your mean is calculating rain-based drought indices and the analyzing quartets (0.25, 0.50,..), I refer to download a useful tool that it can calculate all rain-based drought indices:

www.agrimetsoft.com

Just try it!

Regards,

Nasrin