Plant available water limitation on plant growth

This map is one of the layers used to recreate Figure 2 in Churkina and Running (1998) in Data Basin (file title: Climate controls on plant growth). Each pixel (0.5 degree x 0.5 degree) on the map represents a value derived from a specific function of the water balance coefficient (Figure 1 in Churkina and Running 1998).

Excerpt from Churkina and Running 1998:

To estimate the amount of available water [to plant growth], Churkina and Running calculated a water balance coefficient (WBC) as a difference between mean annual precipitation and potential evapotranspiration where potential evapotranspiration was a function of mean temperature and net solar radiation (Priestley and Taylor 1972). WBC computation was based on global means of annual precipitation, solar radiation, and temperature from the CLIMATE database.

This water balance computation has the advantage of being independent of any models and can be derived purely from climate data. To develop the relationship between NPP limitation and WBCs, Churkina and Running followed a logic similar to the one suggested by Stephenson (1990). Churkina and Running suggested that vegetation productivity of areas with extremely negative WBCs was limited by moisture availability, and this limitation declined as WBCs approached zero. Sites with positive WBCs were not moisture limited or were limited very slightly. The function describing the dependence of the degree of the water limitation on NPP clearly delineated sites with available water deficiencies versus excesses.