Standardised soil moisture deficit 2007-2008

Source:
National Institute for Water and Atmospheric Research

Method:
"Potential evapotranspiration deficit (PED) is the difference between potential evapotranspiration and actual evapotranspiration. Maps of the standardised annual PED (the departure from the 1981–2010 average divided by the 1981–2010 standard deviation, no units) were produced for every growing-season, July to June year, from 1972 to 2013.



Soil needs to be moist enough to allow plants to grow. Evapotranspiration is the process whereby water held in the soil is gradually released to the atmosphere through a combination of direct evaporation and transpiration from plants. Over the course of a growing season, the amount of water lost from the soil through evapotranspiration typically exceeds rainfall. This causes an increase in soil moisture deficit. As soil moisture decreases, pasture production becomes constrained, and evapotranspiration decreases. The amount of evapotranspiration falls below what could potentially occur if there were sufficient soil moisture (potential evapotranspiration) (Porteous et al., 1994).



Some areas of the country always have an annual PED total of 0. These areas are high elevation regions (e.g., in the Southern Alps). At these locations, it is not possible to generate a standardised annual PED value because the standard deviation is 0 (i.e., there is a ‘divide-by-0’ problem). The Geographic Information Systems (GIS) datasets show ‘No Data’ for these grid cells.

The accuracy of the data source is of high quality.



References:

Porteous, AS, Basher, RE, & Salinger, MJ (1994). Calibration and performance of the single‐layer soil water balance model for pasture sites. New Zealand Journal of Agricultural Research, 37(1), 107–118, DOI: 10.1080/00288233.1994.9513047. Available from www.tandfonline.com."