Homepage started: February 20, 2021.
Last update: March 25, 2021.

Climate & Ecology

Gerd A. Esser

Dr. rer. nat., University Professor
Systems Ecology, Geo-Ecology and Modelling
Giessen, Germany

Models of global biogeochemical cycles.

The models of biogeochemical cycles were developed in the working groups of Gerd Esser at the Universitiy of Osnabrück (Germany), at the International Institute for Applied Systems Analysis (IIASA) at Laxenburg (Austria), and at the Justus-Liebig-University of Gießen (Germany).
These high-resolution models (geographical resolution 0.5 deg. latitude and longitude, time resolution one month or less) include the cycles of carbon, nitrogen, or water.
The following documentations of the models are available for download as pdf-files. The documentations are protected by copyright. The material may be cited or otherwise freely used for scientific purposes with full citation of authorship and sources:
HRBM: High Resolution Biosphere Model (carbon cycle)
NCIM: Nitrogen Carbon Interaction Model (coupled nitrogen and carbon cycles)
GIWACOM: Giessen Global Generic Water Conductance Model (coupled water and carbon cycles)


Aridity Index.

The components of the climate and weather systems which contribute to the ecological aridity of a location include: the amount of precipitation in relation to the temperature, the number of dry months, the precipitation deficit during a dry month, the distribution of precipitation over the year, and others. All these components vary in time and are subject to climate change in a different way.
This makes it difficult to compare the ecological aridity of different locations or the change in time. An "aridity index" is suggested which considers all the different components which contribute to the ecological aridity. This "aridity index" characterizes the ecological aridity of a location at a given time by just one figure: 0 percent to 100 percent arditiy.
How is the aridity index calculated?

Application of the aridity index.

The aridity index may be used to calculate time-series of the aridity to document climate change. It is also useful for the documentation of spatial gradients of aridity along geographic transections or for the characterization of climatic conditions of habitats.
With a global data set of monthly mean temperatures and monthly sums of precipitation and a resolution of 0.5 degrees longitude and latitude a high resolution global map of the aridity index was produced:
Global Map of the Aridity Index