How Climate Data Were Generated
Near surface temperature is downloaded from ftp://ftp.cpc.ncep.noaa.gov/wd51yf/GHCN_CAMS/ . It is a (0.5° x 0.5°) data set of monthly average global land surface temperatures from 1948 to near present produced by NOAA. The current month’s value is shown and the current month’s anomaly is calculated by subtracting the 1948-present mean from the current month’s value.
We used two data sets to calculate accumulated rainfall for the current month and the SPI. The first data set is CHIRPS 2.0 which is a 30+ year quasi-global rainfall data set developed by the Climate Hazards Group at University of California - Santa Barbara (UCSB) (http://chg.geog.ucsb.edu/data/chirps/). CHIRPS is a gridded rainfall time series combining in-situ data with satellite observation.
The second data set is TRMM 3B42RT (Tropical Rainfall Measuring Mission) which is a product of NASA-GSFC (http://trmm.gsfc.nasa.gov/). Data are presented as a combination of remote sensing and modeling using 5 instruments: a 3-sensor rainfall suite (PR, TMI, VIRS) and 2 related instruments (LIS and CERES). The real time product is updated daily from March 2000 to near present.
The TRMM data set is used to calculate the SPI. SPI is an indicator used to describe the frequency of a given drought or wet period’s severity during a specified time scale. The SPI is based on the cumulative probability of a given rainfall event occurring at a location and can be interpreted as follows:
- High SPI value (closer to 3 ): heavy precipitation event over time period specified
- Medium SPI value (approximately = 0 ) : normal precipitation event over time period specified
- Low SPI value (closer to -3 ): low precipitation event over time period specified
- Drought classifications vary but typically the following values are used:
[<-3] Extreme drought
[-3, -2] Severe drought
[-2, -1] Moderate drought
[-1, 0] Abnormally dry to normal