Nature & Environment
Animals at the extremes: the desert environment
...De Martonne's aridity index has been used widely and is calculated from the formula: I a = aridity index P = mean annual precipitation/mm T = mean annual temperature/°C Note that values for average precipitation can be misleading because in arid deserts, especially hyper-arid desert, there are many years that have no rainfall at all. Certain coastal deserts such as the...