How many weather data are essential for calculating of the PDSI (Palmer Drought Severity Index)?

The PDSI, based on the Palmer Drought Model (Palmer, 1965), has been one of the most commonly used drought indicators in the United States. The calculations of this index are complicated, and it needs some settings. The PDSI is calculated based on precipitation and temperature data, as well as the local Available Water Content (AWC) of the soil. From the inputs, all the basic terms of the water balance equation can be determined, including evapotranspiration, soil recharge, and moisture loss from the surface layer. Human impacts on the water balance, such as irrigation, are not considered. Complete descriptions of the equations can be found in the original study by Palmer (1965). In the DMAP (Drought Monitoring And Prediction) software, the user can easily calculate PDSI, the severity and duration of drought events and also plot different graphs in different time scale.

The Palmer Drought Severity Index (Palmer, 1965) is probably still one of the most complex drought indices in use today (Titlow, 1987), and it is also one of the few that allows a direct comparison of index values between different climatological regions. The PDSI has been used as a tool to monitor environmental conditions. Instead of taking only precipitation into account, PDSI also accounts for temperature which has a huge impact on evapotranspiration and soil moisture. This index provides a more comprehensive method to assess the impacts of climate change on drought since it requires more climate variables as input (Palmer 1965; Alley 1984; Guttman 1998).

PDSI represents the balance of water inputs to the soil, based on observed monthly precipitation, and water losses from the soil, based on observed monthly temperature. Thus PDSI is often used as an indicator of agricultural drought. This soil-moisture balance calculation accounts for the "memory" of water storage within the soil, so PDSI for a given month or season actually reflects the previous nine to twelve months of weather conditions (Palmer 1965; Alley 1984).

Alley, W. 1984. Te Palmer Drought Severity Index: Limitations and assumptions. Journal of Climatology and Applied Meteorology 23: 1100-1109.

Guttman NB (1998) Comparing the Palmer drought index and the Standardized Precipitation Index. J Am Water Resour Assoc 34:113-121

Titlow JK. 1987. A precipitation-based drought index for the Delaware River basin. Thornthwaite Associates and University of Delaware. Publications in Climatology 40(2).

Palmer WC, 1965. Meteorological drought: US Department of Commerce, Weather Bureau Washington, DC, USA. 45, 58.

PDSI - Palmer Drought Severity Index